save my exams cell membrane and trasnport

Question 1

luid mosaic model also helps to explain:

Answer 1

Passive and active movement between cells and their surroundings
Cell-to-cell interactions
Cell signalling

Question 2

Phospholipids

Answer 2

The phosphate head of a phospholipid is polar (hydrophilic) and therefore soluble in water
The lipid tail is non-polar (hydrophobic) and insoluble in water

Question 3

phospholipid monolayer

Answer 3

phospholipids are spread over the surface of water they form a single layer with the hydrophilic phosphate heads in the water and the hydrophobic fatty acid tails sticking up away from the water

Question 4

micelle

Answer 4

If phospholipids are mixed/shaken with water they form spheres with the hydrophilic phosphate heads facing out towards the water and the hydrophobic fatty acid tails facing in towards each other

Question 5

proteins in membrane

Answer 5

proteins can either be intrinsic or extrinsic

Question 6

intrinsic

Answer 6

are embedded in the membrane with their arrangement determined by their hydrophilic and hydrophobic regions

Question 7

Extrinsic proteins

Answer 7

found on the outer or inner surface of the membrane

Question 8

why fluid mosiac is fluid

Answer 8

The phospholipids and proteins can move around via diffusion
The phospholipids mainly move sideways, within their own layers
The many different types of proteins interspersed throughout the bilayer move about within it

Question 9

fluid mosaic mosaid bc

Answer 9

The scattered pattern produced by the proteins within the phospholipid bilayer looks somewhat like a mosaic when viewed from above

Question 10

three types of lipids

Answer 10

Phospholipids
Cholesterol
Glycolipids

Question 11

two types of proteins

Answer 11

Glycoproteins (also containing carbohydrates)
Other proteins (eg. transport proteins)

Question 12

phospholipids jobs

Answer 12

Form a bilayer
Hydrophobic tails point in towards the membrane interior
Hydrophilic heads point out towards the membrane surface
Individual phospholipid molecules can move around within their own monolayers by diffusion

Question 13

cholestrol

Answer 13

Cholesterol molecules also have hydrophobic tails and hydrophilic heads
Fit between phospholipid molecules and orientated the same way (head out, tail in)
Are absent in prokaryotes membranes

Question 14

glycolipidds

Answer 14

These are lipids with carbohydrate chains attached
These carbohydrate chains project out into whatever fluid is surrounding the cell

Question 15

glycoproteins

Answer 15

These are proteins with carbohydrate chains attached
These carbohydrate chains also project out into whatever fluid is surrounding the cell

Question 16

proteins

Answer 16

proteins embedded within the membrane are known as intrinsic proteins
transmembrane proteins
Transport proteins
extrinsic proteins

Question 17

extrinsic proteins

Answer 17

Proteins can also be found on the inner or outer surface of the membrane

Question 18

transport proteins

Answer 18

are an example of transmembrane proteins as they cross the whole membrane

Question 19

transmembrane proteins

Answer 19

Most commonly, they span the entire membrane

Question 20

phospholipid bilayer structure

Answer 20

tails form a hydrophobic core comprising the innermost part of both the outer and inner layer of the membrane
barrier to most water-soluble substances
ensures water-soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell

Question 21

what do cholestrols do

Answer 21

regulates the fluidity of the membrane
sit in between the phospholipids, preventing them from packing too closely together
nteraction between cholesterol and phospholipid tails also stabilises the cell membrane at higher temperatures by stopping the membrane from becoming too fluid

Question 22

what glycoproteins and glycolipids do

Answer 22

contain carbohydrate chains that exist on the surface enables them to act as receptor molecules
allows glycolipids and glycoproteins to bind with certain substances at the cell’s surface

Question 23

what transport proteins do

Answer 23

create hydrophilic channels to allow ions and polar molecules to travel through the membrane.

Question 24

two types of tansport proteins

Answer 24

channel (pore) proteins
carrier proteins

Question 25

3 main receptor types

Answer 25

signalling receptors for hormones and neurotransmitters
receptors involved in endocytosis
receptors involved in cell adhesion and stabilisation

Question 26

facillitated diffusion

Answer 26

Certain substances cannot diffuse through the phospholipid bilayer of cell membranes. These include:
Large polar molecules such as glucose and amino acids
Ions such as sodium ions (Na+) and chloride ions (Cl-)
These substances can only cross the phospholipid bilayer with the help of certain proteins
This form of diffusion is known as facilitated diffusion
There are two types of proteins that enable facilitated diffusion:
Channel proteins
Carrier proteins
They are highly specifi

Question 27

channel proteins

Answer 27

water-filled pores
allow charged substances (eg. ions) to diffuse through the cell membrane
part of the channel protein on the inside surface of the membrane can move in order to close or open the pore
allows the channel protein to control the exchange of ions

Question 28

carrier proteins

Answer 28

carrier proteins can switch between two shapes
binding site of the carrier protein to be open to one side of the membrane first, and then open to the other side of the membrane when the carrier protein switches shape
down a concentration gradient

Question 29

factors affecting diffusion

Answer 29

steepness of conc gradient
temperature
surface area
properties of molecules of ions

Question 30

steepness of conc gradient

Answer 30

-greater difference in conc means a greater difference in the number of molecules passing in the two directions and therefore a faster rate of diffusions

Question 31

temperature

Answer 31

molecules and ions have more kinestic energy at a higher temperatures
they move faster resulting in higher rate of diffusuion

