Gills:
Counter Current:
- exposed to the exchange environment (act as gas exchange surface)
- (see p180 in Nelson Thornes Bio book)
- deoxygenated water leaves through an opening behind the operculum
- oxygenated water is forced in through the mouth and passes over the gills
- Gill filaments= rows of thin, vertical lamellae with many capillaries and covered by a single layer of cells (short diffusion pathway).
- Lots of filaments= large. S.A
Counter Current:
- Counter-current: water flows over and under the gill filaments and the oxygen is removed by bllood in the capillaries. The blood in the capillaries are carried in the OPPOSITE DIRECTION. This maximises oxygen uptake. Ensures diffusion gradient maintained.
- Blood has lower [ ] of oxygen than water, so oxygen from water moves into the blood by DIFFUSION.
- [blood] and [water] NEVER reaches the same, as the blood is always circulating so [ ] gradient constantly being MAINTAINED.