Y3 Bio chapter 7 Respiration

Q: What are the alternate names for IRV and ERV used in some slides/papers?

• Complemental air = Inspiratory Reserve Volume (IRV) — air that can be inspired forcibly beyond tidal volume

• Supplemental air = Expiratory Reserve Volume (ERV) — air that can be expired forcibly beyond tidal volume

• ⚠ If a question uses "complemental" or "supplemental air" instead of IRV/ERV, they mean the same thing — don't get thrown off by the terminology switch.

Q: By how much does carbon monoxide reduce the blood's oxygen-carrying capacity?

Carboxyhaemoglobin formation can reduce O₂-carrying capacity by ~15% — a specific figure worth quoting if a question asks for magnitude, not just direction of effect.

Q: Refined — KOH/limewater snail experiment, flask by flask.

• Flask A (KOH): absorbs CO₂ from air before it enters the system

• Flask B (limewater, before snails): stays clear — confirms no CO₂ is entering flask C from outside air

• Flask C: snails respiring

• Flask D (limewater, after snails): turns cloudy/milky — confirms CO₂ was produced by the snails

• (Flask E → suction pump, draws air through the whole system)

Q: Typical resting breathing rate used in the exercise experiment?

About 15 breaths per minute at rest is the typical reference value quoted in the pulmonary function test procedure — useful as a sanity-check figure if asked to interpret data.

🔹 Aerobic vs Anaerobic Respiration (TIER 1 — appears almost every year, MCQ + structured)

Q: Define respiration.

• Respiration = OXIDATION of food substances → release of energy in living cells

• ⚠ NOT breathing! Breathing = mechanical ventilation to supply O₂ — examiners trap this constantly.

Q: Compare aerobic and anaerobic respiration.

• Oxygen: Aerobic = presence of O₂ | Anaerobic = absence of O₂

• Energy: Aerobic = large amount of ATP | Anaerobic = comparatively small amount of ATP

• Breakdown: Aerobic = complete oxidation | Anaerobic = incomplete breakdown

• Fun fact: Aerobes are organisms which carry out aerobic respiration to oxidise glucose molecules and to produce ATP

• While anaerobes are organisms which carry out anaerobic respiration and do not require oxygen to produce ATP, MOST (not all) bacteria are anaerobes

Q: Write the word + balanced equation for aerobic respiration.

• glucose + O₂ → CO₂ + H₂O (+ ATP)

• C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

• Reaction occurs in the cytoplasm (glycolysis) & mitochondria

🔹 Fermentation (TIER 1 — classic "compare the two types" structured Q)

Q: State the 2 types of anaerobic respiration and their organisms.

1. Alcoholic fermentation → yeast (facultative anaerobe — can respire both aerobically and anaerobically)

2. Lactic acid fermentation → human muscle cells (under oxygen debt)

Q: Write the equation for alcoholic fermentation & state its significance.

• C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (ethanol + carbon dioxide)

• Incomplete breakdown of glucose → small amount of ATP → energy still stored in ethanol

• Importance: alcohol industry; baking industry (yeast → CO₂ bubbles raise dough)

Q: Write the equation for lactic acid fermentation & the ATP numbers involved.

• glucose → 2 pyruvic acid → 2 lactic acid

• 2 ATP required, 4 ATP produced = net 2 ATP per glucose

• ⚠ Common trap: students write "produces 4 ATP" — it's a NET of 2.

Q: Explain why lactic acid causes muscle fatigue during vigorous exercise.

• Vigorous exercise → O₂ demand > O₂ supply → muscles carry out anaerobic respiration under oxygen debt

• Glucose is partially oxidised → lactic acid produced as waste (energy still stored in it)

• Lactic acid is toxic at high concentrations → causes muscular fatigue, soreness/pain, stiffness

Q: ESSAY — Describe how oxygen debt is repaid.

1. Lactic acid removed from muscles → transported to liver

2. Liver oxidises some lactic acid to produce energy

3. This energy converts remaining lactic acid back to glucose

4. Glucose transported back to muscle → may be stored as glycogen

• 🧠 Mnemonic: "Liver Oxidises, Converts, Sends" (LOCS)

🔹 Respiration Experiments (TIER 2 — occasional structured/practical Q)

Q: KOH + limewater setup (snails) — purpose of each?

