Human Biology – Digestion, Transport, Respiration & Excretion

A comprehensive set of question-and-answer flashcards covering key concepts from Chapters 5–8 on human digestion, circulation, respiration, and excretion.

What two main parts make up the human digestive system?

The alimentary canal and the associated digestive organs.

What is mechanical (physical) digestion in the mouth?

Chewing by teeth to break food into smaller pieces, increasing surface area : volume ratio.

Which enzyme is present in saliva and what does it do?

Salivary amylase; it breaks starch into maltose.

What is peristalsis and where does it occur?

Rhythmic, wave-like muscular contractions that propel food; in oesophagus, stomach, small and large intestines.

Name the two main components of gastric juice and their functions.

Hydrochloric acid (provides acidic pH) and pepsin (protease that digests proteins into polypeptides).

Where is bile produced, stored, and what is its digestive role?

Produced by the liver, stored in the gall bladder, and emulsifies fats into tiny droplets.

List the three enzymes in pancreatic juice.

Trypsin, pancreatic amylase, and pancreatic lipase.

Which intestinal enzymes complete carbohydrate digestion?

Sucrase, lactase, and maltase.

Where does most absorption of digested nutrients occur?

In the small intestine (particularly the ileum).

Give two structural adaptations of the small intestine that increase surface area.

Numerous folds with villi, and microvilli on epithelial cells of villi.

What is the function of a lacteal in a villus?

It absorbs fat globules (re-formed from glycerol and fatty acids).

Which nutrients enter blood capillaries of a villus?

Glucose, amino acids, water, and mineral salts.

What does the hepatic portal vein transport and to where?

Blood rich in glucose and amino acids from the small intestine to the liver.

Define assimilation.

Conversion of absorbed food molecules into new protoplasm or their use to provide energy.

Into what storage molecule is excess glucose converted in the liver?

Glycogen.

What waste product results from deamination of excess amino acids in the liver?

Urea.

State four functions of the liver other than bile production.

Regulates blood glucose, deaminates amino acids forming urea, stores iron from haemoglobin breakdown, detoxifies substances such as alcohol.

Give two harmful effects of excessive alcohol consumption on the liver.

Cirrhosis and increased risk of haemorrhage/liver failure.

Name the three main parts of the human circulatory system.

Heart, blood vessels (arteries, veins, capillaries), and blood.

What is double circulation?

Blood passes through the heart twice per complete body circuit – pulmonary and systemic circulations.

Describe pulmonary circulation in one sentence.

The right heart pumps deoxygenated blood to lungs; blood becomes oxygenated and returns to the left heart.

Why is the left ventricle’s wall thicker than the right?

It must pump oxygenated blood at higher pressure to all parts of the body.

What is the role of the heart’s septum?

A muscular wall preventing mixing of oxygenated and deoxygenated blood.

Trace the main path of blood through the heart starting at the body.

Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta → body.

Name the three major stages of one cardiac cycle.

Atrial systole, ventricular systole, cardiac diastole.

State one structural difference between arteries and veins.

Arteries have thick muscular/elastic walls and small lumens; veins have thinner walls, larger lumens, and valves.

Why do veins possess semi-lunar valves?

To prevent backflow of low-pressure blood toward capillaries.

What happens to tissue fluid at capillaries?

Nutrients and O₂ diffuse from blood to cells; wastes like CO₂ and urea diffuse from cells to blood.

How is a red blood cell adapted for oxygen transport?

Biconcave shape increases SA : V ratio and the cell lacks a nucleus to hold more haemoglobin.

Differentiate phagocytes and lymphocytes.

Phagocytes ingest pathogens; lymphocytes produce antibodies that inactivate or destroy pathogens.

What triggers blood clot formation?

Damaged tissues and platelets release enzymes converting fibrinogen to fibrin, trapping blood cells.

Which blood group is the universal donor and why?

Group O; its red cells lack A or B antigens, so they do not agglutinate with any recipient antibodies.

Define atherosclerosis.

Build-up of fatty deposits in arterial walls, narrowing the lumen.

List two lifestyle changes that reduce coronary heart disease risk.

Diet low in saturated fats/cholesterol and regular physical exercise (others include quitting smoking, stress management).

Write the balanced equation for aerobic respiration in humans.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy).

Give the equation for anaerobic respiration in human muscles.

Glucose → lactic acid (+ small amount of energy).

What is oxygen debt?

The extra oxygen required after exercise to oxidise accumulated lactic acid.

Name three structures that air passes through from nose to alveoli.

Nasal passage → trachea → bronchi → bronchioles → alveoli.

State two features of alveoli that aid gas exchange.

One-cell-thick walls and large total surface area due to numerous alveoli.

What is the function of cilia in the trachea?

They sweep mucus and trapped particles up to the pharynx for removal.

Explain how the diaphragm moves during inspiration.

It contracts and flattens, increasing thoracic volume and drawing air into lungs.

Compare oxygen and carbon dioxide percentages in inspired vs expired air.

Expired air has less O₂ (~16%) and more CO₂ (~4%) than inspired air (21% O₂, 0.04% CO₂).

Name two toxic components of tobacco smoke and one effect of each.

Nicotine – increases heart rate and blood pressure; Carbon monoxide – forms carboxyhaemoglobin, reducing O₂ transport.

How does excretion differ from defaecation?

Excretion removes metabolic wastes like CO₂, urea; defaecation removes mainly undigested food residue.

Match the excretory product to its main organ of removal: urea, carbon dioxide, bile pigment.

Urea – kidneys; Carbon dioxide – lungs; Bile pigment – liver/intestines (in faeces).

Name the two main processes during urine formation.

Ultrafiltration and selective reabsorption.

Where does ultrafiltration occur within the nephron?

In the glomerulus into the Bowman’s capsule.

How does ADH affect urine concentration?

ADH increases collecting-duct permeability to water, leading to more water reabsorption and concentrated, smaller-volume urine.

What is osmoregulation?

Control of blood water potential and solute concentration to maintain internal balance (homeostasis).

Briefly describe how a dialysis machine removes wastes.

Patient’s blood flows through semi-permeable tubing bathed in dialysis fluid; wastes and excess salts diffuse into the fluid, while essential substances remain in blood.