Animal Science Explorer

1.1 Why do animals have skeletons?

A skeleton is the framework of bones that gives an animal its shape. Animals can be split into two big groups:

• Vertebrates — animals with a backbone (humans, dogs, cats, birds, fish, reptiles, amphibians).
• Invertebrates — animals with no backbone (insects, worms, jellyfish, snails).

A skeleton has four main jobs:

1. Support — holds the body up and gives it its shape.
2. Protection — the skull protects the brain; the ribs protect the heart and lungs.
3. Movement — bones work with muscles so the body can move.
4. Making blood cells — new blood cells are made inside some bones.

1.2 The human skeleton

An adult human has 206 bones. Babies are born with around 300 bones, but some join together (fuse) as they grow. Here are some major bones:

• Skull — protects the brain (made of 22 fused bones).
• Spine — 33 vertebrae, holds you upright.
• Ribs — 24 bones (12 pairs) protecting the heart and lungs.
• Pelvis — the hip bones.
• Femur — the thigh bone, your longest bone.
• Humerus — the upper arm bone.
• Radius & ulna — the two lower arm bones.
• Tibia & fibula — the two lower leg bones.

Your smallest bone is the stirrup inside your ear — only about 3 mm long!

1.3 Different skeletons for different lifestyles

Animals have skeletons built for the way they live:

• Birds — hollow bones for flight, fused wing bones, a large breastbone for flight muscles, and a beak instead of heavy teeth.
• Fish — a flexible backbone, many small bones, fins, and a streamlined shape for swimming.
• Snakes — a very long backbone (up to 400 vertebrae!), many ribs, no limbs, and a flexible jaw to swallow big prey.
• Elephants — thick, heavy bones, a large skull with hollow spaces to save weight, and pillar-like legs to carry their weight.
• Bats — very long finger bones that hold up the wing membrane, and lightweight bones for flying.

1.4 Joints and movement

Bones can't move on their own. They need joints (where two bones meet), muscles to pull them, ligaments (which join bone to bone) and tendons (which join muscle to bone).

There are different types of joint:

• Ball & socket (shoulder, hip) — moves in all directions.
• Hinge (knee, elbow, fingers) — moves in one direction, like a door.
• Pivot (neck) — lets you rotate and turn.
• Gliding (wrist, ankle) — bones slide over each other.

1.5 Muscles and movement

Your body has over 600 muscles. Here is the important secret: muscles can only PULL — they can never push! So they work in antagonistic pairs (one pulls one way, its partner pulls the other way).

In your arm:

• Bending your arm: the biceps contracts (shortens) and the triceps relaxes.
• Straightening your arm: the triceps contracts and the biceps relaxes.

There are 3 types of muscle:

• Skeletal — moves your bones; you control it (voluntary).
• Smooth — in your organs; works automatically.
• Cardiac — in your heart; never stops!

1.6 How different animals move

• Running — a cheetah reaches 70 mph with long legs and a flexible spine.
• Swimming — a dolphin reaches 20 mph with a streamlined body, fins and tail.
• Flying — a peregrine falcon dives at 240 mph using wings, a light skeleton and strong chest muscles.
• Slithering — snakes use a flexible backbone, ribs and scales.
• Jumping — a kangaroo leaps 30 ft with strong back legs and springy tendons.
• Crawling — a snail uses one muscular foot and slime, very slowly.

1.7 Exoskeletons

Some animals wear their skeleton on the outside — this is an exoskeleton. You find them on insects, crustaceans (crabs, lobsters, shrimp) and arachnids (spiders, scorpions).

Advantages: tough armour for protection, stops the body drying out (prevents water loss), and gives support without needing internal bones.

Disadvantages: it can't grow, so the animal must moult (shed it); it is heavy, which limits how big the animal can get; and the animal is vulnerable while the new shell hardens.

1.8 Movement adaptations

An adaptation is a feature that helps an animal survive. Look at these movement adaptations:

• Cheetah — long thin legs, a flexible spine, large nostrils, a long tail for balance, and non-retractable claws for grip.
• Eagle — hollow bones, a large wingspan, powerful chest muscles, a hooked beak, and sharp talons.
• Frog — long muscular back legs, webbed feet, sticky toe pads, and springy tendons.

1.9 Topic 1 Review Quiz

2.1 Where does energy come from?

Almost all energy for life starts at the Sun. Plants (called producers) make their own food using sunlight — this is photosynthesis. Animals (called consumers) can't make food, so they must eat.

A simple food chain shows who eats what:

☀️ SUN → 🌿 GRASS → 🐰 RABBIT → 🦊 FOX

2.2 Producers & photosynthesis

Plants make food using sunlight + water + carbon dioxide. This makes glucose (sugar for energy) and gives off oxygen.

Types of producer include: trees, grass, crops, bushes, algae and phytoplankton (tiny sea plants).

