Transport across cell membranes

What is the symbol for water potential?

Ψ

What is the unit for water potential?

kPa

What is water potential?

The pressure created by water molecules

What is the water potential of pure water?

0 kPa

What is the relationship between solute concentration and water potential of the solution?

As solute concentration increases, water potential of the solution decreases

What is osmosis?

The passive net movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane

What does passive mean?

It doesn’t require ATP from respiration

In which direction will water move if the cell has a higher water potential than the surrounding solution?

Out of the cell

What happens to animal cells when water moves into them by osmosis?

They undergo lysis and burst

What happens to plant cells when water moves into them by osmosis?

They become turgid as their cell walls prevent them from bursting

What happens to animal cells when water moves out of them by osmosis?

They shrivel and die

What happens to plant cells when water moves out of them by osmosis?

They undergo plasmolysis and die

What are the two types of transport?

Active transport and passive transport

What is passive transport?

Transport that doesn’t require ATP from respiration

What is active transport?

Transport that requires ATP from respiration

Is diffusion passive or active?

Passive

What are the two types of diffusion?

Simple diffusion and facilitated diffusion

Which features of particles allow them to pass across the membrane via simple diffusion?

• Hydrophobic

• Non-polar

• Uncharged

• Small

Which features of particles don’t allow them to pass across the membrane via simple diffusion?

• Hydrophilic

• Polar

• Charged

• Large

What is a transport protein?

A protein that spans the membrane of a cell, allowing particles across the membrane via facilitated diffusion

What are four adaptations that molecules can have in order to maximise rate of diffusion?

• Maintaining a steep concentration gradient

• Giving the shortest possible diffusion pathway

• Having a high surface area to volume ratio

• Having a high concentration of transport proteins

How does concentration gradient affect the rate of diffusion?

As concentration gradient increases, rate of diffusion increases

How does surface area to volume ratio affect the rate of diffusion?

As surface area to volume ratio increases, rate of diffusion increases

How does concentration of transport proteins affect the rate of diffusion?

As concentration of transport proteins increases, rate of diffusion increases

What is rapid diffusion?

When the rate of diffusion in cells is as high as possible

What do all cell membranes in eukaryotic cells have?

Proteins and a phospholipid bilayer

Which type of molecules can travel across the phospholipid bilayer?

Non-polar molecules

What is the function of phospholipids in a cell membrane?

To control the movement of substances across the membrane

What is the function of cholesterol in a cell membrane?

To regulate membrane fluidity by restricting the movement of phospholipids and proteins in the bilayer

What does cholesterol bind to in a cell membrane?

The fatty acid tails of phospholipids

What is a glycolipid?

A phospholipid attached to a carbohydrate

What is the function of glycolipids in a cell membrane?

To act as recognition sites for other cells, allowing cells to attach to each other to form tissues

Where can extrinsic/ surface proteins be found in a cell membrane?

On the surface of the bilayer

What is the function of surface proteins in a cell membrane?

To provide mechanical support

What are glycoproteins?

Proteins with a carbohydrate attached

What is the function of glycoproteins in a cell membrane?

To act as recognition sites for foreign cells or specific chemicals

What is the function of transport proteins in a cell membrane?

To help transport substances across the membrane

What is the name of the model used to describe a cell membrane?

The fluid-mosaic model

What does the ‘fluid’ part of the fluid-mosaic model mean?

The phospholipids are constantly moving

What does the ‘mosaic’ part of the fluid-mosaic model mean?

The proteins are randomly scattered across the bilayer