IB Biology SL B3.2 Transport Questions

Capillary walls are thin or one cell thick for better diffusion. Capillaries have a small diameter or narrow lumen so they fit into small spaces between cells. Their small diameter gives a greater surface area for molecular exchange. Pores between cells in the walls allow plasma to leak out and allow phagocytes or immune components to enter tissues. Only one red blood cell passes at a time, allowing efficient oxygen uptake.

a. water is lost through the stomata/leaves by evaporation;

b. water is drawn out of xylem vessels / spongy mesophyll into leaf airspaces;

c. adhesion allows water to travel through cell walls (by capillary action) / against gravity;

d. this generates tension/pulling force/negative pressure potentials inside the xylem vessels;

e. tension/transpirational pull draws water up in the xylem;

f. cohesion ensures a continuous column of water in the xylem/OWTTE;

g. concentration gradient created in roots allowing water intake by osmosis (from soil)

a. lack of cell contents making it hollow/empty with minimal resistance to the flow of sap / easier flow of sap/water;
b. incomplete/absent end walls (creating a long continuous tube) for flow;
c. lignocellulose/lignified walls to withstand tensions / prevent collapsing;
d. pits/gaps/pores for entry/exit/ horizontal movement of water;

The adaptation must be accompanied by a brief account