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2023-25 Biology > 2: Studying Cells > Flashcards

2: Studying Cells Flashcards

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1
Q

Describe the structure and function of the nucleus. [6]

A

Structure
1. Nuclear envelope and pores OR Double membrane and pores;
2. Chromosomes/chromatin OR DNA with histones;
3. Nucleolus/nucleoli;

Function
4. (Holds/stores) genetic information/material for polypeptides (production) OR (Is) code for polypeptides;
5. DNA replication (occurs);
6. Production of mRNA/tRNA OR Transcription (occurs);
7. Production of rRNA/ribosomes;

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2
Q

Explain why viruses are described as acellular and non-living. [2]

A
  1. no cell(-surface) membrane OR Not made of cells;
  2. (Non-living) have no metabolism/metabolic
    reactions;
    OR
    Cannot (independently) move / respire / replicate / excrete
    OR
    (Have) no nutrition;

MRSGREN

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3
Q

Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. [5]

A
  1. DNA in nucleus is code (for protein);
  2. Ribosomes/rough endoplasmic reticulum produce (protein);
  3. Mitochondria produce ATP (for protein synthesis);
    4 Golgi apparatus package/modify; OR Carbohydrate added/glycoprotein produced by Golgi apparatus;
    5 Vesicles transport OR Rough endoplasmic reticulum transports;
  4. (Vesicles) fuse with cell(-surface) membrane;
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4
Q

Compare & contrast Eukaryotic and Prokaryotic DNA [5]

A

Comparisons
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bond;
OR Deoxyribose joined to phosphate (in sugar, phosphate backbone);
8. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

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5
Q

State three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

A

Plant v prokaryote
1. (Associated with) histones/proteins v no histones/proteins;
2. Linear v circular;
3. No plasmids v plasmids;
4. Introns v no introns;
5. Long(er) v short(er);

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6
Q

The structure of a cholera bacterium is different from the structure of an epithelial cell from the small intestine. Describe how the structure of a cholera bacterium is different

A
  1. Cholera bacterium is prokaryote;
  2. Does not have a nucleus/nuclear envelope/ has DNA free in cytoplasm/has loop of DNA;

3 and 4 Any two from: [No membrane-bound organelles/no mitochondria / no golgi/no endoplasmic reticulum];
5 Small ribosomes only;
6 and 7 Any two from [Capsule/flagellum/plasmid / cell wall]

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7
Q

Name two structures found in all bacteria that are not found in plant cells.

A
  1. Circular DNA (molecule in cytoplasm);
  2. Murein cell wall OR Peptidoglycan cell wall OR Glycoprotein cell wall;
  3. Small(er)/70S ribosomes (in cytoplasm);
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8
Q

Give one advantage of using a TEM rather than a SEM.

A
  1. Higher resolution;
  2. higher (maximum) magnification / higher detail (of image);
    OR
  3. Allows internal details / structures within (cells) to be seen / cross section to be taken;
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9
Q

The resolution of an image obtained using an electron microscope is higher than the resolution of an image obtained using an optical microscope. Explain why.

A

Shorter wavelength between electrons

OR

Longer wavelength in light (rays);

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10
Q

Give one advantage of using a SEM rather than a TEM.

A

Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;

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11
Q

Scientists use optical microscopes and transmission electron microscopes to investigate cell structure. Explain the advantages and limitations of using a TEM to investigate cell structure. [6]

A

Advantages:
1 Small objects can be seen;
2 TEM has high resolution;
3 Electron wavelength is shorter;

Limitations:
4 Cannot look at living cells;
5 Must be in a vacuum;
6 Must cut section / thin specimen;
7 Preparation may create artefact;

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12
Q

Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold, buffered isotonic solution. Explain why the solution was:
a) Isotonic
b) Ice cold
c) buffered

A

a) ISOTONIC: Prevents osmosis / no (net) movement of water So organelle/named organelle does not burst/shrivel;
b) ICE COLD: Reduce/prevent enzyme activity so organelles are not digested / damaged;
c) BUFFERED: Maintain a constant pH so proteins do not denature;

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13
Q

Describe and explain how cell fractionation and centrifugation can be used to isolate mitochondria from a suspension of animal cells. [6]

A
  1. Cell homogenisation to break open cells and release organelles;
  2. Filter to remove (large) debris/whole cells;
  3. Use isotonic solution to prevent osmotic damage to mitochondria / organelles;
  4. Keep cold to prevent/reduce damage to organelles by enzyme;
  5. Use buffer to maintain pH and prevent protein/enzyme denaturation;
  6. Use differential Centrifuge (at high speed/1000 g) to separate nuclei / cell fragments / heavy organelles;
  7. Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom;
  8. Observe pellet with a microscope to identify mitochondria;
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14
Q

Describe the features of Prophase

A

Nuclear membrane begins to breakdown;
Centrioles move to poles of the cell;
Chromatin supercoils and condense in chromosomes;

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15
Q

Describe the features of Metaphase

A

Spidle fibres form;
Spindle fibres attach;
To the centromere of chromosomes;
Chromosomes align at the equator;

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16
Q

Describe the features of Anaphase

A

Spindle fibres shorten;
Centromere splits;
Sister chromatids are separated;
Chromatids pulled to opposite poles of the cell;

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17
Q

Describe the features of Telophase

A

Nuclear membrane begins to reform;
Chromosomes unwind;

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18
Q

What is a homologous pair of chromosomes?

