Aut1·W4 (Discover) — Explain diffusion and the factors that affect its rate.
Edexcel GCSE Biology 1BI0 Foundation · Paper 1 · Topic 1Pearson Edexcel GCSE (9–1) Biology 1BI0 (Foundation, grades 1–5); GCSE Combined Science 1SC0 F where appropriate; AQA UAS science units
🎯 Learning Objective: I can explain diffusion and the factors that affect its rate.
✅ Success Criteria
I can define diffusion using 'net movement' and 'concentration gradient'.
I can name three factors that change the rate of diffusion.
I can apply diffusion to a real example in the body.
🔗 Assessment link: AQA UAS: 'Cells and transport'.
LAUNCH · one 40-minute session. Title orientation is untimed; keep the full 15-minute independent task.
Staff notes · feedback, participation, real-world link
Staff copy — not for pupil books. Codes live in books, never on pupil slides or printouts.
Lead with VF in the practical, sort and exit tasks. Written feedback is for extended writing only, strategic and not every piece (Curriculum Policy 2026/27 §14.3): here that means the Stretch explanation in the independent task, when it is worth a written next step.
Codes
VF
Verbal feedback given here
WS
Worked with support
I
Independent
NS + …
Next step one specific thing
E
Evidence captured on the school's digital evidence platform
R
Responded loop closed (Audience has happened)
//
Self-edit point
?
Read this back to me
Curriculum Policy 2026/27 §14.3 summary: VF WS I NS E R (six codes; NS “next step”, E “evidence on digital software app”, R “responded to feedback”). The Feedback Policy, the code source, adds // and ? and expands NS to one specific thing and R to loop closed.
Make participation possible
Use regulation time, a trusted adult, accessible response routes and permission to refuse. The one small help prompt in We Do 2 is optional to open; genuine feedback is not optional and is not limited to that moment. Space: lung and breathing content can land close to home, so a pupil may work from the diagram and skip discussion.
Voice
The pupil responds in their own way: an edit in the margin in the same colour on the same page, a re-attempt, a verbal reply, a demonstration, a signed or symbol-chosen answer, or a captured comment. Voice is invited during the sort and again in the exit; it can be recorded as VF only when verbal feedback was actually given.
Audience
An adult genuinely reads, hears or watches the response and names what they heard back to the pupil. Add R only when the pupil responded AND the adult engaged with the response; no button, saved answer or completed exit supplies R on its own.
Influence
Change the next explanation, question, scaffold or task from what the pupil showed. In this lesson the sort tells you which example to re-model before the independent task; the exit tells you which route to open next lesson.
Model, supplied data, observation
The particle diagram and the sort cards are models. The alveolus figures are supplied illustrations. Neither is a measurement; do not record either as practical evidence. The breath test comes in the next lesson and is the pupil's own observation.
Destination link (Launch)
Diffusion is examined in Edexcel GCSE Biology 1BI0 Paper 1 Topic 1 and in Combined Science 1SC0. The same ideas run through Level 3 science and health routes, from nursing and paramedic practice, where gas exchange is the daily reality, to laboratory work on membranes and drug delivery.
Optional video (staff choice)
A short explainer clip exists online; it is linked for staff only, never embedded, never autoplayed and never assumed available. The lesson does not depend on it. If used, play it with captions from the classroom screen.
Response modes
Verbal, written, drawn, signed, symbol or choice selected, demonstrated or re-attempted, adult scribed. All count in the arrival, the sort and the exit.
Codes from the Feedback & Marking Policy 2025/2026 (Pilot), Issue 1, May 2026, verified in session 2026-09-15 (SHA-256 41046284a00c9218679b946134cbc6e53c1897aad28b15fc4bd4aa963720ff3b).
40-minute session: Arrival 4; overview 1; I Do 1 4; We Do 1 4; I Do 2 3; We Do 2 5; independent work 15; exit 4. Title orientation is untimed. The optional two-minute evidence check sits inside independent time. Keep extra practice available; use the core question, a contrasting example and a recheck before extending.
Choose one route. Point, say, sign, draw, type or write. You may pass or say not sure. Use the screen or paper; you do not need to do both.
Nothing here assumes you have met diffusion before. The questions use everyday ideas about smells, drinks and breathing; an adult can read them to you or write your words.
