Diffusion and Active Transport
Lesson notes
Overview
Particles drift down a concentration gradient for free; moving them uphill costs ATP. This topic is rated intermediate and is number 22 of 110 in Biology. Builds on the basics with relationships, methods and trade-offs.
What you are seeing
The panel above shows the steps of a process, laid out in order. Click a step to see what happens next. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
Diffusion is the passive spread of particles from a region of high concentration to one of low concentration due to random motion, and needs no energy. It is fast over short distances, which is why cells are small and gas-exchange surfaces are thin. Active transport moves substances against their concentration gradient, from low to high, using carrier proteins and energy from ATP. Examples are the sodium–potassium pump in nerve cells and the uptake of minerals by plant roots.
Reading the relationship
The expression "high → low (passive)" is a compact summary of the idea. It uses the symbols h, i, g, l, o, w; name what each one stands for before you start. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Predict the outcome first, then test extreme slider values to find where the pattern changes or breaks.
Common pitfalls
Biological processes are rarely all-or-nothing. Look for the feedback, the timing and the exceptions, rather than learning a single fixed sequence by heart.
How it connects
It builds on “Osmosis”, the topic before it in Biology. Once you are comfortable, continue with “The Cell Cycle and Mitosis”.
Why it matters
Biology shows how living things are built and how they work, grow, inherit traits and adapt.
Where you might use it
- Revising “Diffusion and Active Transport” before a class, exam or certification
- Understanding inherited conditions, medicines and how the body responds to disease
- Working in farming, conservation and food production, where populations and genes matter
- Following news about vaccines, genetic testing and climate effects on wildlife
Frequently asked questions
What is Diffusion and Active Transport?
Particles drift down a concentration gradient for free; moving them uphill costs ATP. It is an intermediate topic in Biology.
How do I use the Diffusion and Active Transport simulation?
The panel at the top shows the steps of a process, laid out in order. Click a step to see what happens next. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression high → low (passive) packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Builds on the basics with relationships, methods and trade-offs. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “Osmosis”, the previous topic in Biology. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.