SB1 - Key Concepts In Biology

Question 1

SB1a
1) What is an electron microscope?
2) What is meant by an instrument’s resolution?
3) Explain why some cell structures can be seen with an electron microscope but not with a light microscope

Answer 1

1) Electron microscopes uses electrons instead of light, and it has a much higher magnification and resolution than a light microscope.
2) The resolution of a measuring instrument is the smallest change in a quantity that gives a change in the reading that can be seen.
eg. A thermometer with a mark at every 1.0°C has a resolution of 1.0°C. It has a higher resolution than a thermometer with a mark at every 2.0°C.
3) An electron microscope has a higher magnification and resolution than a light microscope. Some cell structures are so small that they can only be seen on an electron microscope and not a light microscope.

Question 2

SB1a
1) What is the formula to calculate total magnification using a formula
2) What are the SI units and symbols used for measuring cells?
3) What is the standard form used for these units compared to metres?

Answer 2

1) Magnification = scale bar image length/ actual scale bar length (written on the scale bar).
2) Milimetres mm (1000 in a metre), Micrometers μm (1,000,000 in a metre), Nanometres nm (1,000,000,000 in a metre) and picometres pm (1,000,000,000,000 in a metre)
3) mili = 10 to the power of -3, micro = 10 to the power of -6, nano = 10 to the power of -9, picometres = 10 to the power of -12

Question 3

SB1b
1) What is the function of the nucleus?
2) What is the function of the cell membrane?
3) What is the function of mitochondria?
4) What is the function of ribosomes?

Answer 3

1) The nucleus controls the cell and its activities.
2) The cell membrane controls what enters and leaves the cell.
3) Mitochondria are where areobic respiration occurs.
4) Ribosomes are where proteins are made for the cell.

Question 4

SB1b
1) What is the function of a cell wall?
2) What is the function of chloroplasts?
3) What is the function of a pernament vacuole?

Answer 4

1) The cell wall supports and protects the cell.
2) Chloroplasts contain chlorophyll, which trap energy from the sun. The energy is used for photosynthesis.
3) A pernament vacuole stores cell sap.

Question 5

SB1b
1) What sub-cellular structures are in animal cells?
2) What sub-cellular structures are in plant cells?
3) How can the sizes of cells be estimated on a micrograph?

Answer 5

1) Sub-cellular structures in an animal cell are: the nucleus, cell membrane, cytoplasm, mitochondria and ribosomes.
2) A plant cell has chloroplasts, a cell wall, and a permanent vacuole, in addition to the structures in an animal cell.
3) Scale bars are often shown on micrographs (a photo taken with a microscope) and these are also used to estimate the size of the cell, by seeing approximately how many scale bars would fit on the organism.

Question 6

SB1c
1) What is a gamete?
2) What is a haploid nucleus?
3) How are sperm cells adapted to their function?
4) How are egg cells adapted to their functions?
5) How are ciliated epithelial cells adapted to their function?

Answer 6

1) A gamete is a cell with a haploid nucleus used for sexual reproduction.
2) A haploid nucleus is a nucleus that contains half the number of chromosomes as a normal body cell.
3) Sperm cells are adapted by:
- Having an acrosome that contains enzymes that digest through the membrane of the egg cell
- A haploid nucleus
- A tail to swim
- Lots of mitochondria to power the tail.
4) Egg cells are adapted by:
- The cytoplasm having lots of nutrients to nourish the developing embryo
- A haploid nucleus
- A jelly coat to protect the egg cell, and hardens to prevent more than one sperm entering. This makes sure that the offspring ends up with the right amount of DNA
5) Ciliated epithelial cells are adapted by: having cilia, which sweeps substances along (such as the egg cells).

Question 7

SB1d
1) What sub-cellular structures are in bacterial cells?
2) Describe why bacteria are classified as being prokaryotic

Answer 7

1) Bacterial cells have: a cell wall, a cell membrane, chromosomal and plasmid DNA, cytoplasm, and some have a flagellum, and a slime coat.
2) Bacteria cells do not contain membrane bound organelles such as a nucleus and mitochondria.

Question 8

SB1d
1) What are eukaryotic organisms?
2) What are prokaryotic organisms?
3) What are the two different types of DNA in bacteria?
4) What is the function of flagella?

Answer 8

1) Eukaryotic organisms are cells with a nucleus.
2) Prokaryotic organisms are cells without a nucleus.
3) Chromosonal DNA, which controls most of the cell’s activities, and plasmid DNA.
4) The flagellum helps the bacterium to move.

Question 9

SB1e
1) What are enzymes?
2) What is amylase, catalase, lipase and protease?
3) What is the monomer for protein, carbohydrates and lipids?

