IB DP Biology Topic 11: Animal physiology : 11.4 Sexual reproduction HL Paper 2

Question

Cell biologists play an important role in research into disease, fertility, evolution and many other areas of science.

Describe the origin of eukaryotic cells according to the endosymbiotic theory.

[4]
a.

Cell biologists play an important role in research into disease, fertility, evolution and many
other areas of science.

Compare and contrast the processes of spermatogenesis and oogenesis.

[8]
b.

Cell biologists play an important role in research into disease, fertility, evolution and many
other areas of science.

Outline the evidence for evolution provided by selective breeding.

[3]
c.
▶️Answer/Explanation

Markscheme

a. mitochondria and chloroplasts are similar to prokaryotes

b. «host» cell took in another cell by endocytosis/by engulfing «in a vesicle»

    Allow “taking in” in place of “engulfing”

c. but did not digest the cell/kept the «ingested» cell alive

    OR

    symbiotic/mutualistic relationship «between engulfed and host cell»

d. chloroplasts and mitochondria were once independent/free-living «organisms»

e. DNA «loop» in chloroplast/mitochondrion

f. division/binary fission of chloroplast/mitochondrion

g. double membrane around chloroplast/mitochondrion

h. 70s ribosomes «in chloroplast/mitochondrion»

Award up to [2] for evidence from mpe to mph

[Max 4 Marks]

a.

a. both result in haploid cells/gametes

b. both involve mitosis at the start/in the «germinal» epithelium

c. both have cell growth «before meiosis»

d. both involve «two divisions of» meiosis

e. both involve differentiation to produce a gamete

f. both are stimulated by hormones

    OR

    spermatogenesis stimulated by testosterone and oogenesis stimulated by FSH

A table is not required but both statements in one row of the table must either be explicitly stated or clearly implied to award the mark

[Max 8 Marks]

b.

a. crop plants/domesticated animals/livestock produced by selective breeding

b. specific example of a domesticated animal/crop plant and the wild species from which it
was developed

   OR  

   specific example of a domesticated animal/crop plant and the features in it which have been improved «compared with the wild species»

   For example dogs have been developed from wolves

c. artificial selection/crossing selected varieties/eliminating undesirable varieties

d. «selective breeding/artificial selection can cause» significant/rapid change over time/from the original wild species

e. «changes due to selective breeding/artificial selection» shows natural selection can cause change/evolution «in a species»

[Max 3 Marks]

c.

Question

Outline how reproductive isolation can occur in an animal population.

[3]
a.

Describe the different cell types in the seminiferous tubules that are involved in the process of spermatogenesis.

[4]
b.

Explain the roles of specific hormones in the menstrual cycle, including positive and negative feedback mechanisms.

[8]
c.
▶️Answer/Explanation

Markscheme

a. can be sympatric or allopatric 

b. temporal isolation by members of difference populations reproducing at different times  OWTTE

c. behavioural isolation by difference in courtship behaviours  OWTTE

d. geographic isolation by a population being separated by river/mountain/barrier to contact  
An example of a geographic barrier is required.

e. polyploidy

a.

a. spermatogonia «2n» are undifferentiated germ cells  OWTTE

b. spermatogonia mature and divide «by mitosis» into primary spermatocytes «2n» 

c. primary spermatocytes divide by meiosis I into secondary spermatocytes «1n» 

d. secondary spermatocytes divide by meiosis II into spermatids «1n» 

e. spermatids differentiate/mature into spermatozoa/sperm 

f. Sertoli/nurse cells provide nourishment/support to these developing cells 

g. Leydig/interstitial cells produce testosterone

b.

a. anterior pituitary/hypophysis secretes FSH which stimulates ovary for follicles to develop 

b. follicles secrete estrogen 

c. estrogen stimulates more FSH receptors on follicle cells so respond more to FSH 

d. increased estrogen results in positive feedback on «anterior» pituitary 

e. estrogen stimulates LH secretion 

f. estrogen promotes development of endometrium/uterine lining 

g. LH levels increase and cause ovulation 

h. LH results in negative feedback on follicle cells/estrogen production 

i. LH causes follicle to develop into corpus luteum
OR
follicle cells produce more progesterone 

j. progesterone thickens the uterus lining 

k. high progesterone results in negative feedback on pituitary/prevents FSH/LH secretion 

l. progesterone levels drop and allow FSH secretion 

m. falling progesterone leads to menstruation/degradation of uterine lining

Award [5 max] if no reference to feedback is made.

c.

Question

Outline the structure and functions of nucleosomes.

[4]
a.

Explain how DNA is used to pass on genetic information to offspring accurately but also produce variation in species.

[8]
b.

Accurate transmission of base sequences to offspring depends on successful gamete production. Describe how spermatogenesis occurs in humans.

[6]
c.
▶️Answer/Explanation

Markscheme

Remember, up to TWO “quality of construction” marks per essay.

a. found in eukaryotes;
b. consists of DNA wrapped around proteins/histones;
c. histones are in an octamer/group of eight;
d. are held together by another histone/protein;
e. in linker region;
f. help to supercoil chromosomes / to facilitate DNA packing;
g. (function is to) regulate transcription / gene expression;

a.

