Mark Schemes Edexcel Synoptic Essays

Molecules and cells Give an account of the structures of the proteins insulin and collagen 1) Consists of amino acids held together by peptide bonds; 2) Insulin is globular and collagen is fibrous; 3) Hydrogen bonds hold, secondary structure/ (alpha) helix/ beta strands in shape; 4) R groups determine, tertiary/ 3D, shape; 5) Reference to named type of bonding structure; INSULIN - 6) Relatively small protein / 51 amino acids; 7) Reference to, alpha helix / beta sheet; 8) Two polypeptide chains / A and B chain; 9) Reference to disulphide bonds; 10) Reference to binding site for cell membrane receptor; COLLAGEN - 11) Relatively large protein / over 1000 amino acids; 12) 3 polypeptide chains / triple helix; 13) Hydrogen bonds between chains; 14) Regular amino acid sequence / repeating sequence; 15) Molecules form (micro) fibres/ crosslinking between molecules; Give an account of the structure and functions of lipids, including triglycerides and phospholipids 1) contain carbon, hydrogen and oxygen; 2) Insoluble (in water)/ hydrophobic; 3) Triglycerides consist of glycerol plus three fatty acids; 4) Joined by condensation reactions/ formation of ester bonds; 5) correct reference to saturated and unsaturated fatty acids; 6) Phospholipids consist of glycerol plus two fatty acids and a phosphate group; 7) reference to non-polar/ hydrophobic tails/ fatty acids and polar/hydrophilic heads/ phosphates of phospholipids; 8) correct orientation of phospholipids, in cell membrane/ phospholipids bilayer; 9) Role of phospholipids in cell membrane (fluidity/permeability etc) / role of surfactants; 10) Energy store; 11) Reference to energy from fats / oils, compared with carbohydrates; 12) (mechanical) protection/ packing qualified; 13) Insulation qualified (either electrical or thermal); 14) Buoyancy; 15) Qualified reference to waterproofing/ protection against entry of pathogens in plants; Give an account of the structure and functions of the cell surface membrane POINTS MUST BE IN CORRECT CONTEXT 1) phospholipids bilayer; 2) polar/phosphate/ hydrophilic face outward; 3) non-polar/ hydrophobic/ fatty tails face inwards; 4) reference to cholesterol; 5) molecules can move around; 6) Proteins present in membrane; 7) qualification of the location of these proteins; 8) glycosidic/ carbohydrate side chains on lipids/ proteins/ glycolipids/ glycoproteins; 9) involvement of proteins in transport; 10) by active transport/ facilitated diffusion described (e.g. reference to attachment/change in shape) 11) some proteins are enzymes; 12) partially/selectively permeable; 13) reference to cell-cell interaction/ recognition/ antigens; 14) reference to receptors for hormones/ neurotransmitters; 15) vesicle fusion / formation / description of membrane involvement in exo- or endo-cytosis; Give an account of the ways in which molecules and ions move into and out of cells DIFFUSION- 1) molecules/ions move down/with a concentration gradient; 2) rate increased by a greater concentration difference/ higher temperatures/ smaller molecules or ions/ larger surface area of membrane/ smaller diffusion distance; 3) Credit example of diffusion e.g. oxygen, carbon dioxide, water; FACILITATED DIFFUSION- 4) molecules/ions move down/with a concentration gradient; 5) requires protein channel/ carrier membrane; 6) credit example of facilitated diffusion, such as glucose/amino acids/named ion; OSMOSIS- 7) movement of water; 8) From high/less negative water potential; 9) Across partially permeable/ membrane; ACTIVE TRANSPORT- 10) molecules/ions move down/with a concentration gradient; 11) requires protein channel/ carrier

