CHLOROPLAST AND

CHLOROPHYLLS

CHLOROPLAST

INTO THE INTERIOR OF THE LEAF

o Leaves are the kitchen of the biosphere.

o Food is prepared in chloroplasts using sunlight.

o A pigment called chlorophyll present in the chloroplast helps to absorb sunlight.

o Chloroplasts occurs chiefly in the mesophyll cells of leaves.

o The shape of chloroplasts may vary with organism.

STRUCTURE OF A LEAF

stroma

grana

Chloroplast DNA

Ribosome

Stroma lamella

External membrane

Internal membrane

Periplastidal space

Granal thylacoids

Thylacoid membrane

3D STRACTURE OF CHLOROPLAST

Structure of chloroplast

• Chloroplast is a green double membrane bound organelle.

• Chloroplasts occurs chiefly in the mesophyll cells of leaves.

• The shape of chloroplasts may vary with organism these are may lens shaped, oval, spherical, discoid etc.

• It is double walled and fluid filled bag, having a gelatinous matrix, called stroma.

• It consist a lamellar membrane system, ribosomes, double-stranded circular DNA molecules, mRNA, tRNA, starch grains, lipid globules (plastoglobuli), enzymes, proteins, etc.

• A number of organized flattened membranous sacs called thylacoids are present in stroma.

• Thylacoid membranes are store houses of photosynthetic pigments.

• The thylacoid system consists of some cylindrical discs called grana (singular- granum).

• Each granum is a stock of several flattened sacs called granal lamellae or granal thylacoid.

• A few unstacked thylacoids may also be present they are called stromal thylacoid or stromal lamellae.

• Stromal lamellae are flate membranous tubules connecting the thylacoids of different grana.

• The membrane of the thylacoids enclose a space called lumen.

• The stroma of the chloroplast contain enzymes required for the synthesis of carbohydrates and proteins.

• Stroma is the metabolic centre concern with the fixation of CO2, and the synthesis of nucleic acid, sugars, fatty acids etc.

CHLOROPHYLL

Chlorophyll present in the chloroplast helps to absorb sunlight.

There are different types of chlorophylls in leaves such as chlorophyll a, chlorophyll b.

There are other pigments also give colour to leaves.

chlorophyll a – bluish green chlorophyll b – yellowish green Carotenes – yellowish orange Xanthophyll – yellow

All these pigments have the ability to absorb sunlight. But chlorophyll a alone can take part directly in photosynthesis.

The other pigments are called accessory pigments.

The accessory pigments absorb sun light and transfer there energy to chlorophyll a.

chlorophyll a and chlorophyll b absorb mainly the blue and red rays of visible light.

Since the green rays are not absorbed at all, it is reflected making the leaves appear green.

Other photosynthetic pigments are,

• Chlorophyll c in brown algae, diatoms, dinoflagellates.

• Chlorophyll d in some red algae.

• Bacteriochlorophyll in purple and green bacteria.

• Chlorobium chlorophyll (bacterioviridin) in green bacteria.

• Phycoerythrin in red algae and cyanobacteria

• Phycocyanin in red algae and cyanobacteria

• Bacteriorhodopsin in halobacteria.

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