Remember, up to TWO “quality of construction” marks per essay.

a. DNA is replicated/copied semi-conservatively/from a template;
b. mutations can be a source of variation / resulting protein has new or different functions;
c. mutations/changes in the DNA may not result in changes in the amino acid for which the triplet codes;
d. genetic code is redundant;
e. genes occur as paired alleles which can be different;
f. crossing-over occurs;
g. recombines linked alleles producing new combinations;
h. random orientation of bivalents / homologous chromosomes (in metaphase I);
i. large genetic variation in (haploid) gametes / 2n / 223;
j. random recombination of alleles during fertilization (leads to variation);
k. different phenotypes among members of the same population;
l. natural selection may lead to enhanced survival of recombinants;

b.

Remember, up to TWO “quality of construction” marks per essay.

a. germinal cells / spermatogonia undergo mitosis to keep a supply of germinal cells present;
b. some germinal cells / spermatogonia grow larger to become primary spermatocytes;
c. primary spermatocytes go through meiosis I;
d. to form secondary spermatocytes;
e. these secondary spermatocytes go through meiosis II;
f. to produce spermatids;
g. spermatids differentiate/grow a tail and reduce their cytoplasm
h. spermatids associated with nurse cells (Sertoli cells);
i. sperm detach from Sertoli cells and enter lumen of the seminiferous tubule;
j. testosterone stimulates sperm production;

c.

Question

Draw a labelled diagram of the human adult male reproductive system.

[5]
a.

Compare the processes of spermatogenesis and oogenesis

[8]
b.

Describe the consequences of the potential overproduction of offspring.

[5]
c.
▶️Answer/Explanation

Markscheme

a. scrotum – shown around testes;
b. testes/testis/testicles – shown inside scrotum;
c. epididymis – shown adjacent to testis and connected to sperm duct;
d. sperm duct/vas deferens – double line connecting testis/epididymis to urethra;
e. seminal vesicle – sac shown branched off sperm duct (not off the urethra);
f. prostate gland – shown positioned where sperm duct connects with urethra;
g. urethra – shown as double line linking bladder to end of penis;
h. penis – with urethra passing through it;
Award [1] for each structure clearly drawn and labelled that conforms to the italicized guidelines given.

a.

Remember, up to TWO “quality of construction” marks per essay.

a. both produce haploid cells / both produce (mature/male/female) gametes;
b. both have mitosis at start/in epithelium / both involve mitosis and meiosis;
c. both have cell growth before meiosis;
d. both involve differentiation (to produce a specialised gamete);

A table is not required but both statements in one row of the table above must either be explicitly stated or clearly implied for each mark awarded.

b.

Remember, up to TWO “quality of construction” marks per essay.

a. more (offspring) than the environment can support / carrying capacity reached;
b. increased mortality/lower life expectancy/more deaths;
c. competition (for resources) / struggle for survival;
d. food/mates/nest sites/territory/other example of resource shortage / example of greater need;
e. variation between members of population / example of variation;
f. better adapted more likely to survive / converse; (reject Lamarckian statements such as those who adapt survive)
g. better adapted reproduce / pass on (favourable) genes/traits / converse;
h. natural selection / (survival of fittest) leads to evolution;

 

c.

Question

Draw a labelled diagram of a mature human egg.

[5]
a.

Outline a technique used for gene transfer.

[5]
b.

Explain how evolution may happen in response to environmental change with evidence from examples.

[8]
c.
▶️Answer/Explanation

Markscheme

Award [1] for each structure accurately drawn and correctly labelled.

a. haploid nucleus;

b. cytoplasm – with nucleus-to-membrane distance >4 times nucleus diameter;

c. centrioles – two must be shown but only one needs to be labelled;

d. cortical granules – needs to be drawn in vicinity of plasma membrane;

e. plasma membrane – shown as a single line and approximately circular overall;

f. polar cell / (first) polar body – needs to be drawn outside the egg cell;

g. zona pellucida / layer of gel (outside the cell membrane);

h. follicle cells / corona radiata (outside the cell membrane);

i. size shown as 100 μm/0.1mm; (accept 90 μm to 120 μm)

a.

a. plasmid used for gene transfer/removed from bacteria;

b. plasmid is a small/extra circle of DNA;

c. restriction enzymes/endonucleases cut/cleave DNA (of plasmid);

d. each restriction enzyme cuts at specific base sequence/creates sticky ends;

e. same (restriction) enzyme used to cut DNA with (desired) gene;

f. DNA/gene can be added to the open plasmid/sticky ends join gene and plasmid;

g. (DNA) ligase used to splice/join together/seal nicks;

h. recombinant DNA/plasmids inserted into host cell/bacterium/yeast;

b.

a. variation in population;

b. (variation is) due to mutation/sexual reproduction;

c. valid example of variation in a specific population;

d. more offspring are produced than can survive / populations over-populate;

e. competition / struggle for resources/survival;

f. example of competition/struggle for resources;

g. survival of fittest/best adapted (to the changed environment)/those with beneficial adaptations / converse;

h. example of changed environment and adaptation to it;

i. favourable genes/alleles passed on / best adapted reproduce (more) /converse;

j. example of reproduction of individuals better adapted to changed environment;

k. alleles for adaptations to the changed environment increase in the population;

l. example of genes/alleles for adaptations increasing in a population;

m. evolution by natural selection;

n. evolution is (cumulative) change in population/species over time / change in allele frequency;

Suitable examples are antibiotic resistance and the peppered moth but any genuine evidence-based example of adaptation to environmental change can be credited.

c.
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