3.1.6 LIVING ORGANISMS VARY

EQ: Figure 7 shows a fresh-water shrimp. Biologists collected shrimps from a stream inside a cave and from the same stream when it was in the open. They measured the maximum diameter of each shrimp's eye. They also measured the length of its antenna. From these measurements they calculated the mean values for each site. Table 3 shows their results. The biologists investigated shrimps living in other streams. They measured the length of the antennae of these shrimps. They also measured their body length. Figure 8 shows the mean antenna length plotted against mean body length for each site. Do the data in Figure 8 support the conclusion that shrimps with longer bodies have longer antennae? Give the reason for your answer. (1 MARK)

(No) for same body length, antenna are longer/antenna are shorter/some with longer body have short antennae/some with shorter body length have longer antennae; OR (Yes) positive correlation in open/in cave;

EQ: Figure 7 shows a fresh-water shrimp. Biologists collected shrimps from a stream inside a cave and from the same stream when it was in the open. They measured the maximum diameter of each shrimp's eye. They also measured the length of its antenna. From these measurements they calculated the mean values for each site. Table 3 shows their results. The biologists measured the maximum diameter of each shrimp's eye. Explain why they measured the maximum diameter. (1 MARK)

(So results) can be compared/so measurement is the same each time/because eye is not perfectly round/uniform;

Q: The graph shows the variation in length of 86 atlantic salmon. (a) Give two possible causes of variation. (2 MARKS) (b) When comparing variation in size between two groups of organisms, It is often considered more useful to compare standard deviations rather than ranges. Explain why. (2 MARKS)

(a) Age & gender of THE salmon. (b) So that anomalies of either very short or very long do not skew the results

Q: The graph shows variation in the number of spots on the wing cases of a species of ladybird. (a) The number of spots on the wing cases of this species of ladybird is determined by genes. What does the graph suggest about the genetic control of spot number in this species? (1 MARK) (b) Give one piece of evidence from the graph that variation in the number of spots is normally distributed number of ladybirds (1 MARK)

(a) Several genes involved / multiple alleles due to a combination of genes (b) The graph is the shape off a bell curve The graph is quite/roughly symmetrical

Describe a general practical of chromatography.

- Add a concentrated spot of mixture to the bottom of stationary phase - End of chromatography strip (stationary phase) is lowered into the solvent below the pencil line - Pigments / compounds are carried different distances according to their solubility - If compounds not visible use a stain eg amino acids - ninhydrin - Stop before solvent front reaches the end of the stationary phase - Identify compounds by comparing results known samples → Rf values

Quantitive investigations of variation within a species / population: large sample size

- Data should be representative of the whole population → can use a statistical test - Minimise effects of chance (lower probability that chance will influence the data)-->MORE RELIABLE mean / average - Anomalies have less influence and can be identified

CHROMATOGRAPHY: What is the advantage to a plant of having leaves that contain more than one type of pigment? (3 marks)

- Different photosynthetic pigments absorb light most effectively at different wavelengths; - by having more pigments, plants can absorb energy over a wider range of wavelengths; - so they have more energy available for photosynthesis

Q: An investigation into the resistance of the iranian wheat plants to mildew produced the results shown in Fig 5.2 State the type of variation that is shown in Fig 5.2 and describe its characteristics. (2 MARKS)

- Discontinuous / qualitative / discrete categories - Single / few genes involved OR no / small environmental effects

Q: Many species of insects have evolved resistance to chemical insecticides. Three different patterns of resistance in insect species, R, S and T are shown in Fig. 6.1 1. Using the letter(s), R, S and T, state which species show a continuous pattern of variation and which species show a discontinuous pattern. (2 MARKS)

- Discontinuous: S & T - Continoinous: R

Describe the environmental causes of diversity / variation.

