CELLS - Biology - Темы по английскому - Топики - Для тех кто учится!!!
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CELLS

Cells
Cells are the building blocks of all living things, either
unicellular or multicellular. All metabolic activities are
performed within cells. Metabolism, excretion,
reproduction, respiration, irritability and growth are the
basic functions that cells must perform.
Cells have vital roles in the survival of an organism
despite their differences in structure and function. All are
involved in different functions such as movement, support,
energy etc. Thus, the unity of an organism is maintained by
differentiated cells. Although cells differ in function and
shape, they all possess an almost identical structure.
All are composed of a plasma membrane (or cell
membrane), cytoplasm and nucleus. The plasma
membrane is involved in the protection of the cell, providing
shape, transport of materials and communication.
In plant cells, the plasma membrane is surrounded by a
rigid cell wall. It is nonliving and is composed of cellulose
molecules. Gates in the cell wall allow the passage of
materials through the cells.
The cell wall provides shape for the plant cell and protects it
against hazards.
The cytoplasm is the liquid portion of the cell located between
the plasma membrane and the nucleus. It is composed of
organelles, organic and inorganic molecules. The organic
molecules of the cytoplasm are carbohydrates, proteins, fats and
nucleic acids. The inorganic molecules are minerals, water, etc.
The organelles of the cytoplasm are endoplasmic reticulum, Golgi
apparatus, ribosomes etc.
The nucleus is the most vital component of the cell. It contains
coded genetic information within its chromosomes. The cell can
not survive if it is removed.

Категория: Biology | Добавил: Warior (14.12.2012)
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