Paper 2 IB Bio SL section B

(a)Draw a labelled diagram of the molecular structure of DNA, comprising of four nucleotides. (b) Outline the therapeutic use of stem cells. (c) Giving one specific example, discuss genetic modification in organisms including the potential bene ts and possible harmful effects.

(a)deoxyribose, phosphate, and bases ( adenine, thymine, cytosine, guanine) sugar labelled and shown as a pentagon. covalent bods are correctly labelled. complementary base pairing between A-T and C-G H-bonds correctly labelled. show two antiparallel sugar phosphate strands with links between phosphate and sugar connected through bases. B) stem cells retain their capacity to divide; they are unspecialized/undifferentiated; have the ability to differentiate/specialize (along different pathways) / are multipotent/pluripotent/totipotent; during differentiation/specialization some genes are expressed and some are suppressed; example of disease: (eg leukemia / heart disease / diabetes / other possibility) ex. of therapeutic use: leukemia- patients bone marrow cells are killed and replaced with stem cells. (therapeutic) treatments can now use (adult) stem cells (eg adipose tissue, wisdom teeth); C)(genetically modified organisms are) organisms where characteristics are altered/changed by addition or removal of a gene; reference to the specific gene transferred to the host organism; verifiable example of genetic modification; (eg BT- corn/other valid examples) universal genetic code (allows genes to be transferred between species); gene transfer involves splicing genes into a suitable vector/host DNA; after placed in host, host cells are cloned; potential benefits: 1st potential benefit; (eg increased yields/productivity) 2nd potential benefit; (eg allows for the introduction of a characteristic that wasn't present within the gene pool (selective breeding could not have produced desired phenotype)) i. 3rd potential benefit; (eg less use of chemical pesticides) harmful effects: 1st harmful effect; (eg possibility of cross pollination) 2nd harmful effect; (eg could have currently unknown harmful effects / toxin may cause allergic reactions) 3rd harmful effect; (eg reduces genetic variation/biodiversity)

a) state the source, substrate, product and optimum pH conditions for amylase b) outline the energy flow between trophic levels in food chain c) explain the control of blood glucose concentrations in humans

A) 1. source-Salivary amylase substrate- starch product- maltose pH- 6.2-7.0 neutral/ slightly acidic 2. source- pancreatic amylase substrate- starch product- maltose pH- 7.0-8.0 slightly basic/alkaline B) (original) source of energy in a food chain is from (sun)light; captured by plants/autotrophs/producers/first trophic level; by means of photosynthesis/converted to chemical energy/organic compounds; plants use part of energy for own energy requirements/lost through cell respiration; consumers use energy for own requirements from organisms in previous trophic level; energy travels between trophic levels/producer to 1st consumer/1st consumer to 2nd consumer/2nd consumer to 3rd consumer; not all material is assimilated/consumed / not digested / lost in feces / OWTTE; only a small amount of energy/(approximately) 10-20% is passed between trophic levels / most/80-90%/a large amount of the energy of a trophic level is lost (and not transferred); loss of energy from organisms in form of heat; energy is not recycled in an ecosystem (but nutrients are); C)pancreatic cells monitor the blood glucose concentrations; alpha and beta cells are in the islets of Langerhans; negative feedback mechanisms; send hormones (through bloodstream) to target organs; if too high, β cells (in pancreas) produce insulin; insulin stimulates liver/muscle cells to take up glucose; glucose is converted into glycogen (stimulated by insulin); (do not award this marking point where it is stated that insulin directly converts glucose) lowering blood glucose level; other cells are stimulated to absorb glucose and use it in cell respiration; if glucose levels too low, α cells (in pancreas) produce glucagon; glucagon stimulates liver/muscle cells to break down glycogen; (do not award this marking point where it is stated that glucagon directly breaks down glycogen) and release glucose into the blood; raising the blood glucose level;

(a) Describe the genetic code and its relationship to polypeptides and proteins. (b) Outline the role of proteins in active and passive transport of molecules through membranes. (c) Many cell functions, like synthesis of macromolecules and transport, require energy in the form of ATP. Explain how ATP is generated in animal cells.

