Section 3

Question 1

What are antigens?

Answer 1

Proteins that can generate an immune response when detected by the body
Usally found on the surface of cells
Antigens that aren’t found in the body are called foreign antigens - these antigens are the ones that the immune system responds to
Antigens identify pathogens, abnormal body cells, toxins and cells from other individuals of the same species

Question 2

What is a pathogen and how do they link to antigens?

Answer 2

Organisms that cause disease e.g bacteria, viruses and fungi
All pathogens have antigens on their surface which are identified by the immune system

Question 3

What is a toxin and how do they cause an immune response? (short)

Answer 3

Toxins are poisons which are molecules - not cells
They can be produced by bacteria
The toxin itself is an anitgen it doesn’t have auntigens on its surface

Question 4

What is an abnormal body cell and how do they cause an immune response? (short)

Answer 4

Cancerous or pathogen infected cells have abnormal antigens on their surface which trigger an immune response

Question 5

Describe phagocytosis

Answer 5

1) A phagocyte recognises the foreign antigens on a pathogen
2) The cytoplasm of the phagoctye moves around the pathogen engulfing it
3) The pathogen is now contained in a phagocytic vacuole
4) A lysosome fuses with the phagocytic vacuole and lysozmes break down the pathogen
5) The phagocyte then resents the pathogens antigens on its surface to activate other immune system calles

Question 6

Describe the role of T cells in the immune response

Answer 6

A T cell is a type of WBC with receptor proteins on it that bind to complimentary antigens presented to it by phagocytes. This activates the T cell.
Helper T cells relsease chemical signals that activate and stimulate phagocytes and cytotoxic T cells which kills abnormal and foreign cells. Helper T cells also activate B cells whcich secrete antibodies

Question 7

Describe the role of B cells in the immune response

Answer 7

B cells are a type of WBC covered in antibodies - proteins that bind to antigens to form antigen - antibody comples
Each B cell has a different shaped antibody on its membrane so different ones bind to different shaped antigens
When the antibody on the surface of a B cell meets a complimentary shaped antigen they bind this activates the B cell. This process is called clonal selection and the activates B cell divides into plasma cells (clones)

Question 8

Describe antibody production in the immune response

Answer 8

Plasma cells secrete loads of antibodies specific to the antigen - monoclonal antibodies. The bind to the antigens on pathogens to form complexes
An antibody has two binding sites so can bind to two pathogens at the same time so the pathogens become clumped together this is called agglutination.

Question 9

What is antigenic variation?

Answer 9

Pathogens can change their surface antigens, different antigens are formed due to changes in the genes of a pathogen.
This means a secondary response can’t happen for the same pathogen and is makes it difficult to make vaccines.
Pathogens that do this are: HIV and influenza

Question 10

What are the ethical issues surrounding the use of vaccines?

Answer 10

Animal testing/ animal based substances used
Testing on humans - might not work - putting themselves at risk
Side effects
Who gets it first if there is an epidemic and limited supply

Question 11

What are the difference between active and passive immunity?

Answer 11

Active
Requires exposure to antigen
Takes a while for protection to develop
Memory cells produced
Protection is long term becuase the antibody produced is response to antigen being present in the bodu
Passive
Doesn’t require exposure to antigen
Protection is immediate
Memory cells aren’t produced
Protection is short term becuase the antibodies given are broken down

Question 12

What is passive immunity?

Answer 12

Immunity from being given antibodies made by a different organism. There are two types…
1) Natrual - when a baby becomes immune due to the antibodies it receives from its mother through the placenta and breast milk
2) Artificial - when you become immune after being injected with antibodies from someone else

Question 13

What is active immunity?

Answer 13

The immune system makes its own antibodies after being stimulates by an antigen. There are two different types…
1) Natrual - when you become immune after catching a disease
2) Artificial - when you become immune affter a vaccination

Question 14

What is the difference between the primary and the secondary immune response?

Answer 14

Primary
When an antigen enters the body for the first time it activates the immune system. It is slow becuse there aren’t many B cells that can make the antibody needed to bind to it. This will happen overtime meanwhile the person will show symptoms. After being exposed to an antigen, both T and B cells produce memory cells these remain in the body for a long time, they remember the specific antigen and will recognise it
Secondary
If the same pathogen enters the body again the immune system will produce a quicker stronger immune response. Clonal selection happens faster, memory B cells are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T cells are activated and divide into the correct type of T cells to kills the cell carrying the antigen. This response can get rid of the infectio before symptoms start to show.

Question 15

What is the difference between the cellular and humoral responses?

