Plant cells have a thick, relatively rigid outer envelope: the cellulosic wall, also called the cellulosic skeletal membrane; Primary and Secondary Cellulosic Walls Young plant cells have a thin and flexible cellulosic wall called the primary wall. The primary wall is elastic to allow cell growth.

In this process, the substances are transported with energy expenditure and may occur from the lowest to the highest concentration (against the concentration gradient). This gradient can be chemical or electrical, as in ion transport. Active transport acts as a “revolving door”.

Phagocytosis This process is very similar to pinocytosis, the only difference being that the material surrounding the membrane is not diluted. While pinocytosis is a process common to almost all eukaryotic cells, many cells belonging to multicellular organisms do not perform phagocytosis, but are made by specific cells.

Basic sanitation - set of actions, services and works responsible for the collection, treatment and distribution of water for public supply; sewage collection and treatment; collection, transportation, treatment and final disposal of waste. Segmentation - See Cleavage. Natural selection - the process of natural elimination of those less environmentally friendly, who, because they are less likely to succeed than those who are better adapted, leave a smaller offspring.

Salivary amylase digests starch and other polysaccharides (such as glycogen), reducing them to maltose (disaccharide) molecules. Salts, in saliva, neutralize acidic substances and maintain a slightly acidic pH in the mouth (6, 7), ideal for the action of ptialin. The food, which turns into a food bolus, is pushed by the tongue to the bottom of the pharynx, being sent to the esophagus, driven by peristaltic waves (as shown in the figure below), taking between 5 and 10 seconds to travel through the esophagus.

Satellites Until 1610, the only known satellite was Earth's - the Moon. At that time, Galileo Galilei (1564-1642), with his spyglass, discovered satellites orbiting the planet Jupiter. Today we know of dozens of satellites. In astronomy, a natural satellite is a celestial body that moves around a planet thanks to gravitational force.