1. Someone opens a bottle of perfume at the front. Can people at the back smell it after a while? Yes / No.
2. Two glasses of squash: one strong, one weak. Which one has more squash particles in the same amount of water? Strong / Weak.
3. In a gas, are the particles close together or far apart? Close / Far apart.
4. When you breathe in, where does oxygen get into your blood? Lungs / Stomach.
Show Supported arrival answers
Allow four minutes within the arrival stage. Read or scribe as needed. Start from what pupils show; a pass or a not-sure is information about the starting point, not a label. Accept spoken, signed, drawn, pointed, chosen or scribed answers as equal.
Yes. Accept pointing or nodding. The smell spreads through the air on its own.
Strong. More particles in the same volume means a higher concentration.
Far apart, and moving. Accept a gesture that shows spread-out particles.
Lungs. The air sacs in the lungs are where oxygen enters the blood.
1. A smell spreads across a still room. What is actually moving from the bottle to your nose?
2. What does the word concentration mean when we talk about a solution or a gas?
3. Particles move in solids, liquids and gases. In which state do they move most freely?
4. Name the gas that our blood collects in the lungs and the gas it gives up there.
Show Standard arrival answers
Allow four minutes within the arrival stage. Read or scribe as needed. Start from what pupils show; a pass or a not-sure is information about the starting point, not a label. Accept spoken, signed, drawn, pointed, chosen or scribed answers as equal.
Particles of the perfume, mixed into the air. Accept molecules.
How many particles of a substance there are in a given volume. Accept how much is dissolved in a certain amount.
Gases; the particles are far apart and move freely in all directions.
Oxygen is collected; carbon dioxide is given up.
1. A smell reaches the back of a still room. Explain what makes the particles spread when nothing is pushing them.
2. Two areas have different concentrations of the same substance. What name do we give to that difference?
3. Why do particles in a warm gas spread out faster than particles in a cold gas?
4. Oxygen passes from the air sacs of the lungs into the blood. Suggest why it goes that way and not the other.
Show Stretch arrival answers
Allow four minutes within the arrival stage. Read or scribe as needed. Start from what pupils show; a pass or a not-sure is information about the starting point, not a label. Accept spoken, signed, drawn, pointed, chosen or scribed answers as equal.
Particles move randomly all the time. Over time random motion carries more of them from where they are crowded to where they are few, so the smell spreads. Accept a first idea to refine later.
A concentration gradient. Accept the difference in concentration between two places.
Warm particles have more energy and move faster, so they spread out more quickly.
There is more oxygen in the air sac than in the blood arriving there, so the net movement is into the blood. Accept from high to low concentration.
🗺️ Today at a Glance
Three things we do today
1.
Define it precisely
2.
Three rate factors
3.
Apply it to the lungs
👩🏫 I Do · watch me think
Watch me define it properly
🧠 Watch me think: Weak version: 'diffusion is when things spread out'. That earns very little. Marking version: 'the NET movement of particles from an area of HIGHER concentration to an area of LOWER concentration, DOWN a concentration gradient'. Three technical phrases, each doing work.
Diffusion is the NET movement from ● high to ○ low concentration, down the gradient. It goes faster with a steeper gradient, higher temperature or more surface area.
📖 Key definitions
diffusion — The net movement of particles from a higher to a lower concentration.
concentration gradient — The difference in concentration between two areas.
net movement — The overall movement, once movement in both directions is counted.
passive — Requiring no energy from the cell.
❌ Common mistake: Particles only move one way in diffusion. ✅ Actually: They move randomly in all directions. The NET result is down the gradient.
🤝 We Do · together
Faster or slower?
Decide before you tap.Found 0/5
Steeper concentration gradient
Higher temperature
Thicker membrane
Larger surface area
Adding energy from the cell
👩🏫 I Do 2 · the evidence loop
Evidence loop
🧠 Watch me think: You apply it, out loud as you write: 'Oxygen diffuses from the alveolus into the blood because oxygen concentration is higher in the alveolus. The wall is one cell thick, so the diffusion distance is short, which increases the rate.' Direction, reason, adaptation.
Assessor witness · what the adult is watching for
Defined diffusion using 'net movement' and 'concentration gradient'.
Named three factors affecting rate.
Applied diffusion to gas exchange in the alveoli.
📸 Capture: Photograph the pupil's annotated alveolus diagram with all three adaptations labelled.
🤝 We Do 2 · sort, then write
Diffusion or not?
