Cell Membranes & Transport (AQA A Level Biology): Flashcards

False.

Saturated fatty acid chains decrease membrane fluidity because they pack tightly together, increasing intermolecular forces.

At higher temperatures, membrane fluidity increases. At lower temperatures, membrane fluidity decreases.

A partially permeable membrane is a barrier that allows some substances to pass through while restricting the movement of others.

Membranes contain glycoproteins and glycolipids that act as receptors for signalling molecules and antigens, allowing for cell signalling, recognition, and communication.

Channel proteins form pores for specific ions or molecules to pass through, whereas carrier proteins bind and transport specific substances across the membrane.

Cholesterol prevents membranes from freezing at low temperatures and from becoming too fluid at high temperatures.

Diffusion is the net movement of molecules or ions from a region of higher concentration to a region of lower concentration, down a concentration gradient.

Diffusion occurs when molecules move down a concentration gradient, from higher concentration to lower concentration.

The random movement of molecules in diffusion is caused by their natural kinetic energy.

Given sufficient time, diffusion results in an equilibrium situation where molecules are evenly spread within a given volume of space.

A greater difference in concentration (a steeper concentration gradient) increases the net rate of diffusion across the membrane.

Higher temperatures give molecules more kinetic energy, resulting in a higher rate of diffusion.

A larger surface area allows more molecules to diffuse at once, increasing the rate of diffusion.

Non-polar molecules diffuse faster than polar ones across the cell membrane.

Facilitated diffusion is the diffusion of substances across the cell membrane with the help of specific proteins (channel or carrier proteins), down a concentration gradient, without the use of energy.

Large polar molecules such as glucose and amino acids, and ions such as sodium and chloride require facilitated diffusion to cross the cell membrane.

Channel proteins are water-filled pores that allow charged substances to pass, whereas carrier proteins switch shape to transport molecules across the membrane.

Carrier proteins are highly specific to one type of molecule or ion and allow movement down a concentration gradient.

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.

The water potential of pure water at atmospheric pressure is 0kPa.

False.

A dilute solution has a higher water potential than a concentrated solution.

Osmosis is the movement of water from a region of higher water potential to a region of lower.

Plasmolysis is when the protoplast of a plant cell shrinks and pulls away from the cell wall due to water loss by osmosis in a hypertonic solution.

In a hypotonic solution, water enters the plant cell, the vacuole expands, and the cell becomes turgid because the cell wall prevents bursting.

Without enough water, plant cells lose turgor and the plant wilts.

True.

The cell wall provides structural support and prevents the cell from bursting as water enters in a hypotonic solution.

Turgidity is the state of being swollen and firm due to water uptake; it helps support the plant and keep it upright.

In an isotonic solution, water moves in and out of the plant cell equally, so there is no net change and the cell is neither turgid nor plasmolysed.

In a hypertonic solution, water leaves the animal cell, causing it to shrink and shrivel.

If an animal cell is placed in a hypotonic solution, water enters the cell and it may swell (cytolysis).

Maintaining a stable water potential in animal tissue fluid is essential to prevent cell damage, such as shrinking or bursting due to osmosis.

True.

Plant cells undergo plasmolysis as the protoplast pulls away from the cell wall, while animal cells shrink and shrivel because they lack a cell wall.

A calibration curve is a graph used to estimate an unknown value (such as water potential of plant tissue) by comparing it to values from solutions of known concentration.

A positive percentage change in mass means the potato gained water by osmosis, so the solution had a higher water potential than the potato.

If there is no change in mass of the potato cylinder, the solution is isotonic.

A line of best fit is a straight or smooth curved line drawn on a graph to best represent the trend of the data points, with a balance of points above and below the line.

By plotting percentage change in mass against sucrose concentration, the point where the line of best fit crosses the x-axis indicates the sucrose concentration inside the potato cylinders.

A positive percentage change in mass means the potato gained water, while a negative percentage change means it lost water.

Continuous data are numerical data that can take any value within a range, such as height or weight.

Line graphs or scatter graphs are most suitable for continuous data.

For qualitative and discrete data, use bar charts or pie charts, while for continuous data use line or scatter graphs.

False.

The independent variable is always plotted on the x-axis, not the y-axis.

Line graphs or scatter graphs are most suitable for continuous data.

After osmosis, potato cylinders in the most concentrated sucrose solution will have the largest mass decrease because the water potential gradient is greatest.

You must always label axes with units when plotting experimental data.

The potato cells become turgid, making the potato feel firm.

Active transport is the movement of molecules or ions through a cell membrane from a region of lower to higher concentration, using energy from respiration.

Active transport requires carrier proteins, which are specific for particular molecules or ions.

Energy for active transport is provided by the hydrolysis of ATP into ADP and inorganic phosphate.

False.

Active transport requires carrier proteins, not channel proteins.

Co-transport is the coupled movement of two substances across a membrane via a carrier protein.

In the mammalian ileum, glucose is absorbed into epithelial cells together with sodium ions by co-transport.

Active transport moves sodium ions out of the epithelial cell, creating a sodium gradient that is needed for the co-transport of glucose.

During active transport, the carrier protein changes shape when energy is supplied by ATP.

Active transport is important in the reabsorption of useful molecules and ions into the blood after filtration in the kidney tubules.

False.

In co-transport, one substance moves down its concentration gradient, which provides the energy for the other to move against its gradient.

A root hair cell is a specialised plant cell with a long projection that increases surface area for absorption of water and mineral ions from the soil.

Root hair cells absorb water by osmosis and mineral ions by active transport.

The permanent vacuole in a root hair cell stores water and mineral ions as they enter the cell, helping to maintain a steep water potential gradient.

True.

A thin cell wall shortens the diffusion distance for water, increasing uptake rate.

In cell transport, surface area refers to the total area of the cell membrane available for substances to cross, with increased surface area allowing more rapid movement of molecules.

A rich capillary network in the villi maintains a steep concentration gradient.

Microvilli are tiny finger-like projections on the surface of epithelial cells that increase surface area for absorption.

The presence of many co-transport proteins in the membrane enables active uptake of glucose and amino acids.

Microvilli on epithelial cells provide a large surface area for increased diffusion.

Aquaporins are channel proteins in kidney collecting duct cells that allow the facilitated diffusion of water across the membrane, aiding reabsorption.

Cells in the collecting duct of the kidney have membranes with a high number of aquaporins to allow rapid water uptake.

The number and opening/closing of ion channel proteins influence how quickly ions move by facilitated diffusion, directly affecting the speed of electrical transmission.

A larger surface area and a steeper concentration gradient can both increase the rate of substance transport across cell membranes.

Membrane permeability is a measure of how easily substances can pass through the cell membrane.

As temperature increases, the permeability of the beetroot cell membrane also increases, allowing more pigment to leak out.

Beetroot cells contain a dark purple-red pigment that leaks out when the membrane is more permeable.

A colourimeter is used to measure how much light is absorbed by the beetroot pigment in solution.

A cuvette is a small cuboid container used to hold liquid samples for measurement in a colourimeter.

False.

Different sizes of beetroot pieces can affect the amount of pigment released, so all pieces should be cut to the same dimensions.

As temperature increases, phospholipids in the cell membrane move more, making the membrane more permeable.

High temperatures denature membrane proteins by breaking intermolecular forces, which affects their shape and function.

Solvents like alcohol can dissolve the lipids in the cell membrane, increasing its permeability.

Rinsing removes any pigment released during cutting, so only pigment released due to membrane permeability is measured.