Photosynthesis is a reaction that occurs in the chloroplasts and requires the presence of light.
It is when water and carbon dioxide undergo numerous reactions to form glucose and oxygen.
Glucose is the food source for the plant, and can be used in respiration so that a plant can release
the energy from within the food to survive, grow and ultimately reproduce.
It is when water and carbon dioxide undergo numerous reactions to form glucose and oxygen.
Glucose is the food source for the plant, and can be used in respiration so that a plant can release
the energy from within the food to survive, grow and ultimately reproduce.
Where does it occur?
In the chloroplasts
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Chloroplasts
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Double membrane
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Thylakoids and Granum
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Stroma
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Photosynthesis occurs within an organelle that is found in plant cells only - chloroplasts, found inside the leaves. Chloroplasts are full of chlorophyll which is a special pigment that absorbs particular wavelengths of light - making it able to 'capture' light energy to power the conversion of water and carbon dioxide into glucose and oxygen.
Chloroplasts have huge amounts of membranes in it - a double membrane which allows for compartmentalization within the cell, as well as their system of membrane structures called thylakoids, which are staked into structures called grana. This allows for a huge amount of surface area available for the absorption of light energy. The liquid within the chloroplasts, surrounding the granum (plural for grana), is called stroma (don't mix up with stomata). Stroma contain the enzymes required for the light independent phase of photosynthesis.
Chloroplasts have huge amounts of membranes in it - a double membrane which allows for compartmentalization within the cell, as well as their system of membrane structures called thylakoids, which are staked into structures called grana. This allows for a huge amount of surface area available for the absorption of light energy. The liquid within the chloroplasts, surrounding the granum (plural for grana), is called stroma (don't mix up with stomata). Stroma contain the enzymes required for the light independent phase of photosynthesis.
Double membranes within the chloroplasts allow for the environment of the cell and the environment within the organelle to be different. This is called compartmentalization. This means the conditions within the chloroplasts can be the optimum conditions required for photosynthesis without changing the conditions of the overall cell.
Thylakoid membranes provide a huge amount of area in which light can be absorbed. Stacks of thylakoid membranes are called grana. Having grana further increases the available surface area available for light absorption. More light = more energy available to fuel the processes involved in photosynthesis.
Stroma allows for the quick diffusion of carbon dioxide to where it is required within the organelle. It contains enzymes that are involved in the light independent reactions of photosynthesis. It is a clear fluid so that it doesn't obstruct light penetration within the chloroplast.
and chloroplasts are found within
leaves
Leaves have a particular structure which allows them to undergo photosynthesis at fast rate
1. Waxy cuticle - reduces water loss (water is needed for photolysis)
2. Upper epidermis - protective layer - thin to let light through 3. Palisade mesophyll - cells that contain the most chloroplast. Oval shaped to fit lots of cells in. Close to the top of the leaf to get the most light. Chloroplasts close to cell membrane so diffusion of carbon dioxide is faster. 4. Spongy mesophyll - "backup" light-absorbing cells, contains air spaces between them to help carbon dioxide move in from the bottom of the leaf where it enters 5. Guard cells (not numbered) - lets gasses in and out of the leaf - carbon dioxide in and oxygen out. Guard cells close when water levels are low, to stop water evaporating out of leaves 6. Lower epidermis - protective layer, houses guard cells 7. Stoma / stomata - hole in which gases can enter and leave the leaf. |
Photosynthesis occurs in two parts
When there's light and when there's no light
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Light-dependent phase
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Light-independent phase
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Factors that affect the rate of photosynthesis
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aka. Photolysis (occurs in the thylakoid, as this is where light is captured)
Energy from light is used to split water into its two separate atoms (O and H). ATP is released from the bonds that held these atoms together.
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Reactants: Water (from roots) Other requirements: Light (from the sun) Products: Hydrogen (taken by NADP to stroma), oxygen (diffuses out of the leaf) and a small amount of ATP |
aka. Carbon Fixation (occurs in the stroma where the necessary enzymes are found)
Energy from ATP (created in light-dependent phase) is used to join carbon dioxide and hydrogen together to produce glucose (C6H12O6). Sunlight is not needed here - this can happen at night, or during the day!
Glucose can then be sent to the mitochondria or cytoplasm and go on to be used in respiration, or it can be joined together with other glucose molecules and stored as starch for be used later, or it can become cellulose and used to build new structures. |
Reactants: Carbon dioxide (from the atmosphere), hydrogen (released during photolysis) Other requirements: ATP (released from photolysis) Products: Glucose (diffuses into phloem to be stored elsewhere in the plant, or used in respiration to release energy). |
Light intensity
The more/stronger the light, the more energy is available for the light-dependent phase of photosynthesis (to break the water molecules and also produce ATP) - this starts off all other reactions in the chloroplast. If there is little light, the rate of photosynthesis will be low. As light intensity increases, the rate of photosynthesis increases respectively. This occurs until a rate is reached where photosynthesis can't happen any faster; either due to a lack or carbon dioxide or water, or the temperature being too high/low, or having all enzymes functioning and no more to make it go faster!
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Temperature
As temperature increases, the rate of photosynthesis increases - this is because heat provides energy for the enzymes involved in carbon fixation to happen. If the temperature is too cold, the enzymes don't have much energy to carry out their functions and photosynthesis is slow. If the temperature gets too hot then the rate of photosynthesis will drastically decrease due to the denaturation of the enzymes needed for it to occur.
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Carbon dioxide concentration
As the concentration of carbon dioxide increases, so does the rate of photosynthesis. This is because more carbon dioxide is available for the light-independent phase of photosynthesis. The rate of photosynthesis increases as the concentration of carbon dioxide increases, until a point at which no matter how much carbon dioxide is in the air, photosynthesis cannot occur any faster. Again, this could be due to the lack of intense light or water, a drop/increase in temperature or having all enzymes functioning and no more to make it go faster!
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