Unit 2 Revision questions and answers: the variety of living organisms

1.       What is intraspecific variation?2.       What does standard deviation tell you about a dataset?3.       Why are identical twins not perfectly identical?4.       What are the three constituents of a nucleotide?5.       Which base does C pair with?6.       The triplet code is degenerate. What does this mean?7.       What are introns?8.       How is DNA arranged in a prokaryotic cell?9.       Give two ways in which meiosis leads to genetic variation.10.   What is a genetic bottleneck?11.   How does the founder effect reduce genetic diversity?12.   Explain the advantage of the oxygen dissociation curve being shifted to the right in small mammals such as mice.13.   Why does carbon dioxide cause the oxygen dissociation curve to shift to the right?14.   What monomer is cellulose made of?15.   Contrast the structures of cellulose and starch and explain how these different structures allow them to act as structural and storage molecules respectively.16.   What do thylakoids contain, and what is its purpose?17.   What is the role of DNA helicase in DNA replication?18.   Name the four subphases of mitosis in order.19.   What is the role of the centromere in mitosis?20.   What happens during interphase?21.   What is an organ?22.   How does the countercurrent exchange system allow efficient gas exchange in fish?23.   Describe how the structure of a leaf is adapted for gas exchange.24.   Name two structures involved in gas exchange in insects.25.   Give two ways in which xerophytic plants are adapted to limit water loss.26.   Name the blood vessel which goes out of the liver back towards the heart.27.   Explain why arteries have a thicker elastic tissue layer than veins.28.   Explain why arterioles have a thicker muscle fibre layer than arteries.29.   Explain the importance of plasma proteins in the reabsorption of tissue fluid.30.   Give two ways in which tissue fluid is returned to the circulatory system.31.   Give two differences between the apoplast and the symplast pathway.32.   What is the role of casparian strips?33.   Explain how water moves up stems.34.   Give three factors which affect transpiration rate.35.   What is a phylogeny?36.   Name the taxonomic group between phylum and order.37.   Describe how DNA hybridisation can be used to determine the relationship between organisms.38.   What is the importance of courtship in mating?39.   Describe how the frequent use of antibiotics leads to antibiotic resistance in bacteria.40.   What is vertical gene transmission?41.   Describe the events that occur in horizontal gene transmission.42.   Give two ways in which agricultural practices can reduce species diversity.43.   Why is Simpson’s index of diversity a better measure of species diversity than simply counting the number of species?

1.       Variation between individuals of the same species (within a species) 2.       The spread of the data about the mean 3.       There is variation due to environmental factors 4.       Nitrogen-containing base, deoxyribose and phosphate group 5.       T 6.       Multiple codons may encode the same amino acid 7.       Non-coding sections of genes 8.       Circular chromosome and plasmids 9.       Crossing over between homologous chromosomes during prophase I; independent segregation of chromosomes during anaphase I 10.   A sudden large decrease in a population due to a chance event 11.   Small number of individuals have a very limited gene pool; breeding occurs but successive generations have a small variety of alleles, so genetic diversity is low 12.   Small mammals have a large SA:volume ratio so lose heat easily; right-shifted oxygen dissociation curve means reduced affinity of Hb for oxygen, so oxygen is more readily unloaded at low pO2s, i.e. at respiring tissues, for respiration to release energy to keep the body warm 13.    Lowers pH of blood; Hb acts as a buffer, accepting protons which causes it to change shape and lowers its oxygen affinity (the Bohr effect) 14.   Beta-glucose 15.   Cellulose is a straight-chain, allowing it to be packed into microfibrils and macrofibrils with hydrogen bonds between adjacent chains, which gives it tensile strength, making it ideal for support and structure of plant cell walls. By contrast starch is branched, allowing it to be more easily hydrolysed as enzymes can operate on all ends of the branches, and is coiled and compact so that a lot of it can fit into a small space (i.e. starch grains), making it ideal for energy storage. 16.   Chlorophyll, which traps light energy for photosynthesis 17.   Separates the double helix by breaking hydrogen bonds, allowing new bases to be added onto the template strands 18.   Prophase, metaphase, anaphase, telophase 19.   The centromere holds chromatids together and attaches them to opposite ends of the spindle. At anaphase it allows them to split and move towards opposite ends of the spindle. 20.   Growth of the cell; synthesis of new organelles; replication of DNA; regular checkpoints to prevent the cell from dividing uncontrollably 21.   Different types of tissues coordinated to carry out a function or variety of functions 22.   Blood and water flow in opposite directions, so a concentration gradient of oxygen is maintained at all points along the gill lamellae and thus the maximum amount of oxygen can diffuse from the water into the blood. 23.   Stomata allow gases to diffuse in and out; air spaces between spongy mesophyll cells maximise surface area for diffusion 24.   Spiracles, tracheae, tracheoles (any two) 25.   Thin leaves with a small surface area; sunken stomata trap water vapour; hairs trap water vapour; waterproof waxy cuticle stops water passing through 26.   Hepatic vein 27.   Elastic tissue smooths out blood pressure; blood in arteries at higher pressure than in veins 28.   Muscle contracts to constrict lumen and control blood flow; arterioles connect to capillaries which are much smaller in volume, so lumen must be constricted more 29.   Soluble so lower the water potential of the blood, causing water to move from the surrounding tissues into the capillaries by osmosis 30.   Reabsorption into capillaries; drainage into lymph vessels/lymphatic system 31.   Apoplast is through cell walls whereas symplast is through cytoplasm/vacuoles; in apoplast pathway water moves due to cohesion between molecules but in the symplast pathway it moves by osmosis; apoplast pathway prevented by Casparian strips/stops at endodermis but symplast unaffected by Casparian strips (any two) 32.   Waterproof so force water in apoplast pathway into the symplast pathway at the endodermis 33.   As water enters the xylem by osmosis the root pressure created forces water slightly up the xylem. Water vapour diffusing out through the stomata causes water to move from the xylem into mesophyll cells by osmosis, creating a pull on the continuous column of water in the xylem due to intermolecular cohesion. Adhesion between water and the xylem walls also pulls water molecules upwards. 34.   Humidity, wind speed, temperature, light (any three) 35.   Organisms grouped according to evolutionary history/lineage 36.   Class 37.   Single strand of DNA from two organisms fused to form a hybrid and then heated to break hydrogen bonds until the strands separated. The greater the sequence identity (i.e. the closer related the organisms) the more hydrogen bonds form between complementary base pairs and thus the closer the evolutionary relationship. 38.   Allows an individual to recognise a mate of the same species, synchronises fertility and stimulates production/release of gametes 39.   Mutation occurs in one bacterium giving it an allele for antibiotic resistance. Antibiotics kill the non-resistant bacteria but surviving bacteria survive and reproduce, passing on the allele by vertical gene transmission so that the frequency of the allele in the population increases. Horizontal gene transmission by conjugation may occur between bacteria of different species. 40.   The passing on of genes by asexual reproduction (binary fission) 41.   Conjugation tube/pilus extends from donor bacterium and fuses with recipient bacterium; plasmid is replicated and moves through the pilus into the recipient. 42.   Monoculture causes a large area of land to be dominated by a single species; pesticides kill insects and other animals (disrupting food webs); forest cleared, hedgerows chopped down and wetlands drained – less variety of habitats and food sources for animals; deforestation leads to fewer plant species and machinery may kill animals; eutrophication disrupts aquatic ecosystems; predators culled due to their impact on livestock (any two) 43.   Simpson’s index of diversity takes into account the number of organisms of each species, which is important as an ecosystem may have many species but could be dominated by just one or two and thus have a low index of diversity.

Questions

answers