Core Practicals Paper 1 & 2 Flashcards
1
Q
What is the purpose of the core practical using a microscope?
A
To observe and draw cells clearly using a light microscope.
2
Q
What stain is used to see onion cells under a microscope?
A
Iodine solution
3
Q
Why is iodine used to stain onion cells?
A
It binds to starch and makes structures like the nucleus more visible.
4
Q
What type of microscope is used in the core practical?
A
A light microscope
5
Q
What is the magnification formula?
A
Total magnification = eyepiece lens × objective lens
6
Q
How do you calculate actual size of a specimen?
A
Actual size = Image size ÷ Magnification
7
Q
What units should be used for measuring cells under a microscope?
A
Micrometres (µm)
8
Q
List the steps to prepare a slide of an onion cell.
A
- Peel a thin layer of onion skin
- Place it on a slide
- Add iodine stain
- Lower coverslip gently
- Remove excess stain with paper
9
Q
Why must the onion skin layer be thin?
A
To let light pass through so cells can be seen clearly
10
Q
How do you focus on a microscope?
A
Start with the lowest objective lens, use coarse focus, then fine focus for clarity
11
Q
Model 6-mark answer: How to set up a light microscope (simplified)
A
- Place slide on stage
- Use the lowest objective lens
- Use coarse focus to raise stage near lens
- Look through eyepiece
- Slowly lower stage with coarse focus until image is visible
- Use fine focus to sharpen image/ adjust light using mirror or lamp
12
Q
Model 5-mark answer: How to use a microscope (simplified)
A
- Put slide on stage
- Use the lowest power lens
- Use coarse focus to bring image close
- Use fine focus to sharpen
- Adjust light
13
Q
Model 4-mark answer: Microscope setup (simplified)
A
- Put slide on stage
- Use low lens
- Coarse focus to find image
- Fine focus to make clear
14
Q
Why do we start with the lowest magnification lens?
A
Easier to locate specimen and prevent damage to slide or lens
15
Q
How do you make a scientific drawing from a specimen?
A
- Use a sharp pencil
- Draw only what is seen
- Use clear lines (no shading)
- Label structures with straight lines
- Add title and magnification
16
Q
What should not be included in scientific drawings?
A
No shading or sketching; no colours; no unnecessary details
17
Q
How do you label a scientific drawing?
A
Use straight lines from the drawing to labels written on the side
18
Q
Why is magnification included in a drawing?
A
So others know how zoomed-in the view is
19
Q
What is the benefit of using a coverslip?
A
It protects the lens and flattens the sample for better viewing
20
Q
What is the aim of the core practical investigating pH on enzyme activity?
A
To investigate how different pH levels affect the rate of enzyme activity.
21
Q
What is the enzyme used in the core practical?
A
Amylase
22
Q
What substrate is used to test amylase activity in this experiment?
A
Starch
23
Q
What is the role of the iodine solution in this experiment?
A
Iodine is used to test for the presence of starch by turning blue-black when starch is present.
24
Q
What is the independent variable in this experiment?
A
The pH level of the solution
25
What is the dependent variable in this experiment?
The time taken for the starch to be completely broken down (or the rate of enzyme activity)
26
What are the control variables in this experiment?
- Temperature
- Concentration of amylase
- Concentration of starch
- Volume of solutions used
27
What is the method for testing how pH affects amylase activity?
1. Set up test tubes with different pH buffers (e.g., pH 4, pH 7, pH 10)
2. Add a fixed amount of amylase and starch to each test tube
3. Start the timer and use iodine to test for starch every 30 seconds
4. Record the time it takes for starch to be fully broken down (no blue-black colour)
28
How can you ensure the accuracy of the pH levels used in the experiment?
Use a pH meter or pH paper to check and maintain the correct pH level throughout the experiment.
29
What is the purpose of using a water bath in this experiment?
To maintain a constant temperature and prevent temperature from affecting enzyme activity.
30
Why is it important to use a fixed concentration of amylase in this experiment?
To ensure that the only factor affecting the enzyme activity is the pH level, not the amount of enzyme.
31
What is a 6-mark model answer for this experiment setup?
- Set up test tubes with different pH buffers
- Add amylase and starch to each test tube
- Start the timer and mix the solution
- After set intervals, drop the solution onto iodine
- Observe when the solution no longer turns blue-black
- Record the time for starch breakdown at each pH
32
What is a 5-mark model answer for this experiment setup?
- Place pH buffers in test tubes
- Add fixed amounts of amylase and starch
- Start timing and test with iodine
- Record time taken for starch breakdown
- Repeat for each pH level
33
What is a 4-mark model answer for this experiment setup?
- Use test tubes with different pH buffers
- Add starch and amylase
- Time how long it takes for starch to be broken down
- Record results
34
How do you interpret results in this experiment?
Compare the times taken for starch breakdown at each pH level; the faster the breakdown, the higher the enzyme activity.
35
Why does enzyme activity change with pH?
Each enzyme has an optimal pH at which it works best; deviations from this pH reduce the enzyme's ability to catalyse reactions.
