Infections and Immunity

Question 1

What is an infection?

Answer 1

Infection is the invasion of an organism’s body tissues by disease-causing agents. Infections are caused by pathogenic viruses, bacteria, protozoans or fungi.

Question 2

Plant pathogens harm plant ___ and ____.

Answer 2

Growth

Reproduction

Question 3

What type of immune system do plants have?

Answer 3

An Innate Immune system.

Question 4

Define Innate Immunity?

Answer 4

Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen’s appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells that attack foreign cells in the body.

Question 5

How does the plant fight an infection?

Answer 5

1. It recognises the shape of the infecting pathogen. The infected cells are stimulated to:
   - produce salicylic acid
   - activate resistance genes
   - self-destruct
2. The Salicylic Acid moves from the site of infection through the phloem to uninfected parts of plants to activate the immune system to produce defensive compound. It is called system acquired resistance

Question 6

What is Salicylic Acid?

Answer 6

An aspirin-like compound, which is a plant hormone or signal.

Question 7

How are stomata important for the plant preventing infection?

Answer 7

Stomata have been thought of as an easy place for pathogenic bacteria to enter. However, recent studies suggest that stomata by closing can play an active role in limiting bacterial infection.

Question 8

Define first line of defense.

Answer 8

The first line of defence (or outside defence system) includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include your skin, tears, mucus, cilia, stomach acid, urine flow, ‘friendly’ bacteria and white blood cells called neutrophils.

Question 9

Define Second line of defense.

Answer 9

The second line of defense is nonspecific resistance that destroys invaders in a generalized way without targeting specific individuals

Question 10

What are the 2 responses part of the second line of defence?

Answer 10

• Primary Response: It tries to destroy the germs and prevent them from spreading. This can be brought about by: 1. Inflammation (local infection) and 2. fever (raised body temperature)
• Secondary Response: activate the immune system if germs do start to spread.

Question 11

What is immunity?

Answer 11

It is the body’s active response to an infection.

Question 12

What are the two features of a secondary response?

Answer 12

• Destruction of the invading germs

- Holding a memory of this response

Question 13

What the two types of white blood cells?

Answer 13

1. Lymphocytes

2. Phagocytes

Question 14

Where are T and B lymphocytes found?

Answer 14

Lymphoid organs, e.g. tonsil, lymph glands, spleen and in the blood.

Question 15

How do B lymphocytes destroy germs? (6)

Answer 15

• Germs have molecules called antigens on their surface
• Th antigen ‘tells’ the B lymphocytes that the germ is ‘non-human ‘ and is dangerous. There are countless type of B lymphocytes; each is able to recognise its specific antigen
• The B lymphocyte having recognised its specific antigen replicates itself rapidly producing lots of identical cells
• The B lymphocytes are then stimulated to produce proteins called antibodies which are secreted into the plasma through which they circulate
• The antibodies combine with the antigens on the germs surfaces. This will destroy or neutralise the germs
• Some of these B lymphocytes stay on in the lymph glands as memory cells. If they encounter their antigen, they mount a dry quick response, killing the germ before it can multiply.

Question 16

What is another word for an antibody?

Answer 16

Immunoglobulins

Question 17

What is natural immunity?

Answer 17

Immunity that is naturally existing, Natural immunity does not require prior sensitization to an antigen.

Question 18

When does natural immunity occur?

Answer 18

It occurs when a person has an attack of a disease so that antibodies (and memory cells) are produced and give protection against a future attack.

Question 19

Define antigen.

Answer 19

A protein or large polysaccharide molecule in the coating of a virus or a bacterium (and other foreign substances e.g. pollen grains and transplanted tissue) which cause B lymphocytes to make antibodies.

Question 20

Define antibody.

Answer 20

A protein made by B lymphocytes that destroys or neutralises a germ (or foreign particle)

Question 21

How do antibodies destroy the germs? (4)

Answer 21

• Cause the bacterial cells to burst
• Make it easier for the phagocytes to ingest germs by leaking the germs for phagocytosis
• Make the germs clump together which weakens them. The clumps are then more easily ingested by phagocytes.
• Neutralise bacterial toxins , e.g. toxins produced by salmonella bacteria. These antibodies are called antitoxins.

Question 22

Define antitoxin.

Answer 22

Antibody released by a B lymphocytes that neutralises a bacterial toxin or a virus.

Question 23

What are T lymphocytes?

Answer 23

These are T lymphocytes that are matured in the thymus (a gland in the chest) and then migrated to the lymph glands and other lymphatic organs.

Question 24

What are the 3 types of T lymphocytes?

Answer 24

1. CD4 (helper T cells)
2. Killer T cells
   - Suppressor cells

Question 25

What is the role of CD4 cells?

Answer 25

Start immune response to infections. They do this by helping B lymphocytes, killer T cells and phagocytes do their work. These cells help suppress or regulate immune responses.

Question 26

What is the role of Killer T cells?

Answer 26

Killer T cells (also called cytotoxic T cells) destroy body cells infected by viruses and some parasites. Killer cells insert protein called perforin into the target cell, causing it to swell and burst. Killer cells do not harm bacteria.

Question 27

Killer cells can play a role in destroying cancer cells and transplanted organs, unless _____ drugs are given to the patient to stop this from happening.

Answer 27

Immunosuppressive

Question 28

What are suppressor cells?

Answer 28

Suppressor cells act as brakes stopping the immune response once an infection is over

Question 29

What are phagocytes?

Answer 29

Phagocytes are cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. (They are large lymphocytes that can change their shape.)

Question 30

Where are phagocytes produced?

Answer 30

Red bone marrow and move into lymphoid tissues and connective tissue.

Question 31

Steps of phagocytosis. (6)

Answer 31

Step 1:
The cell that will perform phagocytosis is activated.

Step 2:
In the immune system, chemotaxis may occur. Chemotaxis is the movement of phagocytes toward a concentration of molecules.

Step 3:
The cell attaches to the particle that it will ingest. Attachment is necessary for ingestion to occur.

Step 4:
The cell ingests the particle, and the particle is enclosed in a vesicle (a sphere of cell membrane with fluid in it) called a phagosome. The phagosome transports the particle into the cell.

Step 5:

A lysosome fuses with the phagosome and the particle is digested. Lysosomes are vesicles that contain hydrolytic enzymes that break down molecules. A phagosome fused with a lysosome is called a phagolysosome.

Step 6:

Cellular waste, such as broken down molecules that the cell cannot reuse, is discharged from the cell by the process of exocytosis.