Chapter 8: Photosynthesis

Question 1

Photosynthesis

Answer 1

• Photosynthesis is an endothermic reaction
• During photosynthesis energy is transferred from the environment to the chloroplast by light. It is used to convert carbon dioxide and water into sugar (glucose). Oxygen is also formed and released as a by-product.

• Photosynthesis can be summarised as follows:
carbon dioxide + water –> (light) glucose + oxygen

• Leaves are well adapted to allow the maximum amount of photosynthesis to take place

Question 2

The rate of photosynthesis

Answer 2

• The rate of photosynthesis may be affected by light intensity, temperature, level of carbon dioxide and the amount of chlorophyll

  o	Light: the brighter the light the faster the rate of photosynthesis

  o	Temperature: as the temperature increases the rate of photosynthesis increases as the reaction speeds up. However, photosynthesis is controlled by enzymes so as the temperature reaches 40 – 50 degrees C the enzymes start to denature, and the rate of photosynthesis will fall

  o	Carbon dioxide concentration: the atmosphere is 0.04% carbon dioxide, so it often limits the rate of photosynthesis. Increasing co2 concentration will increase the rate of photosynthesis

  o	Chlorophyll levels in the leaf: if the amount of chlorophyll in a leaf is limited, less photosynthesis will take place

• Inverse square law: as the distance of the light increases, the light intensity decreases following the inverse square law. Light intensity is directly proportional to 1/(distance)^2

Question 3

How plants use glucose

Answer 3

• Plants and algal cells use the glucose produced during photosynthesis for respiration, to convert into insoluble starch for storage, to produce cellulose to strengthen walls, and to produce amino acids for protein synthesis
• Plants and algal cells also need nitrate ions absorbed from the soil or water to make the amino acids used to make proteins

Question 4

Making the most photosynthesis

Answer 4

• The factors that limit the rate of photosynthesis interact and any one of them may limit photosynthesis
• Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis, while still maintaining a profit