2: Studying cells Flashcards
1
Q
What is the function of a ribosome?
A
Site of Protein synthesis;
2
Q
What is the function of the Nucleus?
A
Contains genetic material / DNA;
Controls cell activity;
3
Q
Describe the structure and function of the nucleus. [5]
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;
4
Q
What is the function of the nucleolus?
A
- Synthesise nucleotides
- Synthesise cytoplasmic ribosomes (80s)
5
Q
What is the function of a mitochondrion?
A
Site of aerobic respiration;
ATP production;
Site of Link/Krebs/ETC
6
Q
What is the function of the Smooth Endoplasmic Reticulum?
A
Site of lipid synthesis;
7
Q
What is the function of the Rough Endoplasmic reticulum?
A
Encrusted in Ribosomes;
Site of protein synthesis;
Transports and stores protein within the cell
8
Q
What is the function of Golgi Apparatus? [2]
A
Modifies/packages/sorts proteins;
Produces vesicles;
9
Q
What is the function of Lysosomes?
A
Contains hydrolytic enzymes;
Digests worn out organelles/autolysis;
10
Q
What is the function of Cell surface membrane?
A
Made of a Phospholipid Bilayer;
Controls what enters the cell/ is selectively permeable;
Can be folded to increase SA;
11
Q
What is the function of Chloroplasts?
A
Contain thylakoids, stacked into Granum;
Site of photosynthesis;
12
Q
What is the function of a Capsule?
A
Protects cell from immune systems;
Aids bacteria sticking together;
13
Q
What is the function of Plasmid?
A
Circular DNA;
Contains antibiotic resistance genes;
Contains fewer genes that are contantly transcribed;
14
Q
What is the function of Cell Wall?
A
Provides rigid shape / structure;
Stops osmotic lysis;
15
Q
What is the function of Flagellum?
A
Allows movement/propulsion;
16
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
- DNA in nucleus is code (for protein);
- Ribosomes/rough endoplasmic reticulum produce (protein);
- 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; - (Vesicles) fuse with cell(-surface) membrane;
17
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);
3. 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;
18
Q
State three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell. [3]
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);
19
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. [6]
A
- Cholera bacterium is prokaryote;
- 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 / 70s ribosomes only;
6 and 7 Any two from [Capsule/flagellum/plasmid / cell wall]
20
Q
Name two structures found in all bacteria that are not found in plant cells. [2]
A
- Circular DNA (molecule in cytoplasm);
- Murein cell wall OR Peptidoglycan cell wall OR Glycoprotein cell wall;
- Small(er)/70S ribosomes (in cytoplasm);
21
Q
Give one advantage of using a TEM rather than a SEM.
A
- Higher resolution;
- Allows internal details / structures within (cells) to be seen / cross section to be taken;
22
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
Electrons have a shorter wavelength
OR
Longer wavelength in light (rays);
23
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
- 3-D images;
24
Q
Explain the advantages and limitations of using a TEM to investigate cell structure.
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;
25
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) Prevents osmosis / no (net) movement of water **So** organelle/named organelle does not burst/shrivel;
b) Reduce/prevent enzyme activity **so** organelles are not digested / damaged;
c) Maintain a constant pH **so** proteins do not denature;
26
Describe and explain how cell fractionation and centrifugation can be used to isolate mitochondria from a suspension of animal cells. [6]
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;
6. Re-spin (supernatant / after nuclei/pellet removed) at **higher speed** to get mitochondria in pellet/at bottom;
7. Observe pellet with a microscope to identify mitochondria;
27
Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane (3 marks).
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)
28
Explain why a cell membrane may be described as a fluid-mosaic? [2]
* 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 **protein molecules** arranged into a mosaic.
29
Explain the arrangement of phospholipids in a cell-surface membrane.
* Bilayer OR Water is present inside and outside a cell;
* Hydrophobic (fatty acid) tails point away/are repelled from water AND Hydrophilic (phosphate) heads point to/are in/are attracted to water;
30
Describe how an ester bond is formed in a phospholipid molecule. [2]
1. Condensation (reaction) OR Loss of water;
2. Between of glycerol and fatty acid;
31
Many different substances enter and leave a cell by crossing its cell surface membrane.
Describe how substances can cross a cell surface membrane. [6]
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;
32
The movement of substances across cell membranes is affected by membrane structure.
