Topic 7: Homeostasis and Exercise

Question 1

Explain the role of the brain in reducing heart rate after exercise (2)

Answer 1

-Chemoreceptors detect a change in carbon dioxide / PH
-The cardiovascular control centre receives impulses from the chemoreceptors / sends impulses to the heart
-Therefore impulses are transmitted along the parasympathetic nerve to the SAN reducing heart rate

Question 2

Describe how the brain reduces the activity of the sweat glands after the exercise (2)

Answer 2

-Thermoreceptors detect a decrease in temperature
-Hypothalamus / thermoregulatory centre sends fewer impulses to sweat glands

Question 3

Explain how the respiratory centre is involved in the control of ventilation rate after exercise (5)

Answer 3

-High CO2 in the blood stimulates the respiratory centre
-Increase in lactate / fall in PH stimulates the respiratory centre
-More impulses send to the diaphragm and intercostal muscles
-Resulting in an increase in the rate and depth of breathing
-PH returns to normal as CO2 is removed and ventilation rate decreases

Question 4

Heat stress occurs when the core body temperature raises above 40C

Describe how thermoregulatory mechanisms are controlled to help marathon runners avoid heat stress (4)

Answer 4

-Thermoreceptors in the hypothalamus or skin detect increase in temperature
-Impulses sent to thermoregulatory centre in hypothalamus
-Hypothalamus sends impulses (action potentials) to sweat glands
-Increases blood flow to surface of skin by vasodilation
-Decreases metabolic rate

Question 5

Explain the role of the nervous system in bringing about the increase in temperature of the body (5)

Answer 5

-Thermoreceptors in the skin detect and increase in temperature
-Thermoreceptors in the hypothalamus detect temperature increase
-Therefore more impulses are sent along the sympathetic nerves / nervous system
-Which leads to constriction of shunt vessels
-Therefore causing vasodilation of arterioles
-Causing more blood to flow near the skin surface

Question 6

Sweating is a thermoregulatory mechanism

A student concludes that loss of heat when sweating is related to the dipole nature of water molecules

Justify this statement (3)

Answer 6

-Water has an uneven distribution of charge, making it dipole
-So water forms hydrogen bonds with other water molecules
-And it requires a lot of thermal energy to break these bonds
-And allow water to evaporate taking he heat energy with it

Question 7

Explain the importance of the dipole nature of water in sweating (2)

Answer 7

-Dipole nature allows water molecules to form hydrogen bonds / bonds with each other
-Heat energy is used to break bonds between water molecules
-Evaporation of water cause cooling / removal of heat

Question 8

Describe how the production of sweat is controlled during exercise in humans (4)

Answer 8

-By homeostasis / a negative feedback response
-Thermoreceptors in the skin / hypothalamus detect a rise in temperature
-Send impulses to the thermoregulatory centre / hypothalamus
-Thermoregulatory centre / hypothalamus sends impulses to the sweat glands
-To increase sweat production

Question 9

Explain why too much exercise could be harmful to the human body (3)

Answer 9

-Increased exercise results in wear and tear of joints, cartilage, tendons, ligaments
-Therefore leading to joint damage
-Suppression of immune system
-Therefore leading to increased risk of infection

Question 10

Explain the process when blood pressure is too high (4)

Answer 10

-Detected by baroreceptors which send impulses to cardiovascular control centre
-It sends impulses along the parasympathetic neurons which secrete acetylcholine
-Acetylcholine binds the SAN causing it to fire less frequently
-Heart rate slows down and blood pressure decreases back to normal

Question 11

Explain the process when blood pressure is too low (4)

Answer 11

-Detected by baroreceptors which send impulses to cardiovascular control centre
-It sends impulses along sympathetic neurons which secrete noradrenaline
-Noradrenaline binds to receptors to SAN causing it to fire more frequently
-Heart rate speeds up and blood pressure increases back to normal

Question 12

Explain the process when O2 in the blood is high / Low CO2 (4)

Answer 12

-Detected by chemoreceptors which sends impulses to cardiovascular control centre
-It sends impulses along parasympathetic neurons which secrete acetylcholine
-Acetylcholine binds to receptors on SAN causing it to fire less frequently
-Heart rate slows down and O2/CO2 and PH return to normal

Question 13

Explain the process when blood O2 is low / High CO2 (4)

Answer 13

-Detected by chemoreceptors which send impulses to cardiovascular control centre
-It sends impulses along sympathetic neurons which secrete noradrenaline
-Noradrenaline binds to receptors on SAN causing it to fire more frequently
-Heart rate speeds up and O2/CO2 levels return to normal

Question 14

Control of the breathing rate (3)

