Topic 4 - Bioenergetics (photosynthesis)

Question 1

What happens in photosynthesis?

Answer 1

energy is used to change carbon dioxide and water into glucose and oxygen

Question 2

Where does photosynthesis take place and why?

Answer 2

• In the chloroplasts of green plant cells
• contain pigments like chlorophyl that absorb light

Question 3

How is energy transferred to the chloroplasts?

Answer 3

from the environment by light

Question 4

Is photosynthesis exothermic or endothermic?

Answer 4

• endothermic (energy is transferred from the environment)

Question 5

What is the word equation for photosynthesis?

Answer 5

carbon dioxide + water —light—> glucose and oxygen

Question 6

What is the balanced symbol equation for photosynthesis?

Answer 6

6CO2 + 6H2O —–> C6H12O6 + 6O2

Question 7

State the 5 main ways plants use glucose?

Answer 7

1) for respiration
2) making cellulose
3) making amino acids
4) stored as oils or fats
5) stored as starch

Question 8

Why do plants use glucose for respiration?

Answer 8

• this transfers energy from glucose
• enables the plant to convert the rest of the glucose into other useful substances

Question 9

Why do plants use glucose to make cellulose?

Answer 9

cellulose makes strong plant cell walls

Question 10

Why do plants use glucose to make amino acids?

Answer 10

-glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are then made into proteins

Question 11

Why do plants store glucose as fats and oils?

Answer 11

glucose is turned into lipids for storage in seeds

Question 12

Why do plants store glucose as starch?

Answer 12

• 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 better for storing than glucose - a cell with lots of glucose would draw in loads of water and swell up

Question 13

What three factors can limit the rate of photosynthesis?

Answer 13

• intensity of light
• concentration of CO2
• temperature

Question 14

What is a limiting factor?

Answer 14

a factor that is stopping photosynthesis from happening any faster

Question 15

What effects what is the limiting factor?

Answer 15

environmental conditions

Question 16

What is often the limiting factor at night?

Answer 16

light

Question 17

What is often the limiting factor in the winter?

Answer 17

temperature

Question 18

What is often the limiting factor in warm and bright conditions?

Answer 18

amount of carbon dioxide

Question 19

REMEMBER:

Answer 19

all environmental factors have a combined effect on the rate of photosynthesis

Question 20

What non-environmental factor can effect the rate of photosynthesis?

Answer 20

the amount of chlorophyl in a plant

Question 21

What can effect the amount of chlorophyl in a plant?
What are the effects of these?

Answer 21

• disease (e.g. infection with tobacco mosaic virus)
• environmental stress (like lack of nutrients)
• chloroplasts become damages and not able to make enough chlorophyl
• rate of photosynthesis is reduced because they can’t absorb as much light

Question 22

Why is light intensity important to photosynthesis?

Answer 22

light provides the energy needed for photosynthesis

Question 23

What happens to the rate of photosynthesis as the light intensity is raised?

Answer 23

• the rate of photosynthesis increases steadily - but only up to a certain point

Question 24

Why will increasing light intensity only increase the rate up to a certain point?

Answer 24

• the rate will no longer increase because either temperature or CO2 level has become the limiting factor, not light

Question 25

How can you change light intensity in a lab?

Answer 25

by moving a lamp closer or further away from your plant (see required practical)

Question 26

When you plot a graph with "distance of lamp from the plant", you get a weird shape. How do you overcome this?

Answer 26

- either measure the light intensity at the plant using a light meter - or calculate the light intensity

Question 27

Why does % level of CO2 effect the rate of photosynthesis?

Answer 27

carbon dioxide is one of the raw materials needed for photosynthesis

Question 28

What effects does increasing levels of CO2 have on the rate of photosynthesis?

Answer 28

- the rate will increase up to a certain point

Question 29

Why can increasing levels of CO2 only effect the rate up to a certain point?

Answer 29

- the graph will flatten out even if the amount of CO2 continues to increase because CO2 is no longer a limiting factor

Question 30

If light and CO2 are in plentiful supply, what is likely to be the limiting factor for photosynthesis?

Answer 30

temperature

Question 31

Why is temperature usually a limiting factor?

Answer 31

- because it is too low - enzymes needed for photosynthesis work more slowly at lower temperatures (collision theory)

Question 32

What happens when the plant gets too hot?

Answer 32

enzymes needed for reactions in the plant like photosynthesis become damaged (or denatured)

Question 33

At what temperature are enzymes in plants usually denatured?

Answer 33

- about 45 degrees C (this is pretty hot for outdoors, although greenhouses can get that hot if you're not careful)

Question 34

REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis: What can be given off to show the rate of photosynthesis?

Answer 34

Oxygen production

Question 35

REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis: What plant may you use in this reaction?

Answer 35

Canadian pondweed (particularly an aquatic plant)

Question 36

REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis: The rate at which the plant produces oxygen corresponds to what?

Answer 36

The rate at which its photosynthesising

Question 37

REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis: The faster the rate of oxygen production, the faster ...

Answer 37

the rate of photosynthesis

Question 38

REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis: What are two control variables?

Answer 38

- temperature - time that the pondweed is allowed to photosynthesise

Question 39

REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis: What is the independent variable?

Answer 39

- the distance between the pondweed and the light source (light intensity)

Question 40

REQUIRED PRACTICAL 5 - Effect of light intensity of photosynthesis: What is the dependent variable?

Answer 40

- the volume of oxygen produced

Question 41

What is the purpose of a greenhouse?

Answer 41

to artificially create the ideal environment for plants to grow

Question 42

How do greenhouses create the best conditions for plants to grow?

Answer 42

They trap the sun's heat to make sure temperature doesn't become the limiting factor

Question 43

How can the temperature of a greenhouse be prevented from getting too hot or cold?

Answer 43

In the winter- a farmer may use a heater as well to keep the temperature at the ideal level In the summer- it could get too hot, they might use shades and ventilation to cool hings down

Question 44

What do commercial farmers often do to control the level of light intensity on their plants?

Answer 44

They often supply artificial light especially after the sun goes down to give their plant more quality photosynthesis time

Question 45

How can farmers and gardeners increase the level of carbon dioxide in their greenhouse?

Answer 45

They may use a paraffin heater to heat the greenhouse As the paraffin burns, it makes carbon dioxide as a by-product

Question 46

What are two other benefits of a greenhouse?

Answer 46

- easier to keep plants free from pests and diseases - fertilisers can also be added to the soil, to provide all the minerals needed for healthy grown

Question 47

Why is it important that a farmer supplies their plants with everything in the right amount?

Answer 47

- changing the conditions cost money - just right conditions will lead to a faster-growing, better crop which can be sold and harvested more often - supplying the plants with more light or heat than they need would be wasting money