2: Studying Cells Flashcards
Describe the structure and function of the nucleus. [6]
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;
Explain why viruses are described as acellular and non-living. [2]
- no cell(-surface) membrane OR Not made of cells;
- (Non-living) have no metabolism/metabolic
reactions;
OR
Cannot (independently) move / respire / replicate / excrete
OR
(Have) no nutrition;
MRSGREN
Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. [5]
- 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;
Compare & contrast Eukaryotic and Prokaryotic DNA [5]
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;
State three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.
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);
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
- 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 ribosomes only;
6 and 7 Any two from [Capsule/flagellum/plasmid / cell wall]
Name two structures found in all bacteria that are not found in plant cells.
- Circular DNA (molecule in cytoplasm);
- Murein cell wall OR Peptidoglycan cell wall OR Glycoprotein cell wall;
- Small(er)/70S ribosomes (in cytoplasm);
Give one advantage of using a TEM rather than a SEM.
- Higher resolution;
- higher (maximum) magnification / higher detail (of image);
OR - Allows internal details / structures within (cells) to be seen / cross section to be taken;
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.
Shorter wavelength between electrons
OR
Longer wavelength in light (rays);
Give one advantage of using a SEM rather than a TEM.
Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;
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]
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;
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) 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;
Describe and explain how cell fractionation and centrifugation can be used to isolate mitochondria from a suspension of animal cells. [6]
- Cell homogenisation to break open cells and release organelles;
- Filter to remove (large) debris/whole cells;
- Use isotonic solution to prevent osmotic damage to mitochondria / organelles;
- Keep cold to prevent/reduce damage to organelles by enzyme;
- Use buffer to maintain pH and prevent protein/enzyme denaturation;
- Use differential Centrifuge (at high speed/1000 g) to separate nuclei / cell fragments / heavy organelles;
- Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom;
- Observe pellet with a microscope to identify mitochondria;
Describe the features of Prophase
Nuclear membrane begins to breakdown;
Centrioles move to poles of the cell;
Chromatin supercoils and condense in chromosomes;
Describe the features of Metaphase
Spidle fibres form;
Spindle fibres attach;
To the centromere of chromosomes;
Chromosomes align at the equator;
Describe the features of Anaphase
Spindle fibres shorten;
Centromere splits;
Sister chromatids are separated;
Chromatids pulled to opposite poles of the cell;
Describe the features of Telophase
Nuclear membrane begins to reform;
Chromosomes unwind;
What is a homologous pair of chromosomes?
Two chromosomes that carry the same genes in the same loci / location
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.
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
- Method to deal with part cells shown at edge /count only whole cells;
- To standardise counting;
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how.
- Homologous chromosomes pair up;
- maternal and paternal chromosomes are arranged in any order;
- Independent segregation;
- Crossing over;
- (Equal) Portions of chromatids are swapped between chromosomes;
- Produces new combination of alleles;
- Chromatids separated at meiosis II/ later;
Describe the process of crossing over and explain how it increases genetic diversity
- Homologous pairs of chromosomes associate / form a bivalent;
- Chiasma(ta) form;
- (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
- Producing new combinations of alleles;
Give two differences between mitosis and meiosis.
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;
Describe how the process of meiosis results in haploid cells. Do not include descriptions of how genetic variation is produced in meiosis.
- DNA replication (during late interphase);
- Two divisions;
- Separation of homologous chromosomes (in first division); 4. Separation of (sister) chromatids (in second division);
- Produces 4 (haploid) cells/nuclei;
Describe binary fission in bacteria.
- Replication of (circular) DNA;
- Replication of plasmids;
- Division of cytoplasm (to produce daughter cells);
What is a tumour? [2]
- Mass of cells/tissue OR Abnormal cells/tissue;
- Uncontrolled mitosis/cell division;
Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane (3 marks).
- Glycerol joined to two fatty acid tails Phosphate group joined to glycerol on opposite side. (joined by condensation reaction with ester bond).;
- Phospholipid has hydrophilic head (phosphate and glycerol) and hydrophobic tails (fatty acid chains)
- Arrange to form a phospholipid bilayer; (Hydrophilic head facing out. Hydrophobic fatty acid chains facing in)
Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)
This is called PHAGOCYTOSIS
- Pathogen is engulfed by the phagocyte.
- Engulfed pathogen enters the cytoplasm of
the phagocyte in a vesicle; - Lysosomes fuse with vesicle releasing
digestive enzymes; - Lysosome enzymes break down the pathogen.
- Waste materials are ejected from the cell by exocytosis;
Describe how a phagocyte destroys a pathogen present in the blood. [3]
- Engulfs;
- Forming vesicle/phagosome and fuses with lysosome;
- Hydrolytic enzymes digest/hydrolyse;
Give two types of cell, other than pathogens, that can stimulate an immune response.
