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A Level Biology > Topic 2 - Cells > Flashcards

Topic 2 - Cells Flashcards

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1
Q

Prokaryote and animal cell comparison

A
  1. Bacterial cell is much smaller than a human cell;
  2. Bacterial cell has a cell wall but human cell does not;
  3. Bacterial cell lacks a nucleus but human cell has a nucleus;
  4. Bacterial cell lacks membrane-bound organelles but human cell has membrane-bound organelles;
  5. Bacterial ribosomes smaller than human ribosomes / bacteria have 70S ribosomes whereas humans have 80S ribosomes;
  6. Bacterial DNA is circular but human DNA is linear;
  7. Bacterial DNA is ‘naked’ whereas human DNA is bound to histones / proteins
    Must have comparison
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2
Q

Phospholipid arrangement in a membrane

A
  1. Bilayer OR Water is present inside and outside a cell;
  2. Hydrophobic (fatty acid) tails point away/are repelled from water
    OR
    Hydrophilic (phosphate) heads point to/are in/are attracted to water;
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3
Q

How do hydrophobic substances move across membranes

A
  1. Lipid soluble;
  2. (Diffuse through) phospholipid (bilayer);
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4
Q

Role of organelles ( proteins )

DNA -
Ribosomes -
Mitochondria -
Glogi -
Vesicles -
RER -

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

Describe how you would use cell fractionation techniques to obtain a sample of mitochondria from leaf tissue.

A
  1. Macerate / homogenise / blend / break tissues / cells (in solution);
  2. Centrifuge the supernatent;
  3. At different / increasing speeds until mitochondria fraction obtained/until 3rd pellet is obtained;
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6
Q

Explain the conditions that would be necessary for cell fractionation.

A
  1. Ice-cold – Slows / stops enzyme activity to prevent digestion of organelles / mitochondria;
  2. Buffer - Maintains pH so that enzymes / proteins are not denatured;
    Reject reference to cells
  3. Same water potential - Prevents osmosis so no lysis / shrinkage of organelles / mitochondria;
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7
Q

Explain how ultracentrifugation separates different molecules.

A
  1. Spin (liquid / supernatant) at (very) high speed / high g;
    Need context of high, not just ‘faster’, ‘higher’ in context of use of bench centrifuge
  2. Molecules separate depending on (molecular) mass / size / density;
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8
Q

Why is a detergent used to lyse (breaking open) cells and organelles.

A
  1. Cell membranes made from phospholipid;
  2. (Detergent) dissolves membranes / phospholipid (bilayer);
    Ignore breaks down
    Reject hydrolysis
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9
Q

TEM compared to optical microscope

A
  1. TEM use electrons and optical use light;
  2. TEM allows a greater resolution;
  3. (So with TEM) smaller organelles / named cell structure can be observed
    OR
    greater detail in organelles / named cell structure can be observed;
  4. TEM view only dead / dehydrated specimens and optical (can) view live specimens;
  5. TEM does not show colour and optical (can);
  6. TEM requires thinner specimens;
  7. TEM requires a more complex/time consuming preparation;
  8. TEM focuses using magnets and optical uses (glass) lenses
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10
Q

TEM compared to SEM

A

Higher resolution OR View internal structures

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11
Q

Why must a sample for a microscope be thin?

A
  1. Need a single layer of cells / only a few cells thick / not too many layers / detail obscured by cells underneath;
  2. Light must be able to pass through;
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12
Q

Making a temporary mount (microscope slide)

A
  1. Add drop of water to (glass) slide;
  2. Obtain thin section (of plant tissue) and place on slide / float on drop of water;
  3. Stain if necessary;
  4. Lower cover slip using mounted needle.
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13
Q

Measuring dry mass

A
  1. Heat at 100°C / heat to temp to evaporate water;
    Value which would not burn material
  2. Weigh and heat until no further change in mass;
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14
Q

Stages of Mitosis ( all )

A

(During prophase)
1. Chromosomes coil / condense / shorten / 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)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles / ends of the cell / separate;
(During telophase)
8. Chromatids / chromosomes uncoil / unwind / become longer

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15
Q

What happens during prophase?

A

(During prophase)
1. Chromosomes coil / condense / shorten / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the centromere;

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16
Q

What happens during metaphase?

A

(During metaphase)
3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;

17
Q

What happens during anaphase?

A

(During anaphase)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles / ends of the cell / separate;

18
Q

What happens during telophase?

A

(During telophase)
8. Chromatids / chromosomes uncoil / unwind / become longer

19
Q

Mitosis - root tip experiment
Why the tip?
Pressed down firmly on the cover slip?

