Crossing the plasma membrane

Question 1

Lipids are made of which elements?

Answer 1

Carbon, Hydrogen and Oxygen.

Question 2

State three examples of lipids.

Answer 2

Fats, oils and waxes.

Question 3

How are lipids different to carbohydrates in terms of their molecular structure?

Answer 3

Lipids contain less oxygen atoms. Lipids also have long tails made up entirely of C and H.

Question 4

Difference between fats and oils?

Answer 4

Fats are solid at room temperature whilst oils are liquid.

Question 5

State two properties of lipids

Answer 5

Non-polar and insoluble in water. Poor conductors of heat, which means they are good insulators.

Question 6

What are the subunits of a triglyceride molecule?

Answer 6

One glycerol and three fatty acids.

Question 7

What is the name of chemical bond that holds the subunits of a trigyceride together?

Answer 7

Ester bond

Question 8

How many hydroxyl groups does a glycerol contain?

Answer 8

three hydroxyl groups allowing three fatty acids to attach to the glycerol molecule.

Question 9

How do fatty acids attach to the glycerol?

Answer 9

The carboxyl group of the fatty acid joins with the hydroxyl group of the glycerol.

Question 10

Difference between saturated and unsaturated fats?

Answer 10

Saturated fats have no double bonds between carbon atoms in their fatty acid tails, whereas unsaturated fats have double bonds between carbon atoms in their fatty acid tails.

Question 11

Describe the structure of a phospholipid

Answer 11

Hydrophilic polar phosphate head
Hydrophobic non-polar fatty acid tails

Question 12

Difference between phospholipids and triglycerides

Answer 12

A phospholipid contains a phosphate group and two fatty acid tails, whereas a triglyceride contains three fatty acid tails.

Question 13

What is the function of phospholipids?

Answer 13

They form an integral part of all cell membranes.

Question 14

How do phospholipids form a bilayer?

Answer 14

Two layers of phospholipids come together with phosphate heads facing the water rich environments (i.e. extracellular space and cytoplasm) and fatty acid tails facing towards the centre, forming the core of the phospholipid bilayer.

Question 15

What is the function of cholesterol?

Answer 15

It is a lipid found in the plasma membrane that provides stability and flexibility.

Question 16

What is the function of tryglycerides? State at least three functions.

Answer 16

Any three of the following:
Source of energy, Insulation, Protection of vital organs, To prevent evaporation in plants, form myelin sheath around neurons, Source of water (metabolic water produced in respiration).

Question 17

What are steroids?

Answer 17

Steroids are lipid-based hormones; they act as signalling molecules that cause a response in the body of an organism.

Question 18

How do steroids move into or out of the cell?

Answer 18

Because they are lipid-based, they can freely move across the phospholipid bilayer.

Question 19

Protein channels are involved in?

Answer 19

facilitated diffusion

Question 20

Protein pumps are involved in?

Answer 20

Active transport

Question 21

How are glycoproteins and glycolipids formed?

Answer 21

When a carbohydrate chain attaches to a protein & When a carbohydrate chain attaches to a phospholipid.

Question 22

What is the function of glycoprotein and glycolipid?

Answer 22

Cell communication and recognition.

Question 23

What is the fluid mosaic theory about?

Answer 23

It states that membranes are made up of small, varying components like a mosaic. In addition, these components are able to move across the plasma membrane.

Question 24

Define diffusion

Answer 24

Net movement of particles from a high concentration to a low concentration down a concentration gradient (passive movement)

Question 25

Define facilitated diffusion.

Answer 25

Net movement of particles from a high concentration to a low concentration down a concentration gradient through a protein channel (passive movement)

Question 26

State the properties of molecules that will cross the cell membrane via a protein channel.

Answer 26

Hydrophilic (either charged or polar).
Large in size.

Question 27

Describe which types of molecules can cross the phospholipid bilayer directly.

Answer 27

Small, non-polar, hydrophobic molecules can pass through the phospholipid bilayer directly.
Small, polar molecules (like water and ethanol) can also pass through the phospholipid bilayer directly.

Question 28

Describe a hypertonic solution

Answer 28

A solution that is higher in solute (therefore has a lower water concentration) in comparison to another solution.

Question 29

Describe a hypotonic solution.

Answer 29

A solution that is lower in solute (therefore has higher water concentration) in comparison to another solution.

Question 30

Define osmosis

Answer 30

The net movement of water molecules from a hypotonic solution to a hypertonic solution.

Question 31

Describe an isotonic solution.

Answer 31

A solution that has the same solute concentration as another solution.

Question 32

Describe steps in osmosis using the scaffold provided.

Answer 32

1. osmosis has occurred.
2. Water has moved from the hypotonic solution (+ context)
3. through the partially membrane of (+ context)
4. to the hypertonic solution (+ context)
5. outcome (e.g. the animal cell swells and lyses)

Question 33

Define active transport

Answer 33

the net movement of particles from a low concentration, to a high concentration, against the concentration gradient, through a protein pump using ATP .

Question 34

Define exocytosis.

Answer 34

Bulk movement of large molecules OUT of the cell. (This is primarily proteins but can be other polymers or molecules too big to pass through a protein pump or channel)

Question 35

Define endocytosis.

Answer 35

Bulk movement of large molecules INTO the cells.

Question 36

Define pinocytosis.

Answer 36

Bulk movement of liquids into the cell.

Question 37

Define phagocytosis.

Answer 37

Bulk movement of solids into the cell.