Sort, don’t guess. Put each card in the right bin.Sorted 0/6
Oxygen into the blood at the alveoli
Carbon dioxide out of a cell
A smell spreading across a room
Glucose pumped into a root hair against the gradient
Water across a partially permeable membrane
Net movement down a gradient, no energy used
● DIFFUSION
■ NOT DIFFUSION
▲ OSMOSIS
Need a different way to take part? (optional)
During the sort, point, say, sign or show the adult an idea, a question or a change that would help you take part. You may pass or speak privately. The adult listens, says what can change and checks whether it helped.
✏️ Independent Work
Your turn — pick your tier
15 minutes. Choose the tier your adult rings for you.
Use the task time to work, check and improve: reserve up to two of these 15 minutes for an evidence check with your adult or a partner, then act on one useful point. Point, say, sign, demonstrate, write or use an agreed scribe. Manual pause stays available.
15:00
◆ Supported
Label the alveolus diagram and complete three gap-fill definition sentences from the word bank.
▲ Standard
Label and annotate the alveolus diagram, then answer three application questions on rate factors.
★ Stretch
Annotate the diagram, answer the application questions, and explain why a person with damaged alveoli has reduced gas exchange, referring to surface area and distance.
🎫 Exit · two small checks
Before you go
Two small checks to finish. Point, say, sign, draw, type or use paper. An adult can scribe your words. You may pass; complete one route, once.
Compare Supported answers after your attempt
Lower. Particles spread from where they are crowded to where they are few.
Faster. A bigger difference in concentration means a faster net movement.
Use these with an adult. Your response is not automatically marked.
1. Complete the definition: diffusion is the ____ movement of particles from a higher to a lower ____.
2. Name two factors that increase the rate of diffusion.
Compare Standard answers after your attempt
Net; concentration. Accept net movement of particles down a concentration gradient.
Any two of: a steeper concentration gradient, a higher temperature, a larger surface area, a shorter distance to cross.
Use these with an adult. Your response is not automatically marked.
1. Explain why a thinner membrane increases the rate of diffusion. Use the word distance.
2. Explain why warming a gas increases the rate of diffusion. Use the words energy and particles.
Compare Stretch answers after your attempt
A thinner membrane means a shorter distance for particles to cross, so each particle crosses in less time and the rate is higher.
Warmer particles have more energy and move faster, so more of them cross in a given time and the rate rises.
Use these with an adult. Your response is not automatically marked.
Next lesson: Diffusion in the Lungs: Testing Breath
Slide 1/10
🏅📸✍️
Discover: Diffusion — banked!
LAUNCH Science · Week 4 ✅
✓ I can define diffusion using 'net movement' and 'concentration gradient'.✓ I can name three factors that change the rate of diffusion.✓ I can apply diffusion to a real example in the body.
⏸ MID-POINT PEER CHECK
Pens down — quick partner check!
📣 Show your partner where you’re up to. Check together against today’s success: I can define diffusion using 'net movement' and 'concentration gradient'. and I can name three factors that change the rate of diffusion.. If something’s missing, help them add it — kindly.
Optional check: use up to two minutes of the independent-work allocation. Manual pause is available if you need more time.
Knowledge Organiser — Discover: Diffusion
LAUNCH · Edexcel GCSE Biology 1BI0 Foundation · Paper 1 · Topic 1
Learning objective: Explain diffusion and the factors that affect its rate.
Success criteria
Define diffusion using net movement and concentration gradient.
Name three factors that change the rate of diffusion and say which way each one changes it.
Apply diffusion to a real example in the body and to the model shown, keeping the two apart.
Key words, with their tier
Word
Tier
Meaning
Diffusion
Tier 3
The net movement of particles from a higher concentration to a lower concentration.
Concentration
Tier 2
How many particles of a substance there are in a given volume.
Concentration gradient
Tier 3
The difference in concentration between two places. Particles diffuse down it.
Net movement
Tier 3
The overall movement once movement in both directions has been counted.
Passive
Tier 3
Needing no energy from the cell; diffusion is passive.
Surface area
Tier 2
The total area available for particles to cross.
Membrane
Tier 3
A thin layer that particles must cross, such as a cell membrane.
Alveolus
Tier 3
One of the tiny air sacs in the lungs where oxygen enters the blood. Plural: alveoli.
