Gas Exchange 3A

Question 1

Gas exchange surfaces Adaptations

Answer 1

Large surface area - maintains a steep concentration gradient

Thin - short diffusion pathway

Question 2

How do single celled organisms exchange gases

Answer 2

Simple diffusion

Large SA, thin surface, short diffusion pathway

Question 3

Fish gas exchange system

Answer 3

Counter current

Water containing oxygen -> mouth -> gills

Gills have gill filaments which provide large SA for gas exchange

Gill filaments covered in lamellae which further increase the SA

Lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion

Blood flows through the lamellae in one direction and water flows over in the other direction - counter current

It maintains a concentration gradient concentration of oxygen in the water is always higher than the concentration in the blood so as much diffusion diffuses into the blood as possible

Question 4

Insect gas exchange

Answer 4

Trachea

Air moves into the tracheae through pores called spiracles

Oxygen travels down the concentration gradient towards the cells

Tracheae -> tracheoles which go to individual cells

CO2 from the cells moves down its own concentration gradient towards the spiracles to be released

Insects use rhythmic abdominal movements to move air in and out the spiracles

Question 5

Plant gas exchange

Answer 5

Mesophyll cells
Gases move in and out through stomata which open and close this is controlled by guard cells

Question 6

How do insects and plants control water loss

Answer 6

If insects are losing too much water they close their spiracles using muscles they also have a waterproof waxy cuticle all over their body and tiny hairs around their spiracles both to reduce evaporation

Plants stomata are usually kept open during the day to allow gas exchange

Water enters the guard cells making them turgid which opens the stomata

If the plant becomes dehydrated the guard cells lose water and become flaccid which closes the pores

Some plants are adapted for specific climates where water loss is a problem these are called xerophytes

Question 7

Examples of xerophytic adaptations

Answer 7

Stomata sunk in pits reducing the concentration gradient of water between the leaf and the air this reduces evaporation

waxy waterproof cuticles

Curled leaves with the stomata inside protection from wind

Reduced number of stomata so there are less places for water to escape