Short questions Flashcards
3c) Resistance to neonicotinoid pesticides has been observed in some insects. Describe briefly how this resistance could have arisen in populations of insects. (2) (may 2016)
Mutation for resistance in some insects
Mutation causes breakdown of pesticide/changes for receptor site
Natural selection for resistance
4b) Starting from the concept of gene pool, explain briefly how populations of early vertebrates could have evolved into different groups. (3) (may 2016)
Gene pool is all genes
Geographical isolation
Speciation/gene pool splits if populations are reproductively isolated
In different environments there are different selection pressures
Alleles frequency diverge
4c) Mitochondria are thought to have evolved from prokaryotic cells. Describe two adaptations of the mitochondria, each related to its function. (2) (may 2016)
small intermembrane space for a gradient «of protons» to develop
matrix contains enzymes for Krebs cycle/link reaction
ribosomes/DNA for protein synthesis/replication
cristae maximize surface area for ATP synthesis/chemiosmosis/proton pumping/electron transport chains
ATP synthase/stalked particles generates ATP from ADP + Pi
electron transport chains for generating a proton gradient/for releasing energy from reduced NAD
5a) Outline the action of enzymes. (4) (may 2016)
catalyse/speed up reactions substrate-specific lower the activation energy «of a chemical reaction» substrate binds to active site enzyme–substrate complex formed
6b) Outline the effects of putting plant tissue in a hypertonic solution. (4) (may 2016)
hypertonic solution has higher solute concentration than cells
water moves out of the cells by osmosis «into the hypertonic solution»
water moves from lower to higher solute concentration
pressure inside cell drops/cell no longer turgid
volume of cytoplasm drops
7a) Things to include on a eukaryotic plant cell seen in an electron micrograph. (4) (may 2016)
cell wall plasma membrane vacuole mitochondria chloroplast Nucleus
7b) Outline how the energy flow through food chains limits their length. (3) (may 2016)
a. only 10 % «of energy» can pass from one trophic level
to the next
b. energy released by respiration AND lost as heat (Not just respiration or heat.)
c. energy losses due to undigested parts/egestion
d. not enough energy for later stages of a food chain
(2c) Explain gene linkage and its effects on inheritance. [2] (Nov 2021)
a located on the same chromosome;
b genes/gene loci close together
c do not follow (the law of) independent assortment;
d more chance of recombination if genes are further apart;
e inherited together unless crossing over/recombination occurs;
f ratios of offspring in dihybrid crosses are different from expected/non-Mendelian
OR
more offspring with parental phenotype combinations than expected
(2d) Explain the mechanism that prevents polyspermy during fertilization. [2] (Nov 2021)
a cortical reaction (after first sperm nucleus enters the egg);
b vesicles/cortical granules release their contents/enzymes (from the egg/zygote);
c zona pellucida hardened
d enzymes of sperm/acrosome cannot digest (hardened coat)
OR
glycoproteins/ZP3 (in zona pellucida) altered so sperm cannot bind;
(3a) Outline what will happen to human red blood cells if transferred to distilled water. [1] (Nov 2021)
cells absorb water by osmosis and swell/increase in volume
OR
cells burst
(solution with high osmolarity: water leaves cell so cytoplasm shrinks in volume)
(3b) Stem cells can be used to treat Stargardt’s disease. State one other condition treated using stem cells. [1] (Nov 2021)
Leukemia
(3c) Explain the propagation of nerve impulses along the membrane of a neuron. [3] (Nov 2021)
a depolarization of part of axon causes depolarization of next part;
b local currents;
c diffusion of sodium ions between depolarized part and next/polarized part (of axon);
d resting potential reduced from -70 to -50mV;
e sodium channels open when -50mV threshold potential reached;
f entry of sodium ions causes depolarization;
g saltatory conduction in myelinated neurons/axons;
(4b) Describe the secondary structure of proteins. [2] (Nov 2021)
The formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding
- (a) Compare and contrast the mode of nutrition of detritivores and saprotrophs. [2] (Nov 2021)
Similarity: heterotrophic/obtain nutrients from dead organic matter
Detritivores: internal digestion
Saprotrophs: external digestion
(5b) Explain how some plant species are able to respond to changes in their abiotic environment and flower at a precise time of the year. [3] (Nov 2021)
(Include gene expression, detection of light, specific time of year)
a genes for flowering are activated/gene activation/changes to gene expression;
b shoot apex changes from producing leaves/stem to producing flowers;
c daylength detected
d short day plants flower when they have a long period of darkness
OR
long day plants only flower when they have a short period of darkness;
e so short day plants flower in late summer/fall/autumn/winter
OR
so long day plants flower in spring/(early) summer;
(5c) Outline the extension of the stem in plants. [2] (Nov 2021)
a apical meristem (of shoot/stem) produces cells/elongates the stem
OR
cell division/mitosis in tip/apex of shoot/stem;
b auxin stimulates stem growth by…;
c elongation of cells
(8a) Outline the process of protein denaturation. [4] (Nov 2021)
a change to conformation/tertiary structure
b bonds within the protein/intramolecular bonds broken/changed;
c pH and temperature (outside tolerated ranges) can cause denaturation;
d heat at high temperatures breaks bonds;
e extreme pH alters ionization/charges (of amino acids and breaks ionic bonds);
f protein cannot carry out its function
OR
active site of enzymes cannot bind substrates/no enzyme-substate complex;
g irreversible change (usually)
OR
soluble proteins become insoluble/precipitate;
(8c) Distinguish between competitive and non-competitive enzyme inhibition. [4] (Nov 2021)
a binds to active site
binds to allosteric site
b inhibitor and substrate are (chemically) similar
inhibitor different from substrate;
c binding of substrate prevented (because active
site is occupied)
active site changed, preventing substrate binding;
d inhibition reduced by increasing substrate concentration
inhibition not affected by increased substrate concentration;
e useful as pharmaceuticals/toxins (competitive)
useful as end-product inhibitors;
(2b) Explain how the cell cycle is controlled. [4] (Nov 2016)
a. cell cycle is G1, S, G2 and mitosis
b. (control of the cell cycle) by cyclins
c. levels of cyclins fluctuate during the cell cycle
d. conditions inside and outside the cell affect regulation
e. four cyclins
cyclins regulate the timing of the cell cycle
f. cyclins bind to kinases and activate them
g. kinases phosphorylate other proteins
h. phosphorylated proteins perform specific functions in the cell cycle
(3b) Outline the importance of enzymes to metabolic processes. [4] (Nov 2016)
(mention how enzymes affect METABOLIC processes, not talking about action of enzymes)
a. increase rate of reaction
b. lower activation energy
c. a specific enzyme for each substrate
d. metabolic process blocked if an enzyme is inhibited/absent
e. end-product inhibition can control metabolic pathways
f. differences in metabolism as cells produce different enzymes during differentiation
