Photosynthesis and respiration at Higher Level: The same pair as SL, seen in the Amazon by day and by night. At HL you will build on it to measure productivity: how much a producer makes, and how much it respires away.
Practise this as you read
- Write both word equations from memory.
- Draw a system diagram with energy and matter flows from data.
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
A pair of opposite processes: Two processes change both energy and matter in every ecosystem: photosynthesis and cellular respiration. A word equation sums up each one.
The points to remember
- Photosynthesis: carbon dioxide + water → glucose + oxygen, using light energy.
- Cellular respiration: glucose + oxygen → carbon dioxide + water, releasing energy.
- Each is the reverse of the other: the outputs of one are the inputs of the other.
- Photosynthesis happens only in producers; respiration happens in every living thing, producers too.
Remember it as: Photosynthesis builds sugar; respiration breaks it down.
Real example: in the Amazon by day, the trees photosynthesise faster than they respire, so the forest takes in carbon dioxide. At night only respiration goes on, and the forest gives carbon dioxide out.
Plants respire too: Never write that plants only photosynthesise and animals only respire. Producers do both, all the time.
Feeling unprepared for exams?
Get a clear study plan, practice with real questions, and know exactly where you stand before exam day. No more guessing.
Both processes are transformations: they change energy into a new form and matter into new substances. Inorganic matter becomes organic matter, and back again.
What each one transforms
- Energy: photosynthesis turns light energy into chemical energy in glucose.
- Energy: respiration turns that chemical energy into a form cells can use, and some into heat.
- Matter: photosynthesis turns inorganic carbon dioxide and water into organic glucose.
- Matter: respiration turns glucose back into carbon dioxide and water.
- So living things exchange gases with the air: photosynthesis takes in carbon dioxide and gives out oxygen; respiration does the opposite.
Photosynthesis
- Energy: light to chemical
- Takes in carbon dioxide and water
- Gives out oxygen and glucose
Cellular respiration
- Energy: chemical to usable energy and heat
- Takes in glucose and oxygen
- Gives out carbon dioxide and water
Real example: in Biosphere 2, a sealed glass building in Arizona, oxygen fell from 21% to about 14% of the air in 1991-1993: microbes in its rich soil respired more than the plants photosynthesised.
Energy and matter, both: For each process, say what happens to the energy and what happens to the matter. How respiration makes energy usable is on 2.2.6, and why it gives off heat on 2.2.7.
Energy and matter move through an ecosystem in two ways. A transfer moves them; a transformation changes them (1.2.4).
Transfers and transformations in an ecosystem
- Transfer: biomass passes up a food chain by feeding.
- Transfer: dead organisms and waste pass to the decomposers.
- Transfer: energy and matter move in or out by migration, wind and erosion.
- Transformation: light becomes chemical energy in photosynthesis.
- Transformation: eaten biomass becomes the consumer's new biomass.
- Transformation: biomass is respired for work, and chemical energy becomes heat.
Remember it as: Transfer = it moves. Transformation = it changes.
Heat moves too: when water evaporates it carries latent heat away, and gives it out where the vapour condenses.
A diagram can earn the marks: A clear, labelled system diagram can show every transfer and transformation. Real example: millions of monarch butterflies fly from Canada and the USA to the mountains of Mexico each autumn: a transfer of the energy and matter in their bodies.
Memorize terms 3x faster
Smart flashcards show you cards right before you forget them. Perfect for definitions and key concepts.
You may be given data about an ecosystem and asked to draw it as a system diagram. Follow the same steps every time.
From data to diagram, step by step
- Draw each storage (a group of organisms, or a pool such as soil or air) as a box.
- Draw each flow as an arrow pointing the way it goes.
- Label every arrow with its process (feeding, respiration) and its value from the data.
- Show energy in (light) and energy out (heat) crossing the boundary.
- Keep energy and matter apart: two colours or two kinds of arrow, with a key.
Example: Millbrook Pond has energy and matter flows. Energy arrows run from the Sun and leave as heat; the carbon dioxide arrows go round:
Energy never goes round: No energy arrow may point back to the producers. Matter arrows, such as carbon dioxide, can form a loop.
How this comes up: Paper 2, Section B (a): outline how photosynthesis and respiration exchange matter with the atmosphere [4].
The Amazon rainforest covers about 5.5 million square kilometres of South America.
Outline how photosynthesis and cellular respiration exchange matter between the rainforest and the atmosphere.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.