Year 4 Science · Learning & practice

Shark Life Cycles and Ocean Food Webs

Trace a shark from egg case to apex hunter, then connect the ocean's living things into feeding relationships that keep the whole sea in balance.

Section 1 · Life cycles

From egg case to ocean hunter

By the end of this section I can describe the stages in a shark's life cycle and recognise that living things grow, change and reproduce — so I can explain how a shark develops from birth to adulthood.

Success criteria 0 / 4 ticked

Tick each one when you can do it without help.

1A Stages of a shark's life

Like all living things, sharks pass through distinct stages as they grow and develop. Most sharks share the same broad sequence — but the way they begin life can differ.

The five life stages

egg / embryo pup juvenile sub-adult adult

A shark begins as an embryo — either inside an egg case or developing inside the mother. Once born or hatched it is called a pup: a miniature, fully independent shark. It grows into a juvenile, then a sub-adult as it nears full size, and finally an adult able to reproduce and start the cycle again.

Ordering the stages

Egg case → Pup → Juvenile → Sub-adult → Adult each stage follows the one before, just like your own growth from baby to adult
The adult reproduces completing the cycle so a new generation of pups is born

Interactive · order the shark's life stages

Click the stages in order from first (egg) to last (adult). Each click places the next number.

Check yourself

Think of a seaside object named after a mythical sea creature.
The egg case of sharks such as Port Jackson and catsharks is nicknamed a mermaid's purse because its rectangular shape with corner tendrils looked to sailors like a tiny handbag.

pup?

It is the stage between pup and sub-adult — a young but independent shark.
After the pup comes the juvenile stage: a young shark that feeds and travels on its own while still growing toward adult size.

1B Variety in shark life cycles

Not every shark begins life the same way. The three main reproductive strategies give pups very different starts.

Three ways sharks begin life

oviparous — egg-laying viviparous — live birth ovoviviparous — egg inside mother

Oviparous sharks lay egg cases that hatch outside the body. Viviparous sharks give birth to live, free-swimming pups — roughly 70% of shark species do this. Ovoviviparous sharks keep the egg inside the mother until it hatches, then give birth to a live pup.

Whatever the start, every shark reaches the same destination: an adult that reproduces and continues the cycle.

Check yourself

It is the majority — think of a round number close to three-quarters.
About 70% of shark species are viviparous or ovoviviparous and give birth to live pups; the remaining minority lay egg cases.

It is the same word used for a baby dog.
A baby shark is called a pup. Unlike many fish, a pup is usually born fully formed and ready to swim and hunt on its own.

Section 2 · Food webs

Who eats whom in the ocean

By the end of this section I can describe the roles of producers, consumers and decomposers and build a food chain — so I can explain how living things depend on each other within a habitat.

Success criteria 0 / 4 ticked

Tick each one when you can do it without help.

2A Producers, consumers and decomposers

Every living thing in the ocean has a job. These three roles keep energy and matter moving through the ecosystem.

The three roles

producer — makes its own food consumer — eats other living things decomposer — breaks down dead material

Producers such as phytoplankton and seaweed use sunlight to make their own food. Consumers — like zooplankton, fish, seals and sharks — eat other living things. Decomposers such as bacteria and fungi break down dead organisms, returning nutrients to the water so producers can use them again.

Sorting ocean organisms

Phytoplankton = producer makes food from sunlight
Zooplankton, tuna, white shark = consumers each eats other living things
Bacteria on dead kelp = decomposer breaks down dead matter and recycles nutrients

Check yourself

Look up — producers capture energy from the sky during the day.
Producers use sunlight to make food through photosynthesis. Without sunlight there would be no phytoplankton, and almost nothing else in the ocean could survive.

It is the "recycler" role — bacteria and fungi do this job.
Decomposers such as marine bacteria and fungi break down dead material, releasing nutrients back into the water for producers to take up again.

2B Building food chains and webs

A food chain shows one path of energy through an ecosystem. Arrows point from the eaten to the eater — showing the direction energy flows.

Reading the arrows

In the chain phytoplankton → zooplankton → small fish → white shark, each arrow means "is eaten by". Energy travels from the producer at the start all the way to the apex consumer at the top.

A food web is many overlapping food chains joined together, showing that most organisms eat — and are eaten by — more than one thing.

Building a chain

Start with a producer energy must enter the chain from something that makes its own food
Add a consumer that eats the producer each link must feed on the one before it
End at the apex consumer nothing in the web eats it

Interactive · build an ocean food chain

Click organisms in order so that each one eats the one before it. Aim for a chain of at least three, ending with an apex consumer.

Click an organism above to begin your food chain.

Check yourself

phytoplankton → zooplankton → small fish → white shark, what is the special term for the shark's role at the top?

It is the consumer at the very top — nothing in the web hunts it.
The white shark is an apex consumer: the top predator of the food chain, which is not eaten by anything else in that web.

Think about what passes along the chain from one living thing to the next.
The arrows show the flow of energy — energy moves from the organism being eaten to the organism that eats it.

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