B2.1 & D2.3 - Understanding Membranes and Transport

What are the main components of a cell membrane?

• Cell wall

• Ribosomes

• Phospholipid bilayer, proteins, cholesterol, carbohydrates

• Nucleic acids

Answer explanation

The cell membrane is primarily composed of a phospholipid bilayer, which provides structure, along with proteins that facilitate transport and communication, cholesterol that maintains fluidity, and carbohydrates that play a role in cell recognition.

Describe the fluid mosaic model of cell membranes.

• The fluid mosaic model states that cell membranes are composed solely of proteins without lipids.

• The fluid mosaic model describes cell membranes as rigid structures with no movement.

• The fluid mosaic model describes cell membranes as a flexible structure composed of a phospholipid bilayer with embedded proteins, allowing for dynamic movement and various functions.

• The fluid mosaic model suggests that cell membranes are static and do not change over time.

Answer explanation

The correct choice explains that the fluid mosaic model depicts cell membranes as flexible structures made of a phospholipid bilayer with embedded proteins, allowing for movement and diverse functions, contrasting with the other options.

What is the difference between passive and active transport?

• Active transport is energy-free and moves with the gradient.

• Passive transport is energy-free and moves with the gradient; active transport requires energy and moves against the gradient.

• Passive transport requires energy and moves against the gradient.

• Both passive and active transport require energy to function.

Answer explanation

Passive transport does not require energy and moves substances along their concentration gradient, while active transport requires energy to move substances against their gradient. Thus, the correct choice accurately describes both processes.

Name two types of passive transport mechanisms.

• Diffusion, Osmosis

• Facilitated diffusion, Bulk transport

• Endocytosis, Exocytosis

• Active transport, Filtration

Answer explanation

Diffusion and osmosis are both types of passive transport mechanisms. Diffusion involves the movement of molecules from an area of higher concentration to lower concentration, while osmosis specifically refers to the movement of water across a semipermeable membrane.

How does osmosis differ from diffusion?

• Diffusion only occurs in gases, while osmosis occurs in liquids.

• Osmosis is the movement of molecules other than water.

• Osmosis specifically refers to the movement of water across a membrane, while diffusion refers to the movement of any molecules from high to low concentration.

• Osmosis and diffusion are the same process with no differences.

Answer explanation

Osmosis is the specific movement of water across a semipermeable membrane, while diffusion involves the movement of any molecules from an area of high concentration to an area of low concentration.

What role do aquaporins play in osmosis?

• Aquaporins facilitate the rapid transport of water during osmosis.

• Aquaporins block the movement of water during osmosis.

• Aquaporins are responsible for the transport of nutrients in cells.

• Aquaporins regulate the temperature of water during osmosis.

Answer explanation

Aquaporins are specialized proteins that facilitate the rapid transport of water across cell membranes, making them essential for osmosis, where water moves to balance solute concentrations.

Explain how water potential is calculated.

• Water potential is calculated by adding solute concentration and temperature.

• Water potential is determined by measuring temperature and pressure only.

• Water potential is calculated using the formula Ψ = Ψs + Ψp.

• Water potential is calculated using the formula Ψ = Ψt - Ψp.

Answer explanation

Water potential (Ψ) is calculated using the formula Ψ = Ψs + Ψp, where Ψs is the solute potential and Ψp is the pressure potential. This formula accounts for both solute concentration and pressure effects on water movement.

What are the two main components of water potential?

• osmotic potential and atmospheric potential

• solute potential and pressure potential

• density potential and gravitational potential

• temperature potential and kinetic potential

Answer explanation

The two main components of water potential are solute potential, which measures the effect of solutes on water movement, and pressure potential, which measures the physical pressure on water in a system.

How does solute concentration affect water potential?

• As solute concentration increases, water potential decreases.

• Water potential is only affected by temperature, not solute concentration.

• Solute concentration has no effect on water potential.

• As solute concentration increases, water potential increases.

Answer explanation

As solute concentration increases, the number of solute particles in a solution increases, which lowers the water potential. This is because water moves from areas of higher water potential to lower water potential.

What happens to a plant cell in a hypertonic solution?

• The plant cell remains unchanged in size.

• The plant cell absorbs water and swells.

• The plant cell divides and grows larger.

• The plant cell loses water and undergoes plasmolysis.

Answer explanation

In a hypertonic solution, the concentration of solutes outside the plant cell is higher than inside. This causes water to leave the cell, leading to plasmolysis, where the cell membrane pulls away from the cell wall.