Survival and response Flashcards
(17 cards)
How do organisms increase their chance of survival?
Organisms increase their chance of survival by responding to changes in their environment called stimuli, which can be internal or external.
What are the 3 different key responses?
Tropisms, taxes & kineses, and simple reflexes.
What are tropisms?
A tropism is a growth response of a plant to a directional stimulus controlled by growth factors (hormone-like compounds).
Where are growth factors produced?
Growth factors are produced in growing regions (shoot tips) and move to other tissues, where they regulate growth in response to directional stimuli.
What are the main growth factors?
Auxins are the main growth factors. The most abundant is Indoleacetic Acid (IAA).
What does Indoleacetic Acid (IAA) do?
In shoots, IAA causes cell elongation. In roots, it inhibits cell elongation.
What is the process of phototropism?
1) Light is detected by receptors in the shoot
2) IAA diffuses to the darker side
3) IAA increases on this side
4) IAA causes cells on the darker side to elongate so the shoot bends towards the light
This is positive phototropism.
What is the process of phototropism in roots?
In roots, IAA does the opposite: IAA diffuses to the darker side, and inhibits cell elongation here causing the root to bend downwards. This is negative phototropism.
What is the process of gravitropism?
1) IAA diffuses to the lower side of the shoot
2) IAA increases on the lower side
3) IAA causes cells on this side to elongate causing the shoot to bend upwards.
This is negative gravitropism.
What is the process of gravitropism in roots?
In roots, IAA does the opposite: IAA diffuses to the lower side, and inhibits cell elongation here causing the root to bend downwards. This is positive gravitropism.
What are taxes and kineses?
Taxes and kineses are simple responses that maintain a mobile organism in a favourable environment.
What happens in a taxis?
In a taxis, an organism moves towards a directional stimulus, response can be positive or negative.
What happens in a kinesis?
In a kinesis, the organism’s movement is affected by a non-directional stimulus (e.g. humidity).
Which neurons are involved in simple reflexes?
Sensory, relay, motor neurons.
What is the process of a simple reflex?
1) The receptor detects a stimulus (change in environment).
2) The sensory neuron carries the impulse from the receptor to the relay neuron.
3) The relay neuron carries the impulse directly from the sensory to the motor neuron.
4) The motor neuron carries the impulse from the relay neuron to an effector.
5) The effector carries out a response. This may be a muscle (contracts) or a gland (secretes hormones).
What is the importance of reflex arcs?
Due to reflex arcs, responses are fast as they do not involve conscious parts of the brain, localised as the neurotransmitters are secreted directly onto target cells and a particular stimulus always produces the same response, and short-lived as the re-uptake of neutrotransmitters is rapid.
How do simple reflexes help aid survival?
They help protect the body from tissue damage and to escape from predators. The response is involuntary, you cannot consciously override it.
