Biology HL IB Section B, 8 marker questions (part b)

Explain the process of DNA replication. (8)

- occurs during (S phase of) interphase/in preparation for mitosis/cell division;

- DNA replication is semi-conservative;

- unwinding of double helix / separation of strands by helicase;

- hydrogen bonds between two strands are broken;

- each strand of parent DNA used as a template for synthesis;

- synthesis occurs in a 5' to 3' direction;

- adenine pairs with thymine and cytosine pairs with guanine;

Outline how enzymes catalyse reactions. (7)

- they increase rate of reaction;

- remains unused/unchanged at the end of the reaction;

- lower activation energy;

- activation energy is energy needed to overcome energy barrier that prevents reaction;

- annotated graph showing reaction with and without enzyme;

- substrate joins with enzyme at active site;

- to form enzyme-substrate complex;

- active site/enzyme specific for a particular substrate;

- when enzyme binds with substrate, it brings reactants closer together to facilitate chemical reactions;

- induced fit model / change in enzyme conformation (when enzyme-substrate complex forms); makes the substrate more reactive.

Explain how nerve impulses are transmitted along and between neurons. (9)

- the resting potential of a cell is negative inside compared with outside;

- stimulation causes depolarization/reversal of charge on each side; due to Na channels opening / Na flowing into the cell;

- this causes an action potential;

- K channels open / K flows out of the cell;

- sodium potassium pump restores resting potential;

- transmitted between neurons across a synapse;

- neurotransmitter released into synaptic cleft;

- neurotransmitter diffuse across cleft to postsynaptic membrane; where they bind to receptors;

- this leads to an influx of Na into the cell; which may initiate an action potential.

Using the theory of natural selection, explain how new species of dicotyledonous plants develop. (8)

- plants produce huge amounts of pollen/ovules/seeds;

- (overproduction) leads to struggle for survival;

- variety caused by sexual reproduction;

- fertilization is random;

- variety caused during meiosis/recombination;

- variety caused by mutations;

- change in environmental conditions occurs;

- plants with the most favourable variations/best suited survive/are selected;

- they reproduce and pass on (favourable) genes;

- in different (environmental) conditions different plants have better/more suited traits/characteristics so different plants survive;

- reference to geographic isolation;

- formation of reproductive barriers / isolation;

- over time/over many generations new species develop.

Explain the production of antibodies. (8)

- antigens stimulate an immune response;

- antibodies are produced in response to specific antigens;

- antibodies are made by B-cells/lymphocytes/plasma cells;

- antigen is engulfed by macrophages;

- antigen is presented on macrophage membrane;

- helper T-cells bind to antigen (on macrophage);

- helper T-cells are activated;

- helper T-cells activate B-cells;

- B-cells clone; into plasma cells and memory cells

- plasma cells produce specific antibodies to the antigen;

- memory cells for long-term immunity; + a faster/stronger response if pathogen returns.

Explain the process of DNA replication. (8)

- the process is semi-conservative;

- helicase uncoils/splits DNA double helix;

- RNA primase; creates a primer for DNA polymerase III to bind/begin replication;

- deoxyribonucleoside triphosphates (free in cell);

- two phosphates removed to release energy;

- DNA polymerase III adds nucleotides in 5' to 3' direction;

- Adenine pairs with Thymine / Cytosine pairs with Guanine;

- discontinuous copying / Okazaki fragments / short lengths of DNA formed (between RNA primers) on lagging strand;

- continuous on leading strand;

- DNA polymerase I removes RNA primers/replaces them with DNA;

- DNA ligase joins the fragments;

- initiated at many points in the (eukaryotic) chromosome;

Explain the energy flow in a food chain as exemplified by a pyramid of energy. (8)

- a food chain includes a producer and consumers;

- represents the direction of energy flow;

- energy loss occurs between trophic levels;

- due to material not consumed/assimilated; and from heat loss due to cell respiration; energy passed on from one level to next is 10-20%;

- this limits length of a food chain;

- photosynthesis / producers convert solar energy to chemical energy (in organic molecules);

- consumers obtain necessary energy from eating organisms of previous trophic level;

- and energy pyramid shows the flow of energy from one trophic level to the next (in a community);

- units are energy per unit area per unit time;

- Pyramid of energy drawn showing each level nor more than one fifth the width of the previous one, with three correctly labelled trophic levels.

