Gas Exchange In Humans, Smoking, Transport in unicellular vs multicellular

List the main structures of the thorax involved in breathing.

Ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli, pleural membranes, pleural fluid.

What is the role of the ribs and intercostal muscles in ventilation?

External intercostals contract → ribs move up/out → inhalation.
Internal intercostals contract during forced exhalation (coughing/exercise).

Describe the role of the diaphragm during ventilation.

Contracts and flattens during inhalation → increases thoracic volume → draws air in.
Relaxes during exhalation → rises to dome shape → reduces thoracic volume.

What are the pleural membranes and why are they important?

Two thin membranes surrounding lungs. Pleural fluid reduces friction and maintains a sealed, low‑pressure cavity. If punctured → lung collapses (pneumothorax).

How are alveoli adapted for gas exchange?

Huge surface area, one-cell thick walls, moist lining, elastic fibres, dense capillary network, constant ventilation → steep diffusion gradients.

Why do alveoli contain elastic fibres?

Elastic recoil helps force air out during exhalation. Loss of elasticity (e.g., emphysema) reduces airflow and gas exchange.

How are steep concentration gradients maintained in the lungs?

Ventilation refreshes alveolar air; blood flow removes oxygen and brings CO₂. This keeps alveolar O₂ high and capillary O₂ low (and vice versa for CO₂).

What is the difference between ventilation and respiration?

Ventilation = movement of air in/out of lungs.
Respiration = chemical reaction in cells releasing energy.

How does smoking damage cilia?

Tar paralyses and destroys cilia; goblet cells produce excess mucus; mucus cannot be cleared → infections and persistent cough.

What is chronic bronchitis and how does smoking cause it?

Inflammation of bronchi due to mucus build‑up (cilia destroyed). Airways narrowed, increased infections, chronic cough due to needing to manually clear mucus.

What happens in emphysema?

Alveolar walls break down → reduced SA for gas exchange. Loss of elasticity traps air in lungs. Causes breathlessness and low oxygen levels.

How does carbon monoxide from cigarettes affect the body?

Binds to haemoglobin (carboxyhaemoglobin) irreversibly → reduces oxygen transport → heart works harder.

How does nicotine affect the cardiovascular system?

Raises heart rate and blood pressure, constricts blood vessels, increases risk of blood clot formation.

Why does smoking increase the risk of coronary heart disease?

CO reduces O₂ to heart; toxins damage artery walls → atherosclerosis; nicotine raises BP; blood clots can block coronary arteries → heart attack.

How does tar cause lung cancer?

Contains carcinogens that mutate epithelial DNA → uncontrolled cell division → tumour formation.

Why do smokers develop a persistent cough?

Cilia destroyed → mucus accumulates → coughing is the only way to clear it → damages alveoli further.

What is bronchoconstriction and how is it linked to smoking?

Smoke irritants cause smooth muscle in bronchioles to contract → narrowing airways → difficulty breathing.

What does hot cigarette smoke do to the airway lining?

Damages epithelial cells, dries out mucus layer, increases infection risk.

Why does smoking increase susceptibility to lung infections?

Cilia destroyed → pathogens trapped in mucus aren't removed → bacteria multiply.

Why does breathing rate increase during exercise?

Muscles require more O₂ for aerobic respiration; need to remove CO₂ more quickly → increased breathing rate and tidal volume.

Why do athletes have a lower resting heart rate?

Stronger stroke volume and more mitochondria in muscle → more efficient aerobic respiration → less oxygen needed at rest.

Why can unicellular organisms rely on diffusion alone?

High SA:V ratio, low metabolic demand, short diffusion distance, entire surface is close to environment.

Why do multicellular organisms need transport systems?

Low SA:V ratio → diffusion too slow. High metabolic demand. Internal cells far from environment. Need circulatory system + exchange organs.

How does SA:V ratio affect transport?

Larger organisms have smaller SA:V → slower exchange → require specialised systems for oxygen, nutrients, waste removal.

Name specialised exchange surfaces in humans.

Lungs (gas exchange), small intestine (nutrients), kidneys (waste filtration), skin (limited exchange).

What is surfactant and why is it important?

A substance produced in alveoli that reduces surface tension and prevents alveoli from collapsing during exhalation.

Why do premature babies struggle to breathe?

Insufficient surfactant → alveoli collapse → respiratory distress syndrome.

What is residual volume?

The air left in lungs after maximum exhalation; prevents alveoli from collapsing and maintains diffusion even between breaths.

What is a pneumothorax?

When air enters pleural cavity → disrupts low‑pressure environment → lung collapses.

Why is the trachea supported by cartilage rings?

Prevents trachea from collapsing during pressure changes in breathing.