Class 11 Biology - ISC
Photosynthesis in Higher Plants
Photosynthesis in Higher Plants is a crucial chapter in Class 11 ISC Biology that explores how green plants synthesize organic food using sunlight, water, and carbon dioxide. This chapter delves into the site of photosynthesis, pigments involved, light-dependent reactions (photophosphorylation), and light-independent reactions (Calvin cycle and C4 pathway). Understanding these biochemical pathways, along with factors affecting photosynthesis and photorespiration, is vital for board exams as questions frequently test pathways, differences between C3 and C4 plants, and experimental setups.
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).
Pigment Systems
Chlorophyll a, chlorophyll b, xanthophylls, and carotenoids absorb specific wavelengths of light; chlorophyll a acts as the primary reaction center for light energy conversion.
Light Reaction (Photophosphorylation)
Driven by Photosystem II and Photosystem I, light energy splits water (photolysis) to release oxygen, generating ATP and NADPH through cyclic and non-cyclic electron transport.
Calvin Cycle (C3 Pathway)
Occurs in the stroma and involves three distinct phases: carboxylation (fixed by RuBisCO), reduction, and regeneration of RuBP to produce glucose.
C4 and CAM Pathways
Adaptations in plants like maize and sugarcane to minimize photorespiration by using PEP carboxylase for initial carbon fixation and spatial or temporal separation.
Photorespiration
A wasteful process occurring in C3 plants when RuBisCO acts as an oxygenase instead of a carboxylase, consuming ATP and releasing CO2 without sugar production.
Important Formulas
Board Exam Info
In the ISC Class 11 Biology examination, this chapter typically carries around 6-8 marks. Questions often include direct conceptual MCQs, diagram-based questions on chloroplast ultrastructure or the Z-scheme, and short-to-long answer questions comparing C3 and C4 plants or explaining limiting factors.
Frequently Asked Questions
What is the difference between cyclic and non-cyclic photophosphorylation?
Non-cyclic photophosphorylation involves both Photosystem I and II, produces ATP, NADPH, and oxygen, and uses external water as an electron donor. Cyclic photophosphorylation involves only Photosystem I, produces only ATP, and recycles electrons without splitting water.
Why is RuBisCO called both a carboxylase and an oxygenase?
RuBisCO can bind to either carbon dioxide (carboxylase activity in the Calvin cycle) or oxygen (oxygenase activity during photorespiration), depending on their relative concentrations inside the chloroplast.
How are C4 plants more efficient than C3 plants?
C4 plants possess Kranz anatomy and use PEP carboxylase, which has a high affinity for CO2 and lacks affinity for oxygen, completely avoiding photorespiration and operating efficiently at higher temperatures and light intensities.
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