- Environment changes the phenotype - Can change over a lifetime - Eg accent, siamese cats, nutrition

Q: The finches of the Galapagos Islands have different shapes beaks to feed on different food sources. Medium ground finches have a range of beak sizes. Suggest an explanation for the variation in beak sizes in medium ground finches. (2 MARKS)

- Genetic variation / different alleles / large gene pool - Mutations OR polygenic inheritance

Q: A study of insects was carried out in an area of the Cairngorms National Park to determine species richness. The insects were sampled using a sweep net method. With this method, a net is swept through the vegetation. Insects are removed, identified and counted. Describe three ways in which the sampling procedure could be designed to try to make sure that a representative sample was obtained. (3 MARKS)

- Idea of: unbiased method to selecting sampling area ACCEPT e.g. random selection of areas / coordinates OR use of transect - Sample many times and calculate mean / average - Standardised sweeping procedure e.g. same type of movement / same length of time / same number of sweeps / sample at same time of day / ensure insects do not escape (before being identified) / method to prevent recounting

Q: Scientists have identified approximately 1.8 million different species. The number of species that actually exist is likely to be significantly higher than 1.8 million. Suggest three reasons why the number of species identified is likely to be lower than the actual number of species present on earth. (3 MARKS)

- Idea that: not all areas explored / species yet discovered - Microscopic / small / nocturnal / camouflaged species difficult to see / organisms mistakenly identified as one species may actually be two (or more) species - Sampling might miss rare species

Q: What is the difference between comparing the intraspecific genetic diversity and the interspecific genetic diversity?

- Intraspecific = within a species - Interspecific = between species

Q: Maize seeds were an important food crop for the people who lived in Peru. The seeds could be kept for long periods. Each year, some were sown to grow the next crop. Archaeologists have found well-preserved stores. The graph shows the lengths of seeds collected from three stores of different ages. Within each store the maize seeds showed a range of different lengths. Give two causes of this variation and an explanation for each. (4 MARKS)

- Length controlled by many genes / polygenes; - Each gene may have different alleles / idea of additive effects; - Environmental factors / or named factor; - How named factor may affect growth of seeds;

Describe how chromatography works.

- Mixture contains more than one compound - Each compound will have a different solubility in a given solvent - The mobile phase (liquid) moves through the stationary phase - The more soluble the compound is the more further it will move in the mobile phase - The compounds separate in order of their solubility

Describe the environmental causes AND genetic causes of diversity / variation.

- Most variation is a result of both environment and genetic variation - Eg height - Genetic = tall parents usually have tall offspring - Childhood mutation

Q: A mildew fungus infects wheats plants, causing disease.

- Most wheat plants in the UK show little resistance to this disease - Some iranian wheat plants are resistant - The yield from these resistant wheat plants is very low

Describe the genetic causes of diveristy / variation.

- Mutation - Meiosis; crossing over, independent assortment - Random fertilisation due to fusion of gametes; eg blood group / type - Inherited → genetic variation results in evolution Variation in asexually reproducing organisms can only be due to mutations.

Q: The growth rate of the chickens shows continuous variation. Describe three characteristics of this type of variation. (2 MARKS)

- No defined categories OR range of values - Influenced by environment / many genes / genes and environment

Q: A study was carried out on the biodiversity of this habitat. In this study, a student placed his quadrat on areas he considered to have the most biodiversity. Explain what is wrong with this technique. (2 MARKS)

- Not random / should have been random - Unrepresentative / skewed / biased results / creates an overestimate of diversity / may miss some (dominant) species / does not cover full range of species

What is the difference between paper chromatography and thin layer chromatography?

- Paper chromatography: uses paper as the stationary phase - Thin layer chromatography (TLC): uses a thin layer of absorbent material eg silica gel, spread onto a glass sheet as the stationary phase

Quantitive investigations of variation within a species / population: random sampling

- Random sample → eliminates / avoids bias Example of random sampling in a field: - Divide the area into a grid of numbered lines - Using random number from a table, obtain a series of coordinates - Take samples at the intersection of each pair of coordinated i.e. using quadrats

Q: Plants have several different groups of pigments that absorb light energy for photosynthesis. These include two types of chlorophyll, the xanthophylls, and the carotenoids. Different species of plants will have different amounts of these proteins. Describe how you could identify the pigments in leaves from different plants. (5 MARKS)

- Separate the pigments using paper chromatography/thin layer chromatography. (1) - Dissolve the pigments in a solvent/named solvent/propan-2-ol/ethanol. (1) - Using chromatography paper/thin layer chromatography plate. (1) - Allow the solvent to move up the paper/plate and separate the pigments. (1) - Different pigments would move at different speeds up the paper/plate. (1)

