EXPERIMENT QUESTIONS
1. (a) TEST FOR REDUCING SUGAR:
FOOD SOURCE: Glucose (monosaccharide)
CHEMICAL USED: Benedict’s solution (blue)
HEAT REQUIRED: Yes (thermostatically controlled water bath)
+ RESULT: Colour change BLUE to BRICK RED
- RESULT: No colour change (stays blue)
CONTROL: Water + Benedict’s (non-reducing sugar)
PURPOSE OF CONTROL: Acts as a comparison
1. (b) TEST FOR STARCH:
FOOD SOURCE: Potato/ Bread
CHEMICAL USED: Iodine (red/yellow), using a dropper due to small volume needed
HEAT REQUIRED: No
+ RESULT: Colour change RED/ YELLOW to BLUE/BLACK
- RESULT: No colour change (stays red/yellow)
CONTROL: Water and Iodine
1. (c) TEST FOR FAT:
FOOD SOURCE: Oil/ Butter
MATERIALS USED: Brown paper
+ RESULT: Permanent translucent stain
- RESULT: No (translucent) stain
CONTROL: Water + Brown paper
1. (d) TEST FOR PROTEIN:
FOOD SOURCE: Milk/ Egg white
CHEMICALS USED/ TEST NAME: Sodium hydroxide & copper sulphate OR Biuret Reagent
HEAT REQUIRED: No
+ RESULT: Colour change BLUE to VIOLET
- RESULT: No colour change (stays blue)
CONTROL: Water + Biuret
ECOLOGY (FIELD STUDY- GRASSLAND)
Identify 5 plants and 5 animals 🡪 use identification key
IDENTIFY ADAPTATION, AND BENEFIT OF ADAPTATION TO PLANT/ANIMAL
Collect and identify plants 🡪 break /cut off sample
Collect and identify animal’s 🡪 pooter, sweep net, beating tray & pitfall trap
Quantitative study of PLANTS – using quadrat
% FREQUENCY—the chance of finding a species in an area
No. of quadrats with organism present X 100
No. of quadrats thrown 1
% COVER - area of ground occupied by organisms
No. of hits X 100
No. of possible hits 1
POPULATION DENSITY
Average number of organisms in 10 quadrats
Express organism per m2 by multiplying average by area of quadrat
LINE TRANSECT
Distribution of plants at different interval along the line—graph results
SOURCES OF ERROR
Limited sample size
Human error 🡪 miscount organisms or misidentification
Small sample size (faulty equipment)
Quantitative study of ANIMALS 🡪 Capture recapture method
POPULATION SIZE
No. caught & marked 1st visit X No. caught on 2nd visit
No. marked on 2nd visit
THREE ABIOTIC FACTORS (non-living factors)
TEMPERATURE 🡪 use thermometer
pH 🡪 use pH meter
LIGHT INTENSITY 🡪 use light meter
6 and 7. (a) (b) PREPARE ANIMAL AND PLANT CELLS:
Be familiar with the use of a light microscope
TRANSFER CELLS TO SLIDE:
PLANT CELLS: Thin layer of cells, removed using a tweezers
STAIN USED: Iodine
ANIMAL CELLS: Swab inside of cheek using a cotton bud
STAIN USED: Methylene blue
NOTE: First prepare tissue unstained
HOW USE STAIN: Dropper
WHY USE A STAIN: Allows cell parts to be seen more clearly (nucleus)
USE OF COVER SLIP: Prevent tissue drying out or to avoid damage to lens
COVER SLIP @ 45o ANGLE: To eliminate air bubbles (slowly lowered)
HOW ALTER LIGHT: Adjust diaphragm or condenser/ mirror/ light source
WHY ALTER LIGHT: To achieve the sharpest image
EXAMINATION OF CELLS: Focus using coarse focus first (lowest magnification) then using medium power and fine focus
RESULTS: Can clearly identify nucleus, cytoplasm, cell membrane
8 and 9. ENZYME EXPERIMENTS:
ENZYME USED: Catalase SOURCE: Celery
SUBSTRATE USED: Hydrogen Peroxide, H2O2
PRODUCTS FORMED: Water and oxygen
VARYING FACTORS:
pH 🡪 Use different pH buffers (4, 7, 9 AND 13)
Temperature 🡪 Use different thermostatically controlled water baths (0, 10, 20, 60 oC)
FACTORS KEPT CONSTANT:
pH HOW: pH buffer solution
Temperature HOW: Water bath (thermostatically controlled)
Enzyme concentration HOW: Same volume of enzyme used each time
Substrate concentration HOW: Same volume of substrate used each time
WHY USE WASHING UP LIQUID: Traps the oxygen released forming foam
HOW IS RATE OF ENZYME ACTIVITY MEASURED?: By measuring the volume of foam produced per minute
CONTROL: No enzyme (catalase)
10. IMMOBILISED ENZYMES:
ENZYME TO BE IMMOBILISED : Sucrase SOURCE : Yeast
FUNCTION OF SODIUM ALGINATE: Gel used to trap the enzyme
FUNCTION OF CALCIUM CHLORIDE: Hardens beads (insoluble)
SYRINGE HELD ABOVE CALCIUM CHLORIDE: To prevent clumping of beads
APPLICATION: To compare ability of free yeast (CONTROL) and immobilised yeast to convert sucrose to glucose
