Chapter 2 - Cell Membranes

Question 0

What are the functions of the cell membrane?

Answer 0

It separates the contents of the cell from the external environment.

Communicates with other cell.

Regulated the exchange of substance between cytoplasm & environment

Chemical reactions occur in the membrane & acts as a receptor for recognising external stimuli.

Question 1

What is the plasma membrane?

Answer 1

It surrounds all living cells. Controls how substance move in & out of the cell.
Phospholipids, proteins, carbohydrates and cholesterol.

Question 2

What is found in the cell membrane?

Answer 2

Phospholipids that form a thin, flexible sheet while protein which float like icebergs & carbohydrates that extend out from proteins.

Question 3

How are the phospholipids arranged?

Answer 3

They are in a bilayer, with the polar hydrophilic phosphate heads facing outwards and their non-polar fatty tails facing inwards.

Question 4

Why is it considered a barrier?

Answer 4

To all but the smallest molecules, it efficiently isolates the 2 sides of the membrane.

Question 5

Why is cholesterol important?

Answer 5

Links fatty acids together, stabilises and strengthens the membrane.

Question 6

There are 2 types of proteins found in cell membranes. State them.

Answer 6

Intrinsic proteins which span from one side of the phospholipid to the other.
Extrinsic proteins which sit on one of the surfaces.

Question 7

What are the intrinsic proteins used for?

Answer 7

Are usually involved in transporting substances across the membrane.

Question 8

What are the extrinsic proteins used for?

Answer 8

The ones found on the inside are attracted to the cytoskeleton, and are involved in the maintaining of shape and motility.
Whereas the ones found in the outside can act as receptors, by having a specific boding site with hormones/chemicals can bind.

Question 9

Carbohydrates are found on all outer surfaces of cell membranes and are attached to a number of things. Mention a few combinations.

Answer 9

Proteins and carbohydrates form glycoproteins.
Phospholipids and carbohydrates form glycolipids.

The carbohydrates are short polysaccharide that form a cell coat which is involved in protection and recognition of antigens.

Question 10

What is the fluid mosaic model?

Answer 10

The plasma membrane is described to be fluid because of its hydrophobic integral components move throughout the membrane. That means the membrane is not solid, but more like a ‘fluid’.

The membrane is depicted as mosaic because like a mosaic that is made up of many different parts such as proteins, phospholipids and cholesterol.

Question 11

What are channel proteins and carrier proteins?

Answer 11

They are involved in the selective transport of polar molecules & ions through the membrane. (Facilitated diffusion & active transport)

Question 12

What are receptor molecules?

Answer 12

Proteins have very specific shapes, making them ideal as receptor molecules for chemical between cells. (eg: hormones)

Question 13

What are antigens?

Answer 13

These are proteins that act as a cell identity markers.

Question 14

What are glycolipids?

Answer 14

Have branching carbohydrate side chains and are involved in cell recognition. May act as a receptor.

Question 15

Some of the fatty acids are saturated and others are not. What difference does this make?

Answer 15

Unsaturated tails are bent and fit together loosely.

The more unsaturated the tails, the more fluid the membrane is.

Question 16

What is another use for cholesterol?

Answer 16

It acts like a plug reducing even further the escape or entry of polar molecules through membrane.

Question 17

How are proteins used in energy transfer?

Answer 17

In photosynthesis and respiration proteins take part in energy transfer systems that exist in the membranes of mitochondria and chloroplasts.

Question 18

What are the benefits of compartmentalisation?

Answer 18

Allows materials to be concentrate inside, excluded from cell or separate.
Enables reactions to take place that would otherwise be impossible.

Question 19

What is simple diffusion?

Answer 19

For very small molecules such as water, the barrier doesn’t affect them, as such they can’t control it. Can only happen down the concentration gradient.

Is a passive process requiring no energy.

Question 20

What factors affect the rate of diffusion?

Answer 20

The steeper the gradient, the faster the rate, which may be needed if rapid transport is required.

