6 — human physiology

Question 1

outline the role of the thyroid gland in helping control body temperature in humans (4)

Answer 1

• secrets thyroxin
• thyroxin causes the metabolic rate to rise
• heat released by metabolism
• thyroxin stimulates shivering
• more thyroxin secreted if body temperature is too low

Question 2

describe what occurs in a neuron when an action potential is propagated along the axon (4)

Answer 2

• sodium ions diffuse in
• membrane potential changes from negative to positive
• potassium channels open and potassium ions diffuse out
• membrane potential changes back from positive to negative
• local current due to diffusion of sodium ions along the neuron
• local current cause next sodium channels to open

Question 3

explain how cells in the bloodstream cause a specific immune response (7)

Answer 3

• specific immune response is production of antibodies in response to a particular pathogen
• antibody is specific to a specific antigen
• phagocytes engulf antigens from pathogens
• T lymphocytes activated by antigens
• T lymphocytes activate B lymphocytes
• only B lymphocytes that produce antibodies against the antigen are activate
• B lymphocytes divide by mitosis to form plasma cells
• plasma cells then secrete antibodies of the same type
• some B lymphocytes form memory cells
• memory cells give long lasting immunity/ faster response to a pathogen

Question 4

outline how starch in the gut is modified for absorption in humans (3)

Answer 4

• starch is broken down by the enzyme amylase
• amylase secreted by the pancreas
• acts in the duodenum/ small intestine/ mouth
• starch is broken down into monomers
• products of digestion are smaller

Question 5

describe how the small intestine is adapted for efficient absorption of nutrients (5)

Answer 5

• small intestine is very long
• small intestines contains villi/ microvilli
• the epithelial cells of villi have microvilli
• these increase the surface area for absorption
• cells of the small intestine contain a large number of mitochondria
• these provide energy for active transport
• the walls contain proteins for active transport
• the villi have a rich blood supply (for absorption of nutrients)/ lacteal (absorption of fats)
• the walls of the villi are thin so less distance for infusion

Question 6

blood transports nutrients to all tissues of the body. explain the initiation of the heartbeat and how blood flow is controlled in the heart (7)

Answer 6

• the contraction of the heart is myogenic
• heartbeat initiates in the sinoatrial node
• the SA node is located in the right atrium
• electrical impulses pass over the atria then the ventricles
• nerves from the medulla (part of brain) can control the rate of heartbeat
• adrenaline can increase the rate of the heart
• contraction of heart muscle causes blood to flow
• ventricles send blood to the organs of the boy
• the direction of flow is controlled by valves to prevent backflow
• AV (atrioventricular) valves prevent backflow from ventricles
• semilunar valves prevent blood returning to the heart

Question 7

outline how the neuron is stimulated to release the neurotransmitter (2)

Answer 7

• the arrival of a nerve impulse stimulates the release of a neurotransmitter
• depolarisation stimulates calcium ion channels to open
• calcium ions cause the vesicle to fuse with the membrane
• vesicles release neurotransmitter by exocytosis

Question 8

explain the action of neonicotinoid pesticides in insects

Answer 8

• prevents synaptic transmission
• has similar structure to a neurotransmitter
• bin to acetylcholine receptors in the post synaptic membrane
• neonicotinoid pesticides are not broken down as acetylcholine would be by acetylcholinesterase
• the receptors are overstimulated
  paralyses the insects

Question 9

explain how water balance is restored in mammals when they are dehydrated (7)

Answer 9

• become thirsty
• more water reabsorbed from feces in the colon
• osmoreceptors in the hypothalamus detect dehydration
• ADH secrete
• by the pituitary gland
• ADH signals to collecting cut to increase permeability to water
• more aquaporins in plasma membrane of collecting duct
• more water reabsorbed from filtrate
• reabsorption by osmosis
• reabsorbed water passed into the blood
• small volume of urine formed
• less sweating