Explain how sexual reproduction promotes variation in a species. (8)

- meiosis results in four haploid cells/gametes;

- random assortment of chromosomes; in metaphase I;

- it gives rise to variety of haploid gametes;

- 2n possible gametes where n is the haploid number;

- crossover may occur between homologous chromosomes; in prophase I;

- it causes new combinations of genetic material/alleles;

- non-disjunction causes changes in chromosome numbers;

- infinite variety in gametes;

- random process of fertilization;

- random process of mating;

- new combinations even with same parents;

- mutation can occur in prophase I (e.g. deletion / inversion / translocation).

Explain the control of glucose levels in the blood. (8)

- glucose levels increase in blood after eating;

- pancreas cells monitor glucose levels;

- beta cells (of the islets) in the pancreas detect high glucose levels; so they produce insulin;

- this causes cells to take up glucose (for energy use);

- excess stored in liver/muscle as glycogen;

- this decreases glucose levels;

- low glucose levels stimulate alpha (islet) cells in the pancreas; to produce glucagon;

- this stimulates the release of glucose from liver/breakdown of glycogen; which raises the glucose levels;

- normal levels of glucose maintained by homeostatic / negative feedback mechanisms.

Outline the processes involved in spermatogenesis within the testis , including mitosis , cell growth , the two divisions of meiosis and cell differentiation

A. cell division by mitosis to form more cells / spermatogonia ;

B. growth of cells / spermatogonia to form larger cells / primary spermatocytes;

C. cells / primary spermatocytes divide by meiosis;

D. two divisions of meiosis;

E. haploid cells / spermatids formed;

F. differentiation of haploid cells / spermatids into sperm;

G. growth of tail / other feature of differentiation;

H. FSH, testosterone and LH all needed for spermatogenesis;

Draw and label a diagram of a mature sperm and egg.

A. acrosome;

B. head with nucleus;

C. tail;

D. middle piece with mitochondria;

E. haploid nucleus;

F. (two) centrioles;

G. cytoplasm (must show large volume relative to nucleus; suggest four to one ratio of diameter at a minimum);

H. (first) polar cell / polar body (needs to be drawn on the outside of the cell);

I. plasma membrane;

J. follicle cells / corona radiata;

K. cortical granules (need to be drawn in vicinity of plasma membrane)

L. Zona pellucida

Compare the processes of spermatogenesis and oogenesis, including the number of gametes and the timing of the formation and release of gametes

A. both involve meiosis;

B. both involve cell proliferation / mitosis (before meiosis);

C. both involve cell growth / enlargement (before meiosis);

D. LH / FSH involved in both;

E. testes versus ovaries;

F.

spermatogenesis starts at puberty versus oogenesis starts in the fetus;

G. spermatogenesis until death versus oogenesis until menopause;

H.

spermatogenesis continuously versus oogenesis in a cycle;

1. millions of sperm daily versus one egg per month;

J. ejaculation of sperm any time versus ovulation in middle of menstrual cycle;

K.

four sperm per meiosis / spermatogonium versus one egg per meiosis / oogonium;

L. spermatogenesis involves equal divisions versus oogenesis involves unequal cell / cytoplasm divisions;

M. no polar bodies in spermatogenesis versus 2 or 3 polar bodies in oogenesis;

N.

spermatogenesis involves Sertoli / nurse cells versus oogenesis does not;

O. meiosis Il completed before fertilization in spermatogenesis versus after in oogenesis;

P. testosterone needed for spermatogenesis versus not needed for oogenisis

Describe the process of fertilization, including the acrosome reaction, penetration of the egg membrane by a sperm and the cortical reaction.