The greater the surface area of membrane, the greater the rate. (The larger the cell, the smaller the surface area, which places a limit of cell size)

Rate of diffusion decreases dramatically with distance. Only effective short distances.

Question 21

What is osmosis?

Answer 21

It is the diffusion of water across a membrane, just like simple diffusion. However due to its important, it has it’s own name.
The more concentrated the solution (contents of cell), the more solute molecules & therefor the less water molecules available in a volume.

Always down the concentration gradient. Concentrated to dilute.

Question 22

There are 3 types if concentration in osmosis which affect the state of the cell. Mention them.

Answer 22

Isotonic solution: a solution of equal OP to cell.

Hypertonic solution: a solution of higher OP to cell. (Flaccid)

Hypotonic solution: a solution of lower OP to cell. (Turgid)

Question 23

What is facilitated diffusion?

Answer 23

Transport of substances by a transmembrane protein molecule.
Protein molecules tend to be specific for one molecule, so will only be able to pass if it’s the specific molecule.

Passive process requiring no energy
Travel down a concentrated gradient.

Question 24

There are 2 kinds of transport proteins. Mention them.

Answer 24

Channel proteins: Allows charged ions to diffuse across membrane. Most are gated to control entry and exit.

Carrier proteins: have a binding sit for a specific solute and constantly flips between 2 states, so the sit is alternately open to opposite sides of membrane.

Question 25

What is active transport?

Answer 25

Pumping of a substance across a membrane through transmembrane protein.
Protein binds molecule of substance to be transported on one side of the membrane, changed shape & releases it on the other side. Highly specific.
Up the concentration gradient. Required ATP

Question 26

Give a brief outline of the Na+ and K+ pump, commonly found in animals.

Answer 26

It’s a complex system which pumps out 3 sodium out while pumping 2 potassium in, for each ATP spent.

Generated a potential difference across the membrane (nerves use this a lot)

Question 27

If you were to draw a graph on simple diffusion, facilitated diffusion and active transport. How would they differ?
(rate of diffusion vs concentration gradient)

Answer 27

Simple diffusion: rate of diffusion rises with increased concentration gradient.
Facilitated diffusion: although it follow a similar patten, it curves with a max rate due to the rate being limited by the number of transport proteins.
Active transport: it has a high rate even despite the concentration gradient. Only stops for cellular respiration.

Question 28

What are vesicles used for?

Answer 28

Other methods for transporting substances across a membrane, only apply to small molecules.

These can move large molecules, even cells.

Question 29

What is endocytosis?

Answer 29

Transport of materials into a cell.

Materials are enclosed by a fold in the cell membrane, which pinches shut to form closed vesicles.

Question 30

There are 2 types of endocytosis. Name them.

Answer 30

Pinocytosis which is when the materials and the vesicles are small.
Phagocytosis is when the materials are large. (Bacteria)

Question 31

What is exocytosis?

Answer 31

Transport of material out of cell.
Exact reveres of endocytosis.
Materials are usually enclosed from the rough ER or Golgi body.
(Hormones & digestive enzymes)

Question 32

Name the 3 methods which use passive energy in order to transport substances through a cell membrane.

Answer 32

Simple diffusion, osmosis and facilitated diffusion.

Question 33

Name the 2 methods which use energy in order to pass a substance through a cell membrane.

Answer 33

Active transport and vesicles.

Question 34

Which of these processes are specific?

Answer 34

Osmosis, facilitated diffusion, active transport and vesicles.

Question 35

Which of these processes are controllable?

Answer 35

Facilitated diffusion, active transport and vesicles.

Question 36

Which of these processes use proteins?

Answer 36

Facilitated diffusion and active transport.

Question 37

Give an example of diffusion.

Answer 37

Food is mostly absorbed by the intestine this way.

Question 38

Give an example of osmosis.

Answer 38

Osmo-regulation in the kidneys of mammals. It controls the amount of water present in the blood.

Question 39

Give an example of active transport.

Answer 39

Plant root hair cells have protein Carriers that pump substance into the hair cells.