Topic 2 - Cell membrane (Structure and function)

Question 1

MEMBRANE STUCTURE

Question 2

What roles does a cell membrane have?

Answer 2

Controls what enters and exits the cell to maintain homeostasis

Question 3

Structure of the plasma membrane

Answer 3

Made out of phospholipid molecules, layers of these molecules form a phospholipid bilayer

Question 4

Phospholipids

Answer 4

Made of a phosphate head and a fatty acid tail

Question 5

Hydrophilic head (polar)

Answer 5

Hydrophilic, water-loving

Question 6

Hydrophobic tail (non-polar)

Answer 6

Hydrophobic, water-fearing, they can be saturated or unsaturated. The more unsaturated fatty acids the greater the fluidity of the membrane.

Question 7

Role of proteins

Answer 7

They provide SUPPORT and allow cells to recognise other structures. They also allow cells to COMMUNICATE and assist with TRANSPORT of substances across the membrane.

Question 8

Types of proteins

Answer 8

• Receptor : Receive signals
• Channel : Transport
• Carrier : Transpot

Question 9

How can proteins be associated with the membrane (PIT)

Answer 9

Peripheral - surface (temporarily attached)
Integral - strength (permanently attached)
Transmembrane - move/cross through the membrane bilayer

Question 10

Cholesterol role

Answer 10

Helps to keep the membrane flexible (provides fluidity)

Question 11

Selectively permeable

Answer 11

Select only certain molecules to cross the membrane

Question 12

What type of molecules are ‘permeable’ and ‘impermeable’

Answer 12

Permeable (Can cross membrane)
- Iodine, water, glucose
Impermeable (Can’t cross membrane)
- Starch, ions

Question 13

MEMBRANE FUNCTION

Question 14

What is the main difference between PASSIVE and ACTIVE transport across the cell membrane

Answer 14

Passive transport does not require energy, whereas active transport does

Question 15

Define diffusion

Answer 15

The movement of molecules from an area of high concentration to an area of low concentration

Question 16

Simple diffusion (5)

Answer 16

Movement of molecules across the (phospholipid bilayer)
- Hydrophobic molecules
- Small molecules
- Fat-soluble (non-polar)
- Down a concentration gradient (high to low)
- eg water, alcohol, gases (O2, CO2)

Question 17

Facilitated diffusion (5)

Answer 17

Diffusion with the help of transport proteins (through channels)
- Hydrophilic molecules
- Charged ions
- Water-soluble
- Down a concentration gradient (high to low)
- eg glucose, amino acids

Question 18

Similarities/Differences between the two types

Answer 18

• Similarities : Both move down a concentration gradient (High to low)
• Differences : Simple does not require proteins, whereas facilitated does.

Question 19

Does diffusion require a membrane?

Answer 19

No, diffusion itself does not require a membrane. For example gas molecules are diffusing into the open air

Question 20

TONICITY and OSMOSIS

Question 21

What is osmosis

Answer 21

Movement of water from an area of low solute concentration to an area of high solute concentration (Passive)

Question 22

Tonicity

Answer 22

Describes the concentration of solutes on either side of a membrane.
- Hypertonic
- Hypotonic
- Isotonic

Question 23

Hypotonic

Answer 23

Water moves INTO the cell
- Solution has a lower concentration of solutes and a high concentration of water outside of the cell
- Therefore, the water will move into the cell and the cell may burst (lyse in animal cells) or become turgid (plant cells).

Question 24

Hypertonic

Answer 24

Water moves OUT of cell
- Solution has a higher concentration of solutes outside of the cell
- Therefore the water will move out of the cell and the cell will shrink (animal cells) or plasmolyse (plant cells)

Question 25

Isotonic

Answer 25

Cell has the same concentration of solutes on both sides of the membrane and there will be no NET MOVEMENT of water

Question 26

Active transport

Answer 26

Active transport REQUIRES energy to transport substances across a membrane. - Used to move molecules AGAINST a concentration gradient from an area of low solute to an area of high solute

Question 27

Bulk transport

Answer 27

Movement of large molecules (Solids + Liquids) - There are two types of bulk transport : Endocytosis (into cell) and Exocytosis (out of cell)

Question 28

Endocytosis (into cell)

Answer 28

The cell membrane folds around the substance to form a VESICLE containing the 2 types of endocytosis - Solid (Cell eating) = Phagocytosis - Liquid (Cell drinking) = Pinocytosis

Question 29

Exocytosis (out of cell)

Answer 29

Substances are enclosed in a membrane to form a vesicle at the golgi body - Transports hormones, enzymes, or wastes out of the cell