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Question 1

regulating mucus water content: excess water (5 steps)

Answer 1

1. Na+ actively pumped across the basal membrane out of the cell into tissue fluid making a concentration difference between mucus and cell.
2. Na+ diffuses through sodium channel (ENaC) in apical membrane into cell down concentration gradient.
3. electrical gradient between tissue fluid and mucus. Cl- diffuses down electrical gradient from mucus between cells to tissue fluid
4. water is drawn out of cell in tissue fluid by osmosis due to high salt conc. in tissue fluid
5. water is drawn out of mucus by osmosis into cell down concentration gradient.

Question 2

regulating mucus water content: too little water (5 steps)

Answer 2

1. Cl- from tissue fluid is pumped into cell across basal membrane
2. Cl- diffuses through the open CFTR channel into mucus down concentration gradient.
3. Na+ diffuses down electrical gradient from tissue fluid into mucus via gap between cells
4. elevated salt concentration in mucus draws water out of the cell by osmosis
5. water is drawn into cell by osmosis

Question 3

regulating mucus water content: CF lungs

Answer 3

1. CFTR channel is absent or not functioning
2. Na+ channel is permanently open allowing Na+ to diffuse into cell
3. Na+ is pumped out of the cell into tissue fluid
4. Cl- down electrical gradient into tissue fluid
5. water is continually removed from mucus by osmosis

Question 4

what is the result of water being continually removed from the mucus in CF lungs

Answer 4

mucus is too sticky and cant be moved by cilia

1. mucus to build up effecting ventilation of aveoli
2. mucus becomes infected with bacteria
3. phagocytic cells that kill pathogens are produced
4. phagocytes break down releasing DNA which makes the mucus even more sticky
5. causing airway inflammation and lung damage

Question 5

what is the evidence for the fluid mosaic model

Answer 5

• experiments showed types of proteins could dissociated from the membrane and others that could not. this supports fluidity and the fact there are some peripheral proteins and some integrated proteins
• freeze-fracture electron microscopy fractured between the lipid layer to show that the inner surface was a smooth mosaic interspersed with large proteins.
• plant proteins lectins bind to polysaccharides labled and when mixed with membrane lectins only bond to the outer surface membrane showing polysacharides where on outside.
• fusing mouse and human cells after 40 mins protein completely intermixed showing components are fluid

Question 6

the experiment to prove DNA replication is semi conservative

Answer 6

• DNA either replicates fragmentary, semi conservatively or conservatively.
• melso and stah grow escherichia coli DNA bacterium in medium contain heavy isotope N15 alll nucleotides contain heavy nitrogen making DNA more dense.
  bacteria then moved to medium containing normal N14 all new nucleotides light.
  bacteria allowed to divide once. DNA then extracted and centrifuged producing a bond of medium density DNA so DNA did not replicate conservatively
  if allowed to undergo a second division producing a strand of medium DNA and one light band of DNA proving DNA did not replicate fragmentary

Question 7

how to test for CF in fetuses and embryos

Answer 7

amniocentesis: inserting needle into amniotic fluid to collect fetal cells. 15 -17 weeks. 1% risk of miss carriage

chorionic villus sampling: sample of precental tissue removed through wall of abdomen or vagina. 8-12 weeks 1- 2% risk of miss carriage

non invases prenatal diagnosis NIPD: analysing DNA fragments in mother’s blood plasma 10-20% embryo cell free fetal DNA. 7-9 weeks. no risk of misscarrige

testing before implantation PGD: first undergo IVF them embryo at around 8 cells and 1 cell removed DNA tested . the healthy embryos are then implanted. low live birth rate. expensive but no need for abortion

Question 8

stages in atherosclerosis

Answer 8

1. endothelium becomes damaged and dysfunctional
   edothelium becomes damaged and dysfunctional. resulting in high blood pressure. putting extra strain on cells.
2. inflamatory response
   white blood cells move into artery wall. they accumalate chemicals such as cholesterol. a fatty deposit builds up called an atheroma
3. plaque is formed
   calcium salts and fibrous tissue build up at the site resulting in hard swelling called plaque. artery wall loses elasticity and hardens.
4. lumen becomes narrower
   making it more difficult to pump blood
   and leads to a rise in blood pressure
5. feedback
   plaque –> rise in blood pressure —> damage to edothelium —> plaque

Question 9

what are the stages in the blood clotting cascade

Answer 9

1. plaque reptures exposing collagen to the blood
2. platelets and damage tissue release a protein called thromboplastin
3. thromboplastin activates enzyme that catalyses convertion of protein prothrombin into enzyme called thrombin. protein, vitamin k and calcium must be present
4. thrombin then catalyses conversion of soluble plasma protein, fibrinogen insoluble fibrin.
5. a mesh of fibrin forms that traps more platelets and red blood cells to form a clot.

