GoalReview senses, the nervous system, light and sight, and signals and codes.
New words
receptor · a tiny part of a sense organ that reacts to something and starts a messagereflect · to bounce off a surfacesignal · a light, sound or movement that sends information
Explanation
Unit 1 also taught how we sense the world. Sense organs collect information. Receptors start a message that travels along nerves to the brain, and the brain decides what to do. A reflex is a very fast reaction that does not wait for a decision. Reaction time is how long it takes to respond to a signal, and we can measure it with a metre stick. Light travels in straight lines. We see a light source when its light enters the eye, and we see other things when light from a source bounces off them into the eye. Shiny things reflect a lot of light; dark, rough things absorb it. Transparent things let light through, opaque things do not. Animals and people send signals with light, sound and movement. Bats and dolphins use echoes, and bees dance to show the way to flowers. A code is a set of signals that people agree on.
receptor in the sense organ→nerve carries the message→brain decides→muscles move
Worked examples
Ali catches a metre stick after it falls 10 cm. Marwan catches it after 25 cm. Ali caught it sooner, so Ali’s reaction time is shorter. Their results are only one try each, so we cannot say who is better in general.
A torch shines on a mirror and the light bounces to the eye. The mirror reflects it. Light travels in straight lines, so the eye sees the torch’s light only if the bounced light goes into the eye.
Nour and her brother make a code: one flash of a torch means “yes”, two flashes mean “no”. They send three messages across the room. Two arrive correctly out of three.
Class activity
Mystery message. With a friend, agree on a code of four signals (for example, clap, stamp, wave, whistle with your mouth) and write it on a card. One of you sends a message of five signals from across the room; the other writes down what they understood. Count how many were right. Improve the code and try again.
Practice
1
A message goes from a sense organ to the brain. Along which parts of the body does it travel?
Along the nerves (and the spinal cord).
2
Which is transparent and which is opaque? Say the letters for the transparent one.
A, the glass, is transparent. The brick is opaque.
3
A metre stick falls 20 cm before it is caught and 10 cm another time. Which catch was quicker?
The 10 cm catch, because the stick fell less far.
4
How does a bat find a moth in the dark?
It makes high sounds, and listens for the echoes that bounce back.
