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5.6 Photosynthesis - Coggle Diagram
5.6 Photosynthesis
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Structure of Chloroplast
Photosynthesis takes in the chloroplasts of plant cells. Chloroplasts contain fluid-filled sacs called thylakoids. Thylakoids are stacked up like pancakes to form structures which we call grana. Each granum is connected by pieces of thylakoid membrane called lamellae. The gel-like substance which surrounds the thylakoids is called the stroma.
The thylakoids within the chloroplast provide a large surface area to allow as much light to be absorbed as possible. Within the thylakoid membrane are photosystems which consist of pigment molecules attached to proteins. The pigment is what gives plants their colour and includes chlorophyll a, chlorophyll b and carotene. Plants contain two photosystems, called photosystem I and photosystem II. PSI absorbs light at a wavelength of 700 nm while PSII absorbs light at a wavelength of 680 nm.
The overall process of photosynthesis can be split into two stages: the first one stage is known as the light-dependent reaction and (unsurprisingly) requires light to get going. The second is called the light-independent reaction which doesn’t need light but does need the products that were generated in the first stage.
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Limiting Factors
Temperature – in general, the higher the temperature the faster the rate of photosynthesis because the enzymes (e.g. Rubisco) and reacting molecules have more kinetic energy so they collide into each other more frequently. If the temperature becomes too high, the rate of photosynthesis decreases because the enzymes involved in photosynthesis are denatured.
Light intensity – the higher the light intensity, the faster the rate of photosynthesis. This is because light energy is a required to produce ATP and NADPH in the light-dependent reaction. Low ATP/NADPH means that there will be less production of GP and TP in the Calvin cycle.
Carbon dioxide concentration – as the concentration of carbon dioxide increases, the rate of photosynthesis increases because carbon dioxide is a reactant in the first stage of the Calvin cycle (the fixation of carbon dioxide with RuBP. In the absence of carbon dioxide, RuBP levels increase while TP and GP will fall.
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