bmc Flashcards

Question

State reasons why triglycerides are described as hydrophobic

Answer 1

1 (hydrocarbon / fatty acid tails, are) non-polar / have no polar groups / not charged ; A equal sharing of electrons in molecule 2 not soluble / insoluble, (in water) ; 3 cannot form hydrogen bonds with water

Answer 2

1 no, hydrophilic / polar / phosphate, head / part, to, interact with / AW, water ; 2 cannot form hydrogen bonds with water ; I repel water 3 cannot form a bilayer ; in water triglycerides, form micelles / form spheres / ball shaped / form globules / do not form thin films

Answer 3

1 removal of introns (from primary transcript / RNA) ; 2 exons joined together ; or 3 splicing ; 4 of, primary transcript / RNA

Answer 4

1 movement of sucrose with, protons / H+ ions, into companion cells ; A correct ref. to (other named) assimilates 2 (sucrose moved) from, apoplast / cell wall / mesophyll cell ; 3 sucrose moves against its concentration gradient (into companion cell) ; 4 (needs cotransporter protein because) sucrose is polar so cannot pass through membrane ; 5 maintain concentration gradient for sucrose between companion cell and sieve tube (element) ;

Answer 5

(movement of substances) against concentration gradient / from low(er) to high(er) concentration ; (protein has) binding site(s) ; specific ; A description e.g. shape complementary to shape of substance can be in context of protein or binding site ref. to (binding causes protein), conformational change / change of shape

Answer 6

1 glucose is moving against a (concentration) gradient ; AW e.g. low to high 2 movement powered by inward movement of Na+ ; AW 3 Na+ movement (into cell from gut lumen) down an electrochemical gradient or down a (Na+), concentration / diffusion, gradient or by facilitated diffusion ; A diffusion if response includes ref. to the cotransport protein / cotranporter e.g. idea that, cotransport needed so that all glucose will be removed from gut lumen ora facilitated diffusion of glucose will only be to equilibrium / AW cotransporter has (specific) binding site for glucose idea that there is no specific active uptake protein for glucose

Answer 7

oral rehydration (salts / solution / therapy) ; A ORS / ORT A rehydration therapy if ref. to ‘drinking’ stated within response. solution of / water with, glucose and salts ; A named example for salts e.g. sodium / potassium / citrate / chloride. AVP ; e.g. antibiotics / doxycycline / tetracycline / furazolidone / choramphenicol / sulfaguanidine (standard treatment in some countries) zinc treatment (standard treatment for children in some countries) ref. to isolation

Answer 8

at (phloem) source, mineral ion entry (with water), from xylem / through plasmodesmata from companion cells ; dissolved in water / as solutes in water / in solution / in sap solution ; in context of entry from xylem or within phloem sap (transport) as part of mass flow ; must be in context of phloem flow down a pressure gradient

Answer 9

decreases / reduces, transpiration ; A lower transpiration rate accept in the correct context once only counts towards max two max two for cuticle thick (waxy) cuticle ; increased waterproof layer ; increased (diffusion) distance for water vapour / less water vapour lost ; in context of cuticular transpiration max two for stoma sunken stoma ; A stoma in depression / AW moist / humid, air collects in area near to external environment ; AW decreases water potential gradient ; in context of between sub-stomatal air space or area above stoma and external environment. reduces diffusion of water vapour (out) via the stoma

Answer 10

any three from: (one strand only needed) to form mRNA / mRNA is single-stranded ; (m)RNA is, used / needed, to produce, subunit (s) / polypeptide(s) ; (only) one strand (of DNA) is the, template / transcribed, strand ; idea that (complementary) copying / transcribing, other DNA strand would not result in, desired / AW, mRN A / polypeptide

Answer 11

1) portable 2) easier to use; no technical training required 3) able to see natural colours 4) able to see living tissue 5) particular tissues/organelles can be stained for better visibility 6) no heavy metal staining

