Photosynthesis in Higher Plants

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4. DÏFFËRËÑÇËS BËTWËËÑ Ç3 ÅÑD Ç4 PLÅÑTS

C3 Plants

C4 Plants

Photosynthesis occurs in mesophyll

cells

In mesophyll and bundle sheath

cells

Kranz anatomy absent

Present

RuBP is the primary CO2 acceptor

PEP is the primary CO2 acceptor

3-PGA, a 3-C compound in the first

stable product

OOA, a 4-C compound is the first

stable product

Chloroplast are of only one type

(granal)

Dimorphic (granal in mesophyll and

agranal in bundle sheath)

Photo respiratory loss is high

Photo

respiration

is

absent

or

negligible

Optimum

temperature

for

photosynthesis is about 25°C

About 35°C-45°C

Photosynthetically less efficient and

productivity low

Photosynthetically

more

efficent

and productivity high

E.g. Rice, wheat, bean, potato, etc.

E.g. Maize, sugarcane, amaranth,

Sorghum, etc.

FÅÇTØRS ÅFFËÇTÏÑG PHØTØSÝÑTHËSÏS



Internal (plant) factors: The number, size, age and orientation

of leaves, mesophyll cells and chloroplasts, internal CO2

concentration and amount of chlorophyll.



External factors: Sunlight, temperature, CO2 concentration and

water.



Blackman’s Law of Limiting Factors (1905): “If a biochemical

process is affected by more than one factor, its rate is

determined by the factor nearest to its minimal value: it is

the factor which directly affects the process if its quantity is

changed.”



E.g. a plant with green leaf, optimal light & CO2 conditions may

not photosynthesize if the temperature is very low. If optimal

temperature is given, it will start photosynthesis.