Year 7 Science · Unit 1 · Lesson 1
Challenge Worksheet
Learning Goals
Odd one out
In each set, circle the odd one out and give the reason. There is one best answer in each set.
| Set | Circle the odd one out | Reason |
|---|---|---|
| 1 | movement · nutrition · photosynthesis · excretion | |
| 2 | a fossil · a sausage · a glass marble · a piece of timber | |
| 3 | a river · a mushroom · a salt crystal · a bushfire | |
| 4 | Which one of these can a virus do? respiration · growth · reproduction · excretion |
Find the error
Mia’s revision notes
(1) Respiration means breathing air in and out of the lungs. (2) A bacterium is not fully alive, because it is only one cell. (3) A dead thing is something that was never alive, such as a rock. (4) Plants show all seven characteristics, even though their movement is slow.
1. Three of Mia’s four sentences contain one error each. For each wrong sentence, give its number and rewrite it correctly.
Cause and effect: why cells stay small
Complete the chain by filling each empty box. The last box should give the conclusion.
Read the data: crystals on Mars
Scenario: a rover’s discovery
A Mars rover finds a crystal growing in salty water under the surface and watches it for eight weeks. At week 6 the crystal cracks into three pieces, and each piece keeps growing. The crystal gives off a little heat as it grows. It shows no response to light, warming or touch. It does not take in food or make its own: it grows only because minerals from the water settle on its surface. No cells are seen under an electron microscope.
| Week | 0 | 2 | 4 | 6 | 8 |
|---|---|---|---|---|---|
| Total mass (g) | 12 | 15 | 19 | 24 | 30 |
| Number of pieces | 1 | 1 | 1 | 3 | 3 |
Source: made-up mission data for this worksheet.
2. Calculate the average increase in total mass per week between week 0 and week 8.
Answer g per week
3. Which MRS GREN characteristics does the crystal seem to show? Which characteristics does the scenario show it does not have? Use evidence for each.
Plan an investigation: are old seeds alive?
A dry bean seed from a packet opened ten years ago shows almost none of MRS GREN. Plan a fair test to find out whether seeds from this packet are still alive. You also have a packet of new bean seeds.
Hypothesis
Variables
Method
What result would show the old seeds are dead?
4. Growth and movement can occur without life. Explain why seeing one life process is not enough to classify something as living. Give two examples of non-living things and name the characteristic each appears to show.
5. A journalist writes the headline: “Life found on Mars: alien crystals grow and reproduce.” Evaluate the headline. Use all seven MRS GREN characteristics, Table 1 and the scenario, and say what new evidence would make the team change its mind.
Odd one out
1. Photosynthesis: it is not one of the seven characteristics; it is one way plants carry out nutrition. 2. A glass marble: it is non-living (never alive); the others are dead (once alive). 3. A mushroom: it is living and shows all seven; the others are non-living things that show only one or a few. 4. Reproduction: a virus can copy itself, but only inside a host cell; it does none of the others. [4 marks]
Find the error
1. Sentence 1: respiration is a chemical reaction inside cells that releases energy from food; breathing only moves air in and out of the lungs (1). Sentence 2: a bacterium is completely alive; the number of cells only tells you how big an organism is (1). Sentence 3: a dead thing was once alive but is not now, such as a fallen leaf; a rock is non-living (1). Sentence 4 is correct. [3 marks]
Cause and effect: why cells stay small
Box 1: so everything the inside of the cell needs has to be supplied through that surface. Box 2: when a cell gets twice as wide, its inside grows about 8 times but its surface only about 4 times. Box 3: so cells stay small, and a large organism such as a whale is built from a huge number of small cells, each close to its own surface. [3 marks]
Read the data: crystals on Mars
2. Increase = 30 − 12 = 18 g over 8 weeks (1); 18 ÷ 8 = 2.25 g per week (1). [2 marks]
3. Seems to show: growth (mass rises from 12 g to 30 g) and something like reproduction (splits into three pieces that keep growing); the heat may look like respiration (1). Does not have: sensitivity (no response to light, warming or touch) (1); nutrition (takes in no food and makes none; minerals just settle on it), and no cells are seen (1). Accept excretion and movement as not shown. [3 marks]
Plan an investigation: are old seeds alive?
Hypothesis: if old and new seeds are given water and warmth, some old seeds will sprout, because a dry seed may remain alive but dormant (1). Change: the age of the seeds (old packet or new packet). Measure: the number of seeds out of 10 that sprout in 7 days. Keep the same: type of bean, number of seeds, amount of water, temperature, light (1 for all three variables). Method: place 10 old and 10 new seeds on damp paper towel in two labelled containers; keep them in the same warm place and keep the towels damp; count the sprouted seeds each day for 7 days (1). If no old seeds sprout while new seeds do, the test worked but the result only suggests that fewer old seeds were viable or that they remained dormant; it does not prove every unsprouted seed was dead (1). [4 marks]
Question 4
One characteristic alone cannot establish that something is living; scientists look for the set of life processes and capacities across an organism's life (reproduction is a species-level capacity) (1). Two correct non-living examples, each matched to a characteristic it appears to show, e.g. a river (movement or growth), salt crystal (growth), bushfire (takes in fuel, like nutrition), or car (responds to a stimulus when the key turns) (1 for each). [3 marks]
Question 5
Marking guide: 1 clear judgement (the headline is not justified); 1 characteristics it seems to show, with data (growth 12 g to 30 g, splitting into pieces that grow); 1 missing sensitivity, with evidence; 1 missing nutrition and no cells (also no excretion or movement reported); 1 explains that non-living things such as salt crystals can grow and break up, so one or two characteristics are not enough; 1 new evidence, such as cells, a response to a stimulus, or taking in food and releasing waste. [6 marks]
Model answer: The headline is not justified. The crystal seems to grow, from 12 g to 30 g in eight weeks, and it splits into pieces that keep growing, which looks like reproduction. But it does not respond to light, warming or touch, so it has no sensitivity. It takes in no food and makes none, and it shows no excretion. Most importantly, no cells were seen, and every living thing is made of cells. Salt crystals on Earth also grow and break into pieces, so these two characteristics alone cannot show life. The team would change its mind if it found cells, or saw the crystal respond to a stimulus, take in food and release waste.
Common error: accepting growth plus splitting as proof of life. Non-living things can show one or two characteristics; the checklist describes capacities across an organism's life, not all processes visibly happening at once.