Unit 2.5-Biological membranes

Question 1

Peripheral protein definition:

Answer 1

Does not span the entire width of the membrane.

Question 2

Integral protein definition:

Answer 2

Spans the entire width of the cell mambrane.

Question 3

Glycolipid definition:

Answer 3

A carbohydrate chain attached to a lipid.

Question 4

Glycoprotein definition:

Answer 4

A carbohydrate chain attached to a protein molecule.

Question 5

Cholesterol use in cell membranes:

Answer 5

Gives mechanical stability and flexibility.

Question 6

Filaments of cytoskeleton use in cell membranes:

Answer 6

Helps a cell to maintain its shape.

Question 7

Water potential definition:

Answer 7

A measure of the tendency of water molecules to diffuse from one region to another.

Question 8

What is the highest water potential possible?

Answer 8

0KPa (pure water)

Question 9

What happens to the water potential of a substance when a solute is added?

Answer 9

It decreases

Question 10

Cytolysis definition:

Answer 10

When in animal cells, if a lot of water molecules enter, the cell will swell and burst as the plasma membrane breaks

Question 11

Turgid definition:

Answer 11

Plant cells become turgid when they are swollen. This happens when its contents is pushing up against the cell wall which will resist any further swelling.

Question 12

Crenation definition:

Answer 12

Happens when animal cells are placed in a solution of lower water potential and water leaves the cells through osmosis across the partially permeable membrane. The cell becomes shrivelled.

Question 13

Plasmolysis definition:

Answer 13

When the cytoplasm of plant cells shrink and the membrane pulls away from the cellulose wall

Question 14

why does metabolism stop in a plasmolysed cell?

Answer 14

The cells suffer a degree of dehydration and their metabolism cannot proceed as enzyme-catalysed reactions need to be in solution

Question 15

Diffusion definition:

Answer 15

Movement of molecules from an area of high concentration of that molecule to area of low concentration of that molecule. It may or may not be across a membrane, it does not involve ATP.

Question 16

Why does diffusion happen?

Answer 16

If there is a high concentration of a certain type of molecule in an area then the molecules will bump into each other as they randomly move and eventually they will spread further from each other. More will move into an area of lower concentration until they are evenly dispersed.

Question 17

What is an example of simple diffusion?

Answer 17

Oxygen and carbon dioxide passing through cell membranes for respiration.

Question 18

How can lipids move across cell membranes by diffusion?

Answer 18

They dissolve in the lipid bilayer so they become small enough

Question 19

What allows the movement of water in diffusion?

Answer 19

Aquaporins

Question 20

How is the concentration gradient inside a cell maintained?

Answer 20

Many molecules enter the cells then travel into the organelles and are used for metabolic reactions.

Question 21

What are the factors that affect the rate of diffusion?

Answer 21

• Temperature
• Diffusion distance
• Surface area
• Size of diffusing molecule
• Concentration gradient

Question 22

How does temperature affect the rate of diffusion?

Answer 22

As temperature increases, molecules will have more kinetic energy so their rate of diffusion will increase because they will bump into each other more frequently.

Question 23

How does diffusion distance affect the rate of diffusion?

Answer 23

The thicker the membrane across which molecules have to diffuse, the slower the rate of diffusion.

Question 24

How does surface area affect the rate of diffusion?

Answer 24

More diffusion can take place across a larger surface area.

Question 25

How does the size of the diffusing molecule affect the rate of diffusion?

Answer 25

Smaller ions or molecules diffuse more rapidly than larger ones.

Question 26

How does the concentration gradient affect the rate of diffusion?

Answer 26

The steeper the gradient, the faster the rate of diffusion.

Question 27

Facilitated diffusion definition:

Answer 27

Movement of molecules from an area of high concentration of that molecule to an area of low concentration of that molecule across a partially permeable membrane via protein channels or carriers. Does not involve ATP.

Question 28

Why can’t small molecules with polarity pass through the plasma membrane?

