4/5/6 Mark Qs Cells Flashcards
Describe how a sample of chloroplasts could be isolated from leaves. (4)
- Break open cells/tissue and filter OR Grind/blend cells/tissue/leaves and filter; Accept homogenise and filter
- In cold, same water potential/concentration, pH controlled solution; Accept for ‘same water potential/ concentration’, isotonic Accept for ‘pH controlled’, buffered
- Centrifuge/spin and remove nuclei/cell debris;
- (Centrifuge/spin) at high(er) speed, chloroplasts settle out;
Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. Do not include details of transcription and translation in your answer. (4)
- DNA in nucleus is code (for protein);
- Ribosomes/rough endoplasmic reticulum produce (protein); Accept rER for ‘rough endoplasmic reticulum’
- Mitochondria produce ATP (for protein synthesis);
- Golgi apparatus package/modify; OR Carbohydrate added/glycoprotein produced by Golgi apparatus; Accept body for ‘apparatus’
- Vesicles transport OR Rough endoplasmic reticulum transports;
- (Vesicles) fuse with cell(-surface) membrane; Accept exocytosis at cell membrane
Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells. (6)
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- (So with TEM) smaller organelles / named cell structure can be observed OR greater detail in organelles / named cell structure can be observed;
- TEM view only dead / dehydrated specimens and optical (can) view live specimens;
- TEM does not show colour and optical (can);
- TEM requires thinner specimens;
- TEM requires a more complex/time consuming preparation;
- TEM focuses using magnets and optical uses (glass) lenses;
- ‘clearer’ is not equivalent to ‘detail’
- Accept ‘Only optical can view live specimens’
- Accept ‘Only optical can show colour’
- Accept ‘TEM requires a more difficult preparation’ Ignore references to artefacts
Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope. (4)
- Add drop of water to (glass) slide;
- Obtain thin section (of plant tissue) and place on slide / float on drop of water;
- Stain with / add iodine in potassium iodide. Allow any appropriate method that avoids trapping air bubbles
- Lower cover slip using mounted needle.
Describe two aseptic techniques she would have used when transferring a sample of broth culture on to an agar plate. Explain why each was important. (4)
- Keep lid on Petri dish OR Open lid of Petri dish as little as possible.
- To prevent unwanted bacteria contaminating the dish. OR L. monocytogenes may be dangerous / may get out. OR
- Wear gloves OR Wear mask OR Wash hands;
- To prevent contamination from bacteria on hands / mouth OR Prevent spread of bacteria outside the lab; OR
- Use sterile pipette OR Flame the loop OR Flame the neck of the container of the culture;
- To maintain a pure culture of bacteria
Describe the appearance and behaviour of chromosomes during mitosis. (5)
(During prophase)
1. Chromosomes coil / condense / shorten / thicken / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the centromere; (During metaphase)
3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;
(During anaphase)
1. The centromere splits / divides;
2. (Sister) chromatids / chromosomes are pulled to opposite poles / ends of the cell / separate;
(During telophase)
1. Chromatids / chromosomes uncoil / unwind / become longer / thinner. No marks for naming the stages Reject references to homologous chromosomes / pairing of chromosomes Ignore references to spindle formation during prophase
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; If no reference to ‘small/ non-polar’ for 1. accept this idea from ‘large/charged’ given in description of 2.
- Facilitated diffusion down a concentration gradient via protein carrier/channel; Reject if active rather than passive
- 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; For any answer accept a correct example For ‘carrier protein’ accept symport OR cotransport protein
The movement of substances across cell membranes is affected by membrane structure. Describe how. (5)
- Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid-soluble substances;
- and 2. Accept correct named examples
- and 2. Ignore water Accept phospholipid (bilayer) allows movement/diffusion of O2/CO2 Accept water-insoluble
- Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances OR (Membrane) proteins allow polar/charged substances to cross the membrane/bilayer; Accept water-soluble
- Carrier proteins allow active transport;
- Channel/carrier proteins allow facilitated diffusion/co-transport; Accept aquaporins allow osmosis
- 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;
- and 7. Accept correct reference to faster/slower/rate for ‘how much movement’ Accept microvilli / Golgi (apparatus) / ER / rER Accept surface area to volume for ‘surface area’
- Cholesterol affects fluidity/rigidity/permeability; Accept cholesterol affects vesicle formation/ endocytosis/exocytosis/phagocytosis;
Describe how HIV is replicated. (4)
- Attachment proteins attach to receptors on helper T cell/lymphocyte;
- Nucleic acid/RNA enters cell;
- Reverse transcriptase converts RNA to DNA;
- Viral protein/capsid/enzymes produced;
- Virus (particles) assembled and released (from cell);
Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). (4)
- RNA converted into DNA using reverse transcriptase; Reject ‘messenger’ or ‘m’ before RNA
- DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
- DNA transcribed into (HIV m)RNA; Accept descriptions of transcription
- (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles); Accept descriptions of translation Accept named viral protein, eg capsid Reject viral cells
Describe the role of antibodies in producing a positive result in an ELISA test. (4)
Ignore mixing of direct or indirect ELISA Accept annotated diagram(s).
1. (First) antibody binds/attaches /complementary (in shape) to antigen;
2. (Second) antibody with enzyme attached is added;
3. (Second) antibody attaches to antigen; Accept (second) antibody attaches to (first) antibody (indirect ELISA test).
4. (Substrate/solution added) and colour changes; Only award if enzyme mentioned.
In the UK, children are vaccinated against disease. Describe how vaccination can lead to protection against bacterial meningitis. (6)
- Antigen / epitope on surface of N. meninigitidis / bacterium binds to surface protein / surface receptor on a (specific / single) B cell. If answered in context of T cell, allow Antigen binds to (specific / single) T cell
- (Activated) B cell divides by mitosis / produces clone; If answered in context of T cell, allow (Activated) T cell releases cytokine.
- (Division) stimulated by cytokines / by T cells; If answered in context of T cell, allow (Cytokine) stimulates production of plasma cells;
- B cells / plasma cells release antibodies;
- (Some) B cells become memory cells;
- Memory cells produce plasma / antibodies faster
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how. (5)
- Vaccine contains antigen from pathogen;
- Macrophage presents antigen on its surface;
- T cell with complementary receptor protein binds to antigen;
- T cell stimulates B cell;
- (With) complementary antibody on its surface;
- B cell secretes large amounts of antibody;
- B cell divides to form clone all secreting / producing same antibody.
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.
Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells. (5)
Any five from:
1. Cell homogenisation to break open cells;
2. Accept suitable method of breaking open cells.
3. Filter to remove (large) debris / whole cells;
4. Reject removes cell walls.
5. Use isotonic solution to prevent damage to mitochondria / organelles;
6. Ignore to prevent damage to cells.
7. Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation;
8. Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments / heavy organelles;
9. Ignore incorrect numerical values.
10. Re-spin (supernatant / after nuclei / pellet removed) at higher speed to get mitochondria in pellet / at bottom. Must have location Reject ref to plant cell organelles only once
