Adaptation and Food Chains
FoundationPlants and animals have special features and behaviours for their homes — cacti store water, polar bears wear thick fat. Eating and being eaten link living things into food chains where predators and prey depend on each other.
- Four great environments: rainforest, grassland, polar regions and desert.
- Adaptations: cactus needles save water; polar bear fat keeps warmth.
- Migration and hibernation carry animals through hard seasons.
文體小知識：說明文帶你走遍世界四大自然環境，看看動植物怎樣適應家園，再順著吃與被吃的關係畫出食物鏈。
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1The Earth has many kinds of natural environment: hot, rainy tropical rainforests; temperate grasslands with dry and wet seasons; the snowy polar regions; and deserts with little rain. Each has its own temperature, rainfall and living things, and the creatures that live there all have special powers to fit their home.
2Deserts are dry. A cactus turns its leaves into needles to cut water loss, stores water in its thick stem, and spreads long roots deep to drink. A camel's hump is packed with fat, letting it travel long without food or water. In the freezing polar regions, the polar bear keeps warm with thick fat and dense fur, and its white coat hides it in the snow.
3Animals also have special survival behaviours. Before the cold arrives, swallows and wild geese fly in flocks to warm lands for the winter and return in spring — this is migration. Snakes, frogs and turtles hide in holes in winter, eating nothing and moving little while their bodies slow down — this is hibernation. Such behaviours help animals pass the hungry season.
4Eating and being eaten link living things into a chain. Grass is eaten by rabbits, and rabbits are hunted by eagles — a food chain: grass → rabbit → eagle. The chain starts with plants that make their own food, called producers; the animals that eat plants and those that eat animals are all consumers. The eagle is a predator and the rabbit its prey; yet when a rabbit eats grass, the rabbit is a predator too.
5In the same environment, living things compete for sunlight, water, food and space: grasses on the plain fight for sunshine, antelopes and zebras fight for fresh grass. Competition weeds out the weak and pushes living things to grow different powers. Every creature plays a role in its environment, linked with the others; none can be missing.
1Summary 重點摘要
Plants and animals have special features and behaviours for their homes — cacti store water, polar bears wear thick fat. Eating and being eaten link living things into food chains where predators and prey depend on each other.
2Vocabulary cards Vocabulary
Features or behaviours that help a living thing survive in its environment.
A hot, rainy environment full of dense plants, such as the Amazon rainforest.
A wide grassy land with clear dry and wet seasons; its animals run fast.
The freezing, ice-covered lands at the north and south ends of the Earth.
A dry land with little rain and big day-night temperature swings.
The long seasonal journey of animals to a better place to live.
Hiding through winter with the body slowed down, as snakes and frogs do.
A chain of who eats whom, such as grass → rabbit → eagle.
A plant that makes its own food; the start of every food chain.
A predator hunts other animals; the one hunted is called the prey.
3Step by step Steps
- Step 1: The four great environmentsThe Earth's natural environments come in four main kinds. Tropical rainforests are hot and wet all year with towering, crowded trees — the richest in life on Earth. Temperate grasslands have four clear seasons, medium rain, wide grass and few trees. The polar regions at the north and south ends are frozen worlds with long, severe winters. Deserts are dry, scorching by day and cold at night, with few plants. Each environment differs in temperature, rain and food, so the creatures within must each have their own powers to survive.
- Step 2: How desert life adaptsWhat deserts lack is water, so every desert skill is about finding and saving it. The cactus turns its leaves into needles, cutting water loss to the minimum; its thick stem stores water like a tank, and its long, wide roots drink first when rain falls. The camel's hump is packed with fat that can turn into energy and water, letting it cross the desert long without food or drink; long lashes and closable nostrils keep the sand out. All these features are evidence of desert life adapting to drought.