• Flask A (KOH): absorbs CO₂ from air before it enters the system

• Flask B (limewater, before snails): should stay clear — confirms no CO₂ is entering flask C from outside air

• Flask C: snails respiring

• Flask D (limewater, after snails): turns cloudy/milky → confirms CO₂ was produced by the snails

Q: Is CO₂ produced during fermentation? (glucose + yeast experiment)

1. Glucose solution boiled first → kills microorganisms already present, ensuring CO₂ produced is only from added yeast

2. Layer of oil → creates anaerobic environment for yeast (prevents O₂ entry), limits evaporation

3. Control: boiled glucose + oil, no yeast (or dead yeast) — no CO₂ produced, shows living yeast is needed

Q: Purpose of hydrogencarbonate indicator & colour changes?

• Detects CO₂ (respiration)

• CO₂ added → more acidic → turns YELLOW

• CO₂ removed → more alkaline → turns PURPLE

• Red = neutral/normal atmospheric CO₂

Q: Milton solution + cotton wool setup (heat production in pea seeds) — purpose of each?

• Milton solution → sterilises seeds, kills unwanted microorganisms → heat measured is only from seeds' own respiration

• Cotton wool plugs → allow O₂ diffusion in/out, maintain aerobic environment, limit heat loss

• Control (flask B): dead pea seeds in Milton solution — no respiration/heat, confirms temp rise in A is from living seeds

🔹 Respiratory System Structures (TIER 2 — labelling/fill-in-blank favourite)

Q: State the pathway of air from atmosphere to alveoli.

external nostril → nasal passages → pharynx → larynx (voice box) → trachea (sing. — NEVER "windpipe") → bronchi (sing. bronchus) → bronchioles → alveoli (sing. alveolus)

Q: Role of goblet cells and cilia?

• Goblet cells → produce mucus → traps dust/bacteria/foreign matter

• Cilia → hair-like structures → beat constantly → push mucus towards pharynx → swallowed or sneezed out

Q: Role of goblet cells and cilia?

1. Exchange O₂ (air↔blood, blood↔cells)

2. Exchange CO₂ (cells↔blood, blood↔air)

3. Regulate blood pH (also: vocalisation, protect alveoli via filtration)

Q: 3 ways air is "conditioned" before reaching alveoli.

1. Warmed to body temperature

2. Moistened — from mucous membrane

3. Filtered — dust/bacteria trapped by mucus, removed by cilia

Q: ESSAY — Describe the sequence of events during inspiration.

🔹 Breathing Mechanism — Inspiration (TIER 1 — essay favourite)

1. Diaphragm contracts and flattens

2. External intercostal muscles contract, internal intercostal muscles relax

3. Rib cage moves up and outwards; sternum moves up and forward

4. Volume of thoracic cavity increases

5. Air pressure in lungs decreases (below atmospheric)

6. Atmospheric pressure now higher than pressure in lungs → air is sucked/rushes into lungs

• 🧠 Mnemonic: D-I-R-T → Diaphragm → Intercostals → Ribcage → Thoracic volume ↑

• ⚠ Common error: writing "diaphragm relaxes" for inspiration — check contracts vs relaxes.

🔹 Breathing Mechanism — Expiration (TIER 1 — mirror-image essay Q)

Q: ESSAY — Describe the sequence of events during expiration.

1. Diaphragm relaxes and arches upward

2. Internal intercostal muscles contract, external intercostal muscles relax

3. Rib cage moves down and inwards; sternum returns to original position

4. Volume of thoracic cavity decreases

5. Lungs are compressed, air pressure inside increases

6. Air pressure in lungs now higher than atmospheric → air is forced out of lungs

• ⚠ Examiner trap: normal expiration at rest is PASSIVE. FORCED expiration needs active internal intercostal contraction — know the distinction.

🔹 Alveoli & Gas Exchange (TIER 1 — near-guaranteed essay)

Q: ESSAY — Explain how the alveoli are adapted for efficient gaseous exchange.

1. Millions of alveoli → large surface area for gaseous exchange

2. Walls covered with a layer of moisture (water) → gases dissolve before diffusing

3. Walls are only one cell thick → short diffusion distance → rapid diffusion

4. Richly supplied with capillaries → steep concentration gradient → increases diffusion rate

5. Walls contain elastic fibres → allow stretch/recoil during breathing

• ⚠ "Explain" not "state" → link structure → function (e.g. "thin walls SO THAT diffusion distance is short → faster diffusion").

