Essay questions Flashcards
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Describe the genetic and hormonal control of male sexual characteristics in a human.[3]
a. male if (X and) Y chromosomes present ✔
b. gene on Y chromosome/SRY promotes development of testes (from embryonic
gonads) ✔
c. testes secrete testosterone ✔
d. testosterone stimulates sperm production/spermatogenesis ✔
e. testosterone stimulates development (in fetus) of male genitals/primary sexual
characteristics ✔
f. testosterone stimulates development of male secondary sexual characteristics
OR
testosterone causes changes to become adult male during puberty ✔
Outline how the hormone auxin controls phototropism in plant shoots. [5]
a. grows/bends towards (brightest) light/sun ✔
b. auxin moved from lighter to shadier side (of shoot/stem tip/apex) ✔
c. moved by auxin efflux pumps ✔
d. auxin promotes cell elongation/cell growth / auxin causes cell wall acidification/loosening ✔
e. more growth on shady side of stem (due to auxin concentration gradient) ✔
f. binds to auxin receptors (in target cells) ✔
auxin/auxin receptors promote expression of genes (for growth)/for H+ secretion into wall ✔
Compare and contrast hormonal and nervous communication. [7]
Similarities
a. both used for communication between cells/tissues/organs/parts of the body / WTTE ✔
b. both cause a response/change in specific/target cells
OR
both use chemicals that bind to receptors / hormones and neurotransmitters are both chemicals ✔
c. both can stimulate or inhibit (processes in target cells) / WTTE ✔
d. both can work over long distances/between widely separated parts of the body / WTTE ✔
e. both under (overall) control of the brain/CNS / brain (has role in) sending hormones and nerve
impulses ✔
f. both use feedback mechanisms/negative feedback / both used in homeostasis ✔
Differences
Hormones Nerves
g. chemical (messenger) nerve impulse/electrical (signal) ✔
h. transported in blood transported by neurons ✔
i. slower faster ✔
j. carried throughout body carried to single/specific cell/muscle fiber ✔
k. all/wide range of tissues/organs affected only muscles/glands receive signals ✔
l (usually) long term (persistence/response) short duration/short-lived (responses) ✔
m. example of use of hormonal and use of nervous communication ✔
Outline the inheritance of blood types in the ABO blood system in humans [4]
a. i and IA and IB are alleles (of the blood group gene) ✔
b. I
A is dominant and i is recessive / IB is dominant and i is recessive ✔
c. Group O (only) with ii and Group A with IAi or IAI
A / Group B with IBi or IBI
B
d. I
A and IB are co-dominant so Group AB with IAI
B ✔
e. one allele/copy of the gene inherited from each parent/Punnett square showing this ✔
Explain how genetic variation between the individuals in a species can be generated. [7]
a. mutation (in genes/DNA generates variation)
b. base substitution / change to base sequence of gene / makes single nucleotide
polymorphisms /SNPs ✔
c. new alleles formed / different alleles of gene / multiple alleles ✔
d. radiation/mutagenic chemicals/mutagens cause/increase the chance of mutation ✔
e. meiosis (generates variation) ✔
f. recombination/new combinations of genes/alleles produced by crossing over ✔
g. independent assortment/random orientation of (pairs of homologous)
chromosomes/bivalents ✔
h. gametes/chromosomes/DNA/genes from two parents combined (in sexual reproduction)
i. random fertilization (increases genetic variation) ✔
j. in reproductively/geographically isolated populations natural selection may differ ✔
k. in small/isolated populations gene pools change/evolution occurs due to natural
selection/genetic drift ✔
l. disruptive selection can cause different varieties/variants/types/phenotypes to diverge ✔
transfer of genes (between bacteria) in plasmids ✔
Outline the use of analogous and homologous traits in natural classification. [4]
analogous
a. different evolutionary origin/do not share (recent) common ancestor (despite similarities of
function) ✔
b. arise by convergent evolution ✔
c. classification based on analogous traits brings together dissimilar species/is artificial ✔
homologous
d. similar (internal) structures/pentadactyl limb/other example of homologous structures due to
common ancestry ✔
e. different uses/functions ✔
f. arise by adaptive radiation/divergent evolution ✔
g. (natural) classification is based on homologous traits (not analogous) ✔
h. classification based on homologous traits has predictive values/matches evolutionary history ✔
Outline the process of DNA profiling. [4]
a. sample of DNA obtained from person/hair/blood/mouth/crime scene ✔
b. PCR used to amplify/make copies of DNA (in sample) ✔