Rate
Tier 2
How fast something happens; here, how quickly particles move across.
Key ideas
Particles move randomly all the time. Diffusion is the net result of that random movement, not a push.
Three factors raise the rate of diffusion: a steeper concentration gradient, a higher temperature and a larger surface area. A shorter distance to cross also raises it.
Diffusion needs no energy from the cell. Movement against a gradient using energy is active transport, a different process.
In the lungs, oxygen diffuses from the air in an alveolus into the blood; carbon dioxide diffuses the other way. The alveolus wall is one cell thick.
A particle model of diffusion across a membrane. Particles are drawn far larger and fewer than the real thing, and the membrane is drawn as a line. This is an explanatory model, not a measurement of any real gas.
Examples
Diffusion: oxygen into the blood at the alveoli; carbon dioxide out of a respiring cell; a smell spreading across a room.
Not diffusion: glucose pumped into a root hair against its gradient (active transport); water across a partially permeable membrane (osmosis, a special case treated in the next lesson but one).
Session plan: 40-minute session: Arrival 4; overview 1; I Do 1 4; We Do 1 4; I Do 2 3; We Do 2 5; independent work 15; exit 4. Title orientation is untimed. The optional two-minute evidence check sits inside independent time. Keep extra practice available; use the core question, a contrasting example and a recheck before extending.
Discover: Diffusion
Name: ____________________ Tier ringed by adult: ◆ Supported ▲ Standard ★ Stretch Date:
Learning objective
I can explain diffusion and the factors that affect its rate.
Today at a Glance
Define it precisely
Three rate factors
Apply it to the lungs
Diffusion arrival
Choose one route. Point, say, sign, draw, type or write. You may pass or say not sure. Use the screen or paper; you do not need to do both.
Nothing here assumes you have met diffusion before. The questions use everyday ideas about smells, drinks and breathing; an adult can read them to you or write your words.
Supported
1. Someone opens a bottle of perfume at the front. Can people at the back smell it after a while? Yes / No.
2. Two glasses of squash: one strong, one weak. Which one has more squash particles in the same amount of water? Strong / Weak.
3. In a gas, are the particles close together or far apart? Close / Far apart.
4. When you breathe in, where does oxygen get into your blood? Lungs / Stomach.
Standard
1. A smell spreads across a still room. What is actually moving from the bottle to your nose?
2. What does the word concentration mean when we talk about a solution or a gas?
3. Particles move in solids, liquids and gases. In which state do they move most freely?
4. Name the gas that our blood collects in the lungs and the gas it gives up there.
Stretch
1. A smell reaches the back of a still room. Explain what makes the particles spread when nothing is pushing them.
2. Two areas have different concentrations of the same substance. What name do we give to that difference?
3. Why do particles in a warm gas spread out faster than particles in a cold gas?
4. Oxygen passes from the air sacs of the lungs into the blood. Suggest why it goes that way and not the other.
Diffusion arrival — staff answers
Allow four minutes within the arrival stage. Read or scribe as needed. Start from what pupils show; a pass or a not-sure is information about the starting point, not a label. Accept spoken, signed, drawn, pointed, chosen or scribed answers as equal.
Nothing here assumes you have met diffusion before. The questions use everyday ideas about smells, drinks and breathing; an adult can read them to you or write your words.
Supported
1. Someone opens a bottle of perfume at the front. Can people at the back smell it after a while? Yes / No.
Yes. Accept pointing or nodding. The smell spreads through the air on its own.
2. Two glasses of squash: one strong, one weak. Which one has more squash particles in the same amount of water? Strong / Weak.
Strong. More particles in the same volume means a higher concentration.
3. In a gas, are the particles close together or far apart? Close / Far apart.
Far apart, and moving. Accept a gesture that shows spread-out particles.
4. When you breathe in, where does oxygen get into your blood? Lungs / Stomach.
Lungs. The air sacs in the lungs are where oxygen enters the blood.
Standard
1. A smell spreads across a still room. What is actually moving from the bottle to your nose?
Particles of the perfume, mixed into the air. Accept molecules.
2. What does the word concentration mean when we talk about a solution or a gas?
How many particles of a substance there are in a given volume. Accept how much is dissolved in a certain amount.
3. Particles move in solids, liquids and gases. In which state do they move most freely?
Gases; the particles are far apart and move freely in all directions.
