What is a universal characteristic of the genetic code?

A. There are more than 64 different anticodons.

B. There are more nucleotides than codons.

C. There are more codons than amino acids.

D. There are two or more amino acids for each codon.

C

In a copy of Louis Pasteur’s famous experiment, broth was put into flasks as shown in the diagrams.

What results would be expected with no spontaneous generation of life?

A.  Decomposition of broth by microbes occurred only in Flask W.

B.  Decomposition of broth by microbes occurred only in Flasks W and X.

C.  Decomposition of broth by microbes occurred only in Flasks W, X and Y.

D.  Decomposition of broth by microbes occurred only in Flasks W, X and Z.

B

What is evidence for the endosymbiotic theory?

A. RNA can catalyse metabolic reactions.

B. Meteorites contain organic molecules.

C. Amino acids can be synthesized from inorganic compounds.

D. Mitochondria possess their own DNA.

D

Which plasma membrane is the least fluid at high temperatures?

B

This question did not discriminate well with many candidates selecting option D which shows the membrane with no cholesterol.

The first iron ore deposits in rocks appeared about 1.8 billion years ago. What took place to make this occur?

A. Some prokaryotic organisms began to absorb carbon dioxide from seawater.

B. Some eukaryotic organisms began to absorb carbon dioxide from seawater.

C. Some prokaryotic organisms began to release oxygen into seawater.

D. Some eukaryotic organisms began to release oxygen into seawater.

C

This question was one of the two most criticised by teachers, but even so there were only three comments about it. The question was thought to be too difficult and not based on understanding specified in the program. The statistics for the paper show the expected answer was the commonest chosen by candidates, with 45 % answering correctly and a moderately high discrimination index. The question was based on this Application: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis. Candidates were expected to know that photosynthesis caused oxygen to appear in the atmosphere and increase in percentage and that oxygen levels in the oceans would also have increased. They were then expected to deduce that this oxygen will have caused dissolved iron to be oxidised and iron oxide to sediment and become part of rocks formed on the ocean floor. This indicates that either answer C or D is correct. Candidates are not expected to know dates for the origins of photosynthetic prokaryotes and eukaryotes, but they are expected to know that prokaryotes evolved first. Prokaryotes therefore must have produced oxygen before eukaryotes and caused the formation of iron ore deposits. Consequently, answer C is correct.

Three cell types are shown in the micrographs.

[Source: left: UCSF School of Medicine, Courtesy of Prof. D Schmucker. middle: Professor Roger Meicenheimer, Miami University, Department of Botany. right: Courtesy of visualhistology.com.]

What feature distinguishes striated muscle fibres from the three cell types shown in the images?

A. Mitochondria

B. Nucleoid regions

C. Multinucleate structure

D. Membrane-bound organelles

C

Which process explains the observations shown in the images?

A. Active transport

B. Exocytosis

C. Facilitated diffusion

D. Osmosis

D

The giant marine alga Halicystis ovalis is able to move sodium ions from vacuoles to the surrounding seawater through active transport.  Which condition or feature is required for this mode of transport?

A. Movement from a region of higher sodium concentration to a region of lower sodium concentration
B. A partially permeable surface
C. Membrane fluidity
D. Transmembrane proteins

D

Which is an essential feature of the Davson–Danielli model of membrane structure?

A. A phospholipid monolayer with intrinsic and extrinsic proteins

B. A layer of protein sandwiched between two layers of lipid

C. A phospholipid bilayer with intrinsic and extrinsic proteins

D. A layer of lipid sandwiched between two layers of protein

D

This also proved to be too difficult, with scarcely more candidates answering correctly than the guess-level of 25%. The terms use of the terms ‘intrinsic’ and ‘extrinsic’ was unfortunate because ‘integral’ and ‘peripheral’ have been preferred for many years in IB Biology. Perhaps candidates thought that these were the two layers of protein on the membrane surface with the Davson-Danielli model which would lead incorrectly to answer C. Despite this, candidates should have been able to choose answer D, which is an unambiguous description of the Davson-Danielli model. Stronger candidates did tend to choose this answer, as the discrimination index was quite high.

The diagram shows a stage in cell division.

[Source: © International Baccalaureate Organization 2019]

What is the stage shown?

