Gas Exchange (not human)

Question 1

How does the SA:V change in organisms varying in size?

Answer 1

It decreases with size

Question 2

How do single celled/small multicellular organisms meet their gas exchange needs?

Answer 2

Simple diffusion across their surface

Question 3

What is the most effective surface for gas exchange?

Answer 3

Large, thin and permeable area

Question 4

What do insects have to limit water loss?

Answer 4

. Waterproof covering - this is usually a rigid outer skeleton (exoskeleton) covered with a waterproof cuticle
. Small surface area to volume ratio - minimise the area over which water is lost

Question 5

How does oxygen move through the insect?

Answer 5

1. Oxygen enters the insect through spiracles and into the tracheae. The spiracles then close
2. Oxygen diffuses through the tracheae into the tracheoles
3. Oxygen is delivered directly to the respiring tissue

Question 6

Spiricles

Answer 6

Gas enters and leaves the insect through these tiny pores. They are opened and closed to control water loss by evaporation

Question 7

Tracheae

Answer 7

Network of tubes filled with air supported by strengthened rings
They are also filled with fluid that gets sucked into cells when the insect respires. This provides more SA for diffusion of gasses

Question 8

Tracheoles

Answer 8

Many small tubes, which extend throughout the body tissues, that create a large SA

Question 9

How does diffusion happen in the gas exchange system of an insect?

Answer 9

OXYGEN DIFFUSION
1. Tissues respire using oxygen, which reduces the concentration gradient of oxygen at the tissue
2. Oxygen moves from the tracheae to the tissue down a concentration gradient
3. This lowers the oxygen concentration in the tracheae so oxygen moves into the tracheae from outside the insect via the spiracles
CARBON DIOXIDE DIFFUSION
1. Respiration produces CO2, increasing the concentration gradient of CO2 at the tissue
2. CO2 moves into the trachea from the tissue down a concentration gradient
3. This increases the concentration in the tracheae so CO2 moves out of the tracheae to the outside via the spiracles

Question 10

How is ventilation maintained in insects?

Answer 10

Movement of the insect muscles creates a mass movement of air in and out of the tracheae
They also have small air sacs in their tracheae which can be pumped deeper into the trachea when the muscle contracts around the tracheae

Question 11

How do insects get additional oxygen during flight?

Answer 11

When an insect is at rest, water can build up in the tracheoles. During flight the insect may respire anaerobically producing lactic acid which lowers the water potential of the muscle cells, causing water to move from the tracheoles into the muscle cells via osmosis. This draws air into the tracheoles and closer to the muscle cells

Question 12

How many gills do fish have on each side of its head?

Answer 12

4

Question 13

Finger-like projections, starting at the head and finishing towards the body

Answer 13

Gill filaments

Question 14

Lammellae

Answer 14

Gill lamallae are found positioned on the gill fillament at right angles to each other
They contain capillaries and have a thin epithelium to reduce the distance between the blood and the water

Question 15

What is counter current flow?

Answer 15

The position of the filament and lamellae means that blood and water flow happens in opposite directions, this maintains a constant diffusion gradient and ensures no equilibrium is reached so almost all of the oxygen in the water diffuses into the blood

Question 16

Describe the structure of a leaf

Answer 16

Cuticle
Upper epidermis cells
Palisade mesophyll cells
Spongy mesophyll cells
Sub-stomatal air space
Lower epidemis cells
Guard cells
Stoma

Question 17

Name 4 adaptions of a leaf for gaseous exchange

Answer 17

1. Flat - gives large SA:V
2. Stomata - pores to allow CO2 to move into the leaf and oxygen to move out of the leaf during the day
3. Stomata obly open in response to light - stomata only open during the day time when the rate of photosynthesis is at it’s highest. They close at night to prevent water loss
4. Air spaces in leaf so short distance between mesophyll cells and air

Question 18

How does diffusion happen in the gas exchange system a leaf?

Answer 18

DIFFUSION OF CO2 (for photosynthesis)
1. Mesophyll cells photosynthesise and this reduces the concentration of CO2 in the cells
2. CO2 diffuses from the air spaces into the cells
3. This in turn reduces the CO2 concentration in the air spaces causing CO2 to move into the air spaces from the air outside the leaf, through the stomata
DIFFUSION OF OXYGEN
1. Mesophyll cells produce O2 as a result of photosynthesis
2. O2 diffuses into the air spaces from the cells
3. This increases the concentration of O2 in the air spaces, causing O2 to move from the air spaces to outside the leaf via the stomata

Question 19

What is a xerophytic plant?

Answer 19

Plants that live in environments where water availability is low

Question 20

Name 6 adaptations of xerophytic plants and how they reduce water loss

Answer 20

1. Reduced number of stomata - less SA
2. Stomata in pits - reduced concentration gradient and increases diffusion distance
3. Hairs to trap water vapour - reduced concentration gradient as humid air is trapped close to the stomata
4. Rolled leaves - reduced concentration gradient as humid air is trapped in the leaf
5. Leaves reduced to spines - less SA for water loss
6. Thick waxy cuticles - increased diffusion distance and is impermeable to water