Answers to processes revision questions (note)

Answer Key

Multiple Choice 1. c) 2. b) 3. d) 4. a) 5. d)

Short Answer

1. Positive feedback is a change in a physiological variable that is being monitored triggers a response that counteracts the initial fluctuation.
Example: when blood is concentrated neurons in the hypothalamus send signals to the hypothalamic neurosecrtory cells which release ADH. ADH increases the permeability of the collecting ducts in the kidneys so the more water is reabsorbed. Once the blood is diluted, ADH is no longer secreted.

2. Protein hormones activate existing enzymes in the cell, and steroid hormones bring about the synthesis of new proteins. (diagram of cellular activity of protein and steroid hormones also required).

3. Danger (stimulus)
seen by the eye (sensor)
message sent to the brain (control centre)
signals muscles (effector)
to run (response)

4. Insert diagram explaining the contrary actions of insulin and glucagon. The pancreas secretes insulin (which acts to promote storage of nutrients, thereby lowering the blood glucose level) and glucagon (which stimulates the breakdown of stored nutrients, thereby increasing the blood glucose level). In diabetes mellitus, either insulin is not produced or it cannot be utilized; the excess glucose in the blood is excreted by the kidneys

5. The nervous system receives information and processes it before sending out signals to the muscles and gland so an appropriate response is possible. The endocrine system coordinates biological processes with hormonal components that are secreted in the bloodstream. The endocrine system and nervous system interact and are often inseparable.
a. They are structurally related: many endocrine glands are either made of nerve tissue or have evolved from the nervous system.
b. They are chemically related: hormones are used as signals by both systems.
c. They are functionally related: may coordinate biological processes with both nervous and hormonal components arranged in series, or one system can affect the output of the other.

6. Insert diagram of a neuron. Dendrites convey signals to the cell body, and are short, numerous and extensively branched to increase surface area where cell is most likely to be stimulated. Axons axon conduct impulses away from the cell body and is wrapped in concentric layers of Schwann cells which form an insulating myelin sheath.

7. Cerebellum functions in muscle coordination.
Medulla functions to control the internal organs. Cerebrum is responsible for higher mental processes, including the interpretation of sensory input and the initiation of voluntary muscular movements.
Corpus callosum is the horizontal tract that connects the two cerebral hemispheres of the brain allowing them to share information.
Limbic system contains pathways that connect various portions of the brain and allows the experience of many emotions. Thalamus is concerned with sensory reception.

8. Homeostasis is the maintenance of internal conditions in cells or organisms. Example: A lizard basks in the sun to raise its internal temperature. However if the external temperature rises too high, the lizard will scurry for some shade an this will help maintain its normal internal temperature.

9. When a nerve impulse reaches the synaptic vesicle (neurotransmitters are stored here), they move toward and fuse with the presynaptic membrane, discharging their contents. The neurotransmitter substance diffuses across the synaptic cleft and combines with a receptor. Neurotransmitters are rapidly inactivated by enzymes in the cleft.

10. i) filtration of blood
ii) reabsorption of water
iii) secretion of waste

11. Endocrine glands are ductless; they secrete hormones directly into the blood stream for distribution throughout the body. Exocrine glands have ducts, and they secrete their products (i.e. saliva) into these ducts for transport into body cavities. Endocrine glands release hormones.