Biology ISA/EMPA June 2013

In your investigation you tested for the disappearance of starch.Describe a test you could have carried out to show that products of starch hydrolysis are present.

Benedict's solution and heat. Brick red colour indicates reducing sugar present.

Suggest two limitations of the method you used that could have affected your results.

All sides of block not in contact with acid. End point difficult to judge. No repeats.

Healthy people have amylase in their blood. This does not cause any harmful effects in the body. Explain why.

Amylase specific to starch. Starch is not found in human blood cells only plant cells.

A student carried out a similar investigation to yours. The graph shows her results

As surface area to volume ratio increases the time decreases, steeply and then less steeplyChange at 0.85.

The student concluded that there was a strong positive correlation between wrist circumference and hand span. Explain why he came to this conclusion.

As wrist circumference increases so does hand span. Points are close to the line of best fit.

Many of the substances causing food stains are large, insoluble proteins. Suggest how a biological washing powder removes this type of stains.

Biological washing powder contains enzymes which hydrolyse protein to amino acids which are soluble and can therefore be washed away.

The student wondered whether wrist circumference could be used to predict hand span and plotted the scatter diagram shown in Figure 2.Explain why he plotted his data as a scatter diagram.

Both variables are continuous. Two dependent variables. He wanted to see if there is a correlation

Explain how smoking cigarettes increases the risk of developing heart disease.

Carbon monoxide reduces oxygen in the blood. Nicotine increases heart rate and blood pressure. High blood pressure damages blood vessels so there is an ncreases risk of atheroma formation. Increases risk of blood clots/thrombus.Smoking makes platelets more 'sticky'.

Before the glucometer was available, diabetics used test strips to measure the concentration of glucose in their urine as a means of measuring their blood glucose concentration. Give two reasons why this method of testing urine would not give an accurate measurement of blood glucose concentration

Concentration is given as a range, measurement is not precise. Difficult to match colour against chart as colour match is subjective

When he carried out the statistical test on his data he obtained a value of P<0.05. How should he interpret this value?

Correlation not due to chance so null hypothesis rejected because probability is less than 0.05 Results of test would be obtained by chance less than 5% of the time.

Pancreatitis can lead to the release of protein-digesting enzymes into the blood. This is harmful to the body. Suggest one reason why.

Could digest carrier proteins in body cells. Could digest antibodies in blood.

How many repeat counts did you take in each colour of light? Give four reasons why you did this number of repeat counts.

Enough for statistical test. Enough for more representative mean. Limited by time available. Reduce the effect of anomalies on the mean.

Most customers want a washing powder which removes stains from clothes over a range of temperatures. After obtaining the results shown in Figure 3, which enzyme should the scientist recommend for use in a biological powder? Give reasons for your answer.

Enzyme S effective across a wider range of temperatures. Enzyme S more active above 50 °C. Enzyme S more active below 37 °C temperature. Although Enzyme P has higher rate of reaction at optimum, enzyme P denatured above 50 °C.

Another student carried out a similar investigation to yours but he used different concentrations of acid with agar cubes all measuring 10 mm × 10 mm × 10 mm. As in your investigation, he obtained a range of times for the agar cubes to change colour. Explain why

Higher concentration of acid, greater the concentration gradient. Faster the rate of diffusion.

Give one precaution you took when counting the number of stomata in a field of view to make sure the count was accurate.

I repeated the count and avoided areas with air bubbles.

You were told to decide for yourself when the blue-black colour failed to appear. What did you do to ensure your decision was consistent?

I used a previous test where the blue-black colour has been lost i.e. a standard.

Describe two differences between the breathing of a person with emphysema and a person without emphysema.

In emphysema; A lower volume breathed in. Faster breathing. Shallower breaths over time;

Each type of chlorophyll is produced by a specific enzyme-controlled pathway. Use this information to suggest how the same beech tree can produce more chlorophyll b in some leaf cells than others.

In shade leaves there is a greater amount of enzyme activity for the production of chlorophyll b. Greater gene expression( greater transcription of the gene and greater translation as more mRNA is produced). Enzyme is light sensitive so there is a faster rate of reaction with lower light.