RESULT:
Free yeast coverts sucrose to glucose faster than the immobilised enzymes
Product of free enzymes is cloudy due to the enzymes being mixed up with the substrate
HIGHER LEVEL ONLY
11. EFFECT OF HEAT DENATURATION ON CATALASE ACTIVITY
Catalase and Hydrogen peroxide again
BOILING THE ENZYME: Denatures the catalase (60 oC)
CONTROL: Un-boiled catalase
RESULT: No foam produced (no enzyme activity) in the boiled enzyme
12. LIGHT INTENSITY ON RATE OF PHOTOSYNTHESIS
PLANT USED: Elodea (Pond weed)
WHY THIS PLANT?: Produces bubbles of gas that are easily seen
FACTOR VARIED: Light
HOW: By moving the lamp different distances from the Elodea (or vary lamp watt)
FACTORS KEPT CONSTANT:
Carbon dioxide HOW: By adding sodium bicarbonate to water
Temperature HOW: Use thermostatically controlled water bath (25oC)
HOW IS RATE OF PHOTOSYNTHESIS MEASURED?: By counting the amount of oxygen bubbles produced per minute
RESULTS: Increased light intensity increases the rate of photosynthesis
GRAPH: As light intensity increase so too does the rate of photosynthesis (light saturated)
13. PRODUCTION OF ALCOHOL BY YEAST:
PRODUCE ANAEROBIC CONDITIONS: Boil solution and cover with layer of oil
PRODUCTS: Alcohol and carbon dioxide
CO2 PRODUCED: Turns limewater milky
TEST FOR ALCOHOL:
Iodoform test 🡪 potassium iodide and hypochlorite solution 🡪 yellow crystals
Heat sample and test with potassium dichromate 🡪 Orange to green in presence of alcohol
TEMP. 30oC: Thermostatically controlled water bath as enzyme sensitive to temperature changes
CONTROL: Same apparatus used WITHOUT ADDING ANY YEAST (or adding boiled yeast 🡪 no bubbles form and limewaterr remains clear)
14. OSMOSIS:
MATERIALS USED : Visking tubing (acts as a semi permeable membrane)
WHY IS VISKING TUBING PLACED IN WATER BEFORE EXP?: To soften
RESULTS: Tube containing sucrose solution gains mass and becomes fuller due to movement of water molecules by osmosis
CONTROL: Water 🡪 No change in mass
15. DNA EXTRACTION:
SOURCE OF DNA: Kiwi or onion
CHOPPED: To break up cell walls/ membranes 🡪 increase surface area
WASHING UP LIQUID: Cause cell membrane to break 🡪 releasing the DNA
SALT (SODIUM CHLORIDE): Causes DNA to clump together
TEMP 60oC: Inactivates enzymes that breakdown protein in DNA
ICE BATH: Slows down enzyme activity 🡪 the breakdown of DNA
BLEND FOR ONLY 3 secs: Breaks cell walls, any longer than 3 seconds the DNA strands would be also broken
FILTER: Coffee filter paper used, speeds up process as normal filter paper pores are too small. Cell parts (kiwi debris) retained in filter paper. Filtrate DNA and protein
PROTEASE: Enzyme that breaks down protein surrounding the DNA
CONTACT LENS SOLUTION ETC.: Also contain enzymes that break down proteins
FREEZER/ ICE COLD ETHANOL SLOWLY ADDED DOWN THE SIDE OF THE BOILING TUBE: Causes DNA to precipitate at alcohol/filtrate interface, as DNA is insoluble in ice cold alcohol 🡪 DNA becomes visible
RESULT: Clear mesh of DNA 🡪 looks like stringy mucous
16. GROWTH OF LEAF YEAST:
SOURCE OF YEAST: Sycamore leaf (correct time or year, little handling, dry weather)
FUNCTION OF AGAR: Source of nutrient
ASEPTIC/ STERILE CONDITIONS: Wash hands or disinfect worktop or sterilise equipment or keep all containers closed where possible or use Parafilm or open agar plate over the shortest distance for the shortest period of time or heating forceps in flame
ATTACH LEAF TO LID OF PETRI DISH: Use Vaseline
LOWER SURFACE OF LEAF FACING DOWN: More micro- organisms on lower surface of leaf than upper
NUTRIENT AGAR PLATES: Contain all nutrients needed for micro-organisms to grow (malt agar can also be used)
SEAL DISHES WITH PARAFILM: Prevent them from opening accidentally
LABEL UNDERSURFACE OF DISH: Can identify dishes without blocking view of agar surface
LEAVE RIGHT SIDE UP FOR 24 HRS BEFORE INCUBATING: In order for yeast spores to fall onto agar
INCUBATE UPSIDE DOWN: @ 15-30 oC for 2-7 days. Upside down also prevents condensation on lids
RESULT: Pink colonies seen growing on agar
NO COLONIES: Leaf yeast affected by air pollution, if leaf from polluted area there will be few or no colonies on agar
