Cell Membranes

Question 1

In which type of cells eukaryotic or prokaryotic are the organelles surrounded by membranes?

Answer 1

Eukaryotic

Question 2

What is the purpose of a cell surface membrane?

Answer 2

The cell surface membrane acts as a barrier between the cell and its environment , it controls what enters and leaves the cell due to the partially permeable nature of its membrane.

Question 3

By which 3 processes can substances move across the cell surface membrane?

Answer 3

Osmosis
Diffusion
Active Transport

Question 4

Why are plasma membranes that surround organelles important?

Answer 4

The plasma membranes that surround the organelles in eukaryotic cells are important as they help compartmentalise the cell and thus keep its organelles separate from the cytoplasm.

Question 5

What types of molecules is the plasma membrane composed of?

Answer 5

phospholipids
proteins
carbohydrates
cholesterol

Question 6

What phrase would be used to describe formation in which the molecules lie to form a plasma membrane?

Answer 6

A fluid mosaic model

Question 7

What other word could be used as an alternative to cell membrane?

Answer 7

Plasma membrane

Question 8

Why is the phospholipid bilayer said to be fluid?

Answer 8

The bilayer is said to be fluid as the phospholipids are constantly moving

Question 9

Name the 3 types of protein that lie within or on the surface of a plasma membrane

Answer 9

Receptor proteins
Channel proteins
Carrier proteins

Question 10

What do receptor proteins in the cell surface membrane do ?

Answer 10

Allow cell to detect chemicals released from other cells and when triggered by this they can signal the cell to respond in some way

Question 11

What type of molecules do carrier proteins help cross the cell surface membrane?

Answer 11

Large molecules

Question 12

What type of molecules do channel proteins help cross the cell surface membrane?

Answer 12

Charged (ions)

Question 13

If a protein has a carbohydrate chain attached to it what is it referred to as?

Answer 13

glycoprotein

Question 14

If a lipid has a carbohydrate chain attached to it what is it referred to as?

Answer 14

Glycolipid

Question 15

Which part of a phospholipid is hydrophilic?

Answer 15

The phosphate head

Question 16

Which part of a phospholipid is hydrophobic?

Answer 16

hydrocarbon tail

Question 17

What do phospholipid molecules act as a barrier to?

Answer 17

Dissolved (water soluble)

Question 18

How do phospholipids arrange themselves as they form a plasma membrane ?

Answer 18

the heads face out towards the water on either side of the membrane

Question 19

In consequence of the middle of a phospholipid bilayer being hydrophobic which type of substances cannot pass through?

Answer 19

the membrane doesn’t allow water-soluble substances (like ions
and polar molecules) to diffuse through it.

Question 20

What type of substances can pass through the plasma membrane?

Answer 20

Small, non-polar substances (e.g. carbon dioxide) and water can diffuse through the membrane

Question 21

What attribute does cholesterol give to a cell membrane?

Answer 21

Stability

Question 22

Why can water diffuse through cell membrane

Answer 22

Water is actually a polar molecule, but it can diffuse (by osmosis) through the cell membrane because it’s so small

Question 23

Cholesterol is a type of lipid found in all cell membranes with the exception of one, which cell membrane does not contain cholesterol?

Answer 23

Bacterial cell membranes

Question 24

Where do the molecules of cholesterol fit in relation to the phospholipids?

Answer 24

Between the phospholipids

Question 25

What do cholesterol molecules do to make the phospholipid bilayer more stable?

Answer 25

Cholesterol binds to the hydrophobic tails of the phospholipids, causing them to pack more closely together. This restricts the movement of the phospholipids, making the membrane less fluid and more rigid.

Question 26

In cells that don’t have a cell wall why is cholesterol particularly important?

Answer 26

Helps maintain the shape of animal cells that don’t have cell wall or aren’t supported by other cells eg red blood cells

Question 27

Cholesterol has hydrophobic regions , hence does it add or detract from the bilayers nature as a barrier to polar substances/water?

Answer 27

Add

Question 28

How would being in a very cold environment (0 degrees) impact the permeability of a plasma membrane?

Answer 28

The phospholipids don’t have much energy, so they can’t move very much. They’re packed closely together and the membrane is rigid. But channel proteins and carrier proteins in the membrane denature (lose structure and function), increasing the permeability of the membrane. Ice crystals may formand pierce the membrane, making it highly permeable when it thaws.

Question 29

How do membranes change as temperature increases?

Answer 29

the phospholipids move more because they have more energy — this increases the permeability of the membrane.

Question 30

At temperatures which exceed 45 degrees how does the phospholipid bilayer behave?

Answer 30

The phospholipid bilayer starts to melt (break down) and the membrane becomes more permeable. Water inside the cell expands, putting pressure on the membrane.

Question 31

How does putting a plasma membrane in a solvent affect its permeability ?

Answer 31

Channel proteins and carrier proteins in the membrane denature so they can’t control what enters or leaves the cell — this increases the permeability of the membrane