Life Sciences

A learner keeps one slice of bread in a damp plastic bag and another in a dry bag. After four days she writes four sentences. Which sentence is an observation?

In a choice chamber, 18 of 20 woodlice were found on the damp side after ten minutes. Which statement is the inference?

Radish seeds (20 per dish) were placed in dishes with different masses of salt in the water. The number that germinated after seven days was 18 at 0 g, 12 at 2 g, 5 at 4 g and 1 at 6 g. Which conclusion is supported by these results?

A scientist announces that a new herbal tea cures colds. Another laboratory repeats the test carefully and finds no effect. What should happen next?

A learner gives lawn feed to grass in one shady garden. After four weeks the mean height is 14 cm for the fed grass and 9 cm for the unfed grass. Which statement goes beyond what these results show?

A learner grows cress seedlings under red, blue and green cellophane and measures the height of the seedlings after five days. What is the dependent variable?

Aim: to investigate the effect of the mass of sugar added to vase water on the number of days that cut roses stay fresh. Which row names the variables correctly?

A learner tests whether a seaweed extract speeds up the germination of bean seeds. She also sets up a tray in which the seeds are watered with plain water only. What is the purpose of this tray?

A learner investigates the effect of temperature on the area of bread covered by mould after six days. Which list contains only constants?

Tray A holds compost, receives 200 mL of water daily and stands on a sunny window sill. Tray B holds plain sand, receives 100 mL daily and stands in a shaded corner. A learner wants to test the effect of compost on the height of tomato seedlings. Which change makes the test fair?

Which row explains the terms valid and reliable correctly?

A learner counts the lettuce seeds that germinate in one dish at each of three temperatures. Which change makes her results more reliable?

A learner repeats an earthworm test three times and records 14, 6 and 22 worms on the damp side. What do these results suggest?

A learner tests the effect of water volume on the germination of pea seeds. She makes three changes: P, use dishes of the same size; Q, set up four dishes for each water volume; R, keep every dish at 22 °C. Which row classifies the changes correctly?

Two learners test the effect of light on ant activity. Learner X uses two nests at each light level, with the same temperature and time of day. Learner Y uses ten nests at each light level, but tests the dim level in the morning and the bright level in the afternoon. Which evaluation is the best?

A learner draws a line graph of the number of seeds germinated (dependent variable) at five temperatures (independent variable). Where does the temperature go?

A learner measures the mean shell length of snails in millimetres in three gardens and draws a bar graph. Which label is correct for the vertical axis?

The temperatures in a test are 10 °C, 20 °C, 30 °C and 50 °C. Which scale is correct for the horizontal axis of a line graph?

A line graph shows the mean height (cm) of tomato seedlings by week. Fed with compost: 8, 15, 24, 28 and 33 for weeks 0 to 4. Not fed: 8, 12, 15, 21 and 28. How many centimetres taller were the fed seedlings in week 3?

A line graph is marked with a six-point rubric: caption, graph type, axis labels with units, even scale, plotting and joining. The learner's graph has no caption; it is the correct type; both axes are labelled but the vertical axis has no unit; the scale rises in equal steps; one of eight points is plotted wrongly; and the points are joined with a ruler. How many of the six marks does she earn?

Of 80 insects counted in a garden, 20 were beetles. Which calculation gives the percentage of beetles?

A learner counts the seeds that germinated in six dishes at 25 °C: 14, 17, 15, 18, 16 and 12. What is the mean number of seeds that germinated per dish (to one decimal place)?

The mean number of leaves on a spinach plant rose from 6 to 15 in a month. What is the percentage increase?

A hillside patch has 40 plants and 14 of them are aloes. What angle represents the aloes on a pie chart?

Stem P grew from 20 mm to 30 mm and stem Q grew from 40 mm to 55 mm. Which statement is correct?

Which description of the labels on a biological drawing earns the labels mark?

A learner knows the length of her drawing and the actual length of the specimen. Which is the correct way to find the magnification?

A learner cuts a stem lengthwise, from the base towards the tip, so that she can see the long tubes inside. What is this cut called?

A drawing is marked out of 3: one mark for a caption that includes the magnification, one for a clear pencil drawing in proportion without shading, and one for ruled labels that do not cross. Zinhle's drawing has a caption without the magnification, a neat unshaded pencil outline and ruled labels that do not cross. How many marks does she earn?

In a drawing at ×500 a scale line is 25 mm long. What actual length does the scale line stand for?

