Experiments

Question 1

To test a food for starch

Answer 1

IODINE
- turns yellow/red to blue/black

Note : use test tube of water as control

Question 2

To test a food for fat

Answer 2

BROWN PAPER

Fat is present if a permanent translucent stain is present

Question 3

To test for reducing sugar (glucose)

Answer 3

BENEDICTS SOLUTION

• add sucrose to water +dissolve
• apply HEAT but do not boil

Blue to brick red

Question 4

To test a food for protein

Answer 4

BIURET TEST
sodium hydroxide
+ copper sulphate
- blue to purple

Question 5

To prepare a plant cell (onion)

Answer 5

• forceps: thin, transparent epidermis
• add iodine stain
• drop water : prevent drying out
• coverslip at 45^ angle to eliminate air bubbles

Question 6

To prepare an animal cell (cheek cell)

Answer 6

• cotton bud: collect cheek cells
• spread on glass slide
  Methylene blue: stains nucleus deep blue
• water: prevents drying out
• lower coverslip at angle to avoid bubbles

Question 7

Steps involved in using a microscope

Answer 7

1: slide on stage + clip in place
2: switch on light source
3: use COARSE FOCUS KNOB to bring LOW POWER OBJECTIVE LENS into focus
4 use FINE FOCUS KNOB for HIGH POWER OBJECTIVE LENS

Question 8

To demonstrate action of osmosis

Answer 8

VISKING TUBING: selectively permeable membrane

- sucrose and water gained in mass and fullness. Water entered visking tubing due to osmosis

Question 9

Enzyme activity experiments
Enzyme
Substrate
Product

Answer 9

Catalase (liver and celery)
Hydrogen peroxide
Water and oxygen

Question 10

To investigate the effects of pH on the rate of Catalase activity

Answer 10

• pH buffer and washing up liquid (traps oxygen released-forms foam)
• blend celery + add water + filter solution
• hydrogen peroxide (substrate) to beaker
• water bath at 25^ C
• add HP to catalase solution
• note and record volume of foam after 2 mins

pH 9 was OPTIMUM

Question 11

To investigate the effect of temperature on the rate of catalase activity (enzyme activity)

Answer 11

• ph buffer 9, blended celery
• hydrogen peroxide (substrate) in different temp water bath
• pour in together
• add washing up liquid - shows foam
• note and record level of foam after 2 mins

20-30^C is OPTIMUM TEMPERATURE

Question 12

Effect of heat denaturation on catalase activity

Answer 12

• pH buffer 9, blended celery
• boil 1/2 solution for 10 mins
• unboiled catalase = control
• hydrogen peroxide to beaker
• water bath of 25^ C
• add washing up liquid
  BOILED = NO FROTH as DENATURED
  unboiled = froth

Question 13

To investigate the influence of light intensity on the rate of photosynthesis

Answer 13

• ELODEA: water plant : can see bubbles of O2 from photosynthesis
• SODIUM BICARBONATE in excess: constant supply of CO2
• water bath - temperature stays constant
• cut elodea at angle
• buffer solution pH 7 - maintains pH
• allow to stabilise , then count O2 bubbles
• move lamp closer - increase light intensity - bubble production increases

Question 14

Prepare and examine a transverse section of a dicot stem

Answer 14

BEGONIA: non woody herbaceous- easier to cut

• use scalpel to cut section of stem
• wet blade (reduces friction) thin section (allows light through) , cut at right angle
• store on clock glass w water - hydration
• cover slip at angle - no bubbles

Iodine if need more visible

Question 15

Why use a coverslip ?

Answer 15

To protect lens

Question 16

Investigate the effect of exercise on the pulse rate of a human

Answer 16

• strong pulse : neck or wrist
• count number of pulses per minutes 5 time to get average (control)
• exercise strenuously for 4 mins and count pulse rate for minute until return to resting.

Fitter person = lower heartbeat , and returns to normal faster after exercise