Photosynthesis and limiting factors
הוצג| English | משמעות |
|---|---|
| photosynthesis/ˌfəʊtəʊˈsɪnθəsɪs/ | פוטוסינתזה |
| limiting factor/ˈlɪmɪtɪŋ ˈfæktə/ | גורם מגביל |
What would explain this observation?
- A brighter lamp does not always produce more oxygen from pondweed. Another factor may limit the process when light is already sufficient.
Build the model
- Photosynthesis 光合作用 transfers energy from light into chemical stores.
- Carbon dioxide and water form carbohydrate, releasing oxygen.
- Chlorophyll absorbs light; light intensity, temperature and carbon dioxide supply can affect rate.
- limiting factor 限制因素: A factor whose shortage restricts rate.
- photosynthesis: Light-driven formation of carbohydrate.
A rate-light graph reaches a plateau. What follows?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
On the plateau, adding more light no longer raises the rate, so light is no longer the limiting factor; another factor such as carbon dioxide or temperature may now limit it. Photosynthesis has not stopped - the rate is constant, not zero.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Change only one factor when testing a limiting factor.
- At low light, extra light may increase rate.
- At a plateau, the changed factor is no longer the main limit in that range; the graph alone does not identify which other factor is limiting.
In the lab: Measure collected gas volume over a fixed time instead of assuming all bubbles have the same volume. Control temperature, plant size and carbon dioxide supply. Allow the plant to adjust before each reading and repeat.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: 6.0 cubic centimetres of gas are collected in 3.0 minutes.
- Use rate = volume/time.
- Rate = 6.0/3.0 = 2.0 cubic centimetres per minute.
- Bubble counts can be a rough proxy, but bubbles of different size make comparisons less reliable.
Your turn: 9.0 cubic centimetres of gas are collected in 3.0 minutes. Find the rate.
9.0 cubic centimetres of gas are collected in 3.0 minutes. Find the rate.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 3 cm³/min. Known: 9.0 cubic centimetres of gas collected in 3.0 minutes. Use rate = volume / time. Rate = 9.0/3.0 = 3.0 cubic centimetres per minute. This is an average rate over the collection interval.
Check the conclusion and its limits
- Moving a lamp changes light and may also change temperature.
- A photosynthesis experiment needs control of heating, not just a ruler.
Not true: All oxygen bubbles have exactly the same volume. Bubbles from pondweed vary in size and composition, so a bubble count is only a rough proxy for gas volume. Measuring collected volume, as in the calculation above, is more reliable.
- Photosynthesis transfers energy from light into chemical stores.
- Change only one factor when testing a limiting factor.
- Watch for: moving a lamp changes light and may also change temperature.
Write from a gas rate of 2.5 cubic centimetres per minute
- 10.0 cubic centimetres of gas are collected in 4.0 minutes.
- Find the rate. At a plateau, the factor you changed is no longer the main limit.
Bubbles from pondweed vary in size and composition, so a bubble count is only a rough proxy for gas volume.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Bubbles from pondweed vary in size and composition, so a bubble count is only a rough proxy for gas volume. Measuring collected volume, as in the calculation above, is more reliable.
A factor whose shortage restricts rate: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
limiting factor means A factor whose shortage restricts rate.
10.0 cubic centimetres of gas are collected in 4.0 minutes. What is the rate, and what does a plateau mean for the factor being tested?
10.0 divided by 4.0 is 2.5. Bubble counts are weaker evidence when bubble size changes.
What is the rate of gas collection?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
10.0 divided by 4.0 is 2.5 cubic centimetres per minute. Other options — 3.0 cubic centimetres per minute (the earlier calculation's result for 9.0 cubic centimetres in 3.0 minutes); 2.0 cubic centimetres per minute (the lesson example's result for 6.0 cubic centimetres in 3.0 minutes).