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bio aqa a-level > Topic 2 - Cells > Flashcards

Topic 2 - Cells Flashcards

1
Q

Human cell compared with Prokaryotic (bacterium) (7)

A
  1. Bacterial cell is much smaller than a human cell; (or human cell is much larger than a bacterial 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 705 ribosomes
    whereas humans have 805
  6. Bacterial DNA is circular but human DNA is linear
  7. Bacterial DNA is ‘naked’ whereas human
    DNA is bound to histones/proteins
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2
Q

Eukaryotic - Describe the structure and function of the
nucleus. (4)

A

Any four from Structure
Nuclear envelope/double membrane
(Nuclear) pores (in the membrane)
Chromosomes/chromatin/(linear) DNA with histones
Nucleolus/ nucleoli
Function
Holds/stores genetic information for production of proteins
DNA replication OR interphase
Production of mRNA/ERNA OR transcription
Production of rRNA/ribosomes;.

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3
Q

Eukaryotic - Name the main polymer that forms the following cell walls - plants cells & fungal cells (1)

A

Cellulose (plant) and chitin (fungi);

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4
Q

Eukaryotic - Describe the role of one named organelle in digesting these bacteria. (3)

A
  1. Lysosomes;
  2. Fuse with vesicle;
    Accept phagosome for vesicle
  3. (Releases) hydrolytic enzymes;
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5
Q

Eukaryotic - Identify two organelles in cells that enable the production of glycoproteins (1)

A

Rough endoplasmic reticulum/
ribosomes and Golgi apparatus

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6
Q

Eukaryotic - Give two structures found in all prokaryotic cells and in all eukaryotic cells.
(2)

A
  1. Cell(-surface) membrane;
  2. Ribosomes;
    Ignore 705
  3. Cytoplasm;
  4. DNA;
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7
Q

Eukaryotic - Give one feature of the chloroplast that allows protein to be synthesised inside the
chloroplast and describe one difference between this feature in the chloroplast and a eukaryotic cell. (2)

A

Mark in pairs, 1 and 2 OR 3 and 4
1. DNA;
2. Is not associated with protein/ histones but nuclear DNA is
OR
Is circular but nuclear DNA is linear
OR
Is shorter than nuclear DNA;
3. Ribosomes;
4. Are smaller than cytoplasmic ribosomes;

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8
Q

Eukaryotic - Eukaryotic cells produce and release proteins.
Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. (4)

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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9
Q

Eukaryotic - 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;
Do not credit if suggestion that prokaryotic
DNA only exists as plasmids.
4. Introns v no introns;
5. Long(er) v short(er);

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10
Q

Eukaryotic - Name the main biological molecule in the cell membrane (1)

A

Phospholipids;

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11
Q

Eukaryotic - Describe the role of mitochondria in secreting a protein (1)

A

(Many mitochondria) release energy / ATP for movement of vesicles / synthesis of protein / active transport;

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12
Q

Eukaryotic - Describe the role of golgi apparatus in secreting a protein (1)

A

(Many Golgi) vesicles transport protein / glycoprotein / milk to cell membrane / out of cell;

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13
Q

Eukaryotic - Describe the role of the golgi apparatus in lipid absorption

A
  1. Modifies / processes triglycerides;
    2
    Combines triglycerides with proteins;
  2. Packaged for release / exocytosis
    OR
    Forms vesicles;
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14
Q

Prokaryotic - Name the main biological molecule in a bacterial cell wall (1)

A

Murein / glycoprotein;

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15
Q

Prokaryotic - Give two features
of all prokaryotic cells that are not features of eukaryotic cells.

A

Cytoplasm with no membrane-bound organelles
Single, Circular DNA
DNA free in the cytoplasm
DNA that is not associated with proteins/ histones
A cell wall that contains murein

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16
Q

Viruses - Give 2 features of all viruses (2)

A
  1. attachments proteins
  2. capsid
  3. nucleic acid
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17
Q

Microscopes - How to measure objects using an eyepiece graticule (3)

A
  1. Use eyepiece graticule to measure the object e.g. nucleus or capillary
  2. Calibrate eyepiece graticule against stage micrometer
  3. Take a number of measurements and calculate the mean
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18
Q

Microscopes - Advantages and Limitations of Transmission Electron Microscope (TEM) (6

A

Advantages:
1. Small objects can be seen;
2. TEM has high resolution as wavelength of electrons shorter;
Limitations:
1. Cannot look at living cells as cells must be in a vacuum;
2. Must be thin specimen;
3. Preparation may create artefact;
4. Does not produce colour image;

