More than 90 % of cellular cholesterol is located in the cell’s plasma membrane. What is the main role of cholesterol in the plasma membranes of mammalian cells?

A. To regulate membrane fluidity

B. To increase membrane solubility

C. To increase membrane permeability

D. To regulate membrane temperature

Neural pathways in living brains can now be mapped by tracking the movement of water molecules inside axons. What keeps water molecules inside axons?

A. Plasma membrane

B. Hydrogen bonding

C. Pump proteins

D. Synapse

How do both mitochondria and chloroplasts provide evidence for the endosymbiotic theory?

A. They have double membranes.

B. They have 80S ribosomes similar to prokaryotes.

C. They contain the same DNA as the nucleus of the cell.

D. They exist together in eukaryote cells for their mutual benefit.

Apparatus was set up as shown to collect data.

The graph shows the results after 47 minutes of data collection.

What causes the rates to differ?

I.   Different concentration gradients at the start

II.  Diffusion of sugar is initially greater in Y than in X

III. The systems are reaching equilibrium over time

A.  I only

B.  II only

C.  I and III only

D.  II and III only

Pasteur carried out a series of experiments that provided strong evidence against a widely supported theory. What was this theory?

A. Endosymbiosis

B. Spontaneous generation

C. Conservative replication of DNA

D. Evolution

Which structure found in eukaryotes has a single membrane?

A. Nucleus

B. Lysosome

C. Chloroplast

D. Mitochondrion

Which statement is evidence for the endosymbiotic theory?

A. Chloroplasts contain 70S ribosomes.

B. Protein synthesis occurs in the cytoplasm.

C. Organic molecules can be synthesised abiotically.

D. RNA is self-replicating.

Pasteur used swan-necked flasks and a nutrient broth to demonstrate that spontaneous generation of organisms does not occur on Earth. Some students performed a similar experiment using two swan-necked flasks, one containing broth which had been previously boiled and another containing broth which had not been boiled. 

The flasks were left in the school laboratory and observed after one week. What is the evidence against the spontaneous generation theory?

A. Microorganisms died in flask F due to high temperatures.

B. No microorganisms grew in either flask.

C. Microorganisms grew in flask G.

D. No microorganisms grew in flask F but many grew in flask G.

What special property of phospholipid molecules explains their ability to spontaneously assemble into a lipid bilayer?

A. They are hydrophobic.

B. They are amphipathic.

C. They are saturated.

D. They are hydrophilic

Dialysis membrane was set up to model digestion and absorption in the small intestine.

What is a limitation of this model?

A. There can be no active transport.

B. Maltose will pass through the membrane.

C. Lipase should be present with protein.

D. The membrane is not permeable to starch.

How does potassium move across the membrane of a neuron during repolarization?

A. Simple diffusion

B. Facilitated diffusion

C. Endocytosis

D. Active transport

The table shows concentrations of potassium ions and sodium ions inside and outside human cells.

[Source: © International Baccalaureate Organization 2019]

What explains these concentrations?

A. Potassium ions diffuse in and sodium ions diffuse out.

B. Sodium ions diffuse in and potassium ions diffuse out.

C. Active transport pumps sodium ions in and potassium ions out.

D. Active transport pumps sodium ions out and potassium ions in.

In an experiment on osmosis, red blood cells were immersed in a salt solution for two hours. The micrographs show the appearance of these cells before and after immersion in the salt solution.

[Source: Ed Uthman, Acanthocytes, from peripheral blood [image online] Available at:
https://en.wikipedia.org/wiki/Acanthocyte#/media/File:Acanthocytes,_Peripheral_Blood_(3884092551).jpg
This file is licensed under the Creative Commons Attribution 2.0 Generic (CC BY 2.0) https://creativecommons.org/licenses/by/2.0/ Source adapted.]

What explains the observed changes?

A. The salt solution was hypertonic and entered the red blood cells.

B. The salt solution was hypotonic and disrupted the membranes of the red blood cells.

C. The salt solution was hypertonic and water moved into it from the red blood cells.

D. The salt solution was hypotonic and mineral salts were lost from the red blood cells.

The graph shows the mitotic index in the roots of lentil plants at different distances from the end of the root.

[Source: Physiologia Plantarum, Volume 105, Issue 1, January 1999, Pages 171–178, Effect of microgravity on the cell cycle
in the lentil root F. Yu, D. Driss-Ecole, J. Rembur, V. Legué, G. Perbal Wiley Online Library: https://onlinelibrary.wiley.
com/doi/abs/10.1034/j.1399-3054.1999.105125.x]

What can be deduced from the graph?

