Biological membranes

Question 1

What is the function of Phospholipids

Answer 1

Hydrophilic, polar phosphate head on the outside
Hydrophobic, non-polar fatty acid tails on the inside
Form a bilayer.
Selectively permeable - allows non-polar molecules to pass through
Allows cell to maintain different concentrations either side
Membranes are able to form vesicles
Provides fluidity

Question 2

Structure and function of Glycoprotein

Answer 2

Carbohydrate chain attached to protein
Important in cell recognition
So that the immune system can tell the difference between body cells & e.g. invading bacteria.

Question 3

Structure and function of Glycolipid

Answer 3

Carbohydrate chain attached to phospholipid
For cell recognition and to provide energy.

Question 4

Function of Extrinsic protein

Answer 4

Receptor sites for hormones. Detect chemicals released form other cells. For cell recognition.

Question 5

Function of Cholesterol

Answer 5

Cholesterol increases fluidity/ rigidity by reducing movement of other molecules in the membrane.

Question 6

Function of Transport Protein

Answer 6

Can be carrier proteins or channel proteins
The channel proteins create selective hydrophilic pores (for water + water soluble compounds).
Carrier proteins are involved in facilitated diffusion and active transport.
Channel proteins are only used for facilitated diffusion.

Question 7

Why is the plasma membrane referred to as being fluid-mosaic?

Answer 7

Molecules within the membrane able to move (fluid)
Mixture of phospholipid and protein (mosaic)

Question 8

How does the bilayer formed by phospholipids affect entry and exit of substances into and out of a cell?

Answer 8

allows movement of small, lipid soluble, non-polar molecules such as gases through the membrane
prevents movement of large, water soluble, polar molecules such as ions and amino acids
The membrane is selective and partially permeable

Question 9

Define diffusion

Answer 9

Diffusion is a passive process.
It is the movement of substances from an area of high concentration, to an area of low concentration, down a concentration gradient.

Question 10

Where can diffusion take place?

Answer 10

Diffusion can occur from one area to another or across a partially permeable membrane

Question 11

Which substances can simply diffuse across the phospholipid bilayer?

Answer 11

Small, non-polar, non-charged, lipid soluble molecules can diffuse across the phospholipid bilayer

Question 12

Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes.

Answer 12

The hydrophobic fatty acid part of membrane is non-polar
Oxygen and carbon dioxide are small non-polar molecules;
Oxygen/carbon dioxide can diffuse through the fatty acid layer
Down a concentration gradient

Question 13

Which factors increase the rate of diffusion and why?

Answer 13

High concentration gradient
Increase the temperature
Increase the surface area
Increase the pressure
Decrease the diffusion pathway (reduce membrane width)

Question 14

Write the equation for Fick’s law:

Answer 14

Rate of diffusion ∝ concentration gradient x surface area
Diffusion pathway

Question 15

Define the process of facilitated diffusion

Answer 15

The movement of substances from high concentration to a low concentration, down a concentration gradient, through a channel or carrier protein.

Question 16

What sorts of substances are transported using facilitated diffusion? Why? Examples?

Answer 16

It is used for substances which are large, polar, charged or water-soluble
The fatty acid layer of the plasma membrane is hydrophobic and non polar it will not allow polar substances to diffuse though
Ions, amino acids

Question 17

Is it channel proteins, carrier proteins or both that Selectively transports substances across a membrane (specific)

Answer 17

both

Question 18

Is it channel proteins, carrier proteins or both that The protein forms a pore which does not change shape when a substance travels through it

Answer 18

channel

Question 19

Is it channel proteins, carrier proteins or both that The substance to be transported binds to one side of the protein, this causes it to change shape, so the substance is released on the other side of the membrane

Answer 19

carrier

Question 20

Is it channel proteins, carrier proteins or both that Is made of a polypeptide

Answer 20

both

Question 21

Is it channel proteins, carrier proteins or both that Can be used for facilitated diffusion

Answer 21

both

Question 22

Is it channel proteins, carrier proteins or both that Can be used for active transport

Answer 22

carrier

Question 23

What could limit the rate of facilitated diffusion?

Answer 23

The number of transport proteins available in the membrane
the concentration gradient
the surface area

Question 24

Define the process of active transport

Answer 24

Active transport is an active process, it requires energy (which comes from ATP)
It is the movement of a substance from a low concentration to a high concentration, against the concentration gradient
It requires ATP which binds to a carrier protein and enables it to change shape.