membrane; 13) credit example e.g. sodium/potassium/proton pump; ENDOCYTOSIS (exocytosis/pinocytosis/phagocytosis)- 14) Description of process; 15) Active transport/endocytosis etc., require ATP /energy OR diffusion/facilitated/osmosis do not req energy Give an account of the biological significance of polysaccharides 1) polysaccharides consist of many monosaccharide; 2) joined by glycosidic bonds; 3) formation of glycosidic bonds by condensation; 4) ref. to insolubility of polysaccharides; 5) starch storage in plants; 6) two forms of starch, amylose and amylopectin; 7) glycogen storage in animals; 8) alpha glucose in starch/glycogen; 9) these can be broken down to provide glucose/monosaccharide for energy/respiration; 10) ref. to no osmotic effect of polysaccharides; 11) ref. to compact shape of glycogen/starch for storage; 12) cellulose contains beta-glucose; 13) cellulose in plant cell walls; 14) cellulose form long unbranched chains; 15) hydrogen bonding between chains; 16) ref. to orientation of chains in layers/microfibrils of cell wall provide strength; 17) ref. to chitin in cell walls of fungi/ exoskeleton of arthropods; 18) ref. to murein in bacterial cell walls; 19) polysaccharides attached to proteins/ lipids in cell surface membranes; 20) ref to cell id/recognition; 21) credit specific example such as determination of A and B blood groups Give an account of the process of mitosis

1) daughter cells have same number of chromosomes parent cell/ are genetically id to parent cell; 2) concerned with growth/repair/replacement of tissues/asexual reproduction; 3) ref. to cell cycle consisting of interphase, mitosis, cell division; 4) (during prophase) chromosomes condense/ so each consists of a pair chromatids joined by a centromere; 5) ref. to centrioles/movement/position; 6) formation of spindle by microtubules; 7) disappearance of nuclear envelope; 9) (At metaphase) chromosomes attached to spindle fibres; 10) lined up at equator of cell; 11) (at anaphase) centromere split/duplicate/separation of chromatids; 12) Daughter chromosomes/chromatids pulled to opposite poles of cell (at Telophase) chromosomes/chromatids reach poles of cell; 13) formation of nuclear membrane/(daughter) nuclei formed; 14) followed by Cytokinesis (in animal cells)/ or description; 15) formation of a cell plate Give an account of protein synthesis, from the time that the mRNA leaves the nucleus 1) correct reference to translation; 2) mRNA becomes attached to ribosome in cytoplasm; 3)reference to ribosome attachment site/ P site or S'end/sequence/start sequence (AUG); 4) tRNA in cytoplasm attached to specific amino acid; 5) reference to structure of tRNA/anticodon on tRNA; 6) tRNA carries amino acid to ribosome; 7) complementary anti-condon of tRNA lines up with condon of mRNA; 8) Two tRNA molecules held in position; 9) Amino acids joined by peptide bonds; 10) reference to enzyme/enzyme complex in ribosome/ATP in loading tRNA; 11) tRNA free/ released to pick up another amino acid/re-used/recycled; ribosome moves along mRNA until it reaches end/stop codon/non-sense codon (UAA,UGA,UAG); 13) polypeptide chain produced; 14) chain twisted/folded to form protein/ref. to alpha helix/ beta pleated sheet etc.; 15) Ref. to polysomes or description/ free and RER ribosomes/ ref. to modification by Golgi; Give an account of the structure and replication of deoxyribonucleic acid (DNA)

