bio practical

Question 1

iodine test

Answer 1

Use (x) drops of iodine on experimental area

If iodine is present: yellowish brown > blue-black
Iodine absent: remains yellowing brown

Question 2

test for reducing sugars

Answer 2

2 cm of solution + 2cm benedicts solution
Soak in water bath until colour does not change further / for 5 mins

Solution Remains Blue : No Reducing Sugars
Blue > Green : Traces Of Reducing Sugars
Blue > Yellow/Orange ppt. : Moderate Amount Of Reducing Sugars
Blue > Brick-red ppt. : Large Amount Of Reducing Sugars

Question 3

non reducing sugars

Answer 3

sucrose and polysaccharides

Question 4

test for proteins

Answer 4

Use equal volume of biuret reagent in a test tube of sample

If solution turns violet, proteins are present.
solution remains blue, proteins are absent.

Question 5

test for fats

Answer 5

ethanol emulsion

Sample + Ethanol + Water (In this order!)

2 immiscible layers formed, cloudy white emulsion/suspension forms at top of solution, fats are present
solution remains clear, fats are absent

Question 6

Sodium hydrogencarbonate (NaHCO₃) purpose

Answer 6

supplies CO2

Question 7

Soda-lime/Potassium hydroxide purpose

Answer 7

removes CO2

Question 8

graph drawing axis reminders

Answer 8

Remember the d.p. of the scale units!!
Fully label the axes!!

Question 9

graph drawing

Answer 9

Mostly don’t extend the curve beyond the points given

Question 10

organelles that can be seen under light microscope

Answer 10

nucleus, cytoplasm, cell membrane, chloroplasts and cell wall

Question 11

cutting specimen

Answer 11

eg, longitudinal, transverse, cross-sectioned, etc. TRANSVERSE MEANS CROSS SECTION

Question 12

planning question

Answer 12

1. state variables: 1 independent, 1 dependent, 3 constant
2. apparatus used
   - procedure
   - control experiment + purpose
   - outcomes
   - - Reliability/Accuracy: repeat and obtain average results

Question 13

plants test for photosynthesis reminder

Answer 13

keep in dark for eg 12h to destarch the plant

Question 14

hazard of procedure

Answer 14

acid/base- corrosive substance // wear safety goggles to prevent splashes into eye

Question 15

magnification calc

Answer 15

Drawing/Actual (1 d.p.)

Question 16

sample drawing

Answer 16

• as accurately and as detailed as possible
• Dotted line along both ends of the longest axis, draw line between them and write measurement
• Measure sample along same transect

Question 17

experimental errors : bubble counting

Answer 17

• Size of bubbles may vary, volume of gas produced will not proportional to the number of gas bubbles observed

Improve: Collect volume of gas produced

Question 18

experimental errors : colour change

Answer 18

Subjectivity, different people may perceive the change differently. Eg. ppl perceive diff colourless, stop watch at diff times

Improve: Compare to standards (eg tube of water for colourless, use colourimeter

Question 19

experimental errors : temp not maintained

Answer 19

• Will interfere with results (Especially with experiments dealing with enzymes, rate of reaction, etc.)

Improve: Use a thermostatically controlled water bath/keep checking temp of the water with thermometer, add more hot/cold water when needed

Question 20

dp reminders

Answer 20

Magnification = 1 d.p. (dp of instrument used)
Temperature (°C) = 1 d.p.
Mass (g) = 2 d.p. (e.g. 0.01g, 5.83g, etc.)

Question 21

ensuring accuracy: reading volume

Answer 21

Reading meniscus at eye level: reduce parallax error

Question 22

ensuring accuracy: syringe air bubbles

Answer 22

Ensure no air bubbles in syringe : tapping syringe barrel then slowly pushing the piston to to release the bubbles

Question 23

ensuring accuracy: apparatus contamination

Answer 23

Wash syringes with distilled water before using it to measure and transfer another solution

Question 24

outliers when calculating mean

Answer 24

Anomalous results/ outliers should not be used to calculate the mean → injaccurate results

Question 25

yeast reminder

Answer 25

glucose is simple sugar, most easily metabolised by yeast cells. Has enzymes to break down sucrose into glucose (sucrose), but not lactase for lactose.

glucose –> ethanol, co2

Question 25

yeast reminder

Answer 25

glucose is simple sugar, most easily metabolised by yeast cells. Has enzymes to break down sucrose into glucose (sucrose), but not lactase for lactose.

glucose –> ethanol, co2

Question 26

co2 reminder

Answer 26

remember it forms a weak acid when dissolved in water - carbonic acid (pH change)

Question 27

apparatus accuracy

Answer 27

Use of 1cm3 syringe instead of 10cm3 (not precise enough to measure small quantities)
Use burette/micropipette

Question 28

experimental error: using a lamp

Answer 28

using a lamp: not the only source of light in the lab - rate of psis faster than actual → inaccurate (incr LI → incr psis)

Question 29

Why stain cells?

Answer 29

Stain to enhance clarity of cells when viewed under a light microscope

Question 30

Why calculate % of a cell plasmolysed?

Answer 30

Cells are of diff sizes, a percentage is more accurate

Question 31

control setups

Answer 31

— acts as a control setup / provides basis of comparison
Shows (whatever change the experiment brings about eg. shows that iodine turns blue-black w starch)

Question 32

h2o2 reminder

Answer 32

h2o2 decomposes spontaneously when left in booking tube
Store in low temps/ cover beaker with al foil abd pour only when exp start

Question 33

incr reliability

Answer 33

take another set of readings, average them

Question 34

starch reminder

Answer 34

starch suitable storage - larger molecule (cannot diffuse thru cell membrane, hence retain in cell); easily hydrolysed back into glucose when required; insoluble in water (does not change water potential);