2: Studying cells Flashcards
What is the function of a ribosome?
Site of Protein synthesis;
What is the function of the Nucleus?
Contains genetic material / DNA;
Controls cell activity;
Describe the structure and function of the nucleus. [5]
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;
What is the function of the nucleolus?
- Synthesise nucleotides
- Synthesise cytoplasmic ribosomes (80s)
What is the function of a mitochondrion?
Site of aerobic respiration;
ATP production;
Site of Link/Krebs/ETC
What is the function of the Smooth Endoplasmic Reticulum?
Site of lipid synthesis;
What is the function of the Rough Endoplasmic reticulum?
Encrusted in Ribosomes;
Site of protein synthesis;
Transports and stores protein within the cell
What is the function of Golgi Apparatus? [2]
Modifies/packages/sorts proteins;
Produces vesicles;
What is the function of Lysosomes?
Contains hydrolytic enzymes;
Digests worn out organelles/autolysis;
What is the function of Cell surface membrane?
Made of a Phospholipid Bilayer;
Controls what enters the cell/ is selectively permeable;
Can be folded to increase SA;
What is the function of Chloroplasts?
Contain thylakoids, stacked into Granum;
Site of photosynthesis;
What is the function of a Capsule?
Protects cell from immune systems;
Aids bacteria sticking together;
What is the function of Plasmid?
Circular DNA;
Contains antibiotic resistance genes;
Contains fewer genes that are contantly transcribed;
What is the function of Cell Wall?
Provides rigid shape / structure;
Stops osmotic lysis;
What is the function of Flagellum?
Allows movement/propulsion;
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);
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;
State three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell. [3]
**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. [6]
- 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]
Name two structures found in all bacteria that are not found in plant cells. [2]
- 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;
- 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.
Electrons have a shorter wavelength
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
- 3-D images;
Explain the advantages and limitations of using a TEM to investigate cell structure.
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) 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;
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 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)
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.
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;
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. [5]
- (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 [2]
- (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.
- Add 4.5 cm3 of (1.0 mol dm–3) solution to 25.5 cm3 (distilled) water.
- Mix
M1V1= M2V2
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).
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;
State two ways that pathogens cause disease.
- Produce / secrete / release toxins
- Damage/destroy cells / tissues / organs
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;
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 (specific) antigen from pathogen;
- Macrophage presents antigen on its surface;
- T (helper) cell with complementary receptor protein binds to antigen & becomes activated;
- T cell stimulates B cell by complementary receptor binding and releases cytokines;
- (With) complementary antibody on its surface;
- B cell divides to form clone secreting / producing same antibody;
- B cell secretes large amounts of (monoclonal) antibody;
Explain how the humoral response leads to immunity. [3]
- B cells specific to the antigen reproduce by mitosis.
- B cells produce / differentiate into plasma and memory cells
- Second infection produces antibodies in larger quantities AND quicker. (More rapid & More extensive)
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;
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;
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 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.
- Capsid;
- Reverse transcriptase;
- RNA genome;
- Envelope
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;
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;
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;
Describe the features of Metaphase
Spidle fibres form;
Spindle fibres attach;
To the centromere of (each) 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;
(2 distinct nuclei within one cell)
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. [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
- 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. [5]
- Homologous chromosomes pair up; or form a Bivalent
- 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 [4]
- 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. [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;
When, during meiosis, do cells become haploid?
Meiosis 1
When, during meiosis, does crossing over and independent segregation occur?
Meiosis 1
When, during meiosis, do homologues become separated?
Meiosis 1
When, during meiosis, do chromatids become separated to opposite poles?
Meiosis 2
Describe how the process of meiosis results in haploid cells. Do not include descriptions of how genetic variation is produced in meiosis. [5]
- DNA replication (during late interphase);
- Two divisions;
- Separation of homologous chromosomes (in first division);
- Separation of (sister) chromatids (in second division);
- Produces 4 (haploid) cells/nuclei;
Describe binary fission in bacteria. [3]
- Replication of (circular) DNA;
- Replication of plasmids;
- Division of cytoplasm (to produce daughter cells);
What is a tumour?
- Mass of cells/tissue OR Abnormal cells/tissue;
- Uncontrolled mitosis/cell division;
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]
- Count cells in mitosis in field of view;
- Divide this by total number of cells in field of view;
- Repeat many/at least 5 times
OR
Select (fields of view) at random;
Mitotic index formula
Number of cells with visible chromosomes (PMAT)(Divided by)
______________________________________________________
Total number of cells (Field of View)
Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly.
Explain why.
- To create a single/thin layer of cells OR To spread out cells;
- So that light could pass through;
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.
- ( roots) are a different age OR grown in different conditions;
Accept suitable descriptions of conditions, eg in different temperatures
- (Root tips) from different plants/bulbs/species;
- 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;
- (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)
- Cells/roots undergo mitosis/cell division at different times/rates;
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
Determining the genome of the viruses could allow scientists to develop a vaccine.
Explain how. [2]
- (The scientists) could identify proteins (that derive from the genetic code) OR (The scientists) could identify the proteome;
- (They) could (then) identify potential antigens (to use in the vaccine);
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;
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;
What is an antigen? [2]
- Foreign protein; Accept glycoprotein / glycolipid / polysaccharide
- (that) stimulates an immune response / production of antibody;
What is an antibody?
- A protein / immunoglobulin specific to an antigen;
- Produced by B cells OR Secreted by plasma cells;
Give the two types of molecule from which a ribosome is made.
ribosomal RNA / ribosomal ribonucleic acid
and
ribosomal protein;
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;
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
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
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