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19
Q

Microscopes - Comparison of
TEM and optical microscope
(8)

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
  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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20
Q

Microscopes - Advantage of electron microscope over optical microscope (2)

A
  1. High resolution;
  2. Can see internal structure of organelles
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21
Q

Microscopes - 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. (2)

A

Shorter wavelength between electrons;
OR
Longer wavelength in light rays;

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22
Q

Microscopes - Describe and
explain one difference between TEM and
SEM (2)

A
  1. 3D image (with SEM), not 2D image
    OR
    Lower resolution (with SEM)
    OR
    (Only) surface visible with SEM, but internal structures visible with TEM;
  2. (Because) electrons deflected/bounce off (using SEM)
    OR
    Electrons transmitted/pass through (using
    TEM);
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23
Q

Homogenisation - Conditions required for cell homogenisation (3)

A
  1. Ice-cold - Slows/stops enzyme activity to prevent digestion of organelles/ mitochondria;
  2. Buffered - Maintains pH so that enzymes/proteins are not denatured;
  3. Same water potential - Prevents osmosis so no lysis/shrinkage of organelles/ mitochondria;
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24
Q

Homogenisation &
Ultracentrifugation - How to separate mitochondria? (4)

A
  1. Break open cells/homogenise/produce homogenate;
  2. Remove unbroken cells/larger debris by filtration;
  3. Centrifuge highest density organelle nuclei obtained as pellet at slowest speed
  4. Mitochondria in 2nd pellet as less dense than nucleus/organelle in first pellet;
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25
Q

Suggest why scientists can use detergent to break open cells instead of homogenisation (2)

A
  1. Cell membranes made from phospholipid;
  2. (Detergent) dissolves membranes / phospholipid (bilayer);
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26
Q

Viruses - Describe viral replication. (4)

A
  1. Attachment proteins attach to receptors;
    For ‘attachment protein’ accept gp41/gp120/ glycoprotein but ignore ‘receptor protein’.
  2. Virus injects nucleic acid (into host cell);
    For this mp accept ‘genetic material’ for
    ‘nucleic acid?
  3. Host cell replicates viral nucleic acid;
    Accept ‘RNA/DNA’ for ‘nucleic acid’.
  4. Host cell produces (viral) protein/capsid/ enzymes,
  5. Virus (particles) assembled and released (from cell);
27
Q

Bacteria - Describe binary fission in bacteria. (3)

A
  1. Replication of (circular) DNA;
    Accept nucleoid
    Reject chromosome
    Reject mitosis
  2. Replication of plasmids;
  3. Division of cytoplasm (to produce daughter cells);
28
Q

Bacteria -Describe how bacteria divide.(2)

A
  1. Binary fission;
  2. Replication of (circular) DNA;
  3. Division of cytoplasm to produce 2 daughter cells;
  4. Each with single copy of (circular) DNA;
29
Q

Eukaryotic division - What is a tumour? (2)

A
  1. Mass of cells;

Accept abnormal growth for ‘mass’
2. Many cells in mitosis/dividing cells

OR
Uncontrolled cell division;

30
Q

Eukaryotic division - Describe and explain the arrangement of the genetic material in prophase (2)

A
  1. Chromosomes (are) becoming visible/ distinct;
  2. Because (still) condensing;
    OR
    Accept ‘chromosomes are condensed’ for 2 marks.
    Accept shorten or thicken for ‘condensed’
  3. Chromosomes (arranged) at random/ not lined up;
  4. Because no spindle (activity);
    OR
    Because not attached to spindle fibres;
31
Q

Eukaryotic division - Chromosome Behaviour in
all Stages (8)

A

(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)
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/thinner;

32
Q

Eukaryotic division - Describe the role of the spindle fibres and the behaviour of the chromosomes during mitosis (5)

A
  1. (In) prophase, chromosomes condense;
    Accept chromatin for ‘chromosomes’ and for
    ‘condense’, shorten and thicken
  2. (In) prophase OR metaphase, centromeres attach to spindle fibres;
  3. (In) metaphase, chromosomes/pairs of chromatids at equator/centre of spindle/cell;
  4. (In) anaphase, centromeres divide;
  5. (In) anaphase, chromatids (from each pair) pulled to (opposite) poles/ends (of cell);
    Accept for ‘chromatids’, chromosomes but reject homologous chromosomes
  6. (In) prophase/metaphase/anaphase, spindle fibres shorten;
33
Q

Eukaryotic division - state name given to the division of cytoplasm during the cell cycle. (1)

A

Cytokinesis

34
Q

Eukaryotic division - Give two pieces of evidence that the cell was undergoing mitosis (2)