c. using Taq DNA polymerase / using DNA polymerase from thermophilic
bacteria ✔
d. tandem repeats amplified/used ✔
e. gel electrophoresis used to separate DNA (into bands) ✔
f. separation according to length of fragments/number of repeats
OR
fragments of same length/number of repeats travel same distance ✔
g. pattern of bands/numbers of repeats is the profile/is unique to the
individual ✔
h. example of application/forensics/crime investigation/paternity ✔
Outline the role of DNA polymerase III in DNA replication. [4]
a. binds to template strand adjacent to a primer/at the primer ✔
b. adds nucleotides to template strand/to single stranded DNA ✔
c. using complementary base pairing ✔
d. links nucleotides with sugar-phosphate/phosphodiester bonds ✔
e. adds nucleotides/builds new strand in 5’ 3’ direction ✔
f. lagging strand is built in short segments/Okazaki fragments/synthesis is discontinuous ✔
Explain the factors that affect the rate of enzyme-controlled reactions in cells. [7]
a. temperature increases rate up to optimum and higher temperatures decrease rate /
graph ✔
b. faster molecular movement as temperature rises (so more substrate-active site
collisions) ✔
c. high temperature/heat causes denaturation/irreversible change to active site (so rate
reduces) ✔
d. rate decreased if pH is above and below optimum/if pH is too high or low / graph ✔
e. pH affects shape/structure of enzyme/active site /affects ionization (of amino acids) ✔
f. increases in substrate concentration cause rate to rise towards a plateau/WTTE / graph ✔
g. greater chance of substrate-active site collisions with higher substrate concentration
OR
active sites saturated/all full at high substrate concentrations ✔
h. higher enzyme concentration increases rate (as there are more active sites) ✔
i. enzyme inhibitors/competitive inhibitors/non-competitive inhibitors reduce the rate ✔
j. end-product inhibitors switch off metabolic pathway / act on enzyme at start of pathway
rate ✔
OR
allosteric site used to control enzyme activity by binding of (non-competitive) inhibitor
Autosomal genes are located in chromosomes that are not sex chromosomes.The inheritance of autosomal genes is affected by whether the genes are linked or unlinked. Explain the two types of inheritance, using the example of parents that are heterozygous for two genes A and B. [7]
a. unlinked genes are on different chromosomes / vice versa ✔
b. unlinked alleles migrate/segregate/are inherited independently (during meiosis) / vice
versa ✔
c. (In unlinked inheritance) there is an equal chance for all 4 options to occur / AB, Ab,
aB, ab / vice versa ✔
d. (dihybrid crosses involving) linked genes do not produce Mendelian ratios ✔
e. (excluding recombinants) there is a 1:1 chance of inheriting the different options/AB or
ab ✔
f. in linked characteristics alleles might not migrate together if there is crossing over/
recombinants are formed ✔
g. crossing over occurs in prophase I of meiosis ✔
h. when the sister chromatids migrate in meiosis II the characteristics forming gametes
are different/Ab, aB ✔
i. formation of recombinants causes changes in ratio/probability of inheritance/genetic
variation ✔
j. correct named example of inheritance of linked/unlinked characteristics ✔
k. Punnett/paired diagrams of both unlinked and linked characteristics ✔
l. genes which are linked but are far apart on the chromosome can display independent
assortment ✔
Outline how sperm are produced from diploid cells in the testis and how this production can be sustained over many decades of adult life. [4]
a. germinal epithelium divide endlessly (by mitosis giving rise to spermatagonia)
b. spermatogonia are diploid/2n ✔
c. spermatogonia divide by mitosis / provide a continuous supply throughout adult life ✔
d. (some) spermatogonia enlarge forming primary spermatocytes ✔
e. primary spermatocytes undergo the first division of meiosis/meiosis I ✔
f. secondary spermatocytes produced are haploid/n ✔
g. secondary spermatocytes undergo the second division of meiosis (to produce spermatids) ✔
h. spermatids develop tails
OR
spermatids differentiate into spermatozoa / spermatids associate with Sertoli cells ✔
Testis cells are eukaryotic cells. Identify the structures seen under the electron
microscope in testis cells that are not present in prokaryotic cells. [4]
a. nucleus/nuclear membrane ✔
b. membrane bound organelles ✔
c. mitochondria ✔
d. rough ER/smooth ER/golgi apparatus ✔
e. lysosomes / centrioles ✔
f. large/80S ribosomes / ribosomes attached to a membrane ✔
g. linear chromosomes / histones ✔
Explain the role of hydrogen ions used in photosynthesis. [7]
a. hydrogen ions (and oxygen) are obtained from photolysis of water ✔
