Diffusion, osmosis and active transport
These red onion cells were put in salty water. In many of them the purple contents have pulled away from the cell wall, because water left the cells by osmosis. Substances move in and out of every cell all the time, by three processes: diffusion, osmosis and active transport.
By the end of this page you can
- Explain diffusion, osmosis and active transport, with an example of each
- Describe turgid, flaccid and plasmolysed plant cells
- Put the steps of plasmolysis in order
- Define osmosis, concentration gradient and differentially permeable
- Answer exam questions on osmosis practicals
Goals tick themselves off as you try the activities below.
Photo: Trương Minh Khải, CC BY 4.0, via Wikimedia Commons. Cropped, JPEG q72.
Red onion skin cells in salt solution, magnified 400 times. The purple sap shows at a glance which cells have lost water.
How often it shows up in past papers
Paper 1 counts come from our past-paper bank of CSEC Biology Paper 1s. Paper 2 is not included yet.
Three ways in and out of a cell
Two of these need no energy; one needs energy from respiration. Tap each card.
Three processes, three states
Three processes move substances; three words describe a plant cell after osmosis. Tap each one.
What does it mean?
Tap a word on the list to see its meaning.
Animal cells have no wall: in pure water a red blood cell swells and bursts, and in a strong solution it shrinks.
A cell in salty water
A turgid onion cell goes into strong salt solution. Drag or tap each card into its slot.
What happens to the cell first?
Seven terms to know cold
Say what each term means before you flip the card. Osmosis definitions lose marks for leaving out the membrane.
Six quick questions, then a real one
Pick an answer to see why it’s right or wrong.
Osmosis is the movement of
Root hair cells take in mineral ions from soil where they are less concentrated. This is
A red blood cell is placed in pure water. It will
A potato strip is left in a concentrated sugar solution for an hour. It will most likely become
The cell wall of a plant cell is
Which process needs energy from respiration?
exam style · 3 marks
Explain why a plant wilts when it is short of water.
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Practice questions are written by My V.I.P. Academy. They are not official CXC papers.