iGCSE Biology Paper 6 Alternative to Practical flashcard

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[start]

[q] Food Tests

Test for starch:

Get the food sample and crush it in a mortar with water.
Put the sample in a test tube
Add drops of iodine solution
Observe color change from brown to black showing presence of starch

[a] Food Tests

Test for proteins:

Get the food sample and crush it in a mortar with water
Put the sample in a test tube
Add drops of iodine solution
Observe color change from blue to purple showing presence of proteins

[q] Food Tests

Test for reducing sugars:

Get the food sample and crush it in a mortar with water
Put the sample in atest tube
Add Benedict’s solution
Put the test tube in boiling water bath to avoid splashing
Observe color change from blue to brick red showing the presence of reducing sugars

[a] Food Tests

Test for fats “emulsion test”:

Crush the food sample in a mortar with ethanol
Take a sample in a test tube
Add drops of distilled water
Observe turbidity showing the presence of fats

[q] Food Tests

Test for vitamin C “indicator of pH”:

Normally DCPIP has blue color but it becomes colorless when acid is added to it
The number of drops consumed to decolorize the DCPIP indicates the concentration of vitamin C in the solution used (ex:lemon juice)

IF THE SAMPLE IS POWDER DISSOLVE IN WATER
IF THE SAMPLE IS LIQUID DON’T CRUSH

[a] ENZYMES

Describe an experiment that shows the effect of temperature on the activity on amylase.

Get 3 test tubes with equal volume and concentration of amylase enzyme
Add a buffer to each test tube to keep the pH constant
Set 3 water baths at 10°C, 30°C and 50°C
Put atest tube of starch and amylase in each water bath
Leave the test tubes 5 minutes for temperature equilibration
Add amylase to starch in each test tube
Every minute take a sample from each mixture and test with iodine solution on white tile
Record the time when there is no change in color
Repeat the experiment 3 more times and take average

[q] ENZYMES

Make an experiment to show the effect of pH on catalase enzyme in potato extract.

Get potato extract and dip in it filter papers of the same size, mass
Get three test tubes with equal volume and concentration of hydrogen peroxide and put them in thermostatic water bath at 40°C to keep temperature optimum and constant
To the first test tube add acidic solution, to the second add neutral solution, to the third add alkaline solution
Put a filter paper in the first test tube, allow it to sink and record the time taken for the filter paper to rise
Repeat with the other test tubes
The time taken, the more the suitable pH
Make acontrol
Repeat the experiment 2 more times and take average
Put your results inatable and plot a graph

[a] RESPIRATION

How can you measure the amount of energy in food?

Get a boiling tube and put in it 25 cm3 of water
Use athermometer to measure the initial temperature
Attach a piece of food to a mounted needle and put on fire
Place the burning sample below the boiling tube until it is completely burnt
Stir and measure the final temperature
Calculate the rise in temperature “final_initial”
Repeat the experiment 2 more times with same mass of food and same volume of water and take average

[q] RESPIRATION

How to measure the rate of respiration in yeast.

Get a boiling tube and pour in it 10 cm3 of glucose solution
Add 10 cm3 of yeast solution to the glucose solution
Place abung on the top of the boiling tube
Pour 20 cm3 of water in another boiling tube
Connect both tubes with a delivery tube
Place the apparatus in a thermostatic water bath to keep the temperature constant and optimum
leave the apparatus 1 minute for temperature equilibration
Start the timer
Count the number of bubbles evolved
After 4 minutes stop the timer
Find the rate of respiration= number of bubbles/min
Repeat the experiment 2 more times and take average
Exclude anomalous results
Make acontrol using boiled yeast

[a] RESPIRATION

Why the experiment was inaccurate?

1. Bubbles have different sizes
2. Difficult to count the bubbles

[q] RESPIRATION

How to make it more accurate?