A. sperm enters oviduct (fallopian tube) / sperm swims towards egg / (secondary) oocyte / ovum;

B. sperm attracted to egg / sperm attach to receptors in zona pellucida / chemotaxis;

C. acrosome reaction / release of (hydrolytic) enzymes from acrosome

D. penetration of zona pellucida / jelly coat;

E. membranes of egg and sperm fuse / sperm (head) penetrates egg membrane;

F. cortical reaction / granules released to the outside of egg;

G. zona pellucida hardens / fertilization membrane forms to prevent polyspermy;

H. nucleus of secondary oocyte completes meiosis II;

I. fusion of nuclei / (diploid) zygote forms;

Outline the role of HCG in early pregnancy.

A. maintains / stimulates growth of corpus luteum;

Explain how the structure and functions of the placenta, including its hormonal role in secretion of estrogen and progesterone, maintain pregnancy.

A. placenta is composed of fetal and maternal tissues;

B. placenta grows into / is embedded in endometrium / uterus lining;

C. villi increase surface area;

D. vascularization / capillaries within placental villi;

E. intervillous spaces through which maternal blood flows;

F. placenta connected to fetus via umbilical cord;

G. placental / chorionic villi are the site of exchange between maternal and fetal blood;

H. secretes estrogen to maintain uterine lining; secretes progesterone to maintain uterine lining;

J. gas / nutrient exchange for fetus;

K.

removes waste products;

acquiring passive immunity / antibodies cross placenta;

M. site of exchange of antibodies from maternal to fetal blood;

N. produces HCG to maintain corpus luteum;

O. prevents blood mixing / incompatible proteins kept separate;

P. prevents damage from high pressure in maternal arteries.

Outline early embryo development up to the implantation of the blastocyst.

A. fertilized egg called a zygote;

B. cell divides by mitosis;

C. early divisions of zygote result in reduction in quantity of cytoplasm per cell / no increase in overall size;

D. first divisions occur while zygote in fallopian tube / oviduct;

E. several divisions result in the formation of a bundle of cells called a morula;

F. further divisions result in a hollow ball of cells / fluid filled ball of cells / blastocyst;

G. implantation occurs up to seven days after fertilisation

Explain how vesicles are used by cells to move materials.

a. fluidity of membranes allows vesicles to bud off membranes/fuse with membranes;

b. materials taken into cells by endocytosis/vesicle formation;

c. Paramecium takes in food / phagocytes engulf pathogens / another example;

d. materials released from cells by exocytosis/by vesicle fusing with plasma membrane;

e. neurotransmitter released at synapses / protein secretion / secretion from gland cell /

another example;

f. movement/transport of materials (inside vesicles) within cells/through the

cytoplasm/between organelles/from an organelle to the (plasma)membrane/from the

(plasma) membrane to an organelle;

g. movement of proteins from the rough ER to the Golgi / another example;

Describe the transport of carbon compounds such as sucrose and amino acids in phloem.

[7]

a. transport/translocation in (phloem) sieve tubes;

b. flow of sap through pores in end walls/sieve plates;

c. sugar/amino acids are transported dissolved in water/sap;

d. loaded into phloem (companion cells/sieve tubes) by active transport;

e. protons pumped out and sucrose then enters by cotransport;

f. high solute concentration created in phloem/sieve tube;

g. water enters (sieve tube) by osmosis;

h. hydrostatic pressure in sieve tube increases;

i. unloading from sieve tubes in sink/in roots;

j. water leaves by osmosis lowering the hydrostatic pressure;

k. sap movement (in phloem) from higher to lower pressure;

l. movement from source/leaves to sink/roots;

Outline how food is moved from the stomach to the large intestine.

[3]

a. by muscles (contracting);

b. peristalsis/waves of muscle contraction followed by relaxation;

c. longitudinal muscle pushes food along the intestine when it contracts;

d. circular muscle constricts the intestine to ensure movement only onwards/not back to

stomach;

e. movement (from stomach to large intestine) via the small intestine/duodenum/ileum;

Explain how changes to the cell cycle can result in tumour formation.