DNA is a macromolecule polymer made of subunits called nucleotides. The nucleotides are arranged in two chains, which are coiled into a spiral shape called a double helix; DNA is the molecule from which the gene alleles on the chromosomes are made; As with all nucleotides, those in DNA have three parts. These are a pentose sugar called deoxyribose, a phosphate group and a nitrogenous base; The sugar and the phosphate are exactly the same in every nucleotide, but the base varies. There are four bases in DNA and each nucleotide contains one of them. The bases are called Adenine, Guanine, Thymine and Cytosine. (A,G,T and C for short);The nucleotides are joined in a specific order. The order of the nucleotides means that the bases they contain are in a certain order, it is this order which forms the genetic code; The sugar and phosphate join together to make the backbone of the DNA molecule. The 3’ carbon on one sugar is joined to the 5’ carbon on the next by means of a phosphate bridge, like this; Each time the sugar joins to a phosphate, a molecule of water is eliminated in a condensation reaction; This sugar-phosphate-sugar bond is called a phosphodiester bond; The process repeats so that a very long chain of nucleotides is made, a polynucleotide. Note that the bases protrude from the side of the chain; There will be a spare 5’ sugar atom at one end of the chain and a spare 3’ atom at the other. The chain thus has a 3’ to 5’ direction reading up the page; In DNA a second polynucleotide chain forms next to the first, but this runs in the opposite direction. The chains are therefore described as antiparallel; The bases now find themselves opposite one another and bond with weak hydrogen bonds. When this occurs Adenine always pairs with Thymine (A-T) and Guanine with Cytosine (G-C). There is a good reason for this complementary pairing; Adenine and Guanine both have a double ring structure and are classified chemically as Purine bases;Thymine, uracil and Cytosine all have a single ring structure and are classified as Pyrimidines;The actual process of DNA replication is simple. To begin with one strand in the DNA duplex is nicked by the enzyme DNA topoisomerase, allowing part of the molecule to unravel to form a replication fork (the DNA is replicated a bit at a time and the whole molecule is never completely uncoiled);Next, the enzyme DNA helicase splits the two strands by breaking the hydrogen bonds. This exposes the bases;DNA polymerase enzyme then moves along the exposed bases sequences, creating a new complementary strand as it goes. DNA polymerase reads the exposed code from the 3’ to the 5’ end and therefore assembles the new strand from the 5’ to the 3’;Several molecules of DNA polymerase act simultaneously, each assembling a separate section of the new strand of DNA. Each DNA polymerase is preceded by an RNA polymerase enzyme, which constructs an RNA primer to guide the action of the DNA polymerase; These new DNA segments are then joined together by the enzyme DNA ligase. The two new daughter molecules then coil up again to reform the double helix structure. This process occurs during the S-phase of the cell cycle; Give an account of the structure and replication of deoxyribonucleic acid (DNA) 1) DNA is a polypeptide/polymer-monomers called nucleotides/ any ref to DNA made of nucleotides; 2) nucleotides consists of deoxyribose, phosphate and a base; 3) bases are adenine, guanine, cytosine and thymine, 4) A and G are purines 5) C and T are pyrimidines 6) DNA is a double helix; 7) phosphate-sugar linked to form strands/ sugar-phosphate backbone/ ref. to phospho-diester bonds; 8) Strands are antiparallel/run in opposite directions; 9) pairing of A and T, C with G; 10) hydrogen bonding between base pairs; 11) replication semi-conservatrive/ 1 old and 1 new strand in each daughter molecule; 12) replication occurs during interphase/s phase; 13) strands separate by breaking H bonds; 14) new strand synthesised by DNA polymerase; 15) complementary base-pairing in daughter strands/ use of correct base-pairing to give accurate copy; 16) ref. to unwinding/separation of strands by helicase; 17) 5' to 3' direction of synthesis by DNA polymerase; 18) lagging/ strand sections joined by ligase;

Give an account of the ways in which gene technology is used to produce genetically modified organisms 1) definition of GMO as organism with foreign DNA/ genetic material; 2) reverse transcriptase makes (c)DNA for gene using mRNA template; 3) use of DNA polymerase to form double stranded DNA; 4) (bacterial) plasmid used as vector for DNA; 5) use of endonuclease/restriction enzyme to cut DNA; 6) same restriction enzyme/ endonuclease to cut open plasmid and cut donor DNA; 7) short row of unpaired bases produced/ creates sticky ends; 8) complimentary nature of sticky ends explained; 9) ligase joins DNA of plasmid and donor; 10) forming recombinant DNA/ recombinant plasmid; 11) method of inserting plasmid into bacterial cell (e.g. heat shock) 12) Use of marker genes/antibiotic resistance/ to identify bacteria or gene/radioactive probe to id gene; 13) use of particle gun to insert DNA into plant cells /ref to biolistics/Agrobacterium as vector for plant cells; desired gene spliced into Ti plasmid/bacteria cultured with plant cells; 15) use of (retro) virus as a vector; 16) DNA inject directly into nucleus of (animal) cells; 17) credit specific example (insulin, growth hormone, AAT in sheep, flavour savour tomato, glyphosphate resistance in plants, modified pigs for human organ transplantation etc.) Write an essay on gene technology and its applications Introduction could include - definition of gene technology; recombinant DNA explained; use of simple, easily cultured organisms. Sources of DNA - DNA, mRNA; enzyme - endonuclease, substrate - DNA, product - DNA segments; restriction endonuclease, specific DNA base sequence, DNA segments with sticky ends; production of multiple copies of DNA, use of DNA polymerase system; reverse transcriptase; mRNA, cDNA. Modifying the organism - explanation of the terms vector, plasmid; insertion of DNA segment, cDNA; ref. to use of same restriction endonuclease; base paring of sticky ends, use of DNA ligase; insertion into host e.g. bacterium; need for host to be receptive - heat / salt shock; identification of modified organism with recombinant DNA; e.g. use of antibiotic resistance plasmid, replica plating. Synthesis of product, use of organism - culturing of bacterium; role of protein synthesis; isolation of product; named examples use in gene therapy; Credit refs. to social, ethical, economic implications

