Theory & Concepts

Master Biology (Human Body, Plants, Diseases, Nutrition) for SSC CGL

Get comprehensive theory, expert shortcuts, and hand-picked practice questions for Biology (Human Body, Plants, Diseases, Nutrition) specifically designed for the SSC CGL 2025-26 pattern.

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40 min readGK: ScienceWeightage: High

General Biology: Human Physiology, Plant Tissues & Diseases

Biology constitutes the largest share of science questions in the SSC CGL general awareness section. The syllabus demands a sound grasp of human organ functions (enzymes, blood groups, brain structures), plant vascular networks, pathogens causing widespread human diseases, and vitamin classifications. This guide summarizes these topics with a custom interactive dashboard and 20 solved questions.

Learning path

Human Physiology & Blood Groups
Plant Tissues & Ripening Hormones
Pathogens, Vectors & Vitamins
20 Solved Practice Questions

1. Human Body Systems & Blood Groups

Human physiology details the organ systems that keep the body functioning. Focus areas for CGL include:

Digestive System & Enzymes: Chemical digestion starts in the mouth with salivary amylase (ptyalin).
- Stomach: Secretes hydrochloric acid (HCl) and Pepsin (digests proteins).
- Pancreas: Secretes Trypsin (proteins), Lipase (fats), and Amylase (starch).
- Liver: Produces Bile juice (alkaline, emulsifies fats), stored in the gallbladder.
Circulatory System & Blood: Humans have a four-chambered heart.
- Arteries carry oxygenated blood (except the pulmonary artery); Veins carry deoxygenated blood (except the pulmonary vein).
- AB positive is the universal recipient (contains no antibodies).
- O negative is the universal donor (contains no A, B, or Rh antigens).
Nervous System & Brain:
- Cerebrum: Largest part, controls intelligence, memory, and voluntary actions.
- Cerebellum: Coordinates muscle movement, posture, and body balance.
- Medulla Oblongata: Controls involuntary actions (heartbeat, breathing, swallowing).

2. Plant Anatomy, Hormones & Photosynthesis

Vascular Plant Tissues

Plants rely on specialized complex permanent tissues to transport water and food:

Xylem: Transports water and minerals absorbed by roots upward to the leaves. It is a **unidirectional** transport mechanism consisting of vessels and tracheids.
Phloem: Transports synthesized food (sucrose) from leaves to storage organs. It is a **bidirectional** transport mechanism consisting of sieve tubes and companion cells.

Plant Hormones (Phytohormones)

Hormones coordinate growth, development, and environmental responses:

Auxin: Promotes cell elongation, apical dominance, and phototropism (bending toward light).
Gibberellins: Promotes stem elongation, seed germination, and flowering.
Cytokinins: Promotes active cell division, delays leaf senescence.
Abscisic Acid (ABA): Inhibits growth, induces seed dormancy, and causes closure of stomata during water stress (stress hormone).
Ethylene: A unique gaseous hormone that promotes fruit ripening and senescence.

3. Human Diseases, Vectors & Vitamins

Deficiency Diseases Dashboard

Click through the interactive selector below to study vitamin chemical names, solubility, food sources, and deficiency syndromes:

Select Vitamin

Vitamin A

Chemical Name: Retinol

Fat Soluble

Primary Food Sources:
Carrots, Sweet Potatoes, Spinach, Milk, Fish liver oil

Deficiency: Night Blindness (Nyctalopia), Xerophthalmia

Inability to see in low light, dry cornea, increased vulnerability to eye infections.

* CGL Note: Crucial for maintaining healthy photoreceptors in the retina.

Pathogens & Vector Diseases

Understanding what organism causes a disease and how it spreads is high-yield:

Type of Pathogen	Key Diseases	Vector / Mode of Spread
Bacterial	Tuberculosis, Cholera, Typhoid, Tetanus, Diphtheria	Air (TB), Contaminated food/water (Typhoid, Cholera), Soil entry (Tetanus)
Viral	Polio, Influenza, Rabies, Dengue, AIDS (HIV), Smallpox	Aedes mosquito (Dengue), Animal bite (Rabies), Body fluids (HIV)
Protozoan	Malaria, Kala-azar, Sleeping Sickness	Female Anopheles (Malaria), Sandfly (Kala-azar), Tse-tse fly (Sleeping Sickness)

4. Practice Questions (20 Premium Solved Questions)

Question 01CGL Pattern

Which organ of the human digestive system is responsible for producing Bile Juice, which plays a key role in fat emulsification?

A) Gallbladder

B) Pancreas

C) Liver

D) Stomach

Correct answer: C) Liver

Step-by-step Solution

Step 1: Understand where bile is produced vs where it is stored.

Step 2: The Liver synthesizes bile juice.

Step 3: The Gallbladder only stores and concentrates the bile until needed in the small intestine.

Conclusion: Option C is correct.

Question 02CGL Pattern

In the ABO blood group classification, which blood group is designated as the 'universal donor' due to the absence of A and B antigens on RBCs?

