In which of the following processes, active transport is NOT used?
- A.Reabsorption of amino acids and glucose from kidney into blood
- B.Loading sugar from photosynthesizing leaf cells into phloem tissue for transportation
- C.Passage of Na+ and Cl- through hydrophilic channel created by protein molecules
- D.Absorption of glucose and electrolytes into the bloodstream
Correct answer
Explanation
The correct answer is C, Passage of Na+ and Cl- through hydrophilic channel created by protein molecules. Movement of ions through protein channels is facilitated diffusion, a passive process that needs no energy from ATP.
Active transport moves substances against their concentration gradient, from low to high concentration, using carrier proteins and energy, usually from ATP. Passive transport moves substances down the gradient without spending energy; when charged ions or polar molecules cross the membrane through water-filled channel proteins, it is called facilitated diffusion. In the kidney, glucose and amino acids are pulled back from the filtrate into the blood by active transport in the proximal tubule. In plants, sucrose is actively loaded from leaf cells into the phloem, which also builds the pressure that drives its flow. In the small intestine, glucose and electrolytes are absorbed with the help of active pumps.
Option A is wrong because tubular reabsorption of glucose and amino acids uses active transport. Option B is wrong because phloem loading is an active process. Option D is wrong because intestinal absorption of glucose and electrolytes relies on active transport.
Exam tip: ion channels = passive (facilitated diffusion); pumps and carriers against the gradient = active, use ATP.
Practice Questions
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- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
Show answer
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