36
What safety precautions should be taken in this experiment?
Wear safety goggles, handle iodine carefully, and clean up any spills immediately.
37
Why must the concentration of starch be controlled?
To ensure that the only variable affecting the enzyme activity is the pH, not the amount of starch present.
38
Why is temperature a control variable in this experiment?
Temperature can affect enzyme activity, so it must be kept constant to ensure reliable results.
39
How would you modify this experiment to test the effect of temperature on enzyme activity?
Use the same method but change the temperature instead of pH, using water baths at different temperatures.
40
What is the aim of the core practical investigating osmosis?
To investigate the effect of different concentrations of salt or sugar solution on the mass of potato chips.
41
What process is being investigated in this experiment?
Osmosis
42
What is osmosis?
The movement of water molecules from a region of high water concentration to a region of low water concentration through a selectively permeable membrane.
43
What is the independent variable in this experiment?
The concentration of salt or sugar solution
44
What is the dependent variable in this experiment?
The change in mass of the potato chips
45
What are the control variables in this experiment?
- Size of potato chips
- Volume of solution
- Time the chips are left in the solution
- Type of potato used
46
What is the method for investigating osmosis in potato chips?
1. Cut potato chips into uniform sizes
2. Place chips in different concentrations of salt or sugar solution
3. Leave chips in the solution for a set time (e.g., 30 minutes)
4. After the time, remove chips, blot them dry, and measure their mass
5. Calculate the percentage change in mass for each solution
47
Why must the potato chips be the same size?
To ensure that the surface area is the same for all chips, so the rate of osmosis is not affected by size.
48
Why should the potato chips be blotted dry after the experiment?
To remove any excess solution on the surface that could affect the mass measurement.
49
What is a 6-mark model answer for setting up the osmosis experiment?
- Cut uniform potato chips
- Place chips in solutions with different concentrations
- Leave for a set time (e.g., 30 minutes)
- After time, blot dry and measure mass
- Calculate percentage change in mass
- Compare results to find concentration at which no mass change occurs (isotonic)
50
What is a 5-mark model answer for setting up the osmosis experiment?
- Cut uniform potato chips
- Place chips in various concentrations of salt/sugar solutions
- Leave for a fixed time
- Blot and measure mass
- Calculate percentage change in mass
51
What is a 4-mark model answer for setting up the osmosis experiment?
- Cut potato chip
- Place in different concentrations
- Leave for a fixed time
- Measure and record the mass change
52
What would happen if the potato chips are placed in a solution with a higher water concentration than the potato cells?
Water would move into the cells, causing the chips to gain mass (osmosis).
53
What would happen if the potato chips are placed in a solution with a lower water concentration than the potato cells?
Water would move out of the cells, causing the chips to lose mass (osmosis).
54
What is the relationship between solute concentration and the mass change of the potato chips?
As the solute concentration increases, the potato chips typically lose mass because water moves out of the cells by osmosis.
55
Why is it important to use the same type of potato for all samples?
To ensure that the amount of starch and other solutes in the potato cells is the same, which could affect osmosis.
56
Why should the volume of solution be controlled?
To ensure that all potato chips are exposed to the same amount of solution, maintaining consistency in the experiment.
57
How can you ensure the results are reliable in this experiment?
Repeat the experiment multiple times and calculate an average mass change for each concentration.
58
What safety precautions should be taken in this experiment?
Wear safety goggles, be careful with sharp knives when cutting the potato, and clean up any spills immediately.
59
Why is it necessary to measure the mass of the potato chips accurately?
Small changes in mass can indicate osmosis, so accurate measurements are important for reliable results.
60
How do you calculate the percentage change in mass for the potato chips?
Percentage change in mass = ((Final mass - Initial mass) ÷ Initial mass) × 100
61
What does it mean if the potato chips show no mass change in a solution?
The solution is isotonic, meaning the concentration of solutes is the same inside and outside the potato cells, so no water movement occurs.
62
What could cause anomalous results in this experiment?
Errors in measuring the mass, inconsistencies in potato chip size, or evaporation of the solution could affect the results.
63
What is the aim of the core practical measuring energy in food?
To measure the energy content of a food sample by burning it and calculating the temperature increase in water.
64
What is the independent variable in this experiment?
The type of food being tested
65
What is the dependent variable in this experiment?
The temperature increase in the water
66
What are the control variables in this experiment?
- Mass of food
- Volume of water
- Distance between the food and the water
- Time for heating
67
What is the method for measuring the energy content of food?
1. Weigh a small amount of food
2. Set up a calorimeter with a fixed amount of water
3. Heat the food by burning it under the water
4. Measure the temperature change of the water
5. Calculate the energy released using the formula Energy (J) = mass of water (g) × specific heat capacity of water (4.2 J/g°C) × temperature change (°C)
68
Why is it important to weigh the food before burning it?
To know the amount of food being burned and calculate the energy per gram of food.
69
Why is a calorimeter used in this experiment?
To measure the amount of heat transferred to the water as the food burns.
70
Why is it important to measure the temperature change of the water?