Question 10

what happens in an axon when the threshold potential is reached (1)

Answer 10

• sodium channels start to open
• depolarisation
• action potential occurs

Question 11

explain the production of antibodies in humans (7)

Answer 11

• antigens stimulate antibody production
• antibodies produced by lymphocytes
• phagocytes ingest pathogens and display antigens from them
• T cells activate by binding antigen
• activated T cells cause activation of B cells
• mitosis of B cells to produce cell clones
• plasma cells forms from differentiating B cells
• plasma cells secrete antibodies
• plasma cells make the same type of antibody specific to same antigen
• some activated B cells become memory cells

Question 12

explain the propagation of nerve impulses along the membrane of a neuron (3)

Answer 12

• depolarisation of part of axon causes depolarisation of next part
• local currents
• diffusion of sodium ions between polarised part an the next polarised part of axon
• resting potential reduced — change from -70mV to -50mV
• entry of sodium ions cause depolarisation
• saltatory conduction in myelinated neurons

Question 13

explain the adaptations of the small intestine to its function (7)

Answer 13

• small intestine is where nutrients are absorbed into the bloodstream
• very long to maximise absorption
• the small intestine is lined with smooth muscle to allow for the mixing/ moving of digested food
• muscles are circular and longitudinal
• that perform peristalsis
• the pancreas secrete substances into the small intestine to aid digestion
• contain villi to increase surface area
• villi have microvilli to increase surface area even more
• villi absorb products of digestion
• dense capillary network rapidly transports absorbed products
• lacteal absorbs lipids from intestine into the lymphatic system
• most of the chemical infection into monomers occurs in small intestine

Question 14

explain how the specialised structures of arteries help them to achieve their function (3)

Answer 14

• arteries carry blood at high pressure
• rupture of arteries is prevented by thick muscular/ elastic walls
• narrow lumen to maintain a high blood pressure
• elastic tissue allows artery to stretch an recoil
• arteries have muscle layers which contract to increase blood flow
• folding in the endothelium allows stretching

Question 15

outline how sperm are produced from diploid cells in the testis and how this production can be sustained over many decades of adult life (4)

Answer 15

• germinal epithelium divide endlessly by mitosis giving rise to spermatogonia
• spermatogonia are diploid
• spermatogonia divide by mitosis
• some spermatogonia enlarge, forming primary spermatocytes
• primary spermatocytes undergo meiosis I
• secondary spermatocytes produced are haploid
• secondary spermatocytes undergo the second division of meiosis
• spermatids develop tails

Question 16

explain how acetylcholine initiates an action potential in a postsynaptic membrane (2)

Answer 16

• acetylcholine binds to the receptor protein
• causing a change in tertiary structure
• if fusion of Na+ through the receptor allowed

Question 17

explain how amino acids in casein could reach the liver (7)

Answer 17

• food is mechanically digested in the mouth
• mixed with saliva in mouth
• moved through oesophagus through peristalsis
• proteins digested in the stomach
• pancreas secretes enzymes into lumen of small intestine
• enzymes digest macromolecules into monomers
• villi of small intestine absorb amino acids
• amino acids carried to blood capillaries
• blood capillaries carry amino acids to hepatic portal vein
• amino acids absorbed by active transport

Question 18

describe the genetic and hormonal control of male sexual characteristics in a human (3)

Answer 18

• if Y chromosomes present
• gene on Y chromosome promotes development of testes
• testes secrete testosterone
• testosterone stimulates sperm production
• testosterone stimulates development of male genitals
• testosterone stimulates development of male secondary sexual characteristics

Question 19

compare and contrast hormonal and nervous communication (7)

Answer 19

similarities
- both used for communication between cells
- both cause a response in target cells
- both can stimulate or inhibit processes in target cells
- both can work over long distances
- both under control of the brain
- both use feedback mechanisms/ used in homeostasis

differences

hormones
- chemical messenger
- transported in blood
- slower
- carried throughout the body
- wide range of organs affected by
- usually long term response

nerves
- nerve impulse
- transported by neurons
- faster
- carried to specific cell
- only muscles receive signals
- short duration/ short lived responses