Question 10

name the steps in fertilisation

Answer 10

1.the acrosome reaction
when the front of the sperm touches the zona pellucida of the egg the acrosome bursts and releases enzymes which digest a channel in the zona pellucida
2. membrane fusion
the surface membranes of the sperm and egg fuse together allowing the haploid nucleus from the sperm to enter the cytoplasm of the egg
3. cortical reaction
vesicles inside the egg called cortical granules fuse with the cell membrane and release their contents. these cause changes in the surface layer of the egg preventing other sperm from entering
4. meiosis is restarted
the egg is really a secondary ocyte and the presence of the sperm cell causes the 2nd division and meiosis to now occur
5. fertilisation
the chromosomes from the haploid egg and sperm combine to restore the diploid number

Question 11

what is the lac operon model

Answer 11

prokaryote escherichia coli.
only produce the enzyme beta- galactosidase to break down carbohydrate lactose when present in surroundings converts disaccharide lactose to monosaccharides glucose and galactose

when lactose is not present a lactose repressor molecule bonds to the DNA to prevent transcription of beta-glaactosidase gene.
RNA polymerase cannot bind to the DNA promoter region.
when lactose is present it binds to the repressor preventing it from binding to the DNA and the gene is transcribed

Question 12

evolution by natural selection

Answer 12

1. introduction of selection pressure caused by change in environment, competition or predators.
2. random mutations produce new alleles which is advantageous. this is caused by natural genetic variation
3. individuals with the advantageous allele survive and reproduce.
4. advantageous allele is passed on.
5. there is a increased frequency of the advantageous allele in the population / gene pool.

Question 13

taxonomic hierarchy

Answer 13

series of taxa which members all share one or more common feature

1. kingdom
2. phylum
3. class
4. order
5. family
6. genus
7. species

Question 14

types of kingdoms

Answer 14

1. animali
   muticellular eukoryates that are heterotrophs
2. plantae
   muticellular eukoryates that are autotrophs
3. fungi
   muticellular eukoryates that are heterotrophs or absorb nutrients from decaying matter
4. protoctista
   eukaryotes that photosynthesis or feed on organic matter
   but not included in other kingdoms
5. prokyaryotae
   prokaryotic organisms
6. chromista
   includes some groups of fungi plantae and protoctista. which all have tinsel like flagella. the shared features between them make them more closely related to each other than any other kingdom

Question 15

what are plant cell walls made of

Answer 15

cellulose. which is a polymer of alpha and beta glucose.
each chain contains 1000 - 10000 units. straight chain. H bonds form between OH groups of neighbouring chains forming bundles called microfibrils which are about 60 -70 cellulose molecules wound in helical arrangement stuck together with polysacharide glue
hemicellulose and pectins

Question 16

what are the steps in mass transport

Answer 16

1. photosynthetic products are actively loaded into phloem increasing solute concentration. which draws water into sieve tubes by osmosis from adjacent xylem vessels
2. this increases hydrostatic pressure at loading end
3. at sink, solutes are unloaded lowering hydrostatic pressure. the difference in pressure between loading and unloading site causes mass flow along the sieve tube from high to low pressure

Question 17

temperature coefficient Q10

Answer 17

Q10 = rate of reaction at temperature T + 10oc / rate of reaction at temp T
the rate of collision and so the rate of reaction approximately doubles for each 10oc rise in temperature this is shown in the Q10 ratio
describes mathematically what happens to the rate of reactions as temperature increases by 10oc

Question 18

how does allopatric speciation occur

Answer 18

• geographical barrier causes 2 populations to become re-productively isolated.
• the 2 groups are exposed to different selection pressures leading to random advantageous mutations accumulating causing allele frequency in the 2 populations to change
• overtime the allele frequency changes so much that when reintroduced they are not able to interbreed to produce fertile offspring.

