TOPIC 6A - Stimuli and Responses Flashcards
What is a stimulus?
A change in an organisms internal /external environment
How do animals/plants increase their chances of survival?
By responding to external stimuli: e.g. avoiding harmful places that are too hot/cold
And
Internal stimuli: ensuring that the conditions are always optimal for their metabolism (chemical reasons that go on inside of them)
What are receptors?
They are cells or proteins on cell surface membranes that detect different stimuli (different types of receptors detect different stimuli)
What are effectors?
They are cells that bring about a response to a stimulus, to produce an effect.
- they include muscle cells and cells found in glands
How do receptors communicate with effectors?
Via the nervous system or the hormonal system, or sometimes even both
What do are the jobs of the 3 different types of neurones?
- Sensory: transmits electrical impulses from receptors to the CNS
- Motor neurones: transmits electrical impulses from CNS to effectors
- Relay: transmits electrical impulses between sensory neurones and motor neurones
What happens when an electrical impulse reaches the end of a neurone?
Chemicals called neurotransmitters take the info across to the next neurone, which then sends the electrical impulse.
Name the 2 types of nervous system?
- Central nervous system (CNS)
2. Peripheral nervous system (PNS)
Draw a break down of the PNS
PNS
I
Somatic««<»»»Autonomic
I
Sympathetic«»parasympathetic
What does the CNS do?
The CNS processes the information on how to respond to a stimulus
What is a reflex?
A reflex is where the body responds to a stimulus without having to make a conscious decision to respond.
How do simple reflexes help organisms?
As we don’t have to spend time deciding how to respond, information travels really fast down reflex arc.
- This can prevent us from severaly injuring ourselves
What can override a reflex? (give example)
If there’s a relay neurone involved in the simple reflex arc, it’s possible to override the reflex, E.g when you touch something hot, your brain could tell your hand to withstand the heat (due to relay neurone involvement)
Outline 3 words to describe nervous system communication.
- Localised: when electrical impulse reaches the end of a neutron, neurotransmitters are secreted directly onto target cells - so nervous response is localised
- Short-lived: neurotransmitters quickly removed once they do their job
- Rapid
Give 3 adaptations/properties that helps plants respond to stimuli e.g low light availability and gravity
Low light availability:
- They can sense light direction and grow towards it to maximise light absorption for photosynthesis
- Climbing plants have a sense of touch, so they can find things to climb up and reach the sunlight
Gravity:
1. They can sense gravity, so roots/shoots grow in right direction
Define these key words
- Tropism
- Positive tropism
- Negative tropism
- Tropism: response of plant to a directional stimulus (stimulus from certain direction)
- Positive tropism: growth towards stimulus
- Negative tropism: growth away from stimulus
Define phototropism. (include shoots and roots in your answer)
Phototropism: the growth of a plant in response to light
- Shoots: positively phototrophic and grow towards light
- roots: negatively phototrophic and grow away from light
Define gravitropism. (include shoots and roots in your answer)
Gravitropism: the growth of plants in response to gravity
- Shoots: negatively gravitrophic and grow upwards
- roots: positively phototrophic and grow downwards
Define growth factors and state where they’re produced.
They are hormone like-chemicals like speed up/slow down plant growth, helping plants respond to directional stimuli.
- they are produced in growing regions of the plant (E.g. Shoots, leaves) and they move to where they needed in other parts of the plant.
What are auxins?
They are growth factors that stimulate the growth of shoots by cell elongation - this is where the cell walls become loose and stretchy, so the cells get longer.
Fill in this gap in this sentence: “high conc of auxins ……. growth in roots”
Inhibit
What is indoleacetic acid (IAA)?
IAA is an auxin that’s produced in the tips of shoots in flowering plants.
It moves around the plant to control tropisms via diffusion and active transport for short distances or via the phloem for long distances.
- This results in different parts of the plant having an uneven distribution of IAA, and therefore, there’s uneven growth of the plant.
How does IAA react in shoots and roots during phototropism?
PHOTOTROPISM
- shoots: IAA conc increases on more shaded side, so cells elongate and shoot bends towards light ASK: do we assume that the shoot is shooting straight up initially
- roots: IAA conc increases on shaded side, growth is inhibited, so root bends away from light
How does IAA react in shoots and roots during gravitropism?
GRAVITROPISM
- shoots: IAA conc increases on lower side so cells elongate so shoot grows upwards
- roots: IAA conc increases on lower side so growth is inhibited and root grows downwards