Required Practicals

Question 1

What is the independent variable in an enzyme-controlled reaction investigation?

Answer 1

• Enzyme concentration
• Substrate concentration
• pH
• Temperature
• Inhibitors

The independent variable is the one that is manipulated to observe its effect on the rate of reaction.

Question 2

What are some methods to measure the dependent variable in an enzyme-controlled reaction?

Answer 2

• Colour change (colorimetry)
• Mass of substrate or product
• Bubble formation (if substrate is a gas)

The dependent variable is the rate of reaction, which can be measured in various ways.

Question 3

What is the best way to control temperature in an enzyme investigation?

Answer 3

Use a thermostatically controlled water bath

Regular checks with a thermometer are necessary as temperature can fluctuate.

Question 4

What is a buffer in the context of enzyme investigations?

Answer 4

A solution that resists changes in pH

Buffers help maintain a stable pH during the experiment.

Question 5

In enzyme investigations, what should be controlled to ensure accurate results?

Answer 5

• Temperature
• pH
• Concentrations (of substrate, enzyme, or inhibitors)

Only one independent variable should be manipulated while controlling others.

Question 6

What is the purpose of a control in enzyme experiments?

Answer 6

To ensure that the measured effect is due to the enzyme

A control can be a denatured enzyme or no enzyme at all.

Question 7

True or false: In enzyme investigations, it is acceptable to have multiple independent variables.

Answer 7

FALSE

Only one independent variable should be manipulated to isolate its effect.

Question 8

What is the best chance of seeing cells in stages of mitosis?

Answer 8

Examine actively growing plant tissue

This includes root tips or shoot tips, usually from growing onion or garlic roots.

Question 9

What is the purpose of staining biological specimens?

Answer 9

To make cells visible under a microscope

Staining is necessary as almost all biological specimens are not visible without it.

Question 10

What does hydrochloric acid do in the preparation of stained squashes?

Answer 10

Weakens the cellulose walls of plant cells

This allows the stain to penetrate the cells and helps in squashing the tissue to one cell thick.

Question 11

Why must the preparation be only one cell thick?

Answer 11

• Light can pass through the sample
• Chromosomes of one cell can be clearly seen

This prevents overlapping of cells that could obscure visibility.

Question 12

Define mitotic index.

Answer 12

Ratio of the number of cells in mitosis to the total number of cells

It is calculated as: Cells in mitosis / Total number of cells.

Question 13

Calculate the mitotic index given the following: 20 cells in mitosis and 55 cells without visible chromosomes.

Answer 13

0.267

Calculation: 20 ÷ (20 + 55) = 0.267.

Question 14

What is the cell-cycle phase where genetic material is present as chromatin?

Answer 14

Interphase

Individual chromosomes are not visible during this phase.

Question 15

What type of cells are typically used for observing mitosis in plant tissues?

Answer 15

• Onion root tips
• Garlic root tips

These tissues are actively growing, providing the best chance to observe mitosis.

Question 16

What is the purpose of producing a dilution series of a solute?

Answer 16

To produce a calibration curve for identifying the water potential of plant tissue

This involves placing cylinders of potato or carrot in solutions of different concentrations, usually overnight.

Question 17

What happens to potato cells in a dilute solution?

Answer 17

• Water moves IN by osmosis
• Potato cells become turgid
• Potato cores increase in mass/length

This occurs because the water potential of the solution is higher than that of the potato cells.

Question 18

What happens to potato cells in a concentrated solution?

Answer 18

• Water moves OUT by osmosis
• Potato cells become plasmolysed
• Potato cores decrease in mass/length

This occurs because the water potential of the solution is lower than that of the potato cells.

Question 19

When does no net movement of water occur in potato cells?

Answer 19

When the water potential of the potato cells is the same as the water potential of the solution

At this point, there is no change in mass.

Question 20

What does a plateau in the graph indicate regarding potato cells?

Answer 20

• Cells are becoming turgid (full of water)
• Cells are becoming plasmolysed (lost most of their water)

The plateau reflects the balance of water movement in and out of the cells.

Question 21

What is the relationship between the water potential of the solution and potato tissue when there is an increase in mass?

Answer 21

Water potential of the solution is greater than the water potential of potato tissue

This leads to water moving in by osmosis.

Question 22

What is the relationship between the water potential of the solution and potato tissue when there is a decrease in mass?

Answer 22

Water potential of potato tissue is greater than the water potential of the solution

This leads to water moving out by osmosis.

Question 23

If a ratio is used instead of percentage, what does a ratio of 1.0 indicate?

Answer 23

The concentration at which the solution has the same water potential as the potato tissue

This indicates equilibrium between the solution and the potato cells.