Q: Pathway of oxygen from alveolus to red blood cell?

Alveolus (O₂ dissolves in moisture layer) → diffuses across alveolar wall → diffuses across capillary wall → dissolves in plasma → diffuses into RBC → combines with haemoglobin → oxyhaemoglobin

🔹 Gas Transport in the Blood (TIER 1 — often paired with circulatory/kidney essays)

Q: How is oxygen transported in the blood?

• 98% as oxyhaemoglobin: Hb + O₂ ⇌ HbO₂ (in RBCs)

• 2% dissolved directly in plasma

Q: How is CO₂ transported in the blood? (3 forms)

• ~70% as hydrogencarbonate ions (HCO₃⁻) in plasma: CO₂ + H₂O → H₂CO₃ (catalysed by carbonic anhydrase in RBC) → H⁺ + HCO₃⁻

• ~23% as carbaminohaemoglobin (Hb·CO₂)

• ~7% dissolved in plasma

• ⚠ Spell "carbonic anhydrase" correctly — commonly misspelled.

Q: Why does blood need haemoglobin instead of relying on dissolved O₂ alone?

O₂ has low solubility in plasma → Hb acts as an O₂ reserve/carrier → massively increases O₂ blood can carry to cells

🔹 Lung Volumes & Spirometer (TIER 2 — graph-reading Qs)

Q: Define tidal volume, IRV, ERV, vital capacity, residual volume.

• Tidal volume (TV) — air moved in/out with each normal breath

• Inspiratory reserve volume (IRV) / complemental air — extra air forcibly inspired beyond tidal inhale

• Expiratory reserve volume (ERV) / supplemental air — extra air forcibly expired beyond tidal exhale

• Vital capacity = TV + IRV + ERV — total air after deepest breath in, forced out

• Residual volume (RV) — air always remaining, even after strenuous expiration

Q: What does a spirometer measure and why?

Measures breathing rate, depth, lung volumes → evaluate respiratory/pulmonary function

Q: Effect of exercise on rate/depth of breathing — procedure?

1. Count breaths at rest for 1 min (or 3× 30 sec, avg — resting rate is typically ~15 breaths/min)

2. Person does vigorous exercise (e.g. 5 min running)

3. Count breaths in 30 sec periods over 10 min recovery, plot rate vs time

• Expected: rate/depth increase sharply, then decline back to resting rate as O₂ debt is repaid

🔹 Effects of Tobacco Smoke (TIER 1 — near-certain essay)

Q: 3 key harmful chemicals, properties, effects?

• Nicotine (addictive drug) → releases adrenaline → ↑heart rate & BP; blood clots more easily → ↑atherosclerosis risk

• Tar (contains carcinogens) → paralyses cilia → ↑risk of chronic bronchitis & emphysema

• Carbon monoxide (binds haemoglobin) → forms carboxyhaemoglobin → reduces O₂-carrying capacity by ~15% → ↑fatty deposits in arteries

• ⚠ It's CARBON MONOXIDE, not nicotine, that binds haemoglobin.

Q: ESSAY — Explain how smoking causes chronic bronchitis.

1. Irritants inflame epithelium lining airways

2. Excessive mucus secreted

3. Cilia paralysed → mucus/dust can't be removed

4. Airways blocked → breathing difficult

5. Persistent cough → higher risk of lung infections

Q: ESSAY — Explain how smoking causes emphysema.

1. Persistent violent coughing → destruction of alveoli walls

2. Reduced surface area for gas exchange

3. Lungs lose elasticity, inflated with trapped air

4. Result: difficulty breathing, wheezing, breathlessness

• 🧠 COPD = chronic bronchitis + emphysema

Q: How does smoking increase risk of heart attack/stroke?

• Nicotine → adrenaline → ↑heart rate/BP; blood clots more easily

• CO → ↓O₂ transport, damages arterial wall lining

• → atherosclerosis → narrowed arteries → clots block vessels → heart (heart attack) or brain (stroke)

Q: How does smoking affect pregnancy?

• Nicotine → narrows arteries → ↓blood flow to placenta → ↓nutrients to fetus

• Carbon monoxide → ↓O₂ reaching fetus via placenta

• Consequences: low birth weight, risk of miscarriage/stillbirth, impaired brain development