Cell simulator

A cell simulator lets you look inside a cell and watch what happens at its membrane. Our Cell Simulator has two views. Inside a cell, you pick any part of an animal, plant or bacterial cell to see what it does, how big it is and which cells have one. Across a membrane, you watch particles diffuse and water move by osmosis, with the concentrations and water potentials changing live.

Switch between the two views under Explore: Inside a cell, or Across a membrane.

Try it

Cell Simulator

Explore organelles and run diffusion and osmosis across a membrane

Open the simulatorGo to its page

How to use the cell simulator

1. Under Explore, choose Inside a cell or Across a membrane.
2. Inside a cell: choose Animal, Plant or Bacterium, then tap any part to read what it does, its size and where it is found. Turn the labels on or off.
3. Across a membrane: choose Osmosis or Diffusion, set the left and right concentrations (0 to 1 mol/dm³), the temperature and how permeable the membrane is.
4. For osmosis, choose sucrose or salt, and tick Cell wall around the left side to see turgor build up.
5. Press play under Run and watch the readouts: the concentrations, whether the right side is hypertonic, hypotonic or isotonic, and the net water movement.

The working shows the solute potential, which way water moves and where the system settles. Practice and help sets water potential and surface area to volume questions with worked solutions.

Organelles in animal, plant and bacterial cells

The simulator also has the nucleolus, rough and smooth endoplasmic reticulum, Golgi apparatus, lysosomes, centrioles, plasmodesmata, the nucleoid, the capsule and the flagellum. Our animal and plant cells guide covers each one.

Diffusion and osmosis

In diffusion, particles spread out until they are evenly mixed: more move from where they are crowded to where they are sparse than the other way, so the overall flow runs down the concentration gradient. Osmosis is water crossing a membrane that holds back the solute: overall, water flows from the side with the higher water potential to the side with the lower one. Choose Diffusion and the solute particles spread across until both sides are equal. Choose Osmosis and the solute cannot cross, so water moves instead, towards the side with more solute.

Raising the temperature makes the particles move faster, so diffusion speeds up; a more permeable membrane lets particles across more often. Check yourself:

Water potential calculator

Water potential, ψ, is measured in kPa or MPa, and pure water has ψ = 0. Dissolving a solute lowers it, and pressure from a cell wall raises it:

Here i is the number of particles each solute unit splits into (1 for sucrose, 2 for salt), C is the concentration in mol/dm³, R = 0.008314 dm³ MPa/(mol K) and T is the temperature in kelvin. The simulator works out ψs this way for each side.

Example 1: the solute potential of a sugar solution

0.5 mol/dm³ sucrose at 25 °C:

The same concentration of salt splits into two ions, so its solute potential is twice as negative, −2.48 MPa.

Example 2: adding pressure potential

A plant cell with ψs = −800 kPa and a wall pushing back at ψp = +300 kPa has ψ = −800 + 300 = −500 kPa. Water moves into it from a neighbour at −300 kPa, and out of it into a neighbour at −700 kPa. Tick the cell wall in the simulator and watch ψp rise as the left side fills, until the water potentials match and the net flow stops.

Practise the surface area to volume ratio, which limits how big a cell can grow, then press Mark:

What the simulator does not show

• No active transport. The membrane view shows passive diffusion and osmosis only. Active transport, which uses energy to move substances against a gradient, is covered in the Cell Biology course.
• Two solutes, up to 1 mol/dm³. For other solutes or stronger solutions, use ψs = −iCRT by hand.
• Diagrams, not micrographs. The cells are labelled drawings. To see real cells, use the Virtual Microscope.

Common mistakes

• Saying water moves to a higher water potential. It moves from higher (less negative) to lower (more negative).
• Calling −1,000 kPa higher than −500 kPa. −500 kPa is the higher water potential.
• Thinking solutes move in osmosis. In osmosis only water crosses the membrane.
• Forgetting that salt splits into ions. NaCl gives two particles, so i = 2.
• Thinking bacteria have a nucleus. Their DNA sits loose in the cytoplasm as a nucleoid, often with plasmids.

Practise cell biology in a short timed paper

Cell structure, diffusion and osmosis come up in High School Biology practice, and water potential in Honors Biology. In the UK they appear in GCSE Biology Higher and A-level Biology: Year 1. Each daily paper is a short timed paper of 8 questions worth 25 to 35 marks, and the papers mix topics. Our osmosis guide goes further.

Read next

Biology · CellsAnimal and plant cells: GCSE structures and differencesAnimal and plant cells for GCSE Biology: labelled diagrams, what each part does, the differences between them, and how bacterial cells compare.