Gaseous Exchange, Electricity & Pathogenic Diseases: 18 MCQs with answers

Alveoli

The alveoli are the tiny balloon-like sacs at the end of the bronchioles where oxygen diffuses into the blood and carbon dioxide diffuses out. The trachea, bronchi and bronchioles are only conducting airways.

Diffusion from higher to lower concentration

Inhaled air is rich in oxygen while blood arriving at the alveoli is oxygen-poor, so oxygen simply diffuses down its concentration gradient. No energy or pump is required for the gases themselves.

The diaphragm contracts and flattens.

During inhalation the diaphragm contracts and flattens while the ribs move up and out. Chest volume increases, pressure inside drops below atmospheric pressure, and air rushes in.

Ampere

Current is the rate of flow of electric charge and is measured in amperes (A). Volts measure potential difference and ohms measure resistance.

No current flows because the circuit is not closed.

A circuit must be closed for current to flow. An open switch breaks the path, so no charge can move and the bulb does not light.

Vitamin

Pathogens are disease-causing organisms and include bacteria, viruses, fungi and protozoa. A vitamin is a nutrient, not an organism, so it cannot be a pathogen.

True

The alveoli provide a combined surface area roughly the size of a tennis court, which is essential for efficient gaseous exchange.

Haemoglobin inside red blood cells

Oxygen binds to haemoglobin inside red blood cells to form oxyhaemoglobin, which lets blood carry far more oxygen than water alone. Bicarbonate is the main carrier of carbon dioxide, not oxygen.

It doubles.

From Ohm's law, $V = I \times R$, so $I = V/R$. With resistance fixed, doubling $V$ doubles $I$.

Series, because there is only one path for current.

In a series circuit there is only one path for current, so breaking any component stops current everywhere. In a parallel circuit the other branches would keep working.

A is false and R is true.

The assertion is wrong because breathing and respiration are different processes. The reason is correct: breathing is mechanical air movement, while respiration is the chemical release of energy inside cells.

A pathogenic disease spread by a vector

A pathogen transmitted by an insect such as a mosquito makes this a pathogenic (communicable) disease spread by a vector. Malaria and dengue are classic examples.

It shortens the diffusion distance for gases.

Diffusion is faster over short distances. A one-cell-thick wall means oxygen and carbon dioxide cross in the shortest possible path, which is essential for efficient gaseous exchange.

The rooms are wired in parallel, so each branch has its own path.

Household wiring uses parallel circuits so each branch has an independent path. If one branch fails, the others still have a complete path and keep working.

I and II only

Statements I and II are correct. Statement III is wrong: in a series circuit the voltage is shared across components, not the same across each one.

Providing clean drinking water and safe food handling

A water-borne disease spreads through contaminated water and food, so clean drinking water and safe food handling attack the route of transmission directly. Nets target vectors and vaccination targets specific pathogens, not the water route.

The concentration gradient for oxygen diffusion is reduced, leading to decreased oxygen uptake.

The correct option is B. The presence of fluid in the alveoli reduces the concentration gradient for oxygen diffusion, as the oxygen concentration in the alveoli decreases, leading to decreased oxygen uptake into the blood.

The current increases proportionally to the increase in voltage.

The correct option is C. According to Ohm's law ($V = I imes R$), if the voltage ($V$) is increased while resistance ($R$) remains constant, the current ($I$) must increase proportionally.