Control and co-ordination

All the activities  of multicellular organisms require  co-ordinating, some very rapidly and some more slowly. The nervous system and the endocrine system provide co-ordination in mammals. Similar co-ordination systems exist in plants.

Candidates will be expected to use  the knowledge gained  in this section to solve problems in familiar and unfamiliar contexts.

Learning outcomes

Candidates should  be able to:

15.1  Control and co-ordination in mammals

The nervous system provides fast communication between receptors and effectors.
Transmission between neurones takes place at synapses.

a)   compare the nervous and endocrine systems as communication systems that  co-ordinate responses to changes in the internal and external environment (see  14.1a and 14.1b)

b)   describe the structure of a sensory neurone and a motor neurone

c)   outline  the roles of sensory receptor cells in detecting stimuli and stimulating the transmission of nerve  impulses in sensory neurones (a suitable example is the chemoreceptor cell found in human taste buds)

d)   describe the functions of sensory, relay and motor  neurones in a reflex arc

e)   describe and explain the transmission of an action potential in a myelinated neurone and its initiation from a resting potential (the importance of sodium and potassium ions in impulse transmission should  be emphasised)

f) explain the importance of the myelin sheath (saltatory conduction) in determining the speed of nerve  impulses and the refractory period in determining their frequency

g)   describe the structure of a cholinergic  synapse and explain how it functions, including the role of calcium  ions

h)   outline  the roles of synapses in the nervous system in allowing transmission in one direction  and in allowing connections between one neurone and many  others (summation, facilitation and inhibitory synapses are not required)

i) describe the roles of neuromuscular junctions, transverse system tubules and sarcoplasmic reticulum in stimulating contraction in striated muscle

j) describe the ultrastructure of striated muscle with particular reference to sarcomere structure

k)   explain the sliding filament  model  of muscular contraction including the roles of troponin,  tropomyosin, calcium  ions and ATP.

The endocrine system is a slower system that  controls long-term changes. Fertility may be controlled by use  of hormones.

l) explain the roles of the hormones FSH, LH, oestrogen and progesterone in controlling changes in the ovary and uterus during the human menstrual cycle

m)  outline  the biological basis  of contraceptive pills containing oestrogen and/or progesterone

15.2  Control and co-ordination in plants

Plant co-ordination systems involve rapid responses as in the case of the Venus fly trap, but also complex interactions between plant growth regulators, such  as auxin and gibberellin.

Plants  respond quite differently to different concentrations of plant growth regulators.

a)   describe the rapid response of the Venus fly trap to stimulation of hairs on the lobes  of modified  leaves and explain how the closure of the trap is achieved

b)   explain the role of auxin in elongation growth by stimulating proton  pumping to acidify cell walls

c)   describe the role of gibberellin in the germination of wheat or barley

d)   explain the role of gibberellin in stem elongation including the role of the dominant allele, Le, that  codes for a functioning enzyme in the gibberellin synthesis pathway, and the recessive allele, le, that  codes for a non-functional enzyme.