Topic 1b - Biological Molecules and Transport in Cells

Question 1

What is an enzyme?

Answer 1

proteins that act as biological catalysts to speed up the rate of a chemical reaction without being changed or used up in the reaction

Question 2

What do enzymes do?

Answer 2

• reduce the need for high temperatures
• speed up the useful chemical reactions in the body
• help speed up process of breaking down substances

Question 3

What do the enzymes produced by living things act as?

Answer 3

Biological catalysts

Question 4

What is the rule for enzymes and catalysing reactions?

Answer 4

• The active site can only catalyse one reaction at a time.
• Once all the active sites are full, increasing the amount of substrates has no effect on the rate, as there are no available enzymes to catalyse further reactions.
• Increasing the substrate concentration has no effect, so the rate will depend on the number of enzymes around

Question 5

What is a catalyst?

Answer 5

a substance which increases the speed of a reaction, without being changed or used up in the reaction

Question 6

What is a substrate?

Answer 6

the substance the enzyme acts on

Question 7

What is the active site lock and key theory?

Answer 7

When the enzyme is in the optimum temperature, it doesn’t let a chemical reaction occur, with a substrate.
When the enzyme isn’t at optimum temperature, the substrate binds with the enzyme, and then a chemical reaction takes place. After the chemical reaction occurs, products are released.

Question 8

What is the rate of reaction and temperature graph trend?

Answer 8

Increasing the temperature, increases the rate of reaction because the reactions have more energy, so they move about more, and collide with each other more often

Question 9

What does the enzyme rate of reaction and temperature graph show?

Answer 9

• Changing the temperature, changed the rate of an enzyme-catalysed reaction.
• A higher temperature increases the rate at first, but if it gets too hot, some of the bonds holding the enzyme together break. This changes the shape of the enzyme’s active site, so the substrate won’t fit anymore (it is denatured).
• Enzymes in the human body usually work best around 37 degrees celsius.

Question 10

At what temperature to human enzymes denature?

Answer 10

around 45 degrees celsius

Question 11

What does the substrate concentration graph show?

Answer 11

• The higher the substrate concentration, the faster the reaction, because it is more likely that the enzyme will meet up with a substrate molecule.
• There is a steady increase in rate as more substrate molecules are available.
• After that, there are so many substrate molecules that the enzymes have as much as they need, as all the active sites are full, and adding more makes no difference, so the rate remains constant.

Question 12

What is respiration?

Answer 12

the process of breaking down glucose, which transfers energy

Question 13

What does a high pH mean?

Answer 13

it’s alkaline

Question 14

What does a low pH mean?

Answer 14

it’s acidic

Question 15

What happens if the pH is too low or too high?

Answer 15

the pH interferes with the bonds holding the enzyme together, which changes the shape of the active site and denatures the enzyme

Question 16

At what pH does pepsin work best at?

Answer 16

pH 2

Question 17

What is the optimum pH for enzymes?

Answer 17

pH 7

Question 18

How do you investigate the effect of pH on amylase?

Answer 18

1) Put a drop of iodine solution into every well of a spotting tile.
2) Place a Bunsen burner on a heat-proof mat, and a tripod and gauze over the Bunsen burner. Put a beaker of water on top of the tripod and heat the water until it reaches the optimum temperature of the amylase you are using. (Use a thermometer to measure the temperature.) Try to keep the temperature of the water constant throughout the experiment.
3) Use a syringe to add 3 cm^3 of amylase solution and 1 cm^3 of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the boiling tube into the beaker of water and wait for five minutes.
4) Next, use a different syringe to add 3 cm3 of a starch solution to the boiling tube.
5) Immediately mix the contents of the boiling tube and start a stop clock. 6. Use continuous sampling to record how long it takes for the amylase to break down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every thirty seconds and put a drop into a well on the spotting tile. When the iodine solution remains browny-orange, starch is no longer present.
7) Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down.
8) Remember to control any variables each time you repeat the experiment to make it a fair test. Variables that need controlling include the concentration and volume of the amylase and starch solutions and the temperature of the reaction mixture.

Question 19

What is the rate of reaction used to measure?

Answer 19

how much something changes over time

Question 20

How do you calculate the rate of reaction?

Answer 20

rate = 1000 ÷ time taken

Question 21

What is a biological molecule?

Answer 21

molecules found in living organisms

Question 22

What are some examples of biological molecules?

Answer 22

• Carbohydrates
• Lipids
• Proteins

Question 23

What do enzymes catalyse?