Answer 12

1) 7 nm 2) selectively permeable membrane that allows for the exchange of certain substances 3) barrier between cytoplasm and external environment 4) cell recognition (surface antigens) 5) selecting substances that enter and leave the cell 6) cell signalling 7) cell-to-cell adhesion 8) formation of hydrogen bonds with water for stability

Answer 13

1) series of flattened fluid-filled sacs 2) have cisternae (flattened membrane disk) 3) ribosomes are attached to it 4) proteins made by ribosomes enter it 5) they're modified as they go through it 5) small sacs (vesicles) break off of the RER and join together to form the golgi body

Answer 14

1) 9 triplets of microtubules form a centriole 2) outside the nucleus of animal cells, 2 centrioles are present at right angles to each other in a region called centrosome (also referred to as an MTOC) 3) assembles microtubules to produce the mitotic spindle

Answer 15

1) allows transport of water, sucrose, amino acids, ions, etc between cells 2) without crossing membranes 3) this is movement through the symplast 4) allows communication, signalling between cells

Answer 16

1) made by condensation reactions between α-glucose molecules 2) long unbranching chain of 1,4 linked glucose molecules 3) chains are curved and cool up into helical structures making the final molecule more compact

Answer 17

1) also made of 1,4 linked α-glucose 2) chains are shorter than amylose and branch out to sides 3) branches are formed by 1-6 linkages

Answer 18

1) polymer of β-glucose 2) in order to form a glycosidic bond with C atom 4 where OH group is below the ring, one glucose molecule is rotated 180° 3) successive glucose molecules are linked 180° to each other therefore one oxygen is up and other is down

Answer 19

1) hydrogen bonds result in a strong molecule 2) cellulose molecules become tightly cross linked to form bundles called microfibrils 3) microfibrils are held together in bundles called fibres by hydrogen bonding 4) cellulose fibres have very high tensile strength - makes it possible for a cell to withstand high turgopressures

Answer 20

Hydrogen bonding of peptide backbone causing amino acids to fold into a repeating pattern * due to H bonding between oxygen of -CO- group of amino acid and the hydrogen of -NH- group * corkscrew shape - alpha helix * weaker H bonding results in β-pleated sheets

Answer 21

Three dimensional folding of polypeptide chain due to side chain interactions 1) hydrogen bonds (form between strongly polar groups (NH2, CO, OH) 2) disulphide bonds (form between cysteine molecules, strongest) 3) ionic bonds (between ionised amine (NH3+) and carboxylic acid groups (COOH-). Broken by pH changes. 4) hydrophobic interactions (between non polar R groups)

Answer 22

1) spherical/ball shaped eg Hb, myoglobin 2) polar hydrophilic r groups are on the outside which makes mixing + dissociating in water easier 3) usually soluble 6) precise shape - have roles in metabolic activities, specific in nature

Answer 23

1) structural protein 2) found in tendons, skin, cartilage, bone, teeth etc 3) consists of 3 polypeptide chains each in a helical shape 4) 3 polypeptides are wound together creating a triple helix 5) 3 strands are held together by H and console by bonds 6) every 3rd amino acid is glycine 7) each 3 stranded molecule interacts with other collagen molecules running parallel to it 8) covalent bonds form between R groups of amino acids forming fibrils 9) many fibrils lie alongside each other forming strong bonds called fibres 10) flexible but has tremendous tensile strength

Answer 24

1. Enzyme is reused 2. Enzyme is easily recovered 3. Product isn't contaminated with enzymes 4. Reduces product inhibition 5. Enzyme is more stable/less likely to denature 6. Longer shelf-life of enzyme

Answer 25

induced fit 1. shape of substrates not fully complementary to shape of active site 2. active site flexible / moulds around substrates 3. provides better fit / fully complementary lock & key 1. shape of substrates complementary to shape of active site 2. active site does not change shape 3. substrate fits into active site