REQUIRED PRACTICAL 3: Investigating plant pigments using chromatography

- Take your first leaf and cut it into small pieces with the scissors. - Put the leaf pieces into the mortar and add 10 cm³ of propan-2-ol. - Crush the leaf pieces in the mortar with the pestle. - When the propan-2-ol has turned dark green, pour it into a 100 cm3 glass beaker and label it with the chinagraph pencil. - Take chromatography paper mark origin in pencil. - Using a capillary tube, take up a small amount of solution from the 100 cm³ glass beaker and spot it onto the origin and allow solvent to evaporate between application and keep spot of solution as small as possible. - Place one edge of paper in solvent with meniscus below origin - In container with lid (to prevent evaporation) - Allow solvent to run up paper, remove paper and mark solcent front with pencil / measure distance solvent front moved - Turn 90o and use 2nd solvent - Stain to visualise substances (e.g. amino acids are stained by ninhydrin) - Calculate Rf value for each pigment = distance moved by substance / distance moved by solvent front

Describe discontinuous variation.

- individuals fall into distinct, discrete groups with no intermediates → represented on a bar chart eg blood group → Controlled by a single gene with a few alleles - Data tends to be qualitative - Controlled by a single gene of a few genes - Unaffected / not strongly influenced by the environment - Limite range of phenotypes

CHROMATOGRAPHY: You have calculated the Rf values for each pigment. How many decimal places should each Rf value be written to? Explain your answer.

1 decimal place The ruler used to measure the solvent front and distances moved by the pigments in cm can only measure to 1 decimal place.

EQ: Students separated a mixture of amino acids using paper chromatography. Figure 6 shows the apparatus the students used. Describe how the students should have put the solution containing a mixture of amino acids onto the chromatography paper before the paper is put in the jar. (3 MARKS)

1. (Draw) start line / origin in pencil; 2. Use pipette / glass rod / capillary tube / pin (to transfer solution) onto start line / origin; 3. Apply several drops on the same spot; 4. Allow to dry between each application;

Q: This is a diagram of the absorption of light by different types of pigments. 1. Describe the pattern of the graph (3 MARKS) 2. Explain why it is important that plants contain a mixture of different pigments. (2 MARKS)

1. - Chlorophyll a peaks at 450 and 680 nm (1) - Chlorophyll b peaks at 490 and 650 nm (1) - Carotenoids peak at 460 and 500 nm (1) 2. - A mixture of different pigments means a plant can absorb light at different wavelengths.(1) - To allow plants to absorb enough light for photosynthesis.(1)

Q: In 1958, scientists made a breakthrough in artificial reproductive cloning by successfully cloning vertebrate species. The species cloned was the African clawed frog, Xenopus laevis. Fig. 1.1, on page 2 of the insert, shows the cloned offspring produced, labelled D, as well as the three adult frogs (A, B and C) that were used to create them. - Frog A, a brown-coloured female frog, laid eggs, which then had their nuclei removed - Frog B, an albino (white-coloured) female, laid eggs that were fertilised by sperm from C - Frog C, an albino male, produced sperm that fertilised the eggs of B. One of the fertilised eggs from B was allowed to divide. Nuclei were extracted from the resulting cells and placed into the eggs from frog A. These eggs developed into the frogs labelled D in Fig 1.1. The frogs in Fig.1.1 show discontinuous variation in colour. Using your knowledge of discontinuous and continuous variation, and the information given. Suggest: 1. One other phenotypic characteristic in which the frogs show a discontinuous pattern of variation. (1 MARK) 2. One phenotypic characteristic in which they show a continuous pattern of variation. (1 MARK) 3. State the extent to which the environment is likely to affect each of the phenotypic characteristics that you have suggested. (2 MARKS)

1. - Discontinuous - gender / male and female / eye colour - Continuous - size / length / mass 2. No / little environmental effect for continuous variation ACCEPT discontinuous variation is only genetic 3. Some / large environmental effect for continuous variation

Q: The kakapo is one of the world's largest and rarest parrot species. The variation in maass of adult birds in the kakapo population has been reported to be between 950 g and 4000 g. 1. Suggest two reasons why the kakapo varies in size (2 MARKS) 2. Suggest two reasons why the reported mass range for the adult kakapo may not be accurate. (2 MARKS)

