IB DP Biology Topic 1: Cell biology -1.5 The origin of cells Question Bank SL Paper 2

Question

Apart from the ribosomes, explain the evidence for the endosymbiotic theory of the origin of eukaryotic cells.   [3]

▶️Answer/Explanation

Ans

a.mitochondria/chloroplasts show features in common with prokaryotes/similar size;
b.multiply by binary fission/in same manner;
c.have naked loop of DNA/circular DNA/own DNA;
d.surrounded by a double membrane;

Question

Reproduction in eukaryotes can be sexual or asexual.

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

[4]
a.

Explain how hormones are used to control the human menstrual cycle.

[8]
b.

Outline natural methods of cloning in some eukaryotes.

[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. FSH stimulates the development of follicles

b. follicles produce estrogen

c. estrogen stimulates the repair of the uterus lining

d. estrogen stimulates LH secretion

e. LH causes/stimulates ovulation

f. LH causes/stimulates the development of the corpus luteum

g. corpus luteum secretes progesterone

h. progesterone causes/stimulates thickening of the uterus lining

    OR

    prepares uterine lining for implantation

    OR

    maintains the endometrium

i. progesterone/estrogen inhibits the secretion of LH/FSH

j. falling progesterone levels at the end of the cycle allow FSH production/menstruation

k. negative/positive feedback «control» described correctly

l. LH/FSH are pituitary hormones

[Max 8 Marks]

b.

a. clones are genetically identical organisms

    OR

    group of cells derived from a single parent cell

b. asexual reproduction in plants such as tubers/runners/bulbs

Allow other verifiable examples of plants

c. common in non-vertebrates such as budding in hydra

Allow other verifiable examples of invertebrates

d. budding in yeast/fungi

Allow other verifiable examples of fungi

e. identical twins «in humans» are clones because they originate from
the same cell

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

The Chinese soft-shelled turtle, Pelodiscus sinensis, lives in salt water marshes. The turtle can live under water and out of water.

These turtles have fully developed lungs and kidneys, however, many microvilli have been discovered in the mouth of P. sinensis. A study was undertaken to test the hypothesis that oxygen uptake and urea excretion can simultaneously occur in the mouth.

Initial experiments involved collecting nitrogen excretion data from P. sinensis. The turtle urinates both in water and out of water. When in water it allows waste products to be washed out of its mouth. When out of water it regularly dips its head into shallow water to wash its mouth. The table shows the mean rates of ammonia and urea excretion from the mouth and kidney over six days.

It was noted that during long periods out of water, turtles rhythmically moved their mouths to take in water from a shallow source and then discharge it. Changes in the dissolved oxygen and the quantity of accumulated urea in the rinse water discharged by the turtles were monitored over time as shown in this graph.

In order to test whether a urea transporter was present in the mouth tissues of the turtles, phloretin (a known inhibitor of membrane proteins that transport urea) was added to the water in which a further set of turtles submerged their heads. The results of that treatment are shown.

Further research was conducted to determine where mRNA expression of a urea transporter gene might be occurring in P. sinensis. Gel electrophoresis was used to analyse different tissue samples for mRNA activity.

Expression of the urea transporter gene by cells in the turtle’s mouth was assessed by measuring mRNA activity. Turtles were kept out of water for 24 hours and then injected with either a salt solution that matched the salt concentration of the turtle, dissolved ammonia or urea, followed by another 24 hours out of water.

Deduce whether the excretion of ammonia or urea changes more when a turtle emerges from water.

[2]
a.

Compare and contrast the changes in urea excretion in the mouth with the changes in urea excretion in the kidney when a turtle emerges from the water.

[3]
b.

Describe the trends shown by the graph for dissolved oxygen in water discharged from the mouth.

[1]
c.i.

Suggest reasons for these trends in dissolved oxygen.

[2]
c.ii.

Deduce with a reason whether a urea transporter is present in the mouth of P. sinensis.

[2]
d.

Outline the additional evidence provided by the gel electrophoresis results shown above.

[2]
e.

Identify which of these turtle groups represent the control, giving a reason for your answer.

