communicable disease ocr a level biology

What is a pathogen?

A microorganism that causes disease

what are the 4 types of pathogen

bacteria, viruses, protists, fungi

How do bacteria cause disease?

by destroying cells and releasing toxins

How do viruses cause disease?

They invade and reproduce inside living body cells, leading to cell damage.

How does fungi cause disease?

Digest living cells and destroy or produce toxins.

how do protists cause disease

- transported via a vector eg. Malaria is transported via mosquitoes

- Take over cells

- Feed on cell contents

- Divide before breaking out of the cell

Examples of bacterial diseases

tuberculosis, bacterial meningitis, ring rot

examples of viruses

HIV/AIDS, influenza, tobacco mosaic virus

examples of fungal disease

Athletes foot, ring worm, black sigatoka

examples of protists

malaria, tomato or potato blight

how are bacterial diseases treated

antibiotics

how do bacteria reproduce

binary fission

how are diseases transmitted

-direct contact

- exchange of bodily fluids

- vectors

- contamination

- airborne

what is direct transmission

person to person

what is one disease transmitted by direct contact

meningitis

what is one disease transmitted by indirect contact

malaria- by mosquitoes

what are the two types of airborne disease

droplet infection and truly airborne

what is a vector and example of (transmission)

indirect transmission

what are the two types of plant defences against disease

passive physical and chemical defences

what are passive physical plant defences

cellulose

bark

stomatal closure

waxy cuticle

callose

tylose

what is a callose

A large polysaccharide deposit that blocks old phloem sieve tubes

what is tylose

A balloon-like swelling or projection that fills the xylem vessel

what are plant chemical defence examples

terpenoids

tannins

alkaloids

pheremones

what are the two types of human defence

primary and secondary

what is a primary defence

One that prevents pathogens from entering the body

what is a secondary defence

One that is used to combat pathogens that have entered the body

what is the main primary defence

The body is covered by the skin. This is the main primary defence.

why is skin a good primary defence

it is impermeable due to keratin

examples of primary defences

Skin / Blood clotting and skin repair / Mucous membranes / Coughing and sneezing / Inflammation / tear fluid in eyes / wax in ears / mucus plug in cervix

What does inflammation promote

vasodilation

more neutrophils to cell surface

what are the two types of phagocyte

neutrophils and macrophages

features of macrophages

A. Large, irregularly shaped w/ big cytoplasm

B. Extremely long lived

C. Phagocytic

D. Function as antigen presenting cell (APC)

Features of neutrophils

multi-lobed nucleus

short lived

where are neutrophils and macrophages made

bone marrow

What happens in phagocytosis?

1. phagocytes recognises foreign antigen on pathogen

2. opsonins bind to antigen by complementary binding

3. phagocyte binds to opsonin to get close to pathogen

4. pathogen is engulfed by phagocyte and enclosed in phagosome

5. phagosome fuses with lysosomes to release lysozomes which breakdown pathogen

What is an opsonin?

a protein bound to the surface of a pathogen that facilitates its phagocytosis.

what is an antigen presenting cell

A cell with antigens on the surface, macrophages

how are phagocytes specialised and why

- well developed cytoskeleton to help them change shape and move lysosomes around

- many mitochondria to release energy for cell movement

- many ribosomes to synthesis lysosomes

- lobed nucleus to help squeeze through narrow gaps

what are the two types of secondary response

-non-specific- phagocytosis

-specific

what is specific immune response

tailored to a specific pathogen

Where are T lymphocytes produced and matured?

Produced in bone marrow, matured in thymus

where are B lymphocytes produced and matured?

produced and matured in bone marrow

what happens in the cell mediated response

1. T helper cells have receptors which bind to antigens on APC

2. once attached, T helper cells are activated to divide by mitosis to replicate

3. clone T helper cells can differentiate into different cell

what can T helper cells differentiate into

- some remain as T helper cells and activate B lymphocytes

- some stimulate macrophages to undergo more phagocytosis

- some become memory cells

- some become T killer cells

what is a fomite

An object that transmits diseases such as a door knob, microphone, etc...

What are interleukins?

A type of cytokine released by T helper cells to stimulate clonal expansion.

What are agglutinins?

Antibodies that cause pathogens to stick together to allow for better recognition

what are antitoxins

Chemicals that neutralise the poisonous effects of the toxins

what do cytotoxic t cells do

Kill abnormal and foreign cells

how to T killer cells kill abnormal cells

- they release perforin which imbeds into the cell surface membrane allowing a pore to be created

- any substance can now leave or enter and therefore it kills the cell

What is humoral immunity?

This is when antibodies attack antigens that are free in the plasma (exogenous antigens).

What happens in the humoral response?

After being signaled to divide by helper T cells, B cells turn into plasma cells, which release antibodies. In turn, the antibodies attach to antigens, signaling the macrophages to come and get them

what is clonal selection

process by which a lymphocyte proliferates and differentiates in response to a specific antigen

what is clonal expansion

an increase in the number of cells by mitotic cell division

what happens in clonal expansion

B antigen presenting cells divide and differentiate into plasma cells to create specific antibodies

what happens in clonal selection

The undifferentiated T or B lymphocyte has a receptor complementary to the pathogen's antigen (either in an MHC in cell mediated immunity or on a pathogen in humoral immunity). It binds to the antigen using this, and the lymphocyte then divides rapidly by mitosis

what is the cell mediated response

response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

what happens in the cell mediated response

T helper cells bind to APC by their CD4 receptor

- they release interleukins

- stimulates T helper cells to:

create T killer cells

create T memory cells

Promote increase in B cells

Promote more phagocytosis