Biology Notes Fa Fsc Chapter No 13 Immunity

Immunity Biology class 11 Fsc notes for kpk, Fbise, Punjab, and Sindh boards 2021 notes.

Immunity Biology Notes for Class 11 Short Question 2021

What are pyrogens? How do they affect the hypothalamus?

  “Pyrogen is a substance, typically produced by a bacterium, that may cause the setpoint of the hypothalamic thermostat to rise and causes fever.”

   Many proteins, breakdown products of proteins, and certain other substances, such as lipopolysaccharide toxins (LPS or endotoxin) secreted by bacteria, can act as pyrogens. It is pyrogens secreted by toxic bacteria or pyrogen released from degenerating tissues of the body that cause fever during disease conditions. These chemicals are carried by the blood to the brain, where they disturb the functioning of the hypothalamus, the part of the brain that regulates body temperature. 

The pyrogens inhibit heat-sensing neurons and excite cold-sensing ones, and the altering of these temperature sensors deceives the hypothalamus into thinking the body is cooler than it actually is. In response, the hypothalamus raises the body temperature above the normal range, thereby causing a fever.

Q.2 ii) List three benefits of fever.


Benefits of fever:

  • Due to fever, more interferons are produced which blocks the spread of viruses to healthy cells.
  • Increased temperature directly kills invading organisms through heat.
  • Fever stimulates the production of white blood cells which mobilize and attack invaders.

Q.2 iii) How interferon inhibits the ability of viruses to infect cells?



  “Interferons are a group of natural proteins that are produced by human cells in response to viral infection and other stimuli. They have the ability to interfere with viruses that are replicating.”

Interferon mechanism against viruses:

  • Viral acid enters the cell
  • Interferon genes of the cells DNA are turned on
  • Interferon molecules are produced and released by the cell.
  • The first host cell is killed by the virus.
  • The interferons are received by another cell. In response, the second cell makes anti-viral proteins which block viral protection.

Q.2 iv) What would happen if mucous of bronchi fails to do its job?


  Bronchi is a part of the respiratory system which is lined with mucous membrane. If the mucus is not produced in the lining of bronchi, it could lead to serious lung infections because mucus traps foreign materials and unwanted disease-causing pathogens, preventing them from accessing the lungs and other vital structures. Mucus also contains natural antibiotics, which help to destroy bacteria. If mucous dysfunction takes place, lung infections like bronchitis, emphysema, tuberculosis, and asthma occur

leading to a weak immune system.

Q.2 v) What are the agents of non-specific defence and specific defence?


Agents of  nonspecific defence:

  • Skin
  • Mucous-membranes, Sweat, tears, and saliva
  • HCL in stomach
  • WBC’s
  • Lymph nodes
  • Spleen
  • Fever
  • Pus
  • Interferons

Agents of specific defense:

  • Cell-mediated immune response (T-cells)
  • Antibody-mediated immune response (B-cells)

Q.2 vi) Define allergy and allergens. List down some common allergic conditions.



  “Allergies are hypersensitive immune responses to substances that either enter or come in contact with the body, such as pet dander, pollen or bee venom.”


  “A substance that causes an allergic reaction is called an allergen.”

Common allergic conditions:

  The most common allergic conditions include;

  • Hay fever (Allergic rhinitis)
  • Asthma
  • Allergic eyes (Allergic conjunctivitis)
  • Allergic eczema
  • Hives (Urticaria)
  • Allergic shock (Anaphylaxis and anaphylactic shock)

Q.2 vii) Differentiate between the two types of acquired immunity.


Innate/Inborn/Natural immunityAcquired/ Adaptive immunity
Natural immunity is inherited from parents to offspring.      Adaptive immunity is created in response to exposure to a foreign substance.
It is non-specific immunityIt is a specific type of immunity
Innate immunity fights against any foreign invader   Adaptive system fight an only specific infection
The span of innate immunity could be short or lifelong.The span of developed immunity is lifelong because some antibody cells persist as memory cells.

Biology Class 11 Long Question

Q.3 i) What are the main events of inflammatory response?


Inflammatory response:

  “Inflammatory response is a localized physical response in which part of the body becomes red, swollen, and often painful, especially as a reaction to injury or infection.”

 Inflammatory response as one of the nonspecific defences.

Main events of the inflammatory response:

  • The inflammatory response (inflammation) occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause.
  • This damaged tissue releases chemicals including histamine, bradykinin, and serotonin. These chemicals cause blood vessels to leak fluid into the tissues, causing swelling.
  • This helps isolate the foreign substance from further contact with body tissues.
  • The chemicals also attract white blood cells called phagocytes that eat microorganisms and dead or damaged cells. This process is called phagocytosis.
  • Phagocytes eventually die. Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes.