- (Cells from) other organisms/transplants;
- Abnormal/cancer/tumour (cells);
- (Cells) infected by virus;
- Pathogen (Bacterium / Fungus / Protist)
REJECT VIRUS (Acellular)
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how [6]
- Vaccine contains antigen from pathogen;
- Macrophage presents antigen on its surface;
- T (helper) cell with complementary receptor protein binds to antigen;
- T cell stimulates B cell;
- (With) complementary antibody on its surface;
- B cell divides to form clone secreting / producing same antibody;
- B cell / Plasma cell rapidly secretes large numbers of antibody;
Explain how the humoral response leads to immunity. [3]
- B cells specific to the antigen reproduce by mitosis.
- B cells produce plasma and memory cells
- Second infection produces antibodies in larger quantities AND more rapidly.
Describe and explain the role of antibodies in stimulating phagocytosis.
- OPSINISATION: Bind to antigen OR Are markers;
- AGGLUTINATION: (Antibodies) cause clumping/agglutination OR Attract phagocytes;
Describe the difference between active and passive immunity. [5]
- Active involves memory cells, passive does not;
- Active involves production of antibody by plasma cells/memory cells;
- Passive involves antibody introduced into body from outside/named source;
- Active long term, because antibody produced in response to antigen;
- Passive short term, because antibody (given) is broken down;
- Active (can) take time to develop/work, passive fast acting;
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;
Different antibodies from the same organism bind to different antigens. Explain why
- 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.
What is the role of the disulfide bridge in forming the quaternary structure of an antibody?
Joins two (different) polypeptides;
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 / 3D structure / shape;
- (So) Only binds to / fits / complementary to one antigen;
Describe the structure of the human immunodeficiency virus (HIV). [5]
- RNA (as genetic material);
- Reverse transcriptase;
- (Protein) capsomeres/capsid;
- (Phospho)lipid (viral) envelope OR Envelope made of membrane;
- Attachment proteins;
Explain how HIV affects the production of antibodies when AIDS develops in a person. [3]
- Less/no antibody produced;
- (Because HIV) destroys helper T cells; Accept ‘reduces number’ for ‘destroys’
- (So) few/no B cells activated / stimulated OR (So) few/no B cells undergo mitosis/differentiate/form plasma cells;
Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). [4]
- RNA converted into DNA using reverse transcriptase;
- DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
- DNA transcribed into (HIV m)RNA;
- (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);
Name two features of HIV particles that are not found in bacteria. Do not include attachment protein in your answer. [2]
- Capsid;
- Reverse transcriptase;
- RNA genome;
- (viral lipid) Envelope;
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;
Describe the role of antibodies in producing a positive result in an ELISA test. [4]
- (First) antibody binds/attaches /complementary (in shape) to antigen;
- (Second) antibody with enzyme attached is added;
- (Second) antibody attaches to antigen;
- (Substrate/solution added) and colour changes;
Which immune cell destroys (self) cells infected with a virus?
Tc Cell
(Cytotoxic Killer T cell)
Which immune cell destroys bacteria?
Phagocyte
(e.g., Macrophage)
Name a virus that infects bacteria.
Bacteriophage
When is a person / cell / organism infected by a virus such as HIV?
The moment the viral DNA is inserted into the host cells genome.
What is an antigen?
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
State 3 roles of a T helper cell
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
What are the ethical considerations asociated with vaccines and monoclonal antibodies?
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.
What is Herd immunity?
Only applicable to contagious pathogens.
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.
What threatens Herd immunity?
- 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
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 (Proteins) molecules arranged into a mosaic.
Explain the arrangement of phospholipids in a cell-surface membrane. [2]
- 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;
Describe how an ester bond is formed in a phospholipid molecule. [2]
- Condensation (reaction) OR Loss of water;
- Between of glycerol and fatty acid;
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;
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;
Name and describe five ways substances can move across the cell-surface membrane into a cell.
- (Simple) diffusion of small/non-polar molecules down a concentration gradient;
- Facilitated diffusion down a concentration gradient via protein carrier/channel;
- Osmosis of water down a water potential gradient;
- Active transport against a concentration gradient via protein carrier using ATP;
- Co-transport of 2 different substances using a carrier protein;
Compare and contrast the processes by which water and inorganic ions enter cells. [3]
- Comparison: both move down concentration gradient;
- Comparison: both move through (protein) channels in membrane;
Accept aquaporins (for water) and ion channels - Contrast: ions can move against a concentration gradient by active transport
Give two similarities in the movement of substances by diffusion and by osmosis.
- (Movement) down a gradient / from high concentration to low concentration;
- Passive / not active processes; OR Do not use energy from respiration / from ATP / from metabolism; OR Use energy from the solution;
Describe how substances move across cell-surface membranes by facilitated diffusion. [3]
- Carrier / channel protein;
- (Protein) specific / complementary to substance;
- Substance moves down concentration gradient;
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]
- Add 4.5 cm3 of (1.0 mol dm–3) solution to 25.5 cm3 (distilled) water.
- Mix
Explain the decrease in mass of potato tissue in the 0.40 mol dm−3 solution of sucrose. [2]
- Water potential of solution is less than / more negative than that of potato tissue; (Ψ as equivalent to water potential)
- Tissue loses water by osmosis.
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]
- Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;
- Find concentration where curve crosses the x-axis / where percentage change is zero;
- Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis).
