M6 - Plant Tropisms and the NS Flashcards
What is Tropism? (positive and negative?)
The DIRECTIONAL GROWTH of part of a plant in response to a directional stimulus.
Positive (towards stimulus)
negative (away from stimulus)
What is the tropism response of shoots and roots to:
- light
- gravity
- water
- survival benefits
SHOOTS
- positive phototropism
- negative gravitropism
- negative hydrotropism
Shoots group upwards and towards light for maximum photosynthesis.
ROOTS are the opposite to shoots.
They grow downwards towards water to increase absorption of water and mineral ions from the soil.
Why are plant growth factors different to hormones?
- They only affect growth
- Made by many different cells - not just a specific group
- May affect the cells they are produced in, rather than other target cells
How is Tropisms controlled by IAA?
IAA is an example of a…
it belongs to a group called _____.
It is responsible for _____ __________ and can control __________ and ________ in flowering plants.
It has the _______ effect in roots and shoots at certain ___________.
- Plant growth factor
- Auxins
- Cell elongation
- Phototropism
- Gravitropism
- Opposite
- concentrations
What happends to roots and shoots at different concentrations of IAA?
High concentrations of IAA (10ppm) inhibits root growth but stimulates shoot growth. However at 100 ppm, IAA inhibits shoot growth.
Describe the phototropic response of shoots (standard answer). What happens in roots?
- Cells in tip of shoot produce IAA, which is then transported down the shoot.
- The IAA is transported evenly throughout all regions as it moves down shoot.
- Light causes IAA to move from light to shaded side of shoot.
- A greater conc of IAA builds up on the shaded side of the shoot.
- As IAA causes elongation of shoot cells, shoot cells on the shaded side elongate more causing the tip to bend towards the light.
High IAA conc in roots inhibits cell elongation causing a negative phototropic response.
Describe the gravitropic response of roots. What happens to shoots?
- Cells in the tip of the root produce IAA, which is then transported along the root.
- IAA is initially transported evenly throughout the root.
- Gravity influences IAA movement from the upper to lower side of the root.
- Greater conc builds up on the lower side of the root.
- As IAA inhibits elongation of root cells, cells on lower side elongate less causing the root to bend downwards towards the force of gravity.
High IAA conc in shoots stimulates cell elongation causing negative gravitropic response.
What are innate behaviours?
A behaviour that allows animals to respond suitably to a stimulus without delay and without prior experience of the stimulus. They are controlled by genes and ensure success in the natural environment.
What is Kinesis?
The RANDOM movement of an animal in which the rate of movement is related to intensity of stimulus, but not its direction.
e.g. temperature, humidity
Organisms often move around a lot but turn less frequently.
What is taxis?
Movement where direction is determined by direction of stimulus. Movement is either positive or negative - towards or away from stimulus.
e.g. light (things that are immediately visable)
What are Kinesis and taxis related to? What is tropism related to?
Tropism = plants
Kinesis and Taxis = animals
Give examples of things controlled by the autonomic nervous system.
EFFECTORS - Glands, smooth muscle (e.g. gut and blood vessels) and cardiac muscle.
What are the 3 types of muscle?
Smooth, cardiac and skeletal
What is a reflex action? Why do we have them?
A fast, involuntary response to a stimulus.
They are automatic so…
- prevent injury
- posture/balance
- role in homeostasis
Describe the reflex arc.
STIMULUS (e.g. heat form hot object).
RECEPTOR responds to stimulus by generating impulses in the sensory neuron.
SENSORY NEURON passes nerve impulse to the spinal cord.
COORDINATOR - relay/intermediate neuron links the SN to the motor neuron in spinal chord.
MOTOR NEURON carries nerve impulse from spinal cord to an effector (e.g. muscle in upper arm).
EFFECTOR - muscle in upper arm contracts.
RESPONSE - Pulling hand away from the hot object.
Receptor cells respond to a stimulus by intitating a nerve ______. Each receptor responds to a different specific _______ of stimulus.
They may be single cells or _____ in sense organs e.g. eye.
Receptors act as _________ and convert the ______ from the stimulus (e.g. light) into the ________ energy of a nerve impulse.
impulse
type
group
transducers
energy
electrical
Name the pressure receptor you need to know. Describe it.
Pacinian Corpuscle:
- located in dermis of the skin
- sensory neuron that has a non-myelinated ending located inside a capsule formed from several layers of connective tissue
How does the Pacinian Corpuscle stimulate a nerve impulse?
Pacinian Corpusle has stretch mediated Na+ channels that are too narrow for Na+ to pass through in its resting state.
When pressure is applied the capsule deforms and Na+ channels are stretched and open, allowing Na+ ions to enter the cell. This depolarises the membrane (receptor potential).
If local depolarisation reaches threshold a generator potential is generated which then triggers action potentials by opening voltage-gated Na+ channels.
What is the intensity of a stimulus indicated by?
The frequency of action potentials.
APs are produced for as long as the receptor potential is above threshold. Greater pressure applied, the longer it is above threshold.
What is the all or nothing principle?
The idea that an action potential is either present or it isn’t. There aren’t different intensities of action potential.
What is adaptation in terms of receptor?
When a stimulus is first applied, increasing the stimulus increases the frequency of action potentials.
If stimulus continues, the receptor will become adapted and the frequency of action potentials will fall.
This helps to avoid over-stimulation.