- Step 3: Adaptation in polar lands and grasslandsThe greatest enemy in polar lands is cold. The polar bear wears a thick layer of fat under the skin and dense, wind-proof fur, and stays out on the ice in deep winter; penguins huddle together for warmth, their fat a natural down coat. The bear's white coat hides it in the snow and aids hunting. On temperate grasslands, animals prize speed: antelopes and zebras have long slim legs, running fast to chase fresh grass and escape lions and cheetahs; some live in herds, keeping watch together for predators.
- Step 4: Migration and hibernationAnimals' survival behaviours are also tools of adaptation. When seasons turn, food and temperature change greatly; some animals choose to move: before winter, swallows and wild geese fly in flocks to the warm south and return north in spring to breed — migration. Others choose a long sleep: snakes, frogs and turtles eat well before winter, then hide in burrows or tree holes, heartbeat and breathing slowing, neither eating nor moving until spring — hibernation. Both behaviours carry animals through the hungry cold.
- Step 5: The structure of a food chainEating and being eaten link living things like rings of a chain. Take grass → rabbit → eagle: grass makes its own food from sunlight, water and carbon dioxide in the air, so it is the start of the chain, the producer. The rabbit eats the grass for energy — a primary consumer; the eagle hunts the rabbit — a higher consumer. The arrow points from the eaten to the eater, showing the direction energy flows. A food chain usually starts with plants, then plant-eaters, then animal-eaters, and rarely runs more than four or five links.
- Step 6: Predators and preyNo one is always the predator in a chain. When a rabbit eats grass it is the predator and the grass its food; when an eagle hunts the rabbit, the rabbit becomes the prey. Predator and prey numbers shape each other: more rabbits mean plenty of food for eagles, so eagles increase; with more eagles, rabbits are eaten down, grass recovers, and the cycle continues. Rising and falling like a seesaw, they hold a balance. Predators also tend to catch the slower, weaker prey, which in fact keeps the rabbit population strong.
- Step 7: Competition and connectionIn the same environment, living things compete for resources. Plants fight for sunlight, water and soil nutrients: tall trees steal the light while small plants find ways to live in the shade. Animals fight for food, water and homes: antelopes and zebras graze the same field, and lion prides even fight over territory. Competition pushes living things to sharpen different skills. In the whole environment, producers, consumers, predators and prey are all linked; when one ring suffers, the others feel it too. Protecting the environment is protecting every living thing.
5Worked example Example
Example: On a grassland, scientists record that grass is eaten by grasshoppers, grasshoppers by frogs, frogs by snakes, and snakes finally by eagles. Write out this food chain, and point out the producer and an example of a predator and its prey.
- Arrange them by who eats whom: grass → grasshopper → frog → snake → eagle, with arrows pointing to the eater.
- The grass makes its own food, so it is the start of the chain — the producer.
- Grasshoppers, frogs, snakes and eagles are all consumers; in each link the one eaten is the prey and the one eating is the predator.
- For example, the snake is a predator when it eats frogs, but becomes prey when the eagle takes it; the role depends on the link.
- Answer: The food chain is grass → grasshopper → frog → snake → eagle. The grass is the producer; grasshoppers, frogs, snakes and eagles are consumers. Of any neighbouring pair, the eater is the predator and the eaten is the prey — for example, the eagle is the snake's predator and the snake is the eagle's prey.
6Common mistakes Mistakes
7Quick check Quick check
Q1Which part of a cactus stores water?
Q2What keeps a polar bear warm?
Q3What is it called when swallows fly to warm lands in autumn?
Q4In the chain grass → rabbit → eagle, who is the producer?
Q5A snake eats a frog. Which is the prey?
8Recap Recap
- Four great environments: rainforest, grassland, polar regions and desert.
- Adaptations: cactus needles save water; polar bear fat keeps warmth.
- Migration and hibernation carry animals through hard seasons.
- A food chain starts with a producer; arrows point to the eater.
- Predator and prey depend on each other; competition sharpens every skill.