Answer 26

* Enzymes are globular proteins (spherical shape) that catalyse metabolic reactions * Function as biological catalysts * Specific in nature * Precise 3D shape with hydrophilic R groups on the outside ensuring they're soluble

Answer 27

* enzyme is mixed with a solution of sodium alginate * droplets of this mixture are added to calcium chloride solution * a reaction occurs forming jelly/beads * enzyme is immobilised in the bead

Answer 28

'Fluid' refers to the movement of phospholipids while 'mosaic' refers to the scattered proteins (and glycoproteins) in the phospholipid bilayer

Answer 29

* Regulates the fluidity of membrane * At low temperatures, cholesterol increases the fluidity of the membrane preventing it from being too rigid, this is because it prevents close packing of phospholipid tails * At high temperatures, cholesterol decreases the fluidity of membrane and stabilises the cell

Answer 30

carbohydrate chains projecting out of lipids+proteins- * Stabilises the membrane structure by forming hydrogen bonds with water molecules surrounding the cell * Glycocalyx - sugary cell coating formed by carbohydrate chains * Act as receptor molecules: (Signalling receptors - recognise messenger molecules like hormones and neurotransmitters; Endocytosis - bind to molecule to be engulfed by membrane) * Act as cell markers/antigens allowing cell-cell recognition

Answer 31

1. signal arrives at protein receptor in cell membrane 2. the receptor's shape is complementary to the ligand 3. the signal brings about a change in the receptor's shape 4. changing the shape of the receptor allows it to interact with the next component of the pathway so the message gets transmitted 5. binding triggers/stimulates reactions within the cell 6. cell signalling results in a response which may be intracellular or extracellular

Answer 32

cells increase in size and synthesize new proteins and organelles

Answer 33

- synthesis of dna - dna in the nucleus replicated so that each chromosome consists of two identical chromatids

Answer 34

- cell continues to grow - the new dna is checked and any errors are corrected - preparations are made to start cell division eg sharp increase in the production of Tubulin is observed which is needed to make microtubules for mitotic spindle

Answer 35

- chromatin starts to condense - nuclear envelope and nucleolus disappears - centrosomes migrate to opposite poles of the cell and form piles of mitotic spindle - asters and spindle fibres form

Answer 36

centrosomes are at cell poles and organise production of spindle fibres - chromosomes line up across equator of spindle

Answer 37

Chromatids are pulled apart by the contraction of spindle fibres and move to opposite poles of the cell

Answer 38

- nuclear envelope and nucleolus reforms - nucleus divides

Answer 39

Division of the cytoplasm during cell division

Answer 40

1) mutation occurs in gene that controls cell division leading to formation of oncogene from protooncogene 2) this causes uncontrolled division 3) coordination of cell cycle is lost (cell does not respond to or receive signals that tell it to stop dividing) 4) loss of function and lack of specialisation occurs 5) a tumour is formed, an irregular mass of cells showing an abnormal change in shape

Answer 41

1) double helix of DNA is unwound by helicase 2) primase synthesizes a short piece of RNA called primer which marks the starting point for synthesis of new strand 3) DNA polymerase uses the primer and synthesizes a new strand in a 5'-3' direction (which means DNA is read in 3'-5') 4) leading strand is made continuously 5) when using lagging strand as template, DNA polymerase adds nucleotides in short fragments "Okazaki fragments" to overcome directionality problem 6) DNA ligase seals up fragments of DNA in both strands to form a continuous double strand helix -direction in which new DNA strand is synthesized DNA polymerase builds the new strand in 5' to 3' direction; this means it moves along the old template strand in 3' to 5' process of transcription 1. RNA polymerase binds to the promoter signaling DNA to unwind so bases can be read from the sense strand 2. RNA polymerase reads sense strand 3'-5' and generates mRNA in 5'-3' 3. when RNA has reached the terminator sequence at the end of the gene, transcription stops; enzyme detaches from gene and DNA winds again 4. last triplet transcribed to mRNA is DNA triplet coding for 'STOP' (ATT, ATC, ACT)

