Measure photosynthesis rate fairly
הוצג| English | משמעות |
|---|---|
| photosynthesis rate/ˌfəʊtəʊˈsɪnθəsɪs reɪt/ | קצב פוטוסינתזה |
| controlled variable/kənˈtrəʊld ˈveərɪəbl/ | משתנה מבוקר |
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.
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?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Bubbles vary in size, so a bubble count is not a gas volume. Collecting the gas and measuring its volume removes that ambiguity. Temperature certainly still affects the reaction.
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
- 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.
In the lab: 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?
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: 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.
Your turn: A model collects 3.6 cm³ gas in 6 minutes. Calculate the mean output rate.
A model collects 3.6 cm³ gas in 6 minutes. Calculate the mean output rate.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 0.6 cm³/min. Known: 3.6 cm^3 collected in 6 minutes. Use mean rate = volume / time. Rate = 3.6/6 = 0.6 cm^3 per minute. This is net output, since respiration consumes some oxygen at the same time.
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.
Not true: Sixty bubbles always contain sixty cubic centimetres of gas. Bubble volume depends on bubble size, which varies. Sixty large bubbles hold far more gas than sixty small ones, so a count can never be read directly as a volume.
- Photosynthesis rate depends on light intensity, carbon dioxide concentration, temperature and the amount of chlorophyll.
- In required practical 6, an aquatic organism such as pondweed supplies an observable oxygen-output estimate.
- Watch for: do not claim that moving a lamp changes only light if it also heats the water.
Bubble volume depends on bubble size, which varies.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Bubble volume depends on bubble size, which varies. Sixty large bubbles hold far more gas than sixty small ones, so a count can never be read directly as a volume.
Amount of photosynthetic change per unit time: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
photosynthesis rate means Amount of photosynthetic change per unit time.