Biology • Year 11 • Module 3 • Lesson 1
Selection Pressures & Population Change
Lock in the core vocabulary, the biotic/abiotic split, and the two Australian case studies before moving to application tasks.
1. Complete the paragraph
Fill each blank with the correct term from the word bank. Use each term once only. 8 marks
A _______________ is an environmental factor that affects an organism's chance of surviving and reproducing. A living factor such as a predator, competitor or disease is a _______________ factor, while a non-living physical or chemical condition such as temperature or water availability is an _______________ factor. A pressure acts on the natural _______________ already present in a population, so that individuals with advantageous traits survive and reproduce more than others, a process called _______________. An introduced species that spreads and harms native organisms is an _______________. Using a living organism such as a moth to reduce a pest population is called _______________. Over time, a selection pressure can change the proportion of a trait, or raise or lower a population's _______________.
2. Term–definition match
Write the matching term from this list in the right-hand column: selection pressure • biotic factor • abiotic factor • differential survival • invasive species • biological control • variation • local extinction. 8 marks
| # | Definition | Matching term |
|---|---|---|
| 2.1 | An environmental factor that affects an organism's chance of surviving and reproducing. | |
| 2.2 | A living component of the environment, such as predators, competitors or disease. | |
| 2.3 | A non-living physical or chemical condition, such as temperature, water or salinity. | |
| 2.4 | When individuals with certain traits survive and reproduce more than others. | |
| 2.5 | An introduced species that spreads and harms native organisms or ecosystems. | |
| 2.6 | Using a living organism, such as a predator or disease, to reduce a pest population. | |
| 2.7 | The natural differences between individuals in a population that a pressure acts on. | |
| 2.8 | The disappearance of a population from an area when no individuals can cope with a pressure. |
3. Classify each selection pressure
For each example below, write B (biotic) or A (abiotic) in the Type column. 8 marks
| Type (B/A) | Example |
|---|---|
| A long drought reduces water in a grassland | |
| A new fast predator arrives on an island of slow lizards | |
| A fungal disease spreads through a frog population | |
| Increasing salinity affects a wetland plant population | |
| Competition for the same food between two bird species | |
| A colder climate sets in over many years | |
| The toxic cane toad poisons native predators that eat it | |
| A bushfire sweeps through dry forest |
4. True or false, with correction
Circle T or F. If the statement is false, write the corrected version on the line below. 8 marks, 1 for T/F, 1 for correction where needed
4.1 A selection pressure changes an individual organism's own genes during its lifetime so it can suit the environment. T / F
4.2 The toxic cane toad acts as a biotic selection pressure that has reduced some native predator populations. T / F
4.3 The Cactoblastis moth is an example of biological control of the prickly pear. T / F
4.4 Temperature, drought and salinity are examples of biotic selection pressures. T / F
5. Build a concept map
Draw labelled arrows between the five terms below to show how they connect. Each arrow must carry a linking phrase (e.g. “acts on”, “leads to”, “changes”). Aim for at least 5 labelled arrows. 5 marks
Supplied terms: selection pressure • variation • differential survival • population abundance • trait proportion.
Q1, Cloze paragraph
In order: selection pressure • biotic • abiotic • variation • differential survival • invasive species • biological control • abundance.
Q2, Term–definition matches
2.1 selection pressure • 2.2 biotic factor • 2.3 abiotic factor • 2.4 differential survival • 2.5 invasive species • 2.6 biological control • 2.7 variation • 2.8 local extinction.
Q3, Classification answers
A Drought reduces water • B New fast predator • B Fungal disease • A Increasing salinity • B Competition for food • A Colder climate • B Toxic cane toad • A Bushfire.
Q4, True/False with correction
4.1 False. Correction: A selection pressure does not change an individual's genes during its lifetime. It acts on existing variation in the population, individuals with advantageous traits survive and reproduce more, so the population changes over generations.
4.2 True.
4.3 True.
4.4 False. Correction: Temperature, drought and salinity are abiotic (non-living) selection pressures. Biotic pressures come from living things such as predators, competitors and disease.
Q5, Sample concept map
Accept any biologically valid linking phrases. A correct map should include arrows such as:
- selection pressure acts on → variation
- variation leads to → differential survival
- differential survival over generations changes → trait proportion
- selection pressure can raise or lower → population abundance
- trait proportion shifts as → population abundance changes
Award 1 mark per correctly labelled arrow with a valid linking phrase. Maximum 5 marks.