Cell Membranes (1)

Question 1

What do membranes control?

Answer 1

Membranes control what passes through them

Question 2

What are membranes at the surface of cells called?

Answer 2

Plasma membranes

Question 3

What is the function of plasma membranes ?

Answer 3

They are a barrier between the cells and it’s surroundings, controlling which substances enter and leave the cell

Question 4

Plasma membranes are partially permeable. What does this mean?

Answer 4

They let some molecules through but not others

Question 5

Substances can moves across the plasma membrane by which 3 methods?

Answer 5

Diffusion, osmosis or active transport

Question 6

What are two other features of the plasma membrane?

Answer 6

• Allow cell recognition e.g cell of the immune system
• Allow cell communication

Question 7

What is the other type of membrane apart from the one at the surface of cell?

Answer 7

Membranes within cell

Question 8

Why do membranes around the the organelles divide the cell into different compartments ?

Answer 8

• They act as a barrier between the organelle and the cytoplasm
• Makes different functions more efficient

Question 9

Give an example on why splitting the cell into different compartments would make the cell function more efficiently?

Answer 9

Substances needed for respiration
are kept together inside the mitochondria

Question 10

Why do membranes within cells form vesicles?

Answer 10

They can form vesicles to transport substances between different areas of the cell

Question 11

Membranes within cells control which substances enter and leave the organelle. True or false?

Answer 11

True

Question 12

What is the permeability of the membranes within cells like?

Answer 12

They are also partially permeable

Question 13

What are the function of membranes within organelles?

Answer 13

These act as barriers between the membrane contents and the rest of the organelle

Question 14

Membranes within cells can be the site of chemical reaction. Give an example.

Answer 14

Inner membranes of a mitochondrion contains the enzymes needed for respiration

Question 15

What type of structure are cell membranes said to have?

Answer 15

Fluid mosaic structure

Question 16

What are the three molecules that membranes are all composed of?

Answer 16

Lipids , carbohydrates and proteins

Question 17

What was the fluid mosaic model meant to describe?

Answer 17

The arrangement of molecules in the membrane

Question 18

What type of molecules formed a continuous bilayer?

Answer 18

Phospholipid molecules

Question 19

Why is the bilayer said to be fluid?

Answer 19

The phospholipid are constantly moving

Question 20

How are the cholesterol and protein said to be present in the fluid mosaic model?

Answer 20

• Cholesterol molecules are present within the bilayer
• Protein molecules are scattered through the bilayer, like a mosaic

Question 21

Some of these proteins have a polysaccharide ( carbohydrate) chain attached, what are they?

Answer 21

Glycoproteins

Question 22

Some lipids have a polysaccharide chain attached, what are these called?

Answer 22

Glycolipids

Question 23

Why do phospholipids form a barrier?

Answer 23

To act as a barrier to these dissolved substances

Question 24

Phospholipids are made of two different structures. What are they?

Answer 24

A tail and a head.

Question 25

Phospholipid molecules have a head and a tail. The head is hydrophilic. Explain what this means?

Answer 25

It attracts water

Question 26

Phospholipid molecules have a head and a tail. The tail is hydrophobic. Explain what this means?

Answer 26

It repels water

Question 27

Explain the arrangement of the heads in the bilayer?

Answer 27

The heads face outwards towards the water on either side of the membrane.

Question 28

Why does the centre of the bilayer not allow water soluble substances through it ?

Answer 28

The centre of the bilayer is hydrophobic so the membrane doesn’t allow water soluble substances through it.

Question 29

What ha the function of the centre of the bilayer ?

Answer 29

It acts as a barrier to these dissolves substance

Question 30

What type of soluble substances are able to dissolve in the bilayer and pass directly through the membrane? Give an example.

Answer 30

Fat soluble substances. Fat soluble vitamins can dissolve in the bilayer and pass directly through the membrane .

Question 31

What is the function of cholesterol in the membrane

Answer 31

Gives the membranes stability

Question 32

Cholesterol is a type of what ?

Answer 32

Lipid

Question 33

Cholesterol is not present in all types of cell membranes. True or false ?

Answer 33

False

Question 34

Where in the cell membrane are the cholesterol molecules fitted ?

Answer 34

Cholesterol molecules fit between the phospholipid

Question 35

What do the cholesterol molecules bind to and what does that cause?

Answer 35

- Bond to the hydrophobic tails of the phospholipids - Causing them to pack more closely together

Question 36

How does cholesterol affect the fluidity and rigidity of the membrane?

Answer 36

Makes the membrane less fluid and more rigid

Question 37

How does cholesterol change at lower temperatures to help the cell membrane?

Answer 37

At lower temperatures , cholesterol prevents phospholipids from packing too close together and so increases membrane fluidity

Question 38

What is the function of proteins in cell membranes ?

Answer 38

Controls what enters and leaves the cell

Question 39

Some proteins form channels in the membrane. What does that allow them to do?

Answer 39

Allow small or charged particles through

Question 40

What do carrier proteins do?

Answer 40

Transport molecules and ions across the membrane by active transport and facilitated diffusion

Question 41

Proteins can also act as receptors. Explain what that would mean?

Answer 41

- Act as receptors for molecules in cell communication - When a molecules binds to the protein, a chemical reaction is triggered inside the cell

Question 42

What is the function of glycolipids and glycoproteins

Answer 42

Act as receptors for messenger molecules

Question 43

How are the glycolipids and glycoproteins able to stabilise the membrane?

Answer 43

By forming hydrogen bond with the surrounding water molecules

Question 44

What are the 3 functions of glycolipids and glycoproteins

Answer 44

- Sites where drugs, hormones and antibodies bind - act as receptors for cell communication - also antigens