2B | Cell Membranes

Question 1

What is a cell-surface membrane?

Answer 1

Cell-surface membranes are partially permeable barriers between the cell and its environment, controlling which substances enter and leave the cell.

Question 2

How can a substance enter the cell-surface membrane?

Answer 2

A substance can enter the cell-surface membrane by diffusion, osmosis or active transport.

Question 3

Cell membranes have a structure named as what?

Answer 3

Fluid-Mosaic

Question 4

The Cell Membrane’s structure is described as ‘Fluid-Mosaic’.

Describe why it is considered fluid.

Answer 4

The cell membrane is ‘fluid’ as the phospholipids which form a bilayer are constantly moving.

Question 5

In a cell surface membrane, where is Cholesterol located?

Answer 5

Cholesterol molecules are present within the bilayer.

Question 6

The Cell Membrane’s structure is described as ‘Fluid-Mosaic’.

Describe why it is considered mosaic.

Answer 6

The cell membrane is ‘mosaic’ as the proteins present in the cell membrane’s phospholipid bilayer are scattered through it, like tiles in a mosaic.

Question 7

Give 2 types of proteins present on a Cell Membrane.

Answer 7

Extrinsic Protein

Intrinsic Protein

Question 8

What is an Extrinsic Protein?

Answer 8

Extrinsic proteins are proteins that are confined to the inner or outer surface of the cell membrane - they do not span the entire length of the membrane.

Question 9

What is an Intrinsic Protein? Give 1 example.

Answer 9

intrinsic proteins are proteins that are present on cell membranes which span the entire length of the cell membrane.

As a result, carrier and channel proteins are seen as intrinsic.

Question 10

What is a channel protein?

Answer 10

Channel proteins are intrinsic proteins present on the cell surface membrane which allow ions. which are water-soluble, to pass through the membrane.

Question 11

What is a carrier protein?

Answer 11

Carrier proteins are intrinsic proteins present on the cell surface membrane which allow large molecules, such as glucose, to pass through the membrane.

Question 12

Why can’t a large molecule like glucose pass directly through the cell surface membrane?

Answer 12

It is too large to travel through the phospholipid bilayer.

Question 13

Why can’t an ion pass directly through the cell surface membrane?

Answer 13

Ions are water-soluble, and as a result, they are not able to pass through the phospholipid bilayer as the fatty acid tails which are found past the glycerol molecules are hydrophobic - they repel water.

Question 14

Water soluble molecules must go through the cell membrane by what process?

Answer 14

Facilitated diffusion

Question 15

How do Ions and other water soluble molecules pass through the cell surface membrane?

Answer 15

Ions and other water soluble molecules pass through the cell membrane through facilitated diffusion with the help of a channel protein.

Question 16

Large molecules must go through the cell membrane by what process?

Answer 16

Facilitated diffusion

Question 17

How do large molecules pass through the cell surface membrane?

Answer 17

Large molecules, like glucose, are too large to fit through the phospholipid bilayer and as a result they must go through the cell surface membrane by a process called facilitated diffusion through a carrier protein.

Question 18

Cell membranes have receptor proteins.

Name each one.

Answer 18

Glycolipid

Glycoprotein

Question 19

What is the function of receptor proteins on cell membranes?

Answer 19

Receptor proteins on the cell surface membrane allow the cell to detect chemicals released from other cells.

The chemicals signal to the cell to respond in some way, for example, the hormone insulin binds to receptor proteins on liver cells to tell them to absorb glucose.

Question 20

Some proteins have a polysaccharide chain attached. What are they called?

Answer 20

Glycoproteins

Question 21

Some lipids have a polysaccharide chain attached.

What are they called?

Answer 21

Glycolipids

Question 22

What is a Glycoprotein?

Answer 22

A glycoprotein is a receptor protein that is present on the surface of cell surface membranes. It is a protein that has a polysaccharide chain attached.

Question 23

What is a glycolipid?

Answer 23

A glycolipid is a receptor protein that is present on the surface of cell surface membranes. It is a lipid that has a polysaccharide chain attached.