You were told to hold the test tube at an angle and facing away from you and anyone else (step 3).Suggest one reason, other than for safety, why this was a better method than keeping the tube in a vertical position

Larger surface area. More of tube heated at an angle.

You were given three leaves from the same plant. Suggest one reason why the leaves should be from the same plant.

Leaves from the same plant will be genetically identical.

Other than the proportion of light of different colours, give one feature of a lamp that could affect the rate of photosynthesis of the aquatic plants.

Light intensity (power of bulb).Heat given off.

You were told to carry out the reaction in a water bath at 30ºC, rather than at room temperature. Explain why the reaction would be faster at 30ºC than at room temperature.

Molecules at 30 °C have more kinetic energy so more collisions between enzyme and substrate so more enzyme-substrate complexes formed.

Explain why the transpiration rate increases when the temperature increases.

Molecules have more kinetic energy so faster diffusion of water as temperature increases in leaf. Steeper diffusion gradient.

Use Figure 8 to describe the absorption of light of different wavelengths by chlorophyll a.

Peaks at 420-430 and 660-670. No absorption of light between approximately 500 and 600. Highest peak at 420-430.

Explain why people with emphysema find it difficult to breathe during exercise

People with emphysema have reduced ventilation so they can't maintain oxygen concentration. This means that less oxygen reaches the muscle cells for aerobic respiration so less ATP produced and less energy is released.

You investigated characteristics with phenotypes produced by dominant and recessive alleles. What is meant by phenotype?

Physical appearance of characteristic

Which statistical test should he use to see if the correlation between a person's wrist circumference and their hand span is significant or not?

Rank correlation

Rate of production of bubbles can be used for measuring the rate of photosynthesis. Explain why.

Rate of production of bubbles is proportional to the rate of photosynthesis. Oxygen produced in light dependent reaction (photolysis)

The student kept fish and aquatic plants in an aquarium. Suggest five reasons why it would be important to include aquatic plants when keeping fish in an aquarium.

Shelter for fish to reduce stress and avoid predators. Food source for plant eating fish. Oxygen production for fish respiration. Remove carbon dioxide produced from fish respiration so water does not become acidic. Remove nitrogenous waste from fish.

Biological washing powders often contain a number of different enzymes. This enables them to remove a wider range of stains from clothes. Explain why a number of enzymes are required to remove a wider range of stains.

Stains caused by different substances. Enzymes are specific. Active site specific to substrate so other substrates cannot fit active site.

You used agar cubes as model cells to find the relationship between surface area to volume ratio and the rate of diffusion. Evaluate the use of agar cubes as model cells in this investigation.

Suitable because diffusion is passive so blocks do not need to be alive. Limitations include;Cells can be attached to other cells; Cells can be different shapes; Blocks have no cell surface membrane. Processes in cells maintain a concentration gradient. Cubes are larger than cells.

During this time in the acid, the pieces of agar may have had one face in contact with the beaker which could have affected your results. Suggest how the method could be modified to reduce this problem.

Swirl contents at regular intervals

The leaves of plants that grow in dry areas usually have a low number of stomata per mm2. Use your knowledge of leaf structure to suggest three other adaptations that the leaves might have that enable the plants to grow well in dry conditions.

Thick cuticle, Small leaves, hairy leaves, rolled leaves, sunken stomata.

Standard deviation

Used to compare two means

What does the standard deviation show?

Variation of data about the mean.

The student also used her results to explain the advantage of some adaptations of the leaves of xerophytes. Suggest and explain how one adaptation of the leaves of xerophytes affects surface area to volume ratio and water loss.

Xerophytes have form spines rather than leaves which reduces surface area for evaporation of water.

In step 6, you were told to leave the aquatic plant for 10 minutes before starting to count bubbles. Suggest why.

To allow the rate of bubbling to stabilise.

A student carried out a similar experiment to yours. The graph shows her results. Explain the difference in her results at pH3 and pH4.

Change in charge of enzyme. Change in shape of enzyme. More ES complexes formed per second. at pH4.

Other than for age, there was no matching of the subjects in this investigation. Give one reason why it was not necessary to match the subjects in this investigation.