4. Name the gas that our blood collects in the lungs and the gas it gives up there.
Oxygen is collected; carbon dioxide is given up.
Stretch
1. A smell reaches the back of a still room. Explain what makes the particles spread when nothing is pushing them.
Particles move randomly all the time. Over time random motion carries more of them from where they are crowded to where they are few, so the smell spreads. Accept a first idea to refine later.
2. Two areas have different concentrations of the same substance. What name do we give to that difference?
A concentration gradient. Accept the difference in concentration between two places.
3. Why do particles in a warm gas spread out faster than particles in a cold gas?
Warm particles have more energy and move faster, so they spread out more quickly.
4. Oxygen passes from the air sacs of the lungs into the blood. Suggest why it goes that way and not the other.
There is more oxygen in the air sac than in the blood arriving there, so the net movement is into the blood. Accept from high to low concentration.
We Do — Sort each card into the right group
Oxygen into the blood at the alveoli → ______________________________
Carbon dioxide out of a cell → ______________________________
A smell spreading across a room → ______________________________
Glucose pumped into a root hair against the gradient → ______________________________
Water across a partially permeable membrane → ______________________________
Net movement down a gradient, no energy used → ______________________________
WAGOLL
Oxygen diffuses from the alveolus into the blood because there is a higher concentration of oxygen in the alveolus than in the blood. The alveolus wall is one cell thick, so the diffusion distance is short and the rate is high.
Scaffolding — ◆ Supported
Adult notes — access & sensory Breath and exercise work can be personal and physical. Nobody is made to exercise or to talk about their breathing. A pupil who times, records or reads the limewater is doing the assessed science — the star jumps are not the science.
Sentence stems
You apply it, out loud as you write: 'Oxygen diffuses from the alveolus into the blood because oxygen concentration is higher in the alveolus. The wall is one cell thick, so the diffusion distance is short, which increases the rate.' Direction, reason, adaptation.
Word bank
diffusion, concentration gradient, net movement, passive, surface area
Scaffolding — ▲ Standard
Sentence stems
You apply it, out loud as you write: 'Oxygen diffuses from the alveolus into the blood because oxygen concentration is higher in the alveolus. The wall is one cell thick, so the diffusion distance is short, which increases the rate.' Direction, reason, adaptation.
Word bank
diffusion, concentration gradient, net movement, passive, surface area
Scaffolding — ★ Stretch
Sentence stems
You apply it, out loud as you write: 'Oxygen diffuses from the alveolus into the blood because oxygen concentration is higher in the alveolus. The wall is one cell thick, so the diffusion distance is short, which increases the rate.' Direction, reason, adaptation.
Word bank
diffusion, concentration gradient, net movement, passive, surface area
Independent Work — ◆ Supported
Task: Label the alveolus diagram and complete three gap-fill definition sentences from the word bank.
Independent Work — ▲ Standard
Task: Label and annotate the alveolus diagram, then answer three application questions on rate factors.
Independent Work — ★ Stretch
Task: Annotate the diagram, answer the application questions, and explain why a person with damaged alveoli has reduced gas exchange, referring to surface area and distance.
Diffusion exit
Two small checks to finish. Point, say, sign, draw, type or use paper. An adult can scribe your words. You may pass; complete one route, once.
Supported
1. Diffusion is the net movement of particles from a higher concentration to a ____ concentration.(lower / higher)
2. A steeper concentration gradient makes diffusion happen ____.(faster / slower)
Standard
1. Complete the definition: diffusion is the ____ movement of particles from a higher to a lower ____.
2. Name two factors that increase the rate of diffusion.
Stretch
1. Explain why a thinner membrane increases the rate of diffusion. Use the word distance.
2. Explain why warming a gas increases the rate of diffusion. Use the words energy and particles.
Next lesson: Diffusion in the Lungs: Testing Breath
Diffusion exit — staff answers
Use the last four minutes for one exit route. Read the response in light of the help used; accept spoken, signed, drawn, pointed, chosen, typed or scribed answers. A response is not automatically marked; an adult reads or hears it. The next lesson is named on the slide by name only.
Supported
1. Diffusion is the net movement of particles from a higher concentration to a ____ concentration.(lower / higher)
Lower. Particles spread from where they are crowded to where they are few.
2. A steeper concentration gradient makes diffusion happen ____.(faster / slower)
Faster. A bigger difference in concentration means a faster net movement.
