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Some related questions about DNA differences in a single organism

Some related questions about DNA differences in a single organism



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  1. If you took a DNA sample from someone's brain and that same persons liver at more or less the same time, would that DNA - all else being equal (e.g. no mutations from radiation) - be exactly the same?

  2. If you took a DNA sample from an embryo, and then that embryo went on to be born, live a long life for 80 years and become an old man/woman; if you were to then take another DNA sample of this person, would that sample be exactly the same as the one which you took when he/she was in the womb? (again, all things being equal - so dismissing mutations due to radiation for example).


No. even if you exclude the changes in DNA sequences that originate from mismatch errors in DNA replication, mutation etc. Because

1.As a person gets old , the short repeat sequences in the telomere of a chromosome in each cell may be lost or be reduced in amounts leading to a sequence difference.Moreover this changes in telomere sequences may cause cancer/cell apoptosis . Telomere

2.Do not forget transposons (consisted of DNA transposons and retrotransposons). They change their position in genome and multiply their DNA over time.So they also lead to sequence differences in a person(comparing his/her younger and older DNA) Transposons These were the answers to question 2 .You can also think that there might be a slight difference in DNA of two different tissue of the same individual (because of the tolemere and transposons)

As a zygote starts to multiply itself ,slight changes of sequence will happen to the offspring cells .After a dozens of cell division you may encounter a little deviation compared to the original zygote sequence.


From Cell to DNA

Photo Credit: Clipart.com

Purpose

To introduce students to the genetic information stored in DNA within the human cell nucleus.

Context

The goal of this lesson is to introduce students to the human cell and its DNA as the genetic information that governs how the cell will function. It is recommended to teach this lesson before delving into the more technical and biochemical process of replication, transcription, and translation.

When learning about cells, students often jump immediately into structures and functions. This compartmentalized approach lends itself to misunderstanding the relationship between cells and the living organisms that they compose. Cells are described by biology textbooks as the building blocks of life, yet students often cannot explain how something so small can help form a human being, a tree, or bacteria. Students often think that cells are floating within structures, as blood cells are depicted moving through arteries and veins. Even the use of certain language can promote this type of faulty thinking the phrase &ldquocells in the heart&rdquo may be understood to mean that there are cells that are within the heart, but not actually making the heart itself. Research indicates that it may be easier for students to understand that the cell is the basic unit of structure (which they can observe) than that the cell is the basic unit of function (which has to be inferred from experiments) (Dreyfus & Jungwirth, 1989). In this lesson, students will begin to understand cells as a basic unit of structure and begin to explore how DNA informs the function of the cell.

Research also shows that high-school students may hold various misconceptions about cells after traditional instruction (Dreyfus & Jungwirth, 1988). While students learn the details of mitosis, cellular respiration, and photosynthesis, the larger understanding of how these detailed chemical and biological processes relate to life and growth is often not addressed. Furthermore, students are usually taught the form and function of &ldquotypical&rdquo cells, often in isolation to other cells. Differences between prokaryotic and eukaryotic cells are highlighted, as well as differences between plant and animal cells. Conceptually, this encourages students to believe that all plant cells are physically and morphologically the same, and likewise for all animal cells. Since cells are often studied in isolation&mdashparticularly through drawings or models of single animal and plant cell prototypes&mdashstudents also may not be able to describe how cells in a single organism communicate with and relate to one another.

Finally, students are often unable to reconcile two concepts that are taught during a cell biology unit. On the one hand, they learn that all the genetic information that codes for a living organism is encoded within the cell&rsquos DNA and that this genetic code is the same in each cell of the living organism. Yet on the other hand, students learn that cells differentiate and specialize. They may become cells of the liver, xylem, thyroid, etc. How can two cells of a living organism have exactly the same genetic information, yet become different types of cells with specialized functions and morphology?

This lesson is for the high-school level and assumes that students have some previous information about cells and DNA. The Motivation section and the beginning of the Development in this lesson will help you determine student preconceptions.

Motivation

A few days before the lesson, ask students, &ldquoWhat are living things made of?&rdquo Have students write down no more than three responses on a blank piece of paper or on an index card. They do not need to write their names on their responses, but ensure that all students participate in this short activity. Collect the responses and organize them into categories outside of classroom time. The activity can be done verbally as well by asking students to share responses and writing them on the board. However, past experience with this activity has shown that: 1) not all students contribute to the discussion with their thoughts, preventing you from ascertaining what all students think, and 2) students are sometimes shy to share the first thoughts or terms that come into their mind, such as &ldquosperm.&rdquo Collecting responses anonymously ensures that you know the preconceptions of all the students.

Write down the final list of words and phrases on the board or flipchart paper. Related terms should be clumped together, such as &ldquocarbon,&rdquo &ldquowater,&rdquo and &ldquoatoms.&rdquo The term &ldquocell&rdquo will usually be contributed by students. You also may want to include the terms &ldquotissue&rdquo and &ldquoorgan.&rdquo

Ask students to arrange the terms in order of their relationship to one another. Facilitate the discussion through guiding questions, such as:

  • What is the relationship between carbon and atoms?
  • How can we arrange these terms according to the size of the item?
  • Are there other things inside of cells besides DNA?
  • What are some examples of cells? (This is where terms like &ldquosperm&rdquo or &ldquored blood cell&rdquo can be incorporated.)

The outcome may look more like a web than a list. Tell students that the class will begin a unit on cell biology, where they will learn about different types of cells, their functions, and their various compartments. Point out that cells are often described as the building blocks of life. However, cells themselves are made up of different parts, each with a specific function.

Development

In this part of the lesson, student will examine cells more closely by exploring some online animations and interactives. Begin by asking students:

    You may have learned that half of the genetic information of a human being comes from the mother and half from the father. What is this genetic information?
      (It is DNA.)
      (It comes from the egg.)
      (It comes from the sperm.)

    Discuss with students that when the egg and sperm unite, they form one embryonic cell that contains a complete set of DNA.

      How does that first one embryonic cell become two or three or four and so on?
        (It begins to divide.)
        (The DNA duplicates and divides with each cell division.)

      Share with students that each cell has the same copy of the genetic information that was in the very first embryonic cell. Show students the Animal Cell Mitosis animation and describe how the two cells that are produced from cell division are exactly the same as the first cell. If this keeps happening over and over again, as it does for embryos, then each cell is a replica of the first cell with the same DNA that was in that first cell. Based on this, ask students to consider where the liver comes from, or the heart, the skin, the brain, bones, etc.

      Show students Figure 1 from Animal Cells and Tissues. Alternatively, you can print out the picture and provide it to students as a sheet. Ask students:

      Describe how each type of cell of the stomach has a different function. For example, the cells of the smooth muscle tissue contract and expand allowing food and nutrients to move along the digestive tract. The columnar epithelium cells line the inside of the stomach, absorbing nutrients into the bloodstream. The red blood cells provide oxygen to all the other cells of the stomach. Cells that make up the nervous tissue transmit nerve messages to and from the brain. Cells that make up the connective tissue support and protect the stomach. You also can review how the cells morphologically differ from one another. Remind students that all of these cells are the result of cell division from a previous cell. Ultimately, the first cell of that organism was the embryonic cell that contained DNA from both the egg and the sperm. This means that cell division results in cells that are genetically identical to one another. All five types of cells that the students reviewed in the diagram have the exact same genetic information. In other words, even though the cells differ in morphology and function, they are genetically identical.

      Have students use the Introducing the Human Cell and DNA student esheet to access the From Cell to DNA online animation. Students should go through the animation and answer the corresponding questions. They can write their answers on the From Cell to DNA student sheet.

      Go over the questions with the students. Explain any new vocabulary introduced by the animation, such as bacterium, eukaryote, micrometers, nanometers, histone proteins, and polymeric molecule. Review with students that a unique feature of eukaryotic cells is the presence of a nucleus, where the DNA is stored.

        The animation mentions that humans have 46 chromosomes. How many chromosomes come from the mother? From the father?
          (23 chromosomes come from each parent.)
          (They replicate and each new cell gets a copy of the same 46 chromosomes.)
          (There are two strands that wrap around each other in a helical fashion, held together by bases.)

        If available, show students a model of DNA. Point out how attraction between the bases holds the helical structure together. Show students images of the molecular structure of the bases, pointing out the different elements such as carbon and hydrogen. Remind students of their brainstorming activity during the Motivation and point out that the smallest unit is an atom.

        Discuss with students that each cell in the human body has the same 46 chromosomes as every other cell. That is, the genetic information stored in the nucleus of every human cell is identical to every other cell in that organism. However, as the students saw with the image of the stomach, cells of the human body differ from one another in terms of function and morphology. Why do some cells become heart cells while others become liver cells? How do cells know what function they should be performing?

        To explore this question, students should use their esheet to go to Tour of the Basics on the Learn Genetics site and answer the corresponding questions on the esheet. They can record their answers on the What Is DNA? student sheet. You can find answers to the questions on the What Is DNA? teacher sheet.