A

Two chromosomes that carry the same genes in the same loci / location

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19
Q

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.

A

Description; Explanation;
E.g, 1. Examine large number of fields of view / many cells;
2. To ensure representative sample;

OR
3. Repeat count;
4. To ensure figures are correct;

OR

  1. Method to deal with part cells shown at edge /count only whole cells;
  2. To standardise counting;
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20
Q

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how.

A
  1. Homologous chromosomes pair up;
  2. maternal and paternal chromosomes are arranged in any order;
  3. Independent segregation;
  4. Crossing over;
  5. (Equal) Portions of chromatids are swapped between chromosomes;
  6. Produces new combination of alleles;
  7. Chromatids separated at meiosis II/ later;
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21
Q

Describe the process of crossing over and explain how it increases genetic diversity

A
  1. Homologous pairs of chromosomes associate / form a bivalent;
  2. Chiasma(ta) form;
  3. (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
  4. Producing new combinations of alleles;
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22
Q

Give two differences between mitosis and meiosis.

A

Mitosis given first
1. One division, two divisions in meiosis;
2. (Daughter) cells genetically identical, daughter cells genetically different in meiosis;
3. Two cells produced, (usually) four cells produced in meiosis;
4. Diploid to diploid / haploid to haploid, diploid to haploid in meiosis;
5. Separation of homologous chromosomes only in meiosis;
6. Crossing over only in meiosis;
7. Independent segregation only in meiosis;

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23
Q

Describe how the process of meiosis results in haploid cells. Do not include descriptions of how genetic variation is produced in meiosis.

A
  1. DNA replication (during late interphase);
  2. Two divisions;
  3. Separation of homologous chromosomes (in first division); 4. Separation of (sister) chromatids (in second division);
  4. Produces 4 (haploid) cells/nuclei;
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24
Q

Describe binary fission in bacteria.

A
  1. Replication of (circular) DNA;
  2. Replication of plasmids;
  3. Division of cytoplasm (to produce daughter cells);
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25
Q

What is a tumour? [2]

A
  1. Mass of cells/tissue OR Abnormal cells/tissue;
  2. Uncontrolled mitosis/cell division;
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26
Q

Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane (3 marks).

A
  1. Glycerol joined to two fatty acid tails Phosphate group joined to glycerol on opposite side. (joined by condensation reaction with ester bond).;
  2. Phospholipid has hydrophilic head (phosphate and glycerol) and hydrophobic tails (fatty acid chains)
  3. Arrange to form a phospholipid bilayer; (Hydrophilic head facing out. Hydrophobic fatty acid chains facing in)
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27
Q

Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)

A

This is called PHAGOCYTOSIS

  1. Pathogen is engulfed by the phagocyte.
  2. Engulfed pathogen enters the cytoplasm of
    the phagocyte in a vesicle;
  3. Lysosomes fuse with vesicle releasing
    digestive enzymes;
  4. Lysosome enzymes break down the pathogen.
  5. Waste materials are ejected from the cell by exocytosis;
28
Q

Describe how a phagocyte destroys a pathogen present in the blood. [3]

A
  1. Engulfs;
  2. Forming vesicle/phagosome and fuses with lysosome;
  3. Hydrolytic enzymes digest/hydrolyse;
29
Q

Give two types of cell, other than pathogens, that can stimulate an immune response.

A
  1. (Cells from) other organisms/transplants;
  2. Abnormal/cancer/tumour (cells);
  3. (Cells) infected by virus;
  4. Pathogen (Bacterium / Fungus / Protist)

REJECT VIRUS (Acellular)

30
Q

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how [6]

A
  1. Vaccine contains antigen from pathogen;
  2. Macrophage presents antigen on its surface;
  3. T (helper) cell with complementary receptor protein binds to antigen;
  4. T cell stimulates B cell;
  5. (With) complementary antibody on its surface;
  6. B cell divides to form clone secreting / producing same antibody;
  7. B cell / Plasma cell rapidly secretes large numbers of antibody;
31
Q

Explain how the humoral response leads to immunity. [3]

A
  1. B cells specific to the antigen reproduce by mitosis.
  2. B cells produce plasma and memory cells
  3. Second infection produces antibodies in larger quantities AND more rapidly.
32
Q

Describe and explain the role of antibodies in stimulating phagocytosis.