2.3 Primary consumers (herbivores)

Herbivores eat plants. Examples: rabbits, cows, deer, elephants (which eat around 300 kg a day!), caterpillars and grasshoppers.

Adaptations of herbivores:

• Flat molars for grinding and sharp incisors for snipping — but no canines.
• Long intestines or several stomachs (cows have 4!) with helpful bacteria to digest tough plants.
• Eyes on the sides of the head to spot danger all around.
• Defences like running fast, camouflage, or staying in herds.

2.4 Secondary consumers (carnivores)

Carnivores eat meat. Examples: lions, eagles, sharks, snakes, foxes and spiders.

Adaptations: sharp canines for gripping, slicing molars, forward-facing eyes to judge distance, hunting skills, shorter intestines and strong stomach acid.

A predator is the hunter; the prey is the hunted. An animal can be both — a fox is a predator to rabbits, but prey to eagles!

2.5 Omnivores

Omnivores eat both plants and meat. Examples: bears, pigs, rats, chickens, raccoons and humans. (Fun fact: the Pets on the Green rats are omnivores!)

They have mixed teeth, medium-length intestines, and are opportunistic and adaptable — they eat whatever they can find.

Advantages: more food options, they can live in more places, and better survival. Disadvantages: they are not specialised, and need a varied diet to stay healthy.

2.6 Food webs

In real life, many food chains are connected together to make a food web. In a woodland, plants feed rabbits, deer and caterpillars; these feed foxes, owls and birds; and these feed eagles.

2.7 Apex predators

An apex predator sits at the very top of the food chain with no natural predators. Examples: lion, polar bear, eagle, great white shark, saltwater crocodile, wolf and tiger.

They are very important — they control the populations of other animals and keep the whole ecosystem in balance.

2.8 Decomposers — nature's recyclers

Decomposers break down dead plants and animals. They include fungi, bacteria, earthworms, maggots, beetles, slugs and snails.

They break down dead material, return nutrients to the soil, and help new plants grow. Without them, the world would be piled high with dead things!

2.9 Energy transfer & the 10% rule

Energy gets less as you go up a food chain. Only about 10% of the energy passes to the next level. The rest is used for movement, warmth and breathing, or is lost as heat and undigested parts.

That's why an energy pyramid looks like this:

• Producers: 10,000 units
• Primary consumers: 1,000 units
• Secondary consumers: 100 units
• Apex predators: 10 units

2.10 Rainforest food chains

Rainforests are packed with life:

• Producers: trees, vines, ferns
• Herbivores: sloths, monkeys, parrots, leaf-cutter ants
• Carnivores: frogs, snakes, spiders
• Top predators: jaguars, eagles, anacondas
• Decomposers: fungi, termites

The Pets on the Green chameleons and geckos are rainforest predators! Special adaptations include the sloth's algae camouflage, the poison dart frog's warning colours, the toucan's beak, the jaguar's spots, and leaf-cutter ants that farm fungus.

2.11 Endangered species & food chains

Endangered means very few are left. Extinct means gone forever.

Causes: habitat loss, overhunting, pollution, climate change and invasive species.

Examples: tigers (only about 3,900 left), rhinos, giant pandas (numbers improving), and the bald eagle (recovered after the pesticide DDT was banned).

What you can do: reduce, reuse and recycle, don't litter, learn about animals, and support conservation.

2.12 Topic 2 Review Quiz

3.1 What is a life cycle?

Every living thing has a life cycle: birth or hatching → growth → reproduction → death.

Some are simple (like a human, who just grows bigger). Others are complex with metamorphosis — a huge change of body shape. A butterfly goes: egg → caterpillar → chrysalis → butterfly.

Animals reproduce in two ways:

• Sexual reproduction — two parents, so babies have variation (they are all a bit different).
• Asexual reproduction — one parent, and babies are clones (identical). Seen in starfish, some lizards and bacteria.

3.2 Mammal life cycles

Most mammals go: baby (born live — except the platypus and echidna, which lay eggs!) → juvenile → adult → old age → death. Mammals have a pregnancy, feed their babies milk (from mammary glands), and give lots of parental care.

• Dog — pregnant for 63 days, 6–10 pups.
• Elephant — pregnant for 22 months, 1 calf, can live to 70.
• Rabbit — pregnant for 31 days, 4–12 babies.

3.3 Bird life cycles

Birds go: egg → embryo → chick → fledgling → adult. Inside an egg you'll find the shell, albumen (egg white), yolk (food), an air sac and the embryo (the growing chick).

Eggs are kept warm (incubated) at about 37–38°C. Chicken eggs hatch in 21 days; ostrich eggs take 42.

Chicks can be altricial (born helpless — robins, eagles) or precocial (born ready to go — chickens, ducks). Pets on the Green has Rosie the galah and other birds!

