Transport Mechanisms in Cells

What is diffusion and how does it occur in cells?

• Diffusion is the movement of molecules from high to low concentration, occurring in cells across the cell membrane.

• Diffusion is the process of energy production in cells.

• Diffusion occurs only in solid materials, not in cells.

• Diffusion is the movement of molecules from low to high concentration.

Answer explanation

Diffusion is the movement of molecules from high to low concentration, which occurs across the cell membrane. This process is essential for cells to maintain homeostasis and exchange substances with their environment.

Explain the process of osmosis and its importance in cellular function.

• Osmosis is the process of energy production in cells.

• Osmosis is the movement of water across a membrane, vital for maintaining cellular function.

• Osmosis is the movement of nutrients into the cell.

• Osmosis refers to the diffusion of gases in the atmosphere.

Answer explanation

Osmosis is the movement of water across a selectively permeable membrane. This process is crucial for maintaining cellular homeostasis, regulating cell volume, and facilitating nutrient transport, thus supporting overall cellular function.

What factors affect the rate of diffusion across a plasma membrane?

• Presence of cholesterol in the membrane

• Oxygen levels in the environment

• Concentration gradient, temperature, size and polarity of molecules, membrane permeability.

• pH level of the solution

Answer explanation

The rate of diffusion across a plasma membrane is influenced by the concentration gradient, temperature, size and polarity of molecules, and membrane permeability, making this the most comprehensive choice.

What is active transport and how does it differ from passive transport?

• Passive transport requires energy to move substances against their concentration gradient.

• Active transport moves substances along their gradient without energy.

• Active transport requires energy to move substances against their concentration gradient, while passive transport does not require energy and moves substances along their gradient.

• Active transport occurs only in plant cells, while passive transport occurs in animal cells.

Answer explanation

Active transport requires energy to move substances against their concentration gradient, while passive transport does not require energy and moves substances along their gradient. This distinction is crucial in cellular processes.

Give an example of a substance that is transported via active transport.

• Chloride ions (Cl-)

• Sodium ions (Na+)

• Oxygen molecules (O2)

• Glucose

Answer explanation

Sodium ions (Na+) are actively transported across cell membranes via the sodium-potassium pump, which uses ATP to move Na+ against its concentration gradient, making it a prime example of active transport.

What is facilitated diffusion and how does it differ from simple diffusion?

• Facilitated diffusion occurs only in plant cells.

• Facilitated diffusion uses protein channels or carriers for transport, while simple diffusion does not.

• Facilitated diffusion is faster than simple diffusion in all cases.

• Simple diffusion requires energy input for transport.

Answer explanation

Facilitated diffusion involves the use of protein channels or carriers to help transport substances across cell membranes, unlike simple diffusion, which occurs directly through the membrane without assistance.

How do carrier proteins assist in facilitated diffusion?

• Carrier proteins create energy for the cell during diffusion.

• Carrier proteins facilitate the transport of specific molecules across the cell membrane by changing shape.

• Carrier proteins block the movement of molecules across the membrane.

• Carrier proteins are involved in active transport only.

Answer explanation

Carrier proteins assist in facilitated diffusion by changing shape to transport specific molecules across the cell membrane, allowing them to bypass the lipid bilayer without using energy.

How does concentration gradient influence the movement of substances across the plasma membrane?

• Concentration gradients have no effect on the rate of diffusion.

• The concentration gradient influences the movement of substances by driving diffusion from high to low concentration areas across the plasma membrane.

• Higher concentrations always lead to active transport across the membrane.

• Substances move randomly without any influence from concentration gradients.

Answer explanation

The correct choice explains that concentration gradients drive diffusion, causing substances to move from areas of high concentration to low concentration across the plasma membrane, which is fundamental to cellular processes.