Question 25

How does active transport move substances against their concentration gradient?

Answer 25

Substance binds to a carrier protein
ATP binds to carrier protein
ATP is converted to ADP and releases energy
This causes the carrier protein to change shape
The substance is released on the other side of the membrane

Question 26

What could limit the rate of active transport?

Answer 26

The number of carrier proteins
The amount of oxygen available for respiration. (this affects the amount of ATP available)
Very High temperature – if the temperature is high it could denature enzymes involved in respiration so ATP cannot be produced.
If the temperature is moderately high 🡪increased rate of active transport 🡪 as molecules have more kinetic energy 🡪 increased rate of respiration 🡪 more ATP ALSO more collisions between carrier proteins and substance to be transported

Question 27

Give two ways in which active transport differs from diffusion? (you can simply state the differences)

Answer 27

In active transport ATP is used;
and movement is against a concentration gradient

Question 28

Contrast the processes of facilitated diffusion and active transport. (you must write comparisons here)

Answer 28

Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins;
Facilitated diffusion does not use ATP whereas active transport uses ATP;
Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.
Since ‘contrast’, both sides of the differences needed

Question 29

Write a definition of osmosis:

Answer 29

The net movement of water from an area of high water potential to an area of lower water potential through a partially permeable membrane

Question 30

What is the water potential of pure water?

Answer 30

0

Question 31

What happens to the water potential of a solution if more solute is added?

Answer 31

It decreases (becomes more negative)

Question 32

What does it mean if 2 solutions are isotonic?

Answer 32

They have the same water potential

Question 33

When investigating diffusion or osmosis, you might want to make solutions of different concentrations. What is this called?

Answer 33

A dilution series

Question 34

Vegetables are made of different types of tissue, in an experiment where do you take a cutting from and why?

Answer 34

When taking a cutting you must ensure it’s through one tissue only in order for it to be a fair test. As different tissues may affect water potential differently.

Question 35

Why are bungs are placed on test tubes when conducting an experiment overnight?

Answer 35

To stop water from evaporating and therefore changing the water potential of the solution.

Question 36

When you need to find the concentration of the solution that has the SAME water potential as the vegetable/fruit you are investigating you:

Answer 36

Plot data on a graph (give titles of the x and y axis)
Draw a line of best fit
From the graph either: (depending on question)
Find when the ratio is 1 (there is no change in mass/length)
extrapolate the line of best fit and read off
Find where it crosses the x axis

Question 37

Ratio’s or % change in mass are calculated to

Answer 37

allow a valid comparison when the initial length/mass is not the same.

Question 38

Take additional readings/repeat experiments to

Answer 38

identify any anomalies and calculate a mean

Question 39

A graph can be improved if you take additional readings because

Answer 39

your line of best fit will be more reliable
AND - depending on question - where the point crosses the x axis is more precise –

Question 40

Join dot to dot when

Answer 40

you cannot predict intermediate values

Question 41

Summarise how the products of carbohydrate digestion or the products of protein digestion are absorbed

Answer 41

Na+/K+ pump moves 3 Na+ ions out of the cell (into the blood) and 2K+ ions into the cell by active transport. This uses ATP.
This creates a lower concentration of Na+ in the epithelial cell than in the lumen of the intestine
Na+ ions move into the epithelial cell by facilitated diffusion. They travel through a symport protein and bring glucose with them. This is called co-transport.
The glucose is moving into the cell cell against its concentration gradient
The glucose concentration in the epithelial cell increases
Glucose moves into the blood from the epithelial cell through a carrier protein by facilitated diffusion.

Question 42

Adaptations of the epithelial cell

Answer 42

Lots of mitochondria 🡪 Release energy in the form of ATP 🡪 ATP is needed for active transport
Lots of enzymes attached to their membrane 🡪 Breaks down maltose into glucose
Microvilli 🡪 provide a large surface area for maximum absorption
Carrier proteins for active transport
Channel/Carrier proteins for facilitated diffusion
Co-transport (or symport protein for the transport) of sodium ions and glucose or for sodium ions and amino acids

Question 43

What is co-transport?

Answer 43

When a transport protein transports more than one substance at the same time

Question 44

What is a symport protein?

Answer 44

A type of cotransport protein.
A symport protein transports two substances through the membrane in the same direction together (like the Na+/glucose symport protein

Question 45

What is an anti-port protein?

Answer 45

A type of cotransport protein.
An antiport protein transports two substances through the membrane in the opposite directions (e.g. the Na+/K+ pump)