Biology stupied questions part 2

Question 1

List the defences that concentrate on preventing the spread of pathogens through the plant

Answer 1

• Stomatal closure – the stomata close in the part of plant which detects the pathogenic organisms, the guard cells close the stomata preventing entry in that part of the plant
• Callose – this is a large polysaccharide that is deposited in the sieve tubes, around the sieve plates this blocks flow in the sieve tube and prevents the pathogen from spreading around the plant - blocks the plasmodesmata
• Tylose formation – this is a balloon like swelling that fills the xylem vessel, when a tylose is fully formed then the vessel can no longer carry water, therefore the pathogens cannot be spread via the xylem vessel, the water can go out the boarded pits to the other xylem vessels, the tylose contains a high concentration of chemicals such as terpenes that are toxic to pathogens
• Oxidative produces highly reactive oxygen molecules capable of damaging the cells of invading organisms

Question 2

explain the difference between passive and active protection

Answer 2

• Passive defences are defences present before an infection, they prevent the entry and spread of the pathogen
• Active protection is when pathogens attack specific chemicals in pathogenic cell walls can be detected by the plant cells, the plant then increases the defences already present this would be increasing physical defences and making more toxic chemicals

Question 3

How do tyloses protect plants from disease

Answer 3

• Tylose formation is a balloon like swelling that fills the xylem vessel, when the tylose is fully formed the vessel can no longer carry water and the pathogens can no longer be spread by the xylem vessel, tylose contains a high concentration of chemicals such as terpenes that are toxic to the pathogens this kills the pathogens – these are produced after the pathogen has been detected as they require a lot of energy to be produced

Question 4

describe two ways in which callose helps to protect plants from disease

Answer 4

• The callose is deposited in the phloem in the sieve tubes, it is deposited around the sieve tube plates this blocks the flow of the sieve tube and prevents the pathogen from spreading
• The callose deposits are polysaccharide polymers that impede cellular penetration at the site of infection this strengthens the cell wall and blocks the plasmodesmata so the pathogen cannot get out

Question 5

Hoe necrosis can help to save the whole plant

Answer 5

• This is deliberate cell suicide, this is when a few cells are scarificed to save the rest of the plant, by killing the cells surrounding the infection it limits the pathognes access to water and nutrients and stops it from spreading around the plant therefore isolating it and killing it, necrosis is brought about by intracellular enzymes that are activated by injury these enzymes destroy damaged cells and produces brown spots

Question 6

suggest how T-killer cells might recongnise and infected host cells

Answer 6

• T – killer cells would recognise a foreign antigen on the pathogen, the T-killer cell has a complementary shape to the receptors of the t-killer cells membrane so they can lock into place and kill it

Question 7

What is the role of memory cells

Answer 7

• The role of the memory cells is the provide long term immunologically and produce a quick response when there is a secondary infection as they are stimulated and undergo clonal expansion quicker that origninally in the primary immune response

Question 8

Why are T - regulator cells needed

Answer 8

• T-regulator cells are needed as they stop the immune response after the pathogen has been completely eradicated, this prevents autoimmunity

Question 9

Explain why cell-signalling molecules such as interleukins have a very specific shape

Answer 9

• Interleukins have specific shapes so they can bind to naïve B cells in order to stimulate their proliferation, they need to stimulate the correct B cell to clonally expand in order to fight the invading pathogen and have the right receptors on the B cell membrane to complement the shape of the foreign antigens

Question 10

suggest why the immune system does not normally attack our own cells

Answer 10

• The immune system does not attack our own immune system as normally when you are born the B or T cells that are specific to our own antigen shape our destroyed
• Not specific to attack our own body cells and tissues therefore don’t have the complementary shape

Question 11

what might cause an onset of an autoimmune disease

Answer 11

• An autoimmune disease arises when antibodies attack our own antigens as antigens that are not normally exposed become exposed to attack, for example tissue around joints might become exposed that are not normally exposed therefore the antibodies would attack those membranes and antigens on our own tissue
• If the B and T lymphocytes are not destroyed when we are developing that are specific to our immune system

Question 12

Distinguish between an antigen and an antibody

Answer 12

• An antigen is a molecule that stimulates an immune response, these are usually proteins and glycoproteins in the plasma membrane of the pathogen
• Antibodies are molecules that are specific to the antigen, they are immunoglobulins and released in response to an infection, they have a complementary shape to the pathogen, they attach to the antigen and render it harmless

Question 13

why is it important that some opsonins are not specific

Answer 13

• So they can stick to types of molecules that are not found in the host cell, so they can attach to a various amount of pathogens and back to the phagocytes so the phagocytes can do phagocytics

Question 14

what is meant by the term immunoglobulin

Answer 14

• Immunoglobulin is a protein produced by plasma cells and lymphocytes, they play an essential role in the body’s immune system as thy attach to foreign cells assisting in destroying them, they are antibodies

Question 15

How are plasma cells specialised for their role

Answer 15

• numerous ribosomes
• a lot of rough ER - contains the ribosomes and acts as a site for protein synthesis
• a lot of Golgi apparatus - processes proteins for secretion, containing a set of glycosylation enzymes that attach various sugar monomers to proteins as the proteins move through the apparatus.
• numerous mitochondria

Question 16

Explain what is meant by having a shape that is complementary to the shape of the antigen

Answer 16

• This means the shape of the antibodies is specific to the shape of the antigen and it can lock into place on the antigen and fit around it

Question 17

describe how the structure of the antibody enables it to perform its function

Answer 17

• The variable region is the end bit of the antibody which can vary in shape, it has a shape that is specific to the shape of the antigen, to get a different shape there is a different amino acid sequence
• The disulphide bridge/bond holds the antibody polypeptide chains together
• The hinge region allows the antibody to flex so it can fit more than one antigen on to the antibody
• The constant region is the same shape for all antibodies to bond to the receptors and attach to the neutrophils so they can carry out phagocytosis

Question 18

explain why it takes several days for the primary immune response to become effective

Answer 18

• Clonal expansion, clonal selection, antigen to be presented on the cells special protein complex, differentiation and lack of memory cells