        After completing the activity, review the questions with students. Discuss with students that all the genetic information in a cell is stored in the pattern of four bases, which are adenine, guanine, cytosine, and thymine. These are respectively abbreviated A, G, C, and T. The entire genetic code of a living organism&mdashincluding how each cell will grow, function, and look&mdashis stored in the pattern of these four letters. The pattern of these letters make up &ldquosentences&rdquo called genes. A gene is a stretch of DNA that codes for a protein. The DNA never leaves the nucleus so it can&rsquot actually do the function of the cell. Instead, the DNA is like a blueprint made up of genes. The genes are read by the cell&rsquos nuclear machinery and produce specific proteins. Each gene codes for a specific protein. There are genes for proteins that have to do with hearing, heart function, immune defense, nutrient absorption, and so on.

        Assessment

          In your estimation, do you think there are a few or many genes?
            (There are many genes in DNA.)
            (No.)
            (The function of the cell is related to the types of proteins produced. Cells of the heart, for example, produce proteins that are specific to heart function. Cells of the eye, on the other hand, will produce proteins specific to eye function.)
            (The two cells are producing different proteins based on different genes of the DNA being read by the cell&rsquos machinery. The cell of the inner ear produces proteins that have to do with its function, and the cell of the stomach does likewise. This is why they look and function differently.)
            (Yes.)
            (They are produced from mitosis, which is cell division in which the DNA replicates. All cells have the same DNA as the first embryonic cell.)
            (Each cell has 46 chromosomes.)
            (Yes.)
            (Genes are segments of DNA. If the DNA is the same in both cells, the genes are also the same because they are a part of the whole.)
            (No.)
            (Yes.)

          Ask students to consider the following: Every student in the classroom started as a single cell, produced from an egg and a sperm. That first cell had 46 chromosomes, 23 contributed from each parent. How did that single cell become the fully functioning human being that they are today? Encourage students to think about cell division and that cells specialize based on the genes that become active within the DNA.

          Extensions

          Extracting DNA is a Science NetLinks lesson that provides students an opportunity to extract DNA.

          After understanding the concept of genes, students can explore the human genome and the importance of uncoding all the genes within the human DNA. Use the Science NetLinks lesson Cracking the Genetic Code.

          Students can explore the function and morphology of different cells in the human body by looking at prepared slides. An online Histology Laboratory provides numerous images of prepared human slides that can be magnified. Reinforce that while the cells within a human body differ, they contain the same genetic information: 46 chromosomes, where half comes from the mother and half from the father.

          Have students watch the rest of the Tour of the Basics online interactive to get a more complete understanding of how genes code for proteins that determine the actual function and morphology of cells. In addition, students can learn more about DNA and compare it to the genetic information in a mouse and a flower through an online interactive game DNA The Double Helix. The Dolan DNA Learning Center also provides lesson plans and online interactives about the discovery of DNA, the molecule, genetic technology, and future applications.

          For a laboratory activity, have students observe their own cheek cells and extract DNA. A lesson for this experiment can be found at Hands-on Activities for Teaching Biology to High School or Middle School Students.

          Educational resources and information about the Human Genome Project can be found at the National Human Genome Research Institute&rsquos website.


          a. translation converts a sequence of mRNA nucleotides/codons to a sequence of amino acids/polypeptide/protein

          b. «triplets of» nucleotides/bases on «activated» tRNAs pair with complementary «triplets of» nucleotides/bases on mRNA / vice versa

          c. base pairing occurs when adenine/A pairs with uracil/U and guanine/G pairs with cytosine/C

          d. specific amino acids are attached to specific of tRNA

          e. mRNA has codons AND tRNA has anticodons

          a. PCR is process by which a small sample of DNA can be amplified/copied many times

          b. PCR involves repeated cycling through high and lower temperatures «to promote melting and annealing of DNA strands»

          c. «mixture» is heated to high temperatures to break «hydrogen» bonds between strands of DNA/to separate the double-stranded DNA

          d. Taq DNA polymerase can withstand high temperatures without denaturing

          e. primers bind to «targeted» DNA sequences at lower temp

          f. Taq DNA polymerase forms new «double-stranded» DNA by adding «complementary» bases/nucleotides

          a. pest-resistant crops can be made

          b. so less spraying of insecticides/pesticides

          c. less fuel burned in management of crops

          d. longer shelf-life for fruits and vegetables so less spoilage

          e. greater quantity/shorter growing time/less land needed

          f. increase variety of growing locations / can grow in threatened conditions

          g. non-target organisms can be affected

          h. genes transferred to crop plants to make them herbicide resistant could spread to wild plants making super-weeds

          i. GMOs (encourage monoculture which) reduces biodiversity

          j. GM crops encourage overuse of herbicides

          k. nutritional value of food improved by increasing nutrient content

          l. crops could be produced that lack toxins or allergens

          m. crops could be produced to contain edible vaccines to provide natural disease resistance

          n. proteins from transferred genes could be toxic or cause allergic reactions

          o. antibiotic resistance genes used as markers during gene transfer could spread to «pathogenic» bacteria

          p. transferred genes could cause unexpected/not anticipated problems
          OR
          health effects of exposure to GMO unclear


          Sources of Genetic Variation

          In fact, genetic variation is so important for species that many species reproduce sexually to aid the process of producing new varieties. Sexually reproducing organisms carry two copies of the genome, allowing mutations to lie dormant or express themselves more subtly. During sexual reproduction, genes are recombined in new ways. This process, known as recombination, shuffles the alleles present and allows different combinations to be expressed. This adds to the total genetic variation. When observing an isolated population, immigration can also be a source of genetic variation. Organism may bring new alleles that have established elsewhere and introduce them to the population.

          1. What is the formula for quantifying genetic variation?
          A. Genetic Variation = Expected variation + Phenotypic variation
          B. Genetic Variation = Phenotypic variation – Environmental variation
          C. Genetic Variation = Environmental variation + Phenotypic variation

          2. Two identical twins go through life separately. At the age of 55, one is healthy and fit while the other is overweight and in danger of having a heart attack. What is responsible for the difference?
          A. Genetic Variation
          B. Environmental Variation
          C. Phenotypic Variation

          3. Polar bears and grizzly bears have been found to interbreed, creating a hybrid species. How is this related to genetic variation?
          A. It is not related, because the bears are different species
          B. Although there is a lot of genetic variation between the bears, they are still close enough to produce viable offspring
          C. There is no genetic variation between the bears, allowing them to interbreed


          Related Biology Terms

          • Organelle – A membrane-bound sac that specializes in a particular function for a cell.
          • Organ – A collection of tissues, or group of cells, in the body that specializes in a particular function for the body.
          • Eukaryotic – A cell with membrane-bound organelles and a nucleus.
          • Prokaryotic – A cell without membrane-bound organelles or a nucleus.

          1. A single blue whale weighs almost 40,000 pounds. A colony of aspen trees that share a root system and were derived from the same seed weighs almost 13,000,000 pounds. The combined weight of all bacteria on Earth is somewhere around 1.1 x 1014, or 110,000,000,000,000 pounds. What is the largest organism on Earth?
          A. Blue Whale
          B. Aspen Tree
          C. Bacteria

          2. Many plants produce offspring in the form of seeds. To create seeds, the male gamete has to meet the female gamete and fertilization must occur. This can occur to many eggs at once and many plant prepare a huge number of seeds at the same time. You see a dandelion plant in your yard. The yellow petals of the three different flowers have been replaced by a white puffball connected to hundreds of seeds. How many organisms are present?
          A. 1
          B. <300
          C. >300

          3. Aliens visit our planet. They add us to their categorization of life as the domain “Eartharia”. Would they be wrong?
          A. Yes
          B. No
          C. Hmm…


          (ii) Less success was seen here. A number of students mistakenly wrote phosphate bonds or peptide bonds. &ldquoCovalent bonds&rdquo was commonly stated for the mark and, sometimes, even the more sophisticated answer of phosphodiester linkage was given.

          Occasionally, candidates reversed hydrogen and covalent for parts (i) and (ii) and lost both marks.

          Easy marks for many candidates. However, some misread the questions and described differences in the physical/molecular structure of DNA and RNA molecules. Rather than restricting answers to nucleotide differences, double and single strands were described resulting in no credit.

          This question was worth only two marks but explaining the role of tRNA during translation could easily have been worth more. A few candidates wrote stellar answers that far exceeded the two mark maximum. The marking points most often awarded were that tRNA attaches to an amino acid and that tRNA has an anticodon complementary to the mRNA codon. Many candidates provided inaccurate information.


          Multiple Choice Questions
          Single Correct Answer Type

          1. A few statements describing certain features of reproduction are given below
          i. Gametic fusion takes place
          ii. Transfer of genetic material takes place
          iii. Reduction division takes place
          iv. Progeny have some resemblance with parents
          Select the options that are true for both asexual and sexual reproduction from the options given below:
          (a) i and ii (b) ii and iii
          (c) ii and iv (d) i and iii
          Answer. (c) Transfer of genetic material and progeny have some resemblance with parents are the phenomenon common in’both asexual and sexual reproduction while gametic fusion and reduction division takes place in sexual reproduction only.

          2. The term ‘ clone ’ cannot be applied to offspring formed by sexual reproduction because
          (a) Offspring do not possess exact copies of parental DNA
          (b) DNA of only one parent is copied and passed on to the offspring
          (c) Offspring are formed at different times
          (d) DNA of parent and offspring are completely different
          Answer. (a)
          • In asexual reproduction, a single individual (parent) is capable of producing offspring which are not only identical to one another but are also exact copies of their parent. The term clone is used to describe such morphologically and genetically similar individuals.
          • In sexual reproduction because of the fusion of male and female gametes (either by same individual or by different individual of the opposite sex), sexual reproduction results in offspring that are not identical to the parents or amongst themselves.

