Question

Which statements are consistent with the known facts about membrane transport? (a) Active transport moves a substance from a region in which its concentration is lower to one in which its concentration is higher. (b) Transport does not involve any pores or channels in membranes. (c) Transport proteins may be involved in bringing substances into cells.

Short answer

Statements (a) and (c) are consistent with known facts.

Step-by-step solution

- Analyze statement (a)

Active transport typically moves substances against their concentration gradient, from a region of lower concentration to a region of higher concentration. This requires energy, usually in the form of ATP.

- Analyze statement (b)

This statement is incorrect. Membrane transport often involves pores or channels that allow substances to pass through the membrane, especially in the case of facilitated diffusion.

- Analyze statement (c)

This statement is correct. Transport proteins, such as carrier proteins or channel proteins, are often involved in the movement of substances into cells.

Key concepts

Active Transport

Active transport is a method used by cells to move substances against their concentration gradient. This means moving substances from an area of lower concentration to an area of higher concentration. Since this process goes against the natural flow, it requires energy. Usually, this energy comes from adenosine triphosphate or ATP. During active transport, specific transport proteins act like pumps, pushing the molecules through the cell membrane. Common examples of active transport include the sodium-potassium pump and the proton pump.

ATP

ATP, or adenosine triphosphate, is often referred to as the energy currency of the cell. It's essential for many cellular processes, including active transport. ATP stores energy in the bonds between its phosphate groups. When one of these bonds is broken, energy is released, which can then be used for various cellular activities. In the case of active transport, the energy from ATP is used to change the shape of transport proteins, allowing them to move substances across the cell membrane. Without ATP, cells wouldn't have the energy needed to maintain necessary functions.

Transport Proteins

Transport proteins are integral membrane proteins that help move substances across the cell membrane. There are different types of transport proteins, including carrier proteins and channel proteins. Carrier proteins bind to a specific substance, change their shape, and carry the substance across the membrane. Channel proteins, on the other hand, create pores or channels in the membrane that allow specific ions or molecules to pass through. Transport proteins are vital for both passive and active transport processes, making them essential for maintaining cellular function.

Facilitated Diffusion

Facilitated diffusion is a type of passive transport that helps move substances across the cell membrane without using energy. Unlike simple diffusion, facilitated diffusion involves transport proteins. These proteins provide a pathway for molecules to pass through the membrane more easily. Channel proteins and carrier proteins are often involved in this process. For example, glucose and ions like sodium and potassium usually enter cells through facilitated diffusion. Even though it doesn't require energy, facilitated diffusion is crucial for bringing vital substances into cells efficiently.

Membrane Channels

Membrane channels are types of transport proteins that create pathways through the cell membrane. These channels are usually selective, meaning they allow only specific ions or molecules to pass through. Some membrane channels are always open, while others can open or close in response to certain signals, like changes in voltage or the binding of a specific molecule. Membrane channels are essential for various cellular processes, including nerve signal transmission and muscle contraction. They help maintain the cell's internal environment by regulating the flow of ions and other molecules.