SPM Form 4 Biology Test cover chapter 1, 2 and 3.Full description
Chapter 3 ( Coordination and Response )
Organism respond to both external and internal stimuli to adapt to charges in the external environment and for survival. The process that involves the reception of stimuli by the receptors, the intergration of that information and the subsequent responses of the organism is called coordination. The coordination process starts with the receptors receiving the stimulus and ends with the effectors producing a respone towards the stimulus. Coordination in humans involves the nervous system and the endocrine system. The nervous system consists of the central nervous system and the peripheral nervous system: a) The central nervious system is made up of the brain and the spinal cord. b) The peripheral nervous system is mode up of the cranial nerves and the spinal verves. Figures
1 and Figures show the components and organisation of the nervous system
The basic unit of the vervous system is the nerve cells called neurones. There are three types of neurones: a) afferent neurone which carries nerve impulses from the receptor to central nervous system. b) efferent neurone which carries nerve impulses from the central nervous system to the efferent neurone. c) interneurone which links the afferent neurone to the efferent neurone. Synapse is a narrow gap between two neurones in contact. Reflex action is an automatic response which does not involve the brain.
The pathway of nerve impulses from receptor to effector to produce a reflex action is called the reflex arc. In a raflex action, the receptor detects the stimulus that are transmitted by the afferent neurone to the spinal cord across a synapse, which are then transmitted by the efferent neurone to the effector to produce an autonomic response. Nerve impulses are transmitted by the neurone in the form of electric signals but are then tranmitted across a synapse in the form of chemical signals by neurotransmitters. xamples E
of reflex actions are knee jerk and withdrawal from a hot object.
Coordination ny hormones involves the endocrine system The endocrine system coordinates the physiological processes of the body through hormones.
The endocrine system consists of endocrine glands:
ndocrine E ndocrine
glands secrete hormones directly into the bloodstream.The hormones are then carried
bt the blood to the target organs, tissue and cells to produce a response. H omeostasis omeostasis
is the process of regulating the physical and chemical factors in the internal environment. It is inderpendent of unfavourable and fluctuating external conditions. xamples E
of processes regulated by homeostasis are : a) regulation of blood osmatic pressure
(by kidneys) b) regulation of blood sugar level (by liver and pancreas) c) regulation of body temperature (by skin)
omeostasis H omeostasis
occurs by negative feedback system. A deviation from the normal level is detected
and then the negative feedback mechanism is triggered to restore it to the normal level. The
kidneys are involved in regulating the water nalance in the blood or the blood osmotic pressure Hence, the kidneys funcion as the osmoregulation and excretory organs.
Coordination by the nervous system is affected it to the drugs and alcohol. Drugs and alcohol affect the functions of the transmitter and alter the transmission of nerve impulses. Tropism is a growth response of the shoot tips and root tips towards an external stimulus.The direction of the response depends on the direction of the stimulus. Tropism is controlled by the plant hormone called auxins. Auxins are produced in shoot tip which will diffuse away from the unilateral light into the shaded region of the elongation zone.A higher concentration of auxins in the shaded region of the shoot tip promotes cells elongation.
H ence, ence,
the shaded region grows faster and causes the shoot to
bend and grow towards the light,showing positive phototropism. Roots grow downwards towards the pull of gravity,showing positive geotropism. Auxins are used in agriculture to produce fruits from ovaries without fertilisation through the process called parthenocarpy. thylene E thylene
is a plant hormone in the form of gas that is used in agriculture to stimulate the
