Biology has its own technical language that must be used in communication to the examiner.

Common errors in biology included:

  • Terminology examples class insect instead of Insecta phylum arthropods instead of Arthropoda.
  • Grammar – yellow color and not yellowish or whitish instead of white. Impulses are transmitted and not pass or sent.
  • Spelling mistake – spelling mistakes is penalized once they alter the meaning e.g. answer instead of anthers, infiltration instead of ultra filtration.
  • Wrong Biology – writing down magnification should be X3 and not 3xs or x3 very high temperatures denature enzymes not kill enzymes.
  • Incomplete or hanging statement – The analogy that is features and function in adaptation. The structures must be understood before the function.
  • Omission – comparison must be complete example compare xylem and phloem then you must say or describe the two of them to get marks.
  • Wrong use of brackets of conjunction, stroke or hyphen might contradict and negate the correct answer – thick waxy cuticle reduces/prevents transpiration.
  • Lack of following instructions – when a question asks for the name, then that is precise than description is not allowed example name the organism that cause diarrhea then the specific bacteria must be named and not generally bacteria.

In human body there are two types of bladder so you have to be precise it its urinary bladder or gall bladder you are referring to.

  • Lack of knowledge/understanding of key concepts. Examples; state the function of the following parts of the human ear. The learner must describe and identify the different.
  • Tied answers, both parts must be correct or the first might negate the second correct answer.


Graphs: normally have 6 – 7 marks. Graphs must follow the following guidelines.

  • Origin and scale with equal interval.
  • Plotting.
  • Points joined using a smooth continuous curve no ruler.
  • Both axis must be labeled.
  • The curve must be identified.
  • Essay; must choose one question out of two. If two questions are answered only the first will be marked. Sequence is very important.


Skills tested is practical include drawing, labeling, observation, recording, investigating, analysis and interpretation.

Drawing must be large, well labeled and neat, no crossing lines for labeling and the lines must touch the structure that is being labeled no shading. Must be proportion. Continuous lines no breaking.
Procedure must be followed before making observation and finally making a conclusion.

:No marking point.
;Marking point.
/Oblique or
Extra mark
X wrong


Wrong title of test

The common food tests are;

  • Starch test.
  • Non-reducing sugar test.
  • Reducing sugar test.
  • Lipids test.
  • Protein test.
  • Vitamin C test.

The above food tests’ corresponding chemical tests are;

  • Iodine test.
  • Benedict’s test for reducing and non-reducing sugars.
  • Sudan III test or Emulsion test.
  • Biuret’s test.
  • Diehlorophenolindophenol (DCPIP) test.

If title of column of tests if “food tests” then use the respective food tests and not chemical tests and vice versa.

Wrong order of answers.

Answers must be written in the same order as the questions. Examples, answers to section (a) should never be written in section (b) or vice versa. Marks are lost if this done.

Wrong procedure.

The procedure must be correct for a student to be awarded appropriate marks for a correct answer in observation and conclusion.


The common mistakes included;

  • Including heating/boiling/warming as part of the procedure in test that does not require heating such as a starch test or protein test.
  • Excluding heating in the procedure in a test that requires heating, such as Benedict’s.
  • Failure to mention the extent of heating for instance heating to boil in Benedict’s test is a must instead of heating alone.
  • Failure to state iodine solution.
  • Failure to specify the quantity of solution added/used. A student must mention the number of iodine solution drops added e.g. three drops of iodine solution added to the sample.
  • Wrong order of presentation for example, in Biuret’s test, sodium hydroxide solution is added before copper (II) sulphate solution or in non-reducing sugar test dilute hydrochloric acid solution is added and boiled before sodium hydrogen carbonate solution.
    Write procedure but not mentioning the substance or specimen under investigation. For example “ add two drops of iodine solution” instead of “add two drops of iodine solution to substance Q”.
  • Mention of material or information not provided in the question. For example, it is wrong to refer to a powder label as specimen as “starch powder” if such information was not provided to the students in the question.
  • Presenting more than one procedure for the same test shows that the student is not sure which of the procedures is correct. This appear to test the examiner and marks are not awarded.

