Homeostasis
O9. If the body temperature of a healthy person falls below the normal setting of 37 °C:
J. an increased amount of the hormone thyroxine is released, resulting in a decrease in heat loss.
K. a decreased amount of sweating occurs, resulting in an increase in heat production.
L. vasodilation occurs, resulting in an increase in heat production.
M. vasoconstriction occurs, resulting in a decrease in heat loss.
M. vasoconstriction occurs, resulting in a decrease in heat loss.
State the difference between positive and negative feedback and provide an example for each.
Positive feedback occurs to increase the change or output: the result of a reaction is amplified to make it occur more quickly (e.g. oxytocin during childbirth - continues to increase pushing the baby towards the cervix). Negative feedback occurs to reduce the change or output: the result of a reaction is reduced to bring the system back to a stable state (e.g. sweating when we are too hot).
M2. Which one of the following nerve pathways represents the reflex response to the stimulus of stepping on a sharp object?
J. Receptor - motor nerve - spinal cord - sensory nerve - muscle in foot
K. Receptor - motor nerve - brain - sensory nerve - muscle in leg
L. Receptor - sensory nerve - brain - motor nerve - muscle in foot
M. Receptor - sensory nerve - spinal cord - motor nerve - muscle in leg
M. Receptor - sensory nerve - spinal cord - motor nerve - muscle in leg
N4. The response to an increase in the level of antidiuretic hormone in the blood of a healthy human being would include:
J. increased urine output.
K. decreased production of insulin.
L. decreased blood pressure.
M. increased water reabsorption.
M. increased water reabsorption.
013. In 1877 the American biologist Joel Allen observed that the length of arms, legs, and other appendages of warm-blooded animals affected the rate at which they lost heat to the environment.
Allen observed a consistent difference in the limb length of individuals in populations of the same species living in warm climates near the equator, in comparison with those living in cold climates further from the equator.
Which one of the following statements is consistent with Allen's observation?
J. In cold climates, animals need to conserve as much heat as possible and therefore have longer limbs.
K. In warm climates, the larger the surface area of the limbs, the faster the animals lose heat to the environment.
L. In warm climates, animals have longer limbs that increase their surface area and minimise heat loss.
M. In cold climates, animals have shorter limbs and a larger surface area-to-volume ratio.
K. In warm climates, the larger the surface area of the limbs, the faster the animals lose heat to the environment.
L3. A person runs 10 km even though the air temperature is above 35 ° C. In these hot conditions, a person's body temperature can rise above its normal level.
(a) Explain the role of negative feedback in the control of body temperature in humans.
(b) Explain why it is important for body temperature in a human is maintained.
(a) In negative feedback, the response counteracts the stimulus. The stimulus of high body temperature, causes the body to respond by sweating. Evaporation of sweat from the skin cools the skin, therefore lowering body temperature. Could also provide the answer for what occurs when the body temperature is too low.
(b) A body temperature of 37°C allows enzymes to function at their optimum rate. A lower temperature lowers the rate of reaction and a higher temperature may denature enzymes, which also lowers the rate of reaction.
M8 Caffeine is a drug that reduces the effect of the neurotransmitter adenosine. Adenosine isresponsible for inducing sleep in a healthy person. Caffeine prevents adenosine from binding to receptors in the hypothalamus.
Caffeine:
J. decreases the amount of time it takes for a healthy person to fall asleep.
K. binds to active site of adenosine.
L. reduces the number of nerve impulses triggered by adenosine.
M. acts as an inhibitor that prevents the release of adenosine.
L. reduces the number of nerve impulses triggered by adenosine.
N11. Which one of the following statements about the regulation of secretion of the hormones insulin and glucagon from the pancreas is false?
J. Some cells in the pancreas respond to changes in the blood glucose level.
K. In glucose homeostasis, the blood hormone levels are regulated by negative feedback loops.
L. Sensory receptors and effectors in the glucose control pathway are located in the pancreas.
M. After a meal, the increase in the blood glucose level stimulates the release of glucagon.
M. After a meal, the increase in the blood glucose level stimulates the release of glucagon.
016. When a person spends an extended time in a cold environment, their body temperature can fall below its normal level.
(a) Describe how each of the following systems regulates body temperature in human beings who have a lower-than-normal body temperature.
(i) Endocrine system:
(ii) Nervous system:
a) (i) Increased thyroxine increases metabolic rate or metabolism or chemical reactions, which increases heat production or the amount of heat released.
(ii) Increased shivering results in increased heat production. Or vasoconstriction reduces heat loss. Or erection of hairs reduces heat loss.
016 When a person spends an extended time in a cold environment, their body temperature can fall below its normal level.
(a) Explain the role of negative feedback in the control of human body temperature.