          3. Amoeba and Yeast reproduce asexually by fission and budding respectively, because they are
          (a) Microscopic organisms
          (b) Heterotrophic organisms
          (c) Unicellular organisms
          (d) Uninucleate organisms
          Answer. (c) Many single-celled organisms reproduce by binary fission (e.g., Amoeba, Paramecium), where a cell divides into two halves and each rapidly grows into an adult.
          In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which eventually gets separated and mature into new yeast organism (cells). Budding is also found in Hydra.

          4. A few statements with regard to sexual reproduction are given below
          i. Sexual reproduction does not always require two individuals
          ii. Sexual reproduction generally involves gametic fusion
          iii. Meiosis never occurs during sexual reproduction
          iv. External fertilisation is a rule during sexual reproduction
          Choose the correct statements from the options below:
          (a) i and iv , (b) i and ii
          (c) ii and iii (d) i and iv
          Answer. (b)
          • Sexual reproduction requires male and female gametes (either by same individual or by different individual of the opposite sex).
          • Sexual reproduction generally involves gametic fusion.
          • Meiosis occurs during sexual reproduction in dipoloid organisms.
          • External fertilisation is not a rule during sexual reproduction, internal fertilization also takes place

          5. A multicellular, filamentous alga exhibits a type of sexual life cycle in which the meiotic division occurs after the formation of zygote. The adult filament of this alga has
          (a) Haploid vegetative cells and diploid gametangia
          (b) Diploid vegetative cells and diploid gametangia
          (c) Diploid vegetative cells and haploid gametangia
          (d) Haploid vegetative cells and haploid gametangia
          Answer. (d) Adult filament of a multicellular, filamentous alga have haplontic life cycle in which the meiotic division occurs after the formation of zygote. So, the filament of this alga have haploid vegetative cells and haploid gametangia.

          6. The male gametes of rice plant have 12 chromosomes in their nucleus. The chromosome number in the female gamete, zygote and the cells of the seedling will be, respectively,
          (a) 12,24,12 . (b) 24,12,12
          (c) 12,24,24 (d) 24,12,24
          Answer. (c) Gametophytic structure (n) of rice plant contain 12 chromosomes and sporophytic structure (2n) of rice contain 24 chromosomes.
          Female gamete (n) =12,
          Zygote (2n) = 24,
          The cells of the seedling (2n) = 24.

          7. Given below are a few statements related to external fertilization. Choose the correct statements.
          i. The male and female gametes are formed and released simultaneously.
          ii. Only a few gametes are released into the medium.
          iii. Water is the medium in a majority of organisms exhibiting external fertilization.
          iv. Offspring formed as a result of external fertilization have better chance of survival than those formed inside an organism.
          (a) iii and iv (b) i and iii
          (c) ii and iv (d) i and iv .
          Answer. (b) In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy occurs in the external medium (water), i.e., outside the body of the organism. This type of gametic fusion is called external fertilisation. Organisms exhibiting external fertilisation show great synchrony between the sexes and release a number of gametes into the surrounding medium (water) in order to enhance the chances of syngamy. This happens in the bony fishes and frogs where a large number of offspring are produced. A major disadvantage is that the offspring are extremely vulnerable to predators threatening their survival up to adulthood.

          8. The statements given below describe certain features that are observed in the pistil of flowers.
          i. Pistil may have many carpels
          ii. Each carpel may have more than one ovule
          iii. Each carpel has only one ovule
          iv. Pistil have only one carpel
          Choose the statements that are true from the options below:
          (a) i and ii (b) i and iii
          (c) ii and iv (d) iii and iv
          Answer. (a)
          • Pistil may have many carpels (multicapillary pistil like Papaver)
          • Each carpel may have more than one ovule (like Watermelon,.Papaya etc.)

          9. Which of the following situations correctly describe the similarity between an angiosperm egg and a human egg?
          i. Eggs of both are formed only once in a lifetime
          ii. Both the angiosperm egg and human egg are stationary
          iii. Both the angiosperm egg and human egg are motile transported
          iv. Syngamy in both results in the formation of zygote
          Choose the correct answer from the options given below:
          (a) ii and iv (b) iv only
          (c) iii and iv (d) i and iv
          Answer. (b) Syngamy in both results in the formation of zygote is similarity between an angiosperm egg and a human egg.

          10. Appearance of vegetative propagules from the nodes of plants such as sugarcane and ginger is mainly because
          (a) Nodes are shorter than intemodes
          (b) Nodes have meristematic cells
          (c) Nodes are located near the soil
          (d) Nodes have non-photosynthetic cells
          Answer. (b) Appearance of vegetative propagules from the nodes of plants such as sugarcane and ginger is mainly because nodes have meristematic cells. Examples of vegetative propagules: (i) Leaf buds of bryophyllum, (ii) Eyes of potato, (iii) Bulbifof Agave, (iv) Offset of water hyacinth, (v) Rhizome of ginger.

          11. Which of the following statements, support the view that elaborate sexual reproductive process appeared much later in the organic evolution?
          i. Lower groups of organisms have simpler body design
          ii. Asexual reproduction is common in lower groups
          iii. Asexual reproduction is common in higher groups of organisms
          iv. The high incidence of sexual reproduction in angiosperms and vertebrates
          Choose the correct answer from the options given below:
          (a) i, ii and iii (b) i, iii and iv
          (c) i, ii and iv (d) ii, iii and iv
          Answer. (c) Elaborate sexual reproductive process appeared much later in the organic evolution because of
          • Lower groups of organisms have simpler body design.
          • Asexual reproduction is common in lower groups of organisms.
          • High incidence of sexual reproduction in angiosperms and vertebrates.

          12. Offspring formed by sexual reproduction exhibit more variation than those formed by asexual reproduction because
          (a) Sexual reproduction is a lengthy process
          (b) Gametes of parents have qualitatively different genetic composition
          (c) Genetic material comes from parents of two different species
          (d) Greater amount of DNA is involved in sexual reproduction
          Ans. (b)
          • Offspring formed by sexual reproduction exhibit more variation than those formed by asexual reproduction because gametes of parents have qualitatively different genetic composition.
          • In asexual reproduction due to involvement of only one parent, so there is no chance of variation.

          13. Choose the correct statement from amongst the following:
          (a) Dioecious (hermaphrodite) organisms are seen only in animals.
          (b) Dioecious organisms are seen only in plants.
          (c) Dioecious organisms are seen in both plants and animals.
          (d) Dioecious organisms are seen only in vertebrates.
          Answer. (c) Dioecious organisms are seen in both plants (like papaya) and animals (like cockroach).

          14. There is no natural death in single celled organisms like Amoeba and bacteria because
          (a) They cannot reproduce sexually
          (b) They reproduce by binary fission
          (c) Parental body is distributed among the offspring
          (d) They are microscopic
          Answer. (c) There is no natural death in single celled organisms like Amoeba and bacteria because the parental body is distributed among the offspring.

          15. There are various types of reproduction. The type of reproduction adopted by an organism depends on
          (a) The habitat and morphology of the organism
          (b) Morphology of the organism
          (c) Morphology and physiology of the organism
          (d) The organism’s habitat, physiology and genetic make up
          Answer. (d) The organism’s habitat, its internal physiology and several other factors (genetic make up) are collectively responsible for how it reproduces. When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual.

          16. Identify the incorrect statement.
          (a) In asexual reproduction, the offspring produced are morphologically and genetically identical to the parent.
          (b) Zoospores are sexual reproductive structures.
          (c) In asexual reproduction, a single parent produces offspring with or without the formation of gametes.
          (d) Conidia are asexual structures in Penicillium.
          Answer. (b) Zoospores are asexual reproductive structures.

          17.Which of the following is a post-fertilisation event in flowering plants?
          (a) Transfer of pollen grains
          (b) Embryo development
          (c) Formation of flower
          (d) Formation of pollen grains
          Answer. (b)

          18. The number of chromosomes in the shoot tip cells of a maize plant is 20. The number of chromosomes in the micro spore mother cells of the same plant shall be
          (a) 20 (b) 10 (c) 40 (d) 15
          Answer. (a) Shoot tip cells of a maize plant is a sporophytic structure (2n) and microspore mother cells of maize plant is also a sporophytic structure (2n). So, microspore mother cells (MMC) contain 20 chromosomes.

          Very Short Answer Type Questions
          1. Mention two inherent characteristics of Amoeba and yeast that enable them to reproduce asexually.
          Answer. a. They are unicellular organisms.
          b. They have a very simple body structure.

          2. Why do we refer to’offspring formed by asexual method of reproduction as clones?
          Answer. Offspring formed by asexual reproduction are called clones because they are morphologically and genetically similar to the parent.

          3. Although potato tuber is an underground part, it is considered as a stem. Give two reasons.
          Answer. a. The tuber has nodes and intemodes (as stem),
          b. Leafy shoots appear from the nodes.

