Topic 3—A: Exchange and Transport systems- 2. Gas exchange Flashcards
What is a gas exchange surface?
- Gas exchange occurs over it
- A boundary between the outside environment and the internal environment of an organism
What two things does gas exchange surfaces have in common that increase the rate of diffusion?
- Large surface area
- They’re thin (one layer of epithelial cells)- provides a short diffusion pathway across the gas exchange surface
Gas exchange in single-celled organisms
- They absorb and release gases by diffusion through their cell-surface membranes
- They have a large surface area
- Thin surface (short diffusion pathway) so rapid diffusion
Counter-current system
- In the gills of a fish the Blood and water flow in opposite directions
- Maintains concentration gradient across whole length of the gill.
- The water has a relatively high oxygen concentration compared to the blood with a lower oxygen concentration so it allows the oxygen to diffuse from the water into the blood
Where does water enter and leave the fish?
Water enters the fish by its mouth and passes out through the gills.
Structure of gills
Each gill is made up of lots of gill filaments which gives it a large surface area for exchange of gases (increases rate of diffusion)
- Gill filaments are covered in lots of tiny structures called lamellae which increases the surface area even more
- Lamellae have lots of blood capillaries ( remove oxygen and bring carbon dioxide so helps maintain a concentration gradient
and a thin layer of cells to speed up diffusion between the water and the blood
Adaptations of dicotyledonous plants for efficient gas exchange
- Spongy mesophyll (contains air spaces)- they have a large surface area for gases to diffuse through
- Many stomata- guard cells can open and close them so gases can diffuse in and out
- Thin- short diffusion distance
What are terrestrial insects?
They are insects that live on land so they dry out easily
Gas exchange in insects
- Air moves into the tracheae through pores on the surface called spiracles
- Oxygen travels down a concentration gradient towards the cells
- Tracheae branch off into smaller tracheoles which have thin permeable walls and go to individual cells so oxygen diffuses directly into the respiring cells
- the insects circulatory system doesn’t transport oxygen so carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere
Insects (adaptations) for efficient gas exchange
- high numbers of highly branched tracheoles makes a large surface area
- tracheoles have thin walls so a short diffusion distance
- abdominal pumping changes pressure in the body causing air to move in/out which helps maintain a concentration gradient for diffusion
Control of water loss (insects) adaptations
- they can close there spiracles using muscles to reduce water loss
- thick exoskeleton- increases diffusion distance so less water loss
- Hairs around spiracles- traps moist air reducing the water potential gradient so less water loss
Control of water loss (dicotyledonous plants)
- Stomata are usually kept open during the day to allow gaseous exchange
- water enters the guard cells making them turgid opening the stomatal pore
- when plants get dehydrated the guard cells lose water becoming flaccid which closes the pore
What is a xerophyte?
A plant adapted to live in very dry conditions e.g. cacti
Xerophytic plants adaptations for efficient gas exchange while limiting water loss
- Thick waxy cuticle- increases diffusion distance so less evaporation
- Stomata sunk in pits/ hairs to trap water vapour reducing the water potential gradient so less evaporation
- ## Reduced number of stomata so there are fewer places for water to escape
