Topic 4- Bioenergetics

Question 1

What is photosynthesis?

Answer 1

Photosynthesis is the process that produces ‘food’ in PLANTS. The food it produces is GLUCOSE.

Question 2

How is glucose produced in photosynthesis

Answer 2

Photosynthesis uses LIGHT ENERGY from the sun to change CARBON DIOXIDE and WATER into GLUCOSE and OXYGEN.

Question 3

Where does photosynthesis occur?

Answer 3

It takes place in CHLOROPLASTS in GREEN PLANT CELLS- they contain PIGMENTS like CHLOROPHYLL that ABSORB LIGHT.

Question 4

Where does the energy needed for photosynthesis come from?

Answer 4

Energy is TRANSFERRED to the CHLOROPLASTS from the environment by LIGHT.

Question 5

Is photosynthesis an endothermic or exothermic reaction and why?

Answer 5

Photosynthesis is ENDOTHERMIC- this means energy is transferred from the ENVIRONMENT in the process.

Question 6

What is the word equation for photosynthesis?

Answer 6

The word equation for photosynthesis is:

carbon dioxide + water ͢ glucose + oxygen

Question 7

What is the symbol equation for photosynthesis?

Answer 7

The symbol equation for photosynthesis is:

6CO2 + 6H2O ͢ C6H12O6 + 6O2

Question 8

What are the 5 main ways glucose produced in photosynthesis is used?

Answer 8

The glucose produced in photosynthesis may be:
• used for respiration
• converted into insoluble starch for storage
• used to produce fat or oil for storage
• used to produce cellulose, which strengthens the cell wall
• used to produce amino acids for protein synthesis.

Question 9

Why is glucose used in respiration?

Answer 9

• Used for respiration- this TRANSFERS ENERGY from the glucose which enables the plants to CONVERT the rest of the glucose into various OTHER USEFUL SUBSTANCES.

Question 10

Why is glucose used to make cellulose?

Answer 10

Glucose is converted into CELLULOSE for making strong PLANT CELL WALLS.

Question 11

Why is glucose used to produce amino acids?

Answer 11

GLUCOSE is combined with NITRATE IONS (absorbed from the soil) to make AMINO ACIDS, which are then made into proteins.

Question 12

Why is glucose stored as oil or fats?

Answer 12

Glucose is turned into lipids (fats and oils) for storing in SEEDS.

Question 13

Why is glucose converted into soluble starch for storage?

Answer 13

Glucose is turned into STARCH and STORED in roots, stems and leaves, ready for use when photosynthesis isn’t happening, like in WINTER.

Starch is ONSOLUBLE, 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.

Tip- water moves from regions of higher concentration to regions of lower concentration-this is known as osmosis. A cell with lots of glucose would have a lower concentration of water than its surroundings, and so water would move in from outside by osmosis.

Question 14

What can the rate of photosynthesis be affected by?

Answer 14

The rate of photosynthesis is effected by temperature, light intensity, carbon dioxide concentration, and the amount of chlorophyll.

All these things need to be at the right level to allow a plant to photosynthesise as quickly as possible.

If any one of these factors is too high or too low, it will become the LIMITING FACTOR. (what factor is limiting at a particular time depends upon the environment.)

Question 15

How can the amount of chlorophyll affect the rate of photosynthesis?

Answer 15

The amount of chlorophyll in a plant can be affected by DISEASE or ENVIRONMENTAL STRESS, such as a LACK OF NUTRIENTS. These factors can cause CHLOROPLASTS to become DAMAGED or to NOT make ENOUGH CHLOROPHYLL. This means the rate of photosynthesis is REDUCED because they CAN’T ABSORB as much LIGHT.

Question 16

Explain how the rate of photosynthesis can be affected by light intensity?

Answer 16

1) Light intensity provides the ENERGY needed for photosynthesis.
2) As the LIGHT LEVEL is raised, the rate of photosynthesis INCREASES STEADILY- but only up to a CERTAIN POINT.
3) Beyond that, it WON’T make any difference- as light intensity increases, the rate will NO LONGER INCREASE. This is because it’ll either be TEMPERATURE or CO2 LEVEL which is now the limiting factor, not light.
4) In the lab you can change the light intensity by MOVONG A LAMP closer or further away from your plant.
5) But if you just plot the rate of photosynthesis against distance of lamp from the plant, you get a WEIRD-SHAPED GRAPH. To get a graph like the one on pg 58, you need to MEASURE the light intensity at the plant using a LIGHT METER.

Question 17

Explain how the rate of photosynthesis can be affected by the volume of carbon dioxide?

Answer 17

1) CO2 is one of the RAW MATERIALS needed for photosynthesis.
2) As with light intensity, the amount of CO2 will only increase the rate of photosynthesis up to a point. After this the graph FLATTENS OUT- as the amount of CO2 increases, the rate of photosynthesis NO LONGER INCREASES. This shows that CO2 is no longer the LIMITING FACTOR.
3) As long as LIGHT and CO2 are in plentiful supply then the factor limiting photosynthesis must be TEMPERATURE.

Question 18

Explain how the rate of photosynthesis can be affected by temperature.

Answer 18

1) Usually if the temperature is the LIMITING FACTOR it’s because it’s TOO LOW- the ENZYMES needed for photosynthesis work more SLOWLY at low temperatures.
2) But if a plant gets TOO HOT, the enzymes it needs for photosynthesis and its other reactions will be DAMAGED.
3) This happens at about 45℃.

Question 19

Explain why some farmers grow plants in an artificial environment.

Answer 19

If you now the ideal conditions for photosynthesis, then you can create an environment which maximises the rate of photosynthesis, which in turn maximises there rate of plant growth. The most common way to artificially create the ideal environment for plants is to grow them in a greenhouse. Commercial growers often grow large quantities of plants in commercial greenhouses.

Question 20

How can the temperature be managed by a greenhouse?

Answer 20

Greenhouses help to TRAP the Sun’s HEAT, and make sure that the TEMPERATURE doesn’t become LIMITING. In winter a farmer or gardener might use a HEATER as well to keep the temperature at the ideal level. In summer it could get TOO HOT, so they might use SHADES and VENTILATION to cool things down.

Question 21

How can the light be managed by a greenhouse?

Answer 21

LIGHT is always needed for photosynthesis, so commercial farmers often supple ARTIFICIAL LIGHT after the Sun goes down to give their plants more quality photosynthesis time.

Question 22

How can carbon dioxide be managed by a greenhouse?

Answer 22

Farmers and gardeners can also increase the level of CARBON DIOXIDE in the greenhouse. E.g. by a PARAFFIN HEATER to heat the greenhouse. As paraffin burns, it makes carbon dioxide as a BY-PRODUCT.

Question 23

How can the general health of plants be managed by a greenhouse?

Answer 23

Keeping the plants ENCLOSED in a greenhouse also makes it easier to keep them free from PESTS and DISEASES. The farmer can add FERTILISERS to the soil as well, to provide all the MINERALS needed for healthy growth.