CBSE Class 12 Biology Exemplar: Human Health and Diseases NCERT Solutions

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NCERT Solutions PDF Class 12 PDF

This resource provides detailed NCERT Solutions for CBSE Class 12 Biology Exemplar, Chapter 8: Human Health and Diseases. It covers essential topics such as the definition of health, the role of pathogens and vectors in disease transmission, and the diagnosis of common diseases like typhoid and malaria. The solutions explain the differences between infectious and non-infectious diseases, using examples like influenza, smallpox, and cancer. It also delves into the life cycle of disease-causing organisms, such as Plasmodium in malaria transmission, and vectors like Aedes mosquitoes for diseases like chikungunya. These solutions are designed to help students understand the core concepts, clarify doubts, and prepare effectively for their board examinations by offering clear explanations and step-by-step problem-solving approaches.

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Quick info

BoardCBSE
ClassClass 12
SubjectBiology Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 8

Chapter summary

Chapter 8 of the CBSE Class 12 Biology Exemplar focuses on Human Health and Diseases. This section provides NCERT Solutions that clarify the definition of health, identify disease-causing agents (pathogens) and their carriers (vectors), and explain diagnostic methods like the Widal test. It differentiates between infectious and non-infectious diseases, detailing examples and their transmission. The solutions also cover the biological aspects of diseases like malaria and chikungunya, including the role of specific vectors and the stages of infection.

Learning outcomes

  • Understand the comprehensive definition of health beyond the absence of disease.
  • Identify and differentiate between pathogens and vectors responsible for diseases.
  • Recognize various diagnostic tests used for identifying specific diseases.
  • Distinguish between infectious and non-infectious diseases with examples.
  • Explain the transmission mechanisms of diseases like malaria and chikungunya.
  • Describe the role of mosquitoes as vectors in disease transmission.

Topics covered

Paper topics

  • Definition of Health
  • Pathogens
  • Vectors
  • Typhoid Diagnosis
  • Infectious Diseases
  • Non-infectious Diseases
  • Cancer
  • Allergy
  • Malaria Transmission
  • Plasmodium
  • Chikungunya Transmission
  • Aedes Mosquitoes

Important topics

  • Definition of Health
  • Pathogens and Vectors
  • Infectious vs. Non-infectious Diseases
  • Disease Transmission Mechanisms
  • Vector-borne Diseases (Malaria, Chikungunya)
  • Diagnostic Tests (Widal Test)

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Questions and Solutions

Q. 1

The term 'Health' is defined in many ways. The most accurate definition of the health would be
  1. health is the state of body and mind in a balanced condition
  2. health is the reflection of a smiling face
  3. health is a state of complete physical, mental and social well-being
  4. health is the symbol of economic prosperity.
Solution: The most accurate and widely accepted definition of health, as per the World Health Organization (WHO), is "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." This definition highlights that true health encompasses multiple dimensions beyond just not being sick. While a smiling face and economic prosperity can be associated with good health, they are not the primary definition. A balanced body and mind are components of health, but the definition extends to social well-being as well.

Answer: (c) health is a state of complete physical, mental and social well-being

Q. 2

The organisms which cause diseases in plants and animals are called
  1. pathogens (b) vectors (c) insects (d) worms
Solution: Organisms that cause diseases are known as pathogens. This category includes a diverse range of microorganisms such as bacteria, viruses, fungi, protozoans, and parasitic worms (helminths). Vectors, on the other hand, are organisms like insects or worms that carry and transmit pathogens from an infected individual or environment to a healthy one, but they do not cause the disease themselves.

Answer: (a) pathogens

Q. 3

The chemical test that is used for diagnosis of typhoid is
  1. ELISA test (b) ESR test (c) PCR test (d) Widal test
Solution: Typhoid fever is a bacterial infection caused by *Salmonella typhi*. The primary diagnostic test for typhoid fever is the Widal test. This test detects the presence of antibodies produced by the immune system in response to the *Salmonella typhi* bacteria. ELISA (Enzyme Linked Immunosorbent Assay) is commonly used for diagnosing infections like HIV. PCR (Polymerase Chain Reaction) is used to detect the genetic material of pathogens. ESR (Erythrocyte Sedimentation Rate) is a general indicator of inflammation in the body, not specific to typhoid.

