Biology Unit 4 Long answers

1. 5C Ribulose Biphosphate combines with carbon dioxide An unstable 6C compound is formed that immediately breaks down to 2 molecules of 3C GP The GP is reduced to Triose Phosphate (3C sugar), using energy from ATP and Hydrogen from NADPH Some triose phosphate is used to form glucose and other carbohydrates, some is used to regenerate RuBP, using phosphate from ATP ………………………………………………………………………………………………………………………………… 2.Light energy is absorbed by chlorophyll An electron in chlorophyll is excited or raised to a higher energy level The electron is released to an electron acceptor The electron is passed down an electron carrier chain in a series of oxidation and reduction reactions. Energy released is used to make ATP This is photophosphorylation The electron, together with a hydrogen ion from water is used to reduce NADP. At the same time electrons from water replace the ones lost from chlorophyll, and oxygen is liberated ……………………………………………………………………………………………………………………………. 3.Conditions are extreme - bare rock Bare rock is colonised by lichins and algae which form a pioneer community Lichins begin to weather bare rock and organic material begins to accumulate Development of thin soil allows seeds of shallow rooted plants to establish. Further accumulation of organic material Competition eliminates pioneer community Scrub (hawthorn, elder, bramble) develops in the absence of fire or grazing that could lead to a deflected succession Small fast growing trees begin to establish such as birch Large trees such as oak become established and out-compete early colonising trees such as birch There are now no further great changes in the community, which achieves stability. This is known as the climax community. ………………………………………………………………………………………………………………………. Annual rings are identified –spring wood with large xylem vessels and summer wood with more dense wood Rings are counted back from outside, the deeper the wood the earlier the growth To date wood samples common patterns of growth that allow cross-dating are identified A wide ring indicates good growth in that year, narrow rings mean little growth which could indicate drought or a very cold summer. 5.Phagocyte makes contact with bacterial cell Cytoplasmic processes enclose bacterial cell in a vacuole called a phagosome. This is an example of endocytosis Lysosomes in the phagocyte move towards phagosome and fuse their membranes with it Lytic enzymes are released into phagosome and destroy bacterial cell Some proteins (antigens) from the bacterial cell are not destroyed but are displayed on surface of phagocyte together with MHC protein to activate T cells …………………………………………………………………………………………………………………….. 7.Kingdom Animalia Phylum Chordata Class Mammalia Order Primata Family Hominidae Genus Pan Species troglodytes ………………………………………………………………………………………………………………………… 8.B Lymphocyte with complementary receptor binds to antigen B Lymphocyte divides to produce a clone of cells One clone differentiates into effector, then plasma cells, the other into B memory cells Plasma cells secrete antibody specific to the antigen ………………………………………………………………………………………………………………………….. 9.Specific T lymphocyte encounters antigen presenting cell. Antigen and MHC bind to receptor on T lymphocyte to activate it Activated T lymphocyte divides rapidly to produce Helper T cells and memory T cells Active Helper T cells activate B lymphocytes and killer T cells (with cytokines) Killer T cells clone and produce active killer T cells and memory T cells Active killer T cells bind to infected cells displaying specific antigens and destroy both them and infecting virus (with perforin)

……………………………………………………………………………………………………………………………. 10.Histamine is released Arterioles dilate and capillary walls become more leaky Blood flow to affected area is increased and more tissue fluid is formed. White blood cells squeeze out through capillary walls Area reddens because of increased blood flow and swells (oedema) ……………………………………………………………………………………………………………………………. 11.Place a grid with co-ordinates over the area to be sampled Select locations in grid for sampling (quadrats) using random number tables Place quadrat frame at co-ordinates and count numbers of individuals of each species Continue until the running mean number per quadrat has stabilised Calculate species diversity with the formula D = N(N-1)/En(n-1) …………………………………………………………………………………………………………………………… 12.Two populations of organisms are isolated in different environments (with different selection pressures) Variation arises as a result of random mutation (there will already be pre-existing variation in the populations) If a characteristic confers an advantage organisms with that characteristic will be more likely to survive and reproduce Alleles for the successful characteristic are inherited and increase in the gene pool Over a long period of time the gradual accumulation of genetic differences between the two populations means they become better adapted to their respective environments The genetic differences become so great that there are barriers to reproduction between the two populations. They are now separate species DNA is released from a cell using detergent These substances are added ; DNA polymerase, Primers with fluorescent markers, DNA nucleotides DNA heated to 95’C to separate strands (breaking H bonds) denaturation 55’C primers bind to start of STR region annealing 65’C DNA polymerase binds and attaches free nucleotides elongation DNA is heated to 95’C again and cycle repeated, doubling DNA each time Using aseptic techniques e.g. flaming neck of bacterial culture bottles Spread bacteria evenly over agar plate to form a lawn Add discs soaked in range of antibiotic concentrations and also water/ethanol (control) Seal plates and incubate At 30’C for 2 days Examine plates – diameter of zone of inhibition shows how well antibiotic works. Visible light and UV light from sun are absorbed by earth’s surface. Heat is radiated into space as long wavelength IR Greenhouse gases i(carbon dioxide, methane) in atmosphere absorb IR radiation Atmosphere is warmed by this enhanced greenhouse effect = global warming Core is taken from peat bog. Deeper layers are older. Pollen grains are extracted, identified and counted A pollen diagram is drawn By comparison with present day plant communities the climate when the peat was formed is established The peat is dated using radiocarbon dating DNA is obtained using PCR, or gene being searched for is cut out with restriction enzymes DNA fragments are separated by electrophoresis DNA samples are placed in wells in an agarose gel Buffer is added An electrical field is applied across the gel Negatively charged DNA fragments move to anode, smallest fragments fastest DNA treated with alkali to produce single strands DNA is placed in bag with single-stranded DNA probes complementary to the micro-satellites being searched for Radioactive or fluorescent gene probe binds with complementary bases on DNA DNA taken up by nylon membrane (southern blotting) Presence of bound probe (and therefore gene) is shown with UV light or X ray film