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Flashcards · 8461 · Topic 4
Bioenergetics flashcards
12 cards on Topic 4, subtopics 4.4.1 to 4.4.2. Pick a subtopic or study them all.
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4.4.1 Photosynthesis
- Photosynthesis: word equation, and why it is endothermic
- carbon dioxide + water → glucose + oxygen (light needed). Endothermic: energy is transferred from the environment to the chloroplasts by light.
- Four factors that affect the rate of photosynthesis
- Temperature, light intensity, carbon dioxide concentration, and the amount of chlorophyll.
- Limiting factor, and how to spot one on a graph
- The factor in shortest supply, which holds the rate back. Where the line rises, the x-axis factor is limiting; where it is flat, another factor is limiting.
- On a graph with two lines at different CO₂ levels, what does it show where the lines separate?Higher
- The factor that differs between the lines (CO₂ concentration) is limiting there. Where a line is flat, the x-axis factor is not limiting.
- Inverse square law: a lamp moves from 10 cm to 30 cm. A meter read 900 units. New reading?Higher
- Light intensity ∝ 1/distance². Distance × 3 → intensity × 1/9. 900 ÷ 9 = 100 units.
- When is it worth adding heat, light or CO₂ in a greenhouse?Higher
- Only if the value of the extra yield is greater than the cost. Adding a factor that is not limiting raises the cost but not the yield.
- Required practical 6: rate of photosynthesis with pondweed
- Lamp at measured distances; a heat shield and thermometer keep temperature constant; let the weed adjust, then count bubbles or collect oxygen in a fixed time; repeat for a mean. Control: temperature, CO₂, same pondweed.
- Five uses of glucose in a plant
- Respiration; insoluble starch for storage; fat or oil for storage; cellulose to strengthen the cell wall; amino acids for protein synthesis (with nitrate ions from the soil).
4.4.2 Respiration
- Aerobic respiration vs anaerobic respiration in muscles and in yeast
- Aerobic: glucose + oxygen → carbon dioxide + water. Muscles: glucose → lactic acid. Plants and yeast: glucose → ethanol + carbon dioxide (fermentation in yeast). Anaerobic transfers much less energy: glucose is oxidised incompletely.
- How does the body respond to exercise, and why do muscles fatigue?
- Heart rate, breathing rate and breath volume rise, so more oxygenated blood reaches the muscles. If oxygen is still too low, muscles respire anaerobically; lactic acid builds up (an oxygen debt) and long activity fatigues the muscles.
- Oxygen debt, and what happens to lactic acid after exerciseHigher
- Oxygen debt: the extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from cells. Blood carries lactic acid to the liver, where it is converted back into glucose.
- Metabolism, with examples
- The sum of all the reactions in a cell or the body. Examples: glucose → starch, glycogen and cellulose; glycerol + 3 fatty acids → lipid; glucose + nitrate → amino acids → proteins; respiration; excess protein → urea.