1. - The genetic differences / different alleles / inherited differences - Environment / diet / disease 2. - Only small number have been sampled - Idea that individuals sampled may not be representative of population

Q: A group of scientists is trying to develop a new strain of wheat that grows successfully in an area of Africa with low rainfall. They begin by testing two different species. To compare them, the scientists take a random sample of plants from each species. The plants are grown in the same environment and the scientists monitor how long each plant can survive without water. The results are shown in Figure 2. 1. Evaluate the method used by the scientists to obtain their results. (4 marks) 2. The scientists must choose one species to take to Africa for further testing. Discuss the reasons for and against selecting species B. Use data from Figure 2 to support your answer. (2 marks) 3. The scientists try to increase survival of their chosen species by inserting two genes for drought-resistance from other plants. The results are shown in Table 2. Based on the data in Table 2, which gene(s) should the scientists introduce into their chosen plant? Explain your answer. (1 mark)

1. - The method used was good because it used random samples, which helps to make sure the results aren't biased (1 mark). - The plants were grown in the same environment to control the variables, which increases the validity of the results (1 mark). - However, there was no control used, which decreases the validity of the results (1 mark) and they didn't repeat the experiment, which would have increased the precision of the results (1 mark). 2. - The mean number of hours survived without water was higher for species B than species A (168 hours compared to 120 hours), so species B would survive better in the area of Africa with low rainfall (1 mark). - However, the standard deviation is larger for species B than species A, so there is more variation in the results (1 mark). 3. Gene Y, because the mean number of days survived without water is highest and the standard deviation is lowest (1 mark).

EQ: The genetic diversity of species is measured by comparing differences in the base sequence of DNA or differences in the base sequence of mRNA. Give two other ways in which genetic diversity between species is measured. (2 MARKS)

1. Comparing (measurable/observable) features/characteristics; 2. Comparing amino acid sequences/primary structures (of a/named/the same protein);

EQ: Figure 7 shows a fresh-water shrimp. Biologists collected shrimps from a stream inside a cave and from the same stream when it was in the open. They measured the maximum diameter of each shrimp's eye. They also measured the length of its antenna. From these measurements they calculated the mean values for each site. Table 3 shows their results. A scientist working many years earlier suggested that animals which live in caves had similar adaptations. These adaptations included • Smaller eyes • Greater use of sense organs such as those involved in detecting touch. Do the data in Table 3 support this scientist's suggestion? Explain your answer. (2 MARKS)

1. Eye (diameter) is smaller and antennae longer; 2. Antennae detecting touch; 3. Data only refers to shrimps/data may not apply to all animals/only in one area;

EQ: A student obtained a solution of pigments from the leaves of a plant. Then the student used paper chromatography to separate the pigments. Figure 5 shows the chromatogram produced. 1. Explain why the student marked the origin using a pencil rather than using ink. (1 MARK) 2. Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin. (2 MARKS) 3. Calculating the Rf values of the pigments can help to identify each pigment. An Rf value compares the distance the pigment has moved from the origin with the distance the solvent front has moved from the origin. Rf = distance pigment has moved from the origin / distance solvent front has moved from the origin The distance each pigment has moved is measured from the middle of each spot. Pigment A has an Rf value of 0.95 Use Figure 5 to calculate the Rf value of pigment C. (1 MARK) 4. The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves. (1 MARK)

1. Ink and (leaf) pigments would mix OR (With ink) origin/line in different position OR (With pencil) origin/line in same position OR (With pencil) origin/line still visible; 2. - Level of solvent below origin/line; - Remove/stop before (solvent) reaches top/end; 3. Accept any answer in range of 0.58 to 0.62; 4. (Absorb) different/more wavelengths (of light) for photosynthesis;

EQ: Figure 7 shows a fresh-water shrimp. Biologists collected shrimps from a stream inside a cave and from the same stream when it was in the open. They measured the maximum diameter of each shrimp's eye. They also measured the length of its antenna. From these measurements they calculated the mean values for each site. Table 3 shows their results. The data in Table 3 are mean values. Explain how standard deviations of these mean values would help you to interpret the data in Table 3. (2 MARKS)

1. Standard deviation gives a measure of spread/variation; 2. More standard deviations overlap, the less likely it is that differences are real/significant/the more likely they are caused by chance;