The temperature change indicates how much energy has been transferred from the burning food to the water.
71
What is a 6-mark model answer for setting up the experiment to measure energy in food?
- Weigh a small piece of food
- Set up a calorimeter with a known volume of water
- Burn the food and place it under the water
- Measure the temperature change of the water
- Use the equation Energy = mass × specific heat capacity × temperature change to calculate the energy
- Record results for multiple trials for accuracy
72
What is a 5-mark model answer for setting up the experiment to measure energy in food?
- Weigh food and place it under a fixed amount of water
- Burn the food to heat the water
- Measure the temperature change
- Calculate energy released using the equation
- Repeat for accuracy
73
What is a 4-mark model answer for setting up the experiment to measure energy in food?
- Weigh food
- Heat water with the food
- Measure temperature change
- Calculate energy released
74
What is the equation for calculating the energy released by the food?
Energy (J) = mass of water (g) × specific heat capacity of water (4.2 J/g°C) × temperature change (°C)
75
Why is it necessary to use a fixed volume of water in the experiment?
To ensure that the energy calculation is consistent and accurate.
76
Why is it important to measure the distance between the food and the water?
The further the food is from the water, the less energy will be transferred, so it must be consistent to get reliable results.
77
What would happen if the food were burned for too long in the experiment?
It would release more energy than expected, skewing the results.
78
Why should the food be burned completely in this experiment?
To ensure that all the energy stored in the food is released and transferred to the water.
79
What are some limitations of this experiment?
Some heat energy will be lost to the surroundings, so the energy measured may be lower than the actual energy in the food.
80
How can the accuracy of this experiment be improved?
Use a more efficient calorimeter, reduce heat loss, and perform multiple trials to get an average result.
81
What safety precautions should be taken in this experiment?
Wear safety goggles, ensure the food is burned in a safe, controlled environment, and avoid open flames around flammable materials.
82
Why is it important to repeat the experiment multiple times?
Repeating the experiment helps to reduce errors and improve the reliability of the results.
83
Why is it important to use a consistent mass of food?
Using the same mass ensures that the energy calculations are comparable across different tests.
84
What would you expect to happen if you burn a high-calorie food in this experiment?
The temperature of the water would increase more, indicating that more energy is released by burning the food.
85
What could cause anomalous results in this experiment?
Heat loss to the environment, incomplete combustion of the food, or incorrect measurements of mass or temperature.
86
What is the purpose of food tests in this core practical?
To test for the presence of carbohydrates, lipids, and proteins in food samples.
87
What is Benedict's reagent used to test for?
Benedict's reagent is used to test for the presence of reducing sugars.
88
How do you perform the Benedict's test?
1. Add Benedict's reagent to a sample of food.
2. Heat the mixture in a boiling water bath for 2-5 minutes.
3. A red/orange/yellow color indicates the presence of reducing sugars.
89
What are the positive and negative results for the Benedict's test?
Positive: Red/orange/yellow precipitate
Negative: Blue solution (no change)
90
What is the test for starch?
Iodine solution is used to test for starch.
91
How do you perform the iodine test for starch?
1. Add a few drops of iodine solution to the food sample.
2. A blue-black colour indicates the presence of starch.
92
What are the positive and negative results for the starch test?
Positive: Blue-black colour\nNegative: No colour change (yellow/brown solution remains the same)
93
What is the test for lipids?
The emulsion test is used to test for lipids.
94
How do you perform the emulsion test for lipids?
1. Add ethanol to the food sample and shake well.
2. Pour the mixture into water.
3. A milky white emulsion indicates the presence of lipids.
95
What are the positive and negative results for the lipid test?
Positive: Milky white emulsion
Negative: Clear solution
96
What is the test for proteins?
The biuret test is used to test for proteins.
97
How do you perform the biuret test for proteins?
1. Add a few drops of biuret reagent to the food sample.
2. A purple color indicates the presence of proteins.
98
What are the positive and negative results for the protein test?
Positive: Purple color
Negative: Blue solution (no change)
99
What are some common sources of reducing sugars in food?
Common sources include fruits, honey, and some vegetables.
100
Why do we use a boiling water bath during the Benedict's test?
To provide sufficient heat for the reaction to occur and allow the color change to be visible.
101
Why is the iodine solution used in the starch test?
Iodine binds to starch and turns blue-black, allowing the detection of starch in the food sample.
102
Why is ethanol used in the lipid test?
Ethanol dissolves the lipids in the sample, which can then form an emulsion with water, making the lipid presence visible.
103
Why is the biuret reagent used in the protein test?
Biuret reagent reacts with peptide bonds in proteins, causing a color change to purple if proteins are present.
104
What safety precautions should be taken when performing food tests?
Wear safety goggles, handle heated equipment carefully, and avoid skin contact with chemicals like iodine and ethanol.
105
Why must the food sample be in liquid form for some of these tests?
The reagents used in food tests require the sample to be in a liquid form to mix and react effectively.
106
What could cause anomalous results in these food tests?
Contamination of the food sample, improper handling of reagents, or incorrect heating times could lead to unreliable results.