Answer 9

1) Enzymes are a type of protein and are biological catalysts that speed up the rate of reactions.
2) Amylase is found in the saliva and small intestines, and catalyses the breaking down of starch to small sugars.
Catalase is found in most cells, but especially liver cells. It catalyses the breaking down of hydrogen peroxide into simple sugars.
Lipase catalyses the break down of fats into fatty acids and glycerol.
Protease catalyses the break down of proteins into amino acids.
3) The monomer for protein is amino acids. The monomer for carbohydrates are glucose molecules (sugars). The monomer for lipids are fatty acids and glycerol.

Question 10

SB1e
1) Describe what enzymes do
2) Explain why catalysis by enzymes is important for life processes
3) What is starch synthase and DNA polymerase?

Answer 10

1) Enzymes catalyse the synthesis and breakdown of substances, such as carbohydrates, proteins and lipids, by speeding up the rate of reaction.
2) Enzymes are important for life processes because reactions happen much faster. Without enzymes, the synthesis and breakdown of molecules would happen too slowly to stay alive.
3) Starch synthase is found in plants and catalyses the synthesis of starch from glucose. DNA polymerase is found in the nucleus and catalyses the synthesis of DNA from its monomers.

Question 11

SB1f
1) Describe how to test for starch in food
2) Describe how to test for reducing sugars in food
3) Describe how to test for proteins in food

Answer 11

1) Iodine solution test for the presence of starch it turns from yellow orange to a blue black colour.
2) Benedict’s solution test for reducing sugars. Benedict’s solution starts light blue, then changes to green for a small amount of reducing sugars, orange and finally dark red for a lot of reducing sugars.
Reducing sugars are small sugar molecules (such as glucose and fructose).
3) A biruet test tests for protein if the pale blue solution turns purple this indicates that there is protein in the food.

Question 12

SB1f
1) Describe how to test for lipids (fats and oils) in food
2) Explain how calorimetry can be used to measure the energy in food
3) Explain how to improve accuracy of calorimetry test

Answer 12

1) The ethanol emulsion test tests for fats and oils (lipids). First, mix the food with ethanol and water. If the top of the water that it is mixed with becomes cloudy - a white precipitate forms - then this indicates that there are lipids in the food.
2) In the calorimeter a piece of food is burnt and the heat from this food heats up the water inside the calorimeter. The increase in the water temperature tells us how much energy was transferred.
3) More reliable results can be obtained by repeating the experiment many times. The biggest source of error in calorimetry is usually unwanted heat loss to the surroundings. This can be reduced by insulating the sides of the calorimeter and adding a lid.

Question 13

SB1g
1) State what enzyme specificity means
2) Describe the role of the active site in enzyme function (including specificity)

Answer 13

1) Enzymes are specific because different enzymes have differently shaped active sites. An enzyme’s action is due to its active site.
2) The active site is where the substrate of an enzyme fits at the start of a reaction. Different substrates have different 3D shapes and different enzymes have active sites of different shapes. This explains why every enzyme can only work with specific substrates that fit the active site.

Question 14

SB1g
1) Use the lock-and-key model to develop explanations for enzyme activity
2) Explain why enzymes have a particular shape, as a result of the sequence of amino acids in the chain
3) Explain what it means for an enzyme to become denatured

Answer 14

1) The lock and key model is a model that describes the way an enzyme catalyses a reaction when the substrate fits within the active site of the enzyme. In the lock and key model, the shape of the active site matches the shape of its substrate molecules. This makes enzymes highly specific – each type of enzyme can catalyse only one type of reaction (or just a few types of reactions).
2) The order of amino acids determines the shape of an enzyme. This is highly specific to the enzyme, so that it can perform its specific function.
3) An enzyme is denatured when the shape of the enzyme has changed so much that its substrate does not fit and the reaction cannot be catalysed. This may be due to the pH or the temperature of the environment being too high.

Question 15

SB1h
1) Describe the effect of temperature on enzyme activity
2) Describe the effect of substrate concentration on enzyme activity
3) Describe the effect of pH on enzyme activity

Answer 15

1) As the temperature increases so does the rate of enzyme activity. An optimum activity is reached at the enzyme’s optimum temperature. A continued increase in temperature results in a sharp decrease in activity as the enzyme’s active site changes shape. It is now denatured.
2) As the substrate concentration increases so does the rate of enzyme activity. An optimum rate is reached at the enzyme’s optimum substrate concentration. A continued increase in substrate concentration results in the same activity as there are not enough enzyme molecules available to break down the excess substrate molecules.
3) As the pH increases so does the rate of enzyme activity. An optimum activity is reached at the enzyme’s optimum pH, pH 8 in this example. A continued increase in pH results in a sharp decrease in activity as the enzyme’s active site changes shape. It is now denatured.

