9.3, 9.4 Chemical control in plants Flashcards
what stimuli do plants respond to
- light
- gravity
- water
- temperature
how does light affect plants
- plants respond to the intensity of light, the presence or absence of it and the direction from which it comes from
- it affects how much they grow, the direction of their growth and when they reproduce
define growth and how is it brought about
- a permanent increase in the size of an organism or some part of it
- it is brought about by cell division
wat are meristems and where are they found
- they are the main areas of cell division in a plant
- they occur just behind the tip of the root or the shoot
- they are particularly sensitive to plant growth substances
what are auxins
- powerful growth stimulants that are very effective in low concentrations
- responsible for controlling plant phototropic and geotropic responses by regulating cell elongation
- produces in the tip of the shoot and diffuses freely down the shoot
define tropism
directional plant responses
give an example of an auxin
indoleacetic acid (IAA)
what are the phototropic effects of IAA
- positive phototropism in shoots, causes them to grow towards the sunlight
- negative phototropism in roots, causes them to grow away from the sunlight
- causes cell elongation in both cases
what are the geotropic effects of IAA
- negative geotropism in the shoots, causing the shoot to grow away from the direction of gravity
- positive geotropic effects in the roots, causing the roots to grow in the direction of gravity
how does IAA promote cell elongation
- IAA binds to specific receptor sites on the cell surface membrane
- this activates the active pumping of hydrogen ions into the cell wall spaces
- this decreasing the pH to the optimum of 5 for enzymes that break bonds between cellulose microfibrils, allowing them to slide past each other easily keeping them plastic and flexible
- the cells the absorb water and stretch as a result of turgor pressure
what are the functions of auxins
- they are involved in trophic responses
- they control cell elongation
- suppress lateral buds to maintain apical dominance
- promote root growth e.g. in rooting powders
what is the difference between the effect of auxins (IAA) in the roots and in the shoots
- it promotes growth and cell elongation in the shoots
- it suppresses growth and cell elongation in the roots
state to plant hormones (excluding auxin) and their functions
Gibberellins - stimulate elongation of growing cells, promote growth of fruit, they break dormancy seeds in germination (promote germination), stimulate amylase production, breaks down starch and makes glucose available for respiration
Cytokinins - promote cell division in apical meristems , promote development of lateral buds
define photomorphogenesis
- The process by which plant development is controlled by the levels and type of light
what will happen in a plant if it receives a flash of red light, then a flash of far red, then another flash of red
and WHY
- ity will germinate
- this is because far red light inhibits germination in seeds but red light causes germination in seeds
- and if you flash different types of light onto a seed consecutively, it is only the last flash of light that matters
what are phytochromes
- they are blue green pigments that exist in two forms
1. P660 (Pr) that absorbs red light
2. P730 (Pfr) that absorbs far red light
how are the two forms of phytochromes linked
- when one form the of pigments absorbs light, it is converted into the other form
- when a seedling germinates it makes Pr, and as soon as it breaks through the soil surface and is exposed to red light, some is converted into Pfr
- after that point they are both inconvertible
define photomorphogenesis
the effect of light on the growth and development
describe process of germination in regards to photomorphogenesis
when the plant is exposed to light Pr is converted into Pfr, levels of Pfr build up quickly and inhibits growth of internodes. Seedlings turn green and begin to photosynthesise and eventually break through the soil
whats the basic structure of the nervous system
neurones carry impulses from receptor cells to specialised effector cells which are muscles and glands to bring about the appropriate response
what nervous systems do mammals have and what do each contain
- central nervous system
composed of the brain and spinal cord, where incoming information from sensory neurones are processed and impulses are send out through motor neurones which carry impulses to effector organs - peripheral nervous system
includes nerves outside the brain and the spinal chord
what is the structure of the spinal chord
- made up of core grey matter (neurones) and surrounded by white matter (nerve fibres of neurones) that runs from base of brain (medulla oblongata) through vertebra
- impulses from sensory receptors travel travel along sensory fibres up the cord to brain
- instructions from brain travel down motor fibres in spinal cord and out in motor neurones
what is the function of the following:
- medulla oblongata
- cerebellum
- cerebrum
- hypothalamus
- contains reflex centres that control breathing rate, heart rate, blood pressure, coughing, sneezing swallowing saliva, peristalsis (intestinal contraction)
- uses information from the muscles and ears to control balance and remain posture
- controls voluntary behaviour, including movement
- coordinates autonomic nervous system, part of thermoregulation (core body temp), osmoregulation, monitors the chemistry of the blood and controls hormone secretions of the pituitary gland ( and thirst, hunger, aggression)
what is the peripheral nervous system divided into and what are they
- voluntary nervous system
involves motor neurones that function as a result of conscious thought, involving the cerebrum
e.g. picking up a drink, switching on a computer - autonomic nervous system
motor neurones that are under not under the control of conscious thought. e.g. heart and breathing rate, response to changing light levels
what can the autonomic nervous system be divided into
- sympathetic and parasympathetic nervous system
whats the structural difference between the sympathetic and the parasympathetic nervous system
- both leave CNS with myelinated pre ganglionic fibres, synapse a ganglion then have unmyelinated post ganglionic fibres
- in the parasympathetic nervous system ganglia are near to the effector organ, so pre-ganglionic fibres are long
- in the sympathetic nervous system the roles are reversed ad the ganglia are near to the CNS so pre ganglionic fibres are short and the post ganglionic fibres are long
what are the functional differences between the parasympathetic and the sympathetic nervous system
- sympathetic nervous system produces noradrenaline at the synapses, produces rapid response in target organ ‘fight or flight system’
- parasympathetic has inhibitory effect on organ systems and produces acetylcholine, maintains normal function and restores calm after a stressful situation
how and why do the sympathetic and parasympathetic nervous systems act antagonistically
- for example, the sympathetic nervous system will speed up the breathing rate and heart rate and parasympathetic will slow them down
- this allows the complementary systems to conduct control of the bodily responses and match them exactly to the demands laced upon it
