Responding To Changes In Environment Flashcards
(30 cards)
What is a stimulus?
A detectable change in the environment.
What detects a stimulus?
Cells called receptors.
What comprises the central nervous system?
The brain and spinal cord.
What comprises the peripheral nervous system?
Receptors, sensory and motor neurones.
What is the pathway of a simple reflex?
Stimulus → receptor → sensory neurone → coordinator (CNS / relay neurone) → motor neurone → effector (muscle) → response (contraction).
What characterizes a simple reflex?
It is rapid and follows a short pathway.
How many neurones are involved in a simple reflex?
Only three neurones and few synapses.
Is conscious thought involved in simple reflexes?
No, conscious thought is not involved; coordination occurs in the spinal cord.
What is the importance of simple reflexes?
They protect from harmful stimuli, e.g., burning.
What is tropism?
Response of plants to stimuli via growth.
What are the two types of tropism?
Positive (growing towards stimulus) and negative (growing away from stimulus).
What controls tropism in plants?
Specific growth factors, such as Indoleacetic acid (IAA).
What is phototropism?
Response of plants to light.
What is gravitropism?
Response of plants to gravity.
What is hydrotropism?
Response of plants to water.
What is Indoleacetic acid (IAA)?
Type of auxin (plant hormone) that controls cell elongation in shoots and inhibits growth of cells in roots.
Where is IAA produced?
Made in tips of roots and shoots.
How does IAA affect shoots?
IAA diffuses to other cells and accumulates on the shaded side of the shoot, stimulating cell elongation.
What is positive phototropism?
When the plant bends towards light due to IAA accumulation on the shaded side.
What is phototropism in roots?
Root tip produces IAA. IAA concentration increases on lower (darker) side. IAA inhibits cell elongation, causing root cells to grow on the lighter side, resulting in the root bending away from light.
This is an example of negative phototropism.
What is gravitropism in shoots?
Shoot tip produces IAA, which diffuses from the upper side to the lower side of the shoot in response to gravity. IAA stimulates cell elongation, allowing the plant to grow upwards.
This is an example of negative gravitropism.
What is gravitropism in roots?
Root tip produces IAA, which accumulates on the lower side of the root in response to gravity. IAA inhibits cell elongation, causing the root to bend down towards gravity and anchor the plant.
This is an example of positive gravitropism.
What is taxis?
Directional response by simple mobile organisms, moving towards favourable stimuli (positive taxis) or away from unfavourable stimuli (negative taxis).
What is gravitropism in shoots?
Shoot tip produces IAA, which diffuses from the upper side to the lower side of the shoot in response to gravity. IAA stimulates cell elongation, allowing the plant to grow upwards.
This is an example of negative gravitropism.