A. As the distance from the end of the root increases, more cells are undergoing mitosis.

B. At 0.5 mm from the end of the root, most of the cells are in prophase.

C. There were fewer cells observed at 1.5 mm than at 0.5 mm.

D. As the distance from the end of the root increases, the percentage of cells in interphase increases.

What function is performed by the part of the cell shown in the electron micrograph?

[Source: George E. Palade Electron Microscopy Slide Collection Harvey Cushing/John Hay Whitney Medical Library Yale University Library.]

A. Locomotion

B. Synthesis of proteins

C. Movement of chromosomes

D. Breakdown of cellular organelles

Which molecule regulates the fluidity of cell membranes?

A. Phospholipid

B. Cholesterol

C. Glycoprotein

D. Peripheral protein

Which cell component arose first during the formation of the earliest cells?

A. Chloroplast

B. Plasma membrane

C. Mitochondria

D. Cell wall

What part of the plasma membrane is fluid, allowing the movement of proteins in accordance with the fluid mosaic model?

In the chimpanzee (Pan troglodytes), the haploid number of chromosomes is 24. How many sister chromatids are present in the G2 phase of a somatic cell, such as a cell in the bone marrow of the chimpanzee?

A. 12

B. 24

C. 48

D. 96

What evidence from the image of Paramecium indicates whether the organism is a prokaryote or a eukaryote?

A. Compartments in the cell indicate that it is a eukaryote.

B. No nucleus indicates that the cell is a prokaryote.

C. Lack of a cell wall indicates that the cell is a eukaryote.

D. It is a unicellular organism, so it must be a prokaryote.

By which process do potassium ions move through potassium channels in axons?

A. Active transport

B. Exocytosis

C. Facilitated diffusion

D. Simple diffusion

Which features of phospholipids give them their amphipathic properties?

A. Basic phosphate groups and acidic lipids

B. Acidic phosphate groups and basic lipids

C. Hydrophobic phosphate groups and hydrophilic fatty acids

D. Hydrophilic phosphate groups and hydrophobic fatty acids

Which feature of the cell in the micrograph is consistent with the endosymbiotic theory?

A. X has a single membrane.

B. Y has a double membrane.

C. X contains 70S ribosomes.

D. Y contains 80S ribosomes.

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.

Cladograms can be created by comparing DNA or protein sequences. The cladogram on the left is based on DNA sequences and the cladogram on the right is based on comparing protein sequences.

What is the reason that cladograms based on DNA sequences are more reliable predictors of the phylogenetic relationship of species than cladograms based on protein sequences?

A. Amino acids are not as chemically stable as DNA nucleotides.

B. DNA mutates but amino acids do not.

C. Several different triplets of bases can code for the same amino acid.

D. There are 20 different amino acids but only 4 nucleotides.

Which statement provides evidence for endosymbiosis?

A. Early prokaryotes contributed to a large increase in oxygen in the atmosphere.

B. Eukaryotic mitochondria and chloroplasts have their own circular DNA.

C. Certain groups of ancient prokaryotes developed mechanisms to carry out aerobic respiration.

D. Experiments by Miller and Urey produced simple organic molecules in abiotic conditions.

Which statement applies to cholesterol?

A. It is hydrophobic and found on the outside of the phospholipid bilayer.

B. It is hydrophilic and found inside the phospholipid bilayer.

C. It impacts membrane fluidity.

D. It is transported in association with glucose in the blood.

The Davson–Danielli model of membrane structure proposed that membranes were composed of a phospholipid bilayer that lies between two layers of globular proteins, as shown in this diagram.

[Source: Cornell, B. 2016. https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/13-membrane-structure/membrane-models.html]

What evidence supported this model?

A. An electron micrograph that showed two dark lines with a lighter band in between

B. Freeze-fracture electron microscopy

C. Evidence that all membranes are identical

D. The hydrophobic regions of protein would be in contact with water

How is facilitated diffusion in axons similar to active transport?

A. They both require the energy of ATP.

B. They both move substances against a concentration gradient.

C. They both use sodium–potassium pumps.

D. They are both carried out by proteins embedded in the axon membrane.

If cells of a multicellular organism have the same genes, how can there be many different cell types in a body?

A.  Some genes but not others are expressed in each cell type.

B.  Cells lose some genes as development occurs.

C.  Genes do not determine the structure of a cell.

D.  Cells must practice division of labour in order to survive.

The bacterium Neisseria gonorrhoeae causes infections related to the human reproductive system. The graph shows the percentage of samples in which this bacterium showed resistance to six antibiotics over a period of ten years.

What is a possible explanation for the total percentage resistance being larger than 100% in 2010?