Answer 14

-Controlled by the ventilation centres (also called respiratory centres) in the medulla oblongata
-The inspiratory centre controls the movement of air into the lungs (inhalation)
-The expiratory centre controls the movement of air out of the lungs (exhalation)

Question 15

Effects of the inspiratory centre on breathing rate (5)

Answer 15

-It sends nerve impulses along motor neurons to the intercostal muscles of the ribs and diaphragm muscles
-These muscles will contract and cause the volume of the chest to increase
-This lowers the air pressure in the lungs to slightly below atmospheric pressure
-An impulse is also sent to the expiratory centre to inhibit its action
-Due to the difference in pressure between the lungs and outside air, air will flow into the lungs

Question 16

Role of stretch receptors in inspiration (2)

Answer 16

-Stretch receptors in the lungs are stimulated as they inflate with air
-Nerve impulses are sent back to the medulla oblongata which will inhibit the inspiratory centre

Question 17

Effects of the expiratory centre on breathing rate (4)

Answer 17

-It sends nerve impulses to the intercostal and diaphragm muscles
-These muscles will relax and cause the volume of the chest to decrease
-This increases the air pressure in the lungs to slightly above atmospheric pressure
-Due to the higher pressure in the lungs, air will flow out of the lungs

Question 18

Role of stretch receptors in expiration (2)

Answer 18

-As the lungs deflate, the stretch receptors become inactive
-Means that the inspiratory centre is no longer inhibited and the next breathing cycle can begin

Question 19

Chemoreceptors

Answer 19

-Chemoreceptors are found in the medulla oblongata, as well as in the aortic and carotid bodies
-They are stimulated by changes in the levels of carbon dioxide and oxygen in the blood, as well as blood pH

Question 20

Effects of exercise on breathing rate (5)

Answer 20

-Decrease the pH of the blood is detected by chemoreceptors
-Impulses sent to the intercostal muscles and diaphragm
-This increases the rate and depth of breathing
-Results in more oxygen entering the lungs and more CO2 leaving the lungs
-The decrease in carbon dioxide levels will result in the blood pH returning back to normal

Question 21

Baroreceptors

Answer 21

-Found in the aortic and carotid bodies and they are stimulated by high and low blood pressure

Question 22

Benefits of exercise (4)

Answer 22

-Balances LDLs and HDLs
-Better BMI and waist : hip ratio
-Reduced risk of cancer
-Reduced risk of coronary heart disease and stroke (lower blood pressure)

Question 23

Negative impacts of exercise (3)

Answer 23

-Joints may become damaged due to increased wear and tear
-Suppresses the immune system, making the individual more susceptible to disease and infection
-Vigorous exercise can cause low levels of antibody production

Question 24

The demand for oxygen changes during exercise
The change in demand affects the breathing rate

Explain the effect of exercise on the changes in oxygen consumption (4)

Answer 24

-Exercise will increase oxygen consumption
-Because there is increased aerobic respiration
-Because more energy / ATP is needed by muscles
-Oxygen required to convert lactic acid into glucose / pyruvate
-Oxygen consumption begins to decrease after exercise

Question 25

The demand for oxygen changes during exercise The change in demand affects the breathing rate At the start of exercise, breathing rate increases Explain how starting to exercise causes an increase in breathing rate (3)

Answer 25

-Exercise initiates impulses from the motor cortex / stretch receptors in muscle cells -Impulses sent to respiratory / ventilation centre -Leading to increased impulses to intercostal muscles / diaphragm

Question 26

As levels of activity increase, the heart can respond to the changing demand for oxygen Describe how the sinoatrial node (SAN) is involved in bringing about a change in heart rate as the level of activity increases (2)

Answer 26

-More stimulation / depolarisation of the SAN from the sympathetic nervous system -Causing more frequent waves of depolarisation from the SAN to the atria -Leading to more frequent contraction of the atria / stimulation of the SAN

Question 27

As levels of activity increase, the heart can respond to the changing demand for oxygen Which term describes the ability of heart muscle to contract without external stimulation? (1) A) autonomic B) cardiac C) myogenic D) systolic

Answer 27

Myogenic

Question 28

Creatine phosphate

Answer 28

-Substance which is stored in muscle fibres -It supplies the initial energy needed to produce ATP before aerobic respiration -Serves as a rapid release reserve of high energy

Question 29

Oxygen debt

Answer 29

The amount of oxygen needed to oxidise lactic acid to carbon dioxide and water

Question 30

Lactate can build up in the muscles of a sprinter. Suggest why the build up of lactate may prevent any further increase in speed (2)

Answer 30

-Build up of lactate causes a fall in PH / more more acidic -This denatures enzyme shape -Which slows down glycolysis / ATP production / anaerobic respiration

