Biology Guide & Practice

1. Fundamentals & Definitions

• Human Disease: A condition that involves the malfunctioning or improper functioning of various body parts. It can be caused by factors like hormonal imbalance, genetic disorders, or malfunctioning of the immune system.
• Pathogen: A biological agent (microorganism) that causes disease or illness to its host.
• Vector: A living organism that transmits an infectious pathogen to another living organism. Examples include arthropods (mosquitoes, ticks, fleas, sandflies) and vertebrates (dogs, bats).
• Communicable Disease: An infectious disease that is transmissible from one person to another, either directly or indirectly.
• Non-Communicable Disease (NCD): Also known as a chronic disease, it is a non-infectious medical condition that tends to be of long duration. NCDs are the result of a combination of genetic, physiological, environmental, and behavioral factors.
• Transmission: The passing of a pathogen causing communicable disease from an infected host to a particular individual. The main routes are:
  • Air-borne Transmission: Pathogens remain suspended in the air (droplet nuclei) and are transmitted to individuals. Examples: Chickenpox, Influenza (Flu), Measles, Tuberculosis.
  • Contact Transmission: Pathogens spread through person-to-person contact (touching, kissing, sexual contact) or via placenta/blood. Examples: Herpes, AIDS, Syphilis.
  • Vehicle Transmission: Involves inanimate materials (fomites) like utensils, bedding, needles, food, or water that carry the pathogen. Examples: Cholera, Typhoid, Food Poisoning.
  • Vector-Borne Transmission: A living organism (vector) transmits the pathogen. For example, flies carrying bacteria or mosquitoes transmitting parasites.

2. Core Concepts & Classifications

Diseases Caused by Microbes (Communicable)

Protozoan Diseases

Viral Diseases

Bacterial Diseases

Fungal Diseases

Non-Communicable Diseases

Genetic & Chromosomal Disorders

• Turner Syndrome: A chromosomal disorder (44 + X) in females where one X chromosome is missing or partially missing, leading to developmental issues and infertility.
• Klinefelter Syndrome: A genetic condition in males caused by an extra X chromosome (44 + XXY), resulting in underdeveloped testes and infertility.
• Down's Syndrome: Caused by a full or partial extra copy of chromosome 21 (Trisomy 21). It leads to developmental and intellectual delays.
• Patau's Syndrome: A serious genetic disorder caused by an extra copy of chromosome 13 (Trisomy 13). It causes severe intellectual disability and physical defects.
• Color Blindness: A genetic inability to distinguish between certain colors, most commonly red and green. The gene is located on the X chromosome, making it more common in males.
• Haemophilia: A hereditary genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding.

Cancer

• Definition: A group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.
• Benign Tumor: A mass of cells that lacks the ability to invade neighboring tissue or metastasize. It is less harmful.
• Malignant Tumor (Cancer): Cells that grow uncontrollably and can spread from the original site (metastasize) to other parts of the body. It is more harmful.
• Leukemia: Cancer of blood-forming tissues, including bone marrow, resulting in a high number of abnormal white blood cells.
• Sarcoma: Cancer of connective tissues like bones, muscles, and cartilage.
• Oncology: The study and treatment of tumors (cancer).

Typical Exam Weightage

Human physiology (digestive, circulatory, nervous systems) and diseases are the most consistently tested Biology sub-areas.

Figures are typical ranges based on recent-year patterns, not a guarantee for any specific upcoming paper — always cross-check against the latest official syllabus and previous-year papers for Biology.