Answer 15

Cellular - The T cells and other immune system cells that they interact with (phagocytes) form the cellular response
Humoral - B cells,, clonal selection and the production of monoclonal antibodies form the humoral response

Question 16

Describe the general structure of an antibody

Answer 16

Proteins - made up of chains of amino acids
The specificity of an antibody depends on its variable regions which form the antigen binding sites
Each antibody depends has a varible region with a unique tertairy structure that is complimentary to one specific antigen
All antibodies have the same constant regions

Question 17

What are monoclonal antibodies?

Answer 17

Are produced from a single group of genetically identical B cells (plasma cells)

Question 18

How are monoclonal antibodies used in cancer drugs?

Answer 18

Different cells in the body have different surface antigens
Cancer cells have antigens called tumor markers that are not found on normal body cells
Monoclonal antibodies can be made that will bind to the tumor markers
You can also attach anti cancer drugs to the antibodies
When the antibodies come into contact with cancer cells they will bind to tumor markers and the drug will accumulate in the body where the cancer cells are

Question 19

How are monoclonal antibodies used in pregnancy tests?

Answer 19

Pregnancy tests detect the hormone hCG thats found in the urine of pregnant women
The application area contains antibodies that are complimentary to the hCG protein bound to a blue coloured bead
When urine is applied to the application area any hCG will bind to the antibody on the beads forming a complex
The urine moves up the strip carrying the beads with it
The strip contains antibodies to hCG that are stuck in place
If there is hCG present the test strip turns blue becuase the attached antibodies bind to hCG with the blue beads

Question 20

What is the ELISA test?

Answer 20

It can be used in medical diagnosis to test for pathogenic infections or allergies
An antibody is used which has an enzyme attached to it. The enzyme can react with a substrate to produce a coloured product
If there is a colour change it shows the antigen or antibody of interest is present

Question 21

Describe the direct ELISA test

Answer 21

Antigens from a patient sample are bound to the inside of a well
A detection antibody with an attached enzyme that it complimentary to the antigen of interest is added
If the antigen of interest is present the detection antibody will bind to it
It is then washed out
A substrate solution is added
If the detection antibody is present the enzyme will react with the substrate to give a colour change
The intensity of colour change can be measured by absorption

Question 22

Describe the indirect ELISA test

Answer 22

Used to detect antibodies in HIV
1) HIV antigens are bound to the well of a plate
2) A sample of the patients blood plasma is added to the well and the HIV antibodies will bind then it is washed out
3) A secondary antibody that had a specific enzyme attached to it is added. It binds to the HIV specific antibody and is washed again. If there is no primary HIV antibody the seconday antibody will be washed away as there is nothing to bind to
4) A solution is added to the well containing a substrate which will react with the enzyme attached to the secondary antibody and produce a coloured product

Question 23

What are the ethical issues around monoclonal antibodies?

Answer 23

Animals are used

Question 24

Describe the structure of HIV

Answer 24

Contains RNA and reverse transcriptase needed for virus replication
Outer coating if protein called a capsid
Extra outer layer called an envelope made of membrane stolen from previous host cell
Attachment proteins

Question 25

Describe HIV replication

Answer 25

1) Attachment proteins attach to receptor molecule on the cell membrane of a host helper T cell 2) The capsid is released into the cell where it uncoats and releases genetic material into the cytoplasm 3) Reverse transcriptase is used to make complimentary strand of DNA from the viral RNA template 4) DNA is made and inserted into the human DNA 5) Host cell enzymes are used to make viral proteins from the viral DNA 6) Viral proteins assemble and leave to infect other cells

Question 26

How do antibotics work and why don't they work on viruses?

Answer 26

They interfere with metabolic reactions and target bacterial enzymes and ribosomes Viruses don't have their own enzymes and ribosomes

Question 27

Describe the structure of gills in fish and how water passes through

Answer 27

Water enters the fish through its mouth and passes out through the gills Each gill is made of lots of thin plates called gill filaments which give a large surface area for exchange of gasses Gill filaments are covered in lamellae which increase surface area more and have lots of capillaires Gill > fillament > lamellea

Question 28

Describe gas exchange in fish

Answer 28

# The conc gradient is maintained over the whole length of the gill Counter current system Blood flows through the lamelae in one direction and water flows in the opposite direction So water with a high oxygen conc is always next to blood with a low oxygen conc so a steep gradient is maintained The gradient is maintained across the whole lengh off the gill

Question 29

Describe gas exchange in insects

Answer 29

Spiracles (pores) lead to trachea (air filled pipes) branch off into tracheoles (have thin permable walls with go to individual cells) Oxygen diffuses directly to respiring cells CO2 moves down its gradient out the spircales Abdomial pumping moves air in

Question 30

How do insects prevent water loss?