3.4 Amphibian life cycles

Amphibians go through complete metamorphosis, moving from water to land. A frog goes:

1. Frogspawn (eggs in jelly)
2. Tadpole — has gills and a tail, eats algae
3. Tadpole with legs
4. Froglet
5. Adult frog — breathes with lungs and skin, eats insects

This takes about 12–16 weeks. Salamanders, toads and newts are amphibians too. Metamorphosis is clever: the young and adults eat different food, so they don't compete!

3.5 Insect life cycles

Insects have two kinds of life cycle:

• Complete metamorphosis: egg → larva → pupa → adult (butterflies, beetles, flies, bees, ants).
• Incomplete metamorphosis: egg → nymph → adult (grasshoppers, dragonflies, stick insects, cockroaches).

A butterfly: egg (3–5 days) → caterpillar (2–5 weeks) → chrysalis (1–2 weeks) → adult. The Pets on the Green stick insects go through incomplete metamorphosis!

3.6 Reproduction strategies

Animals have different plans for having babies:

• r-selected — lots of babies but little care (fish, frogs, insects). A salmon lays 2,000–5,000 eggs!
• K-selected — few babies but lots of care (mammals, birds). An elephant has 1 calf every 4–5 years.

Small, vulnerable animals usually have many babies. Large, powerful animals have few, well-protected babies.

3.7 Endangered animal reproduction

Slow reproducers struggle to recover: pandas (females are only fertile 2–3 days a year!), rhinos, elephants and blue whales. Fast reproducers bounce back quickly: rats and rabbits.

3.8 Life cycle comparison chart

3.9 The human life cycle

Humans go: baby → toddler → child (you are here!) → teenager (puberty) → young adult → middle age → older adult → elderly.

Humans have the longest childhood of any animal — because we have big brains, lots to learn, and families to support us while we grow.

3.10 Topic 3 Review Quiz

4.1 What is evolution?

Evolution is change over millions of years. All life on Earth is related — it all came from tiny single-celled ancestors long ago. Here's how it works:

1. Babies vary — they are all slightly different.
2. Some survive better than others (natural selection).
3. The survivors pass on their helpful traits.
4. Slowly, over time, the whole species changes.

Evolution is slow, it is not random, and it connects all life.

4.2 Natural selection

Natural selection is sometimes called "survival of the fittest". The steps are: variation → competition → selection → reproduction → change.

A famous example is the peppered moth. Before the Industrial Revolution, most were light to hide on pale tree bark. When soot from factories blackened the trees, dark moths survived better. After the air was cleaned, light moths returned. Evolution in action!

4.3 Adaptations

There are three types of adaptation:

• Structural (body parts): a camel (hump, long eyelashes, wide feet, closable nostrils), a penguin (blubber, waterproof feathers, counter-shading, huddling), a giraffe (long neck & tongue, strong heart), and a cactus (waxy skin, spines, deep roots).
• Behavioural (things they do): bear hibernation, meerkat sentinels (lookouts), and bird migration — the Arctic tern flies 44,000 miles a year!
• Physiological (how their body works): snake venom, Arctic fish with antifreeze blood, and bat echolocation.

4.4 Fossils — evidence of evolution

A fossil is the preserved remains of a living thing from long ago. Here's how a fossil forms:

1. An animal dies and is quickly buried.
2. The soft parts rot away.
3. The hard parts (bones, shell) are preserved.
4. Over millions of years, minerals replace the bone, turning it to stone.
5. Much later, it is discovered!

Types of fossil: body fossils, trace fossils (footprints, coprolites — fossil poo!), amber (trapped insects), and ice (frozen woolly mammoths).

What fossils tell us: how old life is (the oldest is 3.5 billion years!), which animals are extinct, how animals changed (horses went from dog-sized with 4 toes to today's 1-toe hoof), and where animals lived.

4.5 Extinction

Extinction means gone forever. In fact, 99% of all species that ever lived are now extinct!

Causes: habitat loss, climate change, hunting or overfishing, invasive species, and natural disasters.

Famous extinctions: the dinosaurs (an asteroid, 65 million years ago), the woolly mammoth (4,000 years ago), the dodo (1681) and the Tasmanian tiger (1936). Earth has had 5 mass extinctions — and some scientists think we may be entering a 6th.

The good news: some species have been saved — the bald eagle, giant panda, white rhino and humpback whale.

4.6 Human evolution

Here is our own family story:

• 6–7 million years ago — common ancestor shared with chimpanzees.
• Australopithecus (~4 million years, "Lucy") — walked upright, brain about 400cc.
• Homo habilis (~2 million years) — used tools, brain about 600cc.
• Homo erectus (~1.8 million years) — used fire, left Africa, brain about 900cc.
• Homo sapiens (~300,000 years, that's us!) — brain about 1,350cc, with language and art.

What makes humans special: big brains, language, opposable thumbs, cooperation and creativity. And we are still evolving — think of lactose tolerance, blue eyes, and high-altitude adaptations!

4.7 Topic 4 Review Quiz