HL Paper 2
This image shows a normal red blood cell.
These images show two red blood cells that have been placed in solutions with different concentrations of solutes.
Outline the properties of water molecules that permit them to move upwards in plants.
Define osmolarity.
Deduce, with a reason, which red blood cell has been placed in a hypertonic solution.
State what change there has been in the cell surface area to volume ratio in red blood cell 1.
Draw a labelled diagram to show the fluid mosaic model of the plasma membrane.
Outline how neurons generate a resting potential.
Hydrogen bonds can exist both within and between molecules in living organisms and have an impact on their structure and function. Explain the importance of hydrogen bonding for living organisms.
The image shows human red blood cells.
[Source: someoneice/123rf.com.]
Outline what will happen to human red blood cells if transferred to distilled water.
Stem cells can be used to treat Stargardt’s disease. State one other condition treated using stem cells.
Explain the propagation of nerve impulses along the membrane of a neuron.
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.
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.
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.
Hypoxia is a condition in which tissues of the body are deprived of an adequate oxygen supply. A study was carried out in rats to examine the effects of continuing hypoxia on the structure of the diaphragm, and to determine whether nitric oxide is implicated in adaptation of the diaphragm to hypoxia. The diaphragm helps to supply oxygen to tissues and organs in the body by ventilating the lungs.
A group of 36 adult male rats were kept for 6 weeks in low oxygen while 36 adult male rats were kept in normal oxygen levels.
[Source: Reproduced with permission of the © ERS 2011. European Respiratory Journal June 2011, 37 (6) 1474–1481; DOI: 10.1183/09031936.00079810]
The graph shows the effect of hypoxia on the endurance of rats’ diaphragm muscle after 6 weeks. Endurance is the change in force measured as a percentage of the initial force.
[Source: Reproduced with permission of the © ERS 2011. European Respiratory Journal June 2011, 37 (6) 1474–1481; DOI: 10.1183/09031936.00079810]
The sodium–potassium pump plays a role in muscle activity. Nitric oxide may have a role in the recovery of hypoxic muscles. The production of nitric oxide can be blocked with an inhibitor of the enzyme nitric oxide synthase. The graph shows the concentration of sodium–potassium pumps in the diaphragm of control and hypoxic rats without and with nitric oxide synthase inhibitor.
[Source: Reproduced with permission of the © ERS 2011. European Respiratory Journal June 2011, 37 (6) 1474–1481; DOI: 10.1183/09031936.00079810]
Skeletal muscle contractions can take two different forms: if they are stimulated by a single action potential they take the form of a twitch and if they are stimulated by a series of action potentials the contraction is longer lasting (tetanic). The table shows the effects of hypoxia on the force of twitch and peak tetanic contraction in the diaphragm.
[Source: Reproduced with permission of the © ERS 2011. European Respiratory Journal June 2011, 37 (6) 1474–1481; DOI: 10.1183/09031936.00079810]
Outline the effect of hypoxia on body mass and erythrocyte percentage.
Using the data in the graph, deduce whether hypoxia increases or decreases the endurance of the rats’ diaphragm muscle.
Using the data presented in this question, explain the effect of hypoxia on the body.
Analyse the graph to obtain two conclusions about the concentration of sodium–potassium pumps.
Muscle fibres are stimulated to contract by the binding of acetylcholine to receptors in their membranes and the subsequent depolarization.
Suggest a reason for increasing the concentration of sodium–potassium pumps in the membranes of diaphragm muscle fibres.
Outline the effect of hypoxia on the force of contraction of the diaphragm.
Hypoxia caused a 13 % increase in the surface area to volume ratio of the diaphragm. Suggest a reason for this change.
Using all relevant data in the question, evaluate the effectiveness of the rats’ adaptation to hypoxia.
Discuss the advantages and disadvantages of using rats as models in this investigation.
Calcium is absorbed from food in the human gut by both active and passive processes. Outline active transport, including the benefits of the process.
Describe the role of oxygen in aerobic cell respiration.
Adult humans may absorb more than five hundred litres of oxygen per day. Explain how gas exchange is maintained in the human respiratory system.
During photosynthesis plants use water in the conversion of light energy to chemical energy.
State the property of amphipathic phospholipids that enables them to form a bilayer.
State the reason cis and trans fatty acids are said to be unsaturated.
State the name of this process.
