Immune Response and Cell Theory: An Overview, Essays (high school) of Biology

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1.1-1.3 [189 marks]

1. 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

Markscheme

B

[1 mark]

2. 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 Markscheme D
3. 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. Markscheme B
4. 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.

Markscheme A

[1 mark]

[1 mark]

[1 mark]

5. 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 Markscheme A
6. 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 Markscheme A

[1 mark]

[1 mark]

7. 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. Markscheme C
8. 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 Markscheme B

[1 mark]

[1 mark]

9. 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 Markscheme B 10a.

Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium

tuberculosis.

Outline the structures in M. tuberculosis that are not present in a

human cell. Markscheme a. cell wall ✔ b. pili/flagella ✔ c. 70S ribosomes ✔ d. nucleoid / circular DNA

OR

naked DNA ✔ e. plasmids ✔

As candidates do not need to know the structure of Mycobacterium

tuberculosis, all prokaryotic structures are accepted.

Ignore references to membrane bound organelles.

10b. Explain the production of antibodies when a patient is infected with the TB bacterium.

[1 mark]

[3 marks]

[7 marks]

Markscheme a. phagocytes/lymphocytes are white blood cells ✔ b. TB bacterium has a specific antigen ✔ c. this antigen is recognised by white blood cells ✔ d. a clone of lymphocytes/plasma cells/B cells are produced ✔ e. antibodies are produced by lymphocytes ✔ f. each lymphocyte produces just one type of antibody ✔ g. (this is) specific immunity ✔ h. (part of the) antibody/immunoglobulin binds to the antigen / specific antibody binds to the specific antigen ✔ i. antibodies are proteins/immunoglobulins ✔ j. (some) plasma cells become memory cells ✔ k. memory cells reproduce quickly ✔ l. memory cells prevent infection in the future ✔

Allow annotated diagrams to explain the process.

10c. Describe the risk to the human population of indiscriminate use of antibiotics. Markscheme a. antibiotics block bacterial processes ✔

b. example of bacterial process ✔ e.g. cell wall formation

c. variations exist naturally in a population / some are naturally resistant to the antibiotic ✔ d. bacteria that are not resistant to this antibiotic will die / only resistant will survive (when antibiotic given) ✔ e. this characteristic could be passed to next generation ✔ f. (natural selection) leads to changes in the proportions/frequency in the population ✔ g. human population will be exposed to antibiotic resistant bacteria and will not have antibiotic to kill them ✔ h. (antibiotic resistant bacteria) may pass resistance to other bacteria species/types by means of plasmids (so other bacteria species turn resistant too) ✔

[5 marks]

The electron micrograph shows a section through a cell. [Source: Photo © E. Newcomb. Nucleus, glyoxisomes, chloroplasts, and mitochondria - magnification at 13,900x - UWDC - UW-Madison Libraries (wisc.edu) (https://search.library.wisc.edu/digital/AE2SBIWRVTRR5T87).] What is the name of the cell component labelled Y? A. Golgi apparatus B. Nucleus C. Cytoplasm D. Vacuole Markscheme B

12. 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

[1 mark]

[1 mark]

Markscheme B 13a. Outline how the amphipathic properties of phospholipids play a role in membrane structure. Markscheme

a. part hydrophobic/not attracted to water/non-polar AND part

hydrophilic/attracted to water/polar; Both needed.

b. bilayer formed (formed naturally by phospholipids in water);

c. hydrophilic heads/parts face outwards AND hydrophobic tails/parts face

inwards;

Do not allow water loving/hating in mpa or mpc.

13b. The diagram shows part of two neurons. [Source: © International Baccalaureate Organization 2020.] State the name of the structure shown. Markscheme synapse/synaptic 13c. X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.

[2 marks]

[1 mark]

[3 marks]

Markscheme a. depolarization of pre-synaptic membrane / action potential/nerve impulse arrives; b. uptake of calcium / calcium ions diffuse in / calcium channels open; c. structures containing neurotransmitter/vesicles move to/fuse with membrane; d. neurotransmitter/acetylcholine released by exocytosis into cleft/binds to postsynaptic membrane/receptors; 14a. According to the cell theory, living organisms are composed of cells. Draw the ultrastructure of a prokaryotic cell based on electron micrographs. Markscheme a. cell wall;

b. plasma membrane; Clearly shown as a separate line under the cell wall or

the inner line

c. cytoplasm AND 70S ribosomes; Do not allow (small) circles

d. nucleoid/naked DNA; e. plasmid

OR

pili

OR

flagella/flagellum;

Structures correctly drawn and labelled.

Award [2 max] if any exclusively eukaryotic structures are shown.

Do not allow cilia as they are not found in prokaryotes.

14b. Outline what occurs in cells in the first division of meiosis.

