Module 5 Communication and Homeostasis

Question 1

Need for communication systems

Answer 1

• Organisms must respond to internal and external changes in environment and coordinate activities of organs, to maintain the internal environment within restricted limits through physiological control systems. Changes in internal environment can affect enzyme action and cell function.
• The two communication systems of the body are the endocrine system and the nervous system.
• The nervous system consists of the central nervous system – the brain and spinal cord – and the peripheral nervous system – all the nerves of the body. Body functions are controlled and regulated by nerve impulses that pass along neurones.
• The endocrine system involves hormones that are secreted from endocrine glands and are transported in the blood. They transmit information and alter the activity of target organs.
• The maintenance of temperature, pH and blood glucose concentration is essential. Changes in pH can affect enzyme activity and blood glucose concentration affects the availability of respiratory substrate as well as the water potential of the blood.
• Plants control their internal concentration of carbon dioxide through opening and closing the stomata.

Question 2

Principles of homeostasis

Answer 2

• Negative feedback is used to maintain homeostatic balance.
• In a negative feedback loop, a receptor detects a stimulus, a coordination system transfers information, and an effector carries out a response.
• If the stimulus is an increase, the body will make the factor decrease and vice versa.
• A negative feedback loop reduces the initial effect of a stimulus. Receptors detect deviations from restricted limits and result in a corrective mechanism.
• Positive feedback enhances the effect of the original stimulus. For example, oxytocin in childbirth causes widening of the cervix.

Question 3

Cell signalling

Answer 3

• Cell signalling is the process by which cells communicate with each other. It allows multicellular organisms to control and coordinate the body and respond to changes in the environment.
• A stimulus is received by a receptor cell and converted to a signal by transduction. The signal is transmitted to an effector cell, where a response is made.
• Paracrine signalling takes place when cells are close together. Endocrine signalling takes place when cells are far apart. Hormones are transported in the circulatory system.
• Cell membranes play a role in cell signalling as they control what enters and leaves a cell. Signalling molecules are generally small for easy transport across membranes. Receptors found in or on the cell membrane are normally proteins or glycoproteins. When a molecule binds to the receptor it causes specific changes in the target cell.

Question 4

Thermoregulation

Answer 4

• Temperature is a key factor that must be controlled to optimise enzyme activity. Thermoregulation is the control of internal body temperature.
• Endotherms possess physiological mechanisms to control internal body temperature, like mammals and birds.
• Ectotherms rely on behavioural adaptations to ensure the internal temperature is not too low or high, like reptiles and amphibians.
• Endotherms have peripheral receptors on the skin and mucus membranes that detect the external temperature and communicate with the hypothalamus to bring about a response. Thermoreceptors in the hypothalamus also detect the temperature of blood flowing to the gland and initiates a homeostatic response.
• Cooling mechanisms in endotherms include vasodilation, where arteries dilate and increase blood flow to capillaries near the skin, flattening of hairs to prevent the formation of an insulating layer, and sweating, where heat is lost to the surroundings by evaporation.
• Heating mechanisms in endotherms include erecting hairs by contraction of hair erector muscles, vasoconstriction, boosting metabolic rate as metabolic reactions are exothermic (BMR) and shivering, when skeletal muscle contract rapidly and regularly to generate heat.
• Endotherms also show behavioural responses such as seeking shade or huddling.
• Ectotherms cool down by seeking shade and heat up by basking in the sun. Aquatic ectotherms benefit as water is relatively thermostable.
• Ectotherms behaviour is restricted by temperature, so they struggle to colonise habitats of extreme temperature. Endotherms require more energy as they have a higher metabolic rate, so require more food.