Page 24 - Biology_F5

Cytology

Exercise 1.4 organelles. Organelles can be defined as tiny
distinct parts with specialised structures
1. Describe the composition of the and functions found inside the cell. The
cell walls in living organisms. organelles are sub-cellular structures
with characteristic morphological forms,
2. Explain the functions of lignin and distinctive chemical constitutients and
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suberin in the plant cell. definite functions. The organelles perform
specific functions such as oxidative
3. Give the name of the structure
which joins neighboring cell walls. phosphorylation and generation of energy
in the form of ATP in the mitochondria
as well as formulation and storage of
Cytoplasm and cytoplasmic organelles carbohydrates in chloroplast. They also
(sub-cellular units) perform the function of protein synthesis
The space between the cell membrane in ribosomes of the rough endoplasmic
and the nucleus is filled with translucent, reticulum as well as concentration and
homogenous and colloidal fluid called packing of secretions in Golgi apparatus.
a cytoplasmic liquid. The latter is an Other functions include synthesis of lipid
aqueous substance containing different and hormones in smooth endoplasmic
types of cell organelles, water and mineral reticulum, degradation of macromolecules
salts. It also contains organic compounds, in the lysosomes, regulation of all cellular
such as carbohydrates, lipids, proteins, activities by nucleus, and organisation of
nucleic acids and enzymes. spindle apparatus by centrioles.

Functions of the cytoplasm The nucleus
(a) It provides medium for chemical The nucleus is a functional unit of a cell.
reactions such as glycolysis to take It is a membrane-bound structure, located
place. at the periphery of the cell membrane
(b) It stores useful materials such as starch, more or less to the centre of the cell and it
glycogen, and lipids. contains the cell’s hereditary information.
(c) It stores waste materials such as It controls all cellular activities and is
nitrogenous wastes. the most prominent organelle in the cell.
(d) Movement of materials takes place The cell nucleus is bounded by a double
within the cytoplasm. membrane called the nuclear envelope.
(e) It harbours cell organelles that perform It is a selectively permeable membrane,
different functions such as protein allowing some materials to pass in and
synthesis in ribosomes and lipid out and it separates the contents of the
synthesis in smooth endoplasmic nucleus from the cytoplasm. The envelope
reticulum. regulates the flow of molecules into and
out of the nucleus through nuclear pores.
Cytoplasmic organelles The pores allow exchange of substances
Cytoplasmic matrix contains numerous between the nucleus and cytoplasm. The
membranous internal structures called pore has a definite structure formed by

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