3.1 Adaptations for Gas Exchange

Question 1

What happens to the surface area of an organism as it gets bigger?

Answer 1

Increases

Question 2

What happens to the volume of an organism as it gets bigger?

Answer 2

Increases

Question 3

What happens to the surface area:volume of an organism as it gets bigger?

Answer 3

Decreases

Question 4

Why does surface area:volume decrease as an organism gets bigger?

Answer 4

Surface area is divided by volume so if the volume gets larger by a bigger factor the ratio will decrease

Question 5

How can organisms with a large surface area:volume get oxygen and glucose?

Answer 5

Diffusion across surface
No specialised exchange surface is needed

Question 6

Name an organism that relies on getting materials through diffusion across its surface.

Answer 6

Single cell organisms e.g. bacteria

Question 7

Give examples of specialised exchange surfaces.

Answer 7

Lungs, gills, tracheoles, small intestine villi

Question 8

How do organisms exchange materials if they’re bigger than single celled but small enough not to need an exchange system?

Answer 8

Body shape adaptations required to increase rate of diffusion

Question 9

How is a leaf adapted to make diffusion of gases quicker?

Answer 9

Flat - large surface area
Thin - short diffusion pathway
Airspaces in spongy mesophyll

Question 10

What layer of the leaf does carbon dioxide need to reach?

Answer 10

Palisade

Question 11

Where in the leaf is carbon dioxide low in concentration during the day?

Answer 11

Palisade cells as they are constantly using it for photosynthesis

Question 12

Where in the leaf is oxygen high in concentration during the day?

Answer 12

Palisade cells as they are constantly producing it in photosynthesis

Question 13

Which way does oxygen diffuse relevant to leaves?

Answer 13

Out of the palisade cells -> the air

Question 14

Which way does carbon dioxide diffuse relevant to leaves?

Answer 14

Into the leaf from the air -> palisade cells

Question 15

What happens to the rate of photosynthesis at night?

Answer 15

Stops

Question 16

Describe the rate of respiration during the day/night.

Answer 16

Constant level as plant always needs to release energy and respiration does not require sunlight

Question 17

How will the concentration gradient for oxygen in the leaf change at night?

Answer 17

Becomes lower in leaves than air as plant is no longer producing oxygen in photosynthesis and using it up in respiration

Question 18

How will the concentration gradient for carbon dioxide in the leaf change at night?

Answer 18

Becomes higher in leaves than air as plant is no longer using carbon dioxide up in photosynthesis but is producing it in respiration

Question 19

How do plants get gases in/out of the leaves?

Answer 19

Through the stomata

Question 20

How are the stomata of a plant controlled?

Answer 20

The guard cells open/close them

Question 21

What are xerophytes?

Answer 21

Plants that live in low water environments

Question 22

What does a xerophyte need to be adapted for?

Answer 22

Reduced water loss

Question 23

How are rolled leaves an adaptation for xerophytes?

Answer 23

Less surface area of leaf so less water can evaporate

Question 24

How are less stomata an adaptation for xerophytes?

Answer 24

Less water can evaporate out

Question 25

How is a thicker waxy cuticle an adaptation for xerophytes?

Answer 25

Reduces water loss

Question 26

How are stomata sunk in pits/grooves an adaptation for xerophytes?

Answer 26

Keep water vapour close to stomata to reduce the water potential gradient

Question 27

How are hairs surrounding the stomata an adaptation for xerophytes?

Answer 27

Trap water particles close to the stomata to reduce the water potential gradient

Question 28

Describe an experiment to test the hypothesis "xerophytes have less stomata than a common daisy".

Answer 28

Count the stomata on leaf of a daisy and leaf of a xerophyte using a microscope / nail varnish and peel off Multiple repeats and calculate mean for xerophyte plant and mean for daisy Keep surface area of leaf / species of xerophyte / field of view the same each time Use a stats test to see if there is a significant difference

Question 29

Describe an experiment to test the hypothesis "xerophytes have less stomata on their upper surface than a common daisy".

Answer 29

Take leaves from xerophyte and daisy and find the mass Cover the lower surface in waterproof vaseline to block stomata on the lower surface from losing water Leave for same time period and reweigh Compare the mass lost from leaves and should see xerophyte lost less mass Keep surface area of leaves/species of plant/room temperature the same

Question 30

What are spiracles?

Answer 30

Tiny holes in an insects exoskeleton

Question 31

What are tracheoles?

Answer 31

Tubes that connect the spiracles and muscle

Question 32

Why is the concentration of oxygen near an insects muscle always low?

Answer 32

Insects use muscles to make the abdominal cavity bigger and smaller and push air in/out

Question 33

What is abdominal pumping?

Answer 33

The insect uses muscles to make the abdominal cavity bigger and smaller to push air in/out

Question 34

What is the role of abdominal pumping in gas exchange for insects?

Answer 34

Increases the concentration gradient by pulling in oxygenated air

Question 35

Why do large, active insects do more abdominal pumping than smaller ones?

Answer 35

More respiration to release more energy so more oxygen required

Question 36

How does the fluid at the end of the tracheoles make gas exchange quicker?

Answer 36

Increases surface area and shortens diffusion distance

Question 37

What does oxygen do in the fluid at the end of tracheoles?

Answer 37

Dissolves

Question 38

Why does the fluid at the end of tracheoles move into insects muscles?

Answer 38

Muscles respire anaerobically and produce lactic acid Reduces the water potential of the muscle so water moves in by osmosis

Question 39

Where do fish absorb oxygen from the water?

Answer 39

Gills which are full of blood capillaries

Question 40

What problems do fish have to overcome when extracting oxygen from water?

Answer 40

Oxygen at lower concentration in water than air

Question 41

How do gills achieve a large surface area?

Answer 41

Many lamallae and filaments

Question 42

How do gills achieve a short diffusion distance?

Answer 42

Walls of gill fiaments are one cell thick

Question 43

How do gills achieve a large concentration gradient?

Answer 43

Countercurrent flow of water and blood

Question 44

What is the countercurrent mechanism?

Answer 44

Water and blood flow in opposite directions The water always has a higher concentration of oxygen than the blood Oxygen is able to diffuse into the blood along the entire length of the gill filament as equilibrium is never reached

Question 45

Why are fish able to have external gas exchange structures?

Answer 45

Water is denser than air so they can be supported

Question 46

Why are external gills an advantage?

Answer 46

More surface area in contact with water Shorter diffusion distance