Biology: cell, human body, vitamins, blood groups and diseases

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The cell

• Robert Hooke first observed cells (in cork) in 1665. Robert Brown discovered the nucleus. Schleiden and Schwann proposed the cell theory.
• Prokaryotic cells (bacteria) have no true nucleus; eukaryotic cells have a membrane-bound nucleus.
• Largest single cell: ostrich egg. Longest cell in the human body: nerve cell (neuron).
• Human body cells have 46 chromosomes (23 pairs). Watson and Crick proposed the double-helix model of DNA (1953).

Human body systems

• Digestive: digestion begins in the mouth (salivary amylase). The stomach secretes HCl and pepsin. The liver, the largest gland, makes bile, stored in the gall bladder, which emulsifies fats. Most absorption happens in the small intestine through villi.
• Circulatory: the human heart has four chambers. William Harvey described blood circulation. Normal blood pressure is about 120/80 mm Hg. Red blood cells carry oxygen with iron-rich haemoglobin, are made in the bone marrow and live about 120 days. White blood cells fight infection; platelets help clotting.
• Respiratory: gas exchange takes place in the alveoli of the lungs.
• Nervous: the cerebrum is the largest part of the brain (thinking, memory); the cerebellum controls balance; the medulla oblongata controls involuntary actions such as breathing and heartbeat.
• Excretory: the kidneys filter blood; the nephron is their functional unit; urea is the main waste.
• Skeletal: an adult has 206 bones. Largest: femur (thigh). Smallest: stapes (ear).
• Endocrine: the pituitary is the “master gland”. The thyroid makes thyroxine (needs iodine). Insulin comes from the islets of Langerhans in the pancreas. Adrenaline is the “fight or flight” hormone.
• The largest organ of the body is the skin.

Vitamins and deficiency diseases

Mineral deficiencies: iron → anaemia; iodine → goitre. Protein deficiency causes kwashiorkor; protein-energy deficiency causes marasmus.

Blood groups

Karl Landsteiner discovered the ABO blood groups. The Rh factor was named after the rhesus monkey.

O negative is the universal donor; AB positive is the universal recipient.

Diseases and their causes

• Vectors: malaria – female Anopheles mosquito; dengue, chikungunya and yellow fever – Aedes; filariasis – Culex; kala-azar – sandfly; sleeping sickness – tsetse fly.
• Edward Jenner made the smallpox vaccine; Louis Pasteur the rabies vaccine; Jonas Salk the injected polio vaccine and Albert Sabin the oral one. BCG protects against tuberculosis.
• Alexander Fleming discovered penicillin (1928), the first antibiotic. Antibiotics act on bacteria, not viruses.

Quick check

1. Deficiency of which vitamin causes scurvy?
   Vitamin C (ascorbic acid).
2. Which blood group is the universal recipient?
   AB positive.
3. Malaria is caused by which type of organism?
   A protozoan, Plasmodium, spread by the female Anopheles mosquito.