Answer 42

1) mRNA leaves the nucleus and binds to the smaller ribosomal subunit 2) every 3 bases on mRNA (a codon) codes for a specific anticodon which is carried by a tRNA molecule which is covalently linked to a particular amino acid 3) an initiator tRNA adheres to a start codon 4) tRNA that corresponds to next codon enters ribosome carrying an amino acid 5) peptide bonds form between adjacent amino acids (a ribosome can house 2 tRNA molecules at a time) 6) polypeptide chain grows until STOP codon is reached

Answer 43

1) important in contributing to 3-D structure of molecule 2) many hydrogen bonds so gives stability 3) hydrogen bonds more easily broken (than covalent bonds) 4) Hydrogen bonds weak so can be broken 5) (so strands can be separated) for DNA replication 6) hydrogen bonds only form between, specific bases so few mistakes 7) hydrogen bonds can easily re-form (without chemical reaction)

Answer 44

1) cohesive forces between water molecules cause them to be attracted to each other 2) water that is transpired out pulls water molecules below causing a transpiration pull 3) as they ascend up the xylem, water molecules adhere to the lignified walls of xylem which maintains a column of water

Answer 45

1) loss of water from the aerial parts of the plant 2) an inevitable consequence of gas exchange as stomata are open 3) also due to water potential between leaf and atmosphere

Answer 46

1) water taken up by root hairs crosses the root cortex & enters xylem 2) water moving thorough cells walls; apoplastic pathway 3) water moving through plasmodesmata; symplastic pathway 4) water moves from one cell to another till it reaches xylem; movement is due to concentration gradient due to concentrated sap vacuole of cells 5) apoplastic pathway is stopped at endodermis due to cells in it having a band of suberin forming the casparian strip (an impenetrable barrier to water) 6) Suberin deposits increase with age of endodermal cells except for certain passage cells THIS ARRANGEMENT: - gives plants control over what mineral ions pass into xylem vessels (everything has to cross cell membrane) - May help with generation of root pressure 7) once across endodermis, water moves into xylem through pits in their walls

Answer 47

1) removal of water from xylem vessels in leaf reduces hydrostatic pressure in xylem 2) hydrostatic pressure at top of xylem becomes less than bottom 3) pressure difference causes water to move up the xylem

Answer 48

1) sucrose is loaded into sieve tube elements by active transport 2) H+ ions are pumped out of companion cells creating an excess of H+ ions in the apoplastic pathway outside the cell 3) H+ ions move back into the cell down their concentration gradient through a carrier protein for both H+ and sucrose 4) sucrose molecules are carried against their concentration gradient by co-transporter molecules 5) sucrose can them move through plasmodesmata into the sieve tube elements

Answer 49

1) when sucrose is loaded into a sieve tube element, the water potential decreases 2) water movies from surrounding tissue by osmosis 3) this increases the hydrostatic pressure 4) assimilates move down a pressure gradient to the sink

Answer 50

1) thick tunica media to withstand high blood pressure 2) endothelium/tunica intima are smooth so there's little friction to blood flow 3) elastic fibres stretch to allow surges in blood flow and recoil to maintain blood pressure 4) smooth muscle contacts to regulate blood flow 5) collagen fibres avoid rupturing

Answer 51

1) large lumen 2) tunica externa is thickest in veins (mostly collagen fibres) 3) tunica media is very thin (contains some smooth muscle and fibres)

Answer 52

1) as blood flows through capillaries within tissues some plasma leaks out due to the pressure and seeps into places between cells of tissues; this is tissue fluid 2) fluid tends to flow out of capillaries at arterial ends and into capillaries near venuous ends 3) if blood pressure is too high, too much fluid is forced out of capillaries causing accumulation of fluid; oedema 6) it's through tissue fluid that exchange between cells and blood occur

