2.5

Question 1

what is the plasma membrane

Answer 1

the cell surface membrane which separates the cell from it’s external environment

Question 2

role of membrane at surface of cell (5)

Answer 2

1) site of chemical reactions
2) Release chemicals to communicate with other cells
3) Acts as a partially permeable barrier between cell & it’s environment
4) Regulates transport of material into & out of cell
5) Contains antigens so immune system can recognise it & not attack it

Question 3

what is the structure of the membrane like

Answer 3

• formed from 2 layers of phospholipid bilayer
• They hydrophobic tails are on the inside facing each other while the hydrophillic heads are on the outside and face away from each other

Question 4

why is the cell-membrane known as the fluid-mosaic model

Answer 4

• they contents are free to move within the layer relative to each other like fluid
• There are many different components embedded together like a mosaic

Question 5

what are intrinsic/integeral proteins

Answer 5

are transmembrane proteins that are embedded through both layers of a membrane.

Question 6

what are 3 types of intergeral proteins

Answer 6

Channel
carrier

Question 7

what does channel protein do + their structure

Answer 7

• Channel proteins form tubes that fill with water to enable water-soluble + small + polar molecules to passively diffuse through facilitated diffusion.
• Used when certain molecules can’t pass phospholipid bilayer

Question 8

what do carrier proteins do

Answer 8

important role in passive + active transport into cells and often involved in the changing of protein shape to transport by binding to larger molecules

Question 9

what are glycoproteins + their role

Answer 9

• proteins attached to carbon chain
• Has antigens for cell recognition
• Has receptor cells for cell-signalling

Question 10

what are extrensic / peripheral proteins and their role + structure

Answer 10

Present on 1 side of the bilayer They provide mechanical strength + cell recognition as receptors

Question 11

what are glycoproteins

Answer 11

lipids attached to carb chain

Question 12

what is their structure + role

Answer 12

• has antigens for cell recognition
• has receptors for cell-signalling

Question 13

what does cholesterol do

Answer 13

will retsrict lateral movements of other molecules in membrane and making it less liquid at higher temperatures and preventing water + dissolved ions from leaking out of cell

Question 14

how does a temperature below 0 affect membrane structure

Answer 14

Increase in membrane rigidity. As the temperature drops to below zero, phospholipids lose much of their kinetic energy. Therefore, the membrane loses its fluidity which causes it to become very rigid.

Increase in membrane permeability. Proteins within the membrane become heavily denatured, which increases the permeability of the membrane. Ice crystals can form in the membrane, which can cause the membrane to fracture, especially during thawing, which also increases permeability.

Question 15

how does a temperature of 0-45 affect membrane permeability

Answer 15

Membranes are fluid. Between 0-45°C, phospholipids can easily move (although their movement is naturally restricted by cholesterol).

Membranes are semi-permeable. At these temperatures, the membrane is also semipermeable. As temperatures increases, the kinetic energy of the phospholipids also increases, which increases their movement. This increase in movement leads to an increase in permeability of the membrane.

Question 16

how does a temperature of 45+ affect membrane structure

Answer 16

Phospholipid bilayer begins to break down. Increasing kinetic energy allows the phospholipids to move far away from each other, which destroys the structural integrity of the membrane, causing it to “melt”.

Cell Membrane Structure becomes freely permeable. Transport and channel proteins denature, thus making them unable to regulate what gets into and out of cells, which leads to increased membrane permeability.

The membrane may burst. The heat causes water inside of the cells to expand which puts pressure on the membrane, causing it to burst.

Question 17

how do solvents such as ethanol affect membrane structure

Answer 17

Lipids dissolve in alcohol, therefore, the phospholipids in a cell membrane will easily dissolve in solutions such as ethanol. As a result, the cell membrane becomes more fluid and permeable as it starts to break down.

Question 18

how does concentration of solvent affect the permability of membrane

Answer 18

increasing solvent concentration increases membrane permeability.

Question 19

why is this

Answer 19

This is because as the solvent becomes more and more concentrated, it has a greater ability to dissolve phospholipids and disrupt the membrane structure, making it more permeable to external substances

Question 20

steps to invetsigating affect of temperature on betroot membrane structure

Answer 20

Cut beetroot into five equal sized pieces. Wash these pieces afterwards to remove any pigment that leaked out while cutting.

Pipette 5 cm3 of water into five different test tubes.

Prepare water baths at five different temperatures. E.g. 20°C, 30°C, 40°C, 50°C, and 60°C.

Place each test tube in the different water baths. They all need to be incubated for the same duration.

Remove the test tubes from the water baths. Carefully remove the beetroot pieces, leaving the remaining-coloured liquid in the test tubes.

Using a colorimeter (as discussed in tutorial 17), measure how much light is being absorbed by the liquid in each test tube.

The greater the absorbance, the more coloured, or opaque, the liquid in the test tube is. This means that there has been a greater degree of permeability within the beetroot’s cell membranes, resulting in a large amount of pigment leaking out.

Question 21

steps to investigating how solvents like ethanol effect mebrane structure

Answer 21

Cut and wash five equal sized pieces of beetroot.

Prepare 5 different test tubes with 5cm3 of the following concentration of solvents:

Water

10% Ethanol

30% Ethanol

50% Ethanol

70% Ethanol

Put each piece of beetroot into the different test tubes. Seal the test tube openings with a rubber bung and shake the tubes.

Leave the beetroot pieces submerged for an hour. Periodically shake the tubes during this duration.

After an hour, carefully remove the beetroot pieces from the solution. Use a glass rod to help you fish out the pieces. Leave the remaining-coloured liquid behind.

Use a colorimeter to measure light absorbance by the liquid in each test tube.