Write an essay on the causes and effects of chromosome mutation. Introduction could include - Ref. cell division and production of gametes; Ref. mitosis and meiosis; Ref. DNA replication; Ref. chromosome separation; Change in number of chromosomes; Change in structure of chromosomes. Causes - Ionising radiation; Chiasmata and cross over described; Deletion, translation, inversion described; Non disjunction described; Polysomy, polyploidy; In production of somatic and gametic cells. Effects - effects in somatic cells; effects in gametes, give rises to genetic variation; New combinations of linked alleles; Extra alleles r Consequence of fertilization; Failure of fertilisation, mitosis, meiosis; Changes in phenotypes, production of polypeptides; Downs, Klinefelters, Turners; Polyploidy in cereals

Exchange, transport and reproduction Give an account of the process of meiosis and its significance in the production of gametes in humans

1) occurs in ovaries and testes; 2) formation of spindle/ref. to centrioles; 3) (prophase) condensation of chromosomes/disintegration of nuclear envelope/disappearance of nucleolus; 4) (meiosis 1) homologous chromosomes pair/bivalents form; 5) and attach to spindle at metaphase plate/equator; 6) each chromosome consists of two chromatids; 7) crossing over/chiasmata; 8) (anaphase 1) separation of chromosomes; 9) to opposite poles of cell; 10) pulled by spindle fibres/microtubules; 11) (meiosis 2) sister chromatids separate; 12) (haploid/n) cells/gametes formed; 13) fertilisation restores (diploid/2n) number; 14) ref. to genetic variation; 15) Ref. to production of four sperm, and one ovum (egg) plus two/three polar bodies; Describe the structure and function of the ileum in relation to digestion and absorption of carbohydrates 1) presence of villi increases surface area; 2) presence of microvillus/brush border (on epithelial cells); 3) these both increase the rate of uptake/diffusion/absorption; 4) single layer of (epithelial) cells/ simple epithelium; 5) reduces diffusion distance; 6) presence of capillaries to, maintain diffusion gradient/conc gradient; 7) ref. to muscle (layers) and peristalsis/movement; 8) amylase (from pancreas) breaks down starch to maltose; 9) maltase breaks down maltose to gluscose; 10) sucrase breaks down sucrose to glucose and fructose; 11) lactase breaks down lactose to glucose and galactose; 12) enzymes in brush border/ produced by cells in lining of ileum; 13) ref. to carrier proteins, in cell membranes; 14) correct ref. to sodium co-transport/facilitated diffusion/ active transport (into epithelial cells) 15) diffusion of monosaccharide/named monosaccharide (into blood)