By measuring the volume of carbon dioxide gas produced using a gas syringe or graduated measuring cylinder/ min

[a] RESPIRATION

Respirometer

[q] RESPIRATION

Respirometer

explain how and why the colored liquid moves.

maggots take oxygen in aerobic respiration and release carbon dioxide so the lime water absorbs carbon dioxide, volume of air in the tube decreases, pressure inside the tube decreases, the colored liquid moves towards the test tube

[a] RESPIRATION

Hydrogen carbonate as an indicator of pH

A: hydrogen carbonate color turns yellow because on respiration occur and no photosynthesis “acidic”
B: hydrogen carbonate indicator turns purple because there is photosynthesis so less carbon dioxide “alkaline”
C: hydrogen carbonate indicator turns yellow because the snails respire aerobically producing carbon dioxide “acidic”
D: hydrogen carbonate remains red because there is both respiration and photosynthesis “neutral” (compensation point)

[q] BIOTECHNOLOGY

Investigate and describe the role of lactase in the production of
lactose free milk

Add lactase enzyme to sodium alginate
Pour the mixture of lactase and sodium alginate in a barrel of syringe
Allow the solution to drip carefully drop by drop ina beaker containing calcium chloride, inert beads will be formed with with lactase trapped inthem
Collect the beads ina column and drop milk on them
Collect the product in a container
lactose- glucose and galactose

[a] PHOTOSYNTHESIS

Destarching: leaving the plant in a dark cupboard for 2 days

How to ensure thatthe plantis destarched

Take a leaf from the destarched plant and boil in water bath to dissolve the cuticle, denature the enzymes and damage the membranes
Put the leaf in boiling tube containing ethanol
Place the test tube in boiling water bath
Ethanol dissolves the chlorophyll
Remove the leaf from the ethanol and place it in warm water to soften the leaf
Make starch test using iodine solution to ensure that the leaf is
destarched

[q] PHOTOSYNTHESIS

Show that light is necessary for photosynthesis

Destarch the plant
Get a black paper
Get a black paper and cover part of it with a black paper
Place the plant infant of the sunlight and leave it for 3 hours
Test the leaf for the presence of starch using iodine solution

[a] PHOTOSYNTHESIS

Show that chlorophyll is necessary for photosynthesis

Use a plant with variegated leaves
Remove the chlorophyll
Test for starch using iodine solution
The green area will turn blue black and the yellow one will take the yellow brown color showing absence of starch

[q] PHOTOSYNTHESIS

Show that carbon dioxide is necessary for photosynthesis

Destarch the plant
Cover on of the leaves with transparent plastic bag containing soda lime to absorb the carbon dioxide in air
Cover another leaf with transparent plastic bag containing water
Put the plant in the light for 2 days
Remove the plastic bags after 2 days and test for starch using iodine solution
The plant placed in soda lime will change its color to yellow/ brown
The plant placed in water will change its color to blue/ black

[a] PHOTOSYNTHESIS

Prove that light intensity is a limiting factor

Set the apparatus as shown
Use a heat filter to avoid the effect of temperature as a limiting factor
Darken the room and place a source of light in front of the plant at a constant distance
Count the number of bubbles produced within 3 min
Increase the light intensity and count the number of bubbles
Put your results ina table and plot a graph

[q] TRANSPORT IN PLANTS

Potometer

Cut a stem of aleafy shoot under the water surface to prevent air from entering the xylem and blocking it (stops transpiration pull)
Ensure an air tight seal by using rubber tube and vaseline t prevent evaporation of water
Open the clip to fill the capillary with colored water
Close the clip and make sure that the air/water meniscus reach the zero point
As the plant transpires, the water lost by transpiration is replaced by water taken up by the stem
Record the position of the meniscus every two minutes
When the meniscus reaches the end of the scale, open the screw clip
Repeat the experiment but with the photometer in different situations as blowing it with a fan, changing the light intensity, putting it in arefrigerator, cover the sheet with a plastic bag
After changing the conditions take 3 more readings of the rate of uptake and notice whether they represent an increase ora decrease in the rate of transpiration

