Excretory System
Why is the urinary system considered the main excretory system, even though other organs eliminate waste?
Because it filters the blood directly to remove metabolic waste (urea, uric acid).
Why must alveoli be surrounded by capillaries?
To allow fast gas exchange between air and blood.
Why is the left ventricle more muscular than the right ventricle?
It pumps blood to the entire body, requiring higher pressure.
What is the difference between mechanical and chemical digestion?
Mechanical digestion crushes and mixes food; chemical digestion breaks molecules using enzymes.
What do we call the process of moving food down the oesophagus with wave-like motions?
Peristalsis
Describe the function of the nephron in one sentence.
It filters blood, reabsorbs useful substances, and forms urine.
Explain how the diaphragm and ribcage work together during inhalation.
Diaphragm contracts and moves down; ribcage expands—both increase thoracic volume so air enters.
Explain the difference between arteries and veins in structure and function.
Arteries have thicker walls for high-pressure blood leaving the heart; veins have thinner walls and valves to return low-pressure blood.
Why does the stomach need hydrochloric acid (HCl)? Give two reasons.
It kills bacteria and activates enzymes like pepsin to digest proteins.
What process brings oxygen into the blood and removes carbon dioxide?
Respiration/gas exchange.
In what part of the nephron does glomerular filtration occur, and what substances are filtered?
In Bowman’s capsule; water, salts, glucose, and urea are filtered.
Why does exhaled air contain more CO₂ and less O₂ than inhaled air?
Because cells use oxygen for respiration and produce carbon dioxide as waste.
What happens in the systemic tract and what happens in the pulmonary tract?
Systemic: sends oxygenated blood to organs; Pulmonary: exchanges CO₂ for O₂ in the lungs.
Explain why the small intestine is so long and has villi and microvilli.
To greatly increase surface area for maximum nutrient absorption.
What is the name of the liquid part of the blood?
Blood plasma.
Why can kidney failure be life-threatening?
Waste substances and toxins accumulate in the blood if the kidneys cannot filter them.
What would happen if the trachea did not have cartilage rings?
It could collapse, stopping air transport to the lungs.
Why is the circulatory system considered double, closed, and complete?
Double: two circuits; Closed: blood stays in vessels; Complete: oxygenated and deoxygenated blood never mix.
What three digestive juices act in the small intestine, and where is each produced?
Intestinal juice (intestine), bile (liver), pancreatic juice (pancreas).
What process transforms chyle into faeces?
Water and salt absorption in the large intestine.
Explain the full path of a urea molecule from its creation in the liver to its elimination.
Liver → bloodstream → kidneys → nephron → ureter → bladder → urethra → outside the body.
Describe the path of air from the outside of the body to the alveoli, naming at least six structures.
Nose → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.
Trace the path of a red blood cell from the left ventricle to the right atrium, naming at least five vessels or structures.
Left ventricle → aorta → arteries → capillaries (in organs) → veins → venae cavae → right atrium.
What transformation happens to food at each stage: mouth → stomach → small intestine → large intestine?
Mouth: food → bolus; stomach: bolus → chyme; small intestine: chyme → chyle; large intestine: chyle → faeces.
What is the name of the clear fluid carried by lymphatic vessels?
Lymph.