A) Group A

B) Group B

C) Group AB

D) Group O

Correct answer: D) Group O

Step-by-step Solution

Step 1: Universal donors must lack antigens that could trigger recipient immune responses.

Step 2: Group O red blood cells contain neither A nor B antigens on their surface.

Step 3: Specifically, O-negative is the true universal donor, containing no Rh factor either.

Conclusion: Option D is correct.

Question 03CGL Pattern

Which specialized region of the human brain is primary in maintaining muscle tone, bodily posture, and motor balance?

A) Cerebrum

B) Cerebellum

C) Medulla Oblongata

D) Hypothalamus

Correct answer: B) Cerebellum

Step-by-step Solution

Step 1: Identify brain functions. Cerebrum manages memory/thinking. Medulla handles breathing/heart rate.

Step 2: The Cerebellum (hindbrain) coordinates voluntary muscle movements, posture, and equilibrium.

Conclusion: Option B is correct.

Question 04CGL Pattern

Which complex permanent plant vascular tissue is responsible for transporting water and minerals from the roots upwards to the leaves?

A) Phloem

B) Xylem

C) Parenchyma

D) Cambium

Correct answer: B) Xylem

Step-by-step Solution

Step 1: Xylem conducts water and inorganic solutes unidirectionally from roots to shoot.

Step 2: Phloem conducts organic food materials (photosynthates) bidirectionally.

Conclusion: Option B is correct.

Question 05CGL Pattern

Which plant growth hormone is unique because it is a gaseous compound, playing a major role in the ripening of fruits?

A) Auxin

B) Cytokinin

C) Gibberellin

D) Ethylene

Correct answer: D) Ethylene

Step-by-step Solution

Step 1: Phytohormones are chemical regulators. Auxins/Gibberellins are liquid organic acids promoting cell elongation.

Step 2: Ethylene is a gaseous phytohormone synthesized in ripening fruits and aging leaves, accelerating ripening.

Conclusion: Option D is correct.

Question 06CGL Pattern

Chlorophyll, the green pigment in plants that absorbs solar energy for photosynthesis, has which metal ion in its coordination structure?

A) Iron

B) Calcium

C) Magnesium

D) Cobalt

Correct answer: C) Magnesium

Step-by-step Solution

Step 1: Recall the structure of chlorophyll. It is a porphyrin ring structure.

Step 2: Just as Hemoglobin contains Iron (Fe) in its core, Chlorophyll contains a central Magnesium (Mg²⁺) ion.

Conclusion: Option C is correct.

Question 07CGL Pattern

Which pathogen species causes the infectious disease Tuberculosis (TB) in humans?

A) Salmonella typhi

B) Mycobacterium tuberculosis

C) Plasmodium vivax

D) Vibrio cholerae

Correct answer: B) Mycobacterium tuberculosis

Step-by-step Solution

Step 1: Tuberculosis is a chronic bacterial infection affecting lungs.

Step 2: The causative agent is the rod-shaped bacterium Mycobacterium tuberculosis.

Conclusion: Option B is correct.

Question 08CGL Pattern

What vector is responsible for transmitting the Malaria parasite (Plasmodium) between infected individuals and healthy humans?

A) Female Anopheles mosquito

B) Aedes aegypti mosquito

C) Sandfly

D) Tse-tse fly

Correct answer: A) Female Anopheles mosquito

Step-by-step Solution

Step 1: Malaria is a protozoan disease caused by Plasmodium.

Step 2: Female Anopheles mosquitoes serve as the vector, carrying the parasite in salivary glands and transmitting it via bites.

Step 3: Aedes mosquito transmits Dengue and Zika.

Conclusion: Option A is correct.

Question 09CGL Pattern

Vitamins are classified into fat-soluble and water-soluble groups. Which of the following vitamins is water-soluble?

A) Vitamin A

B) Vitamin D

C) Vitamin C

D) Vitamin K

Correct answer: C) Vitamin C

Step-by-step Solution

Step 1: Fat-soluble vitamins are A, D, E, and K.

Step 2: Water-soluble vitamins are B-Complex and C.

Step 3: Therefore, Vitamin C is water-soluble.

Conclusion: Option C is correct.

Question 10CGL Pattern

Scurvy, characterized by spongy bleeding gums and internal bleeding, is caused by the dietary deficiency of which vitamin?

A) Vitamin A

B) Vitamin B1

C) Vitamin C

D) Vitamin D

Correct answer: C) Vitamin C

Step-by-step Solution

Step 1: Scurvy is caused by a lack of Ascorbic Acid (Vitamin C).

Step 2: Vitamin C is vital for collagen synthesis, without which blood vessels weaken.

Conclusion: Option C is correct.

Question 11CGL Pattern

What is the chemical name of Vitamin B12, the complex vitamin containing cobalt that is required for RBC maturation?

A) Thiamine

B) Riboflavin

C) Cyanocobalamin

D) Pyridoxine

Correct answer: C) Cyanocobalamin

Step-by-step Solution

Step 1: Check B-vitamin names: Thiamine is B1, Riboflavin is B2, Pyridoxine is B6.

