Trace light energy into a living organism
Light energy from the Sun can be absorbed by photosynthetic organisms and transferred into chemical energy.
Section B18.1 · Energy flow
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Know that photosynthesis makes organic molecules; do not infer a quantitative efficiency from this qualitative pathway.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which energy form reaches a plant from the Sun?
What you will learn
- Describe light energy entering a biological system
- Connect absorption of light with chemical energy in an organism
Follow the incoming energy
Sunlight travels to Earth as light energy. A green plant or alga can absorb some of this light during photosynthesis. The energy is then transferred into chemical energy in organic molecules made by the organism.
Use energy arrows to show direction: light energy from the Sun enters the organism, and chemical energy is stored in the organism’s organic material. The arrows describe energy transfer, not a movement of sunlight as matter.
Avoid claiming complete capture
A plant does not absorb or store all sunlight that reaches it. Some light is reflected, passes through, or is not used. The basic syllabus pathway asks you to describe the forms and direction of energy; it is not required to calculate how much light is captured for this qualitative description.
Keep the process distinct from the outcome. Photosynthesis is a chemical process that makes organic molecules; the energy account describes light energy being transferred into chemical energy. Do not say that energy itself becomes a nutrient.
Sources for this lesson
Pause and explain
Which statement best describes the energy change in photosynthesis for an energy-flow diagram?
Worked example
Complete the energy route: Sunlight reaches a leaf, and photosynthesis makes glucose. Which form of energy enters, and which form is present in the glucose?
Show the worked solution
- Identify the incoming form as light energy.
- Identify energy stored in glucose as chemical energy.
Answer Light energy from the Sun enters the plant; chemical energy is stored in glucose made during photosynthesis.
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.
Write a two-stage energy route from the Sun to chemical energy in a leaf.
Give me a hint
Name each form and point the arrow forward.
Compare my reasoning
- Sun → light energy reaches leaf.
- Photosynthesis transfers some energy into chemical energy in organic molecules.
Sunlight supplies light energy; a leaf absorbs some of it and photosynthesis transfers energy into chemical energy in organic molecules.
Look for these in your work
- Light source included
- Chemical store identified
A student draws an arrow “chemical energy in grass → sunlight.” Identify the error and give the corrected direction.
Give me a hint
Check which form enters first.
Compare my reasoning
- Light energy enters from the Sun.
- Photosynthesis transfers some of it into chemical energy in the grass.
The arrow is reversed. Show light energy from the Sun entering the grass, then chemical energy stored in organic molecules.
Look for these in your work
- Error identified
- Correct direction stated
In an invented shade-house record, plants receive less light than plants in a brighter plot. What can be stated about energy input without claiming a measured growth outcome?
Give me a hint
Describe the energy supply only.
Compare my reasoning
- The shaded plants receive a smaller light-energy input in the stated comparison.
- Growth or stored chemical energy needs measurements and other conditions.
The shaded plants receive less light energy according to the record. The record alone does not quantify photosynthesis, biomass or growth.
Look for these in your work
- Input described
- Outcome not invented
Common mistakes
- Drawing the energy arrow from the plant back to the Sun
- Saying that energy becomes matter
- Implying all incident light is captured
What can you explain now?
Which energy form reaches a plant from the Sun?
Compare with the explanation
Light energy
This is the incoming energy form.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Describe the direction and form of energy transferred when a photosynthetic organism uses sunlight.
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.