[4]

a. cell cycle is (repeated) sequence of cytokinesis/cell division, (then) interphase(then)

mitosis / cell cycle includes the sequence of interphase, mitosis and cytokinesis/cell

division (to form new cells which repeat the cycle)

b. cyclins control/regulate this cycle / ensure the cell moves on to the next stage of the

cycle when it is appropriate

c. extra cells produced when they are needed

d. tumour formation is the result of uncontrolled cell division/ cells growing and dividing

endlessly

e. repeated mitoses/high mitotic index

f. due to mutations in oncogenes / oncogenes may become active and contribute to the

development of a cancer cell

g. carcinogens/radiation/mutagenic chemicals/mutagens/smoking cause

mutations/tumours;

Outline the role of the right atrium in the cardiac cycle.

a. right atrium collects (deoxygenated) blood from the body;

b. blood drains into atrium through/from the vena cava;

c. deoxygenated blood present in vena cava/right atrium/right ventricle;

d. right atrium pumps blood into the right ventricle;

e. during atrial systole/ventricular diastole/at the start of the cardiac cycle;

f. sinoatrial node is in the right atrium/sinoatrial node acts as the (natural) pacemaker /

sinoatrial node initiates the heartbeat;

g. SA node sends out electrical signal to stimulate contraction in the (walls of the) atria/then

propagated to the AV node / (walls of the) ventricles;

Describe processes in the carbon cycle that produce or use carbon dioxide.

[7]

a. photosynthesis uses carbon dioxide / reduces carbon dioxide concentration of the

atmosphere;

b. autotrophs/plants/cyanobacteria convert/fix carbon dioxide into carbon/organic

compounds;

c. cell respiration produces/releases carbon dioxide;

d. glucose/carbon/organic compounds oxidised/broken down to produce/release carbon

dioxide;

e. carbon dioxide released from aerobic (cell) respiration AND anaerobic respiration in

yeast/plants (but not animals);

f. carbon dioxide released from saprotrophs/detritivores/decomposers from dead organic

matter / during decay/decomposition/respiration;

g. (partially) decomposed organic matter can lead to the formation of peat /fossilized

organic matter (coal/oil/natural gas)

h. carbon dioxide released when carbon/organic compounds burn / during combustion (of

biomass/fossil fuels) / forest fires;

i. carbon dioxide dissolves in aquatic ecosystems / can form carbonic acid/hydrogen

carbonate ions;

j. reef-building corals/molluscs use calcium carbonate to make/build shells/exoskeletons or

other body parts;

k. hard parts/shells/exoskeletons / precipitation of calcium carbonate to form

limestone/tufa;

Outline the changes to chromosomes that occur during prophase in the first division of

meiosis. 4

a. pairing/synapsis of homologous chromosomes / homologous chromosomes form

bivalents;

b. crossing over / chromatid breaks then rejoins to non-sister chromatid;

c. exchange of DNA/alleles/genetic information between chromatids/chromosomes;

d. recombination / new combinations of alleles/genes generated;

e. condensation/shortening/thickening/supercoiling of chromatids/chromosomes;

f. formation of a chiasma where crossing over occurred;

Describe the processes that are carried out by enzymes that bind to DNA.

[7]

replication a. helicase unwinds the double helix/DNA;

b. helicase breaks hydrogen bonds between/separates/unzips DNA strands;

c. (DNA) gyrase/topoisomerase releases tensions in DNA as it unwinds;

d. (DNA) primase adds RNA primers (where DNA polymerase can bind);

e. DNA polymerase (III) replicates DNA/adds nucleotides (to make new strand);

f. DNA polymerase I replaces RNA (primers) with DNA;

g. DNA ligase seals nicks/joins sugar-phosphate backbones/joins

(Okazaki)fragments; transcription h. RNA polymerase used for transcription;

i. RNA polymerase unwinds / separates DNA strands / binds to the promoter;

j. RNA polymerase copies DNA base sequence of a gene/makes mRNA;

k. restriction enzymes/endonucleases cut DNA at specific base sequences;

l. telomerase adds nucleotides to the ends of chromosomes/makes telomeres;

Explain the effects that the environment can have on DNA in living organisms.