Standard
1. Complete the definition: diffusion is the ____ movement of particles from a higher to a lower ____.
Net; concentration. Accept net movement of particles down a concentration gradient.
2. Name two factors that increase the rate of diffusion.
Any two of: a steeper concentration gradient, a higher temperature, a larger surface area, a shorter distance to cross.
Stretch
1. Explain why a thinner membrane increases the rate of diffusion. Use the word distance.
A thinner membrane means a shorter distance for particles to cross, so each particle crosses in less time and the rate is higher.
2. Explain why warming a gas increases the rate of diffusion. Use the words energy and particles.
Warmer particles have more energy and move faster, so more of them cross in a given time and the rate rises.
Next lesson: Diffusion in the Lungs: Testing Breath
Feedback and marking · Diffusion
Staff copy — not for pupil books. Codes live in books, never on pupil slides or printouts.
Lead with VF in the practical, sort and exit tasks. Written feedback is for extended writing only, strategic and not every piece (Curriculum Policy 2026/27 §14.3): here that means the Stretch explanation in the independent task, when it is worth a written next step.
Codes
VF
Verbal feedback given here
WS
Worked with support
I
Independent
NS + …
Next step one specific thing
E
Evidence captured on the school's digital evidence platform
R
Responded loop closed (Audience has happened)
//
Self-edit point
?
Read this back to me
Curriculum Policy 2026/27 §14.3 summary: VF WS I NS E R (six codes; NS “next step”, E “evidence on digital software app”, R “responded to feedback”). The Feedback Policy, the code source, adds // and ? and expands NS to one specific thing and R to loop closed.
Make participation possible
Use regulation time, a trusted adult, accessible response routes and permission to refuse. The one small help prompt in We Do 2 is optional to open; genuine feedback is not optional and is not limited to that moment. Space: lung and breathing content can land close to home, so a pupil may work from the diagram and skip discussion.
Voice
The pupil responds in their own way: an edit in the margin in the same colour on the same page, a re-attempt, a verbal reply, a demonstration, a signed or symbol-chosen answer, or a captured comment. Voice is invited during the sort and again in the exit; it can be recorded as VF only when verbal feedback was actually given.
Audience
An adult genuinely reads, hears or watches the response and names what they heard back to the pupil. Add R only when the pupil responded AND the adult engaged with the response; no button, saved answer or completed exit supplies R on its own.
Influence
Change the next explanation, question, scaffold or task from what the pupil showed. In this lesson the sort tells you which example to re-model before the independent task; the exit tells you which route to open next lesson.
Model, supplied data, observation
The particle diagram and the sort cards are models. The alveolus figures are supplied illustrations. Neither is a measurement; do not record either as practical evidence. The breath test comes in the next lesson and is the pupil's own observation.
Destination link (Launch)
Diffusion is examined in Edexcel GCSE Biology 1BI0 Paper 1 Topic 1 and in Combined Science 1SC0. The same ideas run through Level 3 science and health routes, from nursing and paramedic practice, where gas exchange is the daily reality, to laboratory work on membranes and drug delivery.
Optional video (staff choice)
A short explainer clip exists online; it is linked for staff only, never embedded, never autoplayed and never assumed available. The lesson does not depend on it. If used, play it with captions from the classroom screen.
Response modes
Verbal, written, drawn, signed, symbol or choice selected, demonstrated or re-attempted, adult scribed. All count in the arrival, the sort and the exit.
Codes from the Feedback & Marking Policy 2025/2026 (Pilot), Issue 1, May 2026, verified in session 2026-09-15 (SHA-256 41046284a00c9218679b946134cbc6e53c1897aad28b15fc4bd4aa963720ff3b).
Pearson Edexcel GCSE (9–1) Biology 1BI0 (Foundation, grades 1–5); GCSE Combined Science 1SC0 F where appropriate; AQA UAS science units Records what was observed, and at which level of independence.
Pupil
____________________
Lesson
Discover: Diffusion — LAUNCH Science · Week 4
Date
____________________
Observed in this lesson
☐ Defined diffusion using 'net movement' and 'concentration gradient'.
☐ Named three factors affecting rate.
☐ Applied diffusion to gas exchange in the alveoli.
Assessor comment
Ring the tier the pupil actually worked at
◆ Supported
▲ Standard
★ Stretch
Assessor name ______________ Role ____________ Signature ______________ Date ________