A1. Photosynthesis, Respiration and Energy

Question 1

Why is energy important?
Plant and animal cells need energy for biological processes to occur.
What animals vs plants need energy for?

Answer 1

Plants need energy for things like photosynthesis, active transport (e.g. to take in minerals via their roots), DNA replication, cell division and protein synthesis.

Animals need energy for things like muscle contraction, maintenance of body temperature, active transport, DNA replication, cell division and protein synthesis.

Question 2

Tip: Any organism that carries out photosynthesis is known as a ‘______________’ (an organism that can make its own food using light energy). The process of photosynthesis is the same in all _________________, suggesting that they all evolved from a common ___________.

Answer 2

Tip: Any organism that carries out photosynthesis is known as a ‘photoautotroph’ (an organism that can make its own food using light energy). The process of photosynthesis is the same in all photoautotrophs, suggesting that they all evolved from a common ancestor.

Question 3

ATP’s properties
ATP has specific properties that make it a good energy source.
What are these? (6 things)

Answer 3

• ATP stores or releases only a small, manageable amount of energy at a time, so no energy is wasted as heat.
• It’s a small, soluble molecule so it can be easily transported around the cell.
• It’s easily broken down, so energy can be easily released instantaneously.
• It can be quickly remade.
• It can make other molecules more reactive by transferring one of its phosphate groups to them (phosphorylation).
• ATP can’t pass out of the cell, so the cell always has an immediate supply of energy.

Question 4

The compensation point
There’s a particular level of light intensity at which the rate of photosynthesis exactly matches the rate of respiration. This is called the compensation point for light intensity.
One way to work out the compensation point for a plant is to measure the rate at which oxygen is produced and used by a plant at different light intensities. Because photosynthesis produces oxygen and respiration uses it, in this case, the compensation point is the light intensity at which oxygen is being used as quickly as it is produced (see the example below). The rate of CO2 production and use could also be measured-photosynthesis uses CO2 and respiration produces it.

Answer 4

There’s a particular level of light intensity at which the rate of photosynthesis exactly matches the rate of respiration. This is called the compensation point for light intensity.
One way to work out the compensation point for a plant is to measure the rate at which oxygen is produced and used by a plant at different light intensities. Because photosynthesis produces oxygen and respiration uses it, in this case, the compensation point is the light intensity at which oxygen is being used as quickly as it is produced (see the example below). The rate of CO, production and use could also be measured-photosynthesis uses CO, and respiration produces it.