A) a. (the genetic code is based on) sets of three nucleotides/triplets of bases called codons; b. bases include adenine, guanine, cytosine and thymine in DNA / adenine, guanine, cytosine and uracil in RNA; c. each codon is code for one amino acid; d. some codons are (start or) stop codons; e. DNA is transcribed into mRNA by base-pair matching/complementary base pairing; f. mRNA is translated into a sequence of amino acids/polypeptide; g. each gene codes for a polypeptide; h. polypeptides may be joined/modified to form proteins; B) a. channel proteins allow diffusion/osmosis/passive transport; b. large/polar molecules cannot cross the (hydrophobic) membrane freely; c. facilitated diffusion involves moving molecules through proteins down their concentration gradient/without requiring ATP; d. aquaporins (specific integral membrane proteins) facilitate the movement of water molecules/osmosis; e. some proteins (for facilitated diffusion) are specific to molecule/ions; f. active transport involves moving molecules through proteins against their concentration gradient/requiring ATP; g. (some) proteins in the membrane are pumps / pumps perform active transport / sodium potassium pump; C) a. ATP is a form of energy currency/immediately available for use; b. ATP is generated in cells by cell respiration (from organic compounds); c. aerobic (cell respiration) requires oxygen; d. anaerobic (cell respiration) does not require oxygen; e. glycolysis breaks down glucose into pyruvate; f. glycolysis occurs in cytoplasm; g. (by glycolysis) a small amount of ATP is released; h. ADP changes into ATP with the addition of a phosphate group/phosphoric acid / accept as chemical equation; i. in mitochondria/aerobic respiration produces large amount of ATP / 38 mols (for the cell, per glucose molecule); j. oxygen/aerobic respiration is required for mitochondrial production of ATP; k. in mitochondria/aerobic respiration pyruvate is broken down into carbon dioxide and water;

a) Draw a labelled diagram showing the structure of three water molecules and how they interact. (b) Aquatic and other environments are being affected by a global rise in temperature. Outline the consequences of this on arctic ecosystems. (c) Cell membranes separate aqueous environments in cells. Explain how the properties of phospholipids help to maintain the structure of cell membranes.

A) a. O connected to 2 H forming a V shape; b. line between O and H of same molecule labelled as covalent bond; c. three water molecules bonded together with dashed/dotted lines between O on one molecule and H on another; d. dotted/dashed line labelled as hydrogen bond; e. O labelled as partial negative charge/ and H labelled as partial positive charge/ B) a. warming results in melting (arctic/polar) ice (cap) / loss of ice habitats; b. (warming) raises sea level / floods coastal areas / destroys coastal habitats; c. (warming) of habitat would change species/flora/fauna that can be supported (named examples can be used); d. decrease in size of population(s) / possible extinction of species; e. temperate species move into area / arctic species adapt/move; f. change in distribution of species/changes in migration patterns; g. (ecological) changes will affect higher trophic levels/food webs/food chains; h. increased rates of decomposition of detritus from (melting) permafrost; i. increased success of pest species including pathogens; C) a. (labelled) phospholipid consisting of head and two tails; b. head is glycerol and phosphate; c. tails are fatty acid chains; d. head hydrophilic and tails hydrophobic; e. hydrophilic molecules/heads attracted to/soluble in water; f. hydrophobic molecules/tails not attracted to water but attracted to each other; g. (properties of phospholipids leads to) formation of double layer in water; h. stability in double layer because heads on outer edge are attracted to water and tails are attracted to each other in middle; i. phospholipid bilayer in fluid/flexible state because of attraction of non-polar tails to each other; j. (fluidity) allows membranes to change shape/vesicles to form or fuse with membrane/(fluidity) allows cells to divide; k. non-polar amino acid side chains attracted to (hydrophobic) tails;

a) Draw a labelled diagram of the human heart showing the attached blood vessels. b) Describe the action of the heart in pumping blood. c) Nerves connecting the brain and heart contain neurons that control heart rate. Explain how a nerve message passes from one neuron to another neuron.

