Question

Which of the following situations does diffusion not help, in our bodies?A. Oxygen entering the bloodstream.B. Food entering the bloodstream from the small intestine.C. Carbon dioxide exiting the bloodstream.D. Glucose entering the intestines from the villus.

Answer 1

Answer:

Glucose entering the intestines from the villus.This is by active transport.The latter is defined as the movement of molecules and  solutes from the region of lower concentration to the region of higher concentration against the concentration gradient.

Explanation:

All the above options depends on the diffusion gradients from one  higher region to another.e.g oxygen passing from high concentration from outside to lower concentration in blood stream,like wise Co2 from higher concentration from inside to outside,with passive diffusion lipids and water enter the small intestine(note amino acid and glucose,and fructose are different).

Active transport( through sodium dependent transporter) transports glucose to the intestine  from the villus.This is movements against concentration gradient because,glucose molecule are concentrated in intestine,and needed by the cells, in the body.Therefore they must be transported as a fast rate inn the blood .

However the absorption by the villi is very slow,therefore active transport is needed to move these against the concentration gradient into the intestine.And finally the blood.

If this were to be moved by  passive diffusion,the high concentration in the intestine will force this back into the villi

Therefore extra energy is needed by active transport for the glucose molecules to enter the intestine from the villus.