Question 32

surface area

Answer 32

greater surface area across which diffusion is taking place the greater the number of molecules or ions that can cross it any one moment and therefore that faster diffusion occurs

Question 33

properties of molcules or ions

Answer 33

-large molecules diffuse more slowly than smallerones as they require more energy to move
uncharged non polar moles mdiffuse directly across phospholipid bilayer

Question 34

def of osmosis

Answer 34

net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane

Question 35

water potential

Answer 35

tendency of water to move out of a solution. This term is used to avoid confusion between water concentration and concentration of a solution

Question 36

dilute and conc sol

Answer 36

A dilute solution has a high water potential (the right-hand side of the diagram below) and a concentrated solution has a low water potential

Question 37

what happens during osmosis

Answer 37

diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a partially permeable membrane
In doing this, water is moving down its concentration gradient
The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules)

Question 38

plasmolysis of a plant cells placed in sol w lower water potential

Answer 38

1)turgid cell showing partially permeabe membrsnes as dotted lines
2)plasmlysis in progress water leaves the plant cell by osmosis- protoplast is starting to shrink away from the cell wall
3)fully plasmolysed cell and protoplast has shrunk away from the cell wall and the cell is fully plasmolysed

Question 39

plate in pure water or dilute

Answer 39

water will enter the plant cell through its partially permeable cell surface membrane by osmosis, as the pure water or dilute solution has a higher water potential than the plant cell
volume of the plant cell increases
expanding protoplast
pressure builds up inside the cell
stops too much water entering and this also helps to prevent the cell from bursting
turgid

Question 40

hypertonic rbs

Answer 40

-rbc have a higher water potential than solution so net movement of water out and cell shrivels

Question 41

isotonic rbc

Answer 41

-water potential equal between rbc and solution
-no net movement of water
-nromal cells

Question 42

hypotonic solutions

Answer 42

-red blood.cells have lower water potential than solution
-net movement of water in
-cells swell and may burst

Question 43

why osmosis more severe in animals than plants

Answer 43

As animal cells do not have a supporting cell wall (unlike plant cells), the results of this loss or gain of water on the cell are more severe

Question 44

animal in lower water potetnial

Answer 44

such as a concentrated sucrose solution), water will leave the cell through its partially permeable cell surface membrane by osmosis and the cell will shrink and shrivel up
This occurs when the cell is in a hypertonic environment (the solution outside of the cell has a higher solute

Question 45

hypotonic

Answer 45

placed in pure water or a dilute solution, water will enter
cell will continue to gain water by osmosis until the cell membrane is stretched too far and the cell bursts
no cell wall
the solution outside of the cell has a lower solute concentration than the inside of the cell)

Question 46

active transport

Answer 46

movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

Question 47

what is active trasnport important for

Answer 47

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

Question 48

co transport

Answer 48

coupled movement of substances across a cell membrane via a carrier protein
This means that two types of molecule are moved across the membrane at the same time; the movement of one is dependent on the movement of the other
It involves a combination of facilitated diffusion and active transport

Question 49

what does active transport require

Answer 49

carrier proteins (each carrier protein being specific for a particular type of molecule or ion)
requires energy
to make the carrier protein change shape, allowing it to transfer the molecules or ions across the cell membrane

Question 50

specific co-transport protein is involved in the absorption of glucose and sodium ions as follows:

Answer 50

The active transport of sodium ions from the epithelial cell into the blood lowers the sodium ion concentration inside the cell and generates a sodium ion concentration gradient between the ileum and the epithelial cell
Sodium ions move into the cell from the ileum by facilitated diffusion, carrying glucose molecules along with them via a cotransport protein
The glucose concentration inside the epithelial cell increases, and glucose molecules enter the blood via facilitated diffusion

Question 51

two factors facillitated diffusion depends on

Answer 51

-conc gradient acorss exchange surface
-number of channel or carrier proteins available in the exchange surface

Question 52

number of channel or carrier proteins available in the exchange surface

Answer 52

-uses channel and carrier proteins
-once all the channel or carrrier protrins are in use the rate of facilliatated diffusion of a partifular moleule can no longer increase
-greater number channel or carrier proteins availabe in the exchange surface the higher the fate of facillitated difusion

Question 53

neurones and muscle cellw

Answer 53

Are involved in the transmission of electrical impulses around the body
They have cell membranes that contain channel proteins for sodium, potassium and calcium ions
The opening and closing of these channel proteins (and the resulting facilitated diffusion of these different ions), as well as the number of these channel proteins, plays an important role in the speed of electrical transmission, both along the membranes of neurones (during nerve impulses) and in muscle cells (during muscle contraction)

Question 54

epethilial and small intestines

Answer 54

Have microvilli (highly folded sections of the cell membrane), which increases the cell’s surface area so the rate of diffusion of the products of digestion is greater (more particles can be exchanged in the same amount of time)
Each villus of the small intestine has a constant blood supply, which continually transports the products of digestion away from the epithelial cells. This maintains a high concentration gradient across the epithelial cell exchange surface (between the lumen of the small intestine and the interior of the epithelial cell)

Question 55

root hair cells

Answer 55

Are adapted for the absorption of water and mineral ions from soil
Have a specialised shape (the root ‘hair’) that increases the cell’s surface area so the rate of water uptake by osmosis is greater (can absorb more water and mineral ions than if the surface area was lower)
Have thinner walls than other plant cells so that water can move through easily (due to 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