Explain how water is used in photosynthesis.
The diagram shows part of two neurons.
[Source: © International Baccalaureate Organization 2020.]
Outline how the amphipathic properties of phospholipids play a role in membrane structure.
State the role of cholesterol in animal cell membranes.
Describe what happens to the membranes of an animal cell during mitosis.
State the name of the structure shown.
X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.
Oxygen is needed to complete aerobic cell respiration.
Explain how chemical energy for use in the cell is generated by electron transport and chemiosmosis.
Outline four different functions of membrane proteins.
Distinguish between anabolism, catabolism and metabolism.
Every cell is surrounded by a cell surface membrane which regulates the movement of materials into and out of the cell.
Discuss alternative models of membrane structure including evidence for or against each model.
Outline the process used to load organic compounds into phloem sieve tubes.
Outline reasons for the therapeutic use of stem cells.
Describe how monoclonal antibodies are produced.
Explain the role of the electron transport chain in the generation of ATP by cell respiration.
The image shows a cell in a section of an onion root tip seen under a light microscope.
Identify the structure labelled X.
State the stage of mitosis of this cell.
Compare and contrast the location of ATP synthase and the movement of protons during aerobic cell respiration and photosynthesis.
Using the table, distinguish between the production of ATP, use of oxygen and release of CO2 in aerobic cell respiration between the cytoplasm and the mitochondrion.
The graph shows energy levels throughout an uncatalysed reaction. Draw a curve to show how the action of an enzyme would affect this reaction.
Outline four types of membrane transport, including their use of energy.
Draw the structure of a dipeptide.
ADH (antidiuretic hormone) is a peptide hormone that is produced in the hypothalamus. Explain its action in the human body.
Outline the functions of rough endoplasmic reticulum and Golgi apparatus.
Outline the control of metabolism by end-product inhibition.
Explain how hydrophobic and hydrophilic properties contribute to the arrangement of molecules in a membrane.
The electron micrographs show a typical prokaryote and a mitochondrion.
Compare and contrast the structure of a typical prokaryotic cell with that of a mitochondrion.
Explain how mitochondria could have been formed from free living prokaryotes.
Outline the process of inspiration in humans.
Describe the functions of valves in the mammalian heart.
Explain how blood solute concentrations are kept within narrow limits in the human body.
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.
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.
Describe the trends shown by the graph for dissolved oxygen in water discharged from the mouth.
Suggest reasons for these trends in dissolved oxygen.
Deduce with a reason whether a urea transporter is present in the mouth of P. sinensis.
Outline the additional evidence provided by the gel electrophoresis results shown above.
Identify which of these turtle groups represent the control, giving a reason for your answer.
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.
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.
The mechanism of action of vinblastine, an anticancer drug, was investigated over a range of concentrations. Vinblastine is an alkaloid isolated from the periwinkle plant (Catharansus roseus). The percentage of cells in mitosis and ratio of anaphase to metaphase in cells exposed to this drug in vitro for a fixed time were recorded. The data are displayed in two graphs.
[Source: Republished with permission of American Society for Pharmacology and Experimental Therapeutics, from Mechanism of Mitotic Block and Inhibition of Cell Proliferation by the Semisynthetic Vinca Alkaloids Vinorelbine and Its Newer Derivative Vinflunine, Molecular Pharmacology, Vivian K. Ngan, Krista Bellman, Bridget T. Hill, Leslie Wilson and Mary Ann Jordan, Volume 60 , Issue 1, 2001; permission conveyed through Copyright Clearance Center, Inc.]
By referring to both graphs, evaluate the hypothesis that vinblastine targets cells in mitosis and prevents them from completing the process.
Some anticancer drugs inhibit mitosis by blocking the formation of the spindle. Suggest one other way in which vinblastine could block mitosis.
Discuss one advantage and one disadvantage of using plant tissue to investigate drugs intended to treat cancer in humans.
Advantage:
Disadvantage:
The onion (Allium cepa) root cells shown in the micrograph are in different stages of mitosis.
[Source: Reischig, J., 2014. Mitosis (261 13) [Pressed; root meristem of onion]. [image online] Available at https://commons.wikimedia.org/wiki/File:Mitosis_(261_13)_Pressed;_root_meristem_of_onion_(cells_in_prophase,_metaphase,_anaphase,_telophase).jpg This file is licensed under the Creative Commons Attribution -ShareAlike 3.0 Unported (CC BY-SA 3.0) https://creativecommons.org/licenses/by-sa/3.0/deed.en [Accessed 3 December 2019].]
