Basic Biology: Cell Structure and Human Body Systems

📖 Cell structure and organelles

The cell is the basic structural and functional unit of life. Key organelles: the nucleus (houses genetic material, controls cell activities), mitochondria (the "powerhouse of the cell," generating ATP energy), the endoplasmic reticulum (protein and lipid synthesis/transport), the Golgi apparatus (packages and dispatches proteins), and ribosomes (site of protein synthesis). Cells are broadly classified as prokaryotic (no nucleus — bacteria) or eukaryotic (with a nucleus — plants, animals, fungi).

🫀 Human body systems

• Digestive system — breaks down food into absorbable nutrients (mouth → oesophagus → stomach → small/large intestine), with the liver and pancreas supplying digestive secretions.
• Circulatory system — the heart pumps blood through arteries (away from the heart) and veins (toward the heart), delivering oxygen and nutrients and removing waste.
• Endocrine system — glands (pituitary, thyroid, adrenal, pancreas) secrete hormones directly into the bloodstream to regulate metabolism, growth and other body functions.
• Nervous system — the brain and spinal cord (central nervous system) plus peripheral nerves coordinate the body's responses to internal and external stimuli.

💊 Vitamins and deficiency diseases

Vitamins are essential micronutrients, each linked to specific deficiency diseases: Vitamin A deficiency causes night blindness; Vitamin B1 (thiamine) deficiency causes beriberi; Vitamin C deficiency causes scurvy; Vitamin D deficiency causes rickets (children) and osteomalacia (adults); Vitamin K is essential for blood clotting.

🦠 Communicable vs non-communicable diseases, vaccines, and immunity

Communicable diseases spread from person to person (via pathogens like bacteria, viruses, fungi, or parasites) — examples include tuberculosis, influenza, and malaria. Non-communicable diseases (diabetes, hypertension, cancer) don't spread between people, typically arising from genetic, lifestyle or environmental factors. Vaccines work by training the immune system to recognise a pathogen without causing the disease itself, prompting the body to produce antibodies — proteins that specifically recognise and neutralise a matching antigen (any substance that triggers an immune response) on future exposure.