Photosynthesis and Plants

Question 1

What type of process is photosynthesis and where does it take place?

Answer 1

Photosynthesis is an endothermic process that takes place in chloroplasts, where chlorophyll absorbs light energy and produces sugars and starch

Question 2

What is the word equation and balanced chemical equation for photosynthesis?

Answer 2

Carbon dioxide + water > glucose + oxygen

6CO2 + 6H2O > C6H12O6 + 6O2

Question 3

How and why is a plant destarched?

Answer 3

Put the plant in a dark room for 48 hours. This allows the plant to convert any stored starch to glucose which will be used for energy

It is important to do this as it allows any already existing starch to be used up so that it doesn’t interfere with an experiment. The experiment will be showing that any starch found after destarching was produced during photosynthesis which took place during the investigation

Question 4

How do you test for starch in a plant?

Answer 4

Destarch the leaf and dip it into boiling water for 30 seconds- kills the cells and makes it more permeable to iodine solution
The leaf is boiled in ethanol using a water bath - turns the leaf white so the colour change can be seen easier
Dip into hot water to soften it

Question 5

What other than glucose is produced from photosynthesis?

Answer 5

Oxygen

Question 6

What do you use to absorb carbon dioxide?

Answer 6

Sodium hydroxide

Question 7

Is light needed for photosynthesis?

Answer 7

Yes

Any leaf that is deprived of light doesn’t produce starch while any leaf that is provided light produces starch

Question 8

Is carbon dioxide needed for photosynthesis? What experiment would you use to determine this?

Answer 8

Yes

Place two destarched plants in polythene bags with one of them having saturated sodium hydrogen carbonate which gives out carbon dioxide and the other with soda lime which absorbs carbon dioxide and you will see the one with carbon dioxide has starch while the other doesn’t

Question 9

Is chlorophyll needed for photosynthesis?

Answer 9

Yes

A white part of a variegated leaf has no chlorophyll but the green part does
Test the variegated leaf for starch and you will see that the white part turns a negative for starch while the green part is a positive

Question 10

Explain how carbon dioxide concentration affects the rate of photosynthesis?

Answer 10

Increasing the light intensity hitting the plant will increase the rate of photosynthesis only up to a certain point

Beyond this point extra light makes no difference because there isn’t enough CO2. Where the graph levels off, light has ceased to be limiting and now CO2 is the limiting factor.

The higher level of Carbon dioxide the light intensity remains limiting for longer

Question 11

Explain how light intensity can affect the rate of photosynthesis?

Answer 11

As the carbon dioxide concentration round a plant goes up, so does its photosynthesis rate, but only up to a certain point. Beyond this, more carbon dioxide makes no difference, usually because there is not enough light to cope with it. Light is said to be the limiting factor. In nature the air has about 0.03% CO2, but this can be artificially increased in greenhouses to produce better crops.

Question 12

Explain how temperature can affect the rate of photosynthesis?

Answer 12

As the temperature increases, so does the rate of photosynthesis, up to about 35 Celsius. Above this it stops because the enzymes which control the process denature.

Question 13

Explain how the relationship between photosynthesis and respiration affects the gas exchange between organisms and their environment?

Answer 13

Collect some filamentous alga from the fish tank
Rinse 3 clean boiling tubes with a little hydrogen carbonate indicator before placing 10cm3 of the indicator into each of the tubes
Place a small ball of pondweed into the indicator in two of the tubes and cover one of these with aluminium foil
Stopper all three tubes and place them side by side in a beaker in front of a bench lamp. Leave them for 30 minutes and observe what happens

In tube 1 (pondweed + indicator in light) there is too much light therefore decrease in co2 so the colour change turns to pink. The rate of photosynthesis is higher than rate of respiration so co2 is taken in.

In tube 2 (pondweed + indicator in dark) there is some light therefore increase in co2 so the rate of respiration is higher than photosynthesis therefore co2 is given out

Question 14

How is the waxy cuticle adapted for light absorption/gas exchange?

Answer 14

It is a physical defence that is transparent to allow light through and waterproof to reduce water loss

Question 15

How is the epidermis adapted for light absorption/gas exchange?

Answer 15

With cell walls as a physical defence that are transparent to allow light through it

Question 16

How is the palisade mesophyll adapted for light absorption/gas exchange?

Answer 16

The cells are tightly packed, end on to the upper surface with many chloroplasts to increase photosynthesis

Question 17

How is the spongy mesophyll adapted for light absorption/gas exchange?

Answer 17

Cells with a few choloplasts and a large surface area for gas exchange, more air spaces maximising the diffusion of air

Question 18

How is the intercellular spaces adapted for light absorption/gas exchange?

Answer 18

Allows carbon dioxide to enter and oxygen to leave the photosynthesising cells which are mainly concentrated in the palisade layer

Question 19

How is the guard cells and stomata adapted for light absorption/gas exchange?

Answer 19

Stomata allows carbon dioxide and oxygen to enter and leave the leaf. They are surrounded by guard cells that regulate the opening during the day and closing at the night of the stomata

Question 20

What is meant by compensation point?

Answer 20

The rate at which photosynthesis and respiration are equal