الأسبوع 5 · المحور الأول، الوحدة الأولى، المفهوم 1.2 «كيف تعمل الحواس؟» (ب): زمن الاستجابة والجهاز العصبي · 3 دروس
1
Quick like a jerboa
Discovery Education Science P4: Term 1, Unit 1, pp. 47–57
GoalDescribe the three steps from sensing to reacting, using the Egyptian jerboa.
New words
jerboa · a small desert animal with big ears and long back legs that jumpsreact · to do something because of a message from the sensesmuscle · a body part that gets shorter to make a part of the body move
Explanation
The Egyptian jerboa is a small animal of sandy deserts in Egypt. It has very large ears, long back legs and a long tail. It comes out at night, and an owl or a fox may be hunting it. When the jerboa hears the soft sound of wings, three things happen very fast. First, the ears sense the sound. Second, a message travels along a nerve to the brain, which works out that the sound means danger. Third, the brain sends a message to the muscles of the back legs, and the jerboa leaps away. Its jumps go in zig-zags, which makes it hard for a hunter to follow. Every time an animal or a person reacts, the same three steps happen: sense, think, move.
1 Sense: ears hear the wings→2 Think: brain says danger→3 Move: leg muscles jump
Worked examples
Marwan is the goalkeeper. His eyes see the ball coming, his brain decides where it will go, and his hands move to catch it. Sense, think, move.
A loud bang in the street makes Jana turn her head. Her ears sensed it, her brain understood it, and her neck muscles turned her head.
The jerboa leaps left, then right, then left again, so the owl cannot guess where it will land. The zig-zag is a behavioural adaptation.
Class activity
Owl and jerboa game. On a soft carpet or grass, with a grown-up as the owl. The grown-up whispers, then suddenly claps once. Every jerboa listens, then hops two small steps to the side. Whose body reacted first? Which senses did you use? Play three rounds and talk about the three steps: sense, think, move. Stay away from hard furniture and corners.
Practice
1
Which sense organ does the jerboa use to find out an owl is near?
Its ears.
2
Put the steps in order: leg muscles jump, ears hear a sound, brain says danger.
Ears hear a sound, brain says danger, leg muscles jump.
3
Why are zig-zag jumps useful to the jerboa?
The hunter cannot guess where it will land.
4
In the picture, which step is “think”? Say the picture.