Answer 53

1) SAN (pacemaker) sends waves of excitation which stimulates atria to contact 2) non conducting tissue between atria and ventricles prevent them from contracting together 3) AVN delaying impulse allows atria to empty into ventricles/ contract first 4) AVN sends impulses down to bundle of his and along purkine fibres 5) this causes ventricles to contact from the base upwards - brief break when no impulse is generated allowing blood to enter atria

Answer 54

1) presence of high partial pressures of carbon dioxide causing Hb to release oxygen is the Bohr effect 2) carbon dioxide dissolved in cytoplasm of RBC forming carbonic acid, reaction is catalysed by carbonic anhydrase CO2 + H2O <—-> H2CO3 H2CO3 <—-> H+ + HCO3- 3) Hb has higher affinity for H+ ions than O2 therefore O2 is released

Answer 55

85% - HCO3- diffuse out of RBC into blood plasma and are carried in solution 5% - CO2 that hasn't dissociated dissolves in blood plasma 10% - CO2 combines directly with anime groups of Hb forming carbaminohaemoglobin

Answer 56

1) diffusion of carbon dioxide 2) into red blood cell from correct source 3) carbonic acid formation followed by H+ production due to action of enzyme 4) carbonic anhydrase 5) haemoglobin has a higher affinity for hydrogen ions than oxygen; haemoglobin releases oxygen more easily in acidic conditions 6) formation of haemoglobinic acid 7) higher partial pressures of CO2 linked to (oxy)haemoglobin releasing oxygen more readily; Bohr shift 8) formation of carbamino-haemoglobin

Answer 57

1) small surface area to volume ratio 2) long(er) distances (to reach cells / tissues) 3) diffusion (alone), too slow / insufficient / unable to satisfy needs

Answer 58

1) Hb combines with carbon dioxide 2) carbon dioxide reacts with amine groups 3) to form carbaminohaemoglobin 4) each polypeptide can carry a molecule of CO2 5) CO2 remains bound to Hb until in a region of high pO2 6) carbonic acid dissociates to form H+ ions which bind to Hb forming haemoglobinic acid 7) hydrogencarbonate ions to plasma

Answer 59

1) squamous epithelium is one cell thick 2) for short diffusion distance 3) collectively many so large surface area for gas exchange 4) surrounded by a network of capillaries 5) so RBC can come very close to air maintaining diffusion gradient

Answer 60

1) stretch during inspiration 2) recoil during expiration 3) elasticity allows alveoli to expand according to volume of air breathed in

Answer 61

1. prevention of infections 2. prevents pathogens from entering rest of body/blood 3. carry out phagocytosis 4. engulf pathogens 5. macrophages are antigen presenting cells (APCs)

Answer 62

1. keep airways open 2. provides support 3. allow flexibility 4. rings allow widening during inspiration

Answer 63

1. contraction and relaxation 2. changes diameter of trachea, bronchus, bronchioles 3. controls air flow in bronchioles

Answer 64

1) smallpox virus was stable/did not mutate 2) same vaccine was used for whole programme/vaccine did not need to be changed 3) vaccine was live/gave a strong immune response 4) one dose was enough to give life-long immunity/no boosters required 5) heat stable/freeze dried vaccine 6) suitable for hot countries/isolated areas/rural areas 7) few/no symptomless carriers 8) no animal reservoir/only in humans 9) infected people easy to identify

Answer 65

1) number of cases per 100 000 shows, proportion of population affected 2) easier to visualise, the severity of the problem 3) more reliable for making comparisons between different countries

Answer 66

1) Infected person coughs 2) aerosol droplet carrying the pathogen 3) inhaled by uninfected person 4) consumption of meat/milk of an organism carrying TB