b. (excited) electrons (from Photosystem II) contribute to generate a hydrogen ion/proton
gradient
OR
protons build up in the thylakoid space/inside the thylakoid ✔
c. ATP synthase generates ATP by chemiosmosis/using the proton gradient/by movement of
protons from the thylakoid space to the stroma ✔
d. (two) high energy/excited electrons (from Photosystem II) are passed through an electron
transport chain ✔
e. NADP accepts H+ (from the stroma) / electrons to produce NADPH+/reduced NADP ✔
f. ATP/reduced NADP/NADPH+ are used by light-independent reactions/Calvin cycle in the
stroma ✔
g. (in Calvin cycle) carbon fixation to ribulose bisphosphate/RuBP produces G3P ✔
h. ATP is used to transform G3P to TP ✔
i. reduced NADP/NADPH+ is used to transform G3P to TP ✔
Describe how the structure of the chloroplast is adapted to its function in photosynthesis. [4]
a. thylakoids have a small internal volume to maximize hydrogen gradient / quickly increase
concentration gradient ✔
b. many grana / thylakoids give large surface area ✔
c. (grana) contain (photosynthetic) pigments/electron carriers/ATP synthase enzymes ✔
d. (photosynthetic) pigments/chlorophyll arranged into photosystems allowing maximum
absorption of light energy ✔
e. stroma has suitable pH/ enzymes of Calvin/light independent cycle ✔
f. lamellae connect/separate grana maximizing photosynthetic efficiency ✔
The enzyme Rubisco is used in carbon fixation during photosynthesis. Identify four
other examples of proteins that illustrate the wide range of functions of this group of
biochemicals in living organisms. [4]
a. insulin receptors start the cellular signalling pathway/other receptor
b. leptin is a hormone / other protein hormone ✔
c. immunoglobulins/antibodies defend body from disease ✔
d. rhodopsin/photosystems convert light energy to electrical impulses ✔
e. keratin/collagen/other example is a structural protein ✔
f. tubulin/microtubules part of cytoskeleton/ involved in cell division
g. ATP synthase is an enzyme that catalyzes the formation of ATP / other enzyme and function ✔
h. fibrin/fibrinogen is a protein involved in clotting ✔
i. hemoglobin/sodium potassium pump/other example is a transport protein ✔
j. actin/myosin/other example is involved in muscle contraction ✔
k. any other named example and function ✔
l. a second other named example and function ✔
m. spider silk is used to form spider webs/capture prey ✔
Describe the structure of the DNA molecule. [5]
a. two stranded/double helix ✔
b. antiparallel / strands running in opposite directions
OR
one strand organized 5’ to 3’ and the other 3’ to 5’ ✔
c. sugar-phosphate backbone ✔
d. each strand formed by chains of nucleotides ✔
e. each nucleotide is formed by a phosphate, a deoxyribose and a base /
annotated diagram of a nucleotide clearly indicated as a nucleotide ✔
f. the bases are adenine, guanine, cytosine and thymine ✔
g. strands held together by hydrogen bonds (between complementary
base pairs)
OR
A pairs with T and C pairs with G ✔
Outline the role of three enzymes used in the replication of DNA. [3]
a. helicase to separate/unwind DNA strands ✔
b. gyrase / toposiomerase to relax the tension as bacterial DNA is being uncoiled / prevent
supercoiling ✔
c. primase to synthesise primers ✔
d. polymerase (I) removes primers and replaces with nucleotide ✔
e. polymerase (III) adds nucleotides (in a 5’ to 3’ direction) ✔
f. ligase joins (Okazaki) fragments together ✔
Insulin is produced in β cells of the pancreas and not in other cells of the human body.
Explain how differentiation of cells and regulation of gene expression allow proteins
such as insulin to be produced in only certain types of body cell. [7]
a. insulin production is determined by a gene ✔
b. gene for insulin (is found in all cells), but only activated in (β cells of) pancreas ✔
c. stem cells differentiate into specialized cells/(into pancreatic β) ✔
d. during differentiation some genes are turned on and others off ✔
e. insulin is a hormone that regulates the amount of glucose/sugar in blood ✔
f. pancreatic β cells have sensors that detect glucose level in blood ✔
g. an increase in glucose will increase transcription of mRNA of insulin ✔
h. the site of transcription of insulin is in the pancreatic β cells ✔
i. gene transcription is regulated by proteins that bind to specific base sequence in DNA/
enhancers/silencers/promoter proximal elements ✔
j. regulatory sequences/proteins are specific to the gene they regulate / insulin regulator
proteins are only found in in the pancreatic β cells ✔
k. (DNA) methylation (usually) inhibits gene expression / (histone) acetylation promotes gene
expression / tightness of coiling of DNA around histones affects gene expression ✔
