3.2.3 Transport across cell membranes 2

What is the primary role of carrier proteins in active transport?

• To facilitate the passive diffusion of molecules

• To transport molecules against their concentration gradient

• To increase the surface area of the cell membrane

• To maintain the cell's shape

Answer explanation

Carrier proteins are essential in active transport as they move molecules against their concentration gradient, which requires energy. This is crucial for maintaining cellular functions and homeostasis.

Which of the following is essential for active transport to occur?

• Oxygen

• Glucose

• ATP

• Water

Answer explanation

ATP is essential for active transport as it provides the energy required to move substances against their concentration gradient. Without ATP, active transport cannot occur.

Co-transport in the mammalian ileum involves the absorption of which two substances?

• Sodium ions and potassium ions

• Glucose and amino acids

• Sodium ions and glucose

• Water and glucose

Answer explanation

Co-transport in the mammalian ileum primarily involves sodium ions and glucose. Sodium ions are absorbed alongside glucose, facilitating its uptake into the cells, making 'Sodium ions and glucose' the correct answer.

How can cells increase the rate of transport across their membranes?

• By decreasing the number of protein channels

• By increasing the surface area of the membrane

• By reducing the concentration gradient

• By decreasing the number of carrier molecules

Answer explanation

Cells can increase transport rates by increasing the surface area of the membrane, allowing more protein channels and carrier molecules to be available for transport. This enhances the overall transport capacity.

What is the effect of increasing the number of channel proteins in a cell membrane?

• It decreases the rate of passive transport

• It increases the rate of passive transport

• It has no effect on transport rates

• It decreases the rate of active transport

Answer explanation

Increasing the number of channel proteins enhances the cell membrane's ability to facilitate the movement of molecules across it, thereby increasing the rate of passive transport.

Which factor does NOT affect the rate of movement across cell membranes?

• Surface area

• Number of mitochondria

• Concentration gradient

• Number of carrier proteins

Answer explanation

The number of mitochondria does not directly influence the rate of movement across cell membranes. In contrast, surface area, concentration gradient, and number of carrier proteins all play significant roles in this process.

What is the role of ATP in active transport?

• It acts as a channel for molecules

• It provides energy for the transport process

• It acts as a structural component of the membrane

• It binds to molecules to facilitate their movement

Answer explanation

ATP provides the necessary energy for active transport, allowing molecules to move against their concentration gradient. This is crucial for maintaining cellular functions and homeostasis.

Which of the following adaptations would NOT increase the rate of transport across a cell membrane?

• Increasing the number of carrier proteins

• Increasing the thickness of the cell membrane

• Increasing the surface area of the cell

• Increasing the concentration gradient

Answer explanation

Increasing the thickness of the cell membrane would hinder transport, as it creates a greater distance for substances to diffuse. In contrast, the other options enhance transport efficiency.

What is the primary function of co-transport in the ileum?

• To absorb water

• To absorb sodium ions and glucose

• To secrete digestive enzymes

• To transport oxygen

Answer explanation

The primary function of co-transport in the ileum is to absorb sodium ions and glucose. This process utilizes the sodium gradient to facilitate the uptake of glucose against its concentration gradient.

How does an increase in surface area affect the rate of diffusion?

• It decreases the rate of diffusion

• It has no effect on the rate of diffusion

• It increases the rate of diffusion

• It reverses the direction of diffusion

Answer explanation

An increase in surface area allows more particles to collide and pass through the membrane simultaneously, which increases the rate of diffusion. Therefore, the correct answer is that it increases the rate of diffusion.