          4. Between an annual and a perennial plant, which one has a shorter juvenile phase? Give one reason.
          Answer. An annual has a shorter juvenile phase. Since its entire life cycle has to be completed in one growing season, its juvenile phase is shorter.

          5. Rearrange the following events of sexual reproduction in the sequence in which they occur in a flowering plant: embryogenesis, fertilisation, gametogenesis, pollination.
          Answer. Gametogenesis, Pollination, Fertilisation, Embryogenesis

          6. The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than a dioecious plant. Explain.
          Answer. There is assured fruit set in self pollinated bisexual flower even in the absence of pollinators. In dioecious plants, there is male and female flowers present on different plants, so external pollinating agent is required for pollination.

          7. Is the presence of large number of chromosomes in an organism a hindrance to sexual reproduction? Justify your answer by giving suitable reasons.
          Answer. Presence of large number of chromosomes in an organism is not a hindrance to sexual reproduction. Butterfly has 380 chromosomes but it can reproduce sexually.

          8. Is there a relationship between the size of an organism and its life span? Give two examples in support of your answer.
          Answer. Life spans of organisms are not necessarily correlated with their sizes. The sizes of crows and parrots are not very different yet their life spans show a wide difference. Live span of crow is 15 year and of parrot is 140 years. A mango tree has a much shorter life span as compared to a peepal tree.

          9. In the figure given below, the plant bears two different types of flowers marked ‘A’ and ‘B Identify the types of flowers and state the type of pollination that will occur in them.

          Answer. ‘A’ is chasmogamous flower while ‘B’ is cleistogamous flower. A bisexual flower which normally open is called chasmogamous flower. Cleistogamous flowers do not open at all.
          Cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma.
          In a normal flower which opens and exposes the anthers and stigma complete autogamy is rather rare. Chasmogamous flower may show autogamy, geitonogamy or xenogamy.

          10. Give reasons as to why cell division cannot be a type of reproduction in multicellular organisms.
          Answer. Cell division cannot be a type of reproduction in multicellular organisms because cell division only increases the number of cells in an organism which leads to the growth of body.

          11. In the figure given below, mark the ovule and pericarp.

          Answer.

          12. Why do gametes produced in large numbers in organisms exhibit external fertilisation?
          Answer. Organisms exhibiting external fertilisation release a number of gametes into the surrounding medium (water) in order to enhance the chances of syngamy because there are few’ chances of fusion between male and female gametes.

          13. Which of the followings are monoecious and dioecious organisms?
          a. Earthworm ——————–
          b. Chara ——————–
          c. Marchantia ——————-
          d. Cockroach ——————–
          Answer. a. Earthworm—Monoecious
          b. Chara—Monoecious
          c. Marchantia—Dioecious
          d. Cockroach—Dioecious

          14. Match the organisms given in Column ‘A’ with the vegetative propagules given in column ‘B’.

          Answer. Bryophyllum—leaf buds Agave—bulbils Potato—eyes
          Water hyacinth—offset

          15. What do the following parts of a flower develop into after fertilisation?
          a. Ovary
          b. Ovules
          Answer. a. Ovary—Fruit
          b. Ovules—Seeds

          Short Answer Type Questions
          1. In haploid organisms that undergo sexual reproduction, name the stage in the life cycle when meiosis occurs. Give reasons for your answer.
          Answer. Meiosis takes place during its post-zygotic stage. Since the organism is haploid, meiosis cannot occur during gametogenesis.

          2. The number of taxa exhibiting asexual reproduction is drastically reduced in higher plants (angiosperms) and higher animals (vertebrates) as compared with lower groups of plants and animals. Analyse the possible reasons for this situation.
          Answer. Both angiosperms and vertebrates have a more complex structural organisation. They have evolved very efficient mechanism of sexual reproduction. Since asexual reproduction does not create new genetic pools in the offspring and consequently hampers their adaptability to external conditions, these groups have resorted to reproduction by the sexual method.

          3. Honeybees produce their young ones only by sexual reproduction. Inspite of this, in a colony of bees we find both haploid and diploid individuals. Name the haploid and diploid individuals in the colony and analyse the reasons behind their formation.
          Solution.
          • The colony of honey bees has three types of members: (i) Diploid queen are fertile females, (ii) Worker bees are sterile females and (iii) Drones are haploid males.
          • An offspring formed from the union of a sperm and an egg develops as a female (queen or worker), and an unfertilized egg develops as a male (drone) by means of parthenogenesis. This means that the males have half the number of chromosomes than that of a female.

          4. With which type of reproduction do we associate the reduction division? Analyse the reasons for it.
          Answer. Reduction division (meiosis) is associated with sexual reproduction. The reasons for this are:
          a. Since sexual reproduction involves the fusion of two types of gametes (male and female), they must have haploid number of chromosomes.
          b. The cell (meiocyte) which gives rise to gametes often has diploid number of chromosomes and it is only by reducing the number by half that we can get haploid gametes.
          c. Reduction division also ensures maintenance of constancy of chromosome number from generation to generation.

          5. Is it possible to consider vegetative propagation observed in certain plants like Bryophyllum, water hyacinth, ginger etc., as a type of asexual reproduction? Give two/three reasons.
          Answer. Vegetative propagation is considered as a type of asexual reproduction because
          (i) This is uniparental.
          (ii) Clone formation takes place.
          (iii) There is no fertilisation.

          6. ‘Fertilisation is not an obligatory event for fruit production in certains plants’. Explain the statement.
          Answer. Yes, it is observed in parthenocarpic fruits. The ‘seedless fruits’ that are available in the market such as pomegranate, grapes etc. are in fact good examples. Flowers of these plants are sprayed by a growth hormone that induces fruit development even though fertilisation has not occurred. The ovules of such fruits, however, fail to develop into seeds.

          7. In a developing embryo, analyse the consequences if cell divisions are not followed by cell differentiation.
          Answer. During embryogenesis, zygote undergoes cell-division (mitosis) and cell differentiation. While cell divisions increase the number of cells in the developing embryo Cell differentiation helps groups of cells to undergo certain modifications to form specialised tissues and organs to form an organism.
          If cell divisions are not followed by cell differentiation then there will be no formation of tissues or organs, so a new organisms cannot be formed.

          8. List the changes observed in an angiosperm flower subsequent to pollination and fertilisation.
          Answer. Post-fertilisation modifications

          9. Suggest a possible explanation why the seeds in a pea pod are arranged in a row, whereas those in tomato are scattered in the juicy pulp.
          Answer. In a fruit, seed arrangement depends on type of placentation. Pea and tomato shows different placentation. Pea shows marginal placentation while tomato shows axile placentation.

          10. Draw the sketches of a zoospore and a conidium. Mention two dissimilarities between them and alt least one feature common to both structures.
          Answer.

          11. Justify the statement ‘Vegetative reproduction is also a type of asexual reproduction’.
          Answer. Vegetative propagation is also a type of asexual reproduction because
          (i) This is uniparental.
          (ii) Clone formation takes place.
          (iii) There is no fertilisation.
          (iv) There is no gamete formation.

          Long Answer Type Question
          1. Enumerate the differences between asexual and sexual reproduction. Describe the types of asexual reproduction exhibited by unicellular organisms.
          Answer.

          The types of asexual reproduction exhibited by unicellular organisms:
          • Many single-celled organisms reproduce by binary fission (e.g., Amoeba, Paramecium), where a cell divides into two halves and each rapidly grows into an adult.
          • In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which eventually gets separated and mature into new yeast organism (cells).

          2. Do all the gametes formed from a parent organism have the same genetic composition (identical DNA copies of the parental genome)? Analyse the situation with the background of gametogenesis and provide or give suitable explanation.
          Answer. The gametes of a parent do not have the same genetic composition because they do not have identical copies of DNA. In the pachytene and diplotene stages of meiosis-I, the phenomenon of crossing over and chiasma formation take place between homologous chromosomes. This shifts segments of DNA from one chromatid to another (homologous chromosomes) in a random manner resulting in several new combinations of DNA sequences. As a result, when meiotic division is completed, gametes possess DNA with varying degree of variations.

          3. Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction, many groups of organisms in Kingdom Animalia and Plantae prefer this mode of reproduction. Give at least three reasons for this.
          Answer. a. Sexual reproduction brings about variation in the offspring.
          b. Since gamete formation is preceded by meiosis, genetic recombination occurring during crossing over (meiosis-I), leads to a great deal of variation in the DNA of gametes.
          c. The organism has better chances survival in a changing environment.

          4. Differentiate between (a) oestrus arid menstrual cycles (b) ovipary and vivipary. Cite an example for each type.
          Answer. Differences between oestrus and menstrual cycles


          5. Rose plants produce large, attractive bisexual flowers but they seldom produce Suits. On the other hand a tomato plant produces plenty of fruits though they have small flowers. Analyse the reasons Tor failure of fruit formation in rose.
          Answer. Failure of fruit formation in rose may be due to several reasons. Some of the likely reasons are
          a. Rose plants may not produce viable pollen.
          b. Rose plants may not have functional egg.
          c. Rose plants may have abortive ovules.
          d. Being hybrids, the meiotic process may be abnormal resulting in non-viable gametes. ‘
          e. There may be self-incompatibility.
          f. There may be internal barriers for pollen tube growth and/or fertilisation.


          ISC Biology Question Paper 2015 Solved for Class 12

          (Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this time.)