Question 19

what are the isolating mechanisms that cause sympatric speciation (6)

Answer 19

• ecological isolation
• temporal isolation
• behavioural isolation
• physical incompatibility
• hybrid in-availability
• hybrid sterility

Question 20

what happens in the light dependent reaction (6 steps)

Answer 20

1. light absorbed by chlorophyll in the thylakoid membrane
2. energy from light raises 2 electrons in each chlorophyll molecule to a higher energy level. the chlorophyll are now excited
3. the electrons leave the excited chlorophyll molecules and pass along a series of electron carrier molecules all of which embedded in thylakoid membrane make up electron transport chain
4. electron pass from one carrier to the next in a series of oxidation, reduction reactions losing energy in the process. this energy is used in the synthesis of ATP in process called photophosphorlylation
5. within thylakoid space an enzyme catalyses photolysis to give oxygen, hydrogen ions and electrons. these electrons replace those that were emitted from the chlorophyll molecule so it is no longer + ve charged and electron transport chain can continue
6. the hydrogen concentration in thylakoid space is raised. the electrons which have passed along the electron chain combine with co-enzyme NADP and H+ from water to form reduced NADPH

Question 21

where does light dependent reaction occur

Answer 21

in the thylakoid membrane of the chloroplast

photolysis occurs in the thylakoid space

Question 22

what happens in the light dependent reactions (5 steps)

Answer 22

the calvin cycle

1. carbon dioxide combines with 5 carbon sugar called ribulose bisphosphate RuBP. This is catalysed by enzyme ribulose biphosphate carboxylase RuBISCO
2. the 6 carbon intermediate formed is unstable and immediately breaks down into 2 3-carbon molecules. GP
3. GP is reduced to form a 3 carbon sugar phosphate called GALP. The hydrogen for reduction comes from the reduced NADP from the light dependent reactions. ATP from the light dependent reactions provides the energy required
4. 2 out of every 12 GALPs formed combine to create 6 carbon sugar hexose (glucose) which can be converted to other organic compounds e.g amino acids or lipids.
5. 10 out of every 12 GALPs are involved in the recreation of RuBP. the 10 GALP molecules rearrange to form 6 5-carbon compounds then phosphorylation using ATP forms RuBP

Question 23

where does the light independent reaction occur

Answer 23

in the stroma

Question 24

what is phosphorylation

Answer 24

the addition of an inorganic phosphate Pi in phosphorylation. the phosphate must be separated from water which requires energy
ADP + hydrated Pi + energy –> ATP (aq)

Question 25

when can the hardy weinberg equilibrium apply

Answer 25

• mating must be random
• the population must be large
• there should be no movement of organisms into or out of the population (migration)
• there must be no mutations
• there should be no selection pressure, that is, nothing that favours one allele over another.
  if any of these conditions do not apply, the population will not be in eqm and allele frequencies will change

Question 26

what is the fate of sugars made in photosynthesis (6)

Answer 26

1. used in respiration to produce carbon dioxide, water and energy
2. nucleic acids (DNA and RNA)
   plus phosphates and nitrates from soil
3. polysaccharides
   starch (storage) cellulose (wall)
4. lipids (waterproofing and storage)
5. amino acids ( to make proteins)
   plus nitrates and sulphur from soil
6. proteins (enzymes, and in membranes.

Question 27

what is the link between the light dependent and light independent reactions

Answer 27

ATP and NADPH
the light dependent reaction makes ATP and reduced NADP. these are used in the light dependent reactions (calvin cycle)
- reduced NADP provides reducing power (electrons in hydrogen)
- ATP provides the energy for the process of making carbon dioxide into carbohydrate.

Question 28

what are the stages in PCR

Answer 28

1. 95oc for 30 seconds. the DNA separates into 2 strands as hydrogen bonds between bases break.
2. 55oc for 20 seconds. the primers attach at the start of the STR repeat sequence
3. 70oc for 1 minute. DNA polymerase attach nucleotides are attached, extending the DNA from the primer. The STR repeated sequence and DNA adjacent is replicated.
   this sequence is repeated many times in order to create millions of these STR fragments.

Question 29

stages in gel electrophoresis

Answer 29

1. DNA fragments placed in well of agarose submerged in buffer solution in gel tank
2. negative charged DNA moves towards the positive electrode. Fragments separates into invisible bands according to their size.
3. transferred to nylon or nitrocellulose membrane. DNA probe binds with fragment/
4. X ray film or UV light used to view DNA profile

Question 30

stages in rigor mortis (6)

Answer 30

1. after death, muscle cells become starved of oxygen and oxygen dependent reactions stop.
2. Respiration in the cells becomes anaerobic and produces lactic acid
3. the pH of the cell falls, inhibiting enzymes and thus inhibiting anaerobic respiration.
4. The ATP needed for muscle contraction is no longer produced. as a result, bonds between the muscle proteins become fixed.
5. the proteins can no loner move over one another to shorten the muscle, fixing the muscle and joints.
6. after a whole muscle tissue starts to break down and rigor mortis passes
   Rigor mortis starts with smalled muscles stiffening before larger ones.

