Biology Questions and Answers Form 4

Biology Questions and Answers Form 4

Biology Questions and Answers Form 4

Biology Questions and Answers Form 4

KCSE Revision Questions and Answers

K.C.S.E Online Revision

Biology Form 4 Notes – Biology Form Four Notes

a) i) Define the term genetics


  • the study of heredity(inheritance) and variation or study of mechanisms by which characteristics are passed from parents to offspringii) List some characteristics which are inherited 
  • size
  • height/length
  • colour/type
  • shape
  • yieldiii)State the importance of genetics 
  • helps to explain differences between organisms of the same species
  • helps to explain the transmission of characters from generation‘ to generation
  • improvement in livestock
  • improvement in crops
  • can be used to treat some difficult diseasesb) i) Explain the meaning of the following termsHeredity


  • the resemblance among individuals related by descent
  • transmission of traits from parents to offspringTrait 
  • also called character
  • A character of the organism e.g. type of ear, colour of eyes, height, yield etc.Gene 
  • unit of inheritance
  • it is the heredity factor which transmits traits from parents to offspring
  • genes are located at ‘fixed points on chromosomes
  • each point is called a locus (loci)Allele 
  • genes can exist in a series of alternative forms at a particular locus
  • allele refers to alternative forms of genes controlling a particular characteristicChromosomes 
  • threadlike structures found in nuclei of all plants and animals
  • they carry genes which are hereditary materials
  • they consist of substances called DNA and proteins called histosonesDNA 
  • deoxyribonucleic acid
  • substances that make up chromosomes
  • double helix(strand) molecule that contains genes
  • DNA consists of nucleotides
  • A nucleotide consists of an inorganic phosphate, ribose sugar and a base
  • There are four bases in a DNA molecule i.e. Adenine(A), guanine(G), thymine(T) and cystosine (C)
  • Ribose sugar has four bases attached to it i.e. adenine, cystosine, guanine and thymine
  • Adenine pairs with thymine while guanine pairs with cystosine
  • Nucleotide initiates and controls protein synthesisii) List the types of chromosomes 
  • somatic (body) chromosomes also called autosomes
  • sex chromosomes (related to reproduction)c) i) What is variation? 
  • sequence of differences occurring among individuals of the same speciesii) State the causes of variation in organisms 
  • random assortment of genes during meiosis
  • crossing over
  • fertilization
  • doubling of chromosome numbers(mutation)
  • environmental conditionsiii) Name the types of variation 
  • Continuous variation (differences not clear cut) e. g. height, length, weight, skin colour, intelligence etc. They are quantitative and show intermediates
  • discontinuous variation(differences are clear cut) e. g. ability to roll tongue, ABO blood grouping system, RH factor, patterns of fingerprints, and ability to taste PTC. They are qualitative and have no intermediatesiv) Explain the following termsAcquired characteristics


  • they are as a result of adaptations due to the environment and are not inherited Inherited characteristics
  • are passed down to offspring during sexual reproductionGenotype 
  • genetic constitution of an individual/genetic makeupPhenotype 
  • characteristics of an individual observed or discernible by other means i.e. observable characterDominant gene (character) 
  • expressed in the phenotype when homozygous or heterozygousRecessive gene 
  • only expressed in homozygous stateHomozygous 
  • when two alleles are identical e.g. LL,llHeterozygous
  • when two alleles are different at a particular locus e.g. LlF1 and F2 
  • Fl means first filial generation i.e. the first generation produced when two varieties can be crossed
  • F2 means second generation i.e. product of offspring or from F1 generationd) i) Explain Mendels first law of inheritance 
  • also called law of segregation
  • it states that genes are responsible for the development of individual characters
  • these characters are transmitted individually without any alterations
  • Only one character from a contrasting pair can be carried in a gamete, hence only one character can be inherited.ii) Give an example of this law 
  • In an experiment, Drosophila (fruit fly) with long wings were crossed with those having short wings. Assume letter L denotes gene for wing size. The gene for long wings is dominant to that for short wings
  • the genes for dominant are LL and for recessive ll.
  • State the expected results for the first crossiii) What is monohybrid inheritance? 
  • when inheritance of one character is studied one at a time e.g. wing size only
  • the F2 generation (when selfed) always gives a phenotypic ratio of 3:1 and a genotypic ratio of 1:2:1 in a complete dominancei) What is complete dominance? 
  • refers to where only one dominant character is expressed while the other character which is recessive is not expressed in the heterozygous state e. g. the case of wing size above e) i) What is meant by co dominance?
  • When genes produce independent effects when heterozygous/none of the genes is dominant over the other/where two or more alleles does not show complete dominance/recessiveness due to the failure of any allele to be dominate in a heterozygous condition.ii) Give an example of co dominanceIn a certain plant species, some individual plants may have only white, red or pink flowers. In an experiment a plant with white flowers was crossed with a parent with red flowers. Show results of Fl generation. Use letter R for red gene and W for white gene.