Question 20

explain the advantages of using hybridoma cells in the production of monoclonal antibodies (2)

Answer 20

• endless cell divisions in hybridoma cells
• large population of identical cells produced
• all cells produce the same type of antibody
• large amount of chosen antibody can be produced

Question 21

state one use of monoclonal antibodies (1)

Answer 21

• pregnancy testing kits
• give passive immunity if injected
• blood typing for drugs

Question 22

outline the process of inhalation (4)

Answer 22

• diaphragm contracts
• external intercostal muscles contract
• muscle contraction moves the rib cage upwards and outwards
• increases volume of the thorax
• inference in pressure causes air to flow into lungs

Question 23

explain the process of gas exchange taking place in the alveoli (7)

Answer 23

• O2 diffuses into blood and CO2 if fuses out from blood
• blood entering the alveoli is high in CO2
• diffusion takes place due to concentration gradients
• concentration gradients maintained by ventilation and blood flow
• large surface area created by many alveoli for more efficient diffusion
• rich supply of capillaries allows efficient exchange
• type 1 pneumocytes are thin to allow easy diffusion
• gases must dissolve in liquid lining of alveolus in order to be exchanged
• type II pneumocytes secret surfactants to reduce surface tension
• type II pneumocytes create moist conditions in alveoli

Question 24

outline the role of the sodium potassium pump in maintaining the resting potential (2)

Answer 24

• sodium/ potassium pump pumps sodium ions out of axon and pumps potassium ions in
• requires energy against concentration gradient
• three sodium ions pumped out for every 2
  potassium ions pumped in
• results in charge difference between inside and outside where outside is positive relative to inside

Question 25

explain the consequences of celiac disease for absorption of digested nutrients (2)

Answer 25

• celiac disease causes much smaller villi
• smaller villi leads to less efficient absorption
• celiac sufferers must eat a gluten free diet

Question 26

explain the role of cells in the defence against infectious disease (7)

Answer 26

• cells of skin provide a physical barrier which stops entry of microbes
• stomach cells produce hydrochloric acid which kills microbes
• platelets start the clotting process, preventing access of pathogens
• white blood cells fight infections in the body
• phagocytes ingest pathogens by endocytosis
• gives non specific immunity to diseases
• production of antibodies by lymphocytes
• in response to particular pathogens
• gives specific immunity
• lymphocyte makes only one type of antibody
• plasma cells produce large quantity of antibody
• some lymphocytes remain as memory cells
• can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is reencountered
• results in faster defence against second exposure to specific antigen

Question 27

outline the reasons for the differences in blood concentrations between the renal artery and renal vein (4)

Answer 27

• urea/ waste products lower in vein due to excretion in urine
• oxygen lower in vein due to use in kidney tissue
• carbon dioxide higher in vein due to production by cell respiration
• glucose lower in vein due to use in cell respiration
• ion concentrations lower due to removal of excess
• ion concentrations in vein vary dependent on amount of water reabsorbed in the collecting duct
• toxin concentrations lower in vein due to excretion in urine

Question 28

explain the control mechanism of the heart rate (7)

Answer 28

• sinoatrial node is a specialised group of muscle cells
• acts as a pacemaker
• sends out electrical impulses
• electrical signal stimulates contraction of heart muscle
• signal passes through walls of atria/ passes to AV node
• then through walls of the ventricles
• medulla can change the rate

Question 29

explain how ventilation and lung structure contribute to passive gas exchange (7)

