Adaptations for Gas exchange in plants

Question 1

Cuticle

Answer 1

waxy transparent layer.
It allows light to pass through to
the photosynthetic palisade
mesophyll below but reduces
water lost

Question 2

Palisade mesophyll

Answer 2

main photosynthetic layer packed
with chloroplasts.

Question 3

Upper epidermis

Answer 3

transparent for light to easily
penetrate to photosynthetic
layers.

Question 4

Spongy mesophyl

Answer 4

surrounded by air spaces for
easy diffusion of gases. The
mesophyll cell membranes are
the site of gas exchange.

Question 5

Stomata

Answer 5

the stomatal pores
allow the exchange of gases
down a concentration gradient.

Question 6

Vascular bundle

Answer 6

Xylem = water and mineral transport
Phloem = products of photosynthesis ( sucrose and amino acid )

Question 7

Guard cells

Answer 7

Become turgid and flaccid due to changes in water potential: this opens and closes the stomatal pore

Question 8

Why do plants need to exchange gases?

Answer 8

respiration and photosynthesis

Question 9

Where is the main gas exchange surface and what adaptations does it have?

Answer 9

• The leaf
• Leaf blade is thin and flat with a large surface area
• this allows the diffusion pathway to be short

Question 10

Adaptations for gas exchange

Answer 10

• Spongy mesophyll tissue allows circulation of gases
• Stomatal pores allow gases to enter and leave the cell.
• Gases dissolve in the moist layer which covers each cell and diffuse inside

Question 11

Adaptations for photosynthesis

Answer 11

• Leaves have a large surface area to capture as much light as possible
• Can orientate themselves to angle themselves with as much light as possible
• Palisade cells packed with chloroplasts

Question 12

When do the guard cells change shape ?

Answer 12

-due to turgor

Question 13

Describe how the stomatal pore opens

Answer 13

• Light strikes the chloroplast during the day
• Potassium ions are pumped, via active transport, into the guard cells
• As a result stores starch is converted into malate
• This lowers the water potential in the guard cells
• Water enters via osmosis
• Guard cells become turgid and curve apart due to the inner wall being thicker
• This opens the stomatal pore, allowing gas exchange

Question 14

How does the stomatal pore close?

Answer 14

• Light intensity in the night is too low for photosynthesis
• Potassium ions diffuse out the guard cell
• Malate is converted back into starch by condensation reaction
• Water potential of the guard cell become higher
• Water leaves via osmosis
• Guard cell becomes flaccid and closes the stomatal pore also reducing water loss

Question 15

Hydrophyte

Answer 15

• Water plants
• Grow submerged or partially submerged in water
  e.g waterlily

Question 16

Adaptations of a hydrophyte

Answer 16

• little/ no waxy cuticle = water loss is no problem due to water source
• Stomata on the upper epidermis = underside of leaf is submerged, so needs to allow gas exchange
• Xylem poorly developed
• Stem and leaves have large air spaces : reserviors for O2 and CO2, provide buoyancy

Question 17

Xerophytes

Answer 17

• Plants that live in conditions where water is scarce
• Highly specialised
  e.g marram grass

Question 18

Mesophytes

Answer 18

• flourish in habitats with adequate water supply
• Close stomata during night and open during day

Question 19

Xerophytes adaptations

Answer 19

ROLLED LEAVES = reduce lead area exposed to air and so reduce transpiration

THICK WAXY CUTICLE = waxy covering which reduces water loss by evaporation

HAIRS - stiff, interlocking hairs trap water vapour and reduce water potential gradient

SUNKEN STOMATA = allow water vapour to accumulate above stomatal pore, increasing humidity in the air chamber. Reduces the water potential gradient between inside leaf and air chamber. reduces rate of transpiration