Answer 23

breakdown reactions

Question 24

What are some examples of enzymes catalysing break down reactions?

Answer 24

• Many of the molecules in the food we eat are too big to pass through the walls of our digestive system, so digestive enzymes break them down into smaller, soluble molecules. These can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream. They can then pass into cells to be used by the body.
• Plants store energy in the form of starch (a carbohydrate). When plants need energy, enzymes break down the starch into smaller molecules (sugars). These can then be respired to transfer energy to be used by the cells

Question 25

What does enzyme amylase break down starch to?

Answer 25

maltose

Question 27

How do you investigate the effect of pH on amylase?

Answer 27

1) Put a drop of iodine solution into every well of a spotting tile.
2) Place a Bunsen burner on a heat-proof mat, and a tripod and gauze over the Bunsen burner. Put a beaker of water on top of the tripod and heat the water until it reaches the optimum temperature of the amylase you are using. (Use a thermometer to measure the temperature.) Try to keep the temperature of the water constant throughout the experiment.
3) Use a syringe to add 3 cm3 of amylase solution and 1 cm3 of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the boiling tube into the beaker of water and wait for five minutes.
4) Next, use a different syringe to add 3 cm3 of a starch solution to the boiling tube.
5) Immediately mix the contents of the boiling tube and start a stop clock. 6. Use continuous sampling to record how long it takes for the amylase to break down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every thirty seconds and put a drop into a well on the spotting tile. When the iodine solution remains browny-orange, starch is no longer present.
7) Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down.
8) Remember to control any variables each time you repeat the experiment to make it a fair test. Variables that need controlling include the concentration and volume of the amylase and starch solutions and the temperature of the reaction mixture. See p.10 for more on fair tests.

Question 28

How do you calculate the rate of reaction?

Answer 28

rate = 1000 ÷ time taken

Question 29

What is the unit for the rate of reaction?

Answer 29

s^-1

Question 30

What is the rate used to measure?

Answer 30

how much something changes of time

Question 31

What is a biological molecule?

Answer 31

a molecule found in living organisms

Question 32

What are some examples of biological molecules?

Answer 32

• Carbohydrates
• Proteins
• Lipids

Question 33

What do enzymes catalyse?

Answer 33

breakdown reactions

Question 34

What are some examples of enzymes catalysing breakdown reactions?

Answer 34

• Many of the molecules in the food we eat are too big to pass through the walls of our digestive system, so digestive enzymes break them down into smaller, soluble molecules. These can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream. They can then pass into cells to be used by the body.
• Plants store energy in the form of starch (a carbohydrate). When plants need energy, enzymes break down the starch into smaller molecules (sugars). These can then be respired to transfer energy to be used by the cells

Question 35

What are carbohydrase enzymes?

Answer 35

Carbohydrases convert carbohydrates into simple sugars. Amylase is an example of a carbohydrase. It breaks down starch.

Question 36

What are protease enzymes?

Answer 36

Protease enzymes catalyse the conversion of proteins into amino acids

Question 37

What are lipase enzymes?

Answer 37

Lipase enzymes catalyse the conversion of lipids into glycerol and fatty acids

Question 38

Why do organisms need to be able to synthesise carbohydrates, proteins and lipids?

Answer 38

for their smaller components

Question 39

How are enzymes involved in sythesising reactions?

Answer 39

Enzymes are used to catalyse the reactions involved, however these enzymes are different to the ones in breakdown reactions.

Question 40

How can carbohydrates be sythesised?

Answer 40

by joining together simple sugars (e.g., glycogen synthase is an enzyme that joins together lots of chains of glucose molecules to make glycogen (a molecule used to store energy in animals))

Question 41

How are proteins synthesised?

Answer 41

By joining amino acids together. Enzymes catalyse the reactions needed to do this.

Question 42

How are lipids synthesised?

Answer 42

Enzymes are involved in the synthesis of lipids, from fatty acids and glycerol

Question 43

How do you prepare a food sample which is liquid, to test for biological molecules?

Answer 43

If you are testing a liquid like milk or egg whites, you don’t need to prepare your sample, and like this. You can just go straight ahead and test it?

Question 44

How do you prepare a food sample which is solid, to test for biological molecules?

Answer 44

1) Get a piece of your food and break it up using a pestle and mortar.
2) Transfer the ground up food to a beaker and add some distilled water.
3) Give the mixture a good stir with a glass rod.
4) Allow the mixture to settle out and then pipette out some of the liquid. This is your sample.

