Form 5 workshop
Biological drawings
clean and clear (1)
Realistic (1)
Labels (1)
Size (at least half space given) (1)
Details - double wall eg fruits
- No. of divisions / serrations
- No. of seeds and/ or pattern/ seed arrangement
Calculation of magnification – every biological drawing should have magnification indicated. This is
usually a whole number, or a decimal ( correct to 1dp )
- The answer is accompanied by the unit, which is an X.
Example; specimen length = 20mm
Length of drawing = 45mm
Magnification = size of drawing
Size of specimen
= 45mm
20mm
= 2.25
= X2.3
Differences / similarities between 2 specimen
Eg. lemon / orange and winged fruit
Observations
Expressions like “no change”, ‘remains the same”… are not acceptable.
Example ; experiment of anaerobic respiration of yeast.
- Froth not foam; bubbling/ bubbles produced not
effervescence
- Temperature difference should be noted.eg. t/tube felt warmer
- Volume of froth formed measured(use measuring cylinder)
Food tests
Starch Reagent used; Iodine solution; Observations – Brown no starch; Blue
black colour conclusion -starch present
Reducing sugar ; Benedict’s solution; Observation – orange, yellow,
green(depending on amount of sugar present in a food sample)
Protein; 5 drops Sodium hydroxide solution then 5 drops Copper sulphate solution–
Observations – violet / purple / mauve colour
Fats ; emulsion test: Reagent used: Ethanol, quantify; Positive result/observation –
milky white solution formed
Procedures for testing;
Reducing Sugar
- crush food sample and make a solution
- Add 5 drops Benedict solution and shake
- Place the mixture in a hot water bath
- Observe colour changes
(Brick red colour), orange and yellow, green colours indicate
presence of glucose
Fat test (a) Emulsion test
- Crush food sample
- Add 5 drops ethanol to the food sample and shake
- Allow the mixture to settle and then decant the top layer into
another test tube half filled with water
- Observe colour changes
(Milky white colour)
(b) Using Filter paper
- rub a food sample on a filter paper and leave it to dry
- Observe(Greasy opaque mark appears on paper)
Starch test
-Crush food sample and make a solution
-Add 5 drops of Iodine solution
-Observe colour changes
(Blue-black colour)
Biuret test/ Protein test
- crush(solid)food sample and make a solution
-Add 5 drops sodium hydroxide solution and shake
-Add 5 drops copper Sulphate solution and shake
-Observe colour changes
(Purple (violet / mauve) colour if proteins are present or solution
remains blue if absent)
NB. Sodium Hydroxide solution is added before copper
Sulphate solution.
Common Precautions:
Use a hot water bath for gentle heating
Don’t heat directly to avoid spillages
Use test tube holders when holding a hot glassware
When heating make sure the test tube does not face direction of other students and yourself.
Wear gloves, especially when handling caustic substances eg, sodium hydroxide solution, hydrogen
peroxide
Improvements
Use sterilizing fluid to avoid build up of mould eg during germination of seeds
Repeat the experiment & take averages
Close with a rubber stopper to avoid heat loss
Using same volume of solutions and or reagents.
Using potato strips of same length and width.
Using mass instead of length
Getting all potato strip from same potato
Sources of error
Parallex error( if there is any measurement involved)
Control : this is a set up with all factors necessary for a process to occur.
Experiment: this is a setup with one factor missing for a process to take place.
PAPER 3 EXAM TIPS
1. handling information, application and solving problems to…
1.1. solve problems as they relate to day-to-day life situations including some of a quantitative nature
1.2. use information to identify patterns, report trends, make predictions and propose
hypotheses
1.3 locate, select, organise and present information from a variety of sources
1.4 manipulate numerical and other data
1.5 present explanations for phenomena, patterns and relationships
Questions normally asked here begin with the following words; discuss, suggest, predict, explain, calculate,
determine
Suggest – own opinion ie what do you think?
Explain- describe + why the observed pattern or behaviour
Discuss- write everything
Tips on common exam mistakes
Questions on comparison eg palisade layer vs other layers in a leaf; more chloroplasts to absorb more
light. The words ‘more’ or ‘fewer’ is crucial for comparing 2 things.
Genetic crosses – follow steps accordingly, no short cuts even if the answer is obvious to you.
Presentation of the answer is important. The idea is to show how you arrived at the answer. Punnet
square can only be used if stated. The case study of a test/ back cross to identify an unknown
genotype, begin your answer with words like If…then end your response by referring back to the
scenario.
In case of diseases like STDs, malaria or genetic conditions, if you are to discuss signs / symptoms;
avoid general signs for most ailments eg headache. The same applies for comparing characteristics of
bacteria, fungi, protozoa etc; use features or properties which are specific for a particular group, which
will make it outstanding as bacterium or fungus.
Eutrophication – most students confuse insecticides with fertilizers. Some wrongly suggest that insecticides can
lead to eutrophication. Effects of insecticides in water sources may be; killing non targeted invertebrates hence
disrupting food chains, or that some chemicals are non-biodegradable hence they will accumulate up food
chains. Eutrophication is simply an effect of nutrient enrichment in a water source, it’s important to know steps
in correct sequence. Nutrient enrichment can occur through i) discharge of treated sewage into a river
ii) leaching of excess fertilisers
A table may be adopted for clarity especially when comparing two scenarios. Eg aerobic vs anaerobic
respiration
A diagram does not earn marks, unless otherwise stated that you may use a drawing to explain a
situation or scenario.
Lastly, always consider the marks allocated for a particular question…give points according to the
marks per question; avoid long endless sentences or continuous writing.
