3.5.1 Photosynthesis Flashcards
Describe the structure and function of the chloroplast
hints, thylakoids, stroma.
Thylakoids contains the chlorophyll, enzymes and electron carriers required for the light-dependent reactions. They stack together to form grana, which are connected via the stroma lamellae.
The membranes of the grana create a large surface area to increase the number of light-dependent reactions that can occur as more chloropyll is exposed to light.
The stroma contains enzymes, rna and ribosomes for the light dependant reaction. and starch granules to store sugar.
Describe photolysis.
- The photolysis of water produces oxygen, hydrogen ions and electrons.
- High concentration of hydrogen ions forms a proton gradient inside the thylakoid lumen.
Describe photoionization.
- Chlorophyll in thylakoid absorbs light.
- Chlorophyll becomes photoionised as two electrons are emitted.
- Each excited electron moves down the electron transport chain.
- Photolysis of water replaces lost electrons from the thylakoid.
Describe chemiosmosis.
Energy given through reduction-oxidation reactions by the electrons down the electron transport chain is used to actively transport protons from a low concentration in the stroma to a high concentration in the thylakoid lumen.
what accepts electrons at the end of the electron transport chain?
electrons combine with a hydrogen ion (proton) and NAD to form reduced NAD (NADH).
Describe the light dependent reaction simply.
hints, photoionised, chemiosmosis, PS2, PS1.
- Chlorophyll becomes photoionised as it absorbed light.
- Emitted electrons pass down electron transport chain, during this, chemiosmosis occurs. Concentration gradient produces ATP through photophosphorylation and enzyme ATP synthase.
- Emitted electrons in photosystem 2 are replaced by electrons from the photolysis of water.
- Electrons from photsystem 1 are accepted by NADP and a H ion.
Why cant the Calvin cycle continue forever in darkness?
ATP and NADPH from the light dependent stage are used to reduce glycerate-3phosphate into triose phosphate.
Describe what happens in carbon fixation.
The enzyme rubisco fixates carbion dioxide with ribulose biphosphate to form two molecules of glycerate 3 phosphate.
Describe simply, the Calvin cycle
- Carbon dioxide becomes fixated with ribulose biphosphate by the enzyme rubisco to form two molecules of glycerate 3 phospagete.
- 2 GP becomes reduced with NADPH and ATP to form two molecules of Triose phosphte.
- One in 6 TPs produced go to make glucose. The other 5 replace ribulose biphosphate used. This requires ATP.
Describe the regeneraton of Ribulose Biphosphate.
5 triose phosphate molecules are phosphorlated to form 3 biphosphate molecules with the use of ATP.
What can triose phosphate also form?
- Ribulose biphosphate
- Amino acids
3.Lipids
How does light intensity effect the rate of photosynthesis?
Rate of photosynthesis increases as light intensity increases:
The greater the light intensity, the more energy supplied to the plant and therefore the faster the light-dependent stage of photosynthesis can occur which produces more ATP and NADPH for the Calvin cycle , which can then also occur at a greater rate.
How does CO2concentration effect the rate of photosynthesis.
Rate of photosynthesis increases as carbon dioxide concentration increases:
It is required for the Calvin cycle, when CO2 is fixated ribulose bisphosphate.
This means the more carbon dioxide that is present, the faster the Calvin cycle can occur and the faster the overall rate of photosynthesis.
How does temperature effect the rate of photosynthesis?
hints; LDR or CC? stomata. membranes.
As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes
However this only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases.
Temperature has no effect on the light-dependent reactions, as they use energy from light rather than the kinetic energy of molecules.
The Calvin cycle is affected by temperature, as the reactions are enzyme-controlled (eg. rubisco )
Increasing temperature up to an optimum will increase the rate of the light-independent reactions and therefore the rate of photosynthesis
What are the common agricultural practices used to overcome the effect of limiting factors.
hints, lights, water, pests, evaluate.
Sensors can be used to monitor the light intensity, the humidity of the atmosphere and the carbon dioxide concentration around the crops.
Plants can grow at night with artificial lighting, out of their natural season and habitat because the temperature can be kept constant.
Water can be supplied by irrigation systems throughout the glasshouse or fields which can contain added fertilisers or growth nutrients such as nitrates.
Natural pests that may spread disease or eat the crops can be controlled within agricultural settings by pesticides or by separating the plants from unfiltered outside air.
How does temperature effect the rate of photosynthesis?
hints; stomata. membranes.
Increasing temperature causes stomata on the leaf to close in order to reduce water loss, when the stomata are closed CO2 cannot enter the leaves.
The light-dependent reaction relies on a proton gradient forming across the thylakoid membrane - it is important that a too high or too low temperature does not affect the permeability of the membrane which may lead to a dissipation of the proton gradient
Evaluate the common agricultural practices used to overcome the effect of limiting factors.
Balance between crop yield and price (24hrs a day lighting, sensors, water) and environmental implications(pesticides) for farmers.