Question 31

Explain the fate of lactate following a sprint (4)

Answer 31

-Lactate in the blood is transported to / broken down in the liver -Lactate is converted to pyruvate -Via oxidation / production of reduced NAD+ -Pyruvate is oxidised in the Krebs cycle -This requires extra oxygen / oxygen debt -Carbon dioxide and water are produced

Question 32

Gluconeogenesis

Answer 32

Lactate removed from muscles and carried to the liver in the blood then is converted back into pyruvate and then into glucose. The glucose is then carried around in the blood to replenish glycogen stores in muscles

Question 33

State the location of the SAN in the heart (1)

Answer 33

Right atrium

Question 34

Explain what is meant by the term myogenic (2)

Answer 34

-That stimulation generated from within (muscle) -This results in depolarisation

Question 35

Explain how an electrocardiogram (ECG) can be used to calculate a person’s heart rate (3)

Answer 35

-Shows electrical activity of the heart -Idea of how to identify one heart beat for one heart beat -Count the number of these / peaks in a set time or how long from one set of electrical activity to the next

Question 36

Workers in the brewing industry may be at risk due to the carbon dioxide released by yeast fermentation. Atmospheric air contains between 0.03% and 0.04% carbon dioxide. A concentration of 5% carbon dioxide in the air causes a change in the heart rate of people exposed to this concentration. Explain why a carbon dioxide concentration of 5% causes a change in heart rate (5)

Answer 36

-The concentration of carbon dioxide in the alveoli is higher -The concentration of carbon dioxide in the blood is higher / pH of blood is lower -Detected by chemoreceptors in medulla /carotid artery / aorta -Impulses sent to cardiovascular / cardiac control centre in medulla -Autonomic nervous system / sympathetic nerve stimulated -More impulses to SAN -Noradrenalin / norepinephrine released onto SAN ; -SAN excitation rate increased -Heart rate will increase

Question 37

How do blood vessels in the skin respond to low body temperature? (3)

Answer 37

-Smooth muscle in shunt vessels relaxes and they dilate. -Smooth muscle in arterioles contracts and they constrict (vasoconstriction). -Less blood flows through capillaries close to the skin surface to conserve heat.

Question 38

How does the body respond to low body temperature? (5)

Answer 38

-Sweat glands secrete less sweat due to decreased stimulation from sympathetic neurones from the hypothalamus. -Erector pili muscles contract → hairs on skin stand up to trap an insulating layer of air. -Thyroid gland releases more thyroxine → metabolic rate increases. -Shunt vessels dilate and arterioles constrict. -Skeletal muscles contract rapidly to generate metabolic heat through respiration.

Question 39

Explain how heart rate is controlled during exercise (5)

Answer 39

-Increase in respiration rate in muscle cells -More CO2/carbonic acid in blood More lactate / lactic acid in blood -Idea that chemoreceptors in medulla stimulated -Cardiovascular control centre in medulla -Autonomic nervous system /sympathetic nerve -More impulses from medulla / cardiovascular control centre to SAN OR along neurones to SAN -More noradrenaline / norepinephrine released onto SAN -SAN excitation rate increased -Causing an increased heart rate

Question 40

Explain the role of the nervous system in bringing about the increase in temperature of the fingertip as shown in this investigation (5)

Answer 40

-Thermoreceptors detect increase in temperature -Thermoreceptors in the hypothalamus detect temperature increase -Therefore more impulses are sent along the sympathetic nervous system -Which leads to constriction of shunt vessels -Therefore causing vasodilation (of arterioles) -So more warm blood flows near the skin surface

Question 41

How is oxygen consumption measured using a spirometer?

Answer 41

- The gradient of the decrease in air volume in the spirometer is a measure of oxygen consumption - Therefore the rate of aerobic respiration

Question 42

Explain how the sinoatrial node (SAN) ensures that oxygenated blood enters the aorta (4)

Answer 42

-SAN initiates electrical activity over atria -Which causes atria to contract -Forcing the oxygenated blood into the left ventricle -Electrical activity from SAN {received by AVN / travels through bundle of His / Purkyne fibres -Causing left ventricle to contract forcing blood into aorta

Question 43

Suggest two ethical reasons why the use of drugs, such as EPO, should be banned from sport (2)

Answer 43

-Provides an unfair advantage for those who take the drugs -Health risk to athletes -Cost to NHS / medical services of health implications

Question 44

A number of drugs, including EPO, have been used by athletes. EPO is a drug that stimulates the formation of red blood cells. EPO has been used to enhance the performance of certain types of athlete. Sprinters usually have more fast twitch fibres in their leg muscles than long distance runners. Suggest why EPO may have less of an effect on the performance of a sprinter than on a long distance runner (3)

