OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

Which type of cellular transport is primarily responsible for moving nutrients against their concentration gradient?

1. Passive transport

2. Facilitated diffusion

3. Active transport

4. Osmosis

The correct answer is: Active transport

Active transport is the process responsible for moving nutrients against their concentration gradient, which means that it allows substances to be transported from an area of lower concentration to an area of higher concentration. This movement is not spontaneous and requires energy, typically in the form of ATP. Cells utilize active transport to accumulate essential nutrients that are in lower concentrations outside the cell compared to the inside, allowing them to maintain necessary biochemical functions and homeostasis. This is crucial for cell survival and function, particularly in scenarios where cells might need to import vital ions or molecules against gradients created by other forms of transport or metabolic processes. Passive transport, including processes like facilitated diffusion and osmosis, does not require energy as it enables molecules to move down their concentration gradient, from areas of higher to lower concentration. Consequently, these types of transport cannot import substances against a gradient, which distinguishes them from active transport.