Potometer , other random notes about fish and that.

Potometer:

It is difficult to measure transpiration, because it is difficult to collect and condense, and you can't measure vapour.

A leafy shoot would be cut under water, because otherwise, an air bubble would go into the xylem, breaking the transpiration stream, and stopping the movement up the shoot. If it is in water, water will be drawn in instead, and the column maintained.

The syringe in a potometer is to refill the capillary tube when the bubble reaches the stem so water can continue to be measured.

Assumption made if potometer is used to measure the rate of transpiration - all water taken up is being transpired.

Small organisms have a sufficient gas exchange system as the have a large sa/v ratio.

Large animals have blood systems because with a large animal, gas exchange diffusion distance to cells would be too far, so, blood system is needed for rapid oxygen supply.

Small fish, no gill, because exchange/diffusion can take place through body surface, as they have a high surface area to volume ratio and a short diffusion distance.

Mackerel swim faster then toadfish => Mackerel have thinner lamellae, short diffusion distance, rate of gas exchange is quicker, get oxygen for respiration faster, to release ATP for muscle contraction.

Gill makes oxygen efficient => Thin lamellae, short diffusion distance to blood capilaries

Counter current flow maintains a concentration gradient, doesn't reach an equilibrium, takes place along whole gill.