Life Sciences (Biology) — Railway Group D Study Notes
Overview
Life Sciences (Biology) is a scoring segment in the General Science section of Railway Group D exams, typically contributing 6–10 questions out of the 25 General Science questions. This topic tests your understanding of living organisms, their structure, function, classification and interactions with the environment. Questions are fact-based and drawn from NCERT Class 9–10 Biology, so mastering core concepts from cell biology, human physiology, plant biology, heredity and ecology is essential.
Most questions are direct recall: "What is the powerhouse of the cell?" or "Which vitamin deficiency causes scurvy?" A smaller number require application: linking cause-effect in diseases or ecological relationships. The good news is that Biology does not require calculations; the challenge is memorizing classification schemes, organ systems, disease-pathogen pairs and nutrient-deficiency links. Consistent revision with mnemonics and tabular summaries will give you an edge in this predictable, high-yield section.
Key Concepts
**Cell as the unit of life**: All living organisms are made of cells. Prokaryotic cells (bacteria) lack a nucleus; eukaryotic cells (animals, plants, fungi) have a membrane-bound nucleus and organelles like mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus and lysosomes.
**Five-kingdom classification**: Organisms are grouped into Monera (bacteria), Protista (algae, protozoans), Fungi (yeasts, moulds), Plantae (mosses to flowering plants) and Animalia (sponges to mammals). This classification is based on cell structure, mode of nutrition and body organization.
**Photosynthesis and respiration**: Green plants synthesize glucose from CO₂ and water using sunlight (photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂). All cells release energy by breaking down glucose in the presence of oxygen (aerobic respiration) or without it (anaerobic respiration/fermentation).
**Human organ systems**: The body has digestive, circulatory, respiratory, excretory, nervous, endocrine, reproductive, skeletal and muscular systems working in coordination. For example, the heart pumps oxygenated blood via arteries to tissues, and deoxygenated blood returns via veins to the lungs.
**Heredity and DNA**: Traits pass from parents to offspring through genes located on chromosomes in the nucleus. DNA (deoxyribonucleic acid) is the hereditary material. Gregor Mendel's experiments with pea plants established the laws of inheritance (dominance, segregation, independent assortment).
**Evolution**: Species change over time through natural selection (Charles Darwin). Fossils, comparative anatomy and molecular biology provide evidence. Humans (Homo sapiens) evolved from common ancestors shared with other primates over millions of years.
**Nutrition and deficiency diseases**: Balanced diet includes carbohydrates, proteins, fats, vitamins, minerals, water and roughage. Lack of specific nutrients causes diseases: vitamin A → night blindness, vitamin C → scurvy, vitamin D → rickets, iodine → goiter, iron → anemia.
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Which of the following is known as the 'powerhouse of the cell'?
Q2 · Life Sciences (Biology) · EASY
In humans, the normal number of chromosomes in a diploid cell is:
Q3 · Life Sciences (Biology) · MEDIUM
Which vitamin deficiency causes the disease 'Scurvy'?
Q4 · Life Sciences (Biology) · MEDIUM
The process by which green plants prepare their own food using sunlight, carbon dioxide, and water is called:
Q5 · Life Sciences (Biology) · HARD
According to the five-kingdom classification system, organisms that are unicellular and lack a well-defined nucleus are placed in which kingdom?
Notes generated on 10 May 2026
**Ecology and ecosystems**: An ecosystem comprises biotic (plants, animals, microbes) and abiotic (air, water, soil) components. Energy flows unidirectionally through food chains (grass → grasshopper → frog → snake → hawk). Nutrients cycle (carbon, nitrogen, water cycles). Conservation of biodiversity and natural resources is critical to sustain life on Earth.