Question 45

What are the two sugars, sugar is classified as, due to its chemical properties?

Answer 45

• reducing sugars (e.g., glucose)
• non-reducing sugars (e.g., sucrose)

Question 46

What solution is used to test for sugars?

Answer 46

Benedict’s solution

Question 47

What are reducing sugars found in?

Answer 47

biscuits and cereal

Question 48

How do you test for reducing sugars?

Answer 48

1) Transfer 5 cm^3 of a food sample to a test tube.
2) Prepare a water bath so that it’s set to 75 °C.
3) Add some Benedict’s reagent (which is blue) to the test tube (about 10 drops) using a pipette.
4) Place the test tube in the water bath using a test tube holder and leave it in there for 5 minutes. Make sure the tube is pointing away from you.
5) During this time, if the food sample contains a reducing sugar, a coloured precipitate (solid particles suspended in the solution) will form. The solution in the test tube will change from the normal blue colour to green, yellow or brick-red. The higher the concentration of reducing sugar, the further the colour change goes - you can use this to compare the amount of reducing sugar in different solutions.

Question 49

What solution is used to test for starch?

Answer 49

iodine solution

Question 50

What foods contain lots of starch?

Answer 50

pasta, rice and potatoes

Question 51

How do you test for starch?

Answer 51

1) Transfer 5 cm^3 of a food sample to a test tube.
2) Then add a few drops of iodine solution (iodine dissolved in potassium
iodide solution) and gently shake the tube to mix the contents. If the sample contains starch, the colour of the solution will change from browny-orange to blue-black.

Question 52

What solution is used to test for proteins?

Answer 52

Biuret solution

Question 53

What foods contain lots of protein?

Answer 53

meat and cheese

Question 54

How do you test for proteins?

Answer 54

1. Transfer 2 cm^3 of a food sample to a test tube.
   2) Add 2 cm^3 of potassium hydroxide solution to make the solution alkaline.
   3) Add a few drops of copper(II) sulfate solution (which is bright blue).
   4) If the food sample contains protein, the solution will change from blue to pink or purple. If no protein is present, the solution will stay blue.

Question 55

What solution is used to test for lipids (fats and oils)?

Answer 55

Emulsion solution

Question 56

What foods are lipids (oils and fats) found in?

Answer 56

olive oil, margarine, and milk

Question 57

How do you test for lipids (oils and fats)?

Answer 57

1) Transfer some of the food sample into a test tube.
2) Add 2 cm^3 of ethanol to the test tube.
3) Shake the test tube well for about 1 minute until the test substance dissolves.
4) Pour the solution into a test tube containing 2 cm^3 of distilled water.
5) If there are any lipids present, they will precipitate out of the liquid and show up as a milky emulsion. The more lipid there is, the more noticeable the milky colour will be.

Question 58

What are calorimetry experiments used to do?

Answer 58

Work out how much energy different foods contain?

Question 59

How do you do the calorimetry experiment?

Answer 59

1) Weigh a small amount of dry food and then skewer it on a mounted needle.
2) Add a set volume of water to a boiling tube (held with a clamp)
this will be used to measure the amount of energy that’s transferred when the food is burnt.
3) Measure the temperature of the water with a thermometer, then set fire to the food using a Bunsen burner flame.
4) Immediately hold the burning food under the boiling tube until it goes out. Then relight the food and hold it under the tube - keep doing this until the food won’t catch fire again.
5) Measure the temperature of the water again and record the temperature change.

Question 60

How do you calculate the total amount of energy in food?

Answer 60

energy in food = mass of water * temperature change of water * 4.2

Question 61

What are the units for the energy in food?

Answer 61

J (joules)

Question 62

What are the units for the mass of water?

Answer 62

g (grams)

Question 63

What is the temperature change of water measured in?

Answer 63

degrees celsius

Question 64

How do you calculate the energy in each gram of food?

Answer 64

energy per gram of food = energy in food ÷ mass of food

Question 65

What are the units for the energy per gram of food?

Answer 65

J/g (joules per gram)

Question 66

What can substances pass in and out of cells by?

Answer 66

• diffusion
• active transport
• osmosis

Question 67

What is diffusion?

Answer 67

The spreading out of particles from an area of high concentration (where there is lots of them) to an area of low concentration (where there is only a few of them)

Question 68

Where does diffusion happen?