          • Answer all questions in Part I and six questions in Part II, choosing two questions from each of the three sections A, B and C.
          • All working including rough work should be done on the same sheet as, and adjacent to, the rest of the answer.
          • The intended marks for questions or parts of questions are given in brackets [ ].

          Part-I
          (Attempt all questions)

          Question 1.
          (a) Give a brief answer for each of the following : [4]
          (i) What is heterosis?
          (ii) Why is non-cyclic photophosphorylation considered as a non-cyclic pathway?
          (iii) Define test cross.
          (iv) What are introns?

          (b) Each of the following question(s)/statement(s) has four suggested answers. Choose the correct option in each case. [4]
          1. Triple Fusion involves :
          (i) Fusion of one male gamete with female gamete
          (ii) Fusion of tube nucleus with generative nucleus
          (iii) Fusion of two polar nuclei
          (iv) Fusion of second male gamete with two polar nuclei

          2. An EEG represents spontaneous electrical activity of the :
          (i) Kidney
          (ii) Spinal cord
          (iii) Heart
          (iv) Brain

          3. The genotype of a person with Turner’s syndrome will be :
          (i) 44 + XXY
          (ii) 44 + XYY
          (iii) 44 + XO
          (iv) 44 + XXYY ’

          4. Transcription is the transfer of genetic code from a DNA molecule to :
          (i) RNA molecule
          (ii) Second DNA molecule
          (iii) Ribosomal subunit
          (iv) Sequence of amino acids in a protein molecule

          (c) Give a scientific term for each of the following: [4]
          (i) The first formed category of photosynthetic organisms.
          (ii) The surgical removal of a section of fallopian tube.
          (iii) An animal behaviour which benefits others but is of no advantage to itself.
          (iv) The hydrostatic pressure developed inside the cell on the cell wall due to endosmosis.

          (d) Expand the following abbreviations : [4]
          (i) STD
          (ii) NADP
          (iii) MRI
          (iv) DDT

          (e) Name the scientists who are associated with the following : [4]
          (i) Discovered the fossil of Australopithecus
          (ii) Microspheres
          (iii) Coined the term Diffusion Pressure Deficit
          (iv) Invented the CT scan
          Answer:
          (a) (i) Heterosis is the increased hybrid vigour displayed by the offspring from a cross between
          genetically different parents.
          (ii) Non-cyclic photophosphorylation is considered as non-cyclic pathway because electrons expelled by the excited photo centre does not return to it. It produces both ATP and NADPH.
          (iii) Test cross is a special type of back cross made between the individual with a dominant trait and its recessive parent in order to know whether the homozygous or heterozygous for the trait.
          (iv) Introns are the segment of DNA that does not code for the gene product. They are transcribed in primary transcript but are subsequently removed from the transcript before translation.

          (b)
          1. (iv) Fusion of second male gamete with two polar nuclei.
          2. (iv) Brain
          3. (iii) 44 + XO
          4. (i) RNA molecule

          (c) (i) Photoautotrophic bacteria
          (ii) Tubectomy
          (iii) Commensalism
          (iv) Turgor pressure

          (d) (i) Sexually Transmitted Disease.
          (ii) Nicotinamide Adenine Dinucleotide Phosphate.
          (iii) Magnetic Resonance Imaging.
          (iv) Dichloro diphenyl trichloroethane.

          (e) (i) Dart (1924) fossil of a child called Taung Baby.
          (ii) Fox (1957)
          (iii) Meyer (1938).
          (iv) Godfrey Hounsfield (1972)

          Part-II (50 Marks)
          Section-A
          (Answer any two questions)

          Question 2.
          (a) Give any three characters that have developed during human evolution. [3]
          (b) Explain the term homogeny. [1]
          (c) Give any two distinctive features of Dryopithecus. [1]
          Answer:
          (i) Bipedal locomotion
          (iii) Free grasping hands
          (v) Brain, speech and memory.

          (b) Chemogeny or chemical evolution in which the elements in the early atmosphere combined to produce simple and compound molecules, ultimately leading to the formation of complex organic molecules.

          (c) (i) Walked semi-erect on kunckles.
          (ii) Snout was slightly projecting.
          (iii) Brow ridges were absent.
          (iv) Forelimbs and hindlimbs were of the same size. (Any two points)

          Question 3.
          (a) Explain the evolution of giraffe’s neck according to Lamarck’s theory of evolution. [3]
          (b) Give two chromosomal similarities between man and apes. [1]
          (c) Name any two temporary embryonic structures invertebrates which provide evidence for evolution. [1]
          Answer:
          (a) Giraffe : According to Lamarck, Giraffe was initially deer-like animal who browsed on herbs and shrubs. However, due to famine-like conditions, food became scarce on the ground. It was, however, present on high shrubs and trees. As a result, the ancestors of Giraffe stretched their body, forelimbs and neck. There was slight success. The trait was passed to the next generation where stretching caused a further enlargement. The process continued for several generations. It increased the size of the animals, produced long forelimbs and a long neck of present-day Giraffe.

          (b) Chromosomal similarities between man and apes.

          1. Total amount of DNA in both is more or less similar.
          2. Banding pattern of individual human chromosomes is very similar to the banding pattern of corresponding chromosomes in apes.

          (c) Temporary embryonic structures in vertebrates.

          Question 4.
          (a) Persons suffering from sickle cell anaemia are at an advantage in Malaria infested areas. Explain. [3]
          (b) Define the term gene flow. [ 1 ]
          (c) What are analogous organs? Describe with one example from the plant kingdom. [1]
          Answer:
          (a) Sickle cell anaemia is an autosomal disorder in which the erythrocytes become sickle-shaped under oxygen deficiency as during strenuous exercise and at high altitudes. The disorder or disease is caused by the formation of an abnormal haemoglobin called haemoglobin-S. As found out by Ingram (1958), haemoglobin-S differs from normal haemoglobin-A in only one amino acid-6th amino acid of P-chain, glutamic acid, is replaced by valine. This is the major effect of the allele.

          During conditions of oxygen deficiency 6-valine forms hydrophobic bonds with complementary sites of other globin molecules. It distorts their configuration. As a result, erythrocytes having haemoglobin-S become sickle-shaped. This is one of the secondary effects. The homozygotes having only haemoglobin S usually die before reaching maturity because erythrocyte distortion and degeneration occur even under normal oxygen tension.

          Despite having harmful effect, the allele for sickle-cell anaemia continues to persist in human population because it has survival value in malaria-infested areas like tropical Africa. Malarial parasite is unable to penetrate the erythrocyte membrane and cause any harm. Further, the sickle cell heterozygotes do not suffer from syndrome. Their erythrocytes appear normal till ‘ there is oxygen deficiency when some sickle-shaped etythrocytes may be observed.

          Note : The gene for sickle-celled erythrocytes is represented by Hbs while that of normal erythrocytes is written as HbA. The homozygotes for the two types are Hbs and HbA. The heterozygotes is written as HbA Hbs.

          (b) Gene flow is the addition or loss of alleles from a population due to the entry or exit of a section of population. It reduces the differences in the gene pools of separate populations.

          (c) Analogous organs are those having similar outward form and function but quite different in anatomy and development e.g., tendrils help in climbing, in coiling around a support may be modified stipules (Smilax) in leaf-apex (Gloriosa), leaf-let (Pisum), whole leaf (Lathyrus) and stem-tendril (cucurbita, grapevine, passiflora).

          Section-B
          (Answer any two questions)

          Question 5.
          (a) With the help of diagrams, name and describe the different types of placentation seen in angiosperms. [4]
          (b) Give four points of anatomical differences between a monocot stem and a dicot stem. [4]
          (c) Define the following terms : [2]
          (i) Racemose inflorescence
          (ii) Osmotic pressure
          Answer:
          (a) Placentation : Placenta is a parenchymatous cushion present inside the ovary where ovules are borne. An ovary may have one or more placentae. The number, position and arrangement or distribution of placentae inside an ovary is called placentation. It is of . the following types :

          1. Marginal : A single longitudinal placenta having one or two alternate rows of ovules occurs along the wall of the ovary called ventral suture. Marginal placentation is found in monocarpellary pistils of leguminosae (e.g., Pea, Cassia, Acacia) and other plants (e.g., Larkspur).

          Fig. Parietal placentation. A

          B. normal panetai placentation. C, parietal placentation of Poppy. D, parietal placentation in Brasslca. E, modified parietal placeniation of Cucurbits.

          2. Parietal: Two or more longitudinal placentae develop along the wall of a syncarpous or compound pistil. The number of placentae correspond to the number of fusing carpels, e.g., two (Fun aria), three (Viola), four (Capparis). The ovary is usually unilocular (Fig. A-B) but modifications occur in many. In polycarpellary syncarpous pistil of poppy the ovule bearing placentae grow inwardly to form incomplete septa. A false septum called replum develops between the two parietal placentae in Mustard and other members of family Cruciferae. The ovary becomes bilocular. In the tricarpellary syncarpous pistil of cucurbits the three placentae grow inwards to meet in the centre and then bend outwardly. The ovary, therefore, becomes trilocular.

