Gas exchange Flashcards
Gas exchange in single celled organisms?
By diffusion through their cell surface membrane
Why are microorganisms able to perform exchange via their surfaces?
- Large surface area (surface area to volume ratio)
- Thin surface
- Short diffusion pathway/distance
- Low demands
(therefore no specialised gas exchange system required)
Why do fish have specialised gas exchange systems?
Fish are multicellular so
- Small surface area to volume ratio
- Large diffusion distance
- High demand
- Body surface is impermeable (waterproof)
(Fish specialised gas exchange system = gills
Structure of gills in fish?
- Each gill is made up of lots of thin plates called gill filaments
- which give a large surface area for exchange of gases and therefore, increase the rate of diffusion
- The gill filaments are covered in lots of tiny structures called lamellae which increases the surface area even more
- gill lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion between the water and blood
- they are also permeable, short diffusion distance
Counter current system?
- ventilation brings in pure water (high oxygen, low carbon dioxide) and
- circulation brings in deoxygenated blood (low oxygen, high carbon dioxide),
- the water and blood pass over in opposite directions (counter-current flow),
- which maintains concentration gradient all the way along the gill lamellae
Why do insects have specialised gas exchange systems?
- High demand
- Large diffusion distance
- Body surface made of exoskeleton which is an impermeable barrier
- Multicellular so has a relatively small surface area to volume ratio
Gas exchange in insects?
Structure of tracheal system
- Air moves into the trachea through pores on the surface called spiracles
- Oxygen travels down concentration gradient towards the cells
- The trachea branch off into smaller tracheoles which have thin permeable walls and go to individual cells
- Oxygen moves directly into the respiring cells
- Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere
Control of water loss in insects?
- They close their spiracles using muscles
- They have a waterproof waxy cuticle all over their body
- Tiny hairs around their spiracles
(these all reduce water loss)
Gas exchange by the leaves of dicotyledonous plants?
- Mesophyll cells
- Mesophyll cells have a large surface area
- Gases move in and out through pores in the epidermis called stomata
- The stomata can open to allow exchange of gases and close if the plant is losing too much water
- Guard cells control the opening and closing of stomata
Adaptions of xerophytic plants?
- Stomata sunk in pits to trap water vapour reducing the concentration gradient of water between the leaf and air. This reduces evaporation of water from the leaf.
- A layer of ‘hairs’ on the epidermis to trap water vapor around the stomata
- Curled leaves with the stomata inside, protecting them from wind. (windy conditions increase the rate of diffusion and evaporation)
- A reduced number of stomata, so there are fewer places for water to escape
- Thicker waxy, waterproof cuticles on leaves and stem to reduce evaporation
Why can’t animals/plants perform exchange via their surfaces?
- have a small surface area to volume ratio
- multicellular (large diffusion distance and high demand)
- impermeable surface (prevent pathogens entering and reduce water loss)
- therefore, require specialised Exchange & Transport systems
(exchange system = increases rate of diffusion of nutrients in and wastes out)
(transport system = deliver nutrients and remove waste from all cells)
Why does gas exchange need to occur in humans?
- Humans need to get oxygen into the blood (for respiration) and need to get rid of carbon dioxide (made by respiring cells)
Structure of the gas exchange system in humans?
- As you breathe in, air enters the trachea (windpipe)
- The trachea splits into two bronchi - one bronchus leading to each lung
- Each bronchus then branches off into smaller tubes called bronchioles
- The bronchioles end in small ‘air sacs’ called alveoli
- This is where gases are exchanged
Adaptations of alveoli?
- millions of tiny alveoli that are folded (large surface area)
- thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
- elastic tissue in wall (stretches when breathing in to increase surface area, recoils when breathing out to push the air out)
- ventilation maintains concentration gradient (high oxygen, low carbon dioxide)
Adaptations of capillaries?
- millions of tiny capillaries (large surface area)
- thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
- narrow lumen (increases diffusion time, decreases diffusion distance)
- circulation maintains concentration gradient (low oxygen, high carbon dioxide)
