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NCERT Based Short Notes for Class 12th Biology (For NEET-UG Entrance examination)
-By Vimalraj
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Factors Affecting Our Health
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State of
the immune system has a vital role to play in keeping us in a healthy state
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Genetic information: Genetic information inherited from parents can be cause of many physical abnormalities and
some genetic diseases can be passed on from parents to the offspring
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Our physical environment: People living in clean areas with a proper garbage and sewage disposal system in place and
lot of greenery are healthier than people living under unhygienic conditions and areas lacking greenery
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Economic conditions of individual: affects the health by affecting the buying capacity and also amount of the money
spend by the individuals on health
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Diseases can be classified as Infectious and Non infectious Diseases
~Infectious Diseases –Diseases which are easily transmitted from one person to another are called infectious diseases
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Examples include Common cold, malaria, AIDS

Non infectious Diseases –Disease which cannot be transmitted from one person to another are called non –infectious
diseases
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Pathogens:
Organisms that cause diseases in a host are called pathogens
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Widal test: It is a serological test that can be used for detecting typhoid
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Sporozoites: The infectious form of Plasmodium which enters the human body through the bite of a female
Anopheles mosquito
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Multiplication
on of parasites inside the liver cells
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Attack of the RBCs by the parasites causing the rupture of the RBCs
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Release of a toxic substance called haemozoin by the ruptured RBCs that causes chills and recurring fevers every
three to four days
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Transfer
fer of the parasites into the body of the female Anopheles mosquito when the infected person is bitten by
the mosquito
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Multiplication of the parasites within the mosquito to form sporozoites
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• It is important to note that the malarial parasite Plasmodium requires two hosts to complete its life cyclecycle the
human host and the female Anopheles mosquito
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Maintenance of personal and public hygiene
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Elimination of vectors and their breeding places using chemical and biological methods
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Vaccination
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It works by
preventing the entry of pathogens through various barriers
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Innate immunity consist of four types of barriers
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For example,

the polymorpho-nuclear
nuclear leukocytes (PMNL-neutrophils),
(PMNL neutrophils), monocytes, natural killer (type of lymphocytes) in the
blood, as well as macrophages in tissues
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Acquired Immunity
This type of immunity is pathogen specific and is characterized by a memory
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produced
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This is called secondary or anamnestic response
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B-Lymphocytes
Lymphocytes produce special proteins called antibodies whereas the T lymphocytes help BB
lymphocytes to produce antibodies
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It is represented as H2L2
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Humoral Immune response:
It is the kind of immune response that involve production of antibodies as these antibodies are present in the blood
(body humor)

Cell-mediated immunity
It is an immune response that does not involve antibodies, but rather involves the activation of phagocytes,
antigen-specific cytotoxic T-lymphocytes,
lymphocytes, and the release of various cytokines
cytokines in response to an antigen
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Active immunity v/s Passive immunity

Vaccination and Immunization:
Vaccination:
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The antibodies produced in response to the vaccine will then help
the body fight against the actual infection
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This is called as passive immunization
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As the cellular material of the pathogen is not present in the vaccine, the side effects to the vaccine may also be
lesser in these cases
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The antibodies produced to
these are of IgE type
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Common examples of allergens are mites in dust, pollens, animal dander, etc
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Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing
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Allergy is due to the release of chemicals like histamine and serotonin from the mast cells
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Auto immunity
The human immune system can differentiate antigen which are foreign to the body from the
antigen which are part of the body
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In some cases the body attacks its own cells due to genetic and other unknown reasons
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Example -Rheumatoid arthritis, psoriasis, Mysthenia graves etc
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Lymphoid organs
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Lymphoid organs defend the body against foreign antigens or spread of tumors
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These organs exist as primary, secondary and tertiary
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Of these,
lymphocytes are usually present in the highest percentage regardless of the type of lymphoid organ

Primary lymphoid organs
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Thymus
Helps immature lymphocytes differentiate into antigen- sensitive lymphocytes

Secondary lymphoid organs
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Lymph nodes
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Peyer’s patches of small intestine
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• The thymus is a lobed organ
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The thymus is quite large
at the time of birth but its size keeps decreasing with increase in age and by the time puberty is attained it
reduces to a very small size
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• The spleen is a large bean shaped organ
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It acts as a filter of the
blood by trapping blood-borne microorganisms
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• The lymph nodes are small solid structures located at different points along the lymphatic system
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Antigens that get trapped in
the lymph nodes are responsible for the activation of lymphocytes present within the lymph nodes
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Lymphoid tissue is also located within the lining of the major tracts (respiratory, digestive
and urogenital tracts)
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It forms approximately 50 per
cent of the lymphoid tissue in human body