Colour observed in food tests.

You are required to make sensible observations using the five senses except taste.
Correct observations are using senses like:

Sight for example colour change, brightly coloured petals in a flower.
Hearing for example effervence.
Smell for example a gas with a pungent smell ,scented flowers among others.

Touch for example when noting a temperature change. This can be done using thermometer.

Observe and record all colour change and not just the final colour .For example, in Benedict’s test the colour of the precipitate may change from blue colur to green to yellow followed by orange then to brown –red.

Be faithful to report the observations accurately since not all tests of reducing sugars lead to the final colour. In some reactions the colour may stop at green based on the amount of reducing sugar present.

Record any other change such as the formation of an emulsion or a precipitate.

A wrong observation leads to wrong conclusion besides if the observation is wrong observation; the conclusion is not awarded marks.

Examples of wrong observations include;

  • Use of unacceptable colours like greenish for light green, yellowish for light yellow or bluish for light blue.
  • Stating “no change” when the blue colour of Benedict’s solution remains or “No reaction” When the yellow brown colour of iodine remains.
  • Reference to “blue-black colour” in starch test as “black colour”
  • Wrong conclusions.
    Conclusions should be made using positive statements. A negative statement like “ Reducing sugars are not present” for “Reducing sugars absent” does not get any marks.

Common mistakes in other questions.

  • Spelling mistake, for example Make sure that you spell words correctly.
  • Wrong use of biological language or expressions. For example, stating the function of haemoglobin as “Helps in oxygen transport” instead of “Transports oxygen” or reference of the of the vertebrae column as the spinal cord.
  • Poor identification of specimens.
  • Poor use of plural and singular of biological terms. For example,
  • Vertebrae and vertebra, stomata and stoma.
  • Answering adaptation questions wrongly. This is due to lack of knowledge of functions of biological structures.
  • Interchanged use of biological terms like osmotic pressure and osmotic potential.
  • Use of negative answers for example starch not present.
  • Use of symbols or a abbreviation like ATP (ADH) (adenosine diphophate), NaOH (sodium hydroxide) and CuSO4 (Copper (II) sulphate) in place of their chemical names.


Over the years ,the performance in biology has been inconsistent .A number of reasons have been attributed to this.
Experience by examiners has shown that there are some common areas that candidates need to work on to improve performance in this particulars subject.

These are follows:


A biology student must read through the four years ‘work widely and ensure that the content is well understood. It is wrong to just memorize biological concept. Understanding the content enables the candidate to present the same ideas in logical fashion when asked to do so in the examination.

A candidate must read , understand and apply biological concepts.
EXAMPLE :In osmosis, for red blood cells to haemolyse, water must enter to the cells when surrounded by hypotonic solution.

Spelling mistakes

Some spelling mistakes may give the wrong biological meaning.
Example: river for liver, air for hair, sweat, bleeding for breeding , pitch for pith and lumen for rumen.

Understanding the question before answering

The candidate is advised to read and ensure they can comprehend the question and understand before they answer;

[a]Explain how the human intestinal vilus is adapted to function .Here the candidate must explain how the feature adapts the structure to its functions .for instance ,the vilus epithelium is thin/has one cell thick wall for faster diffusion of digested food.

[B]Differences between respiration and photosynthesis: complete comparison should be made. If it is raw material in respiration mention as much possible.

Use of chemical formula

Candidate should avoid using chemicals formulae of elements, molecules or compounds when giving answers in the theory papers.

For example CO2, O2, and H2O etc Examiners strictly check if the candidate has followed the specific rules used in writing the formula.

Candidate in may cases write these formula in hurry thus flouting the rules. If one has to use them, the rule must be observed and the appropriate symbol used. Also, the IUPAC names for the compounds

Example: Carbon (iv) instead of carbon dioxide, sulpur(iv)Oxide instead of sulpur dioxide.

