Page 46 - General and Inorganic Chemistry for Advanced Secondary Schools Students Book Form Five and Six

Biology for Secondary Schools

of lipids and protein molecules. (a) It determines the chemical processes
This membrane is flexible and semi- that take place in the cell.
permeable. Semi-permeable means that (b) It controls the functions of the cell.
it allows certain substances to pass in (c) It determines the cell’s size, shape,
or out of the cell. Flexibility of animal and functions.
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cell membrane and the lack of cell wall (d) It determines the hereditary
gives it an irregular shape. characteristics of a cell.

Cytoplasm Cell vacuoles
Cell vacuoles are fluid-filled spaces
This is a jelly-like substance made bound by a membrane. Animal cells
up of water and dissolved chemical have small and temporary vacuoles,
substances. The cytoplasm is the mainly used to secrete and excrete
site for many chemical reactions in wastes from the cell.
the cell. Cell organelles, such as the

vacuoles, nucleus, and mitochondria Mitochondria
are suspended in the cytoplasm. Mitochondria (singular is mitochondrion)
are oval-shaped organelles that have
Nucleus two membranes, as shown in Figure
This is a spherical organelle suspended 3.4. The outer membrane is smooth.
in the cytoplasm. The nucleus consists of The inner membrane has folds called
nucleolus and a fluid called nucleoplasm. cristae (singular is crista). The role of

It is surrounded by a membrane called mitochondria is to produce energy for
the nuclear membrane. The following the cell. That is why they are sometimes
are functions of the nucleus. referred to as ‘power houses of cells’.

Outer membrane

Cristae

Inner membrane
Matrix

Fig 3.4: The structure of a mitochondrion

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