Answer 29

• air carried through trachea and bronchi
• alveoli increase the surface area for gas exchange
• gas exchange carried out through type pneumocytes
• type II pneumocytes secrete surfactant to reduce surface tension
• moist surface allows gases to reduce surface tension
• ventilation maintains concentration gradients of oxygen and carbon dioxide
• between air in alveoli and blood in adjacent capillaries
• external intercostal muscles/ diaphragm contract during inspiration
• lowering air pressure and increasing thorax volume
• relaxation of external intercostal muscles enable passive expiration
• internal intercostal muscles contract to force expiration
• expiration due to increasing air pressure in lungs

Question 30

discuss the control of blood glucose levels and the consequences if they are not maintained (8)

Answer 30

control
- homeostasis is the maintenance of a constraint internal environment
- the pancreas produces hormones that control the levels of glucose
- if glucose levels are high, beta cells produce insulin
- insulin causes cells to absorb glucose
- liver stores excess glucose as glycogen
- if glucose levels in blood are low, alpha cells produce glucagon
- glucagon causes the liver to break down glycogen into glucose
- glucagon can increase levels of glucose in the blood
- negative feedback controls glucose levels

consequences
- if the pancreas produces little insulin, a person can develop type I diabetes
- person with type I diabetes usually is dependent on injections of insulin
- type II diabetes occurs when the body becomes resistant to insulin
- type II diabetes is controlled by diet and exercise

Question 31

explain how blood solute concentration are kept within narrow limits in the human body (7)

Answer 31

• solute concentration of blood monitored by the brain
• pituitary gland secretes ADH
• ADH secreted when a person is dehydrated
• collecting duct more permeable to water
• more aquaporins opened in the plasma membrane of the collecting duct cells
• more water reabsorbed into the medulla
• medulla is hypertonic
• smaller volume of urine produced
• less ADH secreted of blood solute concentration is too low
• collecting duct less permeable to water
• insulin causes blood glucose levels to be reduced
• glucose stored as glycogen in the liver
• glucagon causes blood glucose concentration to be increased

Question 32

describe the processes involved in absorbing different nutrients across the cell membrane of villus epithelium cells lining the small intestine (4)

Answer 32

• diffusion of nutrients along a concentration gradient
• facilitated diffusion of nutrients involves movement through channel proteins
• active transport of nutrients against a concentration gradient involving protein pumps
• endocytosis of vesicles

Question 33

explain the events that occur during a nerve impulse and how the impulse is propagated along an axon (7)

Answer 33

• nerve impulses are action potentials propagated along axons of neurons
• resting potential is -70mV
• sodium/ potassium pumps maintain resting potential
• more sodium outside than the inside when at resting potential
• action potential stimulates depolarisation along the membrane
• when neuron is stimulated, if threshold potential is reached, Na+ channels open
• sodium ions diffuse in
• causes depolarisation — inside of the neuron
• becomes more positively charged than the outside of the neuron
• potassium channels open
• K+ move out, causing depolarisation
• myelination increases propagation speed

Question 34

outline the role of the parts of an alveolus in a human hung (4)

Answer 34

• the spherical wall of an alveolus maximuses gas exchange
• pneumocytes I optimise gas exchange
• pneumocytes II produce surfactant
• adjacent capillaries enclose alveoli for efficient gas exchange with blood
• surfactant reduces surface tension
• macrophages help with defence

Question 35

many diseases are caused by bacteria and other pathogens. explain, using examples, how other factors can lead to disease in humans (7)

Answer 35

example 1
- cystic fibrosis
- genetic
- multiple lung infections
- recessive allele

example 2
- rickets
- environmental
- bones are soft
- lack of vitamin D

Question 36

explain how hormones are used to control the human menstrual cycle (8)

Answer 36

• FSH stimulates the development of follicles
• follicles produce oestrogen
• oestrogen stimulates the repair of the uterus lining
• oestrogen stimulates LH secretion
• LH stimulates ovulation
• LH stimulates the development of the corpus luteum
• corpus luteum secretes progesterone
• progesterone causes thickening of the uterus lining
• progesterone/ oestrogen inhibits the secretion of LH/ FSH
• failing progesterone levels at the end of the cycle allow FSH production

