factors affecting membrane's structure and permeability

Question 1

what are the three factors that effect membrane’s permeability

Answer 1

-temperature
-ph
-solvent concentration

Question 2

explain what happens to the permeability of a membrane as temperature increases?

Answer 2

-at higher temperature the phospholipids have more kinetic energy so move around more within the bilayer
-this results in a increased number of gaps present between the phospholipids which in turn increases the fluidity of the bilayer
-the structure of the membrane is now disrupted
-eventually the membrane proteins denature which increases the permeability of membranes to water -soluble/polar substances

-the structure of the membrane is even further disrupted and it can no longer be restored,the effects are now irreversible

-as the membrane no longer acts as an effective barrier to polar substances,allowing them to pass though the membrane

Question 3

what happens to the permeability of a membrane with lower temperature

Answer 3

at lower temperature the phospholipids have less kinetic energy so move around the bilayer less,this decreases the number of gaps present between phospholipids and thus also decreases the fluidity ,but increases the rigidity of the membrane.

Meas that the permeability of the membrane also decreases and the membrane acts as a effective barrier to polar substances so that they cannot pass through the membrane

Question 4

is the changes in the membrane reversible after the membrane proteins denature

Answer 4

no they are not,the membrane structure is permanently disrupted

Question 5

before the membrane proteins denature are the changes to the structure of the membrane reversible?

Answer 5

yes they are reversible,as the temperature lowers the fluidity of the membrane will decrease and the membrane will restore its structure thus decreasing its permeability to polar substances

Question 6

between 0 ad 40 the membrane is described as partially permeable.True or false

Answer 6

true

Question 7

how does a low ph effect the membrane’s permeability

Answer 7

a low/high ph will change the tertiary structure of the membrane proteins causing them to denature,and thus increasing the permeability of the membrane to polar substances

Question 8

what is the general pattern between temperature and permeability of a membrane

Answer 8

when temperature increases so does the permeability of a membrane

Question 8

general pattern for solvent concentration and permeability of a membrane

Answer 8

increasing the solvent concentration increases the permeability of the membrane

Question 9

what happens to membrane protein below 0 degrees and how does that effect the permeability of a membrane

Answer 9

they deform ,disrupting the structure of the membrane and increasing its permeability

-below 0 degrees ice crystals can pierce the membrane making it highly permeable

Question 10

describe what happens to the permeability of a cell membrane with the increase of solvent concentration

Answer 10

-increasing the solvent concentration also increases the permeability of a cells membranes.

-the non-polar solvent molecules enter and stick between phospholipids, disrupting the structure of the membrane.

-This causes the membrane to become more fluid and thus permeable

-increasing the solvent concentration further will result in the non-polar solvent dissolving the phosholipids causing the membrane to lose its structure and disintigrate, killing the cell

Question 11

what happens when the neural membrane are disrupted

Answer 11

nerve impulses are no longer transmitted normally

Question 12

describe the permeability of membrane between 0-40 degrees
then after 40 degrees

and then below 0 degrees

Answer 12

0-40-partually permeable as temp increases so does the permeability of the membrane ,but permeability increases steadily

-after 40-protein denature,membrane becomes highly permeable,rapidly

-below 0 -the proteins deform ,membrane structure is disrupted so permeability increases also ice crystals may pierce the membrane

Question 12

what does the experiment on factors effecting the structure and permeability of membranes involve

Answer 12

-involves beetroot, beetroot contain a purple pigment within them

-the higher the permeability of the beetroot membrane ,the more of the pigment leaks out of the cell
-thus the higher the permeability of the beetroot’s membrane the more purple the solution will be and so will have a lower light absorbance value

Question 13

describe a method you will use to investigate the effects of temperature on the permeability of a beetroot membrane

Answer 13

-cut 5 equal sized beetroot using a scalpel,
why is that important?

ensures they are the same length and have the same dimensions so that they dont have a different SA and Volume which are factors that can affect the rate at which pigment leaks out so final results can be altered

• rinse the beetroot to remove any pigment released during the cutting
• add the beetroot pieces to 5 separate test tubes, each must contain the same volume of water

-put each test tube in a water bath set at a different temperature ,for example 10,20,20,20,50

-allow them to sit for a specific period of time-long enough to allow the pigment to diffuse out the beetroot and into the water-e,g 30 min

-Remove the beetroot from each test tube so you are left with the coloured solution

-calibrate the colourimeter and pour the leftover mixtures into 5 separate cuvettes

-insert the cuvette, ensure to recalibrate between readings

-then use the colourimeter with a blue filter to measure the light absorbance of each coloured solution

-the higher the light absorbance,the more pigment there is present in the solution so the more permeable the beetroot’s membrane is

-as temp increases the membrane permeability also increases so the light absorbance value also increases with temperature

Question 14

how can we find the light absorbance of unknown pigment concentration solution

Answer 14

have solutions of known concentration, measure their values and plot a calibration curve

-do the same for the unknown solution and draw intercept to find the light absorbance of it

Question 14

how can we investigate how solvent concentration affects the permeability of a membrane

Answer 14

-do the same experiment like for temperature,but instead placing the beetroot pieces in water baths at different temperature

-we will place them in 5 test tubes,each with an increasing concentration of solvent for a set amount of time

-the rest of the experiment is the same

Question 15

what are some limitations of the experiment and how do you solve them

Answer 15

-beetroot pieces may not be the same size so some test tubes may contain more beetroot tissue than others

solution: cut them as accurately as possible using a scalpel and a ruler, and repeat each investigation at least 3 times and find a mean

• some parts of the beetroot tissue have more pigment in their cells than others

Solution: conduct repeats using different parts of the beetroot and find a mean

Question 16

why do the beetroot pieces get washed in running water

Answer 16

to remove all surface pigment released from damaged cells

Question 17

suggest why samples of water containing the beetroot were taken five minutes after each temperature was reached

Answer 17

b to allow the mixture to equilibrate

Question 18

suggest why the experiment was repeated 3 times

Answer 18

allows for reliability

Question 19

suggest why the absorbance of the samples was measured using a colorimeter with a blue filter

Answer 19

because the pigment released is red/purple

Question 20

suggest how and explain why the absorbance would change as the amount of pigment increases

Answer 20

higher concentration means there are more pigment molecules. They can absorb more light so light transmitted decreases

Question 21

explain why solvents like water do not disrupt cell membranes

Answer 21

water is a polar solvent (1); phospholipids will not dissolve in water (1)

Question 22

describe how the absorbance of light could be measured as the pigment released increases with temperature

Answer 22

use of colorimeter (1); detail (e.g., use of filter) (1); range of readings taken (at different
temperatures) (1); draw a graph (1)

Question 23

Suggest how an excessive consumption of alcohol lead to liver cell death and ultimately be fatal

Answer 23

• Alcohol is lipid soluble
  -it dissolves in the membrane bilayer
  -this disrupts the bilayer

-and reduces transport of material

-prevents normal functioning and may lead to cell death
- The liver is particularly affected due to its role in filtering substances from the blood

Question 24

what happens to channel and carrier proteins in cell membranes below 0 degrees

Answer 24

they deform increasing the permeability of the membrane

Question 25

explain why a specific hormone only has an effect on specific cells,not the entire body

Answer 25

-hormones bind to receptors that have a complementary shape to theirs.
-Only target cells have the right receptors whereas other body cells do not

Question 25

example of a messenger molecule in the body

Answer 25

-any hormones ,they bind to complementary receptors causing a reaction