A. Anaphase I of mitosis

B. Anaphase II of mitosis

C. Anaphase I of meiosis

D. Anaphase II of meiosis

D

This proved to be a very easy question as 80% of the candidates recognized the cells were in anaphase II of meiosis.

Which evidence falsifies the Davson–Danielli model?

I. The presence of globular proteins within the phospholipid bilayer

II. Non-polar amino acids cause proteins to remain embedded in membranes

III. Membrane proteins remain in a fixed position inside a membrane

A. I only

B. I and II only

C. II and III only

D. I, II and III

B

Which solution has the highest salt concentration?

A. The original solution

B. Solution 1

C. Solution 2

D. Solution 3

B

Three quarters of candidates answered this question correctly so it was not difficult, but the discrimination index was only moderate suggesting that some well-prepared candidates answered incorrectly. The most popular wrong answer showed a cell bursting in the way that would have happened in a hypotonic solution. Either candidates muddled up hypo- and hypertonic or they did not think carefully enough about the direction of water movement in osmosis. It is always worth double checking in one's mind to make sure that a chosen answer is not the opposite of what it should be.

Red blood cells from a small mammal were immersed in NaCl (sodium chloride) solutions of different concentrations for 2 hours. The graph shows the percentage of hemolysed (ruptured) red blood cells at each concentration.

[Source: Zaidan, T. , de Matos, W. , Machado, É. , Junqueira, T. , Vicentini, S. , Presta, G. and Santos-Filho, S. (2010)
Cellular effects of an aqueous solution of Losartan^® on the survival of Escherichia coli AB1157 in the presence
and absence of SnCl2, and on the physiological property (osmotic fragility) of the erytrocyte. Advances
in Bioscience and Biotechnology, 1, 300–304. doi: 10.4236/abb.2010.14039. Available at https://www.scirp.org/pdf/ABB20100400005_18844979.pdf Licensed under a Creative
Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).]

What can be deduced from the graph?

A. At Y, the net movement of Na ions between red blood cells and the NaCl solutions is zero.

B. At X, Na and Cl ions disrupt the structure of cell membranes.

C. At Y, the hypertonic NaCl solutions diffuse into the red blood cells.

D. At X, water has moved by osmosis into the red blood cells.

D

This question performed well in terms in terms of difficulty and in having a high discrimination index on the paper.

How are villi, alveoli and nephrons similar?

A.  They are internal organs.

B.  They provide large surface areas for molecular exchange.

C.  They secrete hormones.

D.  They have a role in excretion.

B

Which method provides biochemical evidence that cells have begun to differentiate?

A.  Observation with a light microscope

B.  Observation with an electron microscope

C.  Examination of the DNA sequence

D.  Analysis of the proteins

D

Which type of transportation happens in the sodium–potassium pump?

A. Facilitated diffusion

B. Osmosis

C. Simple diffusion

D. Active transport

D

Stargardt’s disease, a genetic disorder that causes vision loss, is being treated using retinal cells derived from human embryonic stem cells. Why are embryonic stem cells used?

A. They are already specialized for this function.

B. They are able to differentiate into the required cell type.

C. They retain stem cell properties after specialization.

D. There are no ethical issues concerning their use.

B

The salt concentration inside the Paramecium is 1.8 %. The salt concentration in the surrounding medium suddenly drops to 0.2 %. What will be the likely response?

A. The cell will lose salt to the medium.

B. The contractile vacuole will expel more water.

C. The cell will swell and eventually burst.

D. The membrane will become more permeable to salt.

B

Which feature(s) allow(s) transport of glucose in blood plasma?

I. It is hydrophobic.

II. It is polar.

III. Its solubility is low at 37 °C.

A. I only

B. II only

C. I and II only

D. II and III only

B

It was suggested that this may be difficult for the students, but glucose transport is included in Section 2.2 of the guide, transport of glucose in blood in relation to solubility in water.

What would show that a person has developed metastatic cancer?

A. Alveolus cells forming a tumour in the lungs

B. Cancer cells producing the skin pigment melanin in the liver

C. A tumour in the prostate gland increasing levels of prostate-specific antigen

D. Cancerous lymphocytes in blood plasma

B

This also had a low discrimination index, but for the opposite reason – most candidates struggled with it. Metastasis is included in sub-topic 1.6 of the program, so candidates could be expected to know that it is the spread of cancer to form secondary tumours. Three of the four answers were describing primary tumours, so were not correct. The expected answer was that cancer cells in the liver producing the skin pigment melanin indicate metastasis. Perhaps candidates did not realise that cells producing melanin must have originated from skin cells.