Question 37

explain the roles of named types of blood proteins in different defence mechanisms (8)

Answer 37

• clotting factors are proteins that initiate the clotting process
• fibrin permits blood clotting
• thrombin converts fibrinogen to fibrin
• fibrin forms a clot that prevents the entry of pathogens into the blood
• antibodies are specific proteins that lymphocytes make
• each antibody corresponds to a specific pathogen
• antibodies create specific immunity
• plasma cells produce large amounts of antibodies
• immunoglobulins are antibodies against pathogens
• enzymes in phagocytic white blood cells may digest pathogens

Question 38

describe the functioning of immunoglobins (3)

Answer 38

• antibodies
• variety of binding sites
• specific to antigens on pathogens
• constant region aids destruction of the bacteria
• attracts phagocytes to engulf pathogen

Question 39

explain how the small intestine moves, digests and absorbs food (8)

Answer 39

• peristalsis helps move food
• peristalsis mix food with intestinal enzymes
• enzymes digest macromolecules into monomers
• pancreatic enzymes digest food in the lumen of small intestine
• bile secreted into the small intestine creates favourable pH for enzymes
• some final digestion into monomers is associated with epithelial cells
• mucosa layer contains villi
• villi increase surface area for better absorption
• villi absorb products of digestion

Question 40

outline how leptin controls appetite (3)

Answer 40

• leptin suppresses appetite
• is secreted by adipose tissue
• level is controlled by food intake
• leptin targets cells in hypothalamus
• causes hypothalamus in brain to inhibit appetite
• if amount of adipose tissue increases, blood leptin concentration rises

Question 41

explain how circulation of the blood to the lungs and to other systems is separated in human and what the advantages of this separation are (8)

Answer 41

• double circulation
• heart is a double pump
• deoxygenated blood pumped to the lungs and oxygenated to other organs
• each side of the heart has an atrium and a ventricle
• left ventricle pumps blood to the systems and right ventricle pumps blood to the lungs
• left atrium receives blood from the lungs and right atrium receives blood from systems/ tissues
• left ventricle pumps blood via the aorta and right ventricle pumps blood via the pulmonary artery
• left atrium receives blood via the pulmonary vein and right atrium receives blood via the vena cava
• lungs require lower pressure blood
• higher pressure required to pump blood to all systems
• pressure of blood returning from lungs not high enough to continue to other tissues
• oxygenated and deoxygenated blood kept separate

Question 42

explain the propagation of electrical impulses along a neuron including the role of myelin (7)

Answer 42

• neurotransmitter attaches to receptor site, initiating transmission
• nerve impulses are action potentials propagated along the axons of neurons
• resting potential is more negative inside the membrane
• bolted gated channels open and Na+ ions diffuse in
• causes depolarisation of the membrane
• local current affect adjacent channels
• depolarisation is followed by depolarisation of the neuron
• voltage gated channels open and K ions diffuse out/ depolarise the membrane
• Na-K pumps restore Na/ K balance
• myelin around the neuron insulates the axon
• myelin permits saltatory conduction/ permits jumping from node to node

Question 43

outline how carbon dioxide carried to the lungs in the pulmonary artery is moved to the air outside the body (7)

Answer 43

• carbon dioxide excreted by alveoli
• network of capillaries surrounds the alveolus wall
• diffusion of carbon dioxide
• carbon dioxide form the blood to air
• thin capillary walls shortens distance for diffusion
• high concentration of carbon dioxide in blood
• air from lungs passes out of body
• by ventilation
• due to lungs increase in pressure and decreasing in volume
• air flow from higher to lower pressure
• when diaphragm, external intercostal muscles recoil
• contraction of muscles in internal intercostal muscles
• air containing CO2 flows out through the bronchioles