Cell Membrane And Transport

Question 1

What are phospholipid bilayers

Answer 1

Two layers of phospholipids with hydrophobic tail facing in and hydrophilic head outwards
Make up cell membranes
Proteins in cell membrane are intrinsic or extrinsic

Question 2

Why is the fluid mosaic model described as fluid and mosaic

Answer 2

Fluid: Phospholipids and proteins move around by diffusion
Move sideways within their own layers
Many types of protein throughout bilayer move within it and some fixed position
Mosaic: scattered pattern of proteins looks like a mosaic

Question 3

Describe what the model looks like

Answer 3

Glycolipids on top with hydrophilic head on edges and hydrophobic tail inwards
With channel proteins crossing both sides of membrane

Question 4

What are the three types of lipids

Answer 4

Phospholipids
Cholesterol
Glycolipids

Question 5

Two types of protein

Answer 5

Glycoproteins and other proteins (transport proteins)

Question 6

What are cholesterols uses

Answer 6

In general:
Make hormones = oestrogen, testosterone
Make cell membranes
Make vitamins
In membrane:
Makes membrane fluid, controls fludiity, strength, impermeability

Question 7

What are glycolipids

Answer 7

Lipids with carbohydrate chains attaches
THese chains project out into fluid surrounding cell

Question 8

WHat are glycoprotins

Answer 8

Proteins with carbohydrate chains attaches

Question 9

What are phospholipids purpose in cell surface membranes

Answer 9

-Barrier to water soluble substances
-Ensures water soluble molecules (sugars, amino acids, proteins) dont leave and unwanted water soluble molecules cant enter
-Can be chemically modified to signal molecules by (move within bilayer and hydrolysed to release small water soluble molecules that bind to specific receptors in cytoplasm)

Question 10

What are cholesterols purpose in the cell surface membrane

Answer 10

-fluidity of membrane
-Prevents phospholipids packing together too closely (temps low prevents membrane freezing)
-Stablises membrane at high temps by stopping membane becoming too fluid (cholesterol bind to hydro tails of phospho stabilising them cand causing phospho to pack more closely together)
-Impermeability of membrane and increases mechanical strength without breaking membrane

Question 11

Glycolipids and glycoproteins function in membrane

Answer 11

-Act as receptors as they exist on surface of carbohydrate chains
-Allowing glycolipids and glycoproteins to bind with certain substances on cell surface
-3 receptors roles are signalling, endocytosis and cell adhesion and stabilisation
-Cell markers or antigens for recognition

Question 12

Function of proteins in membrane

Answer 12

Transport proteins create hydrophilic channels allowing ions and polar molecules to travel through membrane
-Channel and carrier proteins
-Each are specific to particular ion or molecule
-Allow cell to control what substances enter or leave

Question 13

When do membranes become more or less fluid

Answer 13

Less fluid:
Increase saturated fatty acid chains packed tightly so higher number of intermolecular forces
Low temps = molecules have less energy and dont move freely (packed together closer)
More fluid:
-Increase unsaturated fatty acids (bent chains) so dont pack tightly and less intermolecular forces
Higher temps molecules have more energy so move more so more fluidity in membrane

Question 14

What is diffusion definition

Answer 14

The net movement as a result of the random motion of its molecules or ions, of a substance from a region of high concentration to low concentration
THe molecules/ ionbs move down a concentration gradient caused by kinetic energy of the molecules

Question 15

What factos affect the rate of diffusion

Answer 15

1) Steepness of concentration gradient (diference in concentration between both regions faster if there is a greater difference)
2) Temperature (more kinetic energy)
3) SUrface area (faster diffusion greater molecules over large surface area)
4) Properties of molecules por ions (large slower than small, uncharged and nonn polar diffuse direcctly across but non polar diffuse quickly because they are soluble to phospholipid bilayer)

Question 16

What is facilitated diffusion

Answer 16

Some substances cant diffuse through membranes - large polar molecules and all types of ions
They have to use channel or carrier proteins to cross
And are highly specific

Question 17

What are channel proteins

Answer 17

Water filled pores
Allow charges substances to diffuse through
Diffusion of ions happens when gates are open or closed
Channel proteins control exchange of ions

Question 18

What are carrier proteins

Answer 18

Switch between shapes, channel proteins have a fixed shape
Binding site of carrier protein to be open on one side and clsoed on the other
Direction of movement of molecules depends on concentration of membrane
Net diffusion of molecules/ ions out of cell occurs down the conc gradient from high to low

Question 19

What is osmosis definition

Answer 19

Diffusion of water molecules from dilute (high conc of water) to more conc solution (low water conc) across a partially permeable membrane, water moves down the conc gradient

Question 20

WHy can water pass through the phospholipid bilayer

Answer 20

Water moelcules small enough to pass between phospholipids in the cel membrane

Question 21

How do plants cells stay turgid

Answer 21

1) Water enters the vacuole of the plant cell, volume of plant cell increases
2) Protoplast pushes against the cell wall and pressure builds inside the cell
3) The inelastic cell wall prevents the cell bursting

Question 22

Plasmolysis of a plant cell

Answer 22

1) Turgid cell
2) Protoplast starts to shrink away from cell wall (plasmolysis) Water leaves the plant cell by osmosis
3) The cell is now fully plasmolysed

Question 23

What happens in a hypotonic environment

Answer 23

Cytolysis
ANimal cell in pure water/ dilute solution
Water enters cells through partially permeable cell surface membrane by osmosis
Pure water has a higher water potential
Cell gains water by osmosis until mmembrane stretched too far and cell bursts

Question 24

What happens if an animal cell is placed in a hypertonic solution

Answer 24

Net movement of water out
Shrivelled cells

Question 25

COmpare what happens to plant cells and animal cells when placed in a solution or highh or lower water potential

