3A Gas Exchange ⭐️ Flashcards
How do single-celled organisms exchange gases?
> They can absorb and release gases by simple DIFFUSION through their CSM
They have a LARGE SA and a THIN surface membrane that provides a SHORT DIFFUSION PATHWAY
Where is the gas exchange surface in fish?
In the gills
What is the structure of fish gills?
> each gill has a lot of thin plates called GILL FILAMENTS which provide a LARGE SA for gas exchange = INCREASED RATE of DIFFUSION
Gill filaments are covered in LAMELLAE which further increase the SA
The lamellae contain lots of CAPILLARIES and a THIN SURFACE LAYER of cells that INCREASE the RATE of diffusion between the water & blood
Describe the counter-current exchange mechanism in fish.
> Water enters the fish through its MOUTH, DOWN a PRESSURE GRADIENT and passes out over the gills
BLOOD flows through the lamellae in one direction and WATER flows over them in the OPPOSITE direction
this means water with a HIGH OXYGEN CONCENTRATION always flows next to blood with a LOW oxygen concentration
this maintains a STEEP CONCENTRATION GRADIENT so the rate of diffusion is FASTER and as much oxygen diffuses into the blood as possible
Describe how gases are exchanged in plants
> Plants need CO2 for photosynthesis where OXYGEN is a WASTE product
Oxygen is needed for RESPIRATION where CO2 is a WASTE product
gases are exchanged through the MESOPHYLL CELL SURFACES
Pores on the leaf surface called STOMATA open and close (which is controlled by GUARD CELLS) to allow gases to diffuse into the leaf to reach the cells
cells in the mesophyll layer have LARGE SAs
Describe how gases are exchanged in insects
> Land insects have TRACHEA that they use for gas exchange
air diffuses into pores on the surface of their abdomen called SPIRACLES
Oxygen diffuses DOWN its CONCENTRATION GRADIENT towards the cells
trachea branch into TRACHEOLES which have single-celled thin permeable walls that go to individual cells
oxygen therefore diffuses directly into cells - it isn’t transported in a circulatory system
CO2 from the cells diffuses DOWN its concentration gradient towards the spiracles and is released into the atmosphere
rhythmic abdominal movements pump air in/out of the spiracles
How do insects control water loss?
> close spiracles using muscle contraction
they have waxy cuticles over their body - reduces evaporation
have tiny hairs around spiracles - reduces evaporation
