Class 11 Biology - WEST-BENGAL
Photosynthesis in Higher Plants
Photosynthesis in Higher Plants is a crucial chapter for Class 11 West Bengal (WBBSE) students that explores how green plants manufacture their own food using light energy. This chapter delves into the site of photosynthesis (chloroplasts), the pigments involved, and the two main phases: light-dependent reactions (photophosphorylation) and light-independent reactions (Calvin cycle). Students also study alternative pathways like C4 and CAM pathways, along with factors affecting the rate of photosynthesis like light intensity and carbon dioxide concentration. Mastering this chapter is essential for scoring well in board exams and understanding plant physiology.
Start Learning FreeKey Concepts
Site of Photosynthesis
Photosynthesis primarily takes place in the chloroplasts of plant leaves, specifically within the thylakoid membranes (light reaction) and the stroma (dark reaction).
Photosynthetic Pigments
Chlorophyll a, chlorophyll b, xanthophylls, and carotenoids are the main pigments that absorb light energy at different wavelengths, with chlorophyll a acting as the primary reaction center.
Light Reaction (Photophosphorylation)
Occurs in the thylakoid membrane where sunlight is trapped to split water molecules (photolysis), generating ATP, NADPH, and releasing oxygen as a byproduct.
Dark Reaction (Calvin Cycle)
Takes place in the stroma using the ATP and NADPH produced in the light reaction to fix carbon dioxide into glucose through carbon fixation, reduction, and regeneration phases.
C4 and CAM Pathways
Specialized carbon fixation adaptations found in plants living in dry or hot climates to minimize photorespiration and efficiently use water and carbon dioxide.
Important Formulas
Board Exam Info
In the West Bengal (WBBSE) Class 11 Biology annual examination, this chapter typically carries around 5 to 7 marks. Questions usually include a mix of Multiple Choice Questions (MCQs), short-answer type questions (2-3 marks) on differences between C3 and C4 plants or cyclic and non-cyclic photophosphorylation, and a long-answer question (5 marks) involving the Calvin cycle or mechanism of photosynthesis.
Frequently Asked Questions
In cyclic photophosphorylation, only Photosystem I is involved, electrons cycle back to P700, and only ATP is produced without NADPH or oxygen. In non-cyclic photophosphorylation, both Photosystem II and I are involved, producing ATP, NADPH, and oxygen through photolysis of water.
Non-cyclic involves both PS I and PS II, producing ATP, NADPH, and O2, while cyclic involves only PS I and produces only ATP.
Why is the Calvin cycle also called the C3 pathway?
It is called the C3 pathway because the first stable product of carbon dioxide fixation is a 3-carbon compound called 3-phosphoglyceric acid (PGA).
What are Blackman's Law of Limiting Factors?
It states that if a chemical process is affected by more than one factor, its rate will be determined by the factor that is nearest to its minimal value, which is the limiting factor.
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