Which one of the following involves active transport?

A movement of carbon dioxide into alveoli in the lungs
B uptake of alcohol (ethanol) through the lining of the stomach
C secretion of sweat onto the skin’s surface
D re-absorption of glucose in the kidney tubules
E loss of urine from the urethra
F transfer of oxygen into the blood from the alveoli

Answer:

1) D

Active transport is the movement of molecules from an area of lower concentration to an area of higher concentration. This requires energy. 

A – Wrong
CO2 moves into the alveoli via diffusion. Carbon dioxide moves from an area of higher concentration (in blood in capillary) to an area of lower concentration (alveoli) 

B – Wrong
This occurs via diffusion. 

C – Wrong
This is the easiest to discard. There is little to no sweat on the skin surface, meaning that the higher concentration is in the sweat gland and lower concentration is on the skin. So this could occur by diffusion.

D – Correct
Reabsorption of glucose from kidney tubules requires movement of glucose form an area of lower concentration to an area of higher concentration. This requires energy; hence, active transport is used. 

E – Wrong
Loss of urine occurs due to change in pressure.

F – Wrong
Same concept as A. Oxygen moves from an area of higher concentration (in alveoli) to an area of lower concentration (blood in capillary)