Step 2: Cyanocobalamin is the chemical name of Vitamin B12, containing a cobalt atom in its center.

Conclusion: Option C is correct.

Question 12CGL Pattern

A deficiency of Vitamin D in children impairs bone mineralization, leading to which disease?

A) Scurvy

B) Rickets

C) Pellagra

D) Beriberi

Correct answer: B) Rickets

Step-by-step Solution

Step 1: Vitamin D facilitates calcium absorption.

Step 2: Deficiency causes weak, soft bones. In growing children, this manifests as Rickets (skeletal deformities, bow legs).

Step 3: In adults, it is called Osteomalacia.

Conclusion: Option B is correct.

Question 13CGL Pattern

Which enzyme present in human saliva acts on dietary starch to begin carbohydrate digestion in the mouth?

A) Pepsin

B) Trypsin

C) Salivary Amylase

D) Renin

Correct answer: C) Salivary Amylase

Step-by-step Solution

Step 1: Saliva contains an enzyme called ptyalin or salivary amylase.

Step 2: It breaks down complex starches into simpler maltose sugars.

Conclusion: Option C is correct.

Question 14CGL Pattern

Which blood vessels possess thin elastic walls and internal valves to transport deoxygenated blood back to the heart?

A) Arteries

B) Veins

C) Capillaries

D) Arterioles

Correct answer: B) Veins

Step-by-step Solution

Step 1: Arteries carry blood away from the heart at high pressure (thick walls, no valves).

Step 2: Veins carry blood towards the heart at low pressure, requiring valves to prevent backward flow.

Conclusion: Option B is correct.

Question 15CGL Pattern

Which plant hormone is responsible for promoting active cell division and delaying the aging (senescence) of leaves?

A) Abscisic Acid

B) Cytokinin

C) Auxin

D) Gibberellin

Correct answer: B) Cytokinin

Step-by-step Solution

Step 1: Break down the word: cyto (cell) + kinin (division/kinesis).

Step 2: Cytokinin stimulates cytokinesis and cell division, delaying leaf aging.

Conclusion: Option B is correct.

Question 16CGL Pattern

Typhoid fever is a systemic bacterial infection. Which bacterium is the causative pathogen?

A) Vibrio cholerae

B) Salmonella typhi

C) Mycobacterium leprae

D) Bacillus anthracis

Correct answer: B) Salmonella typhi

Step-by-step Solution

Step 1: Typhoid is diagnosed via the Widal test.

Step 2: The causative bacterium is Salmonella typhi, contracted via fecal-oral contamination.

Conclusion: Option B is correct.

Question 17CGL Pattern

What is the chemical name of Vitamin A, deficiency of which leads to night blindness?

A) Calciferol

B) Retinol

C) Niacin

D) Tocopherol

Correct answer: B) Retinol

Step-by-step Solution

Step 1: Vitamin A is essential for the retina and vision.

Step 2: Its chemical name is Retinol.

Conclusion: Option B is correct.

Question 18CGL Pattern

Bleeding gums and poor healing of wounds are diagnostic symptoms of a deficiency in which compound?

A) Retinol

B) Thiamine

C) Ascorbic Acid

D) Calciferol

Correct answer: C) Ascorbic Acid

Step-by-step Solution

Step 1: Bleeding gums indicate scurvy.

Step 2: Scurvy is caused by Vitamin C deficiency. The chemical name of Vitamin C is Ascorbic Acid.

Conclusion: Option C is correct.

Question 19CGL Pattern

Which anatomical part of the human brain controls involuntary life-support actions like breathing, heartbeat, and swallowing?

A) Cerebrum

B) Cerebellum

C) Medulla Oblongata

D) Thalamus

Correct answer: C) Medulla Oblongata

Step-by-step Solution

Step 1: Involuntary functions are managed by the brain stem.

Step 2: The Medulla Oblongata contains centers controlling cardiovascular reflexes, respiration, and gastric secretions.

Conclusion: Option C is correct.

Question 20CGL Pattern

Which vitamin is synthesized in the human skin when exposed to ultraviolet radiation from the sun?

A) Vitamin A

B) Vitamin C

C) Vitamin D

D) Vitamin E

Correct answer: C) Vitamin D

Step-by-step Solution

Step 1: Human skin cells contain 7-dehydrocholesterol.

Step 2: UV radiation converts this precursor into cholecalciferol (Vitamin D3), which is metabolized into active Vitamin D.

Conclusion: Option C is correct.

Strategy errors to avoid

Bile Juice Production vs. Storage

Always check the wording. If it asks where bile is produced, the answer is Liver. If it asks where it is stored, the answer is Gallbladder. Mixing these up is a very common mistake.

Vitamin B12 Cobalt Association

Ensure you recall that Vitamin B12 is Cyanocobalamin, containing Cobalt (Co). CGL frequently tests this mineral association, so keep it at the top of your revision list.

Master the next modules

Physics Core Chemistry Concepts Static GK Guide