A) a. atria/right atrium/left atrium - shown above the ventricles and must not be bigger than ventricles; b. ventricle/left ventricle/right ventricle - shown below the atria, must have thicker walls than atria; c. vena cava/superior vena cave/inferior vena cava - connected to right atrium; d. pulmonary artery - shown from right ventricle (to lungs); e. pulmonary vein(s) - shown (from lungs) to left atrium; f. aorta-shownaslargearteryfromleftventricleoutofheart; g. AV valves/atrioventricular valves / mitral/bicuspid and tricuspid - named correctly and shown between both atria and ventricles and labelled at least on one side; h. semilunar valves - shown in aorta/pulmonary artery; Valves need to open in correct direction. B)a. (both) atria collect blood (from veins); b. sinoatrial/SA node sends impulses to muscle/fibres initiating contraction; c. blood is pushed to ventricles by contraction of atria/atrial systole; d. AV (atrioventricular) valves are open (as atria contract); e. semilunar valves are closed so that ventricles fill with blood; f. ventricles contract / ventricular systole; g. AV (atrioventricular) valves close (and preventing backflow); h. blood is pushed out through the semilunar valves/into pulmonary artery and aorta; i. when ventricles relax/diastole, semilunar valves close preventing backflow of blood; C) a. nerve impulse reaches the end of the presynaptic neuron; b. (depolarization causes) calcium channels in membrane (to) open; c. calcium diffuses into the presynaptic neuron; d. vesicles of/containing neurotransmitter move to and fuse with presynaptic membrane; e. (neurotransmitter) released (by exocytosis) into synaptic space/cleft; f. (neurotransmitter) diffuses across the space/synapse; g. (neurotransmitter) attaches to receptors on postsynaptic neuron; h. receptors cause ion channels to open and sodium diffuses into the postsynaptic neuron; i. the postsynaptic neuron membrane is depolarized; j. (depolarization) causes a new action potential; k. (neurotransmitter) on postsynaptic membrane is broken down; l. (neurotransmitter) is reabsorbed into the presynaptic neuron;

a) Meiosis in humans produces cells that participate in fertilization. Outline the processes involved in meiosis. b) Following fertilization, cells in the developing embryo differentiate. Outline a technique for cloning using differentiated animal cells. (c) Discuss ethical issues of therapeutic cloning in humans.

A) a. meiosis reduces a diploid cell into (four) haploid cell(s); b. (during prophase I) homologous chromosomes pair up/synapsis; c. chromatids (break and) recombine / crossing over d. (metaphase I) (homologous chromosomes) at the equator of the spindle / middle of cell; e. (anaphase I) (homologous) chromosomes separate and move to opposite poles; f. (telophase I) chromosomes reach poles and unwind WTTE; g. (prophase II) chromosomes (condense and) become visible, new spindles form; h. (metaphase II) chromosomes line up at the centre of the cells/equator; i. (anaphase II) sister chromatids separate; j. (telophase II) chromatids reach the poles and unwind; B) a. differentiated/somatic/diploid cells taken from donor animal/sheep udder; b. (diploid) nucleus from donor cells removed; c. ova/eggs cells removed from (donor) animal/female sheep; d. (haploid) nucleus removed from eggs/ova; e. (diploid/donor's) nucleus is fused with/inserted into egg/ovum (to form zygote); f. embryo (from cell with donor nucleus and egg from surrogate) implanted in uterus of surrogate mother; g. normal pregnancy and birth is completed; h. offspring is a genetic copy/clone of the donor mother/diploid nucleus WTTE; C) a. therapeutic cloning involves producing embryos from which embryonic stem cells can be harvested for medical use; argument in favour: b. (to many people) any procedure that reduces pain and suffering is ethically/ morally justified; c. stem cells can be used to replace organs/tissues that have been lost/damaged in a patient; d. (thus) pain and suffering can be reduced/lives can be saved/life quality improved; e. cells can be removed from embryos that have stopped developing and would have died anyway; f. cells are removed at a stage when no pain can be felt by the embryo; g. use embryos from IVF that would otherwise be destroyed; argument against: h. embryonic stem cells are no longer needed as adult stem cells can be used without causing loss of life; i. there is danger of embryonic stem cells developing into tumour cells/harmful effects are not yet known; j. every human embryo is a potential human with the right to development; k. more embryos may be produced than can be used and so some would be killed; l. (to many people) any procedure that harms a life/kills is unethical/morally wrong; Accept up to one additional reasonable argument against. To award [8] at least one pro and one con must be addressed.

a) draw a labelled diagram of the human adult male reproductive system. b) describe the application of DNA profiling to determine paternity. c) explain the inheritance of color blindness.