A
  • OPSINISATION: Bind to antigen OR Are markers;
  • AGGLUTINATION: (Antibodies) cause clumping/agglutination OR Attract phagocytes;
33
Q

Describe the difference between active and passive immunity. [5]

A
  1. Active involves memory cells, passive does not;
  2. Active involves production of antibody by plasma cells/memory cells;
  3. Passive involves antibody introduced into body from outside/named source;
  4. Active long term, because antibody produced in response to antigen;
  5. Passive short term, because antibody (given) is broken down;
  6. Active (can) take time to develop/work, passive fast acting;
34
Q

State why some antibodies are referred to as monoclonal

A

(Antibodies) produced from a single clone of B cells / plasma cells;
OR

(Antibodies) produced from the same B cell / plasma cell;

35
Q

Different antibodies from the same organism bind to different antigens. Explain why

A
  • Variable region of each polypeptide has a different tertiary structure.
  • Variable region provides (highly) specific antigen binding site with specific shape.
  • Antigen binding site is only complementary to a specific antigen to form antigen antibody complex.
36
Q

What is the role of the disulfide bridge in forming the quaternary structure of an antibody?

A

Joins two (different) polypeptides;

37
Q

Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why. [3]

A
  • Specific) primary structure / order of amino acids;
  • (Specific) tertiary / 3D structure / shape;
  • (So) Only binds to / fits / complementary to one antigen;
38
Q

Describe the structure of the human immunodeficiency virus (HIV). [5]

A
  1. RNA (as genetic material);
  2. Reverse transcriptase;
  3. (Protein) capsomeres/capsid;
  4. (Phospho)lipid (viral) envelope OR Envelope made of membrane;
  5. Attachment proteins;
39
Q

Explain how HIV affects the production of antibodies when AIDS develops in a person. [3]

A
  1. Less/no antibody produced;
  2. (Because HIV) destroys helper T cells; Accept ‘reduces number’ for ‘destroys’
  3. (So) few/no B cells activated / stimulated OR (So) few/no B cells undergo mitosis/differentiate/form plasma cells;
40
Q

Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). [4]

A
  1. RNA converted into DNA using reverse transcriptase;
  2. DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
  3. DNA transcribed into (HIV m)RNA;
  4. (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);
41
Q

Name two features of HIV particles that are not found in bacteria. Do not include attachment protein in your answer. [2]

A
  1. Capsid;
  2. Reverse transcriptase;
  3. RNA genome;
  4. (viral lipid) Envelope;
42
Q

Describe how a person infected with HIV will develop AIDS (if untreated) and die of secondary infections. [4]

A
  • High viral load leads to increased destruction of helper T/CD4 cells;
  • Less activation of B cells/cytotoxic T cells/phagocytes;
  • Less production of plasma cells/antibodies OR (With cytotoxic T cells) less able to kill virus infected cells;
  • (Less able to) destroy other microbes/pathogens OR (Less able to) destroy mutated/cancer cells;
43
Q

Describe the role of antibodies in producing a positive result in an ELISA test. [4]

A
  1. (First) antibody binds/attaches /complementary (in shape) to antigen;
  2. (Second) antibody with enzyme attached is added;
  3. (Second) antibody attaches to antigen;
  4. (Substrate/solution added) and colour changes;
44
Q

Which immune cell destroys (self) cells infected with a virus?

A

Tc Cell
(Cytotoxic Killer T cell)

45
Q

Which immune cell destroys bacteria?

A

Phagocyte
(e.g., Macrophage)

46
Q

Name a virus that infects bacteria.

A

Bacteriophage

47
Q

When is a person / cell / organism infected by a virus such as HIV?

A

The moment the viral DNA is inserted into the host cells genome.

48
Q

What is an antigen?

A

A molecule (usually a protein) that stimulates an immune response that results in the production of a specific antibody. (Antibody generator)

Common antigens: Glycoproteins & Glycolipids

49
Q

State 3 roles of a T helper cell

A

1) Specific TH cell binds to the antigen presenting cell

2) Release cytokines that attract phagocytes to the area of infection.

3) Release cytokines that activate Cytotoxic Killer T cell (TC).

4) Activates a specifically complementary B cell.

5) Form memory TH cells

50
Q

What are the ethical considerations asociated with vaccines and monoclonal antibodies?

A

Animal & Human testing for production, efficacy and safety.
Animal rights.
Risk : Benefit ratio (if few people have severe side effects but the majority of the population have mild or no symptoms, is this justifiable?)
Vaccine availability: Free for all or who pays for those who can’t afford the preventative treatment.