[3 marks]

[5 marks]

Markscheme a. halves the chromosome number/produces haploid cells; b. at start of meiosis each chromosome consists of two sister chromatids attached by a centromere; c. prophase (I): pairing of homologous chromosomes; d. crossing over occurs; e. chromosomes condense by supercoiling; f. metaphase (I): pairs of homologous chromosomes/bivalents move to equator of spindle

OR

metaphase (I): orientation of pairs of homologous chromosomes (prior to separation) is random; g. anaphase (I): centromeres do not divide

OR

anaphase (I): spindle fibre pulls chromosome/whole centromere with two sister chromatids to opposite poles; h. telophase (I): arrival of centromere with sister chromatids at opposite poles;

Some of these can be awarded for correctly annotated diagrams.

No credit for events in meiosis II.

14c. Explain the role of cells in the defence against infectious disease. [7 marks]

Markscheme a. cells of skin provide a physical barrier/produce fatty acids/lactic acid/lysozyme which stops entry of microbes

OR

mucous membranes produce mucus to trap pathogens

OR

stomach cells produce hydrochloric acid which kills microbes; b. platelets start the clotting process preventing access of pathogens; c. (two types of) white blood cells fight infections in the body; d. phagocytes ingest pathogens (by endocytosis/phagocytosis); e. gives non-specific immunity to diseases / ingest any type of pathogen; f. production of antibodies by lymphocytes/B cells; g. in response to particular pathogens/antigens; h. gives specific immunity; i. lymphocyte/B cell makes only one type of antibody; j. plasma cells produce large quantity of (one type of) antibody; k. some lymphocytes act/remain as memory cells; l. can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered; m. results in faster defence against second exposure to specific antigen/pathogen/disease;

15. 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 Markscheme C 16a. Outline the cell theory. Markscheme a. cells can only arise from preexisting cells ✔ b. living organisms are composed of cells/smallest unit of life ✔ c. organisms consisting of only one cell carry out all functions of life in that cell/cells perform life functions «at some point in their existence» ✔ d. although most organisms conform to cell theory, there are exceptions ✔ 16b. State two functions of life.

[1 mark]

[2 marks]

[2 marks]

Markscheme a. nutrition ✔ b. metabolism/respiration ✔ c. growth ✔ d. response/irritability ✔ e. excretion ✔ f. homeostasis ✔ g. reproduction ✔

Do not allow “feeding”, plants do not “feed”.

Mark the first two answers only.

16c. List three characteristics of eukaryotic homologous chromosomes. Markscheme a. linear DNA molecules

OR

DNA associated with histone «proteins» ✔ b. carry the same sequence of genes ✔ c. «but» not necessarily the same alleles «of those genes» ✔ d. both are present when nucleus is in diploid state ✔

OR

occur in pairs ✔ e. have same size/length/banding patterns ✔ f. centromeres are in the same position ✔

[3 marks]

16d. Using the following table, compare and contrast anaerobic cell respiration in yeasts and in humans. The first row has been completed as an example. Markscheme

Award [1] per correct row.

17a. Draw a section of the Singer-Nicolson model of an animal cell membrane.

[3 marks]

[4 marks]

Markscheme a. bilayer of phospholipids with both “tails” towards the inside «of the bilayer»

✔ This can be taken unlabeled from diagram.

b. hydrophilic/polar and hydrophobic/non-polar annotation ✔ c. cholesterol between phospholipid tails ✔ d. glycoprotein ✔ e. integral proteins/channel proteins ✔

f. peripheral proteins ✔ Allow this if it does not extend across the membrane

Elements should be clearly drawn, correctly positioned and annotated.

17b. Outline the principles used by scientists to classify organisms. Markscheme a. use of the binomial system ✔

b. agreed/developed by scientists / OWTTE ✔

c. hierarchy of taxa used ✔ Names of the seven taxa not required.

d. three domains used/three domain names ✔ OWTTE

e. genome/DNA sequence similarities

OR

amino acid sequence of specific proteins ✔ f. species from a common ancestor are grouped together

OR

included in the same clade/branch in cladogram ✔

g. use evidence of evolutionary origin ✔ Allow example e.g. fossil record

comparison h. shared characteristics within a group

OR

similar embryonic development ✔ 17c. Explain the movement of energy and inorganic nutrients in an ecosystem.

[4 marks]

[7 marks]

Markscheme a. autotrophs/producers/plants obtain inorganic nutrients from the «abiotic» environment ✔ b. energy provided «mainly» by sunlight ✔ c. light energy converted «to chemical energy» through photosynthesis ✔ d. photosynthesis/producers/autotrophs convert inorganic carbon/carbon dioxide and water into carbon/organic compounds ✔ e. «these» carbon compounds/foods contain/are a source of «useable» energy «for life» ✔ f. carbon compounds/energy are transferred along food chains when eaten by

consumers/heterotrophs ✔ Allow OWTTE for mpf for passed up trophic levels.

g. respiration returns carbon «dioxide» to the environment ✔ h. respiration releases stored/chemical energy as ATP/heat ✔ i. energy/ATP is used to carry out life functions/synthesis/growth/movement ✔ j. energy is lost/not recycled ✔

k. nutrients are recycled / example of recycled nutrient e.g. carbon ✔

l. decomposers recycle minerals/inorganic nutrients ✔

18. Which graph represents the change in cell surface area to volume ratio with increasing cell diameter? [Source: © International Baccalaureate Organization 2019]

