2 Transport across cell membranes

Question 1

Cell Surface Membrane

Answer 1

Membrane that surrounds cell and forms boundary to the outside.
Controls the movement of substances in and out of cell.

Question 2

Features of Phospholipid in CSM

Answer 2

Hydrophilic head outside CSM - attracts water

Hydrophobic tail inside CSM - repels water

Question 3

Function of Phospholipid in CSM

Answer 3

• allow lipid-soluble molecules to enter and leave
• prevent water-soluble molecules entering and leaving
• make the membrane flexible and self-sealing

Question 4

Extrinsic Proteins

Answer 4

Embedded in the surface of bilayer

Either used for mechanical support or in conjunction with glycolipids

Question 5

Intrinsic Proteins

Answer 5

Embedded completely in the bilayer

1) Protein channels - allow water soluble ions through
2) Carrier Proteins - used for facilitated diffusion

Question 6

Functions of Proteins in Membranes

Answer 6

• provide structural support
• act as channels for water-soluble substances
• allow active transport across membrane
• form cell surface receptors
• help cells adhere together

Question 7

Cholesterol Molecules

Answer 7

Occur throughout bilayer

Very hydrophobic

Question 8

Function of Cholesterol Molecules

Answer 8

• add strength to membranes
• reduce movement of molecules
• make membranes less fluid at high temperatures
• prevent loss of water and ions

Question 9

Glycolipid

Answer 9

Carbohydrate covalently bonded with a lipid

Carbohydrate section extends out of bilayer into watery environment outside (acts as a receptor)

Question 10

Function of Glycolipids

Answer 10

• act as recognition sites for hormones
• helps maintain stability
• helps cells attach to one another and form tissues

Question 11

Glycoprotein

Answer 11

Carbohydrate chains attached to many extrinsic proteins on outer surface

Question 12

Function of Glycoproteins

Answer 12

• act as recognition sites for hormones and neurotransmitters
• helps cells attach to one another and form tissues
• allows cells to recognise each other (e.g. lymphocytes)

Question 13

Why can’t some molecules diffuse through the membrane?

Answer 13

• not lipid-soluble
• too large
• same charge as channel protein (they are repelled)
• polar

Question 14

Fluid-Mosaic Model

Answer 14

Fluid - phospholipid molecules can move around - gives a flexible structure
Mosaic - proteins embedded in bilayer are varied in shape and size

Question 15

Simple Diffusion

Answer 15

Net movement of particles from high concentration to a low concentration, until evenly distributed.

Question 16

Facilitated Diffusion

Answer 16

Movement of charged ions and polar molecules through the CSM
Passive process - relies on kinetic energy from molecules

Question 17

Facilitated Diffusion - Protein Channels

Answer 17

• form hydrophilic channels

- allow specific water-soluble ions through

Question 18

Facilitated Diffusion - Carrier Proteins

Answer 18

• molecule binds to carrier protein outside
• causes change in shape
• molecule is released on inside

Question 19

Osmosis

Answer 19

Movement of water molecules from high water potential to low water potential through a partially permeable membrane

Question 20

Solute

Answer 20

Substance that is dissolved in solvent

Question 21

Water Potential

Answer 21

Pressure created by water molecules

Question 22

Water Potential of Pure Water

Answer 22

Zero (this is the highest water potential everything else is negative)

Question 23

Addition of Solute to Pure Water

Answer 23

Will lower water potential (be negative)

Question 24

Osmosis in Animal Cells

Answer 24

Less negative water potential = water entering cell, cell swells and bursts (turgid)
Equal water potential = no change (incipient plasmolysis)
More negative water potential = water leaving cell, cell shrinks (plasmolysed)

Question 25

Active Transport

Answer 25

movement of molecules from low concentration to high concentration using ATP and carrier proteins

Question 26

ATP in Active Transport

Answer 26

- directly move molecules | - in co-transport

Question 27

Process of Direct Active Transport

Answer 27

- molecule binds to carrier protein - on the inside ATP binds to carrier protein causing it to split into ADP + inorganic phosphate - protein changes shape and molecule released on the inside - phosphate is released and protein changes back

Question 28

Sodium-Potassium Pump

Answer 28

Sodium ions are actively removed from cell while potassium ions are actively taken in

Question 29

Microvilli

Answer 29

Finger-like projections that line the ileum, provide more surface area for transport

Question 30

Role of Diffusion in Absorption

Answer 30

Greater concentration of glucose and amino acids in ileum than the blood Concentration gradient formed Glucose/amino acids transported into blood by facilitated diffusion

Question 31

Role of Active Transport in Absorption

Answer 31

Not all glucose and amino acids can be absorbed by diffusion Example of co-transport

Question 32

Co-transport of Glucose Molecule

Answer 32

1) Sodium ions are actively transported out of epithelial cells by sodium-potassium pump (protein carrier molecule) 2) higher concentration of sodium ions in lumen of ileum 3) sodium ions diffuse into epithelial cells (by co-transport protein) carrying glucose molecule 4) glucose passes into blood by facilitated diffusion

Question 33

What factors affect the rate of facilitated diffusion?

Answer 33

- the concentration gradient | - the number of channel and carrier proteins

Question 34

What factors affect the rate of osmosis?

Answer 34

- water potential gradient - thickness of the exchange surface - surface area of the exchange surface

Question 35

What is a co-transporter?

Answer 35

type of carrier protein they bind two molecules at a time concentration gradient of one of the molecules is used to move the other molecule against its concentration gradient

Question 36

How is rate of active transport increased?

Answer 36

- having microvilli | - increased number of protein channels and carrier proteins

Question 37

What factors affect the rate of active transport?

Answer 37

- speed of individual carrier proteins - number of carrier proteins present - rate of respiration in the cell and availability of ATP