5- Photosynthesis =) Flashcards
Where precisely in a cell does the Calvin cycle take place? (1)
stroma
A scientist investigated the effect of changing the carbon dioxide concentration on the amounts of glycerate-3-phosphate (GP) and ribulose biphosphate (RuBP) in photosynthesising cells.
The relative amounts of GP and RuGP remained the same even though CO2 concentration was increased from 1% to 2%.
Suggest 2 reasons why. (2)
limiting factors:
1. temp
2. light
3. RuBP available
4. enzyme (Rubisco)
In photosynthesis, what chemicals are needed for the light-dependent reaction? (1)
NADP, ADP, Pi, water
Describe what happens during photoionisation in the light-dependent reaction. (2)
- cholrophyll absorbs light –> light excites e-
- e- lost (chlorophyll becomes +ve charged)
The pigments in leaves are different colours.
Suggest and explain the advantage of having different coloured pigments in leaves. (1)
absorb ↑ λ for photos
The producers in this ecosystem are seaweeds, which have a large surface area to volume ratio. give two advantages to seaweeds of having a large surface area to volume ratio (2)
- ↑ s.a. to absorb light
- short diffusion pathway for gases
- ↑ s.a. to absorb CO2
- light can penetrate all cells
Some species of seaweed are submerged in water for most of the time. Explain how being under water might affect the rate of photosynthesis (3)
- ↓ light reaches chlorophyll
- temp- ↓ temp ↓ rate
- availability of CO2
- diff. wavelengths of light
If a plant is kept in the dark it is still able to produce carbohydrates, as long as it is provided with two products of the light-dependent reaction of photosynthesis.
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Give the name of these products and explain their function in the light-independent reaction of photosynthesis. (4)
- NADPH- reduces GP –> TP
- ATP- provides energy to reduce GP
A student obtained a solution of pigments from the leaves of a plant. Then the student used paper chromatography to separate the pigments.
Explain why the student marked the origin using a pencil rather than using ink. (1)
ink & pigments would mix
Another effect of heat stress is a decrease in the activity of the enzyme rubisco. A decrease in the activity of an enzyme means that the rate of the reaction it catalyses becomes slower.
A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis.
Explain why. (2)
- ↓ CO2 reacts w/ RuBP
- ↓ GP
In natural ecosystems, most of the light falling on producers is not used in photosynthesis.
Suggest two reasons why. (2)
- wrong wavelength
- reflected
- misses chlorophyll/ photosynthetic tissue
- CO2 conc/ temp = limiting factor
Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
Explain how this reduces the rate of photosynthesis in weeds. (4)
- ↓ transfer of H+ across thylakoid mem
- ↓ ATP produced
- ↓ NADPH produced
- LIR stops
Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
When treated with Atrazine, weeds have been shown to give off small amounts of heat.
Suggest an explanation for this observation. (1)
energy released from excited e- that were lost from chlorophyll
Sunlight that passes through leaves has a smaller range of wavelengths.
Few species of plants can live below large trees in a forest.
Suggest why. (3)
- ↓ range of ʎ passes thru leaves
- ↓ energy passes thru leaves
- little light for chlorophyll to absorb
- photos unlikely to exceed resp.
- insufficient photos for growth
In leaves at the top of trees in a forest, carbon dioxide is often the limiting factor for photosynthesis.
Use your knowledge of photosynthesis to suggest and explain one reason why. (2)
- light x limiting –> LDR x limiting
- temp x limiting –> fast enzyme reactions in LIR
- ↑ use of CO2 –> LIR = limiting