  • The tissues in the area are red and warm, as a result of a large amount of blood reaching the site.
  • The tissues in the area are swollen, again due to the increased amount of blood and proteins that are present.
  • The area is painful, due to the expansion of tissues, causing mechanical pressure on nerve cells, and also due to the presence of pain mediators.
  • Once the inflammatory process has begun, it continues until the infection that caused it has been eradicated.

Q.3 ii) Describe the structural features of human skin which provide effective control against microbes.


Human skin as the first line of defence:

   In humans, the skin is the largest organ of the integumentary system.

Functions of the skin:

  Skin is regarded as one of the first lines of defence because it provides an almost impenetrable biological barrier protecting the internal environment. It protects the body (especially the underlying tissues) against pathogens and excessive water loss. It is also involved in providing insulation, temperature regulation, and sensation.

Physical Components of the Skin’s Defense:

   Human body’s first line of defence is non-specific and includes structures, chemicals, and processes that work to prevent pathogens from entering the body. These first-line defenders include the skin and mucous membranes of the respiratory, digestive, urinary, and reproductive systems.

Layers of skin:

   The skin consists of two main layers.

  • 1. Epidermis
  • 2. Dermis

1. Epidermis:

   The epidermis is composed of multiple layers of tightly packed cells, which few pathogens can penetrate on their own. In addition to this structural barrier, the natural shedding of dead skin cells removes many attached microorganisms. Then there are other cells called epidermal dendritic cells that actively patrol the skin to phagocytize (engulf and digest) pathogens.

b. Dermis:

    The dermis is situated beneath the epidermis and contains protein fibres called collagen. Collagen is a tough fibrous protein which gives skin the strength and flexibility to resist abrasions that could introduce microorganisms.

Chemical Components of the Skin’s Defense:

a. Perspiration:

      Secreted by the skin’s sweat glands, perspiration contains salt and enzymes. Few microbes can live in a highly saline environment, like that of the skin’s surface. The lysozymes in sweat are a type of enzyme that can destroy the cell walls of bacteria.

b. Sebum:

      Sebum is secreted by skin sebaceous (oil) glands. The oil helps keep skin pliable and less likely to break or tear and also lowers the pH of the skin to a more acidic level that inhibits the growth of many types of bacteria.

      Sebum is secreted by skin sebaceous (oil) glands. The oil helps keep skin pliable and less likely to break or tear and also lowers the pH of the skin to a more acidic level that inhibits the growth of many types of bacteria.

Q.3 iii) How macrophages and neutrophils help in killing bacteria?


Role of Macrophages and Neutrophils:

  Monocytes and neutrophils are types of white blood cells. White blood cells are involved in providing immunity to the body.

1. Monocytes:

A site of production of Monocytes:

   Monocytes are released by the bone marrow. These float in the bloodstream from where they enter tissues and turn into macrophages. Of all blood cells, macrophages are the biggest. Most boundary tissue has its macrophages.


  Alveolar macrophages live in the lungs and keep the lungs clean and disease-free by ingesting foreign things like smoke, dust bacteria and microbes. Macrophages also swim freely. One of their jobs is to clean up dead neutrophils. Macrophages clean up pus as a part of the healing process.

2. Neutrophils:

      Neutrophils are the most common form of white blood cells in the body.

Site of production of neutrophils:

  Bone marrow produces trillions of WBCs every day and releases them into the bloodstream, but their life span is short generally less than a day. Once in the bloodstream neutrophils can move through capillary walls into the tissue.

Mode of action of neutrophils:

   Neutrophils are attracted to foreign material, inflammation, and bacteria. If a person gets a splinter or a cut, neutrophils will be attracted by a process called chemotaxis. Once a neutrophil finds a foreign particle or a bacteria it will engulf it, releasing enzymes, hydrogen peroxide and other chemicals from its granules to kill the bacteria.

Pus formation: 

    In a site of serious infection (where lots of bacteria have reproduced in the area), pus will form. Pus is simply dead neutrophils and other cellular debris.

Q.3 iv) How cell-mediated immunity is attained?


Cell-mediated immunity:

  The cell-mediated immune system consists of T-cells which originate in the bone marrow but moves to the thymus where their development is completed.


   T-cells are highly specialized cells in the blood and lymph. They fight bacteria, viruses, fungi, protozoans, cancer, etc. within host cells and react against foreign matter such as organ transplants.

Types of T-cells:

   There are three kinds of T-cells.

1. Cytotoxic T-cells:

         Cytotoxic T-cells directly kill invaders.

2. Helper T-cells:

      Helper T-cells aid B cells and other T-cells to do their jobs.

3. Suppressor T-Cells:

       Suppressor T-cells suppress the activities of B and other T-cells so they don’t over-react in the cellular immune response.

