Cambridge A Levels A2 Biology Chapter 13 Photosynthesis
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Course
Cambridge A Levels A2 Biology
Institution
Chapter 13 Photosynthesis: 26 pages
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Chapter 13 Photosynthesis
13.1 Photosynthesis as an Energy Transfer Process
13.2 Investigation of Limiting Factors
13.1 Photosynthesis as an Energy Transfer Process
General Equation of Photosynthesis
Photosynthesis involves:
• The trapping of light energy by photosynthetic pigments resulting in the synthesis of ATP
and reduced NADP which is then used to reduce CO2 to form carbohydrate.
• Taking in carbon dioxide and reducing it by adding hydrogen to it to produce
carbohydrate.
The hydrogen for this process comes from water.
The energy that drives the reactions comes from light, which is absorbed by a
green pigment called chlorophyll.
• Oxygen is a waste product of photosynthesis.
It may be lost from the cells, or it may be used in respiration.
Two Main Stages of Photosynthesis:
1. Light Dependent Stage
2. Light-Independent Stage
,Structure and Function of Chloroplasts
Structure
• Has a biconvex shape.
• Has a diameter of 4-10µm.
• Surrounded by two membranes (the chloroplast envelope).
• Stroma:
• A fluid-filled region.
• Stroma consists of a membrane system which consists of thylakoids.
Thylakoid, Grana, Lamella:
• Thylakoids are membrane bound flattened fluid-filled vesicles.
• Stacks of thylakoid form grana which are connected by intergranal lamella.
• The membrane of the grana provides a large surface area which consists of
photosystems which in turn contain photosynthetic pigments, electron carrier
molecules as well as enzymes (ATP synthase).
These are needed for the light-dependent reactions.
• The thylakoid space is fluid-filled and is the site of photolysis of water.
• Stroma contains energy stores in the form of starch grains and lipid droplets.
• Stroma contains 70s ribosomes, circular DNA and enzyme that catalyse the chemical
reactions in the Calvin cycle, the light independent reactions.
, Adaptations of Leaves as a Photosynthetic Organ
• They provide a large surface area over which light can be reabsorbed.
• They are thin, providing a short diffusion pathway for the gases O2 and CO2.
• The midrib and extensive network of veins provide a good support for the thin
lamina/blade.
• The veins consist of xylem and phloem tissue which transport water and minerals to the
leaf cells and sucrose away from the leaves respectively.
• The mesophyll tissue in the leaf has a large number of chloroplasts that contain
chlorophyll which can absorb light energy.
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