          3. Axile : It occurs in syncarpous pistils. The ovary is partitioned into two or more chambers. Placentae occur in the central region where the septa meet so that an axile column bearing ovules is formed, e.g., Petunia (bilocular), Asphodelus (trilocular), Shoe Flower (pentalocular), Althaea (multilocular).

          4. Free central : The pistil is polycarpellary and syncarpous but the ovary is unilocular. The ovules are borne around a central column which is not connected with the ovary wall by any septum, e.g., Pink (Dianthus), Silene, Primula.

          5. Basal: The pistil can be monocarpellary or syncarpous. The ovary is unilocular. It bears a single placenta at the base with generally a single ovule, e.g., Ranunculus, Sunflower.

          6. Apical : The ovary is unilocular and bears a single ovule that hangs from the tip of the chamber, e.g.. Cannabis. The terms sub-basal or sub-apical are used for single ovules borne on one side near the base or apex.

          7. Superficial: The ovules develop on the whole inner surface of the ovary including the septa, if present. Superficial placentation is found in both monocarpellary (e.g., Butomus) and syncarpous (e.g., Nymphaed) pistils.

          Monocot Stem Dicot Stem
          (i) Epidermal hairs absent. (i) Multicellular epidermal hairs present.
          (ii) Ground tissue undifferentiated. (ii) Ground tissue differentiated into cortex, endodermis and pericycle.
          (iii) Vascular bundles are scattered in ground tissue. (iii) Vascular bundles are arranged in a ring.
          (iv) Vascular bundles are conjoint collateral and closed. (iv) Vascular bundles are conjoint, collateral and open.
          (v) Pith absent. (v) Pith present.
          (vi) Xylem tracheids and vessels oval in outline. (vi) Tracheids and vessels are polygonal in outline.
          (vii) Secondary growth absent. (vii) Secondary growth present.

          1. Racemose inflorescence is a indefinite inflorescence in which the growing point of the flowering axis i.e. peduncle continues its growth, producing flowers laterally in an acropetal manner.
          2. Osmotic pressure is the maximum pressure that cars be developed in a solution separated from pure water by a semipermeable membrane.

          Question 6.
          (a) Draw a diagram of the internal structure of the human ovary.
          (b) Define the term water potential. What are its components? Explain.
          (c) Give definition and importance of:
          (i) Imbibition
          (ii) Parturition
          Answer:

          (b) The difference between the free energy of water molecules in pure water and the energy of water in any other system (e.g., water in a solution or in a plant cell or tissue) is called water potential. The Greek letter psi the symbol for which is Ψ designates the water potential in a system. The water potential is measured in bars a bar is a pressure unit, which equals 14.5 lb! n2 750 mm Hg or 0-987 atm.

          Water potential (Ψ) of protoplasm of the cell is equal but opposite in sign to the diffusion pressure deficit (DPD) or suction pressure (SP). The water potential of a solution can be determined using pure water as standard of reference. The pure water at atmospheric pressure has a water potential of zero (i)). The presence of solute particles reduces the energy of water and thus decreases the water potential (negative). Therefore, the water potential of a solution is always less than zero. The direction of flow of water between the two regions will take place from the region of higher water potential (pure water) to the region of lower water potential (as in a solution), energetically downhill.

          Components a water potential :
          The typical plant cell consists of a cell wall, a vacuole filled with an aqueous solution and a layer of cytoplasm between the vacuole and the cell wall. When such a cell is subjected to the movement of water, many factors begin to operate which ultimately determine the water potential of cell sap. For solutions, such as contents of cells, water potential is determined by three major sets of internal factors viz., matric potential (Ψ rn), solute potential (Ψ s) and pressure potential (Ψ p). The water potential (Ψ) in a plant cell or tissue can be written as the sum of the matric potential (Ψ m) due to binding of water to cell walls and cytoplasm, the solute potential (Ψ s) due to concentration of dissolved solutes, which by its effect on the entropy components reduces the water potential and the pressure potential (Ψ p) due to hvdrostatic pressure, which by its effect on the energy components increases the water potential:

          Each component potential is discussed separately below :

          Matric potential (Ψ m) : Matric is the term used for the surface (such as, soil particles cell walls protoplasms etc.) to which water molecules are adsorbed. The matric potential (Ψ m) is the component of water potential influenced by the presence of a matrix. It has got a negative value. In case of plant cells and tissues, the matric potential is often disregarded because it is not significant in osmosis. Thus, the above equation (1) may be simplified as follows :

          Solute potential (Ψ s) : Solute potential is also known as Osmotic potential. It is defined as the amount by which the water potential is reduced as a result of the presence of solute. Solute potentials or osmotic potentials (Ψ s) are always in negative values (number). The term solute potential takes the place of osmose pressure, expressed in bars with a negative sign.

          Pressure potential (Ψ s) : Plant cell wall is elastic and it exerts a pressure on the cellular contents. As a result of inward wall pressure, hydrostatic pressure is developed in the vacuole termed as turgor pressure. The pressure potential is usually positive and operates in plant cells as wall pressure and turgor pressure.

          1. Imbibition is the phenomenon of adsorption of water or any other liquid by the solid particles of a substance without forming a solution.
          2. Imbibition is the initial step in the germination of seeds, when seed coats imbibe water ‘ followed by embryo and endosperm.
          3. Imbibition cause swelling of seeds and breaking of testa.
          4. The imbibition is dominant in the initial stage of water absorption by root hair cells.
          5. Water moves into ovules which are ripening into seeds by the process of imbibition.

          (d) Parturition : It is the act of expelling the full term young one/foetus from the mother uterus at the end of gestation period. Hormones play a major role in parturition.

          It is important that baby bom when it is mature. The foetal signals that it is mature by secreting certain hormones. The hormones diffuse across the placenta into mother’s blood, where they cause the excretion of oxytocin from her pituitary oxytocin stimulate the uterine contractions. This provides force to expel the baby from the uterus causing birth.

          As a result of parturition, milk is produced in the female’s breasts following the birth of a young one. The actual release of milk, requires the presence of oxytocin, to bring contraction of smooth muscles of the ducts within the mammnary glands.

          Question 7.
          (a) Give four adaptations in flowers pollinated by insects. [4]
          (b) Describe the mass flow hypothesis for translocation of organic solutes (food) in plants. [4]
          (c) Write a brief note on the causes of infertility. [2]
          Answer:
          (a) Characters of Anemophilous Flowers (Insect-pollination)

          • Flowers are small and inconspicuous.
          • Non-essential floral parts are reduced or absent.
          • Flowers are usually colourless, nectarless and odourless.
          • Flowers are developed above the foliage, usually in hanging spikes or catkins.
          • Male flowers are more abundant in case of unisexual flowers. In bisexual flowers stamens are more abundant.
          • Anthers are exserted and versatile.
          • Pollen grains are small and light. They may have air sacs or wings.
          • Pollen grains are dry and unwettable. This protects the pollen from moisture present in the air.
          • Stigmas are exserted, hairy feathery or branched to capture the pollen grains. The cob of Maize has elongated stigmas
          • and styles which sway in wind to trap pollen grains.
          • A very large number of pollen grains are produced, e.g., 500000 per flower in Cannabis, 25 million by a tassel of Maize and 135 million by Mercurialis.
          • Pistils commonly possess single ovules.

          Examples. Anemophily is common in grasses. Other examples are Amaranthus, Cannabis, Chenopodium, Coconut, Date, Mulberry, Poplar, Willow, etc.
          (Any four points)

          (b) Mass Flow or Pressure Flow Hypothesis : It was put forward by Munch (1927, 1930). According to this hypothesis, organic substances move from the region of high osmotic pressure to the region of low osmotic pressure in a mass flow due to the development of a gradient of turgor pressure. This can be proved by taking two interconnected osmometers, one with high solute concentration. The two osmometers of the apparatus are placed in water (Fig.). More water enters the osmometer having high solute concentration as compared to the other. It will, therefore, come to have high turgor ‘pressure which forces the solution to pass into the second osmometer by a mass flow. If the solutes are replenished in the donor osmometer and immobilised in the recipient osmometer, the mass flow can be maintained indefinitely.

          Fig. B. Translocation of organic substances (assimilates) according to mass flow or pressure flow hypothesis Sieve tube system is fully adapted to mass flow of solutes. Here the vacuoles are fully permeable because of the absence of tonoplast. A continuous high osmotic concentration is present in the mesophyll cells (due to photosynthesis) and storage cells (due to mobilization of reserve food). The organic substances present in them are passed into the sieve tubes (by means of transfer cells).

          A high osmotic concentration, therefore, develops in the sieve tubes of the source. The sieve tubes absorb water from the surrounding xylem and develop a high turgor pressure (Fig.). It causes the flow of organic solution toward the area of low turgor pressure. A low turgor is maintained in the sink region by converting soluble organic substances into insoluble form. Water passes back into xylem.

          (c) Causes of infertility : Infertility is the failure to conceive when after to 1-2 years of regular unprotected sex i.e., inability to produce offspring. Infertility can be defined as relative sterility. Infertility is caused by defects found in male, female as well as both.