Functions of T cells:

   Cells of the immune system kill cells of the body that have been infected with a virus or that are cancerous. This response relies on cytotoxic T (Tc) cells. Tc cells contain molecules, called perforins, that they release onto target cells. The performance makes holes in the target cells and thereby kills them.

Phases of the cellular immune response:

  The cellular immune response occurs in two phases.

  • In the first, called the activation phase, Tc cells that have the appropriate T-cell receptors are activated and triggered to divide repeatedly.
  • In the second step called the effectors’ phase, these activated Tc cells encounter target cells and kill them.

Q.3 v) What do you mean by autoimmune diseases? Give some examples of autoimmune diseases.


Autoimmune disorders:

 “Autoimmune disorders are diseases that occur when the body produces an inappropriate immune response against its tissues.”

  Sometimes the immune system will cease to recognize one or more of the body’s normal constituents as self and will produce antibodies that attack its cells, tissues, and/or organs. This causes inflammation and damage and leads to autoimmune disorders.

   In a few types of autoimmune disease (such as rheumatic fever), a virus or infection with bacteria triggers an immune response and the antibodies or T-cells attack normal cells because some part of their structure resembles a part of the infecting microorganism.

Symptoms of autoimmune disorders:

  Symptoms of autoimmune disorders vary by particular disorder but may include fatigue, dizziness, and low-grade fever. Symptoms can also vary in severity of overtime.

Autoimmune diseases:

1. Lupus:

    Lupus is a chronic disease marked by muscle and joint pain and inflammation (the abnormal immune response also may involve attacks on the kidneys and other organs).

2. Juvenile rheumatoid arthritis:

       Juvenile rheumatoid arthritis is a disease in which the body’s immune system acts as though certain body parts (such as the joints of the knee, hand, and foot) are foreign tissue and attacks them.

3. Scleroderma:

   Scleroderma is a chronic autoimmune disease that can lead to inflammation and damage of the skin, joints, and internal organs.

4. Ankylosing spondylitis:

      Ankylosing spondylitis is a disease that involves inflammation of the spine and joints, causing stiffness and pain.

5. Juvenile dermatomyositis:

     Juvenile dermatomyositis is a disorder marked by inflammation and damage of the skin and muscles.

Q.3 vi) Describe the role of T-cells and B-cells in transplant rejections.



  Transplantation is the act of transferring cells, tissues, or organs from one site to another. The malfunction of an organ system can be corrected with transplantation of an organ (e.g kidney, liver, heart, lung, or pancreas) from a donor. However, the immune system remains the most formidable barrier to transplantation as a routine medical treatment. The immune system has developed elaborate and effective mechanisms to combat foreign agents. These mechanisms are also involved in the rejection of transplanted organs, which are recognized as foreign by the recipient’s immune system.

Transplant rejection:  

  Transplant rejection occurs when transplanted tissue is rejected by the recipient’s immune system, which destroys the transplanted tissue. Transplant rejection can be lessened by determining the molecular similitude between donor and recipient and by use of immunosuppressant drugs after the transplant.

Role of B-cells in transplant rejection:

  The humoral response is an important mediator of chronic rejection, and numerous strategies have been developed to target either B cells or plasma cells.  B cells play a crucial role in graft rejection and autoimmune diseases by their ability to induce inflammatory immune response through their role of antigen-presenting cells and their unique ability to produce and secrete deleterious antibodies

Major Histocompatibility Complex (MHC) and the role of T-Cells::

   Major Histocompatibility Complex (MHC) proteins are involved in the presentation of foreign antigens to T-cells, and receptors on the surface of the T-cell (TCR) are uniquely suited to the recognition of proteins of this type. MHC is highly variable between individuals, and therefore the T-cells from the host recognize the foreign MHC with a very high frequency leading to powerful immune responses that cause rejection of transplanted tissue. Identical twins and cloned tissue are MHC matched and are therefore not subject to T-cell mediated rejection.

immunity system Biology Notes for Class 11 kpk boards 2021

DefinitionThe ability of a body which resit against the disease or pathogen is known as immunity.”Immunology:- it is the branch of biology in which we study immunity. 

Q; What is first-line defence, explain  its components:

Firstline defence definition:- “These is non-specific and included structures, chemicals, and processes that work to prevent pathogens from entering the body.

” Components of first-line defence: (also important for MCQs)

The first line defenders include the skin and mucous membranes of the respiratory, digestive, urinary and reproductive systems. 

(A) Skin as a first-line defence:Introduction:- skin is regarded as one of the first lines of defence because it provides a biological barrier, protecting the internal organ. 

Importance: (Role)

  1.  it protects the body especially the underlying tissues against pathogens.
  2.  it protects the body from excessive water loss.
  3. it is also involved in providing insulation and temperature regulations.

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