Question 16

SB1h
1) Explain what is meant by the optimum pH/temperature of an enzyme
2) What is the formula for calculating rate of enzyme activity
3) Explain why temperature, substrate concentration and pH affect enzyme activity

Answer 16

1) The optimum pH or temperature of an enzyme is the pH or temperature when the maximum rate of enzyme activity can occur
2) Rate of enzyme activity = Amount of substrate used ÷ Time
3) The optimum temperature, substrate concentration or pH is the point when the enzyme works at its best. At any value before or after this, the rate of enzyme activity is not as high, apart from for substrate concentration, where the rate of activity stays the same after the optimum concentration.

Question 17

SB1i
1) State 3 ways that substances are transported
2) Describe how substances are transported by active transport
3) Explain how substances are transported by diffusion, what is the difference between two concentrations called?

Answer 17

1) Substances are transported by diffusion, osmosis and active transport.
2) Active transport is the transport of molecules from an area of low concentration to an area of high concentration against a concentration gradient. This requires energy. Cells use active transport to transport molecules against a concentration gradient, or molecules that are too big to diffuse through a membrane.
3) Diffusion is the movement of particles from an area of high concentration to an area of low concentration. Particles diffuse down a concentration gradient.
The difference between two concentrations is called a concentration gradient.

Question 18

SB1i
1) What is osmosis?
2) How does osmosis work?
3) Explain the effects of osmosis on cells and tissues

Answer 18

1) Osmosis is the overall movement of solvent (liquid) particles in a solution across a partially permeable membrane, from a more dilute solution (high concentration of water) to a more concentrated one (low concentration of water). The particles diffuse down a concentration gradient.
2) Cells are semi-permeable and trap large soluble molecules inside cells, while water molecules diffuse through the membrane. If the solution is more concentrated on one side of the membrane, there will be an overall movement of water molecules from the side where there is a dilute solution, to the side where there is a concentrated solution.
3) In a more concentrated solution, the cell contents lose water by osmosis and the cells shrink.
In a less concentrated solution, the cell contents gain water by osmosis and the cells can lyse.

Question 19

SB1i - Core practical
1) What is the aim of the investigating osmosis in potatoes core practical?
2) What is the method of the investigating osmosis in potatoes core practical?

Answer 19

1) The aim is to investigate osmosis in potatoes.
2) A) Label a separate boiling tube with the sucrose concentration of each solution you will test. Place all the tubes in a rack.
B) Cut similar-sized pieces of potato, enough for one per tube (Make sure they fit in the tube).
C) Blot each potato piece dry, measure and record its mass, and put it in an empty tube.
D) Fill each tube with the solution of the appropriate concentration.
E) After at least 15 minutes remove each potato peas and blot it dry. Measure and record its mass again.

Question 20

SB1i - Core practical
1) What are the independent, dependent and control variables for the investigating osmosis in potatoes core practical?
2) What are safety considerations for the investigating osmosis in potatoes core practical?

Answer 20

1) Independent variables: The sucrose concentration of the solutions
Dependent variable: The mass of plant tissue at the end
Control variables:
- Volume of plant tissue.
- Surface area of plant tissue.
- Length of time the plant tissue is left in solution.
- Temperature of the solution.
2) - Wear eye protection
- Do not eat the potato
- Be careful when using a cork borer and sharp knife

Question 21

SB1i - Core practical
1) What is the formula for percentage gain and loss of mass in osmosis?
2) How could you find a concentration of sucrose that would not cause the mass of the potato chip to change, using the graph of results?

Answer 21

1) % change in mass = (final mass - initial mass) / initial mass * 100
2) Find the sucrose concentration where the curve of best fit crosses the x-axis/ where there is no change in mass of the potato chip

Question 22

SB1i
1) What is the aim for the pH and enzymes core practical?
2) What are the risks for the pH and enzymes core practical?
3) What are the issues for the pH and enzymes core practical?

Answer 22

1) The aim is to determine the optimum pH at which an enzyme’s activity is greatest.
2) Risks: Iodine solution is an irritant. If it touches skin it should be washed off.
Goggles should be worn at all times.
If using a Bunsen burner tie long hair back and wear goggles.
3) Issues: Samples are only being takes every 20 seconds, which means that we only have an approximate time for the reaction to complete. We could address this by taking samples every ten seconds. (The time interval between the testing each sample may be too long to accurately find the time taken for all the starch to be broken down.)
We are looking for the time when the iodine solution does not go blue-black. This is not always obvious as the colour change is gradual. A way to address this is by asking several people to look at the spotting tile to decide if the reaction has completed.

Question 23

SB1i
What is the method for the pH and enzymes core practical?