A
  1. The (individual) chromosomes are visible because they have condensed;
  2. (Each) chromosome is made up of two chromatids because DNA has replicated;
  3. The chromosomes are not arranged in homologous pairs, which they would be if it was meiosis;
35
Q

Eukaryotic division - Evidence for a cell in anaphase (2)

A
  1. Chromosomes / chromatids are (in two groups) at poles of spindle / at ends of spindle;
    Do not accept ‘ends of cell’
  2. V-shape shows that (sister) chromatids have been pulled apart at their centromeres / that centromeres of (sister) chromatids have been pulled apart.
36
Q

Eukaryotic division - During the cell cycle, the amount of DNA in a cell changes. Explain how the behaviour of chromosomes causes these changes in the amount of DNA per cell (2)

A

Increase)
1. Chromosomes / DNA replicates;
(First decrease)
2. Homologous chromosomes separate;
(Second decrease)
3. Sister chromatids separate.

37
Q

Eukaryotic division - Suggest why preventing the formation of spindle fibres stopped the cell cycle.

A
  1. Chromosomes/centromeres cannot
    attach (to spindle)
    OR
    Chromosomes cannot line up (on spindle);
  2. (So, no) metaphase;
    OR
  3. spindle);
    Chromatids cannot separate (on
    Accept description of ‘cannot separate’ e.g cannot move to poles
    Ignore ‘split’
  4. (So, no) anaphase;
38
Q

Eukaryotic division - Describe the appearance of chromosomes in anaphase (1)

A

Chromatids are being pulled to opposite poles/ends (of the cell) by spindles/spindle fibres;

39
Q

Eukaryotic division - Suggest and explain how two environmental variables could be changed to increase the growth rate of cells.
4)

A
  1. Increased (concentration of) glucose;
  2. Increased respiration;
  3. Increased (concentration of) oxygen;
  4. Increased respiration;
  5. Increased temperature;
  6. Increased enzyme activity;
  7. Increased (concentration of) phosphate;
  8. Increased ATP/DNA/RNA;
  9. Increased (concentration of) nucleotides;
  10. Increased DNA synthesis
40
Q

Eukaryotic division - Req Prac 2 Suggest why the student soaked the root tips in hydrochloric acid

A
  1. To break down links between/separate cell walls;
  2. Allowing the stain to pass/diffuse into the cells
    OR
    Allowing the cells to be (more easily) squashed;
41
Q

Eukaryotic division - Req Prac 2 Suggest why the student soaked the root tips in hydrochloric acid

A
  1. To break down links between/separate cell walls;
  2. Allowing the stain to pass/diffuse into the cells
    OR
    Allowing the cells to be (more easily) squashed;
42
Q

Eukaryotic division – Req Prac 2- Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly.
Explain why.

A
  1. To break down links between/separate cell walls;
  2. Allowing the stain to pass/diffuse into the cells
    OR
    Allowing the cells to be (more easily) squashed;
43
Q

Eukaryotic division - Req Prac 2 using only the first 5 mm from the tip of an onion root.
(1)

A

Where dividing cells are found / mitosis occurs;
OR
No dividing cells / mitosis in tissue further away / more than 5 mm from tip;
OR
To get (soft) tissue that will squash;
OR
Length that will fit under cover slip;

44
Q

Eukaryotic division - Req Prac 2 - 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.

A
  1. Count cells in mitosis in field of view;
  2. Divide this by total number of cells in field of view;
  3. Repeat many/> 10 times
    OR
    Select (fields of view) at random;
45
Q

Eukaryotic division - Req Prac 2 - 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.

A
  1. Examine large number of fields of view / many cells;
    Mark as pairs only
    Accept large number / 20 or more for many
  2. To ensure representative sample;
    Accept typical / reliable
    OR
  3. Repeat count;
  4. To ensure figures are correct;
    OR
  5. Repeat count;
  6. To ensure figures are correct;
    OR
  7. Method to deal with part cells shown at edge /count only whole cells;
  8. To standardise counting
46
Q

Eukaryotic division - Req Prac 2 -suggest why different student may get a different mitotic index using the same methos (assume no errors) (2)

A
  1. (Garlic) grown for different lengths of time
    OR
    (Garlic) grown in different conditions;
    Accept suitable descriptions of conditions, eg in different temperatures
  2. The root tips from different (garlic) plants/roots/bulbs/species;
  3. Single field of view is not representative of a root tip
    OR
    Different fields of view are different samples
47
Q

Eukaryotic division -The scientists measured the percentage change in tumour volume.
Suggest why they recorded both percentage change and tumour volume. (2)

