Stimuli and Response Flashcards
What is tropism?
The response of a plant to a directional stimulus.
How do plants respond to stimuli?
Using growth factors/hormones.
What are some examples of plant growth factors/hormones?
- Auxin.
- Gibberellins.
Where are plant growth factors made?
In growing regions of the plant (e.g. root tips and shoot tips).
How do plant growth factors move around the body?
- Move short distances by diffusion and active transport.
- Move long distances in the phloem.
What is phototropism?
- The effect of light on root tips and shoot tips (IAA moves to the shaded side of the roots/shoots).
- Shoots - IAA causes elongation so shoots grow towards light.
- Roots - IAA inhibits cell growth so roots grow away from light.
What is gravitropism/geotropism?
- The effect of gravity on root and shoot tips (IAA always moves to the underside).
- Shoots - Grow away from gravity.
- Roots - Grow towards gravity.
What is taxes?
Mobile organism moves towards or away from a directional stimulus.
What is kinesis?
Mobile organisms change their movement in response to a non-directional stimulus.
What are the stages of a reflex?
Stimulus - receptor - sensory neurone - relay neurone - motor neurone - effector - response.
What are the advantages of a reflex?
- Help organism avoid damage.
- Very fast.
- Doesn’t need to be learnt so can protect infants.
What happens when a pacinian corpuscle is stimulated?
- Pressure causes the lamellae to stretch and deform.
- Stretch mediated sodium ion channels open.
- NA+ diffuses into neurone.
- Greater the stimulus, the more Na+ channels open.
- Depolarisation of the neurone is called generator potential.
- If threshold is reached, then an action potential is initiated.
What are the two types of receptor cell in the human eye?
Rod cells and cone cells.
What are some features of Rod cells?
- Monochromatic - one pigment.
- More sensitive to low light.
- Low visual acuity.
- Many rod cells join a single bipolar cell.
- Mostly in peripheral part of the retina.
What are some features of cone cells?
- Trichromatic (red, green and blue).
- Colour vision.
- Less sensitive to low light.
- Higher visual acuity.
- Each cone cell has its own bipolar cell.
What is the role of the sinoatrial node (SAN)?
Initiates heart beat.
What is the role of the atrioventricular node (AVN)?
Delays electrical impulse so allows atria to contract before ventricles contract.
When do the semilunar valves open?
When the blood pressure is greater in the ventricles then the blood vessels.
When do the atrioventricular valves open?
When blood pressure is higher in the atria than ventricles.
What is the role of the purkyne fibres?
Allows the electrical impulse to cause the ventricles to contract from the base upwards.
Why does the heart contain non-conducting tissue?
It stops the electrical impulse from SAN reaching ventricles.
What happens if we have high blood O2, low blood CO2, high pH or high blood pressure?
- Chemoreceptors or baroreceptors detect it.
- Receptors send nerve impulses to the medulla oblongata in the brain.
- Medulla oblongata sends nerve impulses along parasympathetic neurones.
- Parasympathetic neurones secrete acetylcholine (neurotransmitter).
- Heart rate slows down.
What happens if we have low blood O2, high blood CO2, low pH or low blood pressure?
- Chemoreceptors or baroreceptors detect it.
- Receptors send nerve impulses to the medulla oblongata.
- Medulla oblongata sends more impulses along sympathetic neurones.
- Sympathetic neurones secrete noradrenaline (neurotransmitter).
- Heart rate speeds up.
How is heart rate controlled?
- SAN initiates the heart beat.
- Sends an electrical impulse across the atria.
- Atria contract
- Non-conductive tissue prevents the electrical impulse reaching the ventricles.
- AVN delays electrical impulse.
- Allows the atria to contract and empty before the ventricles contract.
- AVN sends the electrical impulse down the bundle of His and along the Purkyne tissue.
- Ventricles contract from the base upwards.
Why does the left ventricle have the most cardiac muscle?
It pumps blood to the whole body.