[1]
f.i.

Suggest a reason for the greater expression of the gene for the urea transporter after an injection with dissolved ammonia than an injection of urea.

[2]
f.ii.

The salt marshes where these turtles live periodically dry up to small pools. Discuss the problems that this will cause for nitrogen excretion in the turtles and how their behaviour might overcome the problems.

[3]
g.
▶️Answer/Explanation

Markscheme

a. urea 

b. for both mouth and kidney 

c. percentage change/change in μmol day−1 g−1 greater with urea/other acceptable numerical comparison

a.

a. both higher/increased on emergence from/with turtle out of water 

b. both increased by 0.66 «μmol−1 g−1 when turtle emerges from water» 

c. % increase is higher in kidney / kidney 940% versus mouth 73/75% / increase is higher proportionately higher in kidney / kidney x10 versus mouth nearly double/x1.73 

d. urea excretion by mouth greater than kidney out of water «despite larger % increase in kidney excretion»

b.

decrease «when head is submerged» and increase when head is out of water

c.i.

a. oxygen absorbed from water/exchanged for urea when head dipped in water«so oxygen concentration decreases» 

b. lungs cannot be used with head in water / can «only» be used with head out of water 

c. oxygen from water «in mouth» used in «aerobic cell» respiration 

d. oxygen from air dissolves in water when head out of water «so oxygen concentration increases»

c.ii.

a. urea transporter is present 

b. less urea «excreted»/ lower rate «of urea excretion» / excretion almost zero when phloretin/inhibitor was present

d.

a. mRNA only in mouth and tongue/in mouth and tongue but not esophagus intestine kidney or bladder 

b. bands / lines indicate mRNA for/expression of urea transporter gene 

c. urea transporter gene expressed / urea transporters in mouth/tongue / not expressed/made in esophagus/intestine/kidneys/bladder 

d. mRNA/transcription/gene expression/urea transporters higher in tongue/more in tongue «than mouth»

e.

salt solution is control because it does not contain a nitrogenous/excretory waste product / it matches the salt concentration of the turtle / the turtle’s body already contains salt / because the turtle lives in salt water/salt marshes / because nothing has been altered

f.i.

a. ammonia is «highly» toxic/harmful 

b. ammonia is more toxic than urea/converse 

c. ammonia converted to urea 

d. urea concentration raised «by injecting ammonia» 

e. difference between ammonia and urea «possibly» not «statistically» significant

f.ii.

Problems:

a. urea becomes more concentrated «in small pools» / lower concentration gradient «between tongue/mouth and water» 

b. less water available for urine production/excretion by kidney
OR
less water in ponds for mouth rinsing/more competition for pools (to use for mouth rinsing)

Behaviour to overcome problems:

c. «still able to» dip mouth into/mouth rinse in water/pools 

d. «still able to» excrete urea «though the mouth» in the small pools 

e. more conversion of ammonia to urea/urea excretion rather than ammonia

f. more urea transporters/expression of urea transporter gene 

g. urea excreted «in mouth/via microvilli» by active transport/using ATP 

h. excretion with little/no loss of water

g.

Question

The image shows a phospholipid bilayer that is a component of the cell membrane.

(a) Annotate the diagram to illustrate the amphipathic nature of phospholipids. [2]
(b) Outline a function of cholesterol in cell membranes. [1]

(c) Describe two pieces of evidence that show that eukaryotic cells originated by endosymbiosis. [2]

▶️Answer/Explanation

a a. line to circle labelled phosphate (head) and (tail) labelled fatty acid/hydrocarbon/lipid (tail);

  b. label hydrophilic/polar/attracted to water/ and hydrophobic/non polar/not attracted to water;

b reduces fluidity of membrane / reduces permeability of membrane (to some molecules);

c a. mitochondria/chloroplasts have their own DNA;

b. mitochondria can self-replicate/undergo a process like binary fission;
c. mitochondria/chloroplasts have double membranes;
d. mitochondria/chloroplasts have(70s) ribosomes;
e. mitochondria/chloroplasts are sensitive to antibiotics;
f. similar in size to bacteria

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