A. People do not take the antibiotics as prescribed.

B. More people have been sampled in that year.

C. There was an epidemic of Neisseria gonorrhoeae in that year.

D. Some bacteria are resistant to more than one antibiotic.

The image shows an electron micrograph of mesophyll cells.

What is the name of the structure labelled X?

A. Cytoplasm

B. Mitochondrion

C. Nucleus

D. Chloroplast

The electron micrograph shows a thin section through a plant mesophyll cell.

[Source: https://commons.wikimedia.org/wiki/File:Euglena_sp.jpg, by Deuterostome
https://creativecommons.org/licenses/by-sa/3.0/legalcode]

What is the magnification of the image?

A. × 75

B. × 300

C. × 3000

D. × 7500

Which organelle provides evidence that eukaryotic cells originated when large prokaryotes engulfed small free-living prokaryotes?

A. Chloroplast

B. Nucleoid

C. 80S ribosome

D. Vacuole

The cell membrane model proposed by Davson–Danielli was a phospholipid bilayer sandwiched between two layers of globular protein.  Which evidence led to the acceptance of the Singer–Nicolson model?

A. The orientation of the hydrophilic phospholipid heads towards the proteins
B. The formation of a hydrophobic region on the surface of the membrane
C. The placement of integral and peripheral proteins in the membrane
D. The interactions due to amphipathic properties of phospholipids

The concentrations of cyclins rise and fall in cells at certain times.

[Source: https://en.wikipedia.org/wiki/Cyclin#/media/File:Cyclin_Expression.svg]

What times are these?

A. Day and night

B. Seasons of the year

C. Stages of mitosis and interphase

D. Developmental stages in the life cycle

The image shows part of a mammalian cell.

[Source: Louisa Howard, Katherine Connollly - Dartmouth Electron Microscope Facility. Available at:
https://en.wikipedia.org/wiki/File:Microvilli.jpg.] 

What is the specialized function of this mammalian cell?

A. Locomotion

B. Absorption

C. Reception of stimuli

D. Gas exchange

Which diagram(s) represent(s) processes used in asexual reproduction?

A. I only

B. I and II only

C. II only

D. I, II and III

The salt concentration inside an animal cell is 1.8 %. The salt concentration in the surrounding medium becomes 5 %. What will be the likely response?

A. The cell will gain water from the medium.

B. The cell will lose salt to the medium.

C. The cell will remain unchanged.

D. The cell will shrink from loss of water.

What provides evidence for the endosymbiotic theory?

A. Mitochondrial DNA in eukaryotic cells
B. 70S ribosomes in prokaryotic cells
C. Gene transfer from prokaryotic cells to eukaryotic cells using plasmids
D. Prokaryotic cells (Escherichia coli) in the large intestine digest proteins

A human organ is being prepared for transplant. In what type of solution must it be bathed?

A. A hypertonic solution

B. A hypotonic solution

C. Pure water containing no solutes

D. A solution with the same osmolarity as the organ tissue

Which organism has DNA located in three organelles?

A. A sponge

B. A fern

C. A flatworm

D. A bacterium

Which graph best represents the relationship between the concentration of chloride ions in the external environment of a cell and the rate at which the chloride ions move by facilitated diffusion into the cytoplasm of the cell?

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

Which process(es) occur(s) by osmosis?

I. Uptake of water by cells in the wall of the intestine

II. Loss of water from a plant cell in a hypertonic environment

III. Evaporation of water from sweat on the skin surface

A. I only

B. I and II only

C. II and III only

D. I, II and III

Which sequence has the cells arranged according to their ability to differentiate, starting from the least able?

A. bone marrow, neuron, embryonic, umbilical

B. neuron, bone marrow, umbilical, embryonic

C. umbilical, embryonic, bone marrow, neuron

D. embryonic, umbilical, bone marrow, neuron

How does mitosis produce two genetically identical nuclei?

A.  By separation of homologous chromosomes

B.  By separation of sister chromatids

C.  By division of the cytoplasm into two equal cells

D.  By division of the nuclear membrane into two equal parts

The diagram shows a section through a membrane. What are the modes of transport in the diagram?

[Source: © International Baccalaureate Organization 2020.]

The diagrams represent cells with the same concentration of dissolved substances in their cytoplasm. If all the cells were placed in the same hypertonic sucrose solution, which cell would show the greatest rate of change in the concentration of its cytoplasm?

The image shows an electron micrograph of part of a cell.

[Source: Dr. Eldon Newcomb – Emeritis Professor at The University of Wisconsin – Madison.]

Which features do the two structures labelled X and Y have in common?