Answer: (d) Widal test

Q. 4

Diseases are broadly grouped into infectious and non-infectious diseases. In the list given below, identify the infectious diseases.
  1. Cancer II. Influenza
  2. Allergy IV. Smallpox
  3. I and II (b) II and III
  4. III and IV (d) II and IV
Solution: Diseases can be classified as infectious or non-infectious. Infectious diseases are caused by pathogens and can be transmitted from one person to another. Non-infectious diseases are not caused by pathogens and cannot be spread through transmission.
  • Influenza (II) is caused by influenza viruses and is highly contagious, making it an infectious disease.
  • Smallpox (IV) is caused by the Variola virus and is also a highly contagious infectious disease.
  • Cancer (I) is characterized by uncontrolled cell growth and is generally considered non-infectious, although some viruses can contribute to certain types of cancer.
  • Allergy (III) is an exaggerated immune response to harmless substances and is a non-infectious condition.
Therefore, the infectious diseases in the list are Influenza and Smallpox.

Answer: (d) II and IV

Q. 5

The sporozoites that cause infection when a female Anopheles mosquito bites a human being are formed in
  1. liver of human (b) RBCs of mosquito
  2. salivary glands of mosquito (d) intestine of human
Solution: Malaria is caused by the protozoan parasite *Plasmodium*, which is transmitted to humans through the bite of infected female *Anopheles* mosquitoes. When a mosquito bites an infected person, it ingests *Plasmodium* gametocytes. In the mosquito's gut, these gametocytes develop into sporozoites. These sporozoites migrate to the mosquito's salivary glands, where they mature and are stored. When the infected mosquito bites a human, these sporozoites are injected into the human bloodstream, initiating the infection. The sporozoites then travel to the liver, where they multiply before infecting red blood cells.

Answer: (c) salivary glands of mosquito

Q. 6

The disease chikungunya is transmitted by
  1. house flies (b) Aedes mosquitoes
  2. cockroach (d) female Anopheles
Solution: Chikungunya is a viral disease that is transmitted to humans through the bite of infected mosquitoes. Specifically, the *Aedes* species of mosquitoes, primarily *Aedes aegypti* and *Aedes albopictus*, are the vectors responsible for transmitting the chikungunya virus. These mosquitoes are also known vectors for other diseases like dengue and Zika. House flies can transmit diseases like cholera, cockroaches can spread various pathogens, and female *Anopheles* mosquitoes are vectors for malaria.

Answer: (b) Aedes mosquitoes

Common mistakes

  • Confusing pathogens with vectors.
  • Misidentifying infectious versus non-infectious diseases.
  • Incorrectly recalling the specific vectors for different diseases.
  • Not understanding the complete definition of health.

Revision tips

  • Focus on understanding the precise definition of health provided.
  • Create a table to list diseases, their pathogens, vectors, and diagnostic tests.
  • Review the differences between infectious and non-infectious diseases carefully.
  • Pay close attention to the life cycles and transmission methods of vector-borne diseases.

Practice MCQs

Q1. Which of the following best defines health according to the most accurate definition?

Q2. What are the organisms that cause diseases in plants and animals called?

Q3. Which chemical test is specifically used for the diagnosis of typhoid fever?

Q4. Which of the following pairs correctly identifies infectious diseases from the given list?

Q5. In the context of malaria transmission, where are the sporozoites that cause infection formed before being transmitted to humans?

Q6. Chikungunya, a viral disease, is primarily transmitted by which type of vector?

Frequently asked questions

What is the most accurate definition of health according to NCERT?

The most accurate definition of health is a state of complete physical, mental, and social well-being, not merely the absence of disease or physical fitness.

What is the difference between a pathogen and a vector?

A pathogen is the organism that directly causes a disease (like a bacterium or virus), while a vector is an organism (often an insect) that transmits the pathogen from one host to another.

How is typhoid diagnosed?

Typhoid fever is typically diagnosed using the Widal test, which detects antibodies against the Salmonella typhi bacteria.

Can you give examples of infectious and non-infectious diseases?

Infectious diseases include influenza and smallpox, which are caused by pathogens and can spread. Non-infectious diseases include cancer and allergies, which are not directly transmissible from person to person.

Which mosquito transmits malaria, and which transmits chikungunya?

Malaria is transmitted by the female Anopheles mosquito, while chikungunya is transmitted by Aedes mosquitoes.

What are the infectious agents involved in malaria transmission to humans?

The infectious agents are sporozoites, which are transmitted by the female Anopheles mosquito and develop within the human liver and red blood cells.

Important links

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