[a] TRANSPORT IN PLANTS

How to find the number pf stomata in the surface of the leaf
using microscope

Use agrid with squares to find the surface area of the leaf
Out the leaf under the microscope and using a cell counter to count the number of stomata in the field of view
Find the surface area of the field of view using trr?
Calculate the total number of stomata on this surface
Repeat 2 more times and take average

[q] TRANSPORT IN PLANTS

How to find the total number of stomata

Repeat the experiment on the other surface

[a] TRANSPORT IN PLANTS

How to count the number of stomata using cobalt chloride paper

Find the surface area of the leaf using transparent grid with Squares
Put 1 cm* cobalt chloride paper (blue) on the surface of the leaf, this represents the number of stomata in 1 cm?
Multiply the number of stomata by the total surface area to get the total number of stomata on this surface
Repeat the experiment 2 more times and take average

[q] SEXUAL REPRODUCTION IN PLANTS

How to get the dry mass

Get 100 seeds of the same species, same size, same mass and same maturity
Plant them in the same amount of water at the same time and same temperature
Leave them under the same environmental conditions (humidity and same nature of soil)
Each day take 10 seeds and dry them in an oven at 110°C, weigh frequently until no more loss in weight is detected
Record the dry mass and plot agraph

[a] SEXUAL REPRODUCTION IN PLANTS

Make an investigation to determine which color is most attractive to insects

Get 3 flowers of the same species, same height and same size but with different colors
Leave at the same temperature, light intensity and give them the same water volume
Get insects of the same species and leave them. with the flowers for 1 hour, count the number of visits done by insects to each flower color
The more the visits, the more the attraction
Repeat the experiment 2 more times to take average
Plot your results in table
Plotagraph

[q] GAS EXCHANGE

Describe an experiment to compare between the concentration
of carbon dioxide in inhaled and exhaled air

Breathe in and out several times gently through the mouth piece
A: less cloudy because inhaled air has less carbon dioxide
B: more cloudy because the exhaled air has more carbon dioxide

[a] GAS EXCHANGE

Precautions: suck air gently to avoid swallowing limewater

[q] Important rules in drawing figures and graphs

DRAWING FIGURES

No shading

[a] Important rules in drawing figures and graphs

DRAWING FIGURES

No feathery lines

[q] Important rules in drawing figures and graphs

DRAWING FIGURES

No broken lines

[a] Important rules in drawing figures and graphs

DRAWING FIGURES

No arrows
The drawing should be as large as the space provided
The thickness should be constant unless shown in the figure
Don’t use rulers
Use sharp pencil (no thick lines )

[q] Important rules in drawing figures and graphs

DRAWING GRAPHS

Label the axes and use the units
X-axis is the independent variable
The Y_axis is the dependent variable
Draw the graph point to point using a ruler

[a] Important rules in drawing figures and graphs

DRAWING GRAPHS

If the graph is bar chart, the bars should be of the same width and same space between each bar

[q] Important rules in drawing figures and graphs

DRAWING GRAPHS

If the graph is line of best fit, the points above the line should be approximately equal the points below the line
The line should take morethanhalfthe space provided

[a] TYPES OF GRAPHS

[q] TYPES OF GRAPHS

BAR CHART

[a] TYPES OF GRAPHS

HISTOGRAM

[q] TYPES OF GRAPHS

LINES OF BEST FIT

[a] Rules for any experiment on enzymes

Same temperature, use thermostatic water bath
Same pH, use a buffer
Same volume and concentration pf enzymes
Same volume and concentration of substrate
Same time, use stopwatch

Same=accuracy

[q] Rules for any experiment on enzymes

Repeat the experiment 2 more times, find anomalous and discard them
Make control to show that the results obtained were from the factor of investigation
Put your results in a table and plot a graph

Reliability

[a] Important questions in paper 6

Ways to improve and investigation.

Make an control
Repeat the experiment 2 more times, to get more reliable results
Use same concentration of………
Same temperature / pH
Use same volume of……………