          • Cryptorchidism or failure of testes to descend into scrotum.lt causes azospermia.
          • Absence or blockage of vasa deferentia and vasa efferentia.
          • Hyperthermia or higher scrotal temperature due to varicocele (varicose veins), hydrocele or filariasis, tight undergarment, thermal undergarment or working in hot environment,
          • Infection like mumps after puberty, infection of seminal vesicle.
          • Alcoholism inhibits spermatogenesis.
          • Gonadotropin deficiency.
          • Cytotoxic drugs, radiations, antidepressant and anticonvulsant drugs depress spermatogenesis.

          Infertility in Females : The various causes of infertility in females are as follow :

          • Anovulation (nonovulation) and oligoovulation (deficient ovulation).
          • Inadequate growth and functioning of corpus luteum resulting in reduced progesterone secretion and deficient secretory changes in endometrium.
          • The ovum is not liberated but remains trapped inside the follicle.
          • Fallopian tube may fail to pick up ovum, have impaired motility, loss of cilia and blocked lumen.
          • Noncanalisation of uterus.
          • Defective uterine endometrium due to either reduced or excessive secretory activity.
          • Congenital malformation of uterus.
          • Fibroid uterus.
          • Defects in cervix like congenital elongation, occlusion of cervix by a polyp, cervicitis, scanty or excessive cervical mucus.
          • Defective vaginal growth like atresia and transverse septum.

          Section-C
          (Answer any two questions)

          Questions 8.
          (a) Give any four reasons for Mendel’s success. [4]
          (b) Briefly describe the technique employed in DNA fingerprinting. [4]
          (c) Give any two features of Genetic Code. [2]
          Answers:
          (a) Reasons for Mendel’s Success :

          • Mendel selected only pure breeding varieties of Pea (Pisum sativum) for his experiments.
          • Mendel took only those traits for his studies which did not show linkage, interaction or incomplete dominance.
          • Mendel took one or two characters at one time for his breeding experiments while his predecessors often studied all the traits simultaneously.
          • Mendel’s experimental plant Pea (Pisum sativum) is ideal for controlled breeding. It is • cross-breed manually while normally it undergoes self breeding.
          • He took care to avoid contamination from foreign pollen grains brought by insects.
          • Mendel kept a complete record of every cross, subsequent self breeding and the number of seeds produced.
          • He formulated theoretical explanations for interpreting his results. His explanations were further tested by him as to their validity.
          • Mendel used statistical methods and law of probability analysing his results.
          • Mendel was lucky in selecting those traits, the genes of which were either present on different chromosomes or showed recombination. (Any four points)

          (b) Southern Blot Technique:
          The Southern blot is one way to analyze the genetic patterns which appear in a person DNA. Performing a Southering Blot involves :

          Source of DNA : White blood corpuscles, blood, semen, saliva, vaginal swabs, skin cells, bone cells, cells from hair root, etc. are used as a source of DNA for fingerprinting. The amount of DNA required can be met by 1 microgram of tissue or 1,00,000 cells.

          • Isolation and Extraction – Isolation of DNA from DNA source cells in a high speed refrigerated centrifuge.
          • DNA Amplification – Many copies of extracted DNA are made by PCR-technique.
          • Fragmentation/Digestion of DNA by restriction endonuclease to produce VNTRs.
          • Separation of DNA fragments (VNTRs) by size through gel electrophoresis.
          • Single stranded DNA – Denaturing of VNTRs either by heating or chemically treating the fragments in the gel.
          • Southern Blotting – Transferring (blotting) of separated single-stranded DNA fragments to synthetic membranes such as nitrocellulose or nylon.
          • Hybridisation – Using radioactive/labelled VNTR probe.
          • Exposure to X-Ray films/Autoradiography – Detection of hybridised DNA by autoradiography.
          • After hybridisation autoradiography shows many dark bands of different sizes.
          • These bands give a characteristic pattern for an individual DNA.

          DNA prints or DNA profiles of dead bodies are compared with DNA prints of the close, blood relatives (sisters, brothers, parents) to determine the identity of the dead bodies.

          (c) Characteristics of Genetic Code :

          1. Triplet Code : Three adjacent nitrogen bases constitute a codon which specifies the placement of one amino acid in a polypeptide.
          2. Start Signal: Polypeptide synthesis is signalled by two initiation codons – methionine AUG or codon and GUG or valine codon.
          3. Stop Signal: Polypeptide chain termination is signalled by three termination codons – UAA (ochre), UAG (amber) and UGA (opal). They do not specify any amino acid and are hence also called nonsense codons.
          4. Universal Code : The genetic code is applicable universally, i.e., a codon specifies the same amino acid from a virus to a tree or human being. Thus, /wRNA from chick oviduct introduced in Escherichia coli produces ovalbumin in the bacterium exactly similar to one formed in chick.
          5. Nonambiguous Codons : One codon specifies only one amino acid and not any other.
          6. Related Codons : Amino acids with similar properties have related codons, e.g., aromatic amino acids tryptophan (UGG), phenylalanine (UUC, UUU), tyrosine (UAC, UAU). (Any four points)

          Question 9.
          (a) Explain the mechanism of action of T-cells to antigens. [4]
          (b) Explain how insulin can be produced using recombinant DNA technology. [4]
          (c) What is pisiculture? Give one advantage. [2]
          Answer:
          (a) Mechanism of action of T-cells : On coming on contact with an antigen, a T-lymphocyte forms a clone of lymphocytes. The clone has 4 types of T-cells – helper T-cells, killer T-cells, supressor T-cells and memory T-cells. Out of these, the first three types are also called effector T-cells.

          (i) Helper T-cells – They form 75% of the total lymphocytes of a clone. They secrete lymphokines for performing several types of functions like proliferation of other T-cells, stimulation of B-lymphocytes, attraction of macrophages and feedback system.

          (ii) Killer or Cytotoxic T-cells – The T-cells reach the site of infection, come in contact with microbes and secrete perforins. Perforins produce holes. It is followed by secretion of toxic chemicals or lymphotoxins into the microbes for killing the same. Soon after a killer T-cell separates and . attacks another pathogen. Cytotoxic T-cells also attack cancer cells, cells of transplanted organs and helper T-cells invaded by HIV.

          (iii) Supressor T-cells – They are protective T-cells which inactivate immune system,

          (vi) Memory T-cells – They are those T-cells which were previously sensitised and retain the sensitisation for future.

          Fig. Killing of foreign cell by cytotoxic T-cells.

          (b) Insulin is a hormone produced by the pancreas which is a large gland present near, the stomach. This hormone is necessary for the body’s correct use of food, especially sugar. Insulin works by helping the sugar that penetrates the cell wall, where it is then utilized by the cell. In diabetic persons, the body either does not make enough insulin or the insulin that is produced cannot be used properly.

          Insulin is the first genetically engineered hormonal drug ever marketed anywhere in the world. It was produced first in 1980 by Eli Lilly (U.S.A.) with the name Humulin by transferring the insulin gene into E. coli.

          Insulin gene is transferred into a bacterial cell (E. coli) in the following two steps :

          1. Transfer of the Insulin Gene into a Plasmid
          Vector : The plasmid is cut across both strands by a restriction Transfer of the insulin gene enzyme leaving the loose, sticky ends to which DNA Restriction ^ human can be attached. Special linking sequences (called linkers) are added to the human cDNA (complemen- aoning the ,nsu|in Gene tary DNA) so that it will fit precisely into the loose ends of the opened ring of plasmid DNA. The plasmid containing the human gene, also called a recombinant plasmid, is now ready to be inserted into another organism such as a bacterial cell (E. coli). fig. Transfer and cloning of insulin gene.

          2. Cloning the Insulin Gene : The recombinant plasmids and the bacterial cells are mixed up. Plasmid enters the bacterial cell through a process called transfection (Fig.) The . plasmid containing the human cDNA present inside bacterial cells is multiplied to get several dozen copies. When the bacteria divide, the plasmids also divide. Thus two daughter cells and the plasmids continue to reproduce. With cells dividing rapidly (every 20 minutes), a bacterium containing human cDNA (encoding for insulin) will shortly produce many millions of similar cells called clones containing the same human gene. In this way a large number of insulin molecules can be commerically produced in a fermentor.

          (b) Insulin Production r-DNA technology

          1. A DNA fragment encoding each insulin chain was made by annealing two complementary oligonucleotides that had been chemically synthesised.
          2. Each fragments was ligated into a bacterial expression vector such that during translation the insulin chain would be fused to the carboxy terminus of the beta-galactosidase enzyme.
          3. The expression vectors, were transformed into E.coli and the beta-insulin fusion proteins accumulated inside the bacterial cells.
          4. The cells were harvested and each beta-gal-insulin fusion protein was purified.
          5. The insulin coding DNA was synthesised so that it started with a methionine codon. This provides a way to cleave off the beta-gal part from the insulin polypeptide.
          6. Treatment of the fusion protein with cyanogens bromide (CNBr) cleave the peptides bonds after the methionine.
            Thus, in this way recombinant insulin is produced in E.coil.

          (c) Pisciculture is cultivating, rearing and harvesting of fish. Fish is an important source of food, rich in iodine and other minerals. Fish liver oil is a good source .of vitamin A and D.