The image shows a phagocytic white blood cell as seen with a transmission electron microscope.

[Source: http://www.wikidoc.org/index.php/File:Monocyte_TEM_0002.jpg, by Cafer Zorkun is licensed
under the Creative Commons Attribution/Share-Alike License]

Which features can be found both within this cell and in a photosynthetic bacterium?

A. Chloroplasts

B. Multiple nuclei

C. 70S ribosomes

D. Lysosomes

C

There were two types of critical comment from teachers – that there was no correct answer and that the micrograph did not help in answering the question. The inclusion of the micrograph was an attempt to place the question within the context of a specific cell type, but it is true to say that it was not a vital element. Answer C was certainly correct – eukaryotic cells have 70S ribosomes in their mitochondria. A larger number of candidates chose answer D, but a photosynthetic bacterium does not contain lysosomes. Answers A and B were more obviously incorrect and were more rarely chosen. All in all, this was not an effective question as it was too hard and the discrimination index was poor. 

The diagram shows the concentration of four cyclins during the cell cycle. Which curve represents the cyclin that promotes the assembly of the mitotic spindle?

D

Chlorella and Paramecium are both unicellular eukaryotic organisms living in freshwater. Chlorella is photosynthetic and has a cell wall. Which organelle will be found in Paramecium but not in Chlorella?

A. Chloroplast

B. Contractile vacuole

C. Rough endoplasmic reticulum

D. Mitochondrion

B

Only about half of candidates chose the contractile vacuole for a structure in the cells of Paramecium but not Chlorella. The expected reasoning was that the cell wall of Chlorella protects it against bursting due to excessive entry of water by osmosis, so a contractile vacuole is not needed. The commonest other answer was rough endoplasmic reticulum. While a photosynthetic cell is not likely to secrete much protein and so will not have an extensive rough ER, generally eukaryotic cells have at least some. This question was thought by the examining team to be just about acceptable, though the issue of whether unicellular algae have contractile vacuoles is complicated by their presence in some species. If there is a flagellum, there is a gap in the cell wall, and the flagellum itself is not protected by cell wall, so as with animal cells there is a danger of bursting and a contractile vacuole is generally needed.

When does DNA replication occur?

A. S phase of interphase

B. Early prophase

C. G phase of interphase

D. Late prophase

A

In which stage of the cell cycle are chromosomes duplicated?

[Source: M1llx, 2019. Cell cycle simple pl. [online] Available at: https://commons.wikimedia.org/wiki/File:Cell_cycle_simple_pl.png This file is licensed
under the Creative Commons Attribution-Share Alike 4.0 International license.
https://creativecommons.org/licenses/by-sa/4.0/deed.en [Accessed 1 August 2019].]

A. G1 phase

B. G2 phase

C. S phase

D. Mitosis

C

Two cells have the following characteristics.

Which deduction is supported by this information?

A. Both cells are from plants.

B. Cell I is more complex than cell II.

C. Cell II is an animal cell.

D. Cell I is prokaryotic.

D

The image shows an electron micrograph of pancreatic exocrine cells.

What is the role of the vesicles shown in the micrograph?

A. To transport hormones between the rough endoplasmic reticulum and the Golgi apparatus

B. To store glycogen when blood glucose levels are high

C. To move enzymes out of the cell by exocytosis

D. To digest cellulose

C

The image shows an electron micrograph of a fungus, Candida albicans.

Which terms identify the structures labelled I and II in the image?

C

Which function is accomplished by structures X and Y in the Paramecium?

A

The image shows an electron micrograph of virus particles known to infect the bacterium Vibrio parahaemolyticus, which is associated with gastroenteritis, wound infections and septicemia in humans and animals.

[Source: Lin, Y. and Lin, C., 2012. Transmission electron micrograph of phage ϕpp2 particles with several structural proteins. [micrograph] (BMC Genomics, 13:224).]

What does a virus have in common with a living cell?

A. 70S ribosomes

B. Genetic material

C. Reproduction by binary fission

D. Anaerobic respiration

B