Describe how. [6]
* 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;
33
Name and describe five ways substances can move across the cell-surface membrane into a cell. [5]
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;
34
Compare and contrast the processes by which water and inorganic ions enter cells. [3]
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
35
Give two similarities in the movement of substances by diffusion and by osmosis [2]
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;
36
Describe how substances move across cell-surface membranes by facilitated diffusion. [3]
1. Carrier / channel protein;
2. (Protein) specific / complementary to substance;
3. Substance moves **down** concentration gradient;
37
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.
* Add 4.5 cm3 of (1.0 mol dm–3) solution to 25.5 cm3 (distilled) water.
* Mix
## Footnote
M1V1= M2V2
38
Explain the decrease in mass of potato tissue in the 0.40 mol dm−3 solution of sucrose. [2]
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.
39
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]
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).
40
Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)
The process is called phagocytosis – No Mark
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;
41
State two ways that pathogens cause disease.
* Produce / secrete / release **toxins**
* **Damage/destroy** cells / tissues / organs
42
Describe how a phagocyte destroys a pathogen present in the blood. [3]
1. Engulfs;
2. Forming vesicle/phagosome and fuses with lysosome;
3. Hydrolytic Enzymes digest/hydrolyse;
43
Give two types of cell, other than pathogens, that can stimulate an immune response.
1. (Cells from) other organisms/transplants;
2. Abnormal/cancer/tumour (cells);
3. (Cells) infected by virus;
44
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how. [6]
1. Vaccine contains (specific) antigen from pathogen;
2. Macrophage presents antigen on its surface;
3. T (helper) cell with complementary receptor protein binds to antigen & becomes activated;
4. T cell stimulates B cell by complementary receptor binding and releases cytokines;
5. (With) complementary antibody on its surface;
6. B cell divides to form clone secreting / producing same antibody;
7. B cell secretes large amounts of (monoclonal) antibody;
45
Explain how the humoral response leads to immunity. [3]
1. B cells specific to the antigen reproduce by **mitosis**.
2. B cells produce / differentiate into plasma and memory cells
3. Second infection produces antibodies in larger quantities AND quicker. (More rapid & More extensive)
46
Describe and explain the role of antibodies in stimulating phagocytosis. [2]
* Bind to antigen OR Are markers (opsinisation);
* (Antibodies) cause agglutination (clumping) OR Attract phagocytes;
47
Describe the difference between active and passive immunity. [5]
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;
48
State why some antibodies are referred to as monoclonal.
(Antibodies) produced from a single **clone of B cells** / **plasma cells**;
OR
(Antibodies) produced from the same B cell / plasma cell;
49
What is the role of the disulfide bridge in forming the quaternary structure of an antibody?
Joins two (different) polypeptides;
50
Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why. [3]
* Specific) primary structure / order of amino acids;
* (Specific) **tertiary structure** / shape;
* (So) Only binds to / fits / complementary to one antigen;
51
Describe the structure of the human immunodeficiency virus (HIV). [5]
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;
52
Explain how HIV affects the production of antibodies when AIDS develops in a person. [3]
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;
53
Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). [4]
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);
54
Name two features of HIV particles that are not found in bacteria. Do not include attachment protein in your answer.
1. Capsid;
2. Reverse transcriptase;
3. RNA genome;
4. Envelope
55
# AO2 (More or Less)
Describe how a person infected with HIV will develop AIDS (if untreated) and die of secondary infections. [4]
* 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;
56
Describe the role of antibodies in producing a positive result in an ELISA test. [4]
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;
57
Describe the features of Prophase
Nuclear membrane begins to breakdown;
Centrioles move to poles of the cell;
Chromatin supercoils and condense into chromosomes;
Chromosomes appear as 2 sister chromatids joined by a centromere;
58
Describe the features of Metaphase
Spidle fibres form;
**Spindle** fibres attach;
To the **centromere** of (each) chromosomes;
Chromosomes align at the **equator**;
59
Describe the features of Anaphase
Spindle fibres shorten;
**Centromere** splits;
Sister chromatids are **separated**;
**Chromatids pulled to opposite poles** of the cell;
60
Describe the features of Telophase
Nuclear membrane begins to reform;
Chromosomes unwind;
(2 distinct nuclei within one cell)
61
What is a homologous pair of chromosomes?
Two chromosomes that carry the **same genes** in the **same** loci / **location**
62
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. [2]
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
5. Method to deal with part cells shown at edge /count only whole cells;
6. To standardise counting;
63
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. [5]
1. Homologous chromosomes pair up; or form a Bivalent
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;
64
Describe the process of crossing over and explain how it increases genetic diversity [4]
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;
65
Give two differences between mitosis and meiosis. [2]
**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;
66
When, during meiosis, do cells become haploid?