          Question 10.
          (a) Name the causative organism and preventive measures for each of the following : [4]
          (i) Swine flu
          (ii) Typhoid
          (iii) Filariasis
          (iv) Syphilis

          (b) State four causes and four consequences of population growth
          (c) Differentiate between:
          (i) Cannabinoids and Barbiturates
          (ii) Biotic potential and Carrying capacity.
          Answer

          DiseaseCausative agentPreventive Measures
          (i) Swine flu H1N1 (virus) Bearing of mask in contact with patients.
          (ii)Typhoid Salmonella typhi (Bacteria) Avoid contaminated food and water.
          (iii) Filariasis Wuchereria bancrofti (Helminth) Avoid mosquito bite of especially culex.
          (iv)Syphilis Treponema pallidum (Spirochete Bacteria) Avoid sex with many partners.

          (b) Population growth is the increase in size of the population over a period of time. Human population is growing at a fast rate exihibiting population explosion. The two primary reasons for increase in human population are :

          Factors favouring population growth :

          1. Decrease in death rate.
          2. Increase in average life span.
          3. Better medical facilities.
          4. Control of insect vector’s of fatal diseases and epidemics.
          5. Better sanitation.
          6. Proper care of new-born children and their mothers.
          7. Better nutrition and life amenities.
          8. Protection against wildlife and adverse weather through living in houses. (Any four points)

          Consequences : Overpopulation has become a serious world problem. With increase in population, the available natural resources will fall short of requirements.
          The more important consequences are :

          1. Housing : New towns and cities are coming up to accommodate the growing population. This has put a great strain on agricultural land and forests. Clearing of forests for habitation and agriculture has caused new problems, particularly soil erosion and floods. Even with the coming up of new residential complexes, housing problem persists.
          2. Food : Large families with moderate means are unable to provide adequate and balanced diet to the children. The latter suffer from malnutrition and grow into less fit members of society.
          3. Employment : Rise in population has resulted in large scale unemployment. New employment schemes introduced by government have failed to absorb the fast growing numbers.
          4. Education : Increase in population has led to rush in educational institutions and lowering of educational standards. A large family is unable to afford higher education to the children.
          5. Medical Aid : Proper medical facilities are also beyond the reach of large families. State too is unable to look after the health of the ever-growing population.
          • Hallucinogenic chemicals obtained from leaves, flowering tops of Cannabis sativa.
          • Cannabinoid receptors are usually present in the air.
          • They are hallucinogenic produce a dream-like state with disorientation loss of contact with reality etc.
          • They are synthetic drugs.
          • They are general depressant for all excitable cells, but the CNS is most sensitive to these drugs.
          • They are hypnotic and sedative in action.

          (ii) Biotic potential:
          It is the maximum rate of increase of any organism if left to itself and isolated from its natural enemies, diseases or other inhibiting factors.


          Levels of Organization of Living Things

          Living things are highly organized and structured, following a hierarchy on a scale from small to large. The atom is the smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Atoms form molecules. A molecule is a chemical structure consisting of at least two atoms held together by a chemical bond. Many molecules that are biologically important are macromolecules, large molecules that are typically formed by combining smaller units called monomers. An example of a macromolecule is deoxyribonucleic acid (DNA), which contains the instructions for the functioning of the organism that contains it.

          Figure 1.7 A molecule, like this large DNA molecule, is composed of atoms.


          17 Ways Bacteria Are Easy to Understand

          Bacteria are prokaryotic and unicellular organisms. Bacteria have a simple organization they contain an external cell wall, a plasma membrane, circular DNA within the cytoplasm and ribosomes for protein synthesis. Some bacteria are encapsulated, meaning that they have a polysaccharide capsule outside their cell wall.

          More Bite-Sized Q&As Below

          2. Are bacteria the only prokaryotic organisms?

          Prokaryotic organisms are classified into two main groups: archaebacteria and bacteria (the latter is also known as eubacteria).

          Compared to bacteria, archaebacteria present basic differences, such as the chemical composition of their plasma membrane and cell wall and different enzymes related to DNA and RNA metabolism.

          3. What are halophilic, thermoacidophilic and methanogen archaebacteria?

          These are three types of archaebacteria. Halophilic archaebacteria only survive in salt-rich environments (even the salinity of the sea is not enough for them). Thermoacidophilic archaebacteria are characterized by living in high temperatures and low pHs. Methanogen archaebacteria are those that release methane gas (CH₄). They are found in swamps.

          Importance of Bacteria

          4. What are the main ecological roles of bacteria?

          Bacteria are responsible for the decomposition process at the end of food chains and food webs. In this process, they also release useful gases and nutrients for other living organism. Bacteria that live within the digestive tracts of ruminants and some insects digest cellulose for these animals. Some bacteria also participate in the nitrogen cycle, carrying out the fixation of nitrogen, nitrification and denitrification, almost always in a mutualistic ecological interaction with plants. Bacteria present within living organisms, such as those that live inside the bowels, compete with other pathogenic bacteria, therefore helping to control the population of noxious agents. There are also bacteria that cause diseases and bacteria used in the production of medical drugs.

          The excessive Growth or mass destruction of bacteria can impact entire ecosystems. For example, when a river is polluted by organic material, the population of aerobic bacteria increases since the organic material is food for them. This large number of bacteria then exhausts the oxygen dissolved in the water and other aerobic organisms (like fish) experience mass death.

          5. What are examples of human diseases caused by bacteria?

          Some human diseases caused by bacteria are tuberculosis, pertussis, diphtheria, bacterial meningitis, gonorrhea, syphilis, the bubonic plague, leptospirosis, cholera, typhoid fever, Hansen’s disease, trachoma, tetanus and anthrax.

          6. What are some industrial processes that use bacteria?

          Bacteria are used by industry in various ways. Some vaccines are made of attenuated pathogenic bacteria or antigens present in bacteria. One of the most ancient uses of bacteria is the fermentation of milk to produce yogurt, cheese and curds (even before people knew of the existence of bacteria, these microorganisms were already used to make those products). Some methods of antibiotic production involve bacteria. Recombinant DNA technology (genetic engineering) allows the industrial production and commercialization of human proteins, such as insulin for diabetics, which is synthesized by mutant bacteria. Some bacteria can produce fuel, like methane gas.

          7. What are some mechanisms by which pathogenic bacteria cause diseases? Why is this knowledge important?

          Pathogenic bacteria have characteristics known as virulence factors, which help them to parasite their hosts. Some bacteria have fimbriae, cilium-like structures that hook the bacterial cell onto the host tissue. Some bacteria are specialized in intracellular parasitism. Others secrete toxins, molecules that cause disease. In some cases, bacterial population growth causes food poisoning by toxins. Generally, bacterial disease is caused by bacterial population growth resulting in the invasion and destruction of tissues or by bacterial toxins that contaminate an organism. 

          8. In which environments do bacteria live?

          Bacteria can be found in various environments all over the planet. There are bacteria in the air, in fresh water, on the surface, in the intermediate depth and on the bottom of the sea, in soil, on our skin and practically in all environments on the planet in which air circulates freely. Some bacteria can be found in volcanic craters under extremely high temperatures.

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          The Classification of Bacteria

          9. How are bacteria classified according to the production of organic material for their energetic metabolism?

          Most bacteria are heterotrophic, meaning that they do not produce their own food. There are also autotrophic bacteria, such as chemosynthetic bacteria or photosynthetic bacteria.

          Some photosynthetic bacteria, such as cyanobacteria, use photosynthesis like plants do, using water. Others, such as the sulfur photosynthetic bacteria, use hydrogen sulfide (H₂S) instead of water.

          10. How are bacteria classified according to their need for oxygen?

          According to their need for oxygen, bacteria are classified into anaerobic (those that survive without oxygen) and aerobic (those that do not survive without oxygen). 

          11. What is meant when it is said that a bacterium is an obligate anaerobe?

          Obligate anaerobes are living organisms that do not survive in the presence of oxygen. For example, the bacteria Clostridium tetani, the agent of tetanus, is an obligate anaerobe.

          In superficial wounds, it is common to use hydrogen peroxide to expose anaerobic microorganisms to oxygen to kill them. 

          12. According to their morphology, how are bacteria classified?

          Bacteria come in different shapes. A bacterium can be classified as coccus, bacillus, vibrion or spirochete.

          Bacterial Cell Structure

          13. What is the main component of the cell wall of bacteria?

          The bacterial cell wall is made of peptidoglycans.

          14. Which intracellular organelles are present in bacteria?

          Heterotrophic bacteria have ribosomes, essential for protein synthesis. 

          Plasmids

          15. What are plasmids? What is the importance of plasmids for recombinant DNA technology?

          Plasmids are circular fragments of DNA that are accessories to the main bacterial DNA. Plasmids are important for genetic engineering because genes from other organisms are inserted into them to produce recombinant organisms, such as mutant bacteria. These bacteria are made to produce useful proteins for humans on an industrial scale, for example.

          Bacterial Cell Review - Image Diversity: plasmid

          Bacterial Reproduction

          16. How do bacteria reproduce?

          Bacteria reproduce through binary fission (scissiparity). However, some bacteria use types of sexual reproduction (transformation, transduction or conjugation) with a combination of genetic material from different specimens.

          17. How does sexual reproduction occur in bacteria? How different are the types of bacterial sexual reproduction?

          Sexual reproduction occurs when bacteria incorporate genetic material into other bacteria of the same species the inserted genetic fragment then becomes a part of the genetic material of the second bacterium. This kind of reproduction can happen by means of transformation, transduction or conjugation.