Photosynthesis and Gas Exchange

Question 1

In photosynthesis, light energy is converted into ……………?

Answer 1

Chemical energy (in the form of glucose; then stored as starch or sucrose)

Question 2

Write a word equation for photosynthesis

Answer 2

Carbon dioxide + water –> glucose + oxygen

Question 3

Write a balanced chemical equation for photosynthesis

Answer 3

6CO2 + 6H2O —> C6H12O6 + 6O2

Question 4

State three factors that affect the rate of photosynthesis

Answer 4

Light intensity, carbon dioxide concentration and temperature

Question 5

Oxygen gas is produced in photosynthesis and can be collected. How would you test that this gas was oxygen?

Answer 5

A glowing splint would be re-lit

Question 6

Describe how the upper epidermis is adapted for photosynthesis

Answer 6

Clear/transparent to allow light through to reach the palisade cells

Question 7

Describe the purpose of a waxy cuticle on the surface of a leaf

Answer 7

Waterproofing, reduced water loss by transpiration; reflects excess sunlight preventing damage

Question 8

Describe how the palisade mesophyll cells are adapted for photosynthesis

Answer 8

Contain many chloroplasts; cells packed tightly together to absorb maximum light for photosynthesis

Question 9

Describe the purpose of the air spaces between cells of the spongy mesophyll layer

Answer 9

Act as reservoirs of gases to maintain diffusion gradients for carbon dioxide to enter the photosynthesising cells and oxygen to leave

Question 10

Plant cell walls are made out of which carbohydrate?

Answer 10

Cellulose

Question 11

What is the function of the xylem vessels?

Answer 11

Transport water from the roots to the leaves

Question 12

What is the function of the phloem vessels?

Answer 12

Transport sucrose/amino acids away from the leaves

Question 13

Describe how stomata change size with light levels during the day

Answer 13

When light, guard cells open stomata (become turgid) so carbon dioxide can enter the leaf; at night, guard cells close stomata (become flaccid) to conserve water and oxygen (respiration)

Question 14

Describe how you would safely test a leaf for the presence of starch

Answer 14

Boil leaf in water to kill it (denatures enzymes); boil in ethanol (no naked flames as ethanol highly flammable; use water bath) to extract chlorophyll; dip in hot water to soften; add iodine solution; if starch present, blue-black colour

Question 15

Explain the purpose of destarching a leaf

Answer 15

To test whether starch is produced as a result of photosynthesis (many glucose molecules produced from photosynthesis are packaged into large, insoluble starch molecules). TO destarch a plant, place in the dark for 24 hours so photosynthesis cannot take place; the plant will convert the starch into glucose and respire it to stay alive

Question 16

Name the chemical used to test the requirement of carbon dioxide for photosynthesis (HINT: it absorbs CO2)

Answer 16

Soda lime (sodium/potassium hydroxide)

Question 17

Name the chemical used to investigate changes in carbon dioxide levels when leaves are photosynthesising under different conditions

Answer 17

Hydrogen carbonate indicator

Question 18

By what process does carbon dioxide enter a leaf and oxygen leave a leaf?

Answer 18

Diffusion

Question 19

TRUE/FALSE: all the oxygen produced in photosynthesis exits a leaf via diffusion through the stomata.

Answer 19

FALSE: some will be used in aerobic respiration within leaf cells

Question 20

What are present in the spongy mesophyll layer that maintain high concentration gradients for diffusion of carbon dioxide into the cells?

Answer 20

Air spaces

Question 21

Through which structures in the leaf do gases enter and leave?

Answer 21

Stomata

Question 22

Which cells control the opening and closing of the stomata? How do they do this?

Answer 22

Guard cells (become turgid to open the stomata; become flaccid to close the stomata)

Question 23

TRUE/FALSE: The rate of respiration is greater than the rate of photosynthesis in a plant AT NIGHT

Answer 23

TRUE: no light available for photosynthesis so plant continues to respire

Question 24

TRUE/FALSE: The rate of respiration is greater than the rate of photosynthesis in a plant during the day

Answer 24

FALSE: plants will use sunlight to convert light energy into chemical energy; plants will still respire but at a lower rate

Question 25

By what process do plants lose water through the stomata?

Answer 25

Transpiration