Formulas / Key Facts
1. **Cell organelles and functions** – Nucleus: controls cell activities, contains genetic material – Mitochondria: cellular respiration, produces ATP (powerhouse) – Chloroplast: photosynthesis in plant cells – Ribosome: protein synthesis – Vacuole: storage in plant cells (large), animal cells (small)
5. **Mendel's laws** – Law of Dominance: dominant trait masks recessive in heterozygotes – Law of Segregation: alleles separate during gamete formation – Law of Independent Assortment: genes for different traits assort independently
7. **Vitamins**: A (vision), B-complex (metabolism), C (connective tissue), D (calcium absorption), E (antioxidant), K (blood clotting).
8. **Photosynthesis equation**: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ (occurs in chloroplast).
9. **Respiration equation**: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP) (occurs in mitochondria).
10. **Taxonomy hierarchy**: Kingdom → Phylum → Class → Order → Family → Genus → Species.
Worked Examples
**Example 1: Identify the odd one out** **Q**: Which does not belong: Mitochondria, Ribosome, Chloroplast, Nucleus? **Solution**: All except **Ribosome** are membrane-bound organelles. Ribosomes are non-membrane structures found free in cytoplasm or attached to endoplasmic reticulum. They synthesize proteins but lack a surrounding membrane. **Answer**: Ribosome.
**Example 2: Disease-deficiency match** **Q**: A child has weak bones and bow-legs. Which deficiency is likely? **Solution**: Weak bones and deformities in children indicate rickets. Rickets is caused by deficiency of **vitamin D**, which is essential for calcium absorption and bone mineralization. **Answer**: Vitamin D deficiency (Rickets).
**Example 3: Blood group inheritance** **Q**: If a father has blood group A and mother has B, can their child have blood group O? **Solution**: Blood group A can be genotype IA IA or IA i; B can be IB IB or IB i. If both parents are heterozygous (IA i and IB i), the child can inherit i from each parent, resulting in genotype ii = blood group **O**. **Answer**: Yes, if both parents are heterozygous.
Common Mistakes
1. **Confusing mitochondria and chloroplast** Wrong: "Chloroplasts release energy from food." Correct: Chloroplasts perform photosynthesis (making food); mitochondria perform respiration (releasing energy from food). Chloroplasts are only in plant cells; mitochondria are in both plant and animal cells.
2. **Mixing up xylem and phloem** Wrong: "Phloem transports water from roots to leaves." Correct: Xylem transports water and minerals upward; phloem transports food (sugars) from leaves to all parts in both directions.
3. **Saying all diseases are caused by bacteria** Wrong: "Malaria is caused by a bacterium." Correct: Malaria is caused by Plasmodium, a protozoan parasite. Diseases can be viral (AIDS, flu), bacterial (TB, typhoid), fungal (ringworm) or protozoan (malaria, amoebic dysentery).
4. **Forgetting universal donor/recipient** Wrong: "AB is the universal donor." Correct: Blood group O is the universal donor (no A/B antigens). AB is the universal recipient (no anti-A or anti-B antibodies).
5. **Ignoring vector vs pathogen** Wrong: "Anopheles mosquito causes malaria." Correct: Plasmodium (protozoan) causes malaria; the Anopheles mosquito is the vector (carrier) that transmits the parasite. Similarly, the housefly is a vector for typhoid, not the causative agent.
Quick Reference
**Cell powerhouse**: Mitochondria (respiration, ATP production).
**Green pigment**: Chlorophyll in chloroplasts enables photosynthesis.
**Human blood**: 4 groups (A, B, AB, O); O is universal donor, AB universal recipient.
**Mendel's organism**: Garden pea (Pisum sativum); established laws of heredity.
**Deficiency diseases**: Vitamin A → night blindness; C → scurvy; D → rickets; B1 → beriberi; iron → anemia; iodine → goiter.
**Evolution pioneer**: Charles Darwin; theory of natural selection; Origin of Species (1859).
**DNA location**: Nucleus (eukaryotes); hereditary material carrying genetic information.
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**Final tip**: Make a chart of diseases with their causative agents, mode of transmission and prevention. Revise nutrient-deficiency pairs daily. Practice classifying organisms and labeling diagrams of cell, heart and flower. Biology is memory-intensive but highly scoring—consistent revision pays off!