Answer 30

Close their spircales Waterproof waxy cuticle Tiny hairs around the spircales which reduced evapouration

Question 31

How do plants prevent water loss?

Answer 31

Stomata close as they become flacid due to water loss Xerophytes Sunken stomata in pits - trap water vapour reducing evapouration Little hairs on the epidermis to trap vapour around the stomata Curled leaves with stomata inside protecting them from wind which would increase evapouration Reduced number of stomata Thick waxy waterproof cuticle preventning evapouration

Question 32

Describe what happens in humans during inspiration (breathing in)

Answer 32

The external intercostals and diaphragm contract causing the ribcage to move upwards and out and the diaphragm to flatten Increasing the volume of the thoracic cavity decreasing the pressure below atmospheric causing air to move down a pressure gradient into the lungs An active process - requires energy

Question 33

Describe what happens in humans during expiration (breathing out)

Answer 33

External intercostals and diaphragm relax moving the ribcage downwards and in and the diaphragm domes Decreasing the volume of the thoracic cavity increaing the pressure above atmospheric cauing air to move down a pressure gradient out of the lungs Passive process unless forced (blowing out)

Question 34

Desribe the structure of an alveoli

Answer 34

Walls made from a single layer of thin flat cells called epithelium Covered in a network of capillaries The walls are elastic which help them to recoil back to its normal shape after inhaling and exhaling air

Question 35

Define Tidal volume Ventilation rate Forced expiratory volume Forced vital capacity

Answer 35

Tidal volume - the colume of air in each breath Ventilation rate - number of breaths per minuet Forced expiratory volume - maximum volume of air that can be breathed out in one second Forced vital capacity - maximum volume of air it is possible to breath forcefully out of the lungs after a deep breath in

Question 36

Describe the digestion of carbohydrates

Answer 36

Amaylase breaks down starch by breaking glycosidc bonds to produce maltose Amalyase is produced by the slivary glands and the pancreas Membrane bound disaccharides are enzymes attached to the cell membrane of the epithelial cells lining the ilem (the final part of the small intestine) they break down disaccharides Sucrase breaks down sucrose into glucose and fructose Maltase breaks down maltose into glucose Lactase breaks down lactose into glucose and galactose

Question 37

Describe the digestion of lipids

Answer 37

Lipase breakdown lipids into monoglycerides and fatty acids by hydrolysing ester bonds. Lipases are produced in the pancrease Bile salts are produced by the liver and emulsify lipids creating a larger surface area for lipases to work on Once the lipid has been broken down the monoglycerides and fatty acids stick with the bile salts to form micelles which allow them to be absorbed

Question 38

Describe the digestion of proteins

Answer 38

Endopeptidases - hydrolyse peptide bonds within the protein Exopeptidases - hydrolyse peptide bonds at the ends of proteins Dipeptidases - work on dipeptides - located on the membrane in the small intestine (membrane bound)

Question 39

How are digestion products of carbohydates (monosaccharides) absorbed?

Answer 39

Glucose and galactose is absrobed by co transport Frucose is absrobed by facilitated diffusion

Question 40

How are digestion products of lipids (monoglycerides and fatty acids) absorbed?

Answer 40

Micelles move monoglycerides and fatty acids towards the epithelium and release them They are lipid soluble so can diffuse direclty across

Question 41

How are digestion products of proteins (amino acids) absorbed?

Answer 41

Co transport

Question 42

What is affinity?

Answer 42

The tendancy a molecule has to bind with oxygen

Question 43

What is the relationship between affinity and ppO2

Answer 43

ppO2 increases haemoglobin affinity increases Oxygen onto haemoglobin loads at high ppO2 Oxyhaemoglobin unloads oxygen at low ppO2

Question 44

Why is the dissociation curve for haemoglobin S -shaped?

Answer 44

When haemoglobin binds with the first O2 molecule the shape alters so its easier for another one to bind But as the haemoglobin becomes saturated it gets harder for O2 to join So the curve has a steep bit in the middle where O2 can easilly bind and shallow parts at each end where it is harder

Question 45

What is the effect of the dissociation curve with CO2?

Answer 45

haemoglobin gives up O2 more easilly as higher ppCO2 to get more O2 to respiring cells during activity When cells respire they raise the ppCO2 which increases the rate of oxygen unloading so the curve shifts right - the Bohr shift

Question 46

How do low oxygen enviroments affect organisms haemoglobin?