Answer 67

1) female anopheles mosquito feed on human blood to obtain protein they need to develop eggs 2) if an infected person is bitten, mosquito takes up pathogen's gametes with the blood meal 3) make and female gametes fuse in mosquito gut and develop into infective stages that move to salivary glands 4) when mosquito feeds again, an anticoagulant is injected from salivary glands causing infective stages to pass out as well 5) anticoagulant is injected to prevent blood from clotting 6) parasites enter bloodstream>liver cells>RBC

Answer 68

1) stocking ponds, irrigation and other permanent bodies of water with fish which feed on mosquito larvae 2) introduction of dip stick to ensure fast diagnosis 3) sequencing entire genome of plasmodium that may lead to development of effective vaccines 4) drugs used in combination to reduce changes of drug resistance arising 5) spraying a preparation containing the bacteria which kills mosquito larvae but isn't toxic to other forms of life

Answer 69

1) genetic material of HIV is RNA 2) viral RNA is converted to DNA inside host cells to be incorporated into human chromosomes 3) infects and destroys t helper cells (control the immune system's response to infection) 4) when no of t helper cells are low, body is unable to defend against infection allowing pathogens to cause opportunistic infections 5) AIDs isn't a disease; it's a collection of opportunistic diseases associated with the immunodeficiency caused by HIV infection

Answer 70

1) drug therapy (eg zidovudine) 2) it binds to viral enzyme reverse transcriptase and blocks its action 3) this stops replication of viral genetic material and leads to increase in body's lymphocytes 4) combination therapies are difficult to follow 5) people unable to keep up with regimen are susceptible to strains of HIV that have developed resistance to drugs

Answer 71

1. no vaccine due to 2. Plasmodium is eukaryotic / antigens differ in different life stages / intracellular parasite / antigenic concealment 3. drug resistance in Plasmodium 4. insecticide resistance in Anopheles 5. cost of drugs 6. problems with funding research 7. lack of knowledge 8. infected people not identified 9. inaccessibility of some regions to healthcare

Answer 72

1) during an infection cells under attack respond by releasing histamines that attract neutrophils 2) this attraction towards a chemical stimulus is called chemotaxis 3) endocytosis 4) bacteria within a phagocytic vacuole 5) fusion of lysosomes and phagocytic vacuole 6) killing and digestion

Answer 73

1) antigen is injected into a mouse 2) spleen cells which produce lymphocytes which produce antibodies are removed 3) plasma cells from spleen are fused with cancer cells/myeloma cells forming hybridoma cells that divide indefinitely 4) they divide by mitosis and produce antibodies

Answer 74

1) used to locate position of blood clots 2) locate cancer cells which have different cell surface proteins and therefore can be detected by antibodies 3) used to identify exact strain of bacterium or virus causing an infection speeding up the treatment

Answer 75

1) vaccine contains antigens that stimulates an immune response 2) macrophages take up virus by phagocytes and act as antigen presenting cells (APCs) 3) lymphocytes bind to these and undergo clonal selection 4) clonal expansion occurs by mitosis 5) memory cells are formed 6) booster is used to further stimulate memory cell formation

Answer 76

1) macrophage engulfs pathogen and becomes an APC 2) Th cell's receptor (which is complementary to the antigen) binds to the antigen displayed by APC 3) Th cell releases interleukins 4) interleukins stimulate B-cells to differentiate into plasma cells and produce antibodies in the humoral response

Answer 77

1) clonal selection (process by which an antigen selectively binds to and activates only those lymphocytes bearing receptors for the antigen) - B cell with receptor for antigen binds to it and becomes a B-APC - Th cell recognises B-APC and becomes activated, releasing interleukins to signal further actions 2) clonal expansion (rapid multiplication of B or T cell clones after activation by an antigen) - B-APC divides and differentiates into plasma cells to make specific antibodies and also into memory cells to prepare for secondary response

Answer 78

1. antibody complementary shape to antigen 2. variable regions different for each antibody 3. specific antigen binding sites on antibody 4. sequence of amino acids varies between antibodies giving specificity 5. difference in primary structure leading to different tertiary structur