2.5 Biological membranes

Question 1

Are phospholipid heads hydrophobic or hydrophilic?

Answer 1

Hydrophilic

Question 2

Are phospholipid tails hydrophobic or hydrophilic?

Answer 2

Hydrophobic

Question 3

Are phospholipid heads water soluble?

Answer 3

Yes

Question 4

Are phospholipid tails water soluble?

Answer 4

No

Question 5

What is an affinity?

Answer 5

An attraction

Question 6

What part of the phospholipid forms an affinity with water?

Answer 6

Heads

Question 7

What do phospholipids form when submerged in water?

Answer 7

Micelles

Question 8

What are plasma membranes made up off?

Answer 8

Phospholipids (which form a bilayer)

Question 9

What can diffuse straight through the bilayer?

Answer 9

Fat soluble organic molecules (polar molecules require proteins)

Question 10

What does the plasma membrane do in terms of acting as a barrier?

Answer 10

Allows cellular compartments to have different conditions.

Question 11

Are plasma membranes flexible?

Answer 11

Yes and they are able to break and fuse easily

Question 12

What is the fluid-mosaic model?

Answer 12

Fluid - the proteins can move freely through the bilayer.
Mosaic - The arrangement of the proteins in the bilayer.
Model - Representation of the structure of the bilayer

Question 13

What are the different types of carrier and channel proteins?

Answer 13

Passive and active
Gated-channel and channel

Question 14

What is diffusion?

Answer 14

Diffusion is the movement of particles (if they are lipid soluble) or gases from an area of higher concentration to an area of lower concentration.
Down the concentration gradient.
Diffusion is a passive process. (means no ATP is required)
It is directly across a partially permeable membrane.

Question 15

What is facilitated diffusion?

Answer 15

Facilitated diffusion is the movement of charged molecules from an area of higher concentration to an area of lower concentration.
Down the concentration gradient.
Facilitated diffusion is a passive process. (means no ATP is required)
A protein channel is needed to move across a partially permeable membrane.

Question 16

What is osmosis?

Answer 16

Osmosis is the movement of water from a higher water potential to a lower water potential.
The water potential is affected by the solute.
It goes down a water potential gradient.
Osmosis is a passive process. (means no ATP is required)
It is directly across a partially permeable membrane.

Question 17

What is active transport?

Answer 17

Active transport is the movement of lipid insoluble molecules or charged particles from a lower concentration gradient to a higher concentration gradient.
It goes up or against the concentration gradient.
It is an active process which means ATP is required.
A protein carrier is required to move across a partially permeable membrane.

Question 18

What does a higher temperature do to membrane permeability?

Answer 18

Increases it

Question 19

How does temperature affect membrane permeability?

Answer 19

As the temperature increases proteins denature (the bonds are disrupted which breaks down the tertiary structure). This leaves gaps in the membrane.
It also increases the kinetic energy, meaning the membrane will move around leaving the gaps bigger.

Question 20

What as an example of membrane permeability increasing?

Answer 20

The tonoplast (membrane of the vacuole) then has gaps. The pigment of the beetroot is kept in the vacuole. As the membrane has gaps in it, the pigment can leak through.

Question 21

How does ethanol affect membrane permeability?

Answer 21

Dissolves lipids which causes gaps in the membrane, increasing permeability.
Changing the solute will change the permeability.

Question 22

What is a glycoprotein?

Answer 22

A carbohydrate chain attatched to a protein molecule (in the bilayer)

Question 23

What is a glycolipid?

Answer 23

A carbohydrate chain attached to a lipid (in the bilayer)

Question 24

What do glycoproteins and glycolipids do?

Answer 24

Stabilise membranes by forming hydrogen bonds with surrounding water molecules.
Receptor sites.
Cell signalling.
Antigens.

Question 25

What is the glycocalyx.

Answer 25

All of the carbohydrate molecules on the outside of the membrane. They are very hydrophilic and attract water with dissolved solutes helping the cell interact with water and obtain dissolved substances.

Question 26

What does the cholesterol do in the bilayer?

Answer 26

Gives mechanical stability and flexibility.

Question 27

What do both channel and carrier proteins do?

Answer 27

Span the whole bilayer.

Question 28

What happens to proteins not spanning the bilayer?

Answer 28

They act as enzymes.

Question 29

What is an erythrocyte?

Answer 29

A red blood cell (animal cells)

Question 30

What happens to a erythrocyte in pure water?

Answer 30

It has OkPa.
Water will move via osmosis.
The water moves into the cell.
The cell enlarges and eventually bursts which is called lysis.

Question 31

What happens to a erythrocyte in a isotonic solution?

Answer 31

No net movement as water moves out of the cell at the same rate it moves in.
The cell doesn’t change shape.

Question 32

What happens to a erythrocyte in salty water (or any solute)?

Answer 32

Water will move via osmosis out of the cell.
The cell shrivels - it crenates (only called that in erythrocytes)

Question 33

What happens to a palisade cell in pure water?

Answer 33

The cell exapnds.
The cell wall gives mechanical strength and shape.
Water moves into the cell and the cell becomes turgid.
The cell doesn’t burst as has cell wall unless damaged which is called turgor pressure.

Question 34

What happens to a palisade cell in a isotonic solution?

Answer 34

No net movement as water moves out of the cell at the same rate it moves in.
The cell doesn’t change shape.

Question 35

What happens to the palisade cell in salty water (or any solute)?

Answer 35

The cell walls stay the same size but everything else shrinks, the cell membrane pulls away and is called a protoplast.
The process is called plasmolysis.

Question 36

Cells take in substances in endocytosis. What is endocytosis?

Answer 36

Some molecules are way too large to be taken into a cell by carrier proteins.
Instead a cell can surround a substance with a section of it’s plasma membrane.
The membrane then pinches off to form a vesicle inside the cell containing the ingested substance (this is endocytosis)
This process uses ATP.

Question 37

Cells can secrete substances by exocytosis. What is exocytosis?

Answer 37

Some substances produced by the cell need to be released from the cell.
Vesicles containing these substances pinch off from the sacs off the golgi apparatus and move towards the plasma membrane.
The vesicles fuse with the plasma membrane and released their contacts the cell.
The process uses ATP.