Which of the following statements best describes active transport
A. Spontaneous movement of a substance through a semipermeable membrane
B. Movement of a substance against a concentration gradient
C. Movement of a specific substance across a membrane
D. Net movement of a substance from a region of higher concentration to a region of lower concentration
B. Movement of a substance against a concentration gradient
The correct answer is B. Movement of a substance against a concentration gradient.
Active transport is a process that involves the movement of substances across a cell membrane against their concentration gradient. This means that the substances are moved from an area of lower concentration to an area of higher concentration. This process requires the use of energy in the form of ATP (adenosine triphosphate) to actively transport the substances across the membrane. Active transport is essential for the transportation of ions, nutrients, and other molecules in cells, allowing them to maintain specific concentrations and perform crucial functions.
The correct answer is B. Movement of a substance against a concentration gradient.
To arrive at this answer, let's go through the other choices one by one:
A. Spontaneous movement of a substance through a semipermeable membrane: This describes passive transport, not active transport. Passive transport refers to the movement of a substance from an area of higher concentration to an area of lower concentration without the need for energy.
C. Movement of a specific substance across a membrane: While this statement does accurately describe active transport, it is not as comprehensive as the correct answer. Active transport involves the movement of a substance against its concentration gradient, implying the movement is from an area of lower concentration to an area of higher concentration. Therefore, choice B is a more complete description.
D. Net movement of a substance from a region of higher concentration to a region of lower concentration: This is the opposite of active transport. It describes a process called passive transport, specifically diffusion. Diffusion is the spontaneous movement of a substance from an area of higher concentration to an area of lower concentration.
Ultimately, active transport stands out among the choices because it specifically involves the movement of a substance against a concentration gradient, requiring energy to accomplish this process.