Using wrong terms which give wrong biological meaning.

These include the following terms:
‘’lack of’’

Example: Compare the blood in the umbilical artery with that in the umbilical vein.

A candidate must say that the blood in the umbilical artery lacks oxygen while that the one in the umbilical vein has oxygen. This is a wrong answer since the blood cannot lack a given gas completely

The correct answer is that blood in the umbilical vein has more oxygen while that in the umbilical artery has less.


Example: state how leaves of xerophytes are adapted to cope with the problem of transpiration.

Wrong answer: Have thick waxy cuticles to prevent transpiration.
Correct answer: Have thick waxy cuticles to reduce transpiration

These are:

Donation instead of transfusion of blood.
Send instead of transfusion of impulses.
Attachment instead of sexual intercourse/copulation/coitus.

Stating specified number of factors.

A candidate must state a particular number of factors that affect in biology.

Number of items as per the requirement of the question.
Avoid themselves while answering such question.

Example: State two environmental factors that would increase the rate of transpiration.

This question requires a candidate to give only two factors out of the six. A candidate who gives more factors for that question will be penalized if additional factors contradict the first two points already given.

Singular and plural.

A candidate must be keen when identifying a structure or structures in diagrams or in other questions. If only one structure is drawn the candidates must be aware of the singular and plurals of the structures.
Example: If asked to identify an or organelle like mitochondrion, whereby only one is asked, avoid writing mitochondria.
Graph drawing and analysis.
It is common o have data based question in Biology paper 2 and is usually based on biological concept and not mathematical one, thus one has to relate the data with the biological knowledge acquired in the course of study.

Marks are awarded for the following;

  • Axes: They must be well labeled and units correctly shown.
  • Scale: The graph should be preferably occupying more than 2/3 of the page.
  • It should be consistent-do not omit any of the values. All the values in the table must be covered by the chosen scale.
  • Not that in most occasions you are supposed to plot more than one graph on the same axes. Hence read and understand the question because if you plot two separate graphs, you will be penalized.
  • Avoid investing the scale.
  • The scale must be workable.
  • Plotting: Candidate must plot all the points clearly. It is advisable to plot using X mark.
  • Curve: A smooth curve is more common in biology. Use sharp dark pencil and a free hand. Avoid using a rule to join the points in a curve even if they appear to be on the same path. Do not use dotted lines to draw the curve.
  • Identification of the curves: In case of more than one curve plotted on the same axis, label the curves clearly. It is appropriate that you identify the curves as you draw them rather than trying to identify them long after you have drawn all of them.

Your graph must have the origin. This can be zero if it is on the table or if the values in the table are small. It can also be the value in the table for either of the axes. Never extend the curves beyond the plotted points.

Analyzing graphs

Understand the nature of the data in the table so that you get idea on what biological process the data represents. The questions you will be asked will be about the data given on the table.

Avoid terms like “the graph is rising” or the “graph is decreasing”. It is actually the factor under investigation that increases or decreases.
The examiner that you to account for that observation. In that case, you are just required to explain giving reason.

Essay questions

In paper 2, question 7 and 8 are essay question. Out of these questions, a candidate chooses one. Each of them has a total of 20marks.

Many a times, candidates are unsure which of the questions to approach because they look at them as either being easy or difficult.

The questions demand that the candidate explains, describes or discusses a process in biology.

Here, one is required to be wise enough to avoid time wastage because the candidate may think they have enough points for one questions only to realize later that they are not sufficient.

It is advisable to do the following;

  • Read each question separately.
  • Determine which of the questions is easier to you.
  • Compare of the number of points you can remember as much as possible for each questions.
  • Answer the question correctly. Remember that in case of description, ideas should be represented in logical flow. Write down all you can remember.
  • Cross out any rough work that appears in the spaces below the questions.
  • Do not answer the two essays. This is because only the first one will be marked.

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