[4]

Mutation a. (environment can cause) mutation;

b. mutations are base sequence changes;

c. radiation/UV/gamma rays can cause mutations/changes to base sequences;

d. mutagenic/carcinogenic chemicals can cause mutations / mustard gas/another

example; Epigenetics e. (environment) can cause changes to gene expression;

f. methylation (patterns) in DNA changed (in response to environmental factors);

g. methylation inhibits (gene transcription) / acetylation promotes (gene

transcription);

h. body temperature/stress/diet (can affect gene expression); For mpd do not

allow 'mutagen' instead of 'mutagenic chemical' as it includes forms of radiation

as well as chemicals. Allow smoking and asbestos as examples of mutagens

/carcinogens in mpd.

Explain the roles of specific hormones in the menstrual cycle, including positive and negative feedback mechanisms (8)

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

b. follicles secrete oestrogen

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

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

e. estrogen stimulates LH secretion

F. oestrogen promotes development of endometrium/uterine lining & LH levels increase and cause ovulation

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

I. LH causes follicle to develop into corpus lateum OR

follicle cells produce more progesterone

J. progesterone thickens the uterus lining

K. High progesterone results in negative feedback on pituitary

L. Progesterone levels drop and allow FSH secretion

M. Falling progesterone leads to menstruation/degradation if the uterine lining

Explain the roles of specific hormones in the menstrual cycle, including positive and negative feedback mechanisms (8)

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

b. follicles secrete oestrogen

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

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

e. estrogen stimulates LH secretion

F. oestrogen promotes development of endometrium/uterine lining & LH levels increase and cause ovulation

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

I. LH causes follicle to develop into corpus lateum OR

follicle cells produce more progesterone

J. progesterone thickens the uterus lining

K. High progesterone results in negative feedback on pituitary

L. Progesterone levels drop and allow FSH secretion

M. Falling progesterone leads to menstruation/degradation if the uterine lining

Explain how insects excrete nitrogenous wastes. [8]

• a. excreted as uric acid

• b. excretion by Malpighian tubules

• c. nitrogenous waste/ammonia «accumulates» in hemolymph

• d. nitrogenous waste/ammonia absorbed by Malpighian tubules

• e. ammonia converted to uric acid

• f. conversion to uric acid requires energy/ATP

• g. high solute concentration in Malpighian tubules OR active transport of ions/Na+/K+ into Malpighian tubules

• h. water absorbed by osmosis flushes uric acid/nitrogenous waste to «hind» gut

• i. water/ions reabsorbed from the faeces and returned to hemolymph

• , uric acid precipitates/becomes solid/forms a paste so can pass out with little water

• k. uric acid excreted/egested with the faeces

• I, water conservation/osmoregulation OR reduces mass of water «in body»

• m. uric acid is non-toxic

Explain how the structures of the nephron and its associated blood vessels enabke the kidney to carry out its functions (8)

a . ( high blood glucose levels ) detected by pancreas islet cells / beta cells ;

b . insulin secreted in response ( to high blood glucose / glucose above threshold level ) ;

c . insulin stimulates cells to absorb glucose ; d . glucose used in cell respiration ( rather than lipids ) ;

e . glucose converted to glycogen ( in liver / muscle cells ) ;

F. glucose converted to fatty acids / triglycerides / fat ;

g . negative feedback process ;

Outline rge reasons for the differences in blood concentrations between the renal artery and the renal vein (4 marks)

a . ultrafiltration in the glomerulus produces ( large volumes of ) filtrate ;

b . 80 % / most of water in filtrate is ( always ) ( re ) absorbed in proximal convoluted tubule ;

c . water reabsorbed from filtrate in descending loop of Henle ;

d . pituitary gland secretes ADH if blood solute concentration is too high ;

e . ADH makes the collecting duct / distal convoluted tubule more permeable to water ; f

. ADH moves aquaporins into the membranes ( of cells in the tubule wall ) ;

g . more water reabsorbed from filtrate / into blood due to ADH ;

h . blood becomes more dilute / small volume of urine with high solute concentration

i . with low / no ADH less water is reabsorbed in the collecting duct

; j . blood becomes more concentrated / large volume of dilute urine ;

k . water reabsorption in collecting duct due to high solute concentration of medulla ;