Answer 46

They have haemoglobin with a higher affinity for oxygen becuase not much oxygen is avaliable the curve shifts to the left

Question 47

How do high activity levels affect organisms haemoglobin?

Answer 47

There is high oxygen demand with a lower affinity for oxygen becuase oxygen needs to be easilly unloaded so the curve shifts right

Question 48

How does size enviroments affect organisms haemoglobin?

Answer 48

Small animals have a higher surface area to volume ratio so they loose heat quickly so they have a high metabolic rate which means they have high oxyen demand They have a lower affinity for oxygen becuase it needs to unload more easilly so the curve shifts right

Question 49

What are the function of the coronary arteries?

Answer 49

Provide the heart with blood

Question 50

Where does .... take blood from and to? Pulmonary artery Pulmonary vein Aorta Vena Cava Renal artery Renal vein

Answer 50

Vessel from Lungs Pulmonary artery Heart Lungs Pulmonary vein Lungs Heart Aorta Heart Body Vena Cava Body Heart Renal artery Body Kidneys Renal vein Kidneys Vena Cava

Question 51

What is the structure of the arteries?

Answer 51

Thick and muscular walls Elastic tissue which stretches and recoils which helps maintain the high pressure The inner lining (endothelium) is folded allowing the artery to stretch and maintain high pressure

Question 52

What is the function of the arteries?

Answer 52

They carry blood from the heat to rhe rest of the body Carry oxygenated blood except for the pulmonary arteries which take deoxygenated blood to the lungs

Question 53

What is the structure and function of arterioles?

Answer 53

Arteries divides into smaller vessels called arterioles which form a network throughout the body Blood is directed to different areas of demand in the body by muscles inside the arterioles which contract to restrict blood flow or relax to allow full blood flow

Question 54

What is the structure and function of veins?

Answer 54

Veins take blood back to the heart under low pressure They have wider lumen and little elastic or muscle tissue Veins have valves to stop backflow Blood flow is helped in the veins by the contraction of body muscles surrounding them All veins carry deoxygenated blood except for pulmonary veins which carry oxygenated blood from the heat to the lungs

Question 55

What is the structure and function of capillaries?

Answer 55

Arterioles branch into capillaries Substances are exchanged between cells and capillaries so are adapted for efficient diffusion They are always near cells, have a one cell thick wall and lots of them Networks of capillaries are called capillary beds They connect arterioles and venules together Venules are small blood vessels that connect to veins

Question 56

What is tissue fluid?

Answer 56

Fluid that surrounds cells in tissues made from small molecules that leave the blood plasma e.g oxygen, water and nutrients Cells take in oxygen and nutrients from the tissue fluid and release metabolic waste into it

Question 57

Describe how tissue fluid is formed

Answer 57

Pressure filtration At the start of the capillary bed nearest the arteries the hydrostatic pressure in the capillaries is greater than in the fluid forcing fluid out of the capillaries and into the space around the cells forming tissue fluid As fluid leaves the hydrostatic pressure is reduced in the capillaires so it is much lower at the venule end Due to the fluid loss and an increasing concentration of plasma proteins which don't leave the capillaries the water potential at the venule end is much lower than the water potential in the tissue fluid Water re enters the capillaries from the tissue fluid by osmosis Excess tissue fluid is drained by the lymphatic system and passes it back into the cirulatory system

Question 58

How do valves work?

Answer 58

If there is greater pressure behind the valve it will be forced open If there is greater pressure infront of the valve it will be forced shut Ensuring a one direction flow of blood

Question 59

Describe the cardiac cycle

Answer 59

1) Ventricels relax atria contract The volume of the atria decreases increasing the pressure pushing blood into the ventricles 2) Ventricles contract atria relax Ventricles volume decreases and pressure increases forcing AV valves shut to prevent back flow The pressure is higher than the aorta and pulmonary artery forcing open the SL valves 3) Both relax The high pressure in the pulmonary artery and the aorta close the SL valves preventing back flow Blood returns to the heart and the atria fill again due to the high pressure in the vena cava and pulmonary vein This increases the pressure of the atria so AV valves open allowing blood to passively flow into the ventricels The atria contract and the process repeates

Question 60

What is the equation to do with the heart

Answer 60

Cardiac output = stroke volume x heat rate Cardiac out put - volume of blood pumped by the heart per minuet Stroke volume - volume of blood pumped out each heart beat Heart rate - number of beats per minuet