Practical

Question 1

how to control temperature

Answer 1

• use a water bath
• use a thermostatically controlled water bath rather than a beaker of water

Question 2

how to control pH

Answer 2

• use buffer solution

Question 3

error

Answer 3

potential error in a measurement is half the value of the smallest division on the scale

error = smallest division / 2

Question 4

% error

Answer 4

(measured value - actual value/ actual value) x 100

Question 5

constructing a table

Answer 5

1) draw table with ruled columns
2) include headings with units
3) independent variable comes first
4) use the same no. of s.f./d.p. everywhere

Question 6

constructing a line graph

Answer 6

1) independent variable → x-axis

2) dependent variable → y-axis

3) graph should be more than half of grid

4) use x or ◉ when plotting points

5) don’t extrapolate unless mentioned

Question 7

systemic errors

Answer 7

errors caused by lack of accuracy and precision

• same in size, act in the same direction on all readings

Question 8

random errors

Answer 8

result from difficulties in controlling standardised or dependent variables

• likely to be different for different stages of investigation

Question 9

methods to increase reliability

Answer 9

1) increase number of samples
2) repeat and take the average
3) exclude anomalous results
4) wide range of temperature/pH/etc

Question 10

improvements in measurement

Answer 10

measure volumes using a burette or a graduated pipette

Question 11

improvements in recording colour change

Answer 11

use colorimeter

Question 12

improvements in the syringe experiment

Answer 12

• use wide mouthed test tube

Question 13

testing non-reducing sugars

Answer 13

1) add 2cm³ food sample to test tube
2) add 1cm³ HCl
3) boil for 1 min
4) allow tube to cool
5) add alkali to neutralise
6) add equal volumes of benedict’s reagent and heat in a water bath at 80°C until colour changes are observed

Question 14

precautions in osmosis experiments

Answer 14

1) cover petri dish to prevent evaporation
2) separate droppers
3) avoid air bubbles
4) completely immerse tissue in solution

Question 15

biuret test without biuret reagent

Answer 15

1) 1 cm³ sample + KOH
2) few drops of CuSO₄

Question 16

Emulsion test for lipids

Answer 16

Shake sample with ethanol, add water. If lipids are present solution turns into a cloudy white suspension

Question 17

Test for starch

Answer 17

add drops of iodine solution to the sample, if a blue black colour is quickly produced, starch is present, if not, iodine solution remains yellow-brown

Question 18

test for reducing sugars

Answer 18

add equal volumes of sample and Benedict’s reagent, heat in a water bath at 80°C
colour changes from blue, green, yellow, orange, brick red ppt

Question 19

how you would modify this procedure to investigate the effect of temperature on rate of enzyme activity

Answer 19

1) use thermostatically controlled water-baths at different temperatures;
2 state at least five different temperatures between 0 °C and 100 °C ;

Question 20

Ways to increase reliability of study

Answer 20

1) use a wider/narrower range of concentrations (depending on questions);
2) use at least five more concentrations;
3) use a method to ensure controlled variables are maintained;
4) run experiments one at a time / stagger the start times;
5) repeat measurements for each concentration and calculate the mean ;

Question 21

How to determine the level of risk of experiment? (Low, medium, high)

Answer 21

The risk level is higher if there are:
1) Harmful chemicals (harmful/ irritant)
2) Heat
3) sharp objects

Question 22

The differences between normal plant and xerophytes (plants that live in very dry environment)

Answer 22

1) sunken stomata
2) Curled leaf
3) Trichomes (Hairy-like structure; Function is to trap a layer of water vapour and reduces the water potential gradient)
4) Thick waxy cuticle / thick layer of cell wall

Question 23

Drawing a large plan diagram of plants

Answer 23

1) Use the 10x objective lens
2) uses most of the available space, at least two layers of tissue, no shading ;
3) draws part of plant organ and no individual cells ;
4) draws correct shape of plant organ ;
5) shows subdivision of the vascular tissue ;
6) label line and label to identify the tissue instructed in the question;

Question 24

Serial dilution

Answer 24

1) correct percentage concentration (labels under correct sequence of beakers) and,% / percentage, once ;
2) shows transfer of 10 (cm3) from first beaker to second beaker and 1 (cm3) from second beaker to third beaker and 1 (cm3) from third beaker to fourth beaker ;
3) shows 10 (cm3) of water added to second, third, and fourth beakers

Question 25

Drawing a few plant cells

Answer 25

1) Use the x40 objective lens.
2) Your drawings must be:
- appropriate size of cells to fill most of space available and lines thin and continuous ;
- draws only the number of cells instructed and each cell touching at least two of the other cells ;
- two lines drawn around each cell and three lines where cells touch ;
- correct shape of cells ;
- label line and label to identify the [structure as per -instructed] of one of the cells ;

Question 26

1 mm = ___ um (micrometer)

Answer 26

1000 um