    If the plants form F1 were selfed, work out the phenotype ratio for the F2 generation Phenotypic ratio 1 red:2 pink: 1 white

    Genotypic ratio 1:2:1

    f) i) What is a test cross?


  • A cross between an individual showing a character for a dominant gene(that is homozygous or heterozygous) with a homozygous recessive individualOR 
  • a cross between individual(organism) of unknown genotype with a homozygous recessive individualii) State the importance of a test cross in genetics 
  • helps in determining the genetic constitution/genotype of an organismiii) What are multiple alleles? 
  • a set of more than two alleles that may determine a characterexample is blood group which can be determined by any two of three alleles i.e. A,B and Oiv) Explain the inheritance of ABO blood groups


  • in humans blood groups are determined by three alleles i.e. A,B and O
  • it is only possible to have two genes at a time
  • genes A and B are co-dominant while gene O is recessive to genes A and B
  • Give a worked example using parents with heterozygous blood groups Ao and BOii) Explain the inheritance of Rhesus factor (Rh) in human beings 
  • in humans blood is either Rh positive or Rh negativepeople who have Rh antigen are Rh(+ve) while those without Rh antigen in their blood are Rh(-ve) 
  • Rh(+ve) is due to a dominant gene while the recessive gene causes lack of Rh factor.
  • When a person who is homozygous dominant marries a person who is homozygousrecessive the result is as shown belowLet the gene for dominant Rh factor be R while gene for recessive be r

    iii) How is sex determined in human beings .


  • there are two sex chromosomes in humans, x and y
  • males are xy and females are xx
  • in females all ova have x chromosome
  • in males 50% of sperms contain x chromosomes While 50% of sperms contain ychromosome 
  • when a sperm containing x chromosome fuses with an ovum this results into a girl
  • when a sperm containing y chromosome fuses with an ovum the result is a boy
  • an example is given belowg) i) What does the term linkage mean?– These are genes which occur together on a chromosome and are passed to offspring without being separated ii) Define the term sex-linked genes


  • genes carried in the sex chromosome that are transmitted along with genes that determine sexiii) What is meant by the term sex linkage? 
  • genes are located on the sex chromosome
  • they are transmitted along with those that determine sexiv) Name the sex-linked traits in humans 
  • colour blindness
  • haemophilia
  • Hairy ears. pinna, nose
  • Baldness
  • Duchene muscular dystrophy (DMD) muscular wastingv) Give an example of a sex linked trait in humans on:Y Chromosome


  • tuft of hair sprouting from pinna/baldnessX Chromosome 
  • colour blindness/haemophiliavi) In humans red-green colour blindness is caused by a recessive gene C, which is sex- linked. A normal man married to a carrier Woman transmits the trait to his children. Show the possible genotypes of the children.Let C represent the gene for normal colour vision (dominant)

    Let c represent the gene for colour blindness

    Parental phenotype Norman man x carrier woman

    iv) State the importance of sex linkage

    possible to determine sex of day old chicks

    v) Haemophilia is due to a recessive gene. The gene is sex-linked and located on the x chromosome. The figure below shows sworn offspring from phenotypically normal parents

    What are the parental genotypes?


  • XY and XhXWork out the genotypes of the offspringh) i) What is mutation?


  • sudden change in the structure of DNA at a particular locus/chromosome/ geneii) Describe how mutations arise 
  • mutations arise due to alterations in normal number of chromosomes
  • change in a portion of a chromosome affecting one or more genes
  • by chromosomal aberration e.g. dleltion/duplication/substitution/inversion/translocation/crossing over
  • caused by mutagenic agents e. g. radiation (x-rays, ultra violet light, gamma rays) and chemicals e. g. mustard gas/colchicinesiii)State the factors that may cause mutation 
  • these are chemicals and radiationsRadiations EffectsX-rays gene/chromosome alteration

