Year 6 Science: Variation within a species
Part of the Year 6 Science offspring, adaptation and evolution chapter. Chapter overview · whole chapter on one page
Variation within a species
Living things of the same species vary. Seeds from the same plant, animals of the same kind, and people in one family, can differ in size, shape or colour.
Scientists measure variation with three ideas:
- the mean, which is the total divided by the number of results;
- the range, which is the highest value minus the lowest value;
- the mode, which is the value that occurs most often.
The table gives the length of each seed.
| Seed | Length (mm) |
|---|---|
| Seed 1 | 10 |
| Seed 2 | 12 |
| Seed 3 | 14 |
| Seed 4 | 12 |
| Seed 5 | 12 |
| Seed 6 | 10 |
Key ideas
- Variation is the difference between living things of the same species.
- The range is the highest value minus the lowest value.
- The mode is the value that occurs most often.
- The mean is the total divided by the number of seeds.
Method. Subtract the lowest value from the highest.
- Find the highest and lowest. The highest seed is 14 mm and the lowest is 10 mm.14 and 10
- Subtract. The range is 14 minus 10.14 - 10 = 4
- Write the answer. 4 mm
Check. 10 + 4 = 14. ✓
Method. Count how often each length occurs.
- Count. A length of 12 mm occurs three times, which is more than any other length.12 occurs 3 times
- Write the mode. So the mode is 12 mm.12
- Write the answer. 12 mm
Check. 10 mm occurs twice and 14 mm occurs once. ✓
Method. Add the three lengths, then divide by 3.
- Add. The total is 10 + 12 + 14.36
- Divide. Divide 36 by 3.36 divided by 3 is 12
- Write the answer. 12 mm
Check. Three seeds with a mean of 12 mm. ✓
Watch out
Watch out: the range tells you how spread out the values are, not the average. The mean and the mode are different measures.
Exam tip
Exam tip. Give the unit with each answer, and say which measure you found: mean, range or mode.
Try it (with your teacher, or a grown-up at home). Measure the length of ten leaves from the same plant, or ten pieces of the same pasta, with a ruler. Find the range and the mode. Explain why the leaves or pasta are not all the same length.
Exercise 6B Variation within a species
Method. Count the rows of the table.
- Count. The table has six seeds, numbered 1 to 6.six
- Write the number. So six seeds were measured.6
- Write the answer. 6
Check. Six seeds, from the same pod. ✓
Method. Find the 14 in the table.
- Read the table. The third seed is 14 mm long.14
- Write the name. So the seed is Seed 3.Seed 3
- Write the answer. Seed 3
Check. Seed 3 is the longest. ✓
Method. Find the highest value.
- Read the table. The highest value in the table is 14.14
- Write the answer. So the longest seed is 14 mm.14 mm
- Write the answer. 14 mm
Check. The shortest seed is 10 mm. ✓
Method. Find the lowest value.
- Read the table. The lowest value in the table is 10.10
- Write the answer. So the shortest seed is 10 mm.10 mm
- Write the answer. 10 mm
Check. Seeds 1 and 6 are both 10 mm. ✓
Method. Subtract the lowest from the highest.
- Read the values. The highest is 14 and the lowest is 10.14 and 10
- Subtract. The range is 14 minus 10.14 - 10 = 4
- Write the answer. 4 mm
Check. 10 + 4 = 14. ✓
Method. Count how often each length occurs.
- Count. The length 12 mm occurs three times.3 times
- Write the mode. So the mode is 12 mm.12 mm
- Write the answer. 12 mm
Check. No other length occurs three times. ✓
Method. Add the six lengths.
- Add. The total is 10 + 12 + 14 + 12 + 12 + 10.70
- Write the total. The total length is 70 mm.70
- Write the answer. 70
Check. 70 divided by 6 is about 11.7, so the mean is a little under 12. ✓
Method. Look at the table.
- Read the table. The lengths are 10, 12 and 14 mm, so they are not all the same.not the same
- Decide. So the answer is no.no
- Write the answer. no
Check. Variation means living things of the same kind differ. ✓
Method. Subtract the smaller length from the larger one.
- Read the lengths. The lengths are 12 and 10.12 and 10
- Subtract. The difference is 12 minus 10.12 - 10 = 2
- Write the answer. 2 mm
Check. 10 + 2 = 12. ✓
Method. Work out the mean.
- Divide the total. The total is 70 mm, and 70 divided by 6 is not exactly 12.70 / 6
- Decide. So Mo is not right.no
- Write the answer. no
Check. Six seeds total 72 if the mean is 12, but the total is 70. ✓
Method. Look at the range.
- Read the range. The range is 4 mm, from 10 mm to 14 mm.4 mm
- Explain. A range above zero shows that the lengths differ, so there is variation.differ
- Write the answer. Accept any sentence that says the seeds have different lengths, from 10 mm to 14 mm, so they vary within the same pod.
Check. A range of zero would mean all the seeds were the same. ✓
Method. Think about the two measures.
- Think about the mode. The mode is the value that occurs most often.most often
- Think about the mean. The mean is an average, which may not match any seed.average
- Write the answer. Accept any sentence that says the mode shows the length that occurs most often, which is the most common value.
Check. Different measures tell us different things. ✓
Method. Think about the range of features.
- Think about variation. Variation gives a wider range of features in the population.wider range
- Think about survival. So some individuals are more likely to suit the new conditions.suit
- Write the answer. Accept any sentence that says a wider range of features gives more chances that some individuals will suit the new conditions.
Check. Variation is the raw material for change. ✓