Gas Exchange - A2

Question 1

Why do cells need to take in oxygen and nutrients?

Answer 1

Metabolic processes and to release waste.

Question 2

What is surface area: volume ratio?

Answer 2

The larger the volume of an organism, generally, the smaller SA:V.

Question 3

What do single cell organisms do for gas exchange?

Answer 3

Substances can just diffuse into or out of the cell across the cell-surface membrane. The diffusion rate is quick.

Question 4

Why is diffusion across the outer-membrane too slow for multicellular organisms?

Answer 4

Larger animals have small SA:V ratio, some cells are deep within the body making the diffusion distance quite large.

Question 5

What do multicellular organisms have rather than completing straightforward diffusion?

Answer 5

Mass transport systems(MTS) to carry substances to and from cells, normally a circulatory system which transports substances such as O2 and CO2.

Question 6

What type of activity releases heat?

Answer 6

Metabolic activity(e.g. respiration) releases heat, yet organisms need to maintain a stable internal temperature.

Question 7

How does size affect heat loss?

Answer 7

The larger the SA:V, the faster heat energy is lost. This means smaller organisms need a relatively high metabolic rate in order to generate enough heat to stay warm.

Question 8

How does body shape affect heat exchange?

Answer 8

Animals with a compact shape have a small SA:V - minimising heat loss. Animals with less compact shapes(sticky out bits) have a large SA:V ratio, increasing heat loss. An animal’s body shape is adapted to suit the temperature of it’s environment.

Question 9

Do insect’s have a large or small SA:V and what physical feature do they have which makes them impermeable to gases?

Answer 9

They have a larger SA:V and a hard outer exoskeleton.

Question 10

What type of system do insect’s use for gas exchange?

Answer 10

Insect’s use a trachae system, which is a system of microscopic air-filled pipes.

Question 11

How does a trachae system work?

Answer 11

Gases enter and leave the trachea through pores in the exoskeleton called spiracles. Gases diffuse down a concentration gradient.

Question 12

What drives the concentration gradients in gas exchange?

Answer 12

Respiration drives the concentration gradient- produces a low conc. of O2 and a high conc. of CO2.

Question 13

What occurs at the spiracles of insects?

Answer 13

Once through the spiracles, O2 diffuses down the trachea into the smaller tracheoles.

Question 14

How are insects adapted for gas exchange?

Answer 14

-Tracheoles have thin walls- short diffusion distance to cells
-Tracheoles are highly branched so there’s a large SA for gas exchange and a short diffusion distance to cells for gas exchange
-body pumping- more oxygen enters quicker which maintains the conc. gradient for O2 and CO2
-fluid in the end of the tracheoles moves into tissue during exercise - larger SA for gas exchange, also faster diffusion gases through air compared to through water to the gas exchange surface.
-tracheoles enter directly onto muscle cells - short diffusion distance

Question 15

What can insects do if they begin to lose too much water?

Answer 15

They can close their spiracles using muscles which prevent the diffusion of water out of the body.

Question 16

What do insects have all over their body that prevents water loss?

Answer 16

They have an impermeable waterproof waxy cuticle all over their body - preventing evaporation and diffusion or water out of the body.

Question 17

Why do fish need a specialised gas exchange system?

Answer 17

They are large so have a relatively small SA:V and they also live in low O2 environments as water has less O2 than air.

Question 18

What is the structure of the gills?

Answer 18

-Each gill is made up of lots of thin plates called gill filaments(large SA)
-gill filaments are then covered in a lot of tiny structures called llamellea(further increasing SA)
-lamellae have lots of blood capillaries(SA) and a thin surface to speed up diffusion
-Many capillaries across the whole length of the lamellae - SA and conc. gradients

Question 19

What is a counter-current system?

Answer 19

Blood and water flow in opposite directions and this maintains the oxygen gradient across the whole length of the lamellae.

Question 20

How does diffusion occur in plants?

Answer 20

Mesophyll cells are the main surface for gas exchange as they have a large SA. Gases move in and out via pores called the stomata and guard cells control the opening and closing of the cell.

Question 21

Why are stomata kept open during the day?

Answer 21

To allow for gas exchange.

Question 22

What causes guard cells to become turgid?

Answer 22

Water enters the guard cells and makes them turgid, and this causes the stomata to open.

Question 23

What happens if a plant becomes dehydrated?

Answer 23

If the plant becomes dehydrated, the guard cells lose water and become flaccid, closing the pore.

Question 24

What are xerophytic plants?

Answer 24

Plants which are specifically adapted to living in warm, dry, or windy habitats. E.g. cacti or maram grass.

Question 25

What are the five main adaptions of xerophytic plants?

Answer 25

• sunken stomata - reducing the water potential gradient between the leaf and the air-reducing diffusion and evaporation
  -hairs around the stomata to trap water vapour - reducing the water potential gradient between the leaf and the air-reducing diffusion and evaporation
  -curled leaves with stomata on the inside(wind protection). Reducing the water potential gradient between the leaf and the air-reducing diffusion ad evaporation.
  -reduced no. of stomata - reduced SA so reduced rate of diffusion.
  -thick waxy waterproof cuticle, increases diffusion distance and reduces evaporation.