Active and passive transport

Movement across the membrane without the need for energy is called _______ transport.

• passive

• active

• facilitated

• bulk

Answer explanation

Movement across the membrane that does not require energy is known as passive transport. This process relies on concentration gradients, allowing substances to move freely without the use of cellular energy.

In an isotonic solution, how does water move across the cell membrane?

• Water moves into the cell.

• Water moves out of the cell.

• Water moves equally in both directions.

• Water does not move at all.

Answer explanation

In an isotonic solution, the concentration of solutes is equal inside and outside the cell. Therefore, water moves equally in both directions across the cell membrane, maintaining balance.

What happens to a cell in a hypertonic solution?

• The cell swells and bursts.

• The cell shrinks.

• The cell remains the same size.

• The cell divides.

Answer explanation

In a hypertonic solution, the concentration of solutes outside the cell is higher than inside. This causes water to move out of the cell, leading to cell shrinkage. Therefore, the correct answer is that the cell shrinks.

The plasma membrane will allow oxygen and carbon dioxide to pass through the membrane while other substances are blocked from passing through the membrane; its unique characteristic is described as _______________________________.

• selective permeability

• complete impermeability

• universal permeability

• random permeability

Answer explanation

The plasma membrane's ability to allow certain substances like oxygen and carbon dioxide to pass while blocking others is known as selective permeability. This characteristic is crucial for maintaining cellular homeostasis.

Naturally, molecules move from an area of _______________________________ to _______________________________ without the need of energy.

• high concentration to low concentration

• low concentration to high concentration

• medium concentration to high concentration

• low concentration to medium concentration

Answer explanation

Molecules naturally move from an area of high concentration to low concentration due to diffusion, which does not require energy. This process continues until equilibrium is reached.

Diffusion is defined as:

• The movement of particles from an area of high concentration to an area of low concentration.

• The process of particles settling at the bottom of a container.

• The movement of particles in a circular motion.

• The process of particles being absorbed by a solid.

Answer explanation

Diffusion is the movement of particles from an area of high concentration to an area of low concentration, which is the correct definition. The other options describe different processes.

What would happen to a cell if placed in each of the following solutions?

• a. The cell remains the same size in an isotonic solution.

• b. The cell swells and may burst in a hypotonic solution.

• c. The cell shrinks in a hypertonic solution.

Answer explanation

In an isotonic solution, the concentration of solutes is equal inside and outside the cell, so water moves in and out at the same rate, keeping the cell size constant. This is why option a is correct.

Facilitated diffusion is a process that involves the movement of molecules across a cell membrane. What structure assists with this process?

• Cell wall

• Transport proteins

• Cytoplasm

• Nucleus

Answer explanation

Transport proteins facilitate the movement of molecules across the cell membrane during facilitated diffusion, allowing substances to pass through more easily than they would through the lipid bilayer.

Which of the following best explains the properties of diffusion, osmosis, and semi-permeable membranes, including concentrations of solutions?

• Diffusion is the movement of particles from high to low concentration, osmosis is the movement of water across a semi-permeable membrane, and semi-permeable membranes allow certain substances to pass through.

• Diffusion is the movement of water from low to high concentration, osmosis is the movement of particles across a semi-permeable membrane, and semi-permeable membranes block all substances.

• Diffusion and osmosis both involve the movement of particles from low to high concentration, and semi-permeable membranes allow all substances to pass through.

• Diffusion is the movement of particles from low to high concentration, osmosis is the movement of water across a semi-permeable membrane, and semi-permeable membranes allow all substances to pass through.

Answer explanation

The correct choice accurately describes diffusion as the movement of particles from high to low concentration, osmosis as the movement of water across a semi-permeable membrane, and that these membranes allow certain substances to pass.

Materials are taken in by a cell in a process called ________________________. Choose the correct option.

• endocytosis

• exocytosis

• concentration gradient

• phagocytosis

Answer explanation

Materials are taken into a cell through endocytosis, a process that allows cells to engulf substances. Exocytosis is the opposite, where materials are expelled. Phagocytosis is a type of endocytosis specifically for large particles.