Topic 4 - Bioenergetics - Photosynthesis and Limiting Factors

Question 1

What does photosynthesis use to change __ and __ into __ and __?

Answer 1

Uses energy to change carbon dioxide and water into glucose and oxygen.

Question 2

Where does photosynthesis take place?

Answer 2

In chloroplasts in green plant cells - they contain pigments like chlorophyll that absorb light.

Question 3

How is energy transferred to the chloroplasts from the environment?

Answer 3

By light.

Question 4

Is photosynthesis endothermic or exothermic? Why?

Answer 4

Endothermic. Energy is transferred from the environment in the process.

Question 5

What is the word equation for photosynthesis?

Answer 5

carbon dioxide + water -(light) > glucose + oxygen

Question 6

What is the symbol equation for photosynthesis?

Answer 6

6CO2 + 6H20 -(light)> C6H12O6 + 6O2

Question 7

What are the five main ways plants use glucose?

Answer 7

1. For respiration - This transfers energy from glucose which enables the plants to convert the rest of the glucose into various other useful substances.
2. Making cellulose - Glucose is converted into cellulose for making strong plant cell walls.
3. Making amino acids - Glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are then made into proteins.
4. Stored as oils or fats - Glucose is turned into lipids (fats and oils) for storing in seeds.
5. Stored as starch - Glucose is turned into starch and stored in roots, stems and leaves, ready for use when photosynthesis isn’t happening, like in the winter. Starch is insoluble, which makes it much better for storing than glucose - a cell with lots of glucose in would draw in loads of water and swell up.

Question 8

What are the factors that affect the rate of photosynthesis?

Answer 8

Intensity of light, concentration of CO2 and temperature. Any of these can become the limiting factor.

Question 9

What depends on which factor is limiting at a particular time?

Answer 9

The environmental conditions:
- at night, light is the limiting factor
- in winter it’s often the temperature
- if it’s warm enough and bright enough, the amount of CO2 is usually limiting
(Chlorophyll can also be a limiting factor of photosynthesis).

Question 10

What can the amount of chlorophyll in a plant be affected by? What can these factors cause?

Answer 10

Disease (e.g. infection with the tobacco mosaic virus) or environmental stress, such as a lack of nutrients. These factors can cause chloroplasts to become damaged or t to not make enough chlorophyll. This means the rate of photosynthesis is reduced because they can’t absorb as much light.