_Pressed;_root_meristem_of_onion_(cells_in_prophase,_metaphase,_anaphase,_telophase).jpg){kind=link}
Identify, with a reason, the stage shown at X.
Calculate the length of the entire cell labelled Y, showing your working.
State the role of cyclins in the cell cycle.
Distinguish between the structure of chromosomes in prokaryotes and eukaryotes.
Explain Cairns’s technique to measure the length of the DNA molecule.
DNA methylation has a critical role in gene regulation by affecting transcription. Samples were taken from two colon cancer tumours (T1 and T2) and two normal colon samples (N1 and N2). A particular gene was implicated as a possible cause of cancer. The promoter of this gene was cloned (A–J). The data show the DNA methylation patterns from these samples. The numbers (32–269) represent different markers in the promoter.
[Source: Philipp Schatz, Dimo Dietrich & Matthias Schuster. Rapid analysis of CpG methylation patterns using RNase T1
cleavage and MALDI-TOF. Nucleic Acids Research (2004) 32 (21): e167, doi:10.1093/nar/gnh165.
Reproduced by permission of Oxford University Press]
Identify the stage of mitosis labelled X in the image, giving a reason.
[Source: Copyright 2002, The Trustees of Indiana University]
Outline what is indicated by the mitotic index of tissue taken from a tumour.
DNA has regions that do not code for proteins. State two functions of these regions.
1.
2.
Outline the difference in methylation pattern between tumorous and normal tissue samples.
Suggest a way methylation may affect tumour cell genes.
Outline four different processes, with examples, that allow substances to pass through the plasma membrane.
Humans need to balance water and solute concentrations and also excrete nitrogenous wastes. Explain how the different parts of the kidney carry out these processes.
Describe adaptations in mammals living in desert ecosystems to maintain osmolarity in their bodies.
Cells go through a repeating cycle of events in growth regions such as plant root tips and animal embryos. Outline this cell cycle.
Draw a labelled diagram of the formation of a chiasma by crossing over.
Explain the control of gene expression in eukaryotes.
The image is an electron micrograph of the lining of the small intestine.
(i) Label the microvilli using the letter M and a nucleus using the letter N.
(ii) State the function of the goblet cell.
(iii) Deduce, with a reason, whether or not the goblet cell is likely to divide.
Explain how the cell cycle is controlled.
This light micrograph shows skeletal muscle.
[Source: adapted from https://en.wikipedia.org/wiki/Skeletal_muscle#/media/File:Skeletal_
muscle_%E6%A8%AA%E7%BA%B9%E8%82%8C1.JPG, Urana/ 乌拉跨氪]
Identify the dark structure indicated by I.
Identify the protein producing the thick filament in the dark band indicated by II.
Identify the structure indicated by III.
Discuss whether the tissue shown in the micrograph consists of cells or not.
Explain how calcium is involved in muscle contraction.
The electron micrograph shows part of a cell including a mitochondrion.
[Source: Used with permission of McGraw-Hill Education, from Harrison’s Principles of Internal Medicine,
J L Jameson et al., 16th edition, 2004; permission conveyed through Copyright Clearance Center, Inc.]
Outline how the structures labelled X and Y are adapted to carry out the function of the mitochondrion.
X:
Y:
Explain how ATP is generated in mitochondria by chemiosmosis.
The image shows part of a plant cell with a chloroplast in close proximity to mitochondria.
[Source: Photo © E. Newcomb.]
State two structural similarities between mitochondria and chloroplasts.
1.
2.
Compare and contrast mitochondria and chloroplasts in terms of the substrates they use and the products they produce.
Outline how the compounds produced by chloroplasts are distributed throughout the plant.
Autosomal genes are located in chromosomes that are not sex chromosomes. The inheritance of autosomal genes is affected by whether the genes are linked or unlinked. Explain the two types of inheritance, using the example of parents that are heterozygous for two genes A and B.
Outline how sperm are produced from diploid cells in the testis and how this production can be sustained over many decades of adult life.
Testis cells are eukaryotic cells. Identify the structures seen under the electron microscope in testis cells that are not present in prokaryotic cells.