A) a. scrotum - shown around testes; b. testis/testis/testicle - shown inside scrotum; c. epididymis - shown adjacent to testis and connected to sperm duct; d. sperm duct/vas deferens - double line connecting testis/epididymis to urethra; e. seminal vesicles - sac shown branched off sperm duct (not off the urethra); f. prostate gland - shown positioned where sperm duct connects with urethra; g. urethra - shown as double line linking bladder to end of penis; h. penis - with urethra passing through it; DNA from child, mother and possible father(s) used to establish paternity; (B) a. DNA from child, mother and possible father used to establish paternity b. (DNA profiling is done) for legal reasons / divorce / inheritance; c. (DNA profiling is done) for personal reasons / self-esteem issues for children/fathers/parents; d. DNA copied/amplified using PCR; e. DNA cut using restriction enzymes; f. (gel) electrophoresis used to separate DNA fragments; g. pattern of bands is produced (in gel); h. analysed for matches between child with mother and possible father; i. (about) half the child's bands will match the father (while the other half will match the mother); C) a. colour blindness caused by recessive allele / colour blindness is recessive; b. gene located on X chromosome/sex-linked; c. Xb is allele for colour blindness and XB is allele for normal color vision/dominant allele; d. male has one X and one Y chromosome; e. male has only one copy of gene(s) located on X chromosome; f. X chromosome (in males) comes from female parent; g. any male receiving allele from mother will express the trait; h. XbY is genotype for colour blind male; i. many more males have colour blindness than females; j. female will express colour blindness only if is homozygous recessive/Xb Xb; k. heterozygous/XB Xb female is a carrier; l. colour blind female could be born to colour blind father and carrier mother;

a) Draw and label a diagram of the carbon cycle. b) Outline the effect of carbon dioxide concentration on the rate of photosynthesis and how this can be measured by carbon dioxide uptake. (c) Explain how carbon dioxide is produced in anaerobic and in aerobic respiration.

A) carbon dioxide/CO2 in atmosphere/water; (cell) respiration producing CO2 in atmosphere; photosynthesis (fixing) CO2 from atmosphere into producers/plants; death/decomposition transforming C in plants/animals to C in bacteria/fungi/saprotrophs; fossilization showing carbon in organisms to fossil fuels/coal, oil, natural gas; combustion/burning of fossil fuels/coal/oil/natural gas/peat producing CO2 / weathering of shells/rocks releasing CO2; combustion/burning of producers/forests producing CO2; feeding (organic C) in producers/plants to (organic C) in consumers/animals; feeding (organic C) in consumers to other consumers; If candidates do not show on their diagram that carbon is in the form of carbon dioxide, do not award the first marking point but allow other marking points. B) no photosynthesis at very low/no CO2 concentration; positive correlation between increasing amounts of CO2 and photosynthesis rate; at high CO2 concentration (rate of photosynthesis) reaches a plateau; Points above may be awarded if clearly shown on an annotated graph. CO2 uptake measured by change in pH / bicarbonate indicator / CO2 sensor (for terrestrial plants); water becomes alkaline/higher pH as CO2 is absorbed; using units of CO2 uptake per unit of time; C) introduction: glycolysis common to both (aerobic and anaerobic respiration); aerobic respiration uses oxygen but anaerobic respiration does not use oxygen; great amount of energy/ATP/CO2 released during aerobic respiration / small amount of CO2/ATP/energy released during anaerobic respiration; (cell respiration) liberates 6 molecules of CO2 (per molecule of glucose); anaerobic respiration: glycolysis occurs in cytoplasm (of cell); glucose/6-carbon transformed into (2 molecules of) pyruvate/pyruvic acid/ 3-carbon compound (per molecule of glucose); pyruvate/pyruvic acid transformed into CO2 and ethanol; in alcohol(ic) fermentation; lactic fermentation does not produce CO2; aerobic respiration: pyruvic acid/pyruvate/3-carbon compound to acetyl CoA; link reaction liberates CO2; aerobic respiration occurs in mitochondria; Krebs cycle/citric acid cycle releases CO2;

a) Draw a labeled diagram of the female reproductive system. b) Discuss the ethical issues associated with IVF c) Describe the application of DNA profiling to determine paternity investigations.