Question 31

stages of decomposition

Answer 31

• autolysis
  when the body own enzymes, from the digestive tract and lysosomes breaks down cells
  bacteria from the gut and gaseous exchange system rapidly invade the tissues after death, releasing enzymes that result in decomposition. the loss of oxygen in the tissues favours the growth of anaerobic bacteria
• putrefaction
  greenish discoloration of the skin of lower abdomen
  due to formation of sulphaemoglobin in the blood
  as it spreads across the body skin will darken to reddish-green and then turn a purple black in colour.
  gas or liquid blisters may appear on the skin.
• bloated
  bloating of body due to gas production
  increased action of bacteria produce gasesthese form in the intestines and tissues. body will smell and become bloated. with further decomposing will deflate
• dry body
  the body deflates and fluids associated with putrefaction drains away.
  soft tissues dry out and shrink

Question 32

what are the no specific responses to infection

Answer 32

• lysozyme
  is an enzyme that kills bacteria by breaking down their cell wall.it is found in tears, saliva and nasal secretions
  protects the body from harmful bacteria in the air we breath in or the food that we eat.
• inflammation
• phagocytosis
• lymph system
• interferon
  provides non specific defence against viruses
  viruses infected cells produce this protein which diffuses to surrounding cells preventing viruses from multiplying
  it inhibits viral protein synthesis to limit the formation of new virus particles

Question 33

inflammation

Answer 33

inflammatory response
damaged white blood cells and mast cells release histamine which causes arterioles to dilate increasing blood flow and capillary permeability causing leakage
plasma fluid, white blood cells and antibodies leaks into tissues causing oedema
infecting bacteria are now attacked by intact white blood cells.

Question 34

phagocytosis

Answer 34

1. chemicals released by bacteria and the cells damaged at the site of infection attract phagocyte white cells
2. neutrophils arrive first followed by macrophages.
3. bacterium with antigen on surface is engulfed by neutrophil or macrophage
4. the phagocyte encloses the bacterium inside a vacuole
5. lysosomes fuse with vacuole releasing enzymes that destroy foreign material
6. residual body is discharged
7. phagocyte removes antigens on bacteria surface and places on own membrane becoming an APC

Question 35

which cells are involved in the specific immune response / cell mediated

Answer 35

lymphocytes
defend the body against specific diseases.
T helper and T killer cells
B cells

Question 36

T lymphocyte production (6)

Answer 36

1. immature T cells produced by division of stem cells in bone marrow
2. immature T cells move to the thymus via the blood
3. T cells mature in the thymus
4. Mature T cells leave the thymus in the blood and move to lymph nodes and the spleen
5. as lymph fluid passes through a lymph node, T cells are activated by any pathogens present
6. as blood passes through the spleen, T cells are activated by any pathogens present

Question 37

activation of T helper cells (4)

Answer 37

1. macrophage engufs bacterium with antigens on surface.
2. macrophage presents antigens on its surface and becomes and antigen presenting cell (APC)
3. T helper cells with complementary CD4 receptors bind to APC. activating the T helper cell
4. T helper cell then divides ( proliferates) to produce
   clone of T memory cells
   clone of active T helper cells
   T memory cells remain in body for months - years. this means upon second infection the immune system can respond more quickly.

Question 38

clonal selection of B cells (5)

Answer 38

1. antigen binds to B cell with complementary receptor becoming APC
2. active T helper cell with complementary receptor binds to APC and produces cytokines (proteins) that stimulate the B cell to divide
3. the B cell divides (proliferate) to give B memory and B effector cells
4. B effector cells differentiate to produce plasma cells which release antibodies.
5. B memory cells remain for months - years in the body enabling an individual to respond more quickly upon second infection.

Question 39

the role of T killer cells

Answer 39

1. cell infected with bacterium becomes APC
2. T killer cells with complemntary receptor binds to APC
3. T helper cell makes cytokines which stimulate T cells to divide to produce
   - Memory T killer cells
   - Active T killer cells
4. active T killer cells bind to infected cells presenting antigens (APC)
5. T killer cell releases chemicals that causes pores to form in the infected cell, causing lysis. the infected cell dies and the bacterium is expelled where it can be labelled by antibodies from B cells as targets for destruction by macrophages.

