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

Function of Cholesterol Molecules in CSM

Answer 7

add strength to membranes

reduce movement of molecules

make membranes less fluid at high temperatures

prevent loss of water and ions

Question 8

Glycolipid

Answer 8

Carbohydrate covalently bonded with a lipid

extends out into environment and acts as recognition sites for hormones

helps maintain stability

helps cells attach to one another and form tissues

Question 9

Glycoprotein

Answer 9

Carbohydrate chains attached to many extrinsic proteins on outer surface

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 10

Why can’t some molecules diffuse through the membrane?

Answer 10

not lipid-soluble

too large

same charge as channel protein

polar

Question 11

Fluid-Mosaic Model

Answer 11

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

Question 12

Simple Diffusion

Answer 12

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

Question 13

Facilitated Diffusion

Answer 13

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

Question 14

Facilitated Diffusion - Protein Channels

Answer 14

form hydrophilic channels
- allow specific water-soluble ions through

Question 15

Facilitated Diffusion - Carrier Proteins

Answer 15

molecule binds to carrier protein outside

causes change in shape

molecule is released on inside

Question 16

Osmosis

Answer 16

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

Question 17

Water Potential

Answer 17

Pressure created by water molecules
Pure Water: Zero
Add Solute: more negative wp/ lower wp
Add water: less negative wp/ higher wp

Question 18

Osmosis in Animal Cells (Plant Cells)

Answer 18

Less negative water potential outside of cell = water entering cell, cell swells and bursts (turgid)

Equal water potential = no change

More negative water potential outside of cell = water leaving cell, cell shrinks (plasmolysed)

Question 19

Active Transport

Answer 19

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

Question 20

Process of Direct Active Transport

Answer 20

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 21

Microvilli

Answer 21

Finger-like projections that line the ileum, provide more surface area for transport.
Causes faster rate of active transport.

Question 22

Role of Diffusion in Absorption

Answer 22

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 23

Role of Active Transport in Absorption

Answer 23

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

Question 24

Co-transport of Glucose Molecule via Sodium -Potassium Pump

Answer 24

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 25

What factors affect the rate of facilitated diffusion?

Answer 25

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

Question 26

What factors affect the rate of osmosis?

Answer 26

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

Question 27

What is a co-transporter?

Answer 27

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 28

What factors affect the rate of active transport?

Answer 28

speed of individual carrier proteins

number of carrier proteins present

rate of respiration in the cell and availability of ATP