1.2 Transport Across Cell Membranes

Flashcard deck covering Key Area 2: Transport Across Cell Membranes, including cell membrane components, selective permeability, diffusion, osmosis, active transport, and experimental problem-solving.

What two components make up the structure of a cell membrane?

Phospholipids and proteins.

What does it mean for the cell membrane to be selectively permeable?

It means that only certain molecules can pass through it, typically depending on their size.

Which structural carbohydrate makes up the plant cell wall?

Cellulose

State the differences in permeability between the cell membrane and the cell wall.

The cell membrane is selectively permeable, allowing certain molecules to pass through, whereas the cell wall is freely permeable, allowing all molecules to pass through.

Name two examples of passive transport in cells.

Diffusion and osmosis.

Diffusion and osmosis are passive processes. Explain what is meant by passive.

Transport across a cell membrane that does not require energy.

Describe what is meant by a concentration gradient.

The difference in concentration of molecules between two areas (inside vs outside of the cell).

Describe diffusion.

The movement of ions or molecules down a concentration gradient from a higher concentration to a lower concentration until equally spread.

Which useful molecules will pass into animal cells by diffusion, and which waste molecules are removed?

Molecules gained include oxygen and glucose; waste products removed include carbon dioxide and urea.

Describe osmosis.

The movement of water molecules from a higher water concentration to a lower water concentration through a selectively permeable membrane. Water molecules move down the concentration gradient as osmosis does not require energy (it is a passive process).

Explain what happens to an animal cell placed in a solution with a higher water concentration?

Water molecules move into cell by osmosis from a higher to a lower water concentration, causing the cell to burst because it lacks a cell wall.

Explain what happens to an animal cell placed in a solution with a lower water concentration (high salt/sugar)?

Water molecules move out of the cell by osmosis from a higher to a lower water concentration, causing the cell to shrink.

What happens to a plant cell placed in a solution with a higher water concentration?

Water molecules move into the cell by osmosis from a higher water concentration to a lower water concentration causing the cell to become turgid.

What happens to a plant cell placed in a solution with a lower water concentration (high salt/sugar)?

Water molecules move out of the cell by osmosis from a higher water concentration to a lower water concentration, causing the cell to become plasmolysed.

What happens to a plant cell placed in a solution with a water concentration equal to its surroundings?

Water moves in and out of the cell by osmosis at the same rate. The plant cell is neither turgid or plasmolysed.

Describe active transport.

The movement of molecules and ions across the cell membrane from a lower concentration to a higher concentration against the concentration gradient. This process requires energy (ATP).

Why does active transport require energy in the form of ATP?

For membrane proteins to move molecules and ions against the concentration gradient.

In which cellular organelle is ATP generated for active transport?

In the mitochondria, where aerobic respiration takes place.

What is the function of membrane proteins in active transport?

They act as pumps to transport molecules and ions against the concentration gradient.

How can the reliability of the results be increased in an experiment/investigation?

Repeat the experiment/investigation for each independent variable tested AND calculating an average (if appropriate) OR increase the sample size/number of groups.

How is validity maintained during an experiment/investigation?

By keeping all other variables the same (constant) except for the independent variable.

State the formula for percentage change.

(Final value - starting value)/(starting value) x 100

Why is percentage change in mass calculated rather than simple change in mass in membrane transport experiments with plant tissues?

Because the initial mass of the tissues are different, so calculating percentage change allows for a valid comparison.

Identify a variable not shown in the diagram that would need to be kept constant for validity.

Temperature of sucrose solution; Volume of sucrose solution; Length of potato cylinder; Type of potato; Time experiment is left for; Size of test tube

State what is meant by independent and dependent variable.

The independent variable is the variable that is being changed. The dependent variable is the variable that is being measured.

Describe what is meant by a control.

A condition in an experiment where the independent variable is removed or replaced, allowing you to prove that the independent variable is what caused the change in the results.

Example: if sucrose concentration is causing a change in the rate of osmosis (measured indirectly by change in mass of tissue), the control is:

Keep everything the same except use distilled water.