Plan a controlled water requirement investigation
Compare dry and moist seeds while keeping oxygen and temperature suitable.
Section B14.1 · Sexual reproduction in plants
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall gametes, nuclear fusion, cellular respiration and the distinction between reproduction and growth.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which comparison isolates water most clearly?
What you will learn
- Change water availability as the intended factor
- Control other conditions and count consistently
Plan a controlled water requirement investigation
Invented day-5 record: dry 0/20; moist 16/20. Oxygen and 22°C matched. Avoid waterlogging, which can also change oxygen availability. Original teaching data.
| Condition | Starting | Germinated | Percentage |
|---|---|---|---|
| Dry, oxygen available, 22°C | 20 | 0 | 0% |
| Moist, oxygen available, 22°C | 20 | 16 | 80% |
| Moist, oxygen limited, 22°C | 20 | 2 | 10% |
| Moist, oxygen available, 5°C | 20 | 1 | 5% |
| Feature | Meaning |
|---|---|
| Changed factor | Dry versus suitable moisture |
| Controls | Seed stock, oxygen, temperature and time |
| Count | Radicle emergence by day 5 |
| Practical limit | Written planning is not supervised practical competence |
Change water availability as the intended factor
To investigate water, compare matched groups of viable seeds with a dry support and a moist support. Keep seed species and batch, group size, temperature, oxygen availability, observation time and any relevant light conditions the same. Randomly allocate seeds from the stock to groups rather than choosing visibly stronger seeds for the moist treatment.
Moist does not mean submerged in an uncontrolled depth of water. Excess water can reduce oxygen access, changing two factors together. Use an appropriate support and measured water provision that leaves oxygen available, and keep the dry treatment dry. A comparison of dry seeds with waterlogged seeds would not isolate the effect of supplying suitable water.
Control other conditions and count consistently
Count radicle emergence using the same criterion and timing for both groups. Repeat with independently prepared groups to check whether the pattern is consistent, and record starting totals as well as germinated counts. A percentage compares groups fairly if totals differ, while matched starting totals simplify direct comparison. Do not count a later fully established seedling as the only successful germination.
In the invented teaching record, 20 dry seeds show 0 germinations and 20 moist seeds show 16 by day 5; oxygen and 22°C are held suitable. This supports the water requirement under the stated conditions. It does not establish that the dry seeds are dead, that exactly 80% of every seed species germinates in moisture, or that the unsprouted four could never emerge later. Actual practical competence still requires supervised work.
Sources for this lesson
Pause and explain
What does zero germination in the dry group by day 5 establish?
Worked example
Calculate germination in the moist group: 16 of 20 by day 5.
Show the worked solution
- Divide germinated by starting total.
- 16 ÷ 20 × 100 = 80.
Answer 80% by day 5.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State a fair comparison for investigating water and name three controls.
Give me a hint
Keep oxygen access suitable in both groups.
Compare my reasoning
- Compare dry and moist supports.
- Hold seed stock, temperature and observation time constant, with oxygen available.
Dry versus moist matched seed groups; control species/batch, suitable temperature, oxygen access and timing.
Look for these in your work
- Make water the changed factor
- Name at least three relevant controls
Why could using deeply submerged seeds as the moist group weaken this investigation?
Give me a hint
Consider another condition affected by excess water.
Compare my reasoning
- Submersion can limit oxygen access.
- Then water and oxygen differ together.
Waterlogging can reduce oxygen availability, so the comparison may confound the effect of water with the effect of oxygen.
Look for these in your work
- Identify the oxygen change
- Explain the confounding
Interpret 0 of 20 dry and 16 of 20 moist germinations by day 5 at matched suitable oxygen and temperature.
Give me a hint
Calculate percentages and keep the boundary.
Compare my reasoning
- Dry 0%; moist 80%.
- The pattern supports a water requirement under these stated conditions.
0% versus 80% by day 5 supports the water requirement in this comparison; it does not prove the dry seeds are dead or give a universal germination percentage.
Look for these in your work
- Calculate both percentages
- Limit the conclusion to the controlled record
Common mistakes
- Changing oxygen by waterlogging the wet group.
- Recording only successes without starting totals.
What can you explain now?
What does zero germination in the dry group by day 5 establish?
Compare with the explanation
No counted emergence by that time
It does not by itself prove death.
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Make it stick
Design a water comparison that does not unintentionally change oxygen availability.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.