51
Q

What is Herd immunity?

Only applicable to contagious pathogens.

A

When the majority of a population is vaccinated / immune to a contagious pathogen;
Those not yet vaccinated (Infants / eldery / immuno-suprressed/deficient) will have protection as the pathogen will spread less rapidly.

Herd Immunity Threshold is (usually) between 85-95% depending on the named pathogen.

Herd immunity applies a selection pressure to the named pathogen.

52
Q

What threatens Herd immunity?

A
  • Low vaccine uptake
  • Vaccine hesitancy / choce not to vaccinate
  • Mutation of pathogen
  • Vaccine does not produce long term immunity
  • Vaccinated population does not mix randomly
53
Q

Explain why a cell membrane may be described as a fluid-mosaic? [2]

A
  • The position of the molecules within the membrane is fluid – they are able to move around within the membrane.
  • Membrane is made up from a variety of different (Proteins) molecules arranged into a mosaic.
54
Q

Explain the arrangement of phospholipids in a cell-surface membrane. [2]

A
  • Bilayer OR Water is present inside and outside a cell;
  • Hydrophobic (fatty acid) tails point away/are repelled from water OR Hydrophilic (phosphate) heads point to/are in/are attracted to water;
55
Q

Describe how an ester bond is formed in a phospholipid molecule. [2]

A
  1. Condensation (reaction) OR Loss of water;
  2. Between of glycerol and fatty acid;
56
Q

Many different substances enter and leave a cell by crossing its cell surface membrane.

Describe how substances can cross a cell surface membrane. [6]

A

1 (Simple / facilitated) diffusion from high to low concentration / down concentration gradient;
2 Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer;
OR
Large / polar / water-soluble molecules go through proteins;
3 Water moves by osmosis / from high water potential to low water potential / from less to more negative water potential;
4 Active transport is movement from low to high concentration / against concentration gradient;
5 Active transport / facilitated diffusion involves proteins / carriers;
6 Active transport requires energy / ATP;
7 Ref. to Na+ / glucose co-transport;

57
Q

The movement of substances across cell membranes is affected by membrane structure.

Describe how. [6]

A
  • Phospholipid (bilayer) allows movement/diffusion of non-polar/lipid-soluble substances;
  • Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances OR (Membrane) proteins allow polar/charged substances to cross the membrane/bilayer;
  • Carrier proteins allow active transport;
  • Channel/carrier proteins allow facilitated diffusion/co-transport;
  • Shape/charge of channel / carrier determines which substances move;
  • Number of channels/carriers determines how much movement;
  • Membrane surface area determines how much diffusion/movement;
  • Cholesterol affects fluidity/rigidity/permeability;
58
Q

Name and describe five ways substances can move across the cell-surface membrane into a cell.

A
  1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
  2. Facilitated diffusion down a concentration gradient via protein carrier/channel;
  3. Osmosis of water down a water potential gradient;
  4. Active transport against a concentration gradient via protein carrier using ATP;
  5. Co-transport of 2 different substances using a carrier protein;
59
Q

Compare and contrast the processes by which water and inorganic ions enter cells. [3]

A
  1. Comparison: both move down concentration gradient;
  2. Comparison: both move through (protein) channels in membrane;
    Accept aquaporins (for water) and ion channels
  3. Contrast: ions can move against a concentration gradient by active transport
60
Q

Give two similarities in the movement of substances by diffusion and by osmosis.

A
  1. (Movement) down a gradient / from high concentration to low concentration;
  2. Passive / not active processes; OR Do not use energy from respiration / from ATP / from metabolism; OR Use energy from the solution;
61
Q

Describe how substances move across cell-surface membranes by facilitated diffusion. [3]

A
  1. Carrier / channel protein;
  2. (Protein) specific / complementary to substance;
  3. Substance moves down concentration gradient;
62
Q

Describe how you would use a 1.0 mol dm−3 solution of sucrose to produce 30 cm3 of a 0.15 mol dm−3 solution of sucrose. [2]

A
  • Add 4.5 cm3 of (1.0 mol dm–3) solution to 25.5 cm3 (distilled) water.
  • Mix
63
Q

Explain the decrease in mass of potato tissue in the 0.40 mol dm−3 solution of sucrose. [2]

A
  1. Water potential of solution is less than / more negative than that of potato tissue; (Ψ as equivalent to water potential)
  2. Tissue loses water by osmosis.
64
Q

Describe how you would use the student’s results (dilution series and % change in mass) to find the water potential of the potato tissue. [3]

A
  1. Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;
  2. Find concentration where curve crosses the x-axis / where percentage change is zero;
  3. Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis).
65
Q
A

2023-25 Biology (9 decks)

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