9.3, 9.4 Chemical control in plants

Question 1

what stimuli do plants respond to

Answer 1

• light
• gravity
• water
• temperature

Question 2

how does light affect plants

Answer 2

• 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

Question 3

define growth and how is it brought about

Answer 3

• a permanent increase in the size of an organism or some part of it
• it is brought about by cell division

Question 4

wat are meristems and where are they found

Answer 4

• 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

Question 5

what are auxins

Answer 5

• 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

Question 6

define tropism

Answer 6

directional plant responses

Question 7

give an example of an auxin

Answer 7

indoleacetic acid (IAA)

Question 8

what are the phototropic effects of IAA

Answer 8

• 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

Question 9

what are the geotropic effects of IAA

Answer 9

• 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

Question 10

how does IAA promote cell elongation

Answer 10

• 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

Question 11

what are the functions of auxins

Answer 11

• 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

Question 12

what is the difference between the effect of auxins (IAA) in the roots and in the shoots

Answer 12

• it promotes growth and cell elongation in the shoots
• it suppresses growth and cell elongation in the roots

Question 13

state to plant hormones (excluding auxin) and their functions

Answer 13

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

Question 14

define photomorphogenesis

Answer 14

• The process by which plant development is controlled by the levels and type of light

Question 15

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

Answer 15

• 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

Question 16

what are phytochromes

Answer 16

• 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

Question 17

how are the two forms of phytochromes linked

Answer 17

• 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

Question 18

define photomorphogenesis

Answer 18

the effect of light on the growth and development

Question 19

describe process of germination in regards to photomorphogenesis

Answer 19

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

Question 20

whats the basic structure of the nervous system

Answer 20

neurones carry impulses from receptor cells to specialised effector cells which are muscles and glands to bring about the appropriate response

Question 21

what nervous systems do mammals have and what do each contain

Answer 21

• 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

Question 22

what is the structure of the spinal chord

Answer 22

• 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

Question 23

what is the function of the following:
- medulla oblongata
- cerebellum
- cerebrum
- hypothalamus

Answer 23

1. contains reflex centres that control breathing rate, heart rate, blood pressure, coughing, sneezing swallowing saliva, peristalsis (intestinal contraction)
2. uses information from the muscles and ears to control balance and remain posture
3. controls voluntary behaviour, including movement
4. 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)

Question 24

what is the peripheral nervous system divided into and what are they

Answer 24

• 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

Question 25

what can the autonomic nervous system be divided into

Answer 25

• sympathetic and parasympathetic nervous system

Question 26

whats the structural difference between the sympathetic and the parasympathetic nervous system

Answer 26

• 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

Question 27

what are the functional differences between the parasympathetic and the sympathetic nervous system

Answer 27

• 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

Question 28

how and why do the sympathetic and parasympathetic nervous systems act antagonistically

Answer 28

• 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