Measure photosynthesis rate fairly
| English | Français |
|---|---|
| photosynthesis rate/ˌfəʊtəʊˈsɪnθəsɪs reɪt/ | photosynthesis rate |
| controlled variable/kənˈtrəʊld ˈveərɪəbl/ | controlled variable |
What would explain this observation?
- Counting bubbles is convenient, but one large bubble can contain more gas than several small ones. Decide what the measurement really estimates.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Photosynthesis rate 光合作用速率 depends on light intensity, carbon dioxide concentration, temperature and the amount of chlorophyll. More light or carbon dioxide can increase rate over a suitable range. Enzyme-controlled reactions are slow at low temperatures; temperatures above a suitable range can damage enzyme function. Reduced chlorophyll can reduce light absorption.
- photosynthesis rate: Amount of photosynthetic change per unit time; controlled variable 控制变量: A relevant factor kept the same for a fair comparison.
Why can collecting gas volume improve on counting bubbles?
In required practical 6, an aquatic organism such as pondweed supplies an observable oxygen-output estimate. Gas volume divided by time is usually a better measure than bubble count when bubble sizes vary. A graph needs the varied factor on the horizontal axis, rate on the vertical axis and a consistent scale with units. A plateau means the changed factor no longer increases rate under those conditions.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- In required practical 6, an aquatic organism such as pondweed supplies an observable oxygen-output estimate. Gas volume divided by time is usually a better measure than bubble count when bubble sizes vary. A graph needs the varied factor on the horizontal axis, rate on the vertical axis and a consistent scale with units. A plateau means the changed factor no longer increases rate under those conditions.
- Use teacher-approved pondweed and equipment. Change lamp distance in a planned range, control water temperature and carbon dioxide supply, keep organism size and observation time comparable, and allow adjustment before measurements. Repeat readings and calculate a mean. Electrical equipment stays safely separated from water; observe school handling and disposal procedures.
Which two habits make the investigation or model in this case more defensible?
Use teacher-approved pondweed and equipment. Change lamp distance in a planned range, control water temperature and carbon dioxide supply, keep organism size and observation time comparable, and allow adjustment before measurements. Repeat readings and calculate a mean. Electrical equipment stays safely separated from water; observe school handling and disposal procedures.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a model collects 2.4 cm³ oxygen in 4 minutes. Mean output rate = 2.4/4 = 0.60 cm³ per minute. A bubble count of 60 in that time would instead give 15 bubbles per minute; it is not 15 cm³ per minute without measured bubble volumes. Net oxygen output also reflects concurrent respiration.
A model collects 3.6 cm³ gas in 6 minutes. Calculate the mean output rate. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A model collects 3.6 cm³ gas in 6 minutes. Calculate the mean output rate.
The result is 0.6 cm³/min. Known: a model collects 2.4 cm³ oxygen in 4 minutes. Mean output rate = 2.4/4 = 0.60 cm³ per minute. A bubble count of 60 in that time would instead give 15 bubbles per minute; it is not 15 cm³ per minute without measured bubble volumes. Net oxygen output also reflects concurrent respiration.
Check the conclusion and its limits
- Do not claim that moving a lamp changes only light if it also heats the water. A measured output rate is an estimate under stated conditions. Multi-factor graphs, inverse-square calculations and greenhouse economics belong to the separate Higher Tier lesson.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Sixty bubbles always contain sixty cubic centimetres of gas. This claim is false: Do not claim that moving a lamp changes only light if it also heats the water. A measured output rate is an estimate under stated conditions. Multi-factor graphs, inverse-square calculations and greenhouse economics belong to the separate Higher Tier lesson.
Measure photosynthesis rate fairly: In required practical 6, an aquatic organism such as pondweed supplies an observable oxygen-output estimate. Gas volume divided by time is usually a better measure than bubble count when bubble sizes vary. A graph needs the varied factor on the horizontal axis, rate on the vertical axis and a consistent scale with units. A plateau means the changed factor no longer increases rate under those conditions.
Sixty bubbles always contain sixty cubic centimetres of gas.
Do not claim that moving a lamp changes only light if it also heats the water. A measured output rate is an estimate under stated conditions. Multi-factor graphs, inverse-square calculations and greenhouse economics belong to the separate Higher Tier lesson.
Amount of photosynthetic change per unit time: write the technical term.
photosynthesis rate means Amount of photosynthetic change per unit time.