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A- Level Biology > C4- Plasma Membranes > Flashcards

C4- Plasma Membranes Flashcards

1
Q

4 functions of membranes

A

Site of chemical reactions

Partially permeable barrier

Cell communication

Compartmentalisation
–> not plasma/ cell surface membranes

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2
Q

Compartmentalisation

A

The formation of separate membrane bound areas in a cell

Allows for specific conditions required for cellular reactions

maintains chemical gradients

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3
Q

Membrane general structure

A

Phospholipid bilayer

hydrophilic heads form inner and outer surfaces of the membranes

Fatty acid tails form the core

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4
Q

Fluid mosaic model

A

Phospholipids are free to move within the layer, giving it flexibility

Proteins in the layer form a mosaic like pattern

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5
Q

Extrinsic protiens

A

embedded on one side of the bilayer or between layers

hydrophobic R group interacts with the hydrophilic heads

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6
Q

Cholesterol

Membranes

A

Extrinsic protein

Regulates fluidity of membranes
–> adds stability to membranes without making them too rigid

Positioned between phospholipids

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7
Q

intrinsic proteins

with example

A

Transmembrane proteins embedded in both layers of proteins

channel and carrier proteins

Glycoproteins- used for cell signalling

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8
Q

Channel vs carrier protiens

A

channel= allows passive movement of polar molecules and ions down a concentration gradient though membranes

carrier proteins= move against the concentration gradient
–> both passive and active transport

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9
Q

membranes

Site of chemical reactions

A

membranes have to be in a particular position for chemical reactions to take place

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10
Q

What happens when a membrane looses its structure

A

If they loose their structure, the cell’s processes will be disrupted

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11
Q

Effect of high temperature on membranes

A

increased kinetic energy

Membrane become more fluid and looses its structure.
–> increasing its permeability

Carrier and channel proteins denature

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12
Q

Effect of Solvent on membranes

water

A

water is polar and keeps bilayer intact

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13
Q

Effect of alcohol on membranes

general, strong conc, weak conc

A

Less polar than water so can dissolve membranes, disrupting cells

Strong concentrations
–> dissolves membranes of bacterium
destroy cells in the body

less concentrated
–>alcohol enters the membrane but cannot dissolve it

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14
Q

Diffusion

A

Passive net movement of particles from a high concentration to a low concentration, down a concentration gradient

Will continue to equilibrium

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15
Q

Factors affecting rate of diffusion

A

Temperature
–> higher temp means particles have more kinetic energy

Concentration difference
–> greater difference= greater rate

Across membranes
- surface area, greater sa greater rate
- thickness of membrane, thin = greater rate

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16
Q

Simple diffusion

A

Diffusion in the absence of a membrane or barrier

17
Q

Facilitated diffusion

A

Diffusion across a membrane using protein channels

Selective permeability

18
Q

The effect of temperature on membrane permeability PAG

Method

A

Beetroot PAG

Using a scalpel, cut five equal-sized cubes of beetroot

Rinse the beetroot pieces

Add the beetroot pieces to five different test tubes, each containing the same volume of distilled water

Put each test tube in a water bath at a different temperature (e.g. 10℃, 20℃, 30℃, 40℃, 50℃) for the same length of time

Remove the beetroot pieces, leaving just the coloured liquid in the five test tubes

Use a colorimeter to measure how much light is absorbed as it passes through each of the five samples of coloured liquid
–> higher the value, greater absorbance so more colour/pigment

19
Q

The effect of temperature on membrane permeability PAG

Limitations

A

Cuvettes may differ in thickness (very slightly). A thicker (or scratched) cuvette will absorb slightly more light than a thinner unscratched cuvette

The beetroot pieces may not be identical in size and shape, meaning some test tubes could contain slightly more beetroot tissue than others

Some parts of beetroot tissue have more pigment in their cells than others

20
Q

Active transport

A

The movement of molecules or ions into or out of a cell against the concentration gradient

Active process that requires energy provided by ATP and carrier proteins

Selective process- specific substances transported by specific carrier proteins

21
Q

Active transport

Process

A

Shape of carrier protein is complimentary to molecule they can carry

One way flow can only fit into carrier protein on one side of the membrane

Molecule binds

ATP binds to carrier protein inside cells

ATP- ADP which changes shape of a protein

Molecule transported across membranes

Phosphate detached and =recombines with ADP
–> protein reverts back original shape

22
Q

Why do cells performing active transport contain numerous mitochondria

A

To generate lots of ATP in aerobic respiration

23
Q

Why can glucose not pass through membrane by passive diffusion

A

Large molecule

therefore phospholipid bilayer acts as a barrier

24
Q

Water Potential

A

The pressure exerted by water as they collide with a membrane or container

The greater the amount of water (the more dilute the solution) the greater the water potential

25
Q

Water potential

Values

A

pure water = 0kpa
–> highest possible value

All solutions have negative water potential, the more concentrated the solution the more negative the water potential

26
Q

Hydrostatic pressure

A

Increased pressure in a closed system such as a cell, due to diffusion of water.

27
Q

Animal cell in different water concentrations

A

Hypotonic= cytolysis

isotonic= normal

Hypertonic= crenated

28
Q

Plant cell in different water concentrations

A

Hypotonic= turgid

isotonic= flaccid

Hypertonic= plasmolysis
–> cell membrane pulls away from cell wall, which keeps its structure. Solution fills the gaps made

29
Q

Osmosis

A

Osmosis is the net movement of water molecules through a partially-permeable membrane, from a region of high water potential to a region of low water potential.

30
Q

Roles of proteins in a cell surface membrane

A

glycoproteins- cell signalling and adhesion

channel proteins- transport by facilitated diffusion;

carrier proteins- active transport

31
Q

Membrane permeability PAG

Why was it reliable and valid

A

valid- use the same beetroot, use cubes of the same size, same volume of water

Reliable- repeat (at least) three times at each temperature, identify anomalies, calculate mean

32
Q

Explain why rate of diffusion increases as temperature increases

A

Increased temperature increases the kinetic energy of particles

causing the particles to move at an increased speed

33
Q

State two changes to a cell surface membrane that would increase the rate that polar molecules diffuse into a cell

A

Increased surface area

Decreased thickness

34
Q

Explain why facilitated diffusion is not a form of active transport

A

Diffusion is always a passive process, it does not require a metabolic energy source

particle shave their own kinetic energy, moving down the concentration gradient

In facilitated diffusion a channel/co-transport protein aids diffusion

35
Q

Why is it impossible to have a water potential above zero

A

The water potential of pure water is zero

addition of solute decreases water potential

therefore all solutions have negative water potential.

36
Q

Explain why its important to maintain concentration of electrolytes in the body to ensure proper hydration

A

Electrolytes/solutes/minerals are necessary for many body processes

and help prevent excess water loss by osmosis

To help maintain correct fluid balance for reactions

37
Q

Explain why glucose cannot pass through a cell membrane by simple diffusion

A

Phospholipids act as a barrier

Molecule is too large

Polar molecule due to polar OH groups- insoluble in bilayer

38
Q

Bulk transport

A

Movement of large molecules such as enzymes or hormones in or out of the cell

Exocytosis

Endocytosis

39
Q

Co transport

A

transport of one soluté against its concentration gradient in tandem with another that is diffusing down it’s concentration gradient

e. g H+ ions active transport via Proton pump alongside diffusion of sucrose

A- Level Biology (7 decks)

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