General Science & Environment

Syllabus Unit: General Ability Test (GAT)

Why it matters

Chapter overview

General Science & Environment spans human body systems and health, nutrition and both communicable and non-communicable diseases, ecological concepts like food chains and nutrient cycling, and current space/environmental technology (India's ISRO missions, atmospheric layers, renewable energy) — the broadest and most current-affairs-adjacent science unit in the GAT.

Mathematics & General Ability General Ability Test (GAT) 60% weightage

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1Right atrium receives bloodDeoxygenated blood arrives from the body

2Pumped to the lungsPulmonary circulation picks up oxygen, releases CO2

3Left atrium receives bloodOxygenated blood returns from the lungs

4Left ventricle pumps to the bodySystemic circulation delivers oxygen everywhere

1The Human Body & Health

The body's major organ systems each run one essential process, and understanding what each system does explains most of NDA's human-biology questions.

Learning Objectives

Name the major organ systems (digestive, circulatory, respiratory, excretory, nervous) and their primary function.
Trace the path of blood through the heart's four chambers and describe pulmonary vs systemic circulation.
Describe the basic digestive pathway and the role of key digestive organs.
Identify common lifestyle diseases (diabetes, hypertension) and their basic causes.

Key Terms

Circulatory SystemThe heart and blood vessels that transport blood, oxygen and nutrients around the body.

Systemic CirculationBlood flow from the heart's left ventricle to the body and back to the right atrium, delivering oxygen.

Pulmonary CirculationBlood flow from the heart's right ventricle to the lungs and back to the left atrium, for oxygenation.

Diabetes MellitusA metabolic disorder where the body cannot properly regulate blood glucose, due to insufficient insulin (Type 1) or insulin resistance (Type 2).

The human body runs on a handful of major organ systems, each responsible for one essential process — together they keep the body alive, moving and coordinated.

Major organ systems at a glance

Digestive — breaks food into absorbable nutrients (mouth to intestines).
Circulatory — heart and vessels transport blood, oxygen and nutrients.
Respiratory — lungs exchange O2 and CO2 with the blood.
Excretory — kidneys filter blood and remove nitrogenous waste as urine.
Nervous — brain, spinal cord and nerves coordinate the body's responses.

The heart and circulation

The heart has 4 chambers — 2 atria (receive blood) and 2 ventricles (pump blood out). Deoxygenated blood from the body enters the right atrium, is pumped to the lungs (pulmonary circulation) to pick up oxygen, returns to the left atrium, and is pumped from the left ventricle to the whole body (systemic circulation).

Key PointThe left ventricle has the thickest muscular wall of all 4 chambers because it must generate enough pressure to pump blood to the entire body.

Digestion in brief

Mouth — salivary amylase begins starch digestion.
Stomach — pepsin and HCl digest proteins.
Small intestine — main site of digestion (bile, pancreatic enzymes) and nutrient absorption.
Large intestine — absorbs water, forms waste.

Lifestyle diseases

Diabetes (high blood glucose from insufficient or ineffective insulin) and hypertension (persistently high blood pressure) are the most commonly tested lifestyle diseases, both linked to diet, obesity and inactivity.