Answer 25

Lower water potential:
Plant = water leaves cell through partially permeable membrane by osmosis, cell plasmolysed
Animal = water leaves… by osmosis, cell shrinks

High water potential:
Plant = water enters, protoplast expands, cell withsands increased pressure, turgid
Animal = water enters, cell wall cannot withstand pressure, cell membrane stretched too far and bursts

Question 26

Osmosis potato practical method

Answer 26

1) Potato cylinders cut all same length, blotted dry
2) Measure initial mass
3) left in solutions for set amount of time (30 mins 30C)
4) Removed and dried to remove exccess liquid
5) Measure mass
Positive percentage change = gained mass
Negative = solution had lower water potential, mass decreased

Question 27

What is active transport

Answer 27

Movement of molecules and ions through cell membrane from a region of lower conc to a region of high conc using energy from respiration
Requires carrier proteins
Uses energy to change protein shape

Question 28

Why is active transport important

Answer 28

Reabsorption of useful molecuels and ions into blood after filtration into kidney tubules
Absorption of products of digestion from digestive tract
Loading sugar from photosynthesising cells of leaves into phloem tissue from transport around the plant
Loading inorganic ions from the soil into root hairs

Question 29

What is cotransport

Answer 29

Coupled movement of substances across membrane via a carrier protein
Two types of molecules move across the membrane at the ssame time movement is dependent on the other
Involved facilitated diffusion and active transport

Question 30

How are glucose ans sodium ions co transported in the epithelial cells

Answer 30

1) Active transport = Na+ from epithelial cell into blood lowers Na+ conc inside the cell, generates a na+ concentration gradient between the ileum and epithelial cell
2) Facilitated diffusion = Na+ move into cell from ileum by carrying glucose molecules along with them through cotransport protein
3) Fac DIf = Glucose conc inside the epithelial increases and glucose molecules enter the blood

Question 31

What factors does the rate of diffusion occur

Answer 31

Temperature
Sirface area
Concentration graddient
Thickness of exchange surface

Question 32

Rate of simple diffusion depends on waht factors

Answer 32

Surface area of exchange surface = large SA higher rate
Conc gradient across exchange surface = greater diff in conc on sides of exchange surface higher rate
Thickness of exchange surface = thinner higher rate (short distance)

Question 33

The rates of facilitated diffusion depend in what

Answer 33

Concentration gradient across exchange surface = greater difference higher rate
Number of channel or carrier proteins available in the exchange surface = greater channels available higher rate

Question 34

How are root hair cells adapted

Answer 34

-specialised shape increases surface area = rate of water uptake by osmosis is greater, absorb more water and mineral ions than if the surface area was lower
-thinner walls = water can move easily shorter diffusion distance
-Have a permanent vacuole containing cell sap, which is more concentrated than soil water. This ensures a high water potential gradient is maintained

Question 35

How are epithelial cells adapted

Answer 35

Microvilli = high SA for difusion greater rate
-Villus of small intestine = constant blood supply maintains high conc gradient

Question 36

What factors affect the permeability of a membrane

Answer 36

Temperature
Solvent concentration

Question 37

Investigating effect of temeprature on membrane permeability

Answer 37

1) Use scalpel cut 5 equal sizes beetroot cubes
2) Rinse pieces to remove pigment released during cutting
3) Put in 5 different test tubes with same volume of water
4) Put each in different temperature 10C, 20C, 30C for same length of time, long enough to allow pigement to diffuse into water (30 mins)
5) Remove betroot pieces and use colourimeter to measure how much light is absorbed as it passes through each of the 5 samples

Question 38

Results from beetroot investigation explanation of phospholipids permeability

Answer 38

As temp increases:
-phospholipids have more energy in cell membrane so move more
-Phospholipids not tightly packed together increasing permeability of membrane
-phospholipid bilayer starts to melt and breakdown further increase permeability of membrane
-Volume of water expands cells so channel and carrier proteins deform and can no longer control waht enters or leaves the cell increasing permeability of membrane
-Shape of proteins = intermolecular forces between amino acids broken affecting proteins specificity and function

Question 39

Limitations of beetroot practical

Answer 39

Curvettes (cubes of beetroot) differ in thickness = use scalpel and ruler and repeat
Some parts of beetroot tissue may have more pigment than others = repeat with different parts

Question 40

Describe cholesterol

Answer 40

Have hydrophobic tails and hydrophiliv heads
Fit between phospholipid molecles and orientate the same way
Not in prokaryotes

Question 41

Functions of membranes in cells

Answer 41

Separate internal and external environment of cell
Separate internal cellular organelles
Enable cellular ocnditions to be different between one enclosed space to another
Regulate movement of substances
Display antigens

Question 42

WHy does the phospholipid bilayer form in an aqueous environment

Answer 42

Have hydrophilic head and hydrophobic tale
So arrange themselves so tail is in contact with surrounding and water is minimised

Question 43

WHy does the phospholipid bilayer form in an aqueous environment

Answer 43

Have hydrophilic head and hydrophobic tale
So arrange themselves so tail is in contact with surrounding and water is minimised

Question 44

How do molecules enter a cell through its cell membrane without using protein channels

Answer 44

Move from outside cell to inside
Directly in between phospholipids by simple diffusion
Because there is a higher conc of th emolecule inside so diffusion takes place down a conc gradient
Molecules are small enough and non polar so can move between phospholipids

Question 45

How do polar substances enter the cell membrane

Answer 45

Facilitated diffusion
Via a specific channel protein

Question 46

Describe the process to transport molecules through carrier proteins

Answer 46

1) molecule binds to specific binding site on carrier protein
2) ATP is hydrolysed
3) Protein changes shape and released molecule to the other side of the membrane
From an area of lwo to high conc