CONTROL: Set up dish with no leaf OR wash leaf in Dettol or alcohol to kill leaf yeast
MORE PLENTIFUL: July to March More leaves or more suitable temperature or more reproduction
17. PREPARE DICOT STEM:
PLANTS USED: Geranium
HOW PREPARE: Cut a thin section, added water (add stain)
USING BLADE: Cut away from yourself to prevent injury
SAMPLE IN WATER: To prevent cells from drying out
STAIN: Iodine, to see cells more clearly
COVER SLIP @ 45o ANGLE: To eliminate air bubbles
WHY USE A COVER SLIP: To prevent cells from drying out/ to protect the lens / to make it easier to see/ to keep sample in place
HERBACEOUS STEM: Rather than a woody stem as it is easier to cut
STEM CUT BETWEEN TWO NODES: To ensure vascular tissue has formed
18. DISSECTION OF HEART:
TO DISTINGUISH FRONT OF HEART FORM BACK: Front (ventral) of heart is more rounded than the back (dorsal) which is flat. The front has a coronary artery running from the left hand side to the right hand side
IDENTIFY: 4 major blood vessels of the heart (Aorta, Vena cava, Pulmonary Artery and Pulmonary Vein)
IDENTIFY LEFT VENTRICLE: Left hand side feels thicker than the right
2 CUTS ALONG THE FRONT OF THE HEART: Scalpel
FIRST INCISION: Top right atrium down to the right ventricle
SECOND INCISION: Top left atrium down to the left ventricle
IDENTIFY: Top two atriums, Bottom two ventricles, Bicuspid valve (between the left atrium and left ventricle), Tricuspid valve (between the right atrium and right ventricle) and Two semilunar valves (Pulmonary artery and Aorta) 🡪 Scalpel
19. (a) EXERCISE & PULSE RATE
LOCATE PULSE: Wrist or neck
RESTING RATE: Count the number of beats per minute while resting (3 times and get an average) 🡪 Control
EXERCISE 1: Walk slowly for 2 minutes and count pulse rate immediately after. Repeat until resting rate reached.
EXERCISE 2: Jog for 2 minutes and count pulse rate immediately after. Repeat until resting rate reached.
EXERCISE 3: Vigorous exercise for 2 minutes and count pulse rate immediately after. Repeat until resting rate reached.
CONTROL: Resting rate (before exercise)
MEASURE REVOVERY TIME: Immediately after exercise count pulse rate per minute until resting rate reached
20. EFFECT OF IAA:
GROWTH REGULATOR USE: IAA (indole acetic acid)
SERIAL DILUTIONS: To form different concentrations of IAA
ACETATE GRIDS: Used to help when measuring root and shoot length
5 RADISH SEEDS: Allows for non-germination of some seeds
DISHES INCUBATED ON THEIR SIDES FOR TWO DAYS: To ensure roots grow down and shoots grow up
CONTROL: No IAA, only distilled water in one of the petri dishes
RESULTS: IAA causes root and shoot growth
High IAA concentration stimulates shoot growth
Low IAA concentration stimulates root growth
21. FACTOR THAT AFFECT GERMINATION:
TO REMOVE WATER: Dry cotton wool
TO REMOVE TEMPERATURE: Place apparatus in fridge
TO REMOVE OXYGEN: (anaerobic conditions) Boil water and layer of oil OR Anaerobic jar
MORE THAN ONE CRESS/RADISH SEED USED (10): To allow for the non-germination of seeds
DETERMINE GERMINATION: Growth of radicle or plumule
RESULTS: Only seeds that have all conditions oxygen, water & temperature grow (germinate) 🡪 CONTROL
22. TO SHOW DIGESTIVE ACTIVITY DURING GERMINATION:
ENZYME IN SEED: Amylase
SOAK BEANS IN WATER: start-up the germination process or soften the test or bring them out of dormancy
WASH BENCH/SEEDS IN DISINFECTANT (Milton🡪 DISINFECTANT): To kill micro-organisms
ASEPTIC TECHNIQUES: Flaming forceps etc.: To prevent micro-organisms from entering
STARCH AGAR: Looking at action of amylase in seeds on starch
CUT BEANS IN HALF & FACE DOWN ON AGAR: To allow enzymes formed in the germinating seed to act on the starch 🡪 Enzymes are exposed to the substrate
TESTING PLATES WITH IODINE: Test for starch, areas of starch go blue/ black
RESULTS: Area under the bean is clear 🡪 no starch present as the enzyme amylase has broken down the starch under the bean. The rest of the plate is blue/ black
CONTROL: Boiled seeds 🡪 this kills them (dead seeds), no enzyme action (become denatured) therefore all the agar plate goes blue/black, no clear areas