Biology Today — May 2017

Functions

•    Synthesise and store ATPs by oxidation of respiratory substrates i.e., carbohydrates, proteins and fats.

•    Its matrix is the site of aerobic respiration i.e., Krebs cycle.

• Electron transport system and oxidative phosphorylation takes place in inner mitochondrial membrane.

• Synthesis of fatty acids, many amino acids as well as storage and release of calcium when required.

Cristae

Oxysomes

Intermembrane space

(Outer chamber)

Inner membrane

Outer membrane

Ribosomes

Mitochondrial matrix (Inner chamber)

Fig.: Ultrastructure of mitochondrium

Intracristal

space

Elementary particles

(oxysomes)

Respiratory

chain

Outer

membrane

Fig.: A. Inner membrane with elementary

particles, B. Elementary particle.

Outer

chamber

Inner

membrane

Porin

Crista

Stalk

F 1

F 0

B

A

Base

Head

PLASTIDS
• The term ‘plastid’ was introduced by E. Haeckel in 1866 but its clear definition was given by A. Schimper in 1883.
• Like mitochondria, they are also semi-autonomous organelles having DNA, ribosomes and RNA molecules.

• Plastids have double membrane envelope which store or synthesise various types of organic compound. They are restricted
only to plant cells, with exception of some protists.

• They develop from colourless precursors called proplastids. They are of three main types depending on colour.

Types of Plastid

Leucoplasts

•    Colourless, no pigment.

•    Generally found in non-green cells.

•    Depending on the type of stored food they are

of 3 types:

• Amyloplasts-store starch e.g., potato, rice,
  wheat.


• Elaioplasts-store fats and oil e.g., tube rose.


• Aleuroplasts-store protein e.g., aleurone
  cells of maize grain, endosperm cells of castor.

Chloroplasts

•    Green in colour, chlorophyll and

carotenoid pigments present.

•    Synthesis of food from inorganic raw

materials in the presence of radiation

energy.

•    Chromatophores are chloroplasts

found in algae that are non-green,

e.g., rhodoplasts in red algae,

phaeoplasts in brown algae.

Chromoplasts

•    Yellow or reddish in colour,

carotenoid pigments present,

chlorophyll absent.

•    Formed from leucoplasts or

chloroplasts.

•    Provide colour to flowers and

fruits, which in turn help in their

pollination and dispersal. They

are also the site of synthesis of

membrane lipids.

Structure of Chloroplast

•    They have various shapes, such as ribbon-like (e.g., Spirogyra), cup-shaped (e.g., Chlamydomonas) and plate-like (e.g.,

Ulothrix). Chloroplasts of higher plants are generally disc-shaped.