[1 mark]

Markscheme B

19. 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. Markscheme A

[1 mark]

20. 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? Markscheme B

21. Which structures are found only in prokaryotic cells? A. Ribosomes B. Pili C. Cell walls D. Flagella

[1 mark]

[1 mark]

Markscheme B

22. The magnification of the micrograph is 2000×. [Source: https://upload.wikimedia.org/wikipedia/commons/6/6c/HeLa_cells_stained_with_Hoechst_ 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 Markscheme A

[1 mark]

23a. Identify which electron micrograph shows a mitochondrion, providing one observation to support your choice. Markscheme «micrograph» C cristae/double membrane is visible/«folds of» membranes inside ✔

Must state observation

23b. Discuss the evidence for the theory that mitochondria may have evolved from free-living prokaryotes by endosymbiosis.

[1 mark]

[3 marks]

Markscheme a. «double» membrane may have formed when engulfed ✔ b. replicate by binary fission like free-living prokaryotes

OR

reproduce separate from «host» cell replication ✔

c. they have their own «circular» DNA AND reproduce on their own ✔

d. they have «70s» ribosomes AND can manufacture «their own» proteins ✔

e. have organelle«s» similar to free-living prokaryotes ✔ f. similar in size to free-living prokaryotes ✔ g. mitochondrial inner membranes manufacture ATP like bacterial membranes ✔ h. currently there is no free-living prokaryote like a mitochondrion ✔ 24a. Outline the stages in the production of mRNA by transcription. Markscheme a. DNA is unwound/strands are separated «by RNA polymerase» ✔ b. new nucleotides attached to template strand «by RNA polymerase» ✔ c. complementary base pairing/base pairing with an example

OR

adenine with thymine/uracil with adenine/cytosine with guanine/guanine with cytosine ✔ d. mRNA detaches from template ✔ e. DNA rewinds ✔ 24b. Describe the functions of proteins in cell membranes.

[4 marks]

[4 marks]

Markscheme a. facilitated diffusion by channel proteins ✔ b. active transport by protein pumps

OR

protein pumps eg sodium-potassium ✔

c. cell recognition by glycoproteins/protein receptors ✔ d. communication/receptors for hormones/signal molecules ✔ e. cell adhesion ✔ f. allow up to one additional mark for AHL material ✔

24c. Explain how natural selection can lead to speciation. [7 marks]

Markscheme a. natural selection is caused by selection pressures in the environment

OR

example of a selection pressure ✔ b. natural selection requires that variation exists within a species ✔ c. variation arises randomly due to mutation

OR

variation is enhanced by meiosis/sexual reproduction ✔ d. over-production of offspring promotes selection

OR

natural selection occurs when there is competition/overpopulation/predators/environmental changes/changes in selection pressures ✔ e. well adapted individuals/individuals with best variations survive to reproduce/survival of fittest ✔ f. «frequency of» genes/alleles conferring an advantage are selected for

OR

genes/alleles conferring a disadvantage are selected against ✔ g. genetic divergence/difference increases

OR

natural selection «genetically» isolates members of a species so eventually they can no longer produce fertile offspring ✔ h. genetic divergence» leads to reproductive isolation ✔ i. geographical/behavioural/ecological factors may lead to «reproductive» isolation ✔ j. prolonged «reproductive» isolation leads to speciation ✔ k. up to one additional mark for AHL information ✔

25a. Membrane structure can be investigated using a technique known as freeze fracture. Cells are frozen and then split. Fracturing often occurs between the two phospholipid layers of membranes in the cell. An electron micrograph of such a fractured membrane is shown. [Source: © Science Photo Library] Using the scale bar, calculate the magnification of the image. Markscheme = × 660 ✔ scale bar length image size 25b. Explain how electron micrographs such as this helped to falsify the Davson–Danielli model of membrane structure. Markscheme a. the Davson–Danielli model proposed two layers of protein on either side of a

lipid bilayer ✔ OWTTE

b. micrographs illustrate proteins in and/or crossing the membrane ✔ 25c. Explain how the amphipathic nature of phospholipids allows them to form bilayers.

[2 marks]

[2 marks]

[2 marks]

Markscheme a. amphipathic means that they are both hydrophilic and hydrophobic ✔ b. the outside hydrophilic parts are exposed to water ✔ c. hydrophobic parts are away from water in the inside ✔

Water or lack of needs to be mentioned for mpb

26a. Two models of plasma membrane structure are shown.

[Source: diagram from article published in The American Journal of Pathology, 65 ,

J Singer and G Nicolson, The structure and chemistry of mammalian cell membranes, 427–437, Copyright Elsevier (1971)] State the scientists who proposed model A. Markscheme Davson–Danielli ✔ 26b. Label the model A diagram to show a region of protein.

[1 mark]

[1 mark]