A

Percentage change
1. To allow comparison as tumours may differ in volume/size (at the start of the investigation);
Tumour volume
2. (As) tumours may differ in length/
width/shape
OR
(As) volume is (best) indication of the number of cells in tumour;

48
Q

Membrane structure - Describe how proteins arrange themselves in the membrane (2)

A
  1. Hydrophobic parts of helix/AP (to the outside) to sit within the (hydrophobic) fatty acid (tails) of the phospholipids;
  2. Hydrophilic parts of helix/AP (to the inside) as ions are charged/polar/water soluble;
49
Q

Membrane structure -
Describe the role of cholesterol (1)

A

Cholesterol stabilises the membrane
OR
Cholesterol restricts the movement of molecules/phospholipids (making up the membrane);

50
Q

Transport methods -
Name and describe five ways substances can move across the cell-surface membrane into a cell. (5)

A
  1. (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.
  2. Facilitated diffusion down a concentration gradient via protein carrier/ channel;
    Reject if active rather than passive
  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;
51
Q

Transport methods - The movement of substances across cell membranes is affected by membrane structure. Describe how. (5)

A
  1. Phospholipid (bilayer) allows movement/diffusion of non-polar/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;
  4. Channel/carrier proteins allow facilitated diffusion/co-transport;
  5. Shape/charge of channel / carrier determines which substances move;
  6. Number of channels/carriers determines how much movement;
  7. Membrane surface area determines how much diffusion/movement;
  8. Cholesterol affects fluidity/rigidity/
    permeability;
52
Q

Transport methods - Give two similarities in the movement of substances by diffusion and by osmosis. (2)

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 me tabolism;
    OR
    Use energy from the solution;
53
Q

Transport methods - What two factors affect the rate of facilitated diffusion (2)

A
  1. (external) concentration
  2. number of channel / carrier proteins
54
Q

Transport methods - Suggest and explain two ways the cell-surface membranes of may be adapted to allow rapid transport of nutrients. (2)

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;
55
Q

Transport methods - Describe how substances move across cell-surface membranes by facilitated diffusion. (3)

A
  1. Carrier / channel protein;
  2. (Protein) specific / complementary to substance;
  3. Substance moves down concentration gradient;
56
Q

Transport methods - Contrast the processes of facilitated diffusion and active transport.
(3)

A
  1. Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins;
  2. Facilitated diffusion does not use ATP / is passive whereas active transport uses ATP;
  3. Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.
57
Q

Transport methods - Why does inhibiting
respiration/using cyanide prevent
active transport? (4)

A
  1. Oxygen is required for aerobic respiration which releases ATP
  2. ATP is needed to change the shape of the protein carrier
  3. Which would cause the release of the transported ion/molecule
  4. So no ATP, no Active Transport
58
Q

Req prac 3- How do we find water potential of
plant tissue practically? (3)

A
  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);
59
Q

Req prac 4 - Describe an experiment that you could do to investigate whether the mangrove root cells have a lower water potential than sea water.
You are given:
a piece of fresh mangrove root
* sea water
* access to laboratory equipment.

A
  1. Record mass/length before and after;
  2. Place in sea water for specified/equal time;
  3. Remove surface water;
  4. Increase in mass/length will show water has been absorbed by osmosis;
  5. Repeat minimum of three times;
60
Q

Req prac 4 - Give one way in which the student could ensure the first three beetroot cylinders were kept at 25 °C throughout her experiment. (1)

A

Measure temperature (in tube) at intervals and use appropriate corrective measure (if temperature has fluctuated)

61
Q

Req prac 4 - How does a high temperature disrupt membranes (2)

A

(By) 700C denaturing/altering membrane protein
OR
(By) 700C increasing fluidity/permeability of membrane;

62
Q

Req prac 4 - How does alcohol disrupt membranes
(1)

A

(By) ethanol dissolving phospholipid bilayer
OR
(By acid) altering membrane protein;

63
Q

Req prac 4 - Use your knowledge of membrane structure to explain how high temperature cause an increase in absorbance 1)

A

Higher absorbance indicates more pigment (released/in solution)
OR
Higher absorbance indicates more membrane damage/permeability

64
Q

Req prac 4 - Explain why it is important to control the volume of water in each test tube (1).

A
  1. (If) too much water the concentration of pigment (in solution) will be lower / solution will appear lighter / more light passes through (than expected);
    OR
    (If) too little water the concentration of pigment (in solution) will be greater / solution will appear darker / less light passes through (than expected);
  2. So results (from different temperatures) are comparable;

bio aqa a-level (5 decks)

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