Answer 68

In both solutions and gases

Question 69

What is a passive process?

Answer 69

Where energy isn’t required to make something work (e.g., in diffusion)

Question 70

How are cell membranes are partially permeable?

Answer 70

They only let some molecules into cells, but not others. Only very small molecules can diffuse through cell membranes (e.g., oxygen( which is needed for respiration), amino acids, glucose and water)

Question 71

What molecules cannot fit through the cell membrane?

Answer 71

protein and starch

Question 72

What is osmosis?

Answer 72

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration (low solute concentration) to a region of lower water concentration (high solute concentration).

Question 73

Which way do water molecules pass through osmosis?

Answer 73

They pass through both ways, as the water molecules move about freely all the time, but because there are more water molecules on one side than on the other, there is a steady net (overall) flow into the region with fewer water molecules (the solution with the high solute concentration). This means that the more concentrated solution gets more diluted (made thinner or weaker by adding water or another solvent to it).

Question 74

What is the concentration surrounding the cell, and the concentration of the fluid inside the cell like?

Answer 74

They both have different concentrations. This means that water will either move into the cell from the surrounding solution, or out of the cell, by osmosis.

Question 75

What happens if the cell is short of water?

Answer 75

If a cell is short of water, the solution inside it will become quite concentrated (i.e. there’ll be a low concentration of water molecules). This usually means the solution outside the cell is more dilute (there’s a higher concentration of water molecules), and so water will move into the cell by osmosis. If a cell has lots of water, the solution inside it will be more dilute, and water will be drawn out of the cell and into the fluid outside by osmosis.

Question 76

What is active transport?

Answer 76

Active transport is the movement of particles against a concentration gradient (i.e. from an area of lower concentration to an area of higher concentration) using energy transferred during respiration.
This process requires energy, unlike diffusion. It allows cells to absorb solution from very dilute substances.

Question 77

What is an example of active transport?

Answer 77

When there’s a higher concentration of nutrients in the gut than in the blood, the nutrients diffuse naturally into the blood, but sometimes there’s a lower concentration of nutrients in the gut than in the blood.
Active transport allows nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way. This is essential to stop us starving. It means that glucose can be taken into the bloodstream when its concentration in the blood is already higher than in the gut. The glucose can then be transported to cells, where it’s used for respiration.

Question 78

How do you investigate the effect of sugar solutions on plant cells?

Answer 78

1) Prepare sucrose solutions of different concentrations ranging from pure water to a very concentrated sucrose solution.
2) Use a cork borer to cut a potato into the same sized pieces (the pieces need to be about 1 cm in diameter and preferably from the same potato).
3) Divide the cylinders into groups of three and use a mass balance to measure the mass of each group.
4) Place one group in each solution.
5) Leave the cylinders in the solution, for at least 40 minutes (making sure that they all get the same amount of time).

Question 79

What are the dependent, control and independent variables of the effect of sugar solutions on plant cells experiment?

Answer 79

• Dependent variable: cylinder mass
• Independent variable: concentration of sucrose solution
• Control variable: volume of solution, size of potato cylinders, amount of drying or age of potatoes used

Question 80

What are the error that may occur during effect of sugar solutions on plant cells experiment?

Answer 80

• potato cylinders weren’t fully dried, so excess water would have given a higher mass
• water evaporated from beakers, so the concentration of the sugar solutions would change

Question 81

How can we stop any error from occurring in the effect of sugar solutions on plant cells experiment?

Answer 81

Do the xperiment 3 times and find the mean percentage change at each concentration

Question 82

How do you calculate the percentage change in mass?

Answer 82

percentage change in mass = ((final mass - initial mass) ÷ initial mass) * 100

Question 83

What do the results on a graph show for the effect of sugar solutions on plant cells experiment?

Answer 83

• At the points above the x-axis, the concentration of water molecules in the sucrose solutions is higher than in the cylinders. The cylinders gain mass as water is drawn in by osmosis.
• At the points below the x-axis, the concentration of water molecules in the sucrose solutions is lower than in the cylinders. This causes the cylinders to lose water, so their mass decreases
• The point at which the line of best fit crosses the x-axis (where the percentage change in mass is 0) is the point at which the concentration of the sucrose solution is the same as the concentration of the solution in the potato cells. You can estimate the concentration of the solution inside the potato cells by reading the value off the x-axis at this point.

Question 84

What is the unit of concentration?

Answer 84

‘M’ or ‘mol dm^-3’