chapter 10 respiration in humans

Question 1

what is aerobic respiration (definition, waste products, occurs where, eqn)

Answer 1

breakdown of food molecules in the presence of oxygen with the release of a large amount of energy
→ waste products: CO2 and water
→ mitochondria perform AR by oxidising food molecules to release energy -> more mitochondria = more AR carried out
→ eqn: C6H12O6 (glucose)+ 6 O2 –> 6CO2 + 6H2O + energy

Question 2

what is anaerobic respiration (definition, waste products, occurs where, eqn)

Answer 2

breakdown of food molecules in the absence of oxygen - release less energy than in AR
→ ANR in humans: lactic acid is a product
→ occurs in the cell’s cytoplasm
→ eqn (for ANR in humans): C6H12O6 2 C3H6O3 (lactic acid) + energy
→ ANR in yeast (alcoholic fermentation): C6H12O6 –> 2 C2H5OH (ethanol) + 2 CO2 + energy

Question 3

how can exercise affect AR

Answer 3

1. during exercise, (skeletal) muscles contract vigorously = requires more energy
2. breathing rate increase: take in more oxygen 3. heart rate increase: more glucose and oxygen (required in AR) is transported by blood to muscle cells
3. increase in rate of AR = release more energy

Question 4

how can exercise affect ANR

Answer 4

1. energy needed for muscle contractions may be too much
2. oxygen demand > oxygen supply = muscles incur oxygen debt
3. ANR takes place in absence of oxygen to release the extra energy needed

Question 5

effect of oxygen debt

Answer 5

ANR produces lactic acid = accumulation of lactic acid in muscle cells may cause fatigue and muscle soreness

Question 6

repaying back of oxygen debt

Answer 6

1. lactic acid from muscles is gradually removed and transported to liver
2. breathing and heart rate has to remain fast for some time = provide sufficient oxygen to muscle cells to repay OD

Question 7

fully repaid oxygen debt + fate of lactic acid (4)

Answer 7

Fate of lactic acid:
1. some lactic acid oxidised in liver to release energy
2. energy used to convert the remaining lactic acid into glucose = glucose is transported back to muscles
3. excess glucose is converted to glycogen (stored in liver)
4. breathing + heart rate back to normal

Fully repaid OD: all lactic acid converted to glucose/fully removed

Question 8

structure of nose and their functions

Answer 8

structure: walls of nostrils have a fringe of hairs + lead into nasal passages that are covered with moist mucous membrane
1. Dust and foreign particles (including bacteria) present in inhaled air trapped by nose hairs and mucus in mucous membrane
2. Air that passes through nasal passages is warmed and moistened

Question 9

structure of trachea

Answer 9

1. supported by C-shaped rings of cartilage = keeps lumen of trachea open (no breathlessness)
2. membrane next to lumen of trachea is epithelium (consists of 2 types of cells)

Question 10

what are the cells that make up the epithelium in trachea (2)

Answer 10

1. Gland cells: secrete (produce + release) mucus to trap dust particles and bacteria
2. Ciliated cells: have hair like structures on their surfaces called cilia = sweep dust trapped mucus up trachea towards larynx
   - if downwards towards lungs, mucus may enter lungs = may accumulate, inflaming bronchus

Question 11

how does gaseous exchange occur in alveoli (7)

Answer 11

1. blood enters lungs by pulmonary artery: high conc of CO2 + low conc of O2
2. air entering lungs has low conc of CO2, + high conc of O2
3. concentration gradient of O2 and CO2 between blood and alveolar air is created
4. oxygen dissolves in thin film of moisture,
5. oxygen diffuses down concentration gradient from alveolar air into blood capillaries
6. Carbon dioxide diffuses down concentration gradient from blood capillaries to alveolar air
7. blood leaving the lung/blood capillary of pulmonary vein is oxygenated

Question 12

how is oxygen transported in RBCs (3)

Answer 12

1. in the blood capillaries, oxygen combines with haemoglobin in RBCs = forms oxyhaemoglobin (reversible reaction)
2. if O2 conc is high (eg cells in lungs): oxyhaemoglobin is formed
3. if O2 conc is low (eg blood passes through oxygen-poor tissues): oxyhaemoglobin releases the oxygen = diffuse through walls of blood capillaries into the tissue cells

Question 13

how is CO2 transported in RBCs (7)

Answer 13

1. conc of CO2 in tissues is higher than blood passing thru the tissues (CO2 is a waste product of tissue respiration) = CO2 diffuses from tissue cells into blood down conc gradient = CO2 enter RBCs
2. carbonic anhydrase present in RBCs catalyses conversion of carbon dioxide and water in RBCs to form carbonic acid =
3. carbonic acid dissociates into hydrogencarbonate (HCO3-) ions
4. HCO3- ions diffuse out of RBCs into blood plasma + small amount of CO2 also carried and dissolved in RBC = most of CO2 is carried as HCO3- ions in blood plasma
5. RBC reaches the blood capillary around the alveoli in the lungs = hydrogencarbonate ions diffuse back into RBCs = converted back into carbonic acid
6. carbonic anhydrase catalyses conversion of carbonic acid back into carbon dioxide and water
7. carbon dioxide diffuses out of blood capillaries into the alveoli = expelled when exhaled

