PHOTO-AUTOTROPHIC MODE OF NUTRITION

PHOTO-AUTOTROPHIC MODE OF NUTRITION

Photo-autotropic mode of nutrition or photosynthesis  is the process by which photoautotrophs synthesize food in the presence of sunlight, CO₂ and H₂O. by this method solar energy is trapped by autotrophic organism and converted into food. In this process carbohydrates are synthesized from simple inorganic compounds like carbon dioxide and water in presence of chlorophyll and sunlight.

In plants the unused carbohydrates are stored in form of starch.

In animals unused food is stored in form of glycogen.

Chloroplast

Chloroplasts(G.k  chloros- grass green   plastos-moulded) are the green plastids which help in the synthesis of organic food. These are uniformly distributed in cytoplasm of plant cell.  Chloroplast is found in the upper surface of leaf, thus exposing it to maximum sunlight so that more solar enery is absorbed.

It is covered by a double membranous structure called chloroplast envelope where each membranous structure is a unit of plasma membrane like structure. This membrane can be observed by electron microscope.

Protein matrix present in chloroplast is called matrix or stroma.

Lamellae or thylakoids are a membrane system which run parallel to each other in stroma. There are two types of thyllakoids present in higher plants. Large thylakoid (stroma thylakoid)  extend from one end to other end of chloroplast , small thylakoid (grana thylakoid) are disk shaped and closely placed to each other to form grana. Grana and stroma thylakoid fuse with each other in the region of granum

Photosynthetic pigments

These are the pigments involved in photosynthesis. e.g.  chlorophyll, carotenoid (carotenes and xanthophylls) , anthocyanin, phycobilins (phycocyanin and phycoerythrin)

Chlorophylls are green pigment present in chloroplast and gives green color to plants. These are of seven types . chlorophyll a, b, c, d, e, bacteriochlorophyll and bacterioviridin. These traps solar energy and converts it into chemical energy during photosynthesis.

Carotenoids are lipid and are classified in two groups: carotenes which are orange red in color. Xanthophylls are yellow in color.

Carotenoid absorb light energy and transfer it to chlorophyll a and act as accessory pigment.

Site of photosynthesis

Photosynthesis takes place in chloroplast which contain the pigment chlorophyll. These pigments are therefore available in the green part of plants like leaves , green stem.

Carbon dioxide diffuses in the leaf through stomata present in lower surface of leaf. Chloroplast which is present in the upper surface of leaf captures more sunlight.  Leaf vein brings the water .

Raw material needed during phtotosynthesis

1.     Carbon dioxide – forms 0.32 % of total atmosphere. Provides carbon for carbohydrate formation. Hydrophytic plant use CO₂ dissolved in water

2.     Water – provides hydrogen for carbohydrate foemation. Helps in keeping stomata pores open. Deficiency of water  can cause closing of stomata thus checking CO₂  to enter the leaf.

Solar Energy is trapped in chloroplast and converted into chemical energy. This chemical energy is ATP ( adenosine triphosphate).

Carbohydrate synthesis during photosynthesis

6CO₂ + 6H₂O   ---^{light+chlorophyll}----à C₆H₁₂O₆ + 6O₂

Photosynthesis is the process where light energy is converted in chemical energy. Solar energy is captured by chlorophyll in presence of carbon-dioxide and oxygen and carbohydrate (food) and oxygen are formed. this biochemical  activity of plant uses solar energy to make their food, this carbohydrate undergoes respiration to release energy to be used in various metabolic activities.

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