1. active transport of Na + ions from filtrate in ascending limb of loop of Henle ;

Explain the role of the nephron in maintaining the water balance of the blood in the human body (8)

a . ultrafiltration in the glomerulus produces ( large volumes of ) filtrate

b . 80 % / most of water in filtrate is ( always ) ( re ) absorbed in proximal convoluted tubule

c . water reabsorbed from filtrate in descending loop of Henle ;

d . pituitary gland secretes ADH if blood solute concentration is too high ;

e . ADH makes the collecting duct / distal convoluted tubule more permeable to water ;

f . ADH moves aquaporins into the membranes ( of cells in the tubule wall ) ;

g . more water reabsorbed from filtrate / into blood due to ADH ;

h . blood becomes more dilute / small volume of urine with high solute concentration

i . with low / no ADH less water is reabsorbed in the collecting duct ;

j . blood becomes more concentrated / large volume of dilute urine ;

k . water reabsorption in collecting duct due to high solute concentration of medulla ; 1. active transport of Na + ions from filtrate in ascending limb of loop of Henle ;

Describe the importance of water to living organisms.

a. coolant in sweat/in transpiration;

b. water has a high heat of vaporisation / heat taken when hydrogen bonds break;

c. water is cohesive so can pulled up/so can be moved under tension in xylem;

d. water is an excellent/universal solvent/dissolves many different substances;

e. medium for transport in blood/xylem/phloem;

f. medium for metabolic reactions / (metabolic) reactions happen dissolved in water;

g. surface tension due to cohesion allows organisms to live on water surface;

h. water has high heat capacity so much energy required to change its temperature;

i. ice floats so lakes/oceans do not freeze allowing life under the ice;

j. high heat capacity so stable habitat/so temperature of water changes slowly;

k. used in chemical reactions/photosynthesis/hydrolysis in organisms;

Explain how mitosis is regulated in cells

Mitosis is regulated by cyclin proteins

These proteins bind to kinases

activating them

so that they begin to attach phosphates to other proteins in the cell.

Both cyclin A and E are involved in the regulation of DNA replication

Cyclin D controls the movement of the cell through the stages of the cell cycle

and cyclin B triggers the assembly of the mitotic spindle

Describe the stages of interphase and their importance to the process of mitosis.

Interphase is split into three stages,

G1 where the cell grows larger in size

and performs its intended function within the organism.

In the S phase, the cell replicates all of its DNA

In the G2 phase, the cell grows even larger

duplicates organelles and makes proteins needed for cell division Both the G1 and G2 phases allow for the cell to grow big enough to split into two cells in preparation for mitosis.

The replication of DNA in the S phase allows for the creation of two identical daughter cells

Discuss the importance of mitosis to living organisms using named examples.

Mitosis is the process of eukaryotic cell division, where cells divide to produce genetically identical cells It is also important for the growth

of organs such as the kidney. It is also important for wound healing

as it provides a physical barrier so that pathogenic microorganisms cannot enter

It is also important for organisms like plants and some animals which use asexual reproduction

to clone themselves. It can be used to replace dead cells and repair tissues. However, if mitosis is uncontrolled, cells continuously divide resulting in the growth of tumours or cancer.

Explain adaptive radiation

whales and birds share a common ancestor

shared common ancestor had a limb similar to both whales and birds OR had pentadactyl limb

(1]

change in environment OR change in circumstances causes different selection pressures

divergent evolution OR ancestral species begins to diversify into different lines

(1]

reproductive isolation OR no gene flow between ancestors of birds and whales

random mutation resulted in new phenotypes OR new alleles OR bone structures

(1]

populations can no longer interbreed, so form new species OR speciation occurs

new species develop traits specialised to their environment OR ecological niche OR different selection pressures selected for different limb structures OR aerial locomotion OR description of selection pressure favouring wing structures AND aquatic life OR description of selection pressure favoured flipper structures