Stimulus, response and reflexes
Touch a millipede and it curls into a tight ring. The touch is a stimulus; curling up is the response. Every living thing detects changes around it and responds, and that is how it stays alive.
By the end of this page you can
- Describe how plants and small animals respond to their surroundings, and why
- Name receptors and effectors in the human body
- Put the steps of a reflex arc in order
- Define stimulus, response, receptor and effector
- Answer exam questions on responses and reflexes
Goals tick themselves off as you try the activities below.
Photo: Wilfredor, CC0, via Wikimedia Commons. Cropped, JPEG q72.
A young bumblebee millipede, common across the Caribbean, curled up after being disturbed. Curling protects its soft underside.
How often it shows up in past papers
Paper 1 counts come from our past-paper bank of CSEC Biology Paper 1s. Paper 2 is not included yet.
Responding keeps them alive
A plant cannot walk away, but it can grow in the direction it needs. Small animals move towards the conditions they need. Tap each card.
Receptors detect, effectors respond
A receptor detects a stimulus. An effector, a muscle or a gland, carries out the response. Tap each one.
Receptor or effector?
Tap a part on the list to see what it detects or does.
Plants have receptors and effectors too: a shoot tip detects light, and the region behind it grows to bend the shoot.
The reflex arc, step by step
You touch a hot pot and jerk away before you feel pain. Drag or tap each card into its slot.
What starts the reflex?
Seven terms to know cold
Say what each term means before you flip the card. The definitions of stimulus and response are asked word for word.
Six quick questions, then a real one
Pick an answer to see why it’s right or wrong.
A detectable change in an organism’s environment is called a
The smell of food cooking makes a girl’s mouth water. Which structure is the effector?
A student touches a hot pan. Which structure is the receptor?
Which order is correct for a nervous response?
Woodlice gather under damp logs. This response helps them to
Why is a reflex action useful?
exam style · 3 marks
A girl touches a hot pot and pulls her hand away before she feels pain. Explain how this reflex takes place.
Sign in to have your answer marked, or check it against the mark scheme. Sign in
Practice questions are written by My V.I.P. Academy. They are not official CXC papers.