AS biology new spec exchange

Organism exchange substances with their environment

·         The surface area to volume determines if an exchange surface is needed. Bacteria have a large SA: V ratio so get their nutrients through their CSM but humans have a small SA: V ratio so need an exchange surface, lungs.

·         Fick’s law = . This says that an effective exchange surface has a large SA: V ratio, a thin diffusion pathway, and some way to maintain the conc gradient (moving internal or external environment).

·         To calculate the surface area of a cylinder 2πrh + 2πr²

·         Insects have an internal network of trachea strengthened by rings to prevent collapse. The trachea divide into smaller dead end tracheoles that extend throughout the tissue.

·         Oxygen diffuses in as oxygen is used up at the end of the tracheoles so there is a concentration gradient between the outside and in. CO2 diffuses out as it is produced in respiration so there is a higher conc in than out.

·         Mas transport also takes place as muscles contract to move the air in and out. Also in major activity, anaerobic respiration occurs and lactate is produced which lowers the water potential so water moves into the cells which decreases the volume in the tracheoles so air is drawn in and it also means that the final diffusion is in the gas phase which is quicker. The spiracles on the body surface open and close to control water loss.

·         Fish have a small SA: V ratio, and have a water proof covering so they need an exchange surface= gills.

·         Gill filaments have lamellae at right angles to it to increase the surface area.

·         The fish lowers its mouth floor, opens its mouth and the operculum to increase the volume, and decrease the pressure so water moved in. It then lifts the floor, closes the operculum to decrease the volume and increase the pressure so water is forces out over the gills.

·         There is a counter current means that 80% of the oxygen is absorbed rather than 50% if the blood wand water were travelling in the same direction. This is because there is always a conc gradient as blood with some O2 meets saturated water and blood with little O2 in meets water with some O2 in.

·         In plants the amount of gas exchange with the air is determined by the rates of photosynthesis and respiration.

·         Plants are well adapted as no cell is far from the external air and exchange is in the faster gas phase.

·         Plants have no specific exchange system but they have a large surface area as leaves are flat and there are lots of air spaces within.

·         Stomata are openings mainly on the underside of the leaf, that…