CHROMATOGRAPHY: As the propan-2-ol solvent moved up the chromatography paper, the different pigments in the solutions from each leaf separated. 1. Why did the pigments move up the paper, rather than staying on the line at the bottom? (1 mark) 2. Why did some pigments move further up the paper than others? (2 marks) 3. Why can you not be certain that all of the pigments separated? (2 marks) 4. Suggest what you might do to see if there were any other types of pigments in the leaves that could be separated. (2 marks)

1. The pigments are more attracted to the solvent than they are to the paper. 2. The pigments that move furthest up the paper are less attracted to the paper (1) and more attracted to the solvent (1) than the pigments that move a shorter distance up the paper. 3. They may not all have separated (1); if some pigments have the same Rf value, they cannot be viewed separately (1). 4. Use a different solvent (1); different pigments will dissolve differently in different solvents and you may see a different pattern on the chromatography paper (1).

EQ: Students separated a mixture of amino acids using paper chromatography. Figure 6 shows the apparatus the students used. Suggest two practical precautions that the students should take when doing this investigation. (2 MARKS)

1. The solvent should start below the pencil line; 2. Stop before the solvent reaches the top of the paper/draw (pencil) line for solvent front before the solvent dries; 3. Don't allow the paper to touch the sides of the jar / don't move the jar during the investigation; 4. Use a fume cupboard; 5. Don't touch the paper with bare hands/wear gloves when touching the paper; 6. No flames near the solvent;

EQ: Describe two ways that the students could use chromatography to separate amino acids Y and Z more clearly. (2 MARKS)

1. Turn the chromatogram 90° / run at right angle; 2. Using a different solvent; 3. Run chromatography for longer time;

EQ: Scientists investigated differences between 260 North American bird species by comparing the base sequence of a gene in mitochondrial DNA. They compared the gene base sequence of each bird with all of the other 259 species. For each comparison they calculated the percentage difference in base sequence. Figure 9 shows the base sequence for part of the gene in two species. Calculate the percentage difference in base sequence for these base sequences. (1 MARK)

36 to 36.4;

CHROMATOGRAPHY: Give one reason why the Rf values you calculated might not be accurate. (1 mark)

Accept any sensible suggestion, e.g. The solvent line may not be completely straight; it can be difficult to determine where the top of the separated pigment spot is.

Quantitive investigations of variation within a species / population: analyse results

Analyse results with a *named depending on the question* statistical test: see if variation observed is or isn't due to chance

EQ: The scientists compared base sequences in: • birds of the same species • birds of different species in the same genus • birds of different species in the same family. The scientists' results are shown in Figure 10. Complete Table 3 by writing A, B or C in the box to correctly match the statement to each histogram shown in Figure 10. (1 MARK) Base sequences of birds of the same species. Base sequences of birds of the same genus. Base sequences of birds of the same family

B, A, C;

CHROMATOGRAPHY: Why was it important that the propan-2-ol in the bottom of the 500 cm3 glass beaker was below the level of the line drawn on the chromatography paper? (1 mark)

If the propan-2-ol was above the line drawn on the chromatography paper, it would not separate the pigments in the solution on the line.

What is intraspecific variation?

Individuals of the same species that have the same genes but different alleles → variation in their phenotype

Q: The adult wandering albatross, Diomedea exulans, has winspans that range from 2.5m to 3.5m. Which of the following describes the variation in wingspan of the wandering albatross? (1 MARK)

Intraspecific and controlled by both genetic and environmental factors

How do you calculate standard deviation?

Look at image.

Quantitive investigations of variation within a species / population: calculating a mean of the collected data and the standard deviation of that mean

Mean = (sum of all measurements) / (total number of measurements) Standard deviation (you wont be required to calculate standard deviations in your exam) - Shows the spread of values around the mean - 68% of all measurements lie within +- 1 standard deviation - About 95% of all measurements lie within +- 2 standard deviations Note: this is only true if data shows a normal distribution i.e. when plotted as graph it forms bell-shaped curve

Quantitive investigations of variation within a species / population: Interpreting the mean values and their standard deviations