Give an account of the principles of chemical coordination in mammals with reference to the control of glucose levels in the blood. regulations of changes in internal environment/homeostasis qualified; hormones are secreted by endocrine/ductless glands; relatively slow effects/effects (often) long lasting; effective in small amounts/ ref. to cascade effect; transported in blood/ circulatory system; affect specific/target organs/ eq. receptor sites on plasma membrane; negative feedback explained (accept. re. insulin); ref. positive feedback in context/ eg oxytocin and uterine muscle; rise in blood glucose level/hyperglycemia causes release of insulin; changes in blood glucose levels detected by pancreas; insulin secreted by Beta cells; in islets of langerhans in pancreas; causes increased absorption of glucose by cells; due to increased permeability of cell surface membranes to glucose; causes/results in conversion of glucose to glycogen/glycogenesis; stored in liver/muscles; credit qualified reference to diabetes; fall in glucose level in blood/hypoglycemia causes secretion of glucagon; by alpha cells; causes/results in conversion of glycogen to glucose; ref. to role of adrenaline/cortisol;

Give an account of the transmission of a nerve impulse along an axon

1. Resting potential qualified / explained / described ; 2. Excess Na' outside axon / eq excess K' inside ; 3. Imbalance maintained by Na+ / K+ pump / eq ; 4. Membrane becomes permeable to Na+ / Na+ diffuses in / Na+ gates open; 5. Action potential / depolarisation / figures quoted; 6. Action potential independent of stimulus strength / correct ref. to threshold / eq ; 7. Stimulus strength affects impulse frequency / eq ; 8. Propagation by local currents / voltage gated channels; 9. Transient event / stated time ref. / less than 3?4 ms ; 10. Unidirectional ; 11. K'+ions diffuse out; 12. Restoration of resting potential ; 13. Refractory period / recovery period ; 14. Ref. to hyperpolarisation ; 15. Saltatory conduction in myelinated axon / or speed increased by increasing diameter of axon / eq ; Energy and the environment Give an account of the flow of energy through a food web 1) source of energy sunlight; 2) absorbed by photosynthetic pigments/named pigment; 3) converted to chemical/bond energy/ used in formation ATP; (energy in the form of organic compounds/ named carbohydrates; 5)by photosynthesis in producers/green plants; 6)ref. to GPP and explanation/elaboration; 7)utilisation by producers/ used in respiration by plants; 8) any ref. to heat/energy losses from metabolism/respiration; 9) ref. to NPP and explanation/elaboration; 10) energy passed on/ by feeding relationships/ food chains/ trophic levels; 11) less energy at top of food chain; 12) efficiency about 10%; 13) ref. to losses due to muscle contraction/locomotion; 14) (energy) in the form of inedible/indigestible material/not all eaten by next trophic level; 15) ref. to energy in faeces/egested material; 16) utilisation of dead organisms by decomposers; 17) energy in the form of excretory material; 18) named excretory material/urine; 19) losses to fossilisation; 20) ref. to chemoautotrophs

Write an essay on the roles of microorgannisms in the cycling of nutrients Introduction could include:-The need for recycling; Ref. to main cycles of carbon and nitrogen.Nitrogen cycle:- Nitrogen fixation; Details of Rhizobium and legumes; Free?living Azotobacter; Reduction of nitrogen to ammonia; Nitrification by Nitrosomonas and Nitrobacter; Ammonia to nitrite to nitrate; Nitrate used for production of amino acids, proteins; Denitrification by Pseudomonas in anaerobic conditions; Ref. to waterlogging, compaction; Nitrate to nitrogen gas; Putrefaction conversion of amino acids, proteins to ammonia. Carbon cycle:- Decomposition by bacteria, fungi; Hydrolytic enzymes, cellulase; Carbohydrate conversion to carbon dioxide; Aerobic respiration; Recycling materials in dead organisms; Ref. to effect on BOD in aquatic media; Eutrophication explained; Anaerobic respiration; Biogas and methanogenic bacteria; Fossilisation; Photosynthetic bacteria Write an essay on "Atmospheric pollution Introduction could include:- balance of gases is important pollutants cause imbalance, give rise to ozone depletion/greenhouse effect/acid rain; source of pollutants, combustion, propellants, utilisation of organisms; Ozone depletion:- reaction between chlorine and nitrogen oxides; mainly due to chlorofluorocarbon/CFC- used in refrigerants and cleaning products; ozone layer filters out UV(B) light ? contributes to development of mutations,