A) ovary - as a circle/oval above/beside funnel of oviduct; oviduct/fallopian tube - as a tube from ovary to uterus; uterus; endometrium - inside/lining of uterus; cervix - at bottom of uterus; vagina - below cervix; B)pros: infertile couples can conceive; -allows children/offspring who are genetically related to them; -decision to have children is clearly a conscious one (and parents are likely to be loving/responsible parents); -screening of embryos decreases chance of (inherited) disease/chromosomal defects; -increases/extends reproductive age; -cancer patients can harvest ova/sperm before chemotherapy; -production of extra embryos may be used for research; cons: -potential risks from drug treatment; -IVF unnatural procedure/practice / IVF against some religious teachings; C) DNA from child, mother and possible father(s) used to establish paternity; for legal reasons / divorce / inheritance; for personal reasons / self-esteem issues for children/fathers/parents; samples of DNA are taken/amplified/digested / fragments separated by electrophoresis; pattern of bands/fragments/lengths (of DNA) is produced (in a gel); analysed for matches between child with mother and possible father; (half) the child's bands will match the father (while the other half will match the mother);

a) Draw and label a diagram to show the structure of membranes. (b) Distinguish between eukaryotic and prokaryotic cells. (c) Explain how vesicles are used to transport proteins within a eukaryotic cell.

A) phospholipid as a bilayer - shown as double row of opposing phospholipids, tails to inside; phosphate head and hydrocarbon/fatty acid tails in phospholipids; hydrophilic/polar heads facing outside and hydrophobic/nonpolar tails in phospholipid facing inside; integral/channel/carrier/transport protein - shown crossing bilayer; peripheral protein - shown on surface or slightly embedded; cholesterol - shown embedded in bilayer and smaller than the hydrophobic tail; glycoprotein - showing protein and carbohydrate chain; B) Eukaryote- DNA w proteins, has a nucleus/ Dna surrounded by membrane, mitochondria, 80S ribosomes, membrane-bound organelles/ have compartments, larger in size, reproduces by mitosis, chromosomes are linear. Prokaryote- DNA w/o proteins/ naked DNA, no nucleus/ DNA in nuclei/cytoplasm, no mitochondria, 70S ribosomes, no membrane-bound organelles/ no compartments, smaller in size, reproduces by fission, chromosome is cricular C)proteins synthesized by ribosomes/rough endoplasmic reticulum/rER; proteins are bound by vesicles; vesicles formed from/bud off from rER; vesicles formed from rER transport proteins to Golgi apparatus; vesicles fuse with Golgi apparatus (membranes); Golgi modifies proteins (as they move along in vesicles); secretory vesicles formed from/bud off (in trans Golgi); vesicles move across the cytoplasm; vesicles fuse with plasma membrane; proteins may be discharged/secreted to exterior/exocytosis; ER, vesicle and plasma membrane have phospholipid bilayer structure;

a) Explain how humans release energy from digested foods to make it available for processes in cells. (b) Describe one example that occurs in axons for each of the following • active transport • and facilitated diffusion. (c) Outline how biologists can ensure that research into energy release involving animals is ethically acceptable.

A) ‹cell› respiration -controlled release of energy -energy released from organic compounds/foods -carbohydrates/glucose/fats/lipids provide energy -blood carries foods/organic compounds to cells - aerobic respiration involves use of oxygen - anaerobic respiration involves production of lactate/lactic acid - energy from respiration is in the form of ATP - more ATP ‹per glucose› from aerobic than anaerobic respiration - carbon dioxide produced by aerobic respiration - aerobic respiration involves the mitochondrion - ATP in the cell moves/diffuses through the cytoplasm to the pumps for active transport B)- sodium-potassium pump - sodium pumped out and potassium pumped in - energy supplied to pump as ATP - potassium channel for facilitated diffusion OR K+ channel allows potassium to diffuse out - pore through channel protein allows only K+ ions to pass through C) -only use animals if other methods are impossible - only use animals if the research is important enough to justify it -avoid any procedures that cause suffering to animals - do not use animals taken from the wild - use anesthetics/painkillers to prevent suffering

a) list four functions of membrane proteins b) explain the process of translation leading to polypeptide formation c) describe the production of antibodies