A. They are surrounded by a double membrane.

B. They contain 70S ribosomes.

C. They contain naked DNA.

D. They are only found in leaf cells.

In the diagram, which part of the membrane structure does the molecule below form?

In the diagram, which structure is an intrinsic or integral protein?

What is a role of cholesterol in animal cells?

A. It increases body fat.

B. It controls membrane fluidity.

C. It lines the inner wall of capillaries.

D. It is a constituent of bile.

What is/are required for facilitated diffusion?

I. A concentration gradient

II. ATP

III. A channel protein

A. I only

B. I and III only

C. II and III only

D. I, II and III

Students examined micrographs and counted cells in the different stages of mitosis as well as those cells with no visible chromosomes. The table shows their results.

What is the mitotic index?

A. 0.2

B. 0.4

C. 0.6

D. 0.7

Which living structure is an exception to the cell theory?

A. Striated muscle fibres

B. A single-celled alga carrying out all of the functions of life

C. The artificial synthesis of the organic molecule urea

D. A multicellular organism with cells undertaking specialized roles

Which feature of striated muscle cells allows them to be considered as a possible exception to the cell theory?

A. They are found in multicellular organisms.
B. They contain more than one nucleus.
C. They are specialized for movement.
D. They do not carry out mitosis.

Which processes are involved in the development of cancer?

I. Mutations occur in oncogenes.

II. Oncogenes prevent cancer.

III. Oncogenes affect cell cycle regulatory proteins.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Which characteristic of stem cells makes them useful for treating Stargardt’s disease?

A. They can differentiate into retinal cells.
B. They are readily available from especially created embryos.
C. They transport white blood cells to the eyes.
D. They divide by binary fission so provide sufficient cells.

The images of the radiolarian, a single-celled marine organism, were produced using a light microscope (left) and a scanning electron microscope (right).

[Source: Munir,S.;Sun,J.;Morton, S.L. The First Record and Classification of Planktonic Radiolarian
(Phylum Retaria) and Phaeodarian (Phylum Cercozoa) in the Eastern Indian Ocean. Biology 2021, 10, 202.
https://doi.org/10.3390/biology10030202 Copyright: © 2021 by the authors. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).]

What is a reason for the difference in quality of these images?

A. Light cannot pass through the specimen.

B. Higher magnification can be achieved with the electron microscope.

C. The resolution of the electron microscope is higher.

D. Samples are stained with methylene blue when viewed with the light microscope.

The graph shows the survival probabilities for current smokers and for those who never smoked among women 30 to 80 years of age.

What can be deduced from this graph?

A. There is a correlation between smoking and cancer.

B. Smoking reduces life expectancy.

C. Smoking causes cancer.

D. 70 % of smokers survive to 80 years old.

Which organelle is involved in generating vesicles destined for the cell membrane?

A. Golgi apparatus

B. Smooth endoplasmic reticulum

C. Rough endoplasmic reticulum

D. Lysosome

The micrograph of a section through a plant stem shows at least ten different types of cells.

[Source: Joan Carles Juarez / Shutterstock.com.]

What explains the differences between these cells?

A. Only one gene is expressed in each cell type.

B. Different genes are expressed in each cell type.

C. Only useful genes remain in the DNA of each cell type.

D. Changes in the DNA sequence take place when these cells develop.

The diagram represents the nucleus of a cell 2 n = 8 in late prophase of mitosis.

Which diagram represents a cell from the same species in anaphase II of meiosis?

Which graph represents the change in cell surface area to volume ratio with increasing cell diameter?

[Source: © International Baccalaureate Organization 2019]

The table shows the number of cells in various stages of the cell cycle in four samples of ovarian tissue from different patients. Which tissue sample A, B, C or D has the highest mitotic index?

The images are microscopic views of two similar cells.

What is a reason for the differences between the two micrographs?

A.  The lower image has a higher magnification.

B.  The lower image has greater resolution.

C.  A nucleus can only be seen in the upper image.

D.  The upper image is an electron micrograph.

A tissue sample was examined under the microscope in order to determine a mitotic index. The number of cells in each stage of the cell cycle was determined and the data were entered into a table.

What is the mitotic index?

A. 0.125

B. 0.25

C. 0.75

D. 1.00

The following electron micrograph shows part of a palisade mesophyll cell. Which of the labelled structures controls the exchange of substances to and from the cell?

What feature of both striated muscle and aseptate fungal hyphae is different from typical cell structure?

A. They have multiple nuclei within a structural unit.

B. They have a cell wall that is not made of cellulose.

C. They have plasmids.

D. They have an absence of cholesterol in the plasma membrane.

The image shows cells in the different stages of mitosis. Which cell is in telophase?

