Bioenergetics flashcards
12 cards on Bioenergetics: the key points, worked examples and the slips to watch. Swipe through them, or print them.
Card 1 of 12
Bioenergetics
Photosynthesis
What is photosynthesis, where does it happen, and why is it endothermic?
Answer it in your head, then turn the card over.
Photosynthesis
Key points
- Plants and algae use light energy to make glucose from carbon dioxide and water.
- It happens in the chloroplasts, where the green pigment chlorophyll absorbs the light.
- It is endothermic: energy is taken in from the surroundings as light and stored in the glucose.
- Oxygen is given off as a waste product.
Formula
carbon dioxide + water → glucose + oxygen (light energy taken in)
Watch out
Endothermic means energy taken in: photosynthesis is endothermic, respiration is exothermic.
Bioenergetics
HigherBalanced symbol equations
What are the balanced symbol equations for photosynthesis and aerobic respiration?
Answer it in your head, then turn the card over.
Balanced symbol equations
Key points
- Glucose is C₆H₁₂O₆, carbon dioxide CO₂, water H₂O and oxygen O₂.
- Six molecules each of CO₂ and H₂O make one glucose and six O₂.
- Aerobic respiration is the same equation written the other way round.
Formulae
Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Check the oxygen atoms balance
Left: 6 × 2 in 6CO₂, plus 6 × 1 in 6H₂O = 18
Right: 6 in C₆H₁₂O₆, plus 6 × 2 in 6O₂ = 18
Watch out
Oxygen is a molecule of two atoms: write 6O₂, never 6O.
Bioenergetics
Limiting factors
What is a limiting factor, and how do you spot one on a photosynthesis graph?
Answer it in your head, then turn the card over.
Limiting factors
Key points
- Light intensity, carbon dioxide concentration, temperature and the amount of chlorophyll all affect the rate.
- The limiting factor is the one in shortest supply: it stops the rate going any higher.
- While the line rises as a factor increases, that factor is limiting.
- Once the line levels off, a different factor is now limiting.
- Above the optimum temperature the rate falls, because the enzymes denature.
Watch out
On the flat part of a light graph, light is no longer limiting: more light changes nothing.
Bioenergetics
The pondweed light practical
How do you investigate the effect of light intensity on the rate of photosynthesis?
Answer it in your head, then turn the card over.
The pondweed light practical
Key points
- Put pondweed in water and place a lamp at a measured distance from it.
- Count the oxygen bubbles given off in one minute, or collect the gas and measure its volume.
- Move the lamp to new distances, repeat each count and find a mean.
- More bubbles a minute means a faster rate of photosynthesis.
- Keep the temperature and carbon dioxide the same, since both change the rate too.
Watch out
A lamp also heats the water: control temperature, or you test two factors at once.
Bioenergetics
HigherLight intensity and distance
How does light intensity change as a lamp is moved further from a plant?
Answer it in your head, then turn the card over.
Light intensity and distance
Key points
- Light intensity is inversely proportional to the square of the distance.
- Double the distance and the light intensity falls to a quarter.
Formula
light intensity ∝ 1 ÷ distance²
Lamp moved from 10 cm to 20 cm
The distance is 2 times as far, and 2² = 4
So the intensity at 20 cm is of that at 10 cm
Watch out
Halving the distance makes the light 4 times as intense, not twice.
Bioenergetics
HigherLimiting factors in greenhouses
How do growers use limiting factors in a greenhouse, and when is it worth the cost?
Answer it in your head, then turn the card over.
Limiting factors in greenhouses
Key points
- Growers add heat, artificial light or carbon dioxide (often from a paraffin heater).
- Faster photosynthesis means faster growth and a bigger crop.
- Adding a factor only helps if it is the one limiting the rate.
- It pays only when the extra crop is worth more than the heat, light or gas costs.
Watch out
Extra light does nothing if the greenhouse is too cold: raise the limiting factor first.
Bioenergetics
How plants use glucose
What do plants use the glucose from photosynthesis for?
Answer it in your head, then turn the card over.
How plants use glucose
Key points
- Respiration, to release energy.
- Storage as starch, which is insoluble, so it does not draw water into cells by osmosis.
- Cellulose, to strengthen cell walls.
- Fats and oils (lipids) for storage, especially in seeds.
- Amino acids, made with nitrate ions from the soil, then joined into proteins.
Watch out
Glucose has no nitrogen in it: without nitrate from the soil a plant cannot make proteins.
Bioenergetics
Aerobic respiration
What is aerobic respiration, where does it happen, and what is the energy used for?
Answer it in your head, then turn the card over.
Aerobic respiration
Key points
- Respiration releases energy from glucose, all the time, in every living cell.
- Aerobic respiration uses oxygen and happens in the mitochondria.
- It is exothermic: it transfers energy to the surroundings.
- Cells use the energy to build large molecules, to move (muscles contracting) and, in mammals and birds, to keep warm.
Formula
glucose + oxygen → carbon dioxide + water
Watch out
Respiration releases energy: never write that it makes or produces energy.
Bioenergetics
Anaerobic respiration
What does anaerobic respiration make in muscles, and in yeast?
Answer it in your head, then turn the card over.
Anaerobic respiration
Key points
- Anaerobic respiration happens without oxygen.
- Glucose is only partly broken down, so much less energy is released than in aerobic respiration.
- In muscles it makes lactic acid only.
- In yeast and plant cells it makes ethanol and carbon dioxide. In yeast this is fermentation, used to make bread and beer.
Formulae
Muscles: glucose → lactic acid
Yeast: glucose → ethanol + carbon dioxide
Watch out
Muscles never make carbon dioxide or ethanol without oxygen: only lactic acid.
Bioenergetics
The body's response to exercise
How do heart rate, breathing and the muscles respond during exercise?
Answer it in your head, then turn the card over.
The body's response to exercise
Key points
- Working muscles respire faster, so they need more oxygen and glucose.
- Heart rate, breathing rate and breath volume rise, to supply more oxygenated blood and remove carbon dioxide.
- If too little oxygen arrives, the muscles also respire anaerobically and lactic acid builds up.
- In long, hard exercise muscles become fatigued and stop contracting efficiently.
A pulse rate before and after exercise
Resting: 72 beats a minute. After exercise: 126
Increase = 126 − 72 = 54 beats a minute
% increase = 54 ÷ 72 × 100 = 75%
Watch out
Percentage change divides by the starting value: 54 ÷ 72, not 54 ÷ 126.
Bioenergetics
HigherOxygen debt
What is oxygen debt, and why do you keep breathing hard after a sprint?
Answer it in your head, then turn the card over.
Oxygen debt
Key points
- Oxygen debt is the extra oxygen needed after exercise to react with the lactic acid that built up and remove it from cells.
- The blood carries the lactic acid from the muscles to the liver.
- The liver converts it back into glucose, which needs oxygen.
- So breathing and heart rate stay high until the debt is repaid.
Watch out
Oxygen debt is the oxygen needed after exercise, not the oxygen you ran short of during it.
Bioenergetics
Metabolism
What is metabolism, and which reactions does it include?
Answer it in your head, then turn the card over.
Metabolism
Key points
- Metabolism is the sum of all the reactions in a cell or the body. Enzymes control them all.
- Building up: glucose into starch, glycogen and cellulose; fatty acids and glycerol into lipids.
- Glucose and nitrate ions make amino acids, which are joined into proteins.
- Breaking down: respiration, and excess proteins broken down to make urea, which is excreted.
- Energy released by respiration powers the building reactions.
Watch out
Metabolism is every reaction, building molecules up as well as breaking them down.
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