2. More on Gas Exchange Flashcards
What do terrestrial insects have which they use for gas exchange?
Microscopic air-filled pipes called tracheae.
Air moves into tracheae through pores on the surface called spiracles.
Oxygen travels down the concentration gradient towards the cells.
What happens to the tracheae in the insects?
Branch off into smaller tracheoles which have thin, permeable walls and go to individual cells.
Oxygen diffuses directly into respiring cells.
What doesn’t the insects circulatory system do?
Transport oxygen.
What is later released into the atmosphere from the insects?
Carbon dioxide, which moves from the cells down its own concentration gradient towards the spiracles then its released into atmosphere.
Use rhythmic abdominal movements to move air in and out of spiracles.
How is air moved in and out of the spiracles in the insects?
Using rhythmic abdominal movements.
What does gas exchange tend to do?
Lose water.
Plants and insects have evolved to minimise water loss without reducing gas exchange too much.
What happens if insects lose too much water?
They close their spiracles using muscles.
Waterproof, waxy cuticle all over their body and tiny hair around the spiracles - reduce evaporation.
How does water get into and out of plants?
Plants’ stomata is open mainly during the day to allow gas exchange.
Water enters the guard cells - making them turgid, which opens the stomatal pore.
Plant gets dehydrated, guard cells lose water and become flaccid, which closes the pores.
What are xerophytes?
Plants that are specially adapted for life in warm, dry and windy habitats where water loss is a problem.
XEROPHYTES EXAMPLE.
What is the stomata like on xerophytes?
- Sunk in pits to trap water vapour, reduces the concentration gradient of water between the leaf and the air - reduces evaporation of water from leaf.
- Reduced numbers of stomata - fewer places for water to escape.
XEROPHYTES EXAMPLE.
What is the epidermis like on xerophytes?
Layers of ‘hairs’ on the epidermis to trap water vapour round the stomata.
XEROPHYTES EXAMPLE.
How do xerophytes protect from wind?
Curled leaves with the stomata inside.
XEROPHYTES EXAMPLE.
In a xerophyte what reduces evaporation?
Thicker waxy, waterproof cuticles on leaves and stems.
