A level Biology 4.2 Movement into and out of cells – Exam style question – Paper 1

Question

Which features increase the efficiency of ion uptake by a root hair cell?

  1. many mitochondria in the cell
  2. high concentration of ions in the vacuole
  3. protein carriers in the cell surface membrane

A 1, 2 and 3          B 1 and 3 only           C 2 and 3 only           D 1 only

▶️Answer/Explanation

Ans:

B

Root hair cells are specialized cells found in the roots of plants. They are adapted for the uptake of water and mineral ions from the soil. The following features increase the efficiency of ion uptake by a root hair cell:

1. Many mitochondria in the cell: Mitochondria are the site of cellular respiration, which generates ATP (adenosine triphosphate) – the energy currency of the cell. ATP is required for the active transport of ions across the cell surface membrane. Therefore, the presence of many mitochondria in the cell increases the efficiency of ion uptake by providing the necessary energy for active transport.

2. High concentration of ions in the vacuole: The vacuole is a large organelle found in plant cells that contains cell sap. The cell sap is a solution of various substances, including ions. The high concentration of ions in the vacuole creates a concentration gradient that drives the movement of ions into the cell. However, this does not directly increase the efficiency of ion uptake.

3. Protein carriers in the cell surface membrane: Protein carriers are specialized proteins that bind to specific ions and transport them across the cell surface membrane. The presence of protein carriers increases the efficiency of ion uptake by increasing the rate of transport across the membrane.

Therefore, the correct answer is B. 1 and 3 only.

Question

Which is correct for facilitated diffusion and active transport?

  1. both depend on the solubility of the transported molecule in the lipid bilayer
  2. both increase as the concentration of the transported molecule increases
  3. both require the use of ATP
  4. both require the use of membrane proteins
▶️Answer/Explanation

The correct answer is D. Both facilitated diffusion and active transport require the use of membrane proteins.

Facilitated diffusion and active transport are two mechanisms by which molecules can be transported across a cell membrane.

Facilitated diffusion is a passive process that does not require the input of energy. It involves the movement of molecules down their concentration gradient, from an area of high concentration to an area of low concentration, through a membrane protein. The protein acts as a channel or a carrier, allowing the molecule to pass through the membrane.

Active transport, on the other hand, is an energy-dependent process that involves the movement of molecules against their concentration gradient, from an area of low concentration to an area of high concentration. This process requires the input of energy, usually in the form of ATP, and the use of a membrane protein, such as a pump or a carrier, to move the molecule across the membrane.

Therefore, the correct answer is D. Both facilitated diffusion and active transport require the use of membrane proteins.

Question

What happens to an animal cell when it is placed in a solution with a more negative water potential?

A. It loses solutes to the solution and swells.
B. It loses water by osmosis and shrinks.
C. It takes in solutes and swells.
D. It takes in water by osmosis and bursts.

▶️Answer/Explanation

Ans:

B

The correct answer is B. It loses water by osmosis and shrinks.

Water potential is the measure of the potential energy of water to move from one place to another. It is influenced by two factors: pressure potential and solute potential. Water moves from an area of higher water potential to an area of lower water potential.

When an animal cell is placed in a solution with a more negative water potential, it means that the solution has a lower concentration of water molecules compared to the inside of the cell. This creates a concentration gradient that causes water to move out of the cell and into the solution, resulting in the cell losing water by osmosis. As a result, the cell shrinks.

Option A is incorrect because the cell would not lose solutes to the solution, but rather, water would move out of the cell by osmosis.

Option C is incorrect because the cell would not take in solutes, but rather, water would move out of the cell by osmosis.

Option D is incorrect because the cell would not take in water, but rather, water would move out of the cell by osmosis.

Question

The stalk of a dandelion flower is a hollow tube. Pieces of the stalk are cut as shown and placed in sucrose solutions of different water potentials.

Which diagram shows the piece that is placed in the sucrose solution with the highest water potential?

▶️Answer/Explanation

Ans:

A

The following diagram shows the piece that is placed in the sucrose solution with the highest water potential. 
 

Question

Which of the following ways of moving substances across cell surface membranes allows
movement in both directions?
          1 active transport
          2 diffusion
          3 facilitated diffusion
          4 osmosis

A 2 only
B 1 and 4 only
C 2 and 3 only
D 1, 2, 3 and 4

▶️Answer/Explanation

Answer     D

The correct answer is D. 1, 2, 3 and 4.

Active transport moves substances across the cell membrane against the concentration gradient, from low to high concentration, and requires energy. Therefore, it is unidirectional.

Diffusion moves substances across the cell membrane from an area of high concentration to an area of low concentration, down the concentration gradient. It is a passive process that does not require energy, and it can occur in both directions.

Facilitated diffusion is a type of passive transport that involves the movement of substances across the cell membrane from an area of high concentration to an area of low concentration, down the concentration gradient. It requires the use of a carrier protein or a channel protein to facilitate the movement of the substance. Like diffusion, it can occur in both directions.

Osmosis is a type of passive transport that involves the movement of water across the cell membrane from an area of high water concentration to an area of low water concentration, down the concentration gradient. Like diffusion and facilitated diffusion, it can occur in both directions.

Therefore, the correct answer is D. 1, 2, 3 and 4.

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