Question 22

what is simple diffusion

Answer 22

Simple Diffusion is the net movement of particles down a concentration gradient, from a high concentration to low concentration until it reaches dynamic equilibruim

Question 23

what is dynamic equilibruim

Answer 23

Concentrations of substance in both regions are equal

Question 24

what molecules can diffuse through membrane

Answer 24

Non-polar molecules can simply diffuse across a membrane. Non-polar (lipid-based) molecules can simply pass through the phospholipid bilayer (if they are small). This is due to the hydrophobic and non-polar nature of the hydrophobic tails of the phospholipid bilayer.

Very small molecules can also simply diffuse. Very small molecules and ions (e.g. CO2) are small enough to pass through the bilayer in between the phospholipid molecules.

Question 25

what factors affect diffusion

Answer 25

concentration gradient
distance
S.A
size of molecule
temperature

Question 26

what is facilitated diffusion

Answer 26

Facilitated diffusion refers to the transport of polar molecules and ions into and out of a cell. It involves the use of carrier and channel proteins.

Question 27

what do channel and carrier proteins do in facilitated diffusion

Answer 27

The channel and carrier are structurally designed to interact with polar molecules:

Many of these channel proteins have pores that are filled with water (attract hydrophilic molecules)

Question 28

2 equations to calulate rate of diffusion

Answer 28

Distance travelled/time

Volume filled/time

Question 29

what is active transport

Answer 29

Active transport: Movement of ions and molecules into & out of cell from a region of low concentration to a region of high concentration, and requires energy and carrier proteins

Question 30

what are the steps

Answer 30

the molecule or ion to be transported binds to receptors in the channel of the carrier protein on the outside of the cell.

On the inside of the cell, ATP binds to the carrier protein and is hydrolyse into ADP and phosphate.

Binding of the phosphate molecule to the carrier protein causes the protein to change shape - opening the inside of the cell

Double the molecule or ion is released to the inside of the cell.

The phosphate molecule is released from the carrier protein and recombines with ADP to form ATP.

The carrier protein returns to its original shape.

Question 31

what is bulk transport

Answer 31

Another form of active transport where large molecules such as enzymes, hormones or bacterial cells are too large to travel through channel or carrier proteins, so they move through bulk transport

Question 32

what is endocytosis

Answer 32

is the transport of material into the cell

Question 33

what are the 2 types of endocytosis and what they do

Answer 33

Phagocytosis is for solids.

Pinocytosis is for liquid.

Question 34

what is the processes for endocytosis

Answer 34

The cell surface membrane bends inwards or invaginates when it comes into contact with the material to be transported. The membrane enfolds the material until eventually the membrane fuses and forms a vesicle. The vesicle pinches. Off and moved into. Cytoplasm to transfer the material for further processing within the cell.

Question 35

what is exocytosis

Answer 35

Is the transport of material out the cell

Question 36

what is the process

Answer 36

The vesicle formed by the Golgi apparatus move towards and fuses with the cell surface membrane. The contents of the vesicle are then released outside the cell.

Question 37

what is osmosis

Answer 37

movement of water molecules from a region of high-water potential to a region of lower water potential through a partially permeable membrane

Question 38

what is water potential

Answer 38

Water potential is the pressure exerted by water molecules as they collide with a membrane or container.

Question 39

what is isotonic

Answer 39

Isotonic is when the water potential of the solution is the same in the solution and the cell within the solution.

Question 40

what is hypertonic

Answer 40

Hypotonic is when the water potential of a solution is more positive (higher water potential) than this cell.

Question 41

what is hypotonic

Answer 41

is when the water potential of a solution is more negative (lower water potential) than itself.

Question 42

what is hydrostatic pressure

Answer 42

is the increase in pressure of a closed system due to the diffusion of water into a solution, leading to an increased volume of solution.

Question 43

what is osmosis in animal cells like

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 severe

Question 44

what happens when animal cell loses water

Answer 44

If an animal cell is placed in a solution with higher water potential than that of the cytoplasm, water will move into the cell by osmosis, increasing the hydrostatic pressure inside the cell.

All cells have them cell surface membrane around 7 nanometres and no cell wall.

The cell membrane cannot stretch much and cannot withstand the increased pressure and it will break and the cell will burst in an event called cytosis.

Question 45

what happens when animal cell loses water

Answer 45

If an animal cell is placed in a solution that has lower water potential than that of the cytoplasm, it will lose water to the solution by osmosis down the potential the water potential gradient. This will cause a reduction in the volume of the cell and the cell surface membrane to crenate

Question 46

what happens to osmosis in plant cells

Answer 46

As plant cells have a supporting cell wall, the results of this loss or gain of water on the cell are less severe than in animal cells

Question 47

what happens when a plant cell loses water

Answer 47

If a plant cell is placed in a solution with a lower water potential than the plant cell (such as a concentrated sucrose solution), water will leave the plant cell through its partially permeable cell surface membrane by osmosis

As water leaves the vacuole of the plant cell, the volume of the plant cell decreases

The protoplast gradually shrinks and no longer exerts pressure on the cell wall

As the protoplast continues to shrink, it begins to pull away from the cell wall

This process is known as plasmolysis – the plant cell is plasmolysed

Question 48

what happens when plant cell gains water

Answer 48

If a plant cell is placed in pure water or a dilute solution, 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

As water enters the vacuole of the plant cell, the volume of the plant cell increases

The expanding protoplast (living part of the cell inside the cell wall) pushes against the cell wall and pressure builds up inside the cell – the inelastic cell wall prevents the cell from bursting

The pressure created by the cell wall also stops too much water from entering and this also helps to prevent the cell from bursting

When a plant cell is fully inflated with water and has become rigid and firm, it is described as fully turgid