Photosynthesis in Higher Plants Class 11 Notes Biology Chapter 13

Chloroplast-The site of photosynthesis:
The most active photosynthetic tissue in higher plants is the mesophyll of leaves. Mesophyll cells have many chloroplasts. Chloroplast is present in all the green parts of plants and leaves. There may be over half a million chloroplasts per square millimetre of leaf surface. In higher plants, the chloroplasts are discoid or lens-shaped. They are usually 4-10mm in diameter and 1-3mm in thickness.

Chloroplast pigments:
Pigments are the organic molecules that absorb light of specific wavelengths in the visible region due to presence of conjugated double bonds in their structures. The chloroplast pigments are fat soluble and are located in the lipid part of the thylakoid membranes.
(i) Chlorophylls: The chlorophylls, the green pigments in chloroplast are of seven types i.e., chlorophyll a, b, c, d, e, bacteriochlorophyll and bacterioviridin.


(ii) Carotenoids : The carotenoids are unsaturated polyhydrocarbons being composed of eight isoprene (C₅H₈) units. They are made up of two six-membered rings having a hydrocarbon chain in between. They are sometimes called lipochromes due to their fat soluble nature.

Difference between Photosystem I and Photosystem II


Difference between C3 Plants and C4 Plants



Difference between Photorespiration, Photosynthesis and True Respiration

Important Points:-
(a) Photosynthetic Materials: 264 gm of CO₂ and 216 gm of water give rise to 108 gm of water, 192 gm of O₂ and 180 gm of glucose.
(b) Rubisco: Rubisco constitutes 16% of chloroplast protein. It is the most abundant protein on this planet.
(c) Actual reduction of CO₂ to carbohydrates is independent of light, i.e., occurs in presence or absence of light, but production of assimilatory powers (ATP and NADPH₂) needs light and is light dependent.
(d) Willmott's bubbler is used to measure rate of O₂ evolution or rate of photosynthesis.
(e) T.W. Engelmann (1882) experimentally verified that in monochromatic lights, photosynthesis is maximum in red light.
(f) Cyclic photophosphorylation is the most effective anaerobic phosphorylation mechanism.
(g) NADP (Nicotinamide adenine dinucleotide phosphate) was earlier called as TPN (Triphosphopyridine nucleotide),
(h) In green plants the hydrogen acceptor is NADP, but in bacteria it is NAD.
(i) No Emerson effect is seen in bacteria.
(j) NAD is considered to be the "Universal hydrogen acceptor".
(k) Non-cyclic photophosphorylation or Z-scheme is inhibited by CMU and DCMU.
(l) As Calvin cycle takes in only one carbon (as CO₂) at a time, so it takes six turns of the cycle to produce a net gain of six carbons (i.e., hexose or glucose).
(m) Cytochromes: the term was coined by Keilin (1925) though the biochemicals were discovered by Mac Munn (1866).
(n) Intensity of light can be measured by Luxmeter.
(o) Isolated chlorophyll 'a' in pure form emits red colour. It is called fluoresence.
(p) Phytochrome is a proteinaceous pigment found in low concentrations in most plant organs. Which absorbs red (P_R or P₆₆₀) and far red (P_fR or P₇₃₀) light.
(q) Anthoxanthins and Anthocyanin pigments are also soluble in water and found in cell sap, due to which white, yellow and orange colour produce in flowers.