skin tumours; Greenhouse effect:- short wave radiation converted to long wave; greenhouse gases act as heat absorbers; greenhouse gases, carbon dioxide, ozone, methane, water vapour; carbon dioxide- roles of combustion, respiration and photosynthesis; methane - anaerobic breakdown,. methanogenic bacteria, organic waste; results in higher global temperature; expansion of water, melting ice caps; changes in weather patterns; Acid rain:- acidic gases - carbon dioxide, oxides of nitrogen and sulphur ; sources of these gases; details of chemical reaction with water ; precipitation in rain; effects on soil, water pH, release of metal ions, oxidation of chlorophyll; allow references to particulate pollutants, carbon monoxide Write an essay on the causes and effects of deforestation Felled for timber / paper / use as fuel /eq ; 2) Cleared for urban/ development / more houses / ref. to industrial use; 3) Cleared for described agricultural use ; 4) Natural disasters / lightning strikes / hurricanes / qual. (natural) forest fire /eq / failure of regeneration because of climate change eq ; 5) Erosion of soil because of absence of tree roots ; 6) Increased flooding / run-off /silting of rivers ; 7) Loss of humus/ from soil // loss of soil texture /eq // nutrients lost / not recycled / leached from soil ;8) Causes desertification ; 9) Loss of / change in habitat / ecosystem ; 10) Possible extinction/eq of other organisms / decrease in biodiversity / species diversity ; 11) Carbon dioxide levels increase if (cleared by) burning /eq ; 12) Less photosynthesis so less carbon dioxide removed/eq ; 13) Some detail of greenhouse effect ; 14) Reduced transpiration /affects local climate /eq ; 15) Reference to loss of future products e.g. undiscovered drugs/ loss of genetic resource Give an account of the ways in which nitrogen is cycled in ecosystems 1) nitrogen gas cannot be used by plants / is inert /eq (1); 2) nitrate / NH4 taken up by plants / producers, used in protein / AA / nucleic acid synthesis (1); 3) ref. to consumers obtaining nitrogen in proteins / AAs hq from plants/ producers (1); 4) putrefaction / decay / decomposition / breakdown of organic matter /eq by saprobiontic / saprophytic / saprotrophic organisms / acteria / fungi [NOT detritivores/]; 5) ref. to nitrification / nitrifying din right context, qualified (1); 6) organic N / urea / protein converted / reduced to ammonium ions/ ammonia (1); 7) ammonium / ammonia oxidised / converted to nitrite / N3 (1); 8) by Nitrosomonasl Nitrosococcus (1) [7 & 8 must be /inked for marks]; 9) nitrite / N3 oxidised / converted to nitrate / N5 (1); 10) by Nitrobacterl Nitrococcus (1); [9 & 10 must be linked for marks]; 11) denitrification / denitrifying [in right context, qualified] (1); 12) nitrates to nitrogen (gas) (1); 13) by PseudomonaslThiobacillus (1); 14)_ under poorly aerated / anaerobic conditions /eq (1); 15) for example, waterlogged soil / conditions / bog / marsh / compacted soil (1); 16) nitrogen fixation [in right context, qualified] (1); 17) Rhizobiuml` named blue?green / cyanobacteria in root nodules / mutualistic / symbiotic converts N2 to ammonia / nitrogen?containing organic compounds (1); 18) Azotobacterl Bacillus/ Clostridium l Klebsiella or named blue?green / cyanobacteria, free?living / in soil /converts N2 to ammonia / nitrogen?containing organic compounds (1); 19) lightning reference (1) (max 10); [points can be credited from clear diagrams] (Tota1-10)

Genetics, evolution and biodiversity

Give an account of the ways in which gene technology is used to produce genetically modified organisms

