BIOLOGY

PRERNA FOR IAS

         Mehnat Aapki, Guidance Humari

         Roz ki Prelims Practice — Experts ke Saath

BIOLOGY

Lymphatic System

The lymphatic system is an important part of the human circulatory and immune systems. It maintains fluid balance by collecting excess tissue fluid and returning it to the bloodstream, preventing swelling. The system consists of lymph, lymphatic vessels, lymph nodes, spleen, thymus, and tonsils. Lymph nodes filter harmful microorganisms, while white blood cells destroy bacteria, viruses, and other pathogens. The spleen filters blood and supports immunity, the thymus matures T-lymphocytes, and the tonsils protect the body from germs entering through the mouth and nose. Overall, the lymphatic system plays a vital role in immunity, infection control, and maintaining body fluid balance.

Small Intestine

The small intestine is the longest part of the digestive system and the primary site for chemical digestion and nutrient absorption. It is divided into three parts: the duodenum, which receives bile and pancreatic enzymes for digestion; the jejunum, where most nutrients are absorbed; and the ileum, which absorbs bile salts and vitamin B₁₂. Its inner lining contains circular folds, villi, and microvilli, greatly increasing the surface area for absorption. Nutrients enter the blood or lymph through capillaries and lacteals. Movements like segmentation and peristalsis mix and propel food. Disorders include celiac disease, Crohn’s disease, lactose intolerance, and intestinal obstruction.

Gene

A gene is the basic unit of heredity and consists of a specific sequence of DNA located at a fixed position (locus) on a chromosome. Genes carry the instructions needed to produce proteins or functional RNA molecules, which control the structure and activities of cells. Most genes contain promoters, exons, and introns. During gene expression, DNA is transcribed into RNA, followed by translation into proteins. Different forms of the same gene are called alleles, which influence inherited traits. Changes in DNA, known as mutations, may be beneficial, harmful, or neutral. Genes determine characteristics, support growth, regulate body functions, and pass hereditary information from parents to offspring.

Cranial Nerves

The cranial nerves are 12 pairs of nerves that arise directly from the brain and brainstem. They control sensory, motor, and autonomic functions of the head, neck, and some internal organs. Their functions include smell (I), vision (II), eye movements (III, IV, VI), facial sensation and chewing (V), facial expression and taste (VII), hearing and balance (VIII), swallowing and taste (IX), control of the heart, lungs and digestive organs through the vagus nerve (X), shoulder and neck movement (XI), and tongue movement (XII). Cranial nerves are essential for communication between the brain and body, supporting movement, sensation, reflexes, speech, and vital life functions.

Probiotics