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
- 15 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 15
Watch first
Photosynthesis, respiration and limiting factors
An English teaching video on this topic from Cognito. Watch it, then scroll down for the lesson.
In a nutshell
Explain cell structure, transport, enzyme action and bioenergetics at GCSE standard.
Learning cycle
Part 2 of 15
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 15
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.
Explore the idea
Part 4 of 15
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 5 of 15
Quick check
Photosynthesis is endothermic because it
Quick check
Part 6 of 15
Quick check
Doubling the distance from a lamp changes light intensity to
Reset break
Part 7 of 15
Pause
That's sitting 1 of 2 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.
Learning cycle
Part 8 of 15
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 9 of 15
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 10 of 15
Quick check
Plants need nitrate ions to make
Quick check
Part 11 of 15
Quick check
Anaerobic respiration in muscle produces
Explore the idea
Part 12 of 15
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 13 of 15
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
Mastery quiz
Part 14 of 15
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 15 of 15
Lesson round-up
Ready when you are
Quiz score
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Games
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Points this lesson
0
Best run
0 in a row
Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaDo the work
Your written work for this lesson
This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.
Why the school greenhouse failed
A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.
The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.
The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.
Written for Good Learning Co.
Reading questions
- Name the variable the club changed the second time, and one variable they kept the same.
- Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
- Write a conclusion for the club's report, saying how far the evidence supports it.
Method and results
WritingWrite the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
WritingExplain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
DiagramDraw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
ReadingRead the lesson text again and write the key ideas in your own words.
Half a page of notes
Saved as you type.
Part 1 of 15 · Watch & discover