AIDS (Acquired Immuno Deficiency Syndrome)
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It is a condition acquired during the lifetime of an individual referring to the fact that it is not a congenital disease
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-AIDS was first reported in 1981 in USA and in approximately the last twenty-five years, it has spread all over the
world killing more than 25 million persons
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They have an envelope enclosing the RNA genome
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Transmission of HIV-infection
(a) Sexual contact with infected person,
(b) By transfusion of contaminated blood and blood products,
(c) By sharing infected needles as in the case of intravenous drug abusers and
(d) From infected mother to her child through placenta
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HIV/AIDS does not spread through mere touch or physical contact
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It is important for the physical and psychological well-being of the infected person that the HIV/AIDS infected
persons not be isolated from family and society
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This incubation
period may vary from a few months to many years (usually 5-10 years)
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- The RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase
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- The macrophages continue to produce virus
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- The progeny viruses released in the blood attack other helper T-lymphocytes
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- During this period, the person suffers from bouts of fever, diarrhea and weight loss
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This includes diseases such as those caused by bacteria
especially Mycobacterium, viruses, fungi and even parasites like Toxoplasma
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Detection:
Enzyme linked immuno-sorbent assay (ELISA):
It is a biochemical technique used in immunology to detect the presence of an antibody or an antigen in a sample
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Treatment:
Use anti-retroviral drugs
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Prevention of AIDS:
As AIDS has no cure, prevention is the best option
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-More effective monitoring can prevent infection through blood transfusion, transmission from mother to newborn
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-National AIDS Control Organisation (NACO) and other non-governmental organisation (NGOs) are making efforts to
educate people about AIDS
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Prevention and Control Methods:
• Making blood transfusions safe from HIV
• Ensuring the use of only disposable needles and syringes in public and private hospitals and clinics
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Role of Society in preventing spread of this disease
- Sympathy for HIV/AIDS patients
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- Co-operation and co-ordination between society and medical fraternity to prevent the spread of the disease
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- In cancer cells, there is breakdown of these regulatory mechanisms
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Due to this contact of a cell with other cells inhibits its uncontrolled
growth
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As a result of this, cancerous cells continue to divide giving rise to masses of
cells called tumors
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Benign tumors normally remain limited to their original location and do not spread to other parts of the
body
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These cells grow very
rapidly
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As these cells are actively dividing and
growing it leads to the starvation of the normal cells by competing for vital nutrients
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Wherever they get lodged in the body they cause the
emergence of a new tumor
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Causes of cancer:
-Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological
agents
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Common carcinogens:
-Ionising radiations:
X-rays and gamma rays
-Non-ionizing radiations:
UV
Both ionizing and non-ionising radiations cause DNA damage that causes neoplastic transformation
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Oncogenic viruses are cancer causing viruses
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Several genes called cellular oncogenes(c-onc) or proto oncogenes have been identified in normal cells which can
be activated under certain conditions and therefore lead to oncogenic transformation of the cells
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Cancer
detection is based on:
- Biopsy: a piece of the suspected tissue cut into thin sections is stained
- Histopathological studies of the tissue (thin sections are examined under the microscope)
- Blood and bone marrow tests: for increased cell counts in the case of leukemias
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- MRI (magnetic resonance imaging): MRI involves use of strong magnetic fields and non-ionizing radiations to
accurately detect pathological and physiological changes in the living tissue
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- Techniques of molecular biology: To detect genes in individuals with inherited susceptibility to certain cancers
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Such individuals may be advised to avoid
exposure to particular carcinogens to which they are susceptible (e
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, tobacco smoke in case of lung cancer)
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The common approaches for
treatment of cancer are surgery, radiation therapy, chemotherapy and immunotherapy
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- Several chemotherapeutic drugs are used to kill cancerous cells
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Most drugs have side effects like hair loss, anemia, etc
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- Tumor cells avoid detection and destruction by immune system
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They are substances such as α-interferon which activate their immune system
and help in destroying the tumor
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Majority of these are
obtained from flowering plants
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Opioids are the drugs, which bind to specific opioid receptors present in our central nervous system and
gastrointestinal tract
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This is obtained by acetylation of morphine which is extracted from the latex of poppy plant Papaver
somniferum
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Cannabinoids are a group of chemicals which interact with cannabinoid receptors present principally in the brain
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Generally taken by inhalation and oral ingestion, these are known for their effects on cardiovascular system of the
body
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It interferes with
the transport of the neuro-transmitter dopamine
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It has
a potent stimulating action on central nervous system, producing a sense of euphoria and increased energy
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Other well-known plants with hallucinogenic properties are Atropa belladona and Datura
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- Contains large amounts of chemical substance including nicotine which is an alkaloid
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-Smoking increases the incidence of lung cancer
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-Tobacco chewing increases the risk of cancer of oral cavity
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This
causes oxygen deficiency in the body leading to anemia
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Adolescence and Drug/Alcohol abuse:
Adolescence is a period during which an individual reaches reproductive maturity
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It is a period where there is emotional and behavioral growth of the individual
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Therefore, during this period an individual is
highly vulnerable
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With repeated use of drugs, the tolerance level of the receptors present
in our body increases
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This leads to
greater intake and more addiction

Dependence:
Dependence is the tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome
if regular dose of drugs/alcohol is abruptly discontinued
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These may be relieved when use is resumed again
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Dependence causes the patient to ignore all social norms just so as to get sufficient funds to satiate his/her needs
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Effects of Drug/Alcohol Abuse
- reckless behavior

- Vandalism and violence
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- Intravenous intake of drugs could lead to increases susceptibility to diseases like AIDS, Hepatitis, etc
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- Stealing to get money to buy drugs/alcohol
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Avoid undue peer pressure
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Seeking help from parents and peers
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Seeking professional and medical help



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