Online Notes on Chapter = 5 ( THE FUNDAMENTAL UNIT OF LIFE) Part 4

This is Online Notes on Chapter =  5 ( THE FUNDAMENTAL UNIT OF LIFE)  Part 4 for preparation of CBSE BOARD Examination, NTSE etc.

Mitochondria:

It is a rod shaped structure found in cytoplasm of all eukaryotic cells except mammalian RBC’s.

• These are also absent in prokaryotes.

• It was first seen by Kolliker in insect cells.

• Maximum mitochondria are found in metabolically active cells.

• It is also called as ‘Power House of the Cell’ or the ‘Storage Battery’.

• It is double membranous structure where outer membrane has specific proteins while inner membrane is folded inside to form chambers called "Cristae".

Functions of Mitochondria :

(a) Its main function is to produce and store the energy in the form of ATP.

(b) It is the site of Kreb cycle of respiration

Ribosomes:

Ribosomes are the sites of protein synthesis.

All structural and functional proteins (enzymes) coded by the nuclear DNA are synthesized upon cytoplasmic ribosomes. The DNA codes are transcripted into messenger RNA (mRNA) molecules in the chromosomes of the nucleus.

Functions of Ribosomes :

(a) Ribosomes are the main site of protein synthesis. Synthesized

proteins is transported by endoplasmic reticulum.

Plastid:

• It is double membranous discoidal structure, found only in plant cells.

• Besides being discoidal of rhombic in plant cells, they occur in variable shapes like in algae. They can be ‘U’-shaped, spiral, coiled, ribbonshaped etc.

Depending upon the type of pigment present in them, they are of following three types :

(i) Leucoplast – White, found in underground parts

(ii) Chloroplast – Red, brown

(iii) Chloroplast – Green in colour, found in aerial parts of plants

These are found only in plant cell. It helps in the process of photosynthesis so it is called the ‘Kitchen of Plants’.

Chloroplast have following two parts :

(i) Grana : It constitutes the lamellar system. These are found layered on top of each other. These stacks are called Grana. Each granum of the chloroplast is formed by superimposed closed compartments called Thylakoids.

Function : They are the sites of light reaction of photosynthesis as they contain photosynthetic pigment chlorophyll. In each thylakoid,

Quantasomes are present which are called as Photosynthetic units.

(ii) Stroma : It is a granular transparent substance also called as

matrix. Grana are embedded in it. Besides Grana they also contain lipid droplets, starch grains, ribosomes etc.

Function : This is the site of dark reaction of photosynthesis. Also helps in protein synthesis due to presence of ribosomes.

Vacuoles:

• These are membrane bounded regions in the cytoplasm containing water and other substances.

• They are bounded by a single membrane called Tonoplast.

• In animal cells vacuoles are smaller in size and numerous while in plant cells a single large vacuole is found which occupies about 90% of the volume of cell.

Functions :

It helps in maintaining osmotic pressure in a cell & stores toxic metabolic products of plant cell.

Lysosome:

• They are tiny sac-like granules containing enzymes of intracellular digestion.

• They are bounded by a single membrane.

• They occur in animal cells and a few plant cells.

• They do not have a definite shape or size.

Functions :

(a) Their main function is phagy = digestion.

(b) They are kind of waste disposal system.

(c) They help in digesting foreign materials & cells.

Suicidal Bag : During disturbances in cellular metabolism i.e., in case of cell damage, lysosomes burst and their enzymes are released into the cytoplasm and they digest their own cell. So they are also called ‘Suicidal Bag’.

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