Question 24

Label A to F:

https://media.discordapp.net/attachments/352951793187029005/828707346380357642/unknown.png

Answer 24

A = Extrinsic protein
B = cholesterol 
C = Intrinsic protein
D = Phospholipid Bilayer
E = Glycolipid
D = Glycoprotein

Question 25

Describe the structure of the phospholipid bilayer.

Answer 25

Phospholipids form a barrier to dissolved substances, as a bilayer.

Phospholipid molecules have a head and a tail.

Phospholipid heads are hydrophilic - they attract water (due to the phosphate group).
Phospholipid tails are hydrophobic - they repel water.

The molecules automatically arrange themselves into a bilayer - the heads face out towards the water on either side of the membrane.

Question 26

Describe and explain the function of the phospholipid bilayer.

Answer 26

The phospholipid bilayer has a head that is hydrophilic, which attracts water, and tails which are hydrophobic, which repel water.

The molecules automatically arrange themselves where their heads face towards the presence of water in either side of the membrane, causing the fatty acid tails to be protected on the inside from water.

The center of the bilayer, as a result, is hydrophobic, so the membrane doesn’t allow water soluble substances like ions through it - this means that the phospholipid bilayer acts as a barrier to certain substances.

As a result, the phospholipid bilayer’s function in the cell membrane is to act as a barrier to certain substances, like water-soluble molecules such as ions and large molecules such as glucose in order to make the cell membrane partially permeable.

Question 27

What type of biological molecule is Cholesterol?

Answer 27

Lipid

Question 28

Describe why cholesterol is important for the function of the cell surface membrane.

Answer 28

Cholesterol’s function in cell membranes are extremely important to maintain the efficiency and function of plasma membranes.

Cholesterol is a lipid that is found between the fatty acid tails of the phospholipid bilayer, wherein they have the ability to pack the phospholipids closer together, making them more rigid and less fluid.

Cholesterol helps to maintain the shape of animal cells, which don’t have cell walls. This is particularly important for cells that aren’t supported by other cells e.g. red blood cells which float free in the blood.

Question 29

Describe in detail where Cholesterol is located in the cell surface membrane.

Answer 29

Cholesterol membranes fit between the phospholipids.

They bind to the hydrophobic fatty tails of the phospholipids, causing them to pack more closely together. This restricts the movement of the phospholipids, making the membrane less fluid and more rigid.

Question 30

Describe the practical process required to investigate the permeability of the cell membrane at different levels of temperature.

Answer 30

Use a scalpel to carefully cut five equal-sized pieces of beetroot. Make sure you do your cutting on a cutting board.

Rinse the pieces to remove any pigment released during cutting.

Add the five pieces to five different test tubes, each containing 5cm^3 of water. Use a measuring cylinder or pipette to measure the water.

Place each test tube into a water bath at different temperatures, e.g. 10,20,30,40 and 50 Celsius, for the same length of time (measured using a stopwatch).

Remove the pieces of beetroot from the tubes when the time is over, leaving just the colored liquid.

Now you need to use a colorimeter - a machine that passes light through the liquid and measures how much of that light is absorbed. The higher the absorbance, the more pigment released, so the higher the permeability of the membrane.

Question 31

Is the correlation between temperature and membrane permeability negative?

Answer 31

Yes

Question 32

Describe A, B and C:

https://media.discordapp.net/attachments/352951793187029005/828720400266428416/unknown.png?width=740&height=564

Answer 32

At A, where temperatures are below 0 Celsius, the phospholipids don’t have much energy, so they can’t move very much. They are packed closely together and the membrane is rigid. But channel proteins and carrier proteins in the membrane deform, increasing the permeability of the membrane.

As well as this, ice crystals may form and pierce the membrane making it highly permeable when it thaws.

At B, the phospholipids can move around and aren’t packed as tightly together - the membrane is partially permeable. As the temperature increases, the phospholipids move more because they have more energy - this increases the permeability of the membrane.

At C, the phospholipid bilayer starts to melt (break down) and the membrane becomes more permeable. Water inside the cell expands, putting pressure on the membrane. Channel proteins and carrier proteins deform so they can’t control what enters or leaves the cell - this increases the permeability of the membrane.

Question 33

The table linked shows the results of an investigation into the effect of alcohol concentration on the permeability of beetroot cell membranes:

Suggest a suitable method that could have been used to obtain these results.

