Control and Coordination

Living organisms constantly respond to changes in their surroundings, from pulling a hand away from a hot object to a plant bending towards light. In animals, this control and coordination is carried out by the nervous system and the endocrine (hormonal) system. In this chapter you will study the structure of a neuron, with its dendrites, cell body and axon, how information travels as electrical impulses and crosses a synapse as chemical signals, and how a reflex arc in the spinal cord produces quick, automatic responses. You will learn the parts of the human brain, the forebrain, midbrain and hindbrain (cerebellum, pons and medulla), their functions and their protection. Plants have no nervous system, yet they respond to stimuli. You will compare the immediate movement of the touch-me-not plant with slow growth movements called tropisms, controlled by plant hormones such as auxins, gibberellins, cytokinins and abscisic acid. Finally, you will study animal hormones such as thyroxin, insulin, adrenaline and growth hormone, and how feedback mechanisms regulate their secretion.

Detailed Worksheet: Control and Coordination Section A - Definitions (10 marks) 1. What is a reflex action? Give two examples. (2 marks) 2. Name the three main parts of a neuron and state the function of each. (2 marks) 3. What is a synapse? How is an impulse transmitted across it? (2 marks) 4. Define tropism. Name the tropisms shown in response to light, gravity, water and chemicals. (2 marks) 5. What are hormones? Name one plant hormone that promotes growth and one that inhibits growth. (2 marks) Section B - Calculations and Applications (15 marks) 6. In a ruler-drop test of reaction time, a ruler released between a student's fingers falls 20 cm before it is caught. Using d = (1/2) g t^2 with g = 10 m/s^2, calculate the reaction time. Why is a reflex action faster than such a voluntary response? (3 marks) 7. A nerve impulse travels at about 100 m/s along a nerve fibre. Calculate the time taken for an impulse to travel from a toe to the spinal cord, a distance of 1 m, and back to the leg muscle, a further 1 m. Why must reflex arcs be located in the spinal cord rather than the brain for such responses? (3 marks) 8. A student records the angle by which a potted seedling bends towards a window: day 1: 5 degrees, day 2: 15 degrees, day 3: 30 degrees, day 4: 45 degrees. Calculate the average bending per day and explain, in terms of auxin, why the shoot bends. (3 marks) 9. The table shows the blood glucose level of a person after a meal: 0 h: 90 mg/dL, 1 h: 150 mg/dL, 2 h: 110 mg/dL, 3 h: 90 mg/dL. Calculate the rise in the first hour and the fall in the next two hours. Name the hormone responsible for the fall and the gland that secretes it. (3 marks) 10. Iodised salt is recommended to prevent goitre. If an adult needs about 150 micrograms of iodine per day and iodised salt contains 15 micrograms of iodine per gram, how many grams of iodised salt meet the daily need? Name the hormone that needs iodine and its function. (3 marks) Section C - Diagrams (10 marks) 11. Draw a neat labelled diagram of a neuron, showing the dendrites, cell body, nucleus, axon and nerve ending, and mark the direction in which an impulse travels. (4 marks) 12. Draw a labelled diagram of the reflex arc involved when a hand touches a hot object, showing the receptor, sensory neuron, relay neuron in the spinal cord, motor neuron and effector muscle. (3 marks) 13. Draw a labelled diagram of the human brain showing the forebrain (cerebrum), midbrain, cerebellum, pons, medulla and spinal cord. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Two students plan an experiment to show hydrotropism. Describe how they could set it up with a seedling and a porous pot of water, what result they would expect, and why the result shows that roots respond to water and not to gravity alone. Distinguish between positive and negative geotropism with examples. (5 marks) 15. The leaves of the touch-me-not plant fold up when touched, but a pea plant climbs a support with tendrils. Compare the mechanisms of these two movements, explaining the role of water in the first and differential growth in the second. Why is the first movement not called a tropism? (5 marks) 16. A child is found to have abnormally short stature and another to have a swollen neck. Name the hormone deficiencies likely in each case and the glands involved. Explain, with the example of insulin and blood sugar, how a feedback mechanism regulates the timing and amount of hormone release. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Draw all diagrams neatly in pencil and label every part. Give examples from daily life wherever possible.