Question 14

adaptations of 1 alveolus (increase rate of diffusion of gases) (3)

Answer 14

1. Alveolar walls and associated capillary walls are one cell thick: provides a short diffusion distance for gases = higher rate of diffusion for exchange of gases
2. thin film of moisture present on inner surface of the alveolus wall: allows oxygen to dissolve in it and diffuse into the capillaries;
3. Alveoli are well supplied with a dense network of blood capillaries: continuous flow of blood = maintains steep concentration gradients of gases (i.e. oxygen and carbon dioxide) = increase rate of diffusion of gases

Question 15

adaptation present in alveoli

Answer 15

Numerous alveoli present in lungs:
provide a large surface area to volume ratio for gaseous exchange of oxygen and carbon dioxide by diffusion = increase rate of gaseous exchange

Question 16

how do humans inhale (6)

Answer 16

1. muscles of diaphragm (DM) contract, diaphragm flattens down
2. external intercostal muscles (EIM) contract, internal intercostal muscles (IIM) relax
3. ribcage moves upwards and outwards, sternum moves up and forward
4. lungs expand = volume of thoraic cavity increases
5. air pressure in lungs decrease
6. atmospheric pressure (AtmP) exceeds air pressure in lungs (LP)
7. AtmP is forced into lungs -> pressure moves from a region of higher to lower pressure

Question 17

how do humans exhale (7)

Answer 17

muscles of diaphragm (DM) relax, diaphragm arches upwards
→ external intercostal muscles (EIM) relax, internal intercostal muscles (IIM) contract
→ ribcage moves downwards and inwards, sternum moves down to original position
→ lungs compress = volume of thoraic cavity decrease
→ air pressure in lungs increase -> LP exceeds AtmP
→ air is forced out of lungs into atmosphere -> pressure moves from a region of higher to lower pressure

Question 18

what are the differences between exhaled and inhaled air (4)

Answer 18

1. Exhaled air has a higher concentration of water vapour than inhaled air: during exhalation, thin film of moisture on alveolar surface evaporates = present as water vapour in exhaled air
2. Exhaled air has a lower concentration of oxygen than inhaled air: aerobic respiration uses up oxygen = less oxygen in exhaled air
3. Exhaled air has higher concentration of carbon dioxide than inhaled air than inhaled air: aerobic respiration releases carbon dioxide = more carbon dioxide in exhaled air
4. Exhaled air has a temperature nearer to body temperature: aerobic respiration oxidises glucose, releasing energy = some energy is converted to heat = temp of exhaled air is higher/closer to body temp than inhaled air

Question 19

how does nicotine affect us (2)

Answer 19

1. makes blood clot easily/increase risk of blood clots = blood clots may block/narrow the arteries = increase risk of coronary heart disease
2. addictive drug that causes the release of hormone adrenaline= increase heartbeat rate and blood pressure (BP)

Question 20

how does carbon monoxide affect us (2)

Answer 20

Carbon monoxide
1. combines with haemoglobin to form carboxyhaemoglobin = reduces ability of blood to carry oxygen = reduce O2 supply to cells = lowering rate of aerobic respiration in cells
2. increases fatty deposits on the inner arterial wall = increases risk of coronary heart disease OR fatty deposits narrow/block of the lumen of arteries = BP increases

Question 21

how does tar affect us (2)

Answer 21

Tar
1. causes uncontrolled cell division = increases risk of cancer in lungs
2. paralyses cilia lining the air passages = mucus cannot be swept up towards larynx = mucus may accumulate in trachea/bronchus = increase risk of bronchitis and emphysema -> have difficulty with breathing = less oxygen supplied to cells

Question 22

how do irritants affect us

Answer 22

paralyses cilia lining the air passages = mucus **cannot be swept up towards larynx = mucus may accumulate in trachea/bronchus = increase risk of bronchitis and emphysema -> have difficulty with breathing = less oxygen supplied to cells

Question 23

how is chronic bronchitis caused and what is its effects

Answer 23

Cause: epithelium of airways become inflamed -> epithelium secretes excessive mucus + cilia becomes paralysed (tar and irritants) = mucus cannot be swept up = airways are blocked
Effects: difficulty in breathing -> persistent coughing to clear airways/breathe = increases risk of lung infections

Question 24

how is emphysema caused and what is its effects

Answer 24

Cause:
1. persistent and violent coughing due to bronchitis (tar and irritants) = partition walls between alveoli break down = decreased surface area for gaseous exchange +
2. lungs also lose elasticity and become inflated with air = lungs cannot take in as much air

Effect: difficulty with breathing = wheezing and severe breathlessness