Answer 28

They cannot interact with the hydrophobic tails of the lipid bilayer.

Question 29

How do glucose molecules travel through a membrane using facilitated diffusion?

Answer 29

The glucose binds to a transmembrane carrier protein which then opens to allow the glucose to pass out of the other side of the membrane.

Question 30

What does cholesterol have the effect of in membranes?

Answer 30

Reducing the permeability of the membrane it is in to small, water soluble molecules.

Question 31

Why are there many types of carrier proteins?

Answer 31

Because different types are needed for different types of molecules.

Question 32

How can cells control the amount of substances passing through?

Answer 32

By having membranes with different proportions of transmembrane protein channels and transmembrane protein carriers.

Question 33

Osmosis definition?

Answer 33

Passage of water molecules down their water potential gradient across a partially permeable membrane.

Question 34

Why can water pass through membranes?

Answer 34

Because of the presence of aquaporins.

Question 35

How can the relative number of water molecules in a solution change?

Answer 35

By adding solute molecules.

Question 36

How do molecules that dissociate into charged ions effect water potential?

Answer 36

They exert more effect on the relative number of water molecules than larger but non-polar molecules.

Question 37

What is the effect of water on a prokaryotic cell?

Answer 37

If they lose enough water then their metabolism cannot proceed and they cannot reproduce.

Question 38

Active transport definition:

Answer 38

The movement of substances against their concentration gradient across a cell membrane. It requires energy provided by ATP.

Question 39

Why is active transport needed?

Answer 39

It allows cells to accumulate substances.

Question 40

Carrier proteins definition:

Answer 40

Specific regions that allow molecules or ions to bind reversibly with them. They also have regions that allow the specific hydrolysis of ATP. This provides energy for the protein to change its shape, allowing the passage of the molecule.

Question 41

Bulk transport definition:

Answer 41

Movement of large molecules through the membrane. This requires ATP so is therefore an active process.

Question 42

Endocytosis definition:

Answer 42

Bulk transport of large molecules INTO a cell. Molecules do not pass through the membrane, instead the plasma membrane surrounds it and encloses it into a vesicle.

Question 43

Exocytosis definition:

Answer 43

Bulk transport of large molecules OUT of a cell. Molecules do not pass through the membrane, instead a vesicle fuses with the membrane, releasing the molecule.

Question 44

What are the types of endocytosis?

Answer 44

• Phagocytosis: means ‘eating by cells’ and refers to this type of intake of solid matter
• Pino(endo)cytosis: when cells ingest liquids by endocytosis.

Question 45

What happens to cell membranes when temperatures drop?

Answer 45

• Saturated FAs become compressed
• Unsaturated FAs become compressed but the kinks in their tails push adjacent phospholipid molecules away which maintains the membrane’s fluidity.
• Therefore the proportion of saturated and unsaturated FAs determines the fluidity at cold temperatures.
• Cholesterol molecules buffer the effect of low temperatures on membranes because they are in between groups of phospholipid molecules and stop them packing to closely together.

Question 46

What happens to cell membranes when temperatures rise?

Answer 46

• The phospholipids acquire more kinetic energy, causing them to move around more in a random way, increasing the membrane’s fluidity.
• Also affects the way membrane embedded proteins are positioned and may function. If some proteins that act as enzymes in a membrane drift sideways, it could alter the rate of reactions they catalyse.
• An increase in the fluidity of the membrane may affect the in folding of the plasma membrane during phagocytosis.
• May change the ability of cells to signal to other cells by releasing chemicals. often by exocytosis.
• Cholesterol buffers to some extent, the effects of increasing heat as it reduces the increase of membrane fluidity.

Question 47

How do high temperatures affect proteins?

Answer 47

• They cause the atoms within their large molecules to vibrate which causes the hydrogen and ionic bonds that hold the structure together to break.
• Their tertiary structure changes and cannot change back again when they cool (denatured).