Chapter 12- Defences Against Pathogens/ Disease Flashcards
(42 cards)
Physical plant defences against pathogens
Callose- plants produce callose when under pathogen invasion. This is deposited between plant cell wall and plasma membranes making it harder for pathogens to enter cells.
Waxy cuticle- provided a physical barrier against pathogens. It also stops water collecting on the leaf, which reduces spread of pathogens by water
Cell wall form a physical barrier against pathigens
Plant chemical defences against pathogens
Insect repellents- eg pine resin
Insecticides - for example pyrethins. They acts as insect neurotoxins
Antibacterial compounds - for example phenols. These disrupts bacterial and fungal cell membranes.
Antifungal compounds -for example chitinases which are enzymes that break down chitin in fungal cell wall.
Animal non specific defences against pathogens
1) the skin- physical barrier, blocking pathogens from entering the body. Also a chemical barrier as it produces chemicals that are anti microbial
2) mucous membranes protect body openings eg nostrils as it traps pathogens and contains anti microbial enzymes
3) blood clots plug wounds to prevent pathogen entry and blood loss. Form from chemical reactions that take place when platelets are exposed to damaged blood vessels.
4) inflammation- damaged tissues release molecules that leak fluid to the surrounding area. This causes swelling and isolates pathogens that have entered damaged tissue. These molecules also cause vasodilation. This makes the area hot and brings white blood cells to fight off pathogens.
5) wound repair- skin is able to repair itself in the event of injury and reform a barrier against pathogen entry. It is repaired using collagen fibres.
6) expulsive fibres - this includes coughing and sneezing. This happens when mucous membranes are irritated by things like dust. Sneezing attempts to expel foreign objects.
What is an immune response
An immune response is the body’s reaction to a foreign antigen. The immune response involves specific and non specific stages.
What are the four main stages of the immune response
1) phagocytosis
2) T lymphocyte activation
3) B lymphocyte activation
4) Antibody production
What are opsonins
Molecules in the blood that attach to foreign antigens to aid phagocytosis
What is the process of phagocytosis
1) a phagocyte recognises the antigens on a pathogen
2) the cytoplasm of the phagocyte moves around the pathogen engulfing it. This may be easier with the presence of opsonins
3) the pathogen is now contained in a phagosome in the cytoplasm of the phagocyte
4) a lysosome fuses with the phagosome. The enzymes break down the pathogen.
5) the phagocyte then sticks the pathogen’s antigens onto its own surface to activate other immune cells. Here it acts as an antigen-presenting cell. (APC)
What are neutrophils
They are a type of phagocyte and the first white blood cells to respond to a pathogen inside the body. They move towards a wound in response to cytokines.
What are cytokines
They are proteins that act as messenger molecules. They are released by cells at the site of the wound.
How does T lymphocyte activation occur
1) Each T lymphocyte is covered in receptors and each lymphocyte is different to the next
2) when the receptor on the surface of the T lymphocyte meets a complementary antigen, it binds to it. (Receptors on APCs)
3) this process activates the T lymphocyte and is known as clonal selection.
4) this activated T lymphocyte undergoes clonal expansion (divided to produce clones of itself)
different types of activated T lymphocyte and their functions
1) T helper cells- release interleukins to activate B lymphocytes and T killed cells
2) T killer cells- attach to and kill cells that are infected with a virus
3) T regulatory cells- suppress the immune response from other white blood cells. This prevents immune system cells mistakenly attacking the host’s body cells.
Some activated T lymphocytes become memory cells.
What is the process of B lymphocyte activation
1) B lymphocytes are covered in antibodies. These antibodies bind to antigens to form an antigen- antibody complex
2) when an antibody on the surface of a B lymphocyte meets a complementary antigen, it binds to it.
3) with help from substances released by T helper cells, this activates the B lymphocyte. (Clonal selection).
4) the activated B lymphocyte the divides by mitosis into plasma cells and memory cells (clonal expansion)
What happens in antibody production
Plasma cells are clones of B lymphocytes. These secrete loads of the antibody, specific to the antigen in the blood. They bind it form lots of antigen-antibody complexes. This is a signal for the immune system to attack and destroy the pathogen.
How to identify cells in a blood smear
1)red blood cells will not be stained as they do not have a nucleus
2) white blood cells have a multi-lobed nucleus and the cytoplasm is grainy
3)monocytes have a kidney bean shaped nucleus
4) lymphocytes are smaller than neutrophils and nucleus takes up most of the cell.
What is the primary immune response
When a pathogen enters the body for the first time, the antigens on the surface activate the immune system. This is a primary response. This response is slow because there aren’t many B lymphocytes that can make the antibody needed to bind to the antigen. Eventually the body will produce enough of the right antibody to overcome the infection
What do Memory T/B lymphocytes do
1) Memory T lymphocytes remember the specific antigen and will recognise it a second time round
2) Memory B lymphocytes record the specific antibodies needed to bind to the antigen
What happens in the secondary immune response
If the same pathogen enters the body again, the immune system produces a quicker, stronger immune response. Clonal selection happens faster. Memory B lymphocytes divide into plasma cells that produce the right antibody to the antigen. Memory T lymphocytes are activated and divide into the correct T lymphocytes to kill the cell carrying the antigen. Secondary response often gets rid of pathogen before symptoms occur.
How to maintain immunity
Memory B and T lymphocytes have a limited lifespan. Once they have died, the person is susceptible to attack by the pathogen again. Immunity is maintained by continual exposure to the pathogen, so you continue to make more B and T lymphocytes.
Comparison between primary and secondary reponse
1) in primary, pathogen enters for 1st time, in secondary, pathogen enters for 2nd time
2) primary response is slow, secondary response is fast
3) in primary response, B and T lymphocytes are activated, in secondary response, memory cells are activated.
4) in primary response, there are symptoms. In secondary response, there is usually no symptoms.
What is an antibody’s structure
1) the variable regions of the antibody form the antigen binding sites. It is complementary to a particular antigen.
2) the hinge region allows flexibility when the antibody binds to the antigen.
3) the constant regions allow binding to receptors on immune system cells eg phagocytes. Constant region is the same in all antibodies, and disulphide bridges hold the polypeptide chains of the protein together.
Describe the process of agglutinating pathogens
1) each antibody has two binding sites, so an antibody can bind to two pathogens at the same time, so the pathogens become clumped together.
2) phagocytes then bind to the antibodies and phagocytose a lot of pathogens all at once.
3) antibodies that behave in this way are called agglutinins.
Describe the process of neutralising toxins
1) like antigens, toxins have different shapes. Antibodies called anti-toxins can bind to the toxins produced by the pathogens.
2) this prevents the toxins from affecting human cells, so the toxins are neutralised.
3) the toxin-antibody complexes are also phagocytosed.
How do antibodies prevent the pathogen from binding to host cells
1) when antibodies bind to the antigens on pathogens, they may block the cell-surface receptors that the pathogens need to bind to the host cells.
2) This means the pathogen can’t attach to or infect the host cells.
What is active immunity
This is the type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen
Natural- this is when you become immune after catching a disease
Artificial - this is when you become immune after you have been given a vaccination containing a harmless dose of antigen.