Answer 44

-RBC will {carry/supply oxygen} -Low number of mitochondria present in fast twitch -So additional oxygen may have limited additional effect -Poor blood supply / capillary network in fast twitch muscle so little additional oxygen received -In fast twitch respiration is (primarily) anaerobic -Short {time duration of race/distance travelled} means minimal additional blood supplied to muscles in timeframe

Question 45

Give two reasons why too little exercise may not be good for the health of a person (2)

Answer 45

-Increased risk of obesity -Coronary heart disease -Diabetes -High blood pressure / strokes -Osteoporosis

Question 46

Give two reasons why too much exercise may not be good for the health of a person (2)

Answer 46

-Wear and tear on joints -Suppression of immune system

Question 47

The pH of the blood of a sprinter falls during a race and returns to its original level after the race. State the homeostatic control mechanism that returns the pH of blood to its original level (1)

Answer 47

Negative feedback

Question 48

Explain how the pH of the blood of a sprinter is returned to its original level after a race (5)

Answer 48

-Low pH is due to acid in the blood -Lactate taken to liver -Oxygen debt -With production of NAD -Pyruvate converted to glucose -Pyruvate into mitochondria -Chemoreceptors detecting change in pH -Increased nerve impulse rate from medulla / breathing rate / heart rate -Dissolved CO2 from blood diffuses into alveoli

Question 49

During the race, heat is generated and is lost from the body through the skin. Describe how muscle, present in blood vessels in the skin, helps to increase heat loss from the body. (4)

Answer 49

-Shunt vessel muscles contracting which lead to vasoconstriction -Muscles of arterioles relaxing to increase diameter (vasodilation) -Which redirects blood {away from deeper arterioles / into surface arterioles} -To increase blood flow into capillaries / towards surface -So more heat lost through radiation

Question 50

Describe how cells in the SAN are involved in controlling heart rate (3)

Answer 50

-SAN is myogenic -Electrical activity from SAN causes atria to contract -Activity of SAN can be changed by nerve impulses e.g. controlled by medulla -More impulses from accelerator increases heart rate

Question 51

Describe and explain how changes in blood flow in the skin will help her to control her body temperature (4)

Answer 51

-More blood flows near the skin surface -Due to vasodilation / dilation of arterioles -Vasoconstriction of shunt vessels -More blood to capillaries -More heat lost -Via radiation

Question 52

A gymnast was offered keyhole surgery to repair her damaged cruciate ligament. Suggest and explain two reasons why she might choose this type of surgery (2)

Answer 52

-Smaller incision so less pain -Smaller incision reduces recovery time -Smaller incision reduces chance of infection

Question 53

Comment on the ethical viewpoints for and against the use of performance-enhancing drugs by athletes (4)

Answer 53

-The absolutist’s view would be that they should never be used -Because of the damage to the body by the side effects -Athletes should compete using their innate {anatomical / physiological} abilities / fair competition should be promoted -The rationalist’s view would be that their use is acceptable if there is a justifiable outcome -Because it is a personal choice

Question 54

If the heart of an animal is removed from its body, the heart will continue to beat for a period of time. The left atrium stops contracting if it is separated from the rest of the heart. However, the right atrium and the rest of the heart will continue to beat. Eventually, the right atrium and the rest of the heart will also stop beating. Explain why the left atrium stops beating when it is separated from the right atrium (2)

Answer 54

-The SAN / sinoatrial node is in the right atrium -(left atrium) cannot contract without impulses from the SAN

Question 55

If the heart of an animal is removed from its body, the heart will continue to beat for a period of time. The left atrium stops contracting if it is separated from the rest of the heart. However, the right atrium and the rest of the heart will continue to beat. Eventually, the right atrium and the rest of the heart will also stop beating. Explain why the right atrium and the rest of the heart eventually stop beating (2)

Answer 55

-(heart / muscle cells) run out of oxygen -(aerobic) respiration stops -(heart / muscle cells) stop making ATP

Question 56

What is VITAL capacity

Answer 56

Maximum volume of air that can be breathed in or out in one forced breath.

Question 57

What is residual volume?

Answer 57

Air that always remains in the lungs and cannot be breathed out.

Question 58

What controls ventilation rate (3)

Answer 58

-Stretch receptors in muscles detect muscles stretching due to increased exercise and send impulses along sensory neurones to the respiratory control centre. -The respiratory control centre in the medulla oblongata receives impulses from stretch receptors, acts as the coordination centre, and sends impulses along motor neurones to effectors. -Effectors (diaphragm and intercostal muscles) contract and relax more frequently to increase breathing rate.