Photosynthesis, respiration and limiting factors
Bioenergetics is the accounting of energy in living things: how it enters through photosynthesis and how it is released by respiration.
Lesson overview
What you'll learn in this lesson
Explain cell structure, transport, enzyme action and bioenergetics at GCSE standard.
Key learning points
- • Photosynthesis
- • Limiting factors
- • Respiration and metabolism
This lesson at a glance
- 30 minutes
- 19 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 19
Visual introductionPicture this
Photosynthesis, respiration and limiting factors
Bioenergetics is the accounting of energy in living things: how it enters through photosynthesis and how it is released by respiration.
In a nutshell
Explain cell structure, transport, enzyme action and bioenergetics at GCSE standard.
Learning cycle
Part 2 of 19
Learning cycle 1 of 2
Part 1 · Photosynthesis
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 19
Learn
Photosynthesis
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, an endothermic reaction driven by light absorbed by chlorophyll. Glucose is used for respiration, converted to starch or cellulose, or combined with nitrate ions to make amino acids and then proteins.
Reset break
Part 4 of 19
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 19
Learn
Limiting factors
Light intensity, carbon dioxide concentration and temperature can each limit the rate. On a graph, the limiting factor is whichever one, if increased, would raise the rate. Light intensity follows the inverse square law, so doubling the distance from a lamp quarters the intensity — a favourite calculation.
Quick check
Part 6 of 19
Quick check
Part 7 of 19
Reset break
Part 8 of 19
Pause
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Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 19
Learning cycle 2 of 2
Part 2 · Respiration and metabolism
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 19
Learn
Respiration and metabolism
Aerobic respiration releases far more energy per glucose molecule than anaerobic respiration. In muscle, anaerobic respiration produces lactic acid and an oxygen debt; in yeast it produces ethanol and carbon dioxide. Metabolism is the sum of all reactions, including building larger molecules from the products of respiration.
Quick check
Part 11 of 19
Reset break
Part 12 of 19
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 19
Explore the idea
Part 14 of 19
Worked example
Worked answer: a graph of photosynthesis rate against CO₂ concentration levels off. Explain what limits it (3 marks)
At low concentrations, carbon dioxide is the limiting factor, so increasing it raises the rate (1). At the plateau, further carbon dioxide has no effect, so it is no longer limiting (1). Another factor, such as light intensity or temperature, is now limiting the rate, and increasing that factor would raise the plateau (1).
Challenge round
Part 15 of 19
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Reset break
Part 16 of 19
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 19
Game · Recall cards
Photosynthesis is endothermic because it
Card 1 of 4
Mastery quiz
Part 18 of 19
Marked quiz
End of lesson quiz: Photosynthesis, respiration and limiting factors
4 questions, marked with the reasoning shown. No timer.
1. Photosynthesis is endothermic because it
2. Doubling the distance from a lamp changes light intensity to
3. Plants need nitrate ions to make
4. Anaerobic respiration in muscle produces
Lesson round-up
Part 19 of 19
Lesson round-up
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