Answer 33

Firstly, use a scalpel to carefully cut 5 equally sized pieces of beetroot on a cutting board.

Rinse all of them to get rid of any excess pigment released during cutting.

Add the 5 pieces to 5 different test tubes at the same time, each containing a solution with a % concentration of alcohol, 0%,25%,50%,75% and 100%. Each test tube must have the same amount of solution, ideally 5cm^3.

Every single beetroot piece must be in the solution for the same amount of time, so a stopwatch should be used and when the stopwatch ends, remove all pieces of beetroot from the tubes, leaving just the colored liquid.

Now use a colorimeter. Put a portion of each solution into separate cuvettes, so you have 5 with different concentrations of alcohol.

Put each cuvette into the colorimeter one at a time and record the absorption recorded as well as the % alcohol solution used. The higher the absorption, the higher the permeability of the membrane as more pigment has been released from the beetroot.

Question 34

Give 3 molecules that are present in animal cell membranes.

Answer 34

Cholesterol
Intrinsic protein (channel & carrier proteins)
Glycolipid
Glycoprotein
Phospholipid

Question 35

Explain why the plasma membrane can be described as having a fluid mosaic structure.

Answer 35

The proteins present on the plasma membrane are scattered throughout the membrane randomly, just like tiles on a mosaic.

The phospholipids in the bilayer is always moving, thus giving the cell membrane a fluid like motion.

Question 36

What is Diffusion?

Answer 36

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.

Question 37

How does a concentration gradient occur?

Answer 37

A concentration gradient occurs when the concentration of particles is higher in one area than another

Question 38

In diffusion, do particles with down against up a concentration gradient?

Answer 38

With (Down the concentration gradient), as particles go from higher to lower

Question 39

In osmosis, do particles go with or against a concentration gradient?

Answer 39

With (Down the concentration gradient), as water particles go from higher to lower

Question 40

In active transport, do particles with for or against a concentration gradient?

Answer 40

Against (Up the concentration gradient), as particles go from lower to higher

Question 41

Is diffusion passive?

Answer 41

Yes

Question 42

What does it mean when a process is ‘passive’?

Answer 42

Energy is not required.

Question 43

Why can oxygen and carbon dioxide diffuse freely through the cell membrane by simple diffusion?

Answer 43

They are small, meaning they can pass through spaces between the phospholipids.

They are also non-polar, meaning they are soluble in lipids, so they can dissolve in the hydrophobic bilayer.

Question 44

Why may a particle pass through the plasma membrane when it’s non-polar?

Answer 44

A particle being non-polar means it is soluble in lipids, so they can dissolve in the hydrophobic bilayer.

This may mean they are able to pass through the plasma membrane.

Question 45

When molecules diffuse directly through a cell membrane, what’s it known as?

Answer 45

Simple diffusion

Question 46

What does facilitated diffusion rely on the usage of?

Answer 46

Carrier proteins and channel proteins

Question 47

Why do some larger molecules like amino acids and glucose not pass through the plasma membrane by simple diffusion?

Answer 47

Glucose and amino acids would diffuse extremely slowly through the phospholipid bilayer due to the fact they’re very big, thus it is inconvenient for them to pass through by simple diffusion.

Question 48

Why are some charged particles (ions) and polar molecules not able to pass the plasma membrane by simple diffusion?

Answer 48

Charged ions like ions and polar molecules would diffuse slowly - that’s because they’re water soluble, and the center of the bilayer is hydrophobic and so the fatty acid tails would repel them, stopping them from passing the cell surface membrane.

Question 49

What process allows ions and polar molecules to pass through the plasma membrane?

Answer 49

Facilitated Diffusion

Question 50

Is facilitated diffusion active?

Answer 50

No - it is passive

Question 51

What is facilitated diffusion?

Answer 51

Facilitated diffusion is the net movement of particles across the cell membrane via the aid of a protein, down the concentration gradient.

Question 52

What do carrier proteins do?

Answer 52

Carrier proteins move large molecules across membranes, down their concentration gradient.

Question 53

Describe how carrier proteins allow large molecules to pass through the plasma membrane.

