Week 4 · Theme 1 Systems, Unit 1 Interactions of Organisms, Concept 1.2 Energy Flow in Ecosystems (B) · 3 lessons
2
Chains with arrows
Discovery Education Science P5: Term 1, Unit 1, pp. 54–56
GoalDraw a food chain with arrows from food to eater, and name predators and prey.
New words
predator · an animal that hunts and eats other animalsprey · an animal that is hunted and eaten by anotherenergy flow · the way energy moves from one living thing to the next
Explanation
A food chain shows who eats whom. We draw an arrow from the food to the animal that eats it, because the arrow shows the way energy moves. In the chain grass, mouse, snake, eagle, the grass gives energy to the mouse, the mouse to the snake and the snake to the eagle. The snake and the eagle are predators because they hunt other animals. The mouse and the snake are prey because they are hunted. An animal can be both: the snake is a predator of the mouse and the prey of the eagle. At each link some energy is lost as heat, which is why chains are rarely longer than four or five links.
Worked examples
In a quiet bend of the Nile, small water plants feed small fish, and a crocodile eats the fish. The arrows point from food to eater.
Karim draws the arrow from the hare to the grass. This is wrong. Energy goes from the grass to the hare, so the arrow must point to the hare.
A beetle eats grass and a bird eats the beetle. The new chain has three links: grass, beetle, bird.
Class activity
Chain cards. Write five cards: grass, cricket, lizard, snake, falcon. Lay them in a line to make a chain and draw arrows from food to eater. Say which are predators and which are prey. Then add a new card, a mouse that eats grass, and make a second chain that starts with the same grass.
Practice
1
In grass, hare, fox, which way do the arrows point and what do they show?
From the food to the eater (grass to hare to fox). They show the way energy moves.
2
Fill the empty box: grass, ?, lizard. Name an insect that eats grass.
A cricket (or a grasshopper or a beetle).
3
In grass, mouse, snake, eagle, name two predators and two prey animals.
Predators: snake and eagle. Prey: mouse and snake.
4
Which animal in that chain is both a predator and prey?
The snake: it hunts the mouse and is hunted by the eagle.
