Programme 15: Responding to Stimuli

Answers to Activity Sheet 1

Programme Questions

The Eye

1. The lens of the eye is flexible because it is made of jelly. Its shape is changed to focus an image.
2. Your brain makes sense of the information received through the optic nerve. It takes account of the fact that the image on your retina is upside down.
3. Fat.
4. When a bright light shines on your eye the iris constricts so that the pupil gets smaller. Less light falls on the retina so that light sensitive cells are not damaged.
5. This is the part of the retina where nerve fibres come together and pass through the sclera. There are no light-sensitive cells in this part of the retina.

The Nervous System

1. The brain and spinal cord make up the central nervous system. It coordinates our responses to stimuli.
2. Stimulus, receptor (sensory organs), sensory nerve, relay nerve (in central nervous system), motor nerve, effector (usually a muscle), response.
3. Electricity.

Plant Tropisms

1. Tropism is a growth response. It cannot be repeated in the way that the movement of an arm can be.
2. The root and shoot respond in different ways to gravity. The root will always grow down and the shoot will always grow upwards.