RP 1-6 Flashcards
RP1: You used a buffer in your investigation. Explain why buffer solutions are used
Maintain constant pH
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.
To equilibrate/reach temperature at which reaction will take place
RP1: Describe and explain what you did to make sure the temperatures of the water baths were as reliable as possible.
- Measure temperature of water bath at beginning and end of reaction period (as a minimum number of times);
- To assess the effect of any temperature changes during the reaction/to show that there was no/little variation in temperature;
OR - Measure temperature (several times) and add hot or cold water as appropriate;
- To try to keep the temperature close to that required;
RP1: Suggest a more appropriate control for this enzyme-controlled investigation.
Boiled trypsin; / Denatured enzymes.
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.
- Use a colorimeter;
- Record time taken to reach constant/set value (of absorbance / transmission)
RP1: How should the students make sure that the pH of the protease solution did not change?
Use buffer / test pH (at end / at intervals);
RP2: Describe how temporary mounts of plant tissue are made. [3]
- Thin slice/section;
- Put on slide in water / solution / stain;
- Add cover slip;
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]
- Select large number of cells
- 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 - Count number of chloroplasts;
- Divide number of chloroplasts by number of cells;
RP2: The student cut thin sections of tissue to view with an optical microscope.
- To allow (more) light through; Accept: transparent
- A single / few layer(s) of cells to be viewed. Accept: (thin) for better / easier stain penetration
RP2: When the student was making their microscope slides, they were told to ensure they did not move the coverslip sideways. Explain why.
- To prevent cells from rolling on top of each other / to not damage the chromosomes
RP2: Mitosis is important in the life of an organism. Give two reasons why.
- Growth / increase in cell number;
Ignore growth of cell -
Replace cells / repair tissue / organs / body;
Ignore repair cells
Reject bacteria - Genetically identical cells;
‘Produces 2 genetically identical cells’ does not reach MP1 as well as MP3 - Asexual reproduction / cloning;
RP2: Explain why
(i) a root tip was used;
(ii) a stain was used;
(iii) the root tip was firmly squashed.
(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;
RP2: Define Mitotic index
Number of cells with visible or condensed chromosomes DIVIDED BY
Total number of cells (in the field of view)
RP2: Why is the mitotic index expressed as a decimal?
It is a proportion of cells within a sample.
RP2: Suggest why the student soaked the root tips in hydrochloric acid [2]
- 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
- Allowing the stain to pass/diffuse into the cells OR Allowing the cells to be (more easily) squashed;
- To stop mitosis; Or To stop cell division/cell cycle