RP 1-6 Flashcards

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1
Q

RP1: You used a buffer in your investigation. Explain why buffer solutions are used

A

Maintain constant pH

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2
Q

RP1: You left the test tubes in the water bath for 10 minutes before you added the enzyme to the milk powder solutions. Explain why you did this.

A

To equilibrate/reach temperature at which reaction will take place

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3
Q

RP1: Describe and explain what you did to make sure the temperatures of the water baths were as reliable as possible.

A
  1. Measure temperature of water bath at beginning and end of reaction period (as a minimum number of times);
  2. To assess the effect of any temperature changes during the reaction/to show that there was no/little variation in temperature;
    OR
  3. Measure temperature (several times) and add hot or cold water as appropriate;
  4. To try to keep the temperature close to that required;
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4
Q

RP1: Suggest a more appropriate control for this enzyme-controlled investigation.

A

Boiled trypsin; / Denatured enzymes.

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5
Q

RP1: It is difficult to decide when the solution of milk powder goes clear. Suggest one better way of determining when the solution of milk powder goes clear.

A
  • Use a colorimeter;
  • Record time taken to reach constant/set value (of absorbance / transmission)
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6
Q

RP1: How should the students make sure that the pH of the protease solution did not change?

A

Use buffer / test pH (at end / at intervals);

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7
Q

RP2: Describe how temporary mounts of plant tissue are made. [3]

A
  1. Thin slice/section;
  2. Put on slide in water / solution / stain;
  3. Add cover slip;
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8
Q

RP2: Describe how the scientist could have used the temporary mounts of leaves to determine the mean number of chloroplasts in mesophyll cells of a leaf. [3]

A
  1. Select large number of cells
  2. Select cells at random;
    Accept: > 5 for “large number”
    Accept: many fields of view for ‘large number of cells’
    Accept: all cells in field of view
  3. Count number of chloroplasts;
  4. Divide number of chloroplasts by number of cells;
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9
Q

RP2: The student cut thin sections of tissue to view with an optical microscope.

A
  1. To allow (more) light through; Accept: transparent
  2. A single / few layer(s) of cells to be viewed. Accept: (thin) for better / easier stain penetration
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10
Q

RP2: When the student was making their microscope slides, they were told to ensure they did not move the coverslip sideways. Explain why.

A
  1. To prevent cells from rolling on top of each other / to not damage the chromosomes
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11
Q

RP2: Mitosis is important in the life of an organism. Give two reasons why.

A
  1. Growth / increase in cell number;
    Ignore growth of cell
  2. Replace cells / repair tissue / organs / body;
    Ignore repair cells
    Reject bacteria
  3. Genetically identical cells;
    ‘Produces 2 genetically identical cells’ does not reach MP1 as well as MP3
  4. Asexual reproduction / cloning;
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12
Q

RP2: Explain why
(i) a root tip was used;

(ii) a stain was used;

(iii) the root tip was firmly squashed.

A

(i) where mitosis / division / growing / occurs
(reject growing cells)
(ii) to distinguish chromosomes / chromosomes not visible without stain;
(iii) to let light through / thin layer;

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13
Q

RP2: Define Mitotic index

A

Number of cells with visible or condensed chromosomes DIVIDED BY
Total number of cells (in the field of view)

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14
Q

RP2: Why is the mitotic index expressed as a decimal?

A

It is a proportion of cells within a sample.

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15
Q

RP2: Suggest why the student soaked the root tips in hydrochloric acid [2]

A
  1. To break down links between cells/cell walls OR
    To separate cells/cell walls OR To break down/hydrolyse cellulose/cell wall;

Ignore references to any bonds

  1. Allowing the stain to pass/diffuse into the cells OR Allowing the cells to be (more easily) squashed;
  2. To stop mitosis; Or To stop cell division/cell cycle
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16
Q

RP2: Other students in the class followed the same method, but calculated different mitotic indices. Apart from student errors, suggest two explanations why.

A
  1. (Garlic roots) are a different age OR (Garlic) grown in different conditions;

Accept suitable descriptions of conditions, eg in different temperatures

  1. (Root tips) from different (garlic) plants/bulbs/species;
  2. 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;

Accept ‘samples’ for ‘fields of view’

  1. (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)

  1. Cells/roots undergo mitosis/cell division at different times/rates;