# Adaptations

> Selection pressures, and structural, physiological and behavioural adaptations, with Australian plants and animals as examples.

From HSC Biology on WhizzNotes, free study notes for NSW students: https://whizznotes.com/biology/adaptations/. Updated 3 November 2026.
Year 11 and Year 12 boxes go deeper than the Year 10 text around them.

### Story time: The thorny devil's magic skin
In the red deserts of central Australia lives a small spiky lizard called the thorny devil. It almost never sees a pond, yet it never goes thirsty.

Its skin is covered in tiny grooves between its scales. When it stands on damp sand or in morning dew, water creeps along the grooves by capillary action, all the way to the corners of its mouth. It drinks with its feet. Over millions of years, the dry desert has shaped a lizard that can sip water from the ground it walks on.

**In short:** An adaptation is an inherited feature that helps an organism survive and reproduce in its environment. Adaptations can be structural (body parts), physiological (body processes) or behavioural (actions), like the epicormic buds that let eucalypts regrow after fire.

## Starting point: what you already know

- Living things have features that suit their environment (Year 7 and 10 science).
- Living things compete for food, water, space and mates.
- DNA carries the instructions for an organism's features.

## Selection pressures

A **selection pressure** is anything in the environment that affects which organisms survive and reproduce.

| Type | Examples |
|---|---|
| **Biotic** (living) | Predators, disease, competition for food or mates, availability of prey |
| **Abiotic** (non-living) | Temperature, water, light, soil nutrients, fire, salinity |

Australia has some strong ones: low rainfall, poor soils, regular bushfires and high temperatures.

## Three kinds of adaptation

An **adaptation** is an inherited feature that helps an organism survive and reproduce in its environment.

| Type | Meaning | Australian examples |
|---|---|---|
| **Structural** | A body part or shape | Thorny devil's grooved skin. Eucalyptus leaves hang vertically, so less of their surface faces the midday sun. Kangaroo's strong tail and back legs |
| **Physiological** | How the body works inside | Kangaroos make very concentrated urine to save water. Eucalyptus oil discourages insects. Many wattle seeds only germinate after fire |
| **Behavioural** | What the organism does | Kangaroos lick their forearms to cool down. Bilbies dig burrows and come out at night. Magpies swoop to guard their nests |

### Exam tip: How to tell them apart
Ask: can you **see** it on the body? Structural. Is it **inside** chemistry or a body process? Physiological. Is it something the animal **does**? Behavioural.

## Plants of fire and drought

Many Australian plants are adapted to **bushfire**.

- **Epicormic buds** under the thick bark of eucalypts sprout new leaves after a fire.
- **Lignotubers**, woody swellings at the base of mallee eucalypts, store food and buds to regrow.
- **Banksia** cones open and release seeds after fire (serotiny).

Aboriginal people have used **cultural burning** for tens of thousands of years: cool, patchy fires at the right time of year, which shaped many of these landscapes. Many groups now share this knowledge with fire services to reduce fuel and protect country.

Drought adaptations (**xerophytes**) include small or needle-like leaves, a thick waxy **cuticle**, sunken stomata, hairs that trap moist air and deep roots.

**Mind map**

```text
Adaptations
  Selection pressures
    Biotic: predators, disease
    Abiotic: heat, drought, fire
  Structural
    Body shape and parts
    Thorny devil skin
    Hanging eucalypt leaves
  Physiological
    Body chemistry
    Concentrated urine
    Fire-triggered germination
  Behavioural
    What it does
    Burrowing, nocturnal
    Licking forearms
  Fire and drought plants
    Epicormic buds
    Lignotubers
    Waxy cuticle
```

### Year 11: Adaptations to the Australian environment: depth questions
Year 11 exams often ask you to **link** an adaptation to a selection pressure with a reason. Use this pattern: **feature → how it works → how it helps survival in this environment**.

> Kangaroos have long loops of Henle in their kidneys. These reabsorb more water, producing concentrated urine. This reduces water loss in arid environments where drinking water is scarce.

Other strong examples:

- **Platypus** have electroreceptors in their bill to find prey with closed eyes in muddy water.
- **Mangroves** have **pneumatophores** (roots that stick up out of the mud) to get oxygen, and leaves that excrete salt.
- **Spinifex** grass rolls its leaves to protect stomata from dry wind.

Studying adaptations is how scientists like Charles Darwin and Alfred Russel Wallace first saw the pattern that led to the theory of evolution, in the next chapter.

### Year 12: Adaptations and population genetics
An adaptation spreads only if the alleles that cause it are passed on. In Module 5 and 6 you will see this as a change in **allele frequency** in the gene pool. For example, rabbits in Australia became more resistant to the myxoma virus because resistant rabbits survived and passed on their alleles.

## Quick summary

- A selection pressure is a biotic or abiotic factor that affects survival and reproduction.
- An adaptation is an inherited feature that improves survival and reproduction.
- Structural: body parts. Physiological: body processes. Behavioural: actions.
- Many Australian plants are adapted to fire (epicormic buds, lignotubers, fire-opened seeds) and drought (waxy cuticle, small leaves).

## Quiz

Try these questions from the chapter quiz.

1. Which is an abiotic selection pressure?
   - A. A predator
   - B. A disease
   - C. Low rainfall
   - D. Competition for mates
   - Answer: C. Low rainfall. Abiotic means non-living.

2. A kangaroo licks its forearms to cool down. This is a
   - A. structural adaptation
   - B. physiological adaptation
   - C. behavioural adaptation
   - D. selection pressure
   - Answer: C. behavioural adaptation. It is something the kangaroo does.

3. Eucalyptus leaves hang vertically. This is a
   - A. structural adaptation
   - B. behavioural adaptation
   - C. physiological adaptation
   - D. biotic factor
   - Answer: A. structural adaptation. It is about the shape and position of a body part.

The whole chapter quiz is on the page, for signed-in students: https://whizznotes.com/biology/adaptations/#quiz