[Source: © The Trustees of Indiana University]

The image shows a micrograph of a cell.

[Source: © 2014, https://commons.wikimedia.org/wiki/File:Mitosis_(261_13)_Pressed;_root_meristem_of_onion_(cells_
in_prophase,_metaphase,_anaphase,_telophase).jpg by Doc. RNDr. Josef Reischig, CSc.]

What explains the appearance of the cell in the micrograph?

A. The cell is dying.

B. The DNA is replicating.

C. The cell is in metaphase.

D. The cell is in telophase.

When compared to other body cells, which characteristic of stem cells is the most important for therapeutic uses?

A. Less differentiation

B. Less excretion

C. Lower rate of reproduction

D. Lower rate of metabolism

The giant alga Acetabularia has a feature that suggests it is an exception to the cell theory. What feature is this?

A. It lacks a nucleus.

B. It lacks a cell wall.

C. It has only one mitochondrion.

D. It lacks subdivision into separate cells.

The images show a sequence of changes in an organism.

[Source: Copyright (2007) National Academy of Sciences, U.S.A. 'A comparative analysis of frog early development'.
Eugenia M. del Pino, Michael Venegas-Ferrín, Andrés Romero-Carvajal, Paola Montenegro-Larrea, Natalia
Sáenz-Ponce, Iván M. Moya, Ingrid Alarcón, Norihiro Sudou, Shinji Yamamoto, and Masanori Taira,
PNAS July 17, 2007 104 (29) 11882–11888; https://doi.org/10.1073/pnas.0705092104]

What is the change and which process is necessary for it to occur?

Cisplatin is an anti-cancer drug that prevents tumour cells from dividing by mitosis as it inhibits cell processes at stage S of interphase. How does cisplatin prevent cancer cells from dividing?

A. It inhibits the replication of DNA.

B. It inhibits the growth of the spindle fibres.

C. It prevents the breakdown of the nuclear membrane.

D. It prevents the condensation of chromosomes.

How many chromosomes are there in a cell during anaphase of mitosis, if the diploid number of the cell is 20?

A. 10

B. 20

C. 40

D. 80

What is the name of the cell component labelled Y?

A. Golgi apparatus

B. Nucleus

C. Cytoplasm

D. Vacuole

The electron micrograph shows part of a cell. Which organelle is the site of aerobic respiration?

A cell contains chloroplasts, plasma membrane and 80S ribosomes. What type of cell could it be?

A. Bryophyte

B. Lymphocyte

C. Prokaryote

D. Neuron

Which structures are found only in prokaryotic cells?

A. Ribosomes

B. Pili

C. Cell walls

D. Flagella

In the micrograph, which letter points to a cell in anaphase?

[Source: Berkshire Community College Bioscience Image Library,
https://commons.wikimedia.org/wiki/File:Mitotic_Stages_in_Apical_Meristem_of_Allium_Root_Tip_(36762516673).jpg,
licensed under Creative Commons CC0 1.0 Universal Public Domain Dedication]

Where could genes be located in a prokaryotic cell?

Which mitotic phase is labelled X in the micrograph of an onion (Allium cepa) root tip?

A. Prophase
B. Metaphase
C. Anaphase
D. Telophase

What occurs during meiosis but not mitosis?

A. Spindles are formed from microtubules.

B. Chromosome number is conserved.

C. Homologous chromosomes pair up.

D. Centromeres split.

What do chloroplasts and mitochondria have in common?

A. Both are found in the cells of Filicinophyta.

B. Both contain grana.

C. Both occur in all eukaryotic cells.

D. Both are found in a Paramecium.

When during the cell cycle does DNA replication take place?

In mammals, mature red blood cells are specialized in that they lack nuclei, mitochondria or ribosomes. Which statement applies to red blood cells?

A. No chemical reactions take place within their cytoplasm.

B. They cannot produce new enzymes.

C. Materials cannot enter red blood cells.

D. Materials cannot exit red blood cells.

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

The image shows an electron micrograph of a cell.

[Source: Junqueira’s Basic Histology, 15th edition, by Anthony L. Mescher, McGraw-Hill publisher.]

Which organelles correspond to the labels in the electron micrograph of this cell?

The magnification of the micrograph is 2000×.

[Source: https://upload.wikimedia.org/wikipedia/commons/6/6c/HeLa_cells_stained_with_Hoechst_33258.jpg
by TenOfAllTrades.]

What is the maximum diameter of the nucleus in the cell labelled X?

A. 10 μm

B. 10 nm

C. 20 μm

D. 20 nm