Gas Exchange: Plants

Question 1

What type of leaf do we speak about adpations of as a gas exchange surface?

Answer 1

• Dicotyledonous leaves of plants.

Question 2

What is the structure of the dicotyledonous leaf for gas exchange?

Answer 2

• 3 main components:
• Stomata: where gas exchange occurs.
• Spongy mesophyll: gaps, allow CO2 to diffuse into the plant/ reach palisade mesophyll.
• Palisade mesophyll: many chloroplasts/ top of leaf –> site of photosynthesis.

Question 3

What gases diffuse in and out of stomata of on the leaves of dicotyledonous plants? What do stomata do to reduce water loss, (functional adaptation) to prevent water loss?

Answer 3

• Oxygen diffuses out of the stomata.
• Carbon dioxide diffuses in through the stomata.
• Reduce water loss by evaporation/ transpiration, stomata close at night when photosynthesis wouldn’t be occuring, no need for the exchange of gases.

Question 4

What does there need to be a compromise between in xerophytic plants?

Answer 4

• Structural and functional compromises between opposing needs of efficient gas exchange and limitation of water loss.

Question 5

What are xerophytic plants?

Answer 5

• Xerophytic plants are those adapted to survive in environments with limited water.

Question 6

What structural features do xerophytic plants have to enable efficient gas exchange whilst also limiting the water vapour loss?

MS copy and paste - learn word for word!

Answer 6

1. Hairs so ‘trap’ water vapour
   and water potential gradient
   decreased;
2. Stomata in pits so
   ‘trap’ water vapour and water
   potential gradient decreased;
3. Thick cuticle layer so
   increases diffusion distance;
4. Waxy cuticle so reduces
   evaporation/transpiration.
5. Curled leaves so
   ‘trap’ water vapour and water
   potential gradient decreased;
6. Spines/needles so reduces
   surface area to volume ratio;

Question 7

How will curled leaves in xerophytic plants limit water vapour loss?

Answer 7

• Traps water vapour, reducing water potential gradient.

Question 8

Adaptations that leaves have for efficient gas exchange.

Answer 8

1.) Large surface area to volume ratio, increases rate of exchange of gases (many stomata.)
2.) Thin = short diffusion distance, increased rate of exchange of gases.
3.) Maintain concentration gradient: spongy mesophyll having gaps for CO2 to pass through before diffusing into palisade mesophyll.

Question 9

4 different tissues you find is dicotylendonous leaves.

Answer 9

• Upper epidermis
• Lower epidermis
• Spongy mesophyll.
• Palisade mesophyll.

Question 10

Past Paper Q

Advantage of limited water vapour loss.

Answer 10

• More water available for photosynthesis.