• Millions of tasks performed by our body become possible
due to the presence of ‘cell’, which is the ‘basic unit of
life’. Cells can be broadly categorised into two types,
prokaryotic (without membrane bound organelles and
presence of nucleoid) and eukaryotic (with membrane
bound organelles and presence of nucleus) cells.
• Both prokaryotic and eukaryotic cells are surrounded
by a plasma membrane. Plasma membrane is mainly
composed of phospholipids. It is selectively permeable and
facilitates transport of molecules in and out of the cell.
Besides plasma membrane, cells of bacteria, algae, fungi
and some higher plants are surrounded by a rigid cell wall.
• Eukaryotic cell has two major compartments: nucleus
and cytoplasm. Nucleus is enclosed by a nuclear envelope
which has nuclear pores. The nuclear envelope encloses
nucleoplasm, nucleolus and the genetic material in form
of chromatin. Nucleolus helps in rRNA synthesis. A pair
of centrioles form spindle apparatus during cell division
in animal cells. Centrosome and centrioles form the basal
body of the cilia and flagella which facilitate locomotion.
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• Endomembrane system includes the Endoplasmic
Reticulum (ER), Golgi Apparatus, Lysosomes and Vacuoles.
ER is constituted by tubules called cisternae. It is of
two types: rough (with ribosomes) and smooth (without
ribosomes). Ribosomes are non-membranous structures
involved in protein synthesis.
• Ribosomes may be present freely in the cytoplasm or in
bound state on rough ER.
• The function of the ER is to help in synthesis and transport
of proteins, lipoproteins and glycogen.
• Golgi apparatus is a membranous organelle composed
of flattened sacs. It performs the packaging of secretory
substances and their transport from the cell.
• Lysosomes are single membrane structures containing
enzymes for digestion of all types of macromolecules.
• Vacuoles are membrane bound organelles that function
in storage, structural support and recycling in the cell.
• Peroxisomes and microbodies take part in oxidation
reactions within the cell. Glyoxysomes are peroxisomes
involved in fat metabolism.
• Mitochondria are bound by two membranes. Its
inner membrane has infoldings called cristae. The
mitochondria help in oxidative phosphorylation and
generation of ATP.
• In plant cells, pigment containing granules are called
plastids. The plastids containing the green pigment,
chlorophyll, are known as chloroplasts. Chloroplasts
are essential for photosynthesis.