A)-hormone binding sites; -immobilized enzymes; -cell adhesion; -cell-to-cell communication/cell recognition; -channels for passive transportation; -pumps for active transport B) genetic code consists of codons of base triplets; mRNA is complementary to the DNA strand; mRNA carries information (transcribed) from the DNA gene; translation occurs in a ribosome; mRNA attaches to the (small subunit of the) ribosome; has specific codons; each (codon) codes for one amino acid; tRNA matches its anticodons with the codons of mRNA; by hydrogen bonds between complementary bases; each tRNA carries a specific/OWTTE amino acid; the amino acids are attached to each other by condensation reactions/peptide bonds; the process is repeated; forming polypeptides; C) antibodies are produced by (B) lymphocytes; many types of lymphocytes exist in the body; each recognizes one specific/OWTTE antigen (from foreign body); antigen binds to (proteins in plasma membrane of) specific lymphocyte; activates the lymphocyte; (lymphocytes) clone (through mitosis); to produce many identical lymphocytes; which secrete the specific/OWTTE antibody against the antigen; that are proteins made through translation/protein synthesis;

(a) Draw a labelled diagram of a prokaryotic cell. (b) Bacteria are prokaryotes that sometimes act as pathogens. Describe how the body can defend itself against pathogens. (c) Explain the evolution of antibiotic resistance in bacteria.

A). a. cell wall - uniformly thick and drawn outside the plasma membrane; b. plasma membrane - a continuous single line; c. cytoplasm/cytosol; d. nucleoid/(naked) DNA - shown as a tangle of thread or irregular shape without a nuclear membrane; e. (70S) ribosomes - drawn as a small circle or dark dot; f. pili - hair like structures / flagellum - shown to be longer than any pili; g. plasmid - circular ring of DNA; h. capsule - drawn outside the cell wall; B) a. skin/mucus membranes act as barrier (to pathogens); b. sebaceous glands secrete lactic acid/fatty acids/sebum / make surface of skin acidic; c. (skin/stomach) acid prevents growth of many pathogens; d. lysozyme in mucus can kill bacteria; e. pathogens caught in sticky mucus and removed from body; f. inflammatory response/inflammation can cause swelling/redness/fever (to inhibit the pathogen); g.phagocytes/macrophages/leucocytes/white blood cells (non-specifically) identify (pathogens/bacteria/fungi/viruses) as foreign; h. (phagocytes macrophages/leucocytes/white blood cells) ingest pathogens; i. specific lymphocytes recognize one specific antigen; j. (antigen-specific) lymphocytes clone themselves; k. lymphocytes/leucocytes produce antibodies; l. antigen-antibody complex formed and stimulates destruction of pathogen; C) a. antibiotics (are chemicals) used to treat bacterial diseases; b. within populations, bacteria vary in their (genetic) resistance to antibiotics/fitness; c. resistance arises by (random) gene mutation; d. when antibiotics are used antibiotic-sensitive bacteria are killed; e. (natural) selection favours those with resistance; f. resistant bacteria survive, reproduce and spread the gene / increase allele frequency of resistant bacteria; g. the more an antibiotic is used, the more bacterial resistance/the larger the population of antibiotic-resistant bacteria; h. genes can be transferred to other bacteria by plasmids; i. doctors/vets use different antibiotics but resistance develops to these as well; j. multiple-antibiotic resistant bacteria evolve/it becomes difficult to treat some infections;

a) Distinguish between the structure of prokaryotes and eukaryotes. (b) Evaluate the drug tests that Florey and Chain carried out on penicillin. (c) Explain the reasons for the ineffectiveness of antibiotics in the treatment of viral diseases

a) -simpler cell structure in prokaryotes -no compartmentalizing in prokaryotes - DNA associated with histones in eukaryotes -naked DNA in ‹most› prokaryotes -nucleus in eukaryotes but not prokaryotes - nucleoid in prokaryotes - mitochondria in eukaryotes but not in prokaryotes - ribosomes are smaller in prokaryotes -70S versus 80S ribosomes - chloroplasts/Golgi/ER/lysosomes in eukaryotes but not in prokaryotes - cell wall in prokaryotes but only in some eukaryotes -loop of DNA in prokaryotes - linear chromosomes in eukaryotes b)- tested penicillin on mice before testing on humans - only one test before risking use in humans -results of the test were very clear -first humans given penicillin were close to death - initial samples of penicillin were very impure - could have been toxic substances in the samples c)-antibiotics are effective against bacterial diseases because they block metabolic pathways -no/very little viral metabolism - few/no viral enzymes -virus uses host cell metabolism/processes - any chemical that stops the virus from reproducing would also harm the host cells