Mean → can show if there is variation / differences between samples - Useful for comparison, but provides no info about the range Standard deviation: a measure of the average variation of the data away from the mean - The higher the value standard deviation, the higher the variation - If standard deviations overlap, causing values of each set of data to be shared, any difference between the two may be due to chance Mean and standard deviation can be shown in different ways, e.g. - 9 + 3 mean = 9 and standard deviation = 3 - Standard deviation can be plotted on graph / chart of mean values using error bars - Error bars extend one standard deviation above and below the mean

EQ: Figure 7 shows a fresh-water shrimp. Biologists collected shrimps from a stream inside a cave and from the same stream when it was in the open. They measured the maximum diameter of each shrimp's eye. They also measured the length of its antenna. From these measurements they calculated the mean values for each site. Table 3 shows their results. The biologists investigated shrimps living in other streams. They measured the length of the antennae of these shrimps. They also measured their body length. Figure 8 shows the mean antenna length plotted against mean body length for each site. Other biologists investigated the genetic diversity of these shrimps. Table 4 shows some of the data they collected. The biologists concluded that the shrimps in the open had a higher genetic diversity than those in the cave. Explain how the data in Table 4 support this conclusion. (1 MARK)

More alleles of each gene/shrimps in open have all the alleles;

Q: Some potato plants carry a gene that gives the plants resistance to potato blight. State the most likely cause of this genetic variation. (1 MARK)

Mutation

What is chromatography?

Process used to separate mixtures of coloured compounds

Q: A study of the biodiversity of an area considers not only the total number of species but also the relative number of individuals within each species. State one further factor that could be taken into account when describing the biodiversity of an area. (1 MARK)

Range / number of habitats / ecosystems / genetic variation (within species)

Q: Malaria is a disease caused by a parasite. Scientists investigated the effect of malaria on competition between two species of Anolis lizard on a small Caribbean island. They sampled both populations by collecting lizards from a large number of sites on the island. Explain the importance of collecting lizards from a large number of sites. (1 MARK)

Reliable / representative / for statistical tests

EQ: Some students separated the sugars in the fruit juice using paper chromatography. Figure 10 shows how the students set up the chromatography apparatus. Suggest reasons for each of the following steps in the students' method: 1. The origin line was drawn on the paper in pencil, not ink. 2. The level of the solvent surface in the chromatography tank was at least 2 cm below the origin. 3. A very small volume of fruit juice was added to the origin and dried with a hairdryer before adding more fruit juice. 4. When the chromatography paper was removed from the tank, the position of the solvent front was marked immediately. (4 MARKS)

Step 1 - Ink (pigments) would dissolve in solvent / would be carried up paper by solvent / might mask positions of sugars; Step 2 - Otherwise sugars enter solvent at base of tank / not carried up paper / would be spread (sideways) on paper; Step 3 - To give better separation (in a mixture) / spots would overlap more if larger area / to prevent contamination of adjacent sugars; Step 4 - Solvent evaporates so front vanishes - need to measure sugar mobility relative to front / to measure Rf;

When investigating variation within a species / population, what factors are important?

Taking a representative sample: - Random sample - Large sample size - Analyse results - Calculating a mean of the collected data and the standard deviation of that mean

Q: Scientists investigating the diversity between two different species of rabbit decided to measure fur length in the two populations. They used the standard deviations to judge whether or not the results were significantly different. What does the term 'standard deviation' mean when discussing a set of data? (1 MARK)

The average variation of the data away from the mean

CHROMATOGRAPHY: How did running both chromatography papers in a single glass beaker at the same time increase the experiment's validity? (1 mark)

The conditions for both chromatograms were the same.

CHROMATOGRAPHY: Why was it important to draw the line and 'x' on the chromatography paper in pencil? (1 mark)

The pencil line does not dissolve in the propan-2-ol solvent, (and does not make a smudge or mark on the paper).

CHROMATOGRAPHY: What was happening to the pigment in the leaves as you crushed them with the propan-2-ol? (1 mark)

The pigment dissolved in the propan-2-ol.

Describe continuous variation.

Variation is smooth + continuous (not discrete) → represented on a line graph (e.g. height + weight) - No distinct categories - Data tends to be quantitative - Controlled by many genes - Strongly influenced by the environment

What are the causes of diveristy / variation?

genetic environmental

What is interspecific variation?

individuals of different species have different genes and live in different environments → variation in their phenotypes.