Starter quiz
- What is the role of light in photosynthesis?
- it transfers the energy needed for the reactions of photosynthesis ✓
- it cools the plant during the photosynthesis process
- it releases energy from glucose
- it increases the absorption of carbon dioxide
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- What is a light source?
- an object that emits light ✓
- an object that absorbs light
- an object that reflects light
- an object that blocks light
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- ______ is a pigment in plant cells that absorbs light energy, primarily from the sun, to drive the process of photosynthesis.
- 'chlorophyll' ✓
- What does it mean for two variables to be proportional?
- both variables increase and decrease independently
- there is no relationship between the variables
- when one variable increases, the other decreases
- when one variable increases, the other increases at a constant rate ✓
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- What is the primary source of light for photosynthesis?
- artificial light
- moonlight
- starlight
- sunlight ✓
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- Which factor is most likely to be a limiting factor of photosynthesis at night?
- carbon dioxide concentration
- light intensity ✓
- temperature
- water availability
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Exit quiz
- In what way does light intensity affect the rate of photosynthesis in plants?
- higher light intensity decreases the rate of photosynthesis
- higher light intensity increases the rate of photosynthesis ✓
- light intensity has no effect on photosynthesis
- the effect of light intensity varies with plant species
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- What is the relationship between light intensity and the rate of photosynthesis?
- the rate increases with light intensity up to a point, then plateaus ✓
- the rate decreases as light intensity increases
- light intensity has no effect on the rate of photosynthesis
- the rate increases indefinitely with increasing light intensity
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- Why does light intensity decrease as the distance from the light source increases?
- because light energy is absorbed by the air
- because light waves change direction
- because the power of the light source decreases
- because the same amount of light is spread over a larger area ✓
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- What is the inverse square law?
- the intensity of light is directly proportional to the distance from the source
- the intensity of light increases with the square of the distance
- the intensity of light remains constant regardless of distance
- the intensity of light is inversely proportional to the square of the distance ✓
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- What would happen to the light intensity if the distance from the light source is tripled?
- it becomes one-third
- it becomes one-sixth
- it becomes one-ninth ✓
- it remains the same
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- What is the relationship between the rate of photosynthesis and the distance from a light source?
- rate is directly proportional to the distance from the light source
- rate is inversely proportional to the distance from the light source ✓
- rate is not related to the distance from the light source
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Worksheet
Presentation
Video
Lesson Details
Key learning points
- Light waves spread out as they travel from a light source.
- Further away from the light source, the same amount of light is spread out over a greater area.
- This means the light intensity decreases with increasing distance from a light source.
- Light intensity is inversely proportional to the square of the distance from a light source (inverse square law).
Common misconception
Many pupils will believe that by halving the distance from a light source, the light intensity will double.
As a result of light travelling in all directions, this aspect needs to be thought of in terms of area (two dimensions). The lesson takes pupils through an example which demonstrates how light intensity is proportional to the square of the distance.
Keywords
Light intensity - the amount of light reaching a given surface area in a period of time
Light source - an object that emits light
Light waves - oscillations/ripples in electric and magnetic fields
Inversely proportional - variables are inversely proportional when one increases and the other decreases at the same (proportional) rate, e.g. as one variable doubles, the other variable halves
Inverse square law - light intensity is inversely proportional to the square of the distance from the light source