Biology 11–12 · Year 11

Unicellular, colonial and multicellular organisms in pond water by the hanging-drop method

Module 2: Organisation of Living Things (Organisation of Cells)

PracticalLow risk

The idea

A drop of pond water holds organisms at three levels of organisation, and watching them live shows how a single cell, a colony of like cells and a body of specialised cells each move, feed and respond.

What you need

Pond or aquarium water with visible green scum or debris, 50 mL, or cultures of Chlamydomonas, Volvox, Paramecium and Daphnia from an educational supplier
Cavity slides or a film-canister lid and adhesive putty (the source method); plain slides and coverslips; pipettes
Compound microscope to 400x; stereo microscope for Daphnia
Acetate grid or eyepiece graticule to estimate size; cotton fibres or methyl cellulose to slow swimmers

How to do it

Place a drop of sample on a coverslip, invert it over the cavity so the drop hangs, and view the edge of the drop at 100x then 400x.
Identify at least one unicellular organism (a single motile cell such as Chlamydomonas or Paramecium), one colonial organism (a sphere of similar cells such as Pandorina, or Volvox, whose cells are specialised) and one multicellular animal (Daphnia or a rotifer).
For each, record how it moves, whether all its cells look alike, and whether any part is specialised for feeding, sensing or reproduction.
Estimate the size of each organism with the grid and record it with the magnification.
Draw and label each organism with a scale bar, and tabulate the three levels of organisation with your evidence for each.

What you should see

Unicellular organisms are seen as single cells moving by flagella or cilia, Volvox as a hollow ball of many small flagellated somatic cells with a few larger reproductive cells or daughter colonies inside, and Daphnia as a translucent animal with a beating heart, jointed limbs, a compound eye and a gut, none of which any single cell could provide. Sizes span from about 10 micrometres for a single Chlamydomonas cell to a few millimetres for an adult Daphnia. The learner knows it worked when an example of each level has been seen live and drawn to scale.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Every colony is a group of identical cells; some colonial algae are built of cells that are alike, while Volvox has flagellated somatic cells that do not reproduce and a smaller number of reproductive cells.
Single-celled organisms are simple; one cell carries out every function a body does.
Microscopic means unicellular; Daphnia and rotifers are multicellular and microscopic.

Safety card

Low riskLearners carry it out

Hazards

Pond water may contain disease-causing microbes
Broken coverslips

Controls

Cover cuts with waterproof dressings or wear gloves; wash hands before leaving
Do not eat or drink; wipe benches after use
Return organisms to a holding tank

Note

Hygiene precautions for pond water per the source. The Department's Animals in Schools framework sets out a school's animal welfare obligations (https://education.nsw.gov.au/teaching-and-learning/animals-in-schools); every animal here is held only for as long as the activity needs and is returned to where it came from.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Biology Stage 6 Syllabus (2017), current: Year 11 taught to the end of 2026 and Year 12 to Term 3 2027BIO11-9 BIO11/12-4 BIO11/12-7
Biology 11–12 Syllabus (2025), Year 11 focus area Cells to systems; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-02
Biology 11–12 Syllabus (2025), Year 11 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11WS-04 BI-11WS-07
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities