Biology 11–12 · Year 11

Abiotic factors and biotic indicators of a freshwater site

Module 4: Ecosystem Dynamics (Population Dynamics)

PracticalMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

The idea

The invertebrates living in a stream or pond reflect its water quality, so a sample of what lives there, taken with abiotic readings, shows how abiotic and biotic factors are linked.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

Slips and falls at the water's edge; deep or fast water
Microorganisms in water; bites from invertebrates
Sun exposure

Controls

Sample only from the bank or shallow margins with adult supervision; life jackets if the site requires
Cover cuts, wear gloves, no eating, wash hands afterwards
Hats and sunscreen

Note

Excursion risk assessment under the school's outdoor procedures. 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.

What you need

Pond net or kick net; white sorting trays; pipettes and spoons; hand lenses; identification chart of freshwater invertebrates
Thermometer; pH strips or meter; dissolved oxygen kit or meter if available; turbidity tube or Secchi disc; flow float and stop clock
Waterproof dressings; gloves; hand-washing water and soap; holding tank

How to do it

At two sites (for example an open stretch and a shaded stretch, or upstream and downstream of a drain) record water temperature, pH, dissolved oxygen, turbidity and flow rate (float over 10 m, three timings).
At each site disturb the bottom for 1 minute upstream of the net and collect what drifts in; empty into a tray of site water.
Sort and identify the invertebrates to the level the chart allows; record the number of each type and classify each as pollution-sensitive (for example mayfly and stonefly nymphs, caddis larvae) or pollution-tolerant (for example bloodworms, sludge worms), as the source distinguishes.
Return every animal promptly to the site.
Tabulate abiotic readings and biotic counts side by side and describe which site has the greater diversity and what abiotic difference could explain it.

What you should see

Where the two sites differ in dissolved oxygen, temperature or turbidity, their invertebrate communities are expected to differ too: the cleaner, cooler, better-oxygenated site yields more pollution-sensitive types and the other more tolerant ones, which the source explains by the oxygen needs of nymphs and worms. The learner knows it worked when both sites were sampled with the same effort and method, every animal was returned, and the abiotic readings and counts are tabulated side by side so the link can be judged.

What changes

What you change: site (and the abiotic conditions that differ between sites)
What you measure: number and diversity of invertebrate types found, and proportion of pollution-sensitive types
What you keep the same: sampling time and effort
net and method
season
identification chart

Common misconceptions

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

Clear water is clean water; some pollutants are invisible and biotic indicators reveal them.
More animals means a healthier site; a site dominated by a few tolerant types is the poorer one.
Abiotic factors act independently of one another; temperature changes dissolved oxygen, which changes which animals can live there.

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 2027BIO11-11 BIO11/12-1 BIO11/12-3 BIO11/12-5
Biology 11–12 Syllabus (2025), Year 11 focus area Evolution and ecosystems; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-03
Biology 11–12 Syllabus (2025), Year 12 focus area Biodiversity; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-12-03
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-01 BI-11WS-03 BI-11WS-05
Biology 11–12 Syllabus (2025), Year 12 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-12WS-05
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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