Ensuring accuracy

A

Where dividing cells are found / mitosis occurs
Single / thin layer of cells / spread out cells so light passes through

  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
20
Q

Cytokinesis

A

The division of the cytoplasm

21
Q

Explain how bacterial cells divide

A
  1. Binary fission;
  2. Replication of (circular) DNA;
  3. Replication of plasmids
  4. Division of cytoplasm to produce 2 daughter cells;
  5. Each with single copy of (circular) DNA;
22
Q

Transport across membranes

A
  1. Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid-soluble substances;
  2. Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances OR (Membrane) proteins allow polar/charged substances to cross the membrane/bilayer; 3. Carrier proteins allow active transport;
  3. Channel/carrier proteins allow facilitated diffusion/co-transport;
  4. Shape/charge of channel / carrier determines which substances move;
  5. Number of channels/carriers determines how much movement;
  6. Membrane surface area determines how much diffusion/movement;
  7. Cholesterol affects fluidity/rigidity/permeability;
23
Q

Facilitated diffusion

A
  1. Carrier / channel protein;
  2. (Protein) specific / complementary to substance;
  3. Substance moves down concentration gradient
24
Q

Diffusion and osmosis similarities

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;
25
Q

Co-transport of glucose

A
  1. Sodium ions actively transported from ileum cell to blood;
  2. Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);
  3. Glucose enters by facilitated diffusion with sodium ions;
26
Q

ATP hydrolase and active transport

A
  1. (ATP to ADP + Pi ) Releases energy;
  2. (energy) allows ions to be moved against a concentration gradient
    OR
    (energy) allows active transport of ions;
27
Q

Osmosis – tissue in more concentrated solution

A
  1. Water potential of solution is less than / more negative than that of potato tissue;
    Allow Ψ as equivalent to water potential
  2. Tissue loses water by osmosis.
28
Q

Membrane adaptations for absorption

A
  1. Membrane folded so increased / large surface area;
    OR
    Membrane has increased / large surface area for (fast) diffusion / facilitated diffusion / active transport / co-transport;
  2. Large number of protein channels / carriers (in membrane) for facilitated diffusion;
  3. Large number of protein carriers (in membrane) for active transport;
  4. Large number of protein (channels / carriers in membrane) for co-transport
29
Q

What is a monoclonal antibody?

A

(Antibodies with the) same tertiary structure;
OR
(Antibody produced from) identical/cloned plasma cells/B cells/B lymphocytes;

30
Q

Cells that stimulate an immune response

A
  1. (Cells from) other organisms/transplants;
  2. Abnormal/cancer/tumour (cells);
  3. (Cells) infected by virus
  4. Pathogens
31
Q

What is an antigen?

A
  1. Protein;
  2. Found on a cell surface membrane/pathogen surface
  3. (that) stimulates an immune response / production of antibody;
32
Q

What is an antibody?

A
  1. A protein / immunoglobulin specific to an antigen;
  2. Produced by B cells
    OR
    Secreted by plasma cells;
33
Q

Antibody specificity

A
  1. Each protein has a different tertiary structure;
  2. (Each) antibody has a specific antigen / binding / variable region / site;
  3. So, (each antibody) forms different antigen-antibody complex
    OR
    (each antibody) only binds to complementary (protein);
34
Q

Phagocytosis

A
  1. Phagocyte engulfs to form vacuole / vesicle / phagosome;
  2. Lysosome fuses and empties contents into vacuole / vesicle / phagosome;
  3. (Releasing) enzymes that digest / hydrolyse bacteria;
35
Q

Role of the disulphide bridge in antibody structure

A

Joins two (different) polypeptides;

36
Q

Production of antibodies

A
  1. Helper T cell / TH cell binds to the antigen (on the antigen-presenting cell / phagocyte);
  2. This helper T / TH cell stimulates a specific B cell;
  3. B cell clones
    OR
    B cell divides by mitosis;
  4. (Forms) plasma cells that release antibodies;
37
Q

Vaccination

A
  1. Antigen / epitope on surface of pathogen binds to surface protein / surface receptor on a (specific / single) B cell.
  2. (Activated) B cell divides by mitosis / produces clone;
  3. (Division) stimulated by cytokines / by T cells;
  4. B cells / plasma cells release antibodies;
  5. (Some) B cells become memory cells;
  6. Memory cells produce plasma / antibodies faster
38
Q

Active v passive immunity

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
39
Q

ELISA test

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;
Accept (second) antibody attaches to (first) antibody (indirect ELISA test).
4.   (Substrate/solution added) and colour changes;
Only award if enzyme mentioned

A Level Biology (5 decks)

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