1) definition of GMO as organism with foreign DNA/ genetic material; 2) reverse transcriptase makes (c)DNA for gene using mRNA template; 3) use of DNA polymerase to form double stranded DNA; 4) (bacterial) plasmid used as vector for DNA; 5) use of endonuclease/restriction enzyme to cut DNA; 6) same restriction enzyme/ endonuclease to cut open plasmid and cut donor DNA; 7) short row of unpaired bases produced/ creates sticky ends; 8) complimentary nature of sticky ends explained; 9) ligase joins DNA of plasmid and donor; 10) forming recombinant DNA/ recombinant plasmid; 11) method of inserting plasmid into bacterial cell (e.g. heat shock) 12) Use of marker genes/antibiotic resistance/ to identify bacteria or gene/radioactive probe to id gene; 13) use of particle gun to insert DNA into plant cells /ref to biolistics/Agrobacterium as vector for plant cells; desired gene spliced into ti plasmid/bacteria cultured with plant cells; 15) use of (retro) virus as a vector; 16) DNA inject directly into nucleus of (animal) cells; 17) credit specific example (insulin, growth hormone, AAT in sheep, flavour savour tomato, glyphosphate resistance in plants, modified pigs for human organ transplantation etc.) Write an essay on "The factors affecting the growth and size of populations population defined; typical population growth curve; exponential growth; stationary phase; decline / death phase; carrying capacity; environmental resistance; birth rate; death rate; migration; abiotic factors; example (light / nutrients / oxygen / temperature / wind / currents etc.); biotic factors; food supply; spread of disease / parasitism; space / territory; competition for abiotic factors such as light; predation; predator/prey relationship; example - intraspecific competition; interspecific competition; competitive exclusion. Write an essay on "The use of management techniques in the conservation of ecosystems" Introduction could include:- definition of ecosystem; biotic, abiotic factors; adaptation of species to particular habitat; interdependence of species. Pressures on land:- agricultural practices, construction, quarrying, mining, others; need to maintain habitat at optimum; ref. to succession, climax community; conservation of species, species diversity / biodiversity. Mowing:- lawns, meadows; ref. to nature of species present; limiting factors e.g. light; description of mowing, timing; other maintained factors e.g. drainage, fertilizer; effect of not mowing. Water levels:fens, bogs; ref. to nature of species present; limiting factor e.g. water availability, depth; previous practice removed peat, reeds; description of technique, pumping back of water, clearing of reeds; effect of not maintaining water levels. Others:- e.g. of ecosystem; nature of species; limiting factor; description of technique; effect of not managing. Write an essay on "Autotrophic nutrition Introduction could include:- synthesis of carbohydrate from inorganic molecules; energy source light, inorganic chemical reaction; ref. to producers and role in food chains. Obtaining sunlight:leaf structure described; role in obtaining carbon dioxide, water; distribution of chloroplasts; structure of chloroplasts; photosynthetic pigments. Light dependent reaction:- occurs on granal lamellae; source of reactants and production of NADP + H; description of production of ATP; production of oxygen; ref. to absorption, action spectra; credit ref. to photolysis of water, role of electrons, cytochromes, cyclic and non cyclic photophosphorylation. Light independent reaction:Calvin cycle, occurs in stroma; carbon dioxide fixation; role of 5C compound; production of phosphoglyceric acid; role of ATP; role of NADPH + H; production of glucose, 6C compound; regeneration of 5C compound; credit ref. to ribulose bisphosphate.

Write an essay on gene technology and its applications

Introduction could include - definition of gene technology; recombinant DNA explained; use of simple, easily cultured organisms. Sources of DNA - DNA, mRNA; enzyme endonuclease, substrate - DNA, product - DNA segments; restriction endonuclease, specific DNA base sequence, DNA segments with sticky ends; production of multiple copies of DNA, use of DNA polymerase system; reverse transcriptase; mRNA, cDNA. Modifying the organism - explanation of the terms vector, plasmid; insertion of DNA segment, cDNA; ref. to use of same restriction endonuclease; base paring of sticky ends, use of DNA ligase; insertion into host e.g. bacterium; need for host to be receptive - heat / salt shock; identification of modified organism with recombinant DNA; e.g. use of antibiotic resistance plasmid, replica plating. Synthesis of product, use of organism culturing of bacterium; role of protein synthesis; isolation of product; named examples use in gene therapy; Credit refs. to social, ethical, economic implications.