Everybody has these characteristics. Characteristics not specific to gender, ethnicity,

You were told to count the number of stomata in a field of view using the highest power magnification of your microscope (step 6). The magnification depends on the eyepiece lens and the objective lens. Describe how you would find the magnification you used.

Eyepiece x objective lenses

Some people with type 2 diabetes have cells which do not respond to insulin. Explain how this leads to a reduced ability to regulate blood glucose concentration.

Fewer receptors on cell membrane so fewer glucose transport proteins so less glucose can enter cells so less glucose converted to glycogen so, without treatment blood glucose concentration not lowered when high.

People suffering from emphysema have less elastic tissue in their lungs. Explain how this affects the efficiency of gas exchange in the alveoli.

Inability to recoil and stretch. Reduced tidal volume. Less oxygen enters the alveoli. Decreased concentration gradient;

Few species of plant can live below large trees in a forest. Use the information in Figure 8 and Figure 9 to suggest why

Less light energy passes through leaves and reaches ground. Smaller range of wavelengths passes through leaves. Little light for chlorophyll to absorb. So insufficient photosynthesis for growth. Photosynthesis unlikely to exceed respiration.

In her investigation, the student compared leaves from a xerophytic plant with a plant similar to the one you used. She found that the leaves of the xerophytic plant had a lower number of stomata per mm2. Explain why having fewer stomata would be of benefit to the xerophytic plant

Less water lost. This is beneficial because xerophytes are adapted to areas where water is scarce.

Give 8 environmental variables, other than temperature, that the scientists would have controlled when growing the plants.

Light intensity, carbon dioxide concentration, type of soil,minerals, water in soil, humidity of air, pH of soil, planting density.

In leaves at the top of trees in a forest, carbon dioxide is often the limiting factor for photosynthesis. Use your knowledge of photosynthesis to suggest and explain three reasons why.

Light not limiting as there is no shading so ight-dependent reaction not limiting.Temperature not limiting as there is no shading so fast reactions of enzymes in light independent reaction. High use of carbon dioxide light-independent reaction is limiting.

For how long did you decide to count bubbles? Explain why you chose this length of time.

Long enough to minimise effect of miscounting. Short enough to maintain accurate counting. Time to allow sufficient repeats to be carried out.

A student carried out an investigation similar to yours. In her investigation, she found the area of the field of view and then estimated the number of stomata in the lower epidermis of one leaf. Describe how she could have used her calculation of the area of the field of view when estimating how many stomata were in the lower epidermis of one leaf.

Mean number of stomata × leaf area all divided by Area of field of view

The manufacturer of type A and type B washing powder claimed that these results showed that biological washing powders are better at removing stains from clothes. Use the information in Figure 2 to evaluate this claim.

More effective with all stains. Greater improvement with salad dressing. Little improvement with raspberry sorbe. Only tested 5 stains. Only chose stains that would work. Only included results that did work. Only one set of results, the experiment was not repeated. Only compared against one washing powder so may not be true for other washing powders.

During a glucose tolerance test the person remains at rest. Why is it important that the person remains at rest?

Movement uses muscle. Movement increases (ate of respiration. Respiration uses glucose and so respiration reduces blood glucose concentration

Suggest 5 reasons why the Hardy-Weinberg principle may not apply to human populations.

Mutations occur in humans. People migrate so genes flow into a population. Mating is not random. Generations overlap, generations are not discrete. Natural selection so there is change in allele frequencies.

In a person with a blocked pancreatic duct, starch digestion is affected. Explain how.

No amylase can enter small intestine so no starch is digested in intestine. Salivary amylase not affected so some starch will be digested by salivary amylase.

The student concluded that wrist circumference was not determined by a single gene. Use his data to suggest why he came to this conclusion.

No dominant or recessive categories

The student chose to join the points on the graph with straight lines, rather than drawing a line of best fit. Suggest why she did this.

No intermediate values. Cannot predict between plotted values.

The ecologist collected shade leaves at random from a branch. Suggest a method he could have used to collect shade leaves at random from a branch.

Number leaves on the branch and use a random number generator to determine which leaf to pick.

You were told to decide for yourself how many fields of view to use to count the number of stomata. Explain how you decided how many fields of view to use.