Answer 53

Firstly, a large molecule attaches to a carrier protein in the membrane.

Then, the carrier protein changes shape, to release the molecule on the opposite side of the membrane, down the concentration gradient.

Question 54

What do channel proteins do?

Answer 54

Channel proteins move ions and polar molecules across membranes, down their concentration gradient.

Question 55

Describe how channel proteins allow ions or polar molecules to pass through the plasma membrane.

Answer 55

Channel proteins form pores in the membrane for charged particles to diffuse through down their concentration gradient.

Different channel proteins facilitate the diffusion of different charged particles.

A charged molecule will enter the channel protein and travel down the channel protein, reaching the opposite side of the plasma membrane, down the concentration gradient.

Question 56

Give 3 things that the rate of simple diffusion is affected by.

Answer 56

The concentration gradient - the higher it is, the faster the rate of diffusion.

The thickness of the exchange surface - the thinner the exchange surface, the shorter the distance the particles have to travel which increase the rate of diffusion.

The surface area - the larger the surface area, the faster the rate of diffusion.

Question 57

The walls of the small intestine have lots of finger-like projections. What is this called?

Answer 57

Villi

Question 58

The epithelial cells on the surface of the villi have folds in their cell-surface membranes. What is this called?

Answer 58

Microvilli

Question 59

Describe why the use of microscopic finger like projections formed by the cell surface membrane folding up on itself on the villi increases the rate of diffusion.

Also, name what has been described.

Answer 59

These are called ‘Microvilli’ and they increase the surface area of the villi in the small intestine. This means that the rate of diffusion increases as there are more surfaces for particles to interact with at one time.

Microvilli

Question 60

Give 2 things that affects the rate of facilitated diffusion.

Answer 60

The concentration gradient - the higher the concentration gradient, the faster the rate of facilitated diffusion (UP to a point).

The number of channel or carrier proteins - once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, even if you increase the concentration gradient. So, the greater the number of channel or carrier proteins in the cell membrane, the faster the rate of facilitated diffusion.

Question 61

Describe why increasing concentration gradient eventually won’t increase the rate of reaction in facilitated diffusion.

Answer 61

This is because all channel and carrier proteins are in use and so they become a limiting factor to any further increase in rate of reaction - it doesn’t matter how much more you increase the concentration gradient.

Question 62

Chloride ions are transported into a cell across its cell surface membrane by facilitated diffusion.

Chloride ions in the cell are not immediately used up. Describe and explain what will happen to the rate of facilitated diffusion of the chloride ions into the cell over time.

Answer 62

Over time, the rate of facilitated diffusion will decrease. and eventually flatten off.

This is because the concentration gradient between the environment and the cell will decrease as less chloride ions are found in the environment until the concentration in both the cell and environment are the same wherein it flattens off (reaches equilibrium).

Question 63

An individual puts some powder in water.

Imagine the powder in the water - is this osmosis or diffusion?

Answer 63

Diffusion - there’s no partially permeable membrane.

Question 64

What is Osmosis?

Answer 64

Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential (down the water potential gradient).

Question 65

If two solutions have the same water potential, what is this known as?

Answer 65

Isotonic

Question 66

Outline 2 factors that affect the rate of osmosis.

Answer 66

The water potential gradient - the higher the water potential gradient, the faster the rate of osmosis.

The thickness of the exchange surface - the thinner the exchange surface (the partially permeable membrane), the faster the rate of osmosis.

The surface area of the exchange surface - if surface area is high in the exchange surface, the faster the rate of osmosis.

Question 67

An individual has 5 test tubes - they want to make up several solutions of different, known concentrations in each.

He has a jar that has a solution of 2M sucrose concentration.

Describe and explain the technique to doing this and what it is called.

Answer 67

This is known as serial dilutions.

Firstly, get 5 test tubes on a rack.

Put 10cm^3 of 2M sucrose solution into test tube 1.

Put 5cm^3 of distilled water into test tube 2,3,4 and 5.

Draw 5cm^3 of 2m sucrose solution out of test tube 1 by a pipette and add it to test tube 2.

Mix thoroughly. You now have test tube 1 with 2m sucrose solution and test tube 2 with 1m sucrose solution.