(b) Explain why it is necessary for human beings to maintain a body temperature at about 37°c
a) The stimulus is a change in body temperature. This is detected by the thermoregulatory centre in the brain. The response reverses or inhibits the stimulus.
b) Cell metabolism requires a temperature within tolerance as enzymes work best within an optimum range. If the temperature is too high or too low enzymes will not work effectively.
M15 The taste buds on the tongue contain many different sensory receptors.
a) State the function of sensory receptors.
b) (i) Describe the nerve pathway from the tongue to the brain that results in a person experiencing a taste, such as 'salty'.
(ii)Explain how the brain can distinguish between two different tastes, such as 'salty' and 'sour'.
a) To detect stimuli/ detect changes in the external/internal environment.
b) (i) Sensory receptors or chemoreceptors on the tongue initiate a signal in a sensory neuron. This signal then travels to an interneuron in the brain.
(ii) Each different taste receptors in the tongue are specific to the types of stimuli /shape of the different chemical molecule. The brain can distinguishes which receptor was stimulated.
N24 The nervous system and the endocrine system are involved in the control of body temperature in human beings.
(a) Identify the pathway taken by the signal between an endocrine gland and its targetcells.
(b) Describe the role of thyroid-stimulating hormone.
( c) Describe the structural feature of all target cells that are affected by thyroxine that allows them to respond to thyroxine.
a) Blood or bloodstream or circulatory system or cardiovascular system.
b) Stimulates the thyroid gland to release thyroxine.
c) They have receptors with binding sites that have a shape that is complementary to thyroxine. Thyroxine can bind to the receptors due to this complementary shape.
027. Refer to the following flow chart, which shows the hormones involved in a human being's response to a decrease in body temperature:
Decrease in body temperature --> detected by hypothalamus --> releases TRH --> travels to pituitary gland --> releases TSH --> thyroid gland --> releases hormone X --> effect takes place
a) State the name of hormone X.
b) Explain how hormone X affects body temperature.
c) Compare two characteristics of the action of the nervous system and the endocrine system.
a) Thyroxine or T4
b) Thyroxine increases the metabolic rate of cells, this increases heat production which leads to an increase in body temperature.
c) Choose any two characteristics to compare e.g. speed of action; the nervous system is generally faster than the endocrine system.
020 Certain mechanisms in human beings control body temperature. A decrease in temperature below normal triggers a number of responses that restore it to normal (37°C).
State two responses that would restore the body temperature of a human being to normal if it fell below (37°C) and explain how each one works.
e.g. Shivering- reference to nervous system, makes body move to generate heat, increase in heat, leads to increase in body temperature. Vasoconstriction - reference to nervous system, blood vessels near skin decrease in diameter, less heat loss, leads to increase in body temperature.
Increase in metabolic rate: reference to hormonal system, faster chemical processes, produces more heat, increase in body temperature.
M 16 The human body uses homeostatic control mechanisms to regulate aspects of its internal environment, such as body temperature, blood glucose level, blood volume, and blood osmolarity.
(a) Hyperthermia is a medical condition in which a patient has an abnormally high body temperature. This often occurs due to prolonged exercise in a very hot environment, and it can result in a change in blood volume.
(i) Explain how one response controlled by the nervous system would cause a change in blood volume following an increase in body temperature.
(ii) Explain why an increase in body temperature would lead to a change in blood flow t the surface of the skin.
(i) Sweating, results in evaporation of water from skin (hence water is lost to the environment), decreasing the blood volume.
(ii) Increased blood flow to skin surface results in increased heat loss from the skin.
N25 The human body uses homeostatic control mechanisms to regulate aspects of its internal environment, such as body temperature, blood glucose level, blood volume, and blood osmolarity.
a) Cells from a rare type of pancreatic tumour, known as an insulinoma, secrete excessive amounts of insulin. The secretion is not regulated by the body's normal homeostatic mechanisms, and this causes a significant change in blood glucose level.
i) Describe the likely effect of insulinoma on blood glucose level.
b) Blood donors need to drink plenty of fluids, including water, after donating blood. This helps to restore blood volume.
(i) Explain what is likely to happen to blood osmolarity (the concentration of solutes in the blood) following the consumption of a large quantity of water.
(ii) Describe the role of the endocrine system in restoring blood volume and blood osmolarity to normal levels following the consumption of a large quantity of water.
a) Release of thyroxine, leads to increased metabolic rate and increased heat production.
b) (i) More water in the blood or an increased blood volume, decreases blood osmolarity.
(ii) Reduced production/release of ADH (anti-diuretic hormone) results in a reduced permeability due to less aquaporins in the tubules/collecting ducts of the kidney such that less water will be reabsorbed. This will decrease the blood volume and increase blood osmolarity