Number of fields of view must be enough to get a representative mean so anomalies can be identified.

". Stand the beaker on the white tile. Pour dilute hydrochloric acid into the beaker until it is half full.". You did not add a fixed volume of acid to the beaker. Why was it not necessary to use a fixed volume of acid?

Only need to cover the agar;

In this investigation, you were given buffers with a pH range from 5 to 8. Suggest why.

Outside this range reaction is slow because enzyme is denatured outside this range. Optimum pH is within this range.

In step 2, you were told to use the same piece of aquatic plant throughout your Task 2 investigation. Explain why.

Same concentration of chlorophyll/same number of chloroplasts/same number of leaves/same surface area.

You could plot a graph of your results to see if there is a relationship between the mass of a marshmallow and its energy content. What type of graph should you use to show whether there is a relationship between the mass and the energy content of each marshmallow? Explain your answer.

Scatter graph. Two continuous variables. Data are in pairs.

Another student carried out a similar investigation to yours but she used the apparatus shown in Figure 7 to measure the gas produced by the aquatic plant. What is the syringe used for?

To draw bubble(s) onto scale for measuring. To draw solution into tube. To remove bubbles to enable repeat reading.

You were told to count the number of stomata in different fields of view of the same leaf (step 7). Explain why this was important

To get results representative of the whole leaf as the density of stomata may not be uniform e.g. there could be more/fewer stomata at the edges.

You placed the boiling tube containing the aquatic plant into a beaker of water. Explain why

To minimise temperature changes as water has a high specific heat capacity.

People with type 1 diabetes are described as being insulin-dependent. Suggest why they are described as insulin-dependent.

Treatment requires person receiving insulin in some way ee.g. insulin injection.

The Hardy-Weinberg equation is p2 + 2pq + q2 = 1 The Hardy-Weinberg equation can be used to estimate the frequency of a recessive allele in a population. Haemochromatosis is a condition caused by a recessive allele. In one country, 1 in every 400 people was found to have haemochromatosis.Describe how you would use the Hardy-Weinberg equation to calculate the frequency of people who are healthy but carriers (heterozygotes) of the allele for haemochromatosis.

Use 1 in 400 to find frequency of homozygous recessive (q²) which gives a frequency of 0.0025. Find square root of 0.0025. Use of p + q = 1.0 to determine frequency of both alleles. p = 0.95 and q = 0.05. Use of 2pq to find heterozygotes

A student carried out an investigation similar to yours. In her investigation, she found the area of the field of view and then estimated the number of stomata in the lower epidermis of one leaf. Describe a method she could have used to find the area of the field of view.

Use a graticule to measure radius then use 𝜋𝑟² to calculate the area.

Describe a method that you could use to count the number of stomata in different fields of view of a microscope

Use forceps to peel off a small piece of the lower epidermis of the leaf. Place this small piece of epidermis in the centre of a microscope slide and add a drop of water. Use a mounted needle to lower a cover slip in place. Put your slide onto the stage of the microscope and focus on the stomata. Count the number of stomata in one field of view using the highest power magnification of your microscope. Repeat previous step with different fields of view taken at random until you have sufficient data. Repeat steps 1-7 using the two other leaves.

Another student carried out a similar investigation to yours but she used the apparatus shown in Figure 7 to measure the gas produced by the aquatic plant. Using this apparatus, the student obtained a more accurate measurement of the volume of gas produced than by counting bubbles. Explain why.

Volume of gas measured: 𝜋𝑟² × length where 𝑟 = radius of bore of tube. Avoids problem of bubbles being differing sizes. Avoids problem of miscounting number of bubbles.

Apart from deciding when the blue-black colour failed to appear, give 5 limitations of the method you used that could have affected the reliability of your results.

Volume of iodine not fixed/not controlled. Volume of mixture not controlled. End point is qualitative not quantitative.Temperature could fluctuate. No repeats.

The cells in the aquatic plant will also be carrying out respiration. Will this affect your results? Explain your answer.

Yes because respiration uses oxygen so there will be fewer bubbles. No because respiration uses oxygen and produces carbon dioxide. Rate of respiration likely to be constant (carbon dioxide is soluble).