Question 40

fever

Answer 40

• part of the inflammatory response
• caused by substances released from neutrophils and macrophages
  these chemicals effect they hypothalamus setting core body temperature higher.
  effectors act to raise temperature
  enhances immune function of phagocytosis.
  bacteria / viruses may reproduce more slowly
  temperature above 40oc denatures enzymes and 42 -43oc is life threatening.
  TB will stop reproducing above 42oc

Question 41

how does HIV hijack the T cells protein synthesis

Answer 41

once inside the host T helper cell, the virus needs to make the host cell replicate new virus components.

1. Reverse transcriptase is en enzyme used by the virus to revers normal transciption and to manufacturer DNA from the RNA template.
2. once the HIV DNA strand is produced, it is integrated into the host’s DNA by another HIV enzyme, integrase.
3. once the HIV genome is integrated into the host cell’s genome, it can be transcribed and translated to produce new virus protein.

Question 42

mRNA splicing

Answer 42

between transcription and translation, messenger RNA is often edited.
the non coding introns are removed and the remaining sequences are spliced together and will be expressed, are exons.
this means that several proteins can be formed from 1 length of mRNA spliced in different ways.
one gene –> several related proteins

Question 43

how do we prevent the entry of pathogens

Answer 43

• the skin
  skin is a tough barrier which only allows pathogens to enter if cut
  skin flora: own microbes out compete pathogens
  sebum made by skin also kills microbes
• mucous membranes
  contains a mucus membrane which traps bacteria.
  the mucus is then swallowed and passed into the digestive system
• stomach acid
  stomach acid. helps to destroy microbes which are eaten
  gut bacteria
• gut flora
  compete with pathogens for food and space. they competitively exclude them. these bacteria also excrete lactic acid which deters pathogens.
• eyes
  tears contain enzyme lysozyme which helps to digest microbes

Question 44

what are the different ways in which antibiotics work? (5)

Answer 44

• inhibition of specific enzymes found in bacterial cell but not in host
• inhibiting bacterial cell wall synthesis leading to lysis
• inhibiting of nucleic acid synthesis, replication and transcription preventing cell division and enzyme synthesis
• disruption of cell membrane changing the permeability leading to lysis
• inhibition of protein synthesis enzymes and other essential proteins not produced.

Question 45

medications for treating CHD (5)

Answer 45

• ACE inhibitors
  reduce synthesis of angiotensin II which is a hormone that causes vasoconstriction so lowers blood pressure.
• calcium channel blockers
  block calcium channels in muscles lining arteries. stopping them from contracting. lowering blood pressure. fatal with someone with heart failure
  -diuretics
  increase volume of urine riding the body of excess fluids and salts decreasing blood plasma volume lowering blood pressure
• antihypersentive beta blockers
  prevents stimulation of adrenergic receptors responsible for increase cardiac action. control hear rhythm and treat angina as well as reducing high blood pressure.
• amticoagulant and platelet inhibiting drugs
  asprin and clopidogrel reduces stickness of platlets.
  walfrin interfers with vitamin K affects synthesis of clotting factors.

Question 46

carbohydrates

Answer 46

monomers
-glucose, galactose, fructose
disaccharides
- sucrose: glucose + fructose
- maltose: glucose + glucose
- lactose: glucose + galactose
polysaccharides
- starch: amylose (straight) and amylopectin (branched)
- glycogen: animals. numerous side branches
- cellulose. alpha and beta glucose. microfilis is bundles of cellulose joined by H bonds and microfibrils are held together by hemicellulose and pectin

Question 47

properties of water

Answer 47

solvent:
dissolve other polar and ions
allowing biochemicals reactions to occur in cytoplasm. dissolve substances transported in blood/lymph or xylem/phloem. to enable transport lipids must combine with proteins forming lipoproteins
thermal properties
- high specific heat capacity
strong H bonds. water warms and cools slowly. useful for organisms avoid rapid changes in internal temperature. aquatic life
cohesion: hydrogen bonds between water molecules.
adhesion: Hydrogen bonds between water and cell wall
capillary action
density and freezing points
water expands when frozen as when molecules slow down the max number of hydrogen bonds can form holding them further apart. ice less dense than water.