Draw 5cm^3 of 1m sucrose solution out of test tube 2 by a pipette and put it into test tube 3.

Mix thoroughly. You now have test tube 2 with 1m sucrose solution and test tube 3 with 0.5.

Repeat this for test tube 4 and 5 to get concentrations of 0.25 and 0.125M sucrose solution.

Question 68

Describe how you will make several solutions of different, known concentrations of Glucose in 5 test tubes.

Your initial concentration is 2M glucose solution in a jar.

Answer 68

Firstly, get 5 test tubes on a rack.

Put 10cm^3 of 2M glucose solution into test tube 1.

Put 5cm^3 of distilled water into test tube 2,3,4 and 5.

Draw 5cm^3 of 2m glucose solution out of test tube 1 by a pipette and add it to test tube 2.

Mix thoroughly. You now have test tube 1 with 2m glucose solution and test tube 2 with 1m glucose solution.

Draw 5cm^3 of 1m glucose solution out of test tube 2 by a pipette and put it into test tube 3.

Mix thoroughly. You now have test tube 2 with 1m glucose solution and test tube 3 with 0.5.

Repeat this for test tube 4 and 5 to get concentrations of 0.25 and 0.125M glucose solution.

Question 69

Someone carries out serial dilutions.

The concentrations they get in each test tube are 2M,1M,0.5M,0.25M and 0.125M.

What is the dilution factor?

Answer 69

2

This is because:

2/2 = 1
1 / 2 = 0.5
0.5 / 2 = 0.25
0.25 / 2 = 0.125

We’re dividing by 2 each time - each solution is 2x weaker than the last one

Question 70

https://media.discordapp.net/attachments/352951793187029005/829074964107755590/unknown.png

Which one is simple diffusion?
Which one is facilitated diffusion?

Answer 70

Green = Simple
Red = Facilitated

Question 71

This graph shows the affect concentration has on the rate of uptake:

https://media.discordapp.net/attachments/352951793187029005/829074964107755590/unknown.png

Red = Facilitated
Green = Simple

Explain the curves presented.

Answer 71

Firstly, the green curve (which shows simple diffusion) is constant due to the fact that an increase in concentration will always increase the rate of uptake - it never flattens off, as there is always extra space for the diffusion of more particles, as this is simple diffusion - no proteins are needed.

On the red curve, which shows facilitated diffusion, we can see that initially the curve is increasing at a constant rate as the proteins that facilitate the diffusion are not yet a limiting factor - not all of them are occupied, so each increase in concentration does increase the rate of uptake.

However, it flattens off due to the fact that all proteins end up occupied - they end up as a limiting factor and now any increase in concentration will not increase the rate of uptake as the uptake is limited due to the limited amount of carrier and channel proteins present.

Question 72

Pieces of potato of equal mass were put into different concentrations of sucrose solution for 24 hours.

The difference in mass for each is recorded in the table:

https://media.discordapp.net/attachments/352951793187029005/840717369524748338/unknown.png

Explain why the pieces of potato in 1% and 2% sucrose solution gained mass.

Answer 72

The pieces of potato in the 1% and 2% sucrose solution gained mass due to the fact that the water potential in the solution is greater then the water potential in the potato.

As a result of this, the net movement of water molecules through a partially permeable membrane will overall be towards the potato, as there is a movement of water molecules from higher water potential to lower water potential.

Question 73

Pieces of potato of equal mass were put into different concentrations of sucrose solution for 24 hours.

The difference in mass for each is recorded in the table:

https://media.discordapp.net/attachments/352951793187029005/840717369524748338/unknown.png

Suggest a reason why the mass of the piece of potato in 3% sucrose solution stayed the same.

Answer 73

The solution is isotonic the potato, meaning that they have the same water potential.

This means that the net movement of molecules is towards neither as the water potential is equal between them, thus the potato does not gain or lose mass.

Question 74

Pieces of potato of equal mass were put into different concentrations of sucrose solution for 24 hours.

The difference in mass for each is recorded in the table:

https://media.discordapp.net/attachments/352951793187029005/840717369524748338/unknown.png

What would you expect the mass difference for a potato in a 5% solution to be? Explain your answer.

