Life Process, Topic Chloroplast (For Class 8 and  class 10 ) By PK Verma

* Chloroplast are the green plastids which occur in all the green parts of the plants.

* Chloroplasts are often called food production centres of the cell.

* Chloroplast are the actual site of photosynthesis. The chloroplast contain chlorophyll and carotenoids pigments which are responsible for trapping light energy essential for photosynthesis.

* Majority of the chloroplast of the green plants are formed in the mesophyll cells of the leaves. They are lens shaped oval , spherical, discoid or even Ribbon like organelles having variable length. 

* The chloroplasts  are double membrane bound organelles. The space limited by the inner membrane of the chloroplast is called the stroma.

* A number of organised flattened membranous sacs called the thylakoids are present in the stroma.

*Thylakoids are arranged in stacks like piles of coins called grana.

* The stroma of the chloroplast contains enzymes required for the synthesis of  Carbohydrates and proteins.

* The photosynthetically active pigments are are chlorophylls, carotenoids and  phycobilins.

* As many as eight major types of chlorophyll are known to exist in the plant Kingdom for example chlorophyll a, b, c, d and e bacterio chlorophyll a and b and chlorobium chlorophyll.

* Chlorophyll shows porphyrin structure . Chlorophyll consists of four pyrole ring attached to a magnesium atom at the centre and also phytol tail containing numerous carbon atoms.

* The pigments which absorb light and transmit it to the chlorophyll reaction Centre are carotenoids. Carotenoids mainly absorbs violet ,Indigo and the blue wavelength of spectrum but maximum absorption occurs at blue region.

* Carotenoids  are fat soluble and sometimes called as lipochromes. 

*Carotenoids   are accessory pigments present in chloroplast. And protect the chlorophyll from lethal condition namely photo-oxidation by a light of high  intensity. Hence this pigments are called Shield pigments.

*Chlorophyll absorbs more of blue wavelength than red as indicated by absorption spectrum. A graph showing absorption of light by chlorophyll a and b at different wavelengths is called the absorption spectrum.

*When Radiant energy reflects completely from the surface of a substance that substance appears white. Substances appear dark when they absorb Radiant energy completely and do not reflect it. Partly reflected light appears coloured.

* Chlorophyll absorbs all the light except green portion. Hence chloroplast with their chlorophylls impart green colour to the plant parts. Therefore leaves appear green.

* Type of protein present in the stroma is fraction 1 protein. This protein contains an enzyme RuBP Carboxylase. Dark phase reactions of photosynthesis take place in the stroma. Light phase reactions of photosynthesis occurs in grana regions.