Biology • Year 11 • Module 4 • Lesson 6
Abiotic Factors: The Physical and Chemical Environment
Lock in the core vocabulary, the tolerance-range model, and the major abiotic factors that shape organism distribution across Australian ecosystems.
1. Term–definition match
The eight definitions below are shuffled. In the right-hand column write the matching term from this list: abiotic factor, biotic factor, tolerance range, optimal zone, limiting factor, Liebig's Law of the Minimum, Shelford's Law of Tolerance, ectotherm. 8 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | A non-living physical or chemical component of an ecosystem that influences organism survival, distribution and abundance. | |
| 1.2 | The range of values for a single abiotic factor within which an organism can survive, from minimum tolerable to maximum tolerable. | |
| 1.3 | The portion of the tolerance range where growth is fastest, reproduction is most successful, and survival is highest. | |
| 1.4 | A living component of an ecosystem that influences other organisms, such as predation, competition or disease. | |
| 1.5 | The single abiotic factor that is furthest from an organism's optimal range, most strongly limiting its growth or distribution at a given time. | |
| 1.6 | States that growth is dictated not by total resources available, but by the scarcest resource. | |
| 1.7 | States that an organism's distribution is controlled by the environmental factor for which it has the narrowest tolerance range. | |
| 1.8 | An organism whose body temperature is regulated primarily by external heat sources; metabolic rate is strongly temperature-dependent. |
2. Label the tolerance range diagram
The diagram below shows the tolerance range model for an Australian ectotherm. Write the correct label for each zone or feature (A–G). Use terms from this list: lethal low, zone of physiological stress (low), optimal zone, zone of physiological stress (high), lethal high, maximum tolerable limit, minimum tolerable limit. 7 marks
Temperature tolerance schematic for an ectothermic lizard (e.g. Eastern Water Dragon)
| Label | Zone or feature name |
|---|---|
| A | |
| B | |
| C | |
| D | |
| E | |
| F | |
| G |
3. Classify as abiotic or biotic
For each factor below, tick the correct column and write one sentence explaining how it affects organism distribution in an Australian ecosystem. 10 marks (1 tick + 1 sentence each)
| Factor | Abiotic | Biotic | How it affects distribution (one sentence) |
|---|---|---|---|
| Soil pH in a eucalypt woodland | |||
| Predation by dingoes on kangaroos | |||
| Salinity of an estuary | |||
| Rainfall of 250 mm/year in semi-arid shrubland | |||
| Competition between grasses for sunlight | |||
| Water temperature in the Great Barrier Reef | |||
| Dissolved oxygen concentration in a river | |||
| Mycorrhizal fungi assisting plant root absorption | |||
| Day length (photoperiod) in spring | |||
| Disease caused by a parasite |
4. Limiting factor recall
Answer each in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 State Liebig's Law of the Minimum in your own words and give one Australian agricultural example.
4.2 Explain why a limiting factor can change between summer and winter in an Australian grassland.
4.3 State Shelford's Law of Tolerance and explain why it is useful for predicting species distribution.
4.4 Using the snow gum treeline example from the lesson, identify three abiotic factors that interact to create the treeline at approximately 1,800 m.
5. Build a concept map
Draw labelled arrows between the six terms below to show how they connect. Each arrow must carry a linking phrase (e.g. “restricts”, “determines”, “is described by”). Aim for at least 6 labelled arrows. 6 marks
Supplied terms: abiotic factor · tolerance range · limiting factor · organism distribution · Liebig's Law · optimal zone.
Q1 — Term–definition matches
1.1 abiotic factor • 1.2 tolerance range • 1.3 optimal zone • 1.4 biotic factor • 1.5 limiting factor • 1.6 Liebig's Law of the Minimum • 1.7 Shelford's Law of Tolerance • 1.8 ectotherm.
Q2 — Tolerance range diagram labels
A: lethal low. B: zone of physiological stress (low). C: optimal zone. D: zone of physiological stress (high). E: lethal high. F: minimum tolerable limit. G: maximum tolerable limit.
Q3 — Abiotic / biotic classification
Abiotic: soil pH, salinity of estuary, rainfall 250 mm/year, water temperature GBR, dissolved oxygen, day length. (6 factors)
Biotic: predation by dingoes, competition between grasses, mycorrhizal fungi, disease/parasite. (4 factors)
Sample sentences — award 1 mark for any biologically correct sentence that links the factor to distribution. Examples: Soil pH below 5.5 locks up phosphorus, preventing many eucalypts from establishing in acidic soils. / Salinity above 35 ppt excludes most freshwater fish from estuaries because of osmotic stress across cell membranes.
Q4.1 — Liebig's Law + Australian example
Liebig's Law states that plant growth is limited by the scarcest resource, not by the total amount of all resources combined. Example: Australian wheat crops on phosphorus-deficient soils grow poorly even when sunlight, temperature and water are adequate — phosphorus is the limiting factor. [2 marks: 1 for law, 1 for example]
Q4.2 — Seasonal change in limiting factor
In summer, water (rainfall) is the limiting factor in Australian grasslands because evaporation exceeds rainfall and soil moisture is depleted. In winter, temperature becomes limiting because cold temperatures slow metabolic rates, reducing plant growth even when soil moisture is adequate. [2 marks: 1 per season with factor named]
Q4.3 — Shelford's Law
Shelford's Law states that an organism's distribution is controlled by the environmental factor for which it has the narrowest tolerance range. It is useful because it identifies the single most critical abiotic constraint — improving all other conditions will not expand the organism's range if the narrowest factor remains outside the tolerance limit. [2 marks: 1 for law, 1 for usefulness]
Q4.4 — Snow gum treeline factors
Three abiotic factors: (1) Temperature — growing season above 1,800 m is too short for snow gums to accumulate carbohydrates needed for growth and reproduction. (2) Wind — high winds cause physical damage and desiccation beyond what roots can replace. (3) Soil — alpine soils are thin, poorly developed, and subject to frost heave that damages root systems. [2 marks: 1 per factor named + explained, max 2]
Q5 — Sample concept map
Correct maps should include arrows such as:
- abiotic factor — has a → tolerance range
- tolerance range — contains an → optimal zone
- abiotic factor — can act as a → limiting factor
- limiting factor — restricts → organism distribution
- Liebig's Law — identifies → limiting factor
- tolerance range — determines range of → organism distribution
Award 1 mark per correctly labelled, causally directional arrow. Maximum 6 marks.