limiting factors Flashcards
Why is high light intensity important for photosynthesis? (4)
- Light provides the energy for the light-dependent reactions,
- Higher intensity provides more energy for photosynthesis,
- Chlorophyll a, chlorophyll b, and carotene absorb red and blue light but reflect green light, which is why plants appear green,
- Having multiple photosynthetic pigments allows plants to absorb more light and increase the efficiency of photosynthesis
Why is an ideal temperature of 25°C crucial for photosynthesis? (4)
- Photosynthesis relies on enzymes like RuBisCo and ATP synthase,
- Enzymes become inactive below 10°C and denature above 45°C,
- High temperatures can cause stomata to close, limiting CO₂ intake, and may damage the thylakoid membranes, chloroplast membranes, or chlorophyll, reducing the rate of photosynthesis,
- Greenhouses help maintain the optimum temperature for photosynthesis
What is the ideal CO₂ concentration for photosynthesis? (3)
- The atmospheric CO₂ concentration is normally 0.04%,
- Increasing it to 0.4% can increase the rate of photosynthesis, but if it gets too high, stomata may close, limiting CO₂ intake,
- Growers can increase CO₂ levels by burning propane
How do high temperatures affect photosynthesis? (3)
- Can cause stomata to close, limiting CO₂ intake,
- Thylakoid membranes and chloroplast membranes may be damaged, reducing light-dependent reactions and enzyme activity in the Calvin cycle,
- Chlorophyll may be damaged, reducing the plant’s ability to absorb light.
How do factors limiting photosynthesis affect plant growth? (3)
- Light intensity, temperature, and CO₂ concentration,
- Need to be at the right levels for photosynthesis to occur as quickly as possible,
- If any one factor is too low or too high, it will limit the rate of photosynthesis and, consequently, plant growth
How does water stress limit photosynthesis? (2)
- When plants don’t have enough water, the stomata close to conserve water,
- This reduces the amount of CO₂ entering the leaf for the Calvin cycle, slowing down photosynthesis
How does light intensity affect the levels of GP, TP, and RuBP in photosynthesis? (3)
- Low light intensity reduces the supply of ATP and reduced NADP from the light-dependent stage,
- This slows the conversion of GP to TP and RuBP, 3. As a result, GP levels rise (as it can still be made), but TP and RuBP levels fall
How do temperature and CO₂ concentration affect the levels of GP, TP, and RuBP in the Calvin cycle? (5)
- Low temperatures slow all reactions in the Calvin cycle,
- Causing levels of GP, TP, and RuBP to fall,
- High temperatures denature enzymes, leading to a similar drop in GP, TP, and RuBP,
- Low CO₂ concentrations slow the conversion of RuBP to GP,
- Causing RuBP levels to rise and GP and TP levels to fall
How can Canadian pondweed be used to investigate factors affecting the rate of photosynthesis? (3)
- Used in a test tube with water connected to a capillary tube full of water and a syringe,
- A light source is placed at a specific distance, and the pondweed is left to photosynthesise,
- The oxygen released collects in the capillary tube, and the length of the gas bubble is measured to estimate the amount of O₂ produced
How do you measure the amount of oxygen produced during photosynthesis in the Canadian pondweed experiment? (3)
- After photosynthesis, the syringe is used to draw the gas bubble in the capillary tube alongside a ruler,
- The length of the gas bubble is measured,
- Which is proportional to the amount of O₂ produced
What variables should be controlled when investigating the effect of light intensity on the rate of photosynthesis? (2)
- Temperature,
- The time the pondweed is left to photosynthesise
How can you improve the precision of the experiment on light intensity and photosynthesis? (2)
- Repeat the experiment multiple times and calculate the average length of the gas bubble to make results more precise,
- Change the distance of the light source and repeat the experiment to study the effect of light intensity
