Gaseous Exchange & Excretion – Grade 11 Term 3 Core Content

A comprehensive set of question-and-answer flashcards covering key concepts of gaseous exchange and human excretory systems for Grade 11 Life Sciences revision.

What is the main difference between breathing and gas exchange?

Breathing is the physical movement of air into and out of the lungs, whereas gas exchange is the diffusion of O₂ and CO₂ across a gaseous-exchange surface.

Define cellular respiration.

A chemical process inside cells in which glucose and other food molecules are broken down to release energy.

List four requirements of an efficient gas-exchange surface.

Large surface area, thin surface, moist surface, and good ventilation (plus protection and transport system).

Why must a gas-exchange surface be thin?

To shorten the diffusion pathway and allow rapid diffusion of gases.

Which structures constitute the human ventilation system?

Nasal cavities, trachea, two bronchi, many bronchioles, two lungs, and respiratory muscles (diaphragm & intercostal muscles).

How do the hairs in the nasal cavities assist ventilation?

They filter out large particles from inhaled air.

What is the role of the turbinate bones in the nasal cavity?

They divide each cavity into passages that increase surface area for warming and moistening air.

State two functions of mucus in the respiratory tract.

Moistens incoming air and traps dust and germs (also antiseptic).

Why are the cartilage rings of the trachea C-shaped?

To keep the airway open while allowing the oesophagus to expand during swallowing.

What structural difference exists between bronchi and bronchioles?

Bronchi have O-shaped cartilage rings; bronchioles lack cartilage and have smooth muscle that alters airflow.

How do alveoli increase the efficiency of gaseous exchange?

They provide a vast, thin, moist surface surrounded by capillaries for rapid diffusion of gases.

Describe the role of the diaphragm during inhalation.

It contracts and flattens, increasing thoracic cavity volume and allowing lungs to expand.

Which phase of breathing is active and why?

Inhalation is active because it involves muscle contractions (external intercostals and diaphragm).

During exhalation, why does air flow out of the lungs?

Thoracic volume decreases, intrapulmonary pressure rises above atmospheric pressure, forcing air out.

Explain the diffusion gradient at the alveolar surface for oxygen.

Oxygen concentration is higher in alveolar air than in capillary blood, so O₂ diffuses into the blood.

How is most oxygen transported in the blood?

By combining with haemoglobin in red blood cells to form oxyhaemoglobin.

In what form is most carbon dioxide carried in the blood?

As bicarbonate ions (HCO₃⁻) in the plasma.

Define excretion.

The removal of metabolic waste products from the body.

Name the five human excretory organs.

Lungs, kidneys, liver, skin, alimentary canal.

What wastes are removed by the lungs?

Carbon dioxide and water vapour.

Identify the nitrogenous waste in urine and its origin.

Urea, produced in the liver by deamination of excess amino acids.

Which structure stores urine temporarily?

The urinary bladder.

What is the functional unit of the kidney?

The nephron.

Where do the renal artery and vein enter/leave the kidney?

At the hilum on the concave side of the kidney.

List the two main parts of a nephron.

Malpighian (renal) corpuscle and renal tubule.

What structures form the Malpighian body?

Bowman’s capsule and the glomerulus.

Why is blood pressure high in the glomerulus?

Because the afferent arteriole is wider than the efferent arteriole, creating resistance.

Define glomerular filtrate.

The fluid that passes from the blood into Bowman’s capsule, containing water, glucose, amino acids, salts and wastes but no large proteins or blood cells.

Where does most tubular reabsorption of glucose occur?

In the proximal convoluted tubule.

How is water reabsorbed in the descending loop of Henle?

Passively by osmosis due to a high salt concentration in the medulla.

State one substance actively secreted into the renal tubule during tubular excretion.

Hydrogen ions (others include potassium ions, creatinine, certain drugs).

What hormone controls water permeability of the distal convoluted tubule?

ADH (anti-diuretic hormone).

From which gland is ADH released?

The pituitary gland (hypophysis).

How does ADH respond to dehydration?

Its secretion increases, making tubules more permeable to water, so more water is reabsorbed and urine becomes concentrated.

Which hormone regulates blood sodium levels?

Aldosterone.

Where is aldosterone produced?

In the adrenal glands located atop the kidneys.

What effect does aldosterone have on the kidney tubules?

It increases reabsorption of sodium ions from the renal tubules into the blood.

Explain the role of podocytes in filtration.

Podocytes line Bowman’s capsule, with filtration slits that help form an ultrafine filter allowing plasma through but retaining cells and proteins.

Why are the lungs described as ‘spongy and elastic’?

Their tissue can expand and recoil, aiding ventilation.

Name the muscles located between the ribs and their role.

Intercostal muscles (external & internal); they contract/relax to raise or lower the rib cage during breathing.

How does the kidney respond when blood salt level rises?

Less aldosterone is secreted, resulting in reduced sodium reabsorption and increased excretion of excess salt.

What creates the sodium gradient in the medulla of the kidney?

Active pumping of sodium ions out of the ascending limb of the loop of Henle.

Why is the urine of a well-hydrated person usually dilute?

Low ADH levels make collecting ducts less permeable to water, so excess water stays in the filtrate and is excreted.

Give two components of sweat and their source.

Water and salts; both originate from excess intake and metabolic processes (small urea also included).