Sizwe wants to find out whether light affects how many pumpkin seeds germinate. He puts 5 seeds on damp cotton wool with 10 mL of water in a dark cupboard, and 5 seeds on damp cotton wool with 30 mL of water on a sunny window sill. After one week he counts the seeds that have germinated and says that light makes pumpkin seeds germinate. Use his investigation to answer the questions.
(a) Name the independent variable and the dependent variable. (2)
(b) Identify ONE flaw that makes his test not valid and say how to correct it. (2)
(c) Identify ONE flaw that makes his results not reliable and say how to correct it. (2)

1. Independent variable: light (light or dark, sunny or dark)The independent variable is the factor the learner changes on purpose. Here it is the presence of light, so name the factor and not the cupboard or the seeds.
2. Dependent variable: the number of seeds that germinatedThe dependent variable is the quantity measured. Write 'number of seeds that germinated', a countable quantity, not 'the seeds'.
3. Validity flaw: the two groups received different volumes of water (10 mL and 30 mL), or different temperaturesA valid test changes only the independent variable. Any second difference between the groups (here water, or temperature) breaks it. Accept either flaw.
4. Correction: give both groups the same volume of water (or keep temperature the same)The correction must equalise the factor that was unequal, so that only light differs. A flaw without its correction earns no mark here.
5. Reliability flaw: only 5 seeds in each group, and the test was not repeatedReliability comes from repeats and a larger sample. Few seeds and a single trial let chance decide the result.
6. Correction: use more seeds, or repeat the test several times, and calculate the meanThe remedy is more samples or repeats with a mean. This is the reliability remedy, not the same remedy as for validity.

The independent variable is the light (the seeds in the dark compared with the seeds in the sun). The dependent variable is the number of seeds that germinated. His test is not valid because the two groups received different volumes of water, 10 mL and 30 mL, so light is not the only difference. He should give both groups the same volume of water, for example 20 mL each. His results are not reliable because he used only five seeds in each group and did not repeat the test. He should use more seeds in each group, or repeat the test several times, and calculate the mean.

A learner counted how many of 20 seeds germinated in dim light and in bright light for three kinds of seed. Radish: dim 12, bright 18. Bean: dim 8, bright 14. Lettuce: dim 5, bright 16. Describe how she should draw a graph of these results so that she earns all six marks of the graph rubric. (6)

1. Caption: a heading that names both variablesThe caption is the easiest mark: a heading above the graph that says what is plotted against what.
2. Type: a bar graph, because the kinds of seed are separate categoriesSeparate categories (radish, bean, lettuce) need a bar graph. A line graph is for change over time and a histogram for continuous classes.
3. Axis labels: horizontal axis for the kind of seed, vertical axis for the number of seeds germinatedEach axis names its quantity (and unit where there is one). The independent variable is on the horizontal axis and the count goes up the vertical axis.
4. Scale: even steps on the vertical axis, starting at 0 and reaching at least 18The scale must rise in equal steps from 0 and be long enough for the largest value (18). Uneven steps distort the graph.
5. Plotting: each bar drawn to its exact height (six bars)Every bar must reach its value, such as radish in bright light at 18. One wrong bar loses the plotting mark.
6. Bars and key: bars of equal width with gaps between the kinds of seed, and a key for dim and bright lightBars are drawn neatly in equal widths with gaps, and two series on one set of axes need a key to tell dim and bright apart.

Give the graph a caption that names both variables, such as the number of seeds germinated in dim and bright light for three kinds of seed. Draw a bar graph, because radish, bean and lettuce are separate categories. Label the horizontal axis kind of seed and the vertical axis number of seeds germinated (out of 20). Use an even scale on the vertical axis that starts at 0 and rises in equal steps of 2 to 20. Plot each bar to its exact height, for example radish in bright light up to 18. Draw the bars the same width with gaps between the kinds of seed, and add a key that shows which bar is dim light and which is bright light.

The mean mass of cress seedlings at the start of an investigation was 8 g. After 12 days three seedlings from the group had masses of 17 g, 21 g and 22 g.
(a) Calculate the mean mass of the three seedlings after 12 days. (2)
(b) Calculate the percentage increase in the mean mass. (2)
(c) Explain why the increase is divided by the starting mass and not by the final mass. (1)
Show all your working in full sentences or steps.

1. Add the three masses: 17 + 21 + 22 = 60 gOne line of working: the total of the three masses. A slip here carries forward, but the sum itself earns the mark.
2. Divide by 3: mean = 20 gThe mean is the total divided by the number of values, which is 3, not the 12 days. The final value is 20 g.
3. Working for the increase: (20 - 8) ÷ 8 × 100The change (20 - 8 = 12) is divided by the original 8 and multiplied by 100. Dividing by 20 is the commonest mistake and loses this mark.
4. Percentage increase = 150%Final answer with the working above: 12 ÷ 8 × 100 = 150%.
5. Explanation: the change is measured against the starting (original) valueA percentage increase says how much bigger the group became compared with where it started, so the starting mass is the whole. Dividing by the final mass compares with the wrong whole.

17 + 21 + 22 = 60 g. 60 ÷ 3 = 20 g, so the mean mass after 12 days is 20 g. Percentage increase = (20 − 8) ÷ 8 × 100, which is 12 ÷ 8 × 100 = 150%. I divide by the starting mass because the increase is measured against the value the group began with, and dividing by the final mass would compare it with the wrong whole.

Explain to a Grade 8 learner the difference between an observation and an inference, using a footprint in wet sand as your example.

Explain to a Grade 8 learner how to work out a percentage increase, and why you must divide by the starting value.

Explain to a Grade 8 learner how to find the real size of a cell from a drawing that is magnified, and why both measurements must be in the same unit.