Meiosis 1
67
When, during meiosis, does crossing over and independent segregation occur?
Meiosis 1
68
When, during meiosis, do homologues become separated?
Meiosis 1
69
When, during meiosis, do chromatids become separated to opposite poles?
Meiosis 2
70
Describe how the process of meiosis results in haploid cells. Do not include descriptions of how genetic variation is produced in meiosis. [5]
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);
5. Produces 4 (haploid) cells/nuclei;
71
Describe binary fission in bacteria. [3]
1. Replication of (circular) DNA;
2. Replication of plasmids;
3. Division of cytoplasm (to produce daughter cells);
72
What is a tumour?
1. Mass of cells/tissue OR Abnormal cells/tissue;
2. Uncontrolled mitosis/cell division;
73
Describe how you would determine a reliable mitotic index (MI) from tissue observed with an optical microscope.
Do not include details of how you would prepare the tissue observed with an optical microscope. [3]
1. Count cells in mitosis in field of view;
2. Divide this by total number of cells in field of view;
3. Repeat many/at least 5 times
OR
Select (fields of view) at random;
74
Mitotic index formula
Number of cells with visible chromosomes (PMAT)(Divided by)
______________________________________________________
Total number of cells (Field of View)
75
Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly.
Explain why.
1. To create a single/thin layer of cells OR To spread out cells;
2. So that light could pass through;
76
Other students in the class followed the same method for the Root Tip Squash (RP2) practical, but calculated different mitotic indices.
Apart from student errors, suggest two explanations why.
1. ( roots) are a different age OR grown in different conditions;
Accept suitable descriptions of conditions, eg in different temperatures
2. (Root tips) from different plants/bulbs/species;
3. Single field of view is not representative of a root tip
OR
(Other) students may have looked at more fields of view
OR
(Other) students may have calculated a mean;
4. (Different fields of view are from) different parts of the root tip;
Reject different sized fields of view
Reject different number of cells (per field of view)
5. Cells/roots undergo mitosis/cell division at different times/rates;
77
Name the main polymer that forms the following cell walls.
Plant cell wall
Fungal cell wall
Plant cell wall = Cellulose
Fungal cell wall = Chitin
| Pronounced KIY-TIN
78
Determining the genome of the viruses could allow scientists to develop a vaccine.
Explain how. [2]
1. (The scientists) could identify proteins (that derive from the genetic code) OR (The scientists) could identify the proteome;
2. (They) could (then) identify potential antigens (to use in the vaccine);
79
After a disease is diagnosed, monoclonal antibodies are used in some medical treatments.
Give one example of using monoclonal antibodies in a medical treatment.
Targets/binds/carries drug/medicine to specific cells/antigens/receptors
OR
Block antigens/receptors on cells;
80
Describe and explain the role of antibodies in stimulating phagocytosis. [2]
1. Bind to antigen OR Are markers;
Accept opsonin for ‘marker’
Accept form (antibody-antigen) complexes/are complementary to antigen
2. (Antibodies) cause clumping/agglutination OR Attract phagocytes;
81
What is an antigen? [2]
1. Foreign protein; Accept glycoprotein / glycolipid / polysaccharide
2. (that) stimulates an immune response / production of antibody;
82
What is an antibody?
1. A protein / immunoglobulin specific to an antigen;
2. Produced by B cells OR Secreted by plasma cells;
83
Give the two types of molecule from which a ribosome is made.
ribosomal RNA / ribosomal ribonucleic acid
and
ribosomal protein;
84
The scientists measured the percentage change in tumour volume.
Suggest why they recorded both percentage change and tumour volume.
**Percentage change:** To allow comparison as tumours may differ in volume/size
**Tumour volume: ** (As) tumours may differ in length/width/shape **OR**
(As) volume is (best) indication of the number of cells in tumour;
85
State 2 methods of delivering passive immunity
* Antibodies from mother pass across the placenta to bind to specifically complementary antigens on pathogens that have also crossed the placenta
* Through breast milk
* Through plasma transfusion
* Through ANTI-VENOM / ANTI-TOXIN injections
86
Explain how a fetus is protected against a pathogen that infects its mother during pregnancy.
* Antibodies have variable regions with specific tertiary structures
* Complementary to antigens
* Found on pathogen which has crossed the placenta
* forms antigen-antibody complexes
87
Explain why viruses are described as acellular and non-living. [2]
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**
