Year 7 Science · Unit 1 · Lesson 11
Challenge Worksheet
Learning Goals
Complete the chain: one wombat, the whole unit
Fill each empty box with the Unit 1 idea that links the box before it to the box after it. Name the idea and apply it to the wombat.
1. State the fair-test rule. Explain why changing two variables at once makes a result impossible to interpret.
Testable or not?
Write Yes or No in the middle column. If it is testable, name what would be measured. If it is not, give the reason.
| Statement | Testable? | What is measured, or why not |
|---|---|---|
| (a) Wombats are amazing animals. | ||
| (b) If a bean seedling is watered more often, then it will grow taller in 3 weeks. | ||
| (c) If duckweed gets more light, then it will make more new leaves each week, because it uses light for photosynthesis. | ||
| (d) Bacteria are the most important living things. |
2. Statement (b) has no “because”. Add a sensible reason, then name its independent variable, its dependent variable and two controlled variables.
Evaluate an experiment
Lily’s music experiment
Lily wants to test the claim that plants grow taller when classical music is played. She sows wheat seeds in six identical trays of the same potting mix. The three “music” trays sit on a sunny windowsill beside a speaker that plays classical music for 8 hours a day. The three “silence” trays sit on a shelf at the back of the room. After 14 days she measures the average seedling height in each tray.
| Group | Tray 1 | Tray 2 | Tray 3 | Average |
|---|---|---|---|---|
| Music (windowsill) | 58 | 71 | 63 | |
| Silence (back shelf) | 54 | 69 | 60 | 61 |
Source: made-up sample results for this worksheet.
Lily’s conclusion: “The music seedlings grew taller on average, so classical music makes plants grow taller.”
3. Calculate the average height of the music trays.
Average mm
4. Compare the difference between the two averages with the spread of the three trays inside each group. What does this comparison tell you about Lily’s conclusion?
5. Lily’s method has a second problem that has nothing to do with the numbers. Identify it and explain why it matters.
Redesign Lily’s investigation
Plan a fair test of the same question. You have the same six trays, seeds and potting mix.
Hypothesis
Variables
Method
Results table
Conclusion
Describe the result that would let you conclude that music makes no difference.
6. Choose one Australian organism other than the wombat. Use it to show that Unit 1 is one connected system, not separate topics: explain how MRS GREN, classification, cell theory and the levels of organisation each lead to the next.
Complete the chain: one wombat, the whole unit
Box 1: it shows all seven MRS GREN characteristics, so it is living and can be classified: animal kingdom, vertebrate, mammal (a marsupial). Box 2: cell theory: like every living thing it is made of cells that came from existing cells, and in a large animal those cells specialise (e.g. muscle cells).
Question 1
Change only one (independent) variable and keep every other variable the same (1). If two variables change, you cannot tell which one caused the change in the dependent variable (1). [2 marks]
Testable or not?
(a) No: “amazing” cannot be measured, and no result could prove it wrong. (b) Yes: seedling height after 3 weeks (mm). (c) Yes: number of new leaves per week. (d) No: “most important” is an opinion that cannot be measured.
Question 2
Reason, e.g. “because plants need water to grow” (1). IV: how often it is watered (1). DV: seedling height after 3 weeks (1). Two controls, e.g. volume of water each time, pot size, soil type, light, temperature, bean variety (1). [4 marks]
Question 3
(58 + 71 + 63) ÷ 3 = 64 mm. [1 mark]
Question 4
The averages differ by only 3 mm (64 vs 61) (1), but the trays inside each group differ by 13 mm (music) and 15 mm (silence) (1). The difference is smaller than the variation already in the data, so the experiment did not detect an effect of music; the conclusion is not supported (1). [3 marks]
Question 5
The music trays were also on the sunny windowsill, so light (and temperature) differed as well as music (1). Two variables changed, so any difference could be caused by the light rather than the music (1). [2 marks]
Redesign Lily’s investigation
Hypothesis in If…then…because form, e.g. “If wheat seedlings hear classical music for 8 hours a day, then they will be taller after 14 days, because the claim is that music helps plants grow” (1). IV: music or no music; DV: seedling height after 14 days (mm); controls: light, temperature, water, potting mix, number of seeds, tray size (1). Method: all six trays in the same light and temperature, three with music and three in a separate but identical place without music (e.g. another room with the same window), same watering, measure height after 14 days and average (1). Results headings: Group; Tray 1; Tray 2; Tray 3; Average height (mm) (1). Conclusion: if the difference between averages is no bigger than the spread within each group, music made no detectable difference (1). [5 marks]
Question 6
Marking guide: 1 MRS GREN shows it is alive; 1 correct classification (kingdom plus a smaller group); 1 cell theory with a cell part matching its kingdom (e.g. cell wall and chloroplasts for a plant); 1 specialised cells to tissues; 1 organs and systems with a real example; 1 linking language showing each idea leads to the next. [6 marks]
Model answer (waratah): A waratah grows, makes its own food by photosynthesis, reproduces with flowers and seeds and shows the other MRS GREN signs, so it is living. Because it is living it can be classified: it is in the plant kingdom and is a flowering plant. Cell theory says it must be made of cells, so its cells have the plant-only parts: a cell wall, chloroplasts and a large vacuole. Those cells specialise, so leaf cells packed with chloroplasts form tissues, the tissues build organs such as leaves, roots and flowers, and the organs work together as systems. Each idea leads to the next.
Common error: listing the four topics one after another without saying how each one leads to the next.