Answer 23

A) Set up a heating apparatus using a tripod, gauze, heat resistant mat, Bunsen burner and a large beaker half filled with water. Heat the water to 40°C, and then use the collar on the Bunsen burner to produce a flame that keeps the water at this temperature.
B) Place one drop of iodine solution into a well tray (dimple tile).
C) Measure 2 cm³ of amylase solution and 1 cm³ of a solution with a particular pH into the tube.
D) Add 2 cm³ of starch solution to the tube and place it carefully into the water bath. Start the stopwatch and stir the mixture.
E) Every 20 seconds, take a small amount of mixture and place one drop of it into a fresh drop of iodine solution. Stop testing when the iodine solution stops changing colour.
F) Repeat the experiment using a different pH solution in step C

Question 24

SB1b - Core Practical
1) What is the aim of the microscope core practical?
2) What are the steps to using a microscope?

Answer 24

1) Investigate biological specimens using microscopes, including magnification calculations and labelled scientific drawings from observations.
2) A) First take a small sample of cells
B) Add a drop of water to the centre of a microscope slide.
C) Add a drop of stain to the centre of a microscope slide.
D) Place the specimen on the drop of water or stain.
E) Use a toothpick to slowly lower the coverslip onto the specimen. The coverslip keeps the specimen flat and holds it in place.
F) Examine the specimen under a microscope. Start with the lowest magnification and work up to higher magnifications.

Question 25

SB1b - Core Practical
1) Explain the 2 different types of lenses?
2) Describe the purpose of adjustment knobs
3) What are the steps for adjusting magnification?

Answer 25

1) The objective lens magnifies the image and is above the specimen. The eyepiece lens is the one that you look through.
2) The course and fine adjustment knobs help focus the image so it is clearer.
3) Always start with the lowest objective lens magnification (for example x4) and use the adjustment knobs to bring the sample into focus. To view the image at a greater magnification, select a higher powered objective lens (for example x10) and bring the sample back into focus.

Question 26

SB1b - Core Practical
1) How can you ensure that you have an accurate and useful microscopic drawing?
2) How do you calculate a microscope’s magnification using the lens’ magnifications?
3) What are the formulae to calculate the real size and the image size?

Answer 26

1) Label with straight, uncrossing lines, include the magnification used and a scale, keep the parts in proportion, and not colour or shade the drawing.
2) Multiply the objective lens and eyepiece lens’ magnifications together.
3) Image size = magnification x real size
Real size = image size / magnification

Question 27

SB1b - Core Practical
1) What are the risks for the microscopes core practical?
2) What are the issues for the microscopes core practical?

Answer 27

1) - Care must be taken when looking down the microscope that the illumination is not too bright as eye damage could be caused.
- Care when using microscope stains as some are harmful.
- Care when handling coverslips and microscope slides as broken glass could cut skin.
2) - A stain may be required to make the structures visible.
- Always start with the objective lens to make it easier to focus on the image, and avoid blurry images

Question 28

1) What is the enzyme that breaks down carbohydrates?
2) What is the enzyme that breaks down protein?
3) Explain why the breakdown of large molecules into smaller components is necessary for organisms

Answer 28

1) Carboydrase breaks down carbohydrates into simple sugars.
2) Protease breaks down protein into amino acids.
3) Organisms need to be able to break down large molecules into smaller components so that they can be absorbed into the bloodstream and into cells. This is so that they can be used for growth and other life processes.

Question 29

SB1b - Core Practical
1) Describe the steps should a person should take to focus the microscope
2) What is the equation to calculate the magnification?
3) Why are circles seen when looking through the microscope, and how can this be solved?

Answer 29

1) Place the slide on the stage and look through the eyepiece lens. Start with the lowest power objective lens. Stage in the highest position. Lower the stage until the image comes into focus. Switch to a higher magnification objective lens and refocus using the focusing wheel.
2) Magnification = image size/ real size
3) The circles are due to air bubbles. This can be solved by lowering the coverslip more slow and carefully.

Question 30

SB1f
1) Give two advantages of knowing what compounds are in a food
2) Define qualitative
3) Define quantitative

Answer 30

1) In case of food allergies, and dietary information so people can make informed choices about what they are eating.
2) Qualitative: data that is descriptive or categorical.
3) Quantitative: data that is numerical or a measurement.

Question 31

1) What is the purpose of the coverslip?
2) Explain why a small slice of an organism is used when viewing it under a microscope, instead of the whole tissue or organism (such as a whole leaf)

Answer 31

1) To keep the specimen flat, to keep the specimen in place, to protect the objective lens, and protect the specimen.
2) The entire organism or tissue (such as a leaf) is too thick. An entire organism would not allow light to shine through it, to enable the cells to be identified.