Answer 74

I would expect it to be -0.4 because the increase of 1% in the concentration of sucrose means that mass difference decreases by 0.2g, as shown on the table.

Question 75

Is active transport passive?

Answer 75

No

Question 76

Why does active transport require energy?

Answer 76

Because it refers to the movement of molecules against the concentration gradient, from a lower concentration to a higher concentration.

Question 77

What channel proteins are involved in active transport?

Answer 77

Carrier proteins

Channel proteins are not involved in active transport.

Question 78

List 2 differences between active transport and facilitated diffusion.

Answer 78

Active transport usually moves solutes from a low to a high concentration (up the concentration gradient) - in facilitated diffusion, the movement of solutes are from a high to low concentration.

Active transport is active, facilitated diffusion is passive.

Question 79

How is energy sourced for active transport?

Answer 79

ATP goes to wherever in the cell energy is required, thus in active transport ATP arrives and undergoes a hydrolysis reaction, splitting into ADP and Pi.

This released energy so that solutes can be transported.

Question 80

Describe the use of carrier proteins in active transport.

Answer 80

Firstly, the molecule required for active transport will go to the carrier protein and bind to the binding site complementary to the molecule present on it.

Since energy is required, it is sourced from the hydrolysis of ATP to ADP + Pi which sources sufficient energy.

Then, the carrier protein changes shape with the molecule bonded onto it, releasing the molecule onto the other side of the plasma membrane against the concentration gradient.

Question 81

What are co-transporters a type of?

Answer 81

Carrier protein

Question 82

What are co-transporters?

Answer 82

Co-transporters are carrier proteins involved in active transport.

They carry two molecules at a time; the concentration gradient of one molecule is used to move the other molecule against it’s concentration gradient.

Question 83

How do co-transporters work?

Answer 83

Co-transporters carry two molecules at a time; the concentration gradient of one molecule is used to move the other molecule against it’s concentration gradient.

Question 84

Describe how co transporters actively transport sodium ions and glucose across the cell membrane.

Information you need to know:

The sodium concentration moves into the cell down the concentration gradient.

The glucose molecules move into the cell against the concentration gradient.

Answer 84

When looking at the co transport of sodium ions and glucose into the cell, sodium ions go down the concentration gradient as there is lower concentration inside the cell than outside, while glucose molecules must go against the concentration gradient, as there is a higher concentration inside the cell than outside.

As a result of this Co-Transport carrier proteins have 2 attachment sites, wherein a sodium ion binds to one attachment site and glucose molecule binds to the other - the co-transport protein allows both the sodium ion and the glucose molecule to be released to the other side of the plasma membrane by using the concentration gradient of one molecule, being sodium to move the other molecule against it’s concentration gradient, being glucose. PASSIVE process

Question 85

List 2 factors that limit Active Transport.

Answer 85

The speed of individual carrier proteins - the faster they work, the faster the rate of active transport.

The number of carrier proteins present - the more proteins there are, the faster the rate of active transport.

The rate of respiration in the cell and availability of ATP - if respiration is inhibited, active transport can’t take place.

Question 86

Label A to E:

https://media.discordapp.net/attachments/352951793187029005/829423281920409671/unknown.png

B and E refer to the environments on the shown side.

Answer 86

B = Lumen of ileum

A = Sodium-glucose co transporter protein

C = epithelial cell surface membrane

D = Sodium potassium pump

E = blood

Question 87

Glucose is absorbed into the bloodstream, from where?

Answer 87

Glucose is absorbed into the bloodstream from the small intestine.

Question 88

Glucose enters the ileum epithelium with sodium ions.

Describe this process.

Answer 88

Firstly, sodium ions are actively transported out of the ileum epithelial cells into the blood by the sodium potassium pump. This creates a concentration gradient - there’s now a higher concentration of sodium ions in the lumen of the ileum than inside the cell.

Since this concentration gradient is established, co transporters can now use the concentration gradient of sodium ions, which go with the concentration gradient, to transport other molecules against their concentration gradient, this being glucose.

This causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell, down their concentration gradient. They do this via the sodium-glucose co-transporter proteins.

The co-transporter carries glucose into the cell with the sodium. As a result, the concentration of glucose inside the cell increases.

Glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel by facilitated diffusion.

Question 89

Which molecule provides energy for active transport?

Answer 89

ATP

Question 90

The graph shows the results from an experiment into the uptake of two different solutes (X and Y) by simple bacterial cells.

Which solute, X or Y, entered the cells by active transport? give a reason for your answer.

Answer 90

X due to the fact that the concentration of solutes inside the cell continues to increase at a constant rate as time goes on, showing uptake against the concentration gradient

It does not flatten out, like in Y as equilibrium is never reached.

Question 91

You add 400 mL of water to 200 mL of a 3 mol/L solution of hydrogen peroxide.

Calculate the new concentration.

Answer 91

C1V1 = C2V2

c2 = ?
v2 = 600ml
v1 = 200ml
c1 = 3mol/l

c1v1 = c2v2

(c1v1) /v2 = c2
(200x3) = (? x 600)

So,

(200x3)/600 = 1mol/l .

Question 92

You are supplied with 250 mL of a 0.4 mol/L solution. You add 250 mL of water to the solution.

What is the concentration of the resulting solution?

Answer 92

C1V1 = C2V2

v1 = 250ml
c1 = 0.4mol/l
v2 = 500ml
c2 = ?

(250x0.4)/500 = 0.2 = c2

Question 93

What volume of 6 mol/L HCl is required in the preparation of 100 mL of 1 mol/L HCl?

Answer 93

We’re required to prepare 100ml of 1mol/l HCl therefore the final concentration and volume are shown - they are what we are preparing to make

c1 = 6mol/L HCl
v1 = ?
c2 = 1mol/l HCl
v2 = 100ml

(1x100)/6 = 16.666…7 = v1

Question 94

You are supplied with a 200-mL plastic bottle filled to capacity with 6mol/L solution of KCN, a poison. The plastic bottle is placed in a large beaker containing 1.0 L of water.

The plastic bottle leaks. What is the final concentration of the solution in the large beaker when the plastic bottle is completely empty?

Answer 94

C1V1 = C2V2

200 mL plastic bottle is filled to capacity - this is 200mL of 6mol/L solution of KCN

It is then placed in a large beaker, 1L only. Plastic bottle is what contains the concentration which is 200ML this is V1.

The plastic bottle protects the solution from leaking into the large beaker’s water, until it does not - it leaks, so after the plastic bottle is empty it’s all in the water.

Therefore the 0.2ml of KCN goes into the 1L water this is 0.2ml + 1L = 1.2L. This is V2

C1 = 6mol/L
V1 = 0.2L
C2 = ?
V2 = 1.2L CONVERT -> 1200mL

(6x.2)/1200 = 1mol/L C2

Question 95

Create 15cm^3 of 0.4 M sucrose solution starting with a known concentration of 1 M sucrose.

Answer 95

Firstly, divide your known concentration by the concentration you want to make

1 M / 0.4 M = 2.5

Therefore, your solution has to be 2.5x weaker, so add in 2.5x more water.

15 / 2.5 = 6cm^3, and you can top this up in a test tube. Add the remaining 9cm^3 as distilled water to get 15cm^3 of 0.4 M sucrose solution.

Question 96

Create 6cm^3 of .5 M glucose solution starting with a known concentration of 1 M glucose.

Answer 96

Firstly divide your concentration by the concentration you want to make

1 / .5 = 2

This means that your current solution must be 2x weaker than it currently is.

6 / 2 = 3cm^3. This means that 3cm^3 of 1 M glucose must be used, and then you should top it up with another 3cm^3 of distilled water to get 6cm^3 of .5 M glucose.

Question 97

An individual carries out serial dilutions and gets a series of these concentrations:

30,10,1

What is the dilution factor?

Answer 97

30 / 10 = 3
10 /10 = 1

Your dilution factor is 10 because you’re dividing by 10 each time.

Question 98

An individual carries out serial dilutions and gets a series of these concentrations:

1923,641,213.6666667

What is the dilution factor?

Answer 98

1923 / ? = 641
641 / ? = 213.6666667

Rearrange -> ? = 1923 / 641 = 3
641 / 213.6666667 = 3
Your dilution factor is 3 because you’re dividing by 3 each time.