    Ultra violet rays structural distortion of DNA

    Chemicals Effect

    colchicines prevents spindle formation

    Cyclamate chromosome aberrations

    Mustard gas chromosomes aberrations

    Nitrous acid adenine in DNA is deaminated so behaves like guanine

    Acridone orange addition and removal of bases of DNA


    iv) State the characteristics of mutations


  • arise suddenly
  • are unpredictable
  • random
  • generally rare
  • may breed true
  • some are desirable while others are lethalv) Explain chromosomal mutation– Change in nature, structure or number of chromosomes

    vi) Explain how the following types of chromosomal mutations occur



  • a section of a chromosome is repeated/replicates
  • therefore genes are repeatedInversion 
  • occurs when chromatids break at 2 places and when rejoining the middle piece rotates and joins in an inverted positionDeletion 
  • portion of a chromosome is left out after it breaks off
  • alters number and sequence of genesTranslocation 
  • occurs when a section of a chromatid breaks off and becomes attached to another chromatid of another chromosomeNon-disjuntion 
  • Failure of homologous chromosomes/sister chromatids to separate/segregate during meiosisPolyploidy 
  • where number of chromosomes double or triple
  • beneficial in plants due to the following
  • increased yields/hybrid vigour//heterosis
  • resistance to pests
  • early maturity
  • resistance to drought
  • resistance to diseasesvii) What are gene mutations? 
  • an alteration in the structure of a genei) Explain how the following occur during gene mutationDeletion


  • some bases/nucleotides of a gene are removedInversion 
  • the order of some bases/nucleotides of a gene is reversedInsertion 
  • addition of a base between two existing basesSubstitution 
  • a portion of a gene is replaced by a new portionii) Name the disorders in humans caused by gene mutation
  • albinism
  • sickle cell anaemia
  • achondroplasia/chondordystorphic dwarfism
  • haemophilia
  • colour blindness
  • phenylketonuriaI. State the practical applications of geneticsi. Breeding programmes (research)


  • high yielding/hybrid vigour/heterosis
  • resistance to diseases
  • resistance to drought/salinity
  • early maturingii. Genetic engineering 
  • genetic manipulation to produce desired characteristicsiii. Law– legal questions of paternity knowledge of blood groups or blood transfusion

    iv) Genetic counseling

    Biology Questions and Answers Form 4

  • aimed at reducing harmful traits e.g. albinism, congenital idiots, colour blindness Others– Pre-sex determination

    Understanding human evolution and origin of other species.

    2. a) i) Explain the meaning of evolution


  • a gradual change in living organisms from simple life forms to more complex forms over a long period of time.ii) Differentiate organic evolution from chemical evolution as theories of origin of life 
  • organic evolution refers to the emergence of present forms of organisms gradually from pre-existing forms (some of which no longer exist)
  • chemical evolution explains the origin of life as having occurred when simple chemical compounds reacted to form the simplest life formsiii) What is special creation? 
  • maintains that the whole universe and all living organisms came into being due to the act of a supernatural beingb) Discuss the various kinds of evidence for evolutioni) Fossils

    Biology Questions and Answers Form 4

  • fossils are remains of organisms preserved in naturally occurring materials for many years
  • they give evidence of types of plants/animals that existed at certain geological age/long ago/millions of years ago
  • gives evidence of morphological/anatomical/structural changes that have taken place over a long period of time e. g. human skull, leg of horseii) Comparative anatomy 
  • gives evidence of relationship among organisms/gives evidence of a common ancestry of a group of organisms
  • organisms have similar structures/organs performing the same function e. g. digestive system] urinary system/nervous system/vestigial structures and vertebrate heart
  • Divergence where the basic structural form is modified to serve different functions e.g. vertebrate forelimb/beak structure in birds/birds feet/parts of a flower. These are called homologous structures
  • homologous structures have a common embryonic origin but are modified to perform different functions e.g. the pentadactyl limb
  • adaptive radiation is a situation where organism have a homologous structure with common embryonic origin which is modified to perform different functions to adapt organisms to different ecological niches/habitats e.g. beaks of Darwinian finches(birds)
  • Convergence is where different structures are modified to perform a similar function e.g. wings of birds and insects/eyes of humans and octopuses. These are called analogous structures
  • Vestigial structures are greatly reduced in size and have ceased to function e.g. human appendix/caecium/coccix in humans, wings of kiwi (flightless bird), presence of hind limb pad in python, halters in insects, human hair nictitating membrane in human eye, human ear muscle, pelvic girdle in whale and third digit of wing of bird.iii) Comparative embryology 
  • some embryos of different animals appear very similar thus showing relationship and possibility of a common ancestry
  • e.g. different classes of vertebrates larvae of annelida and mollusca are similar (tocophere)iii) Comparative serology/physiologyBiology Questions and Answers Form 4
  • these show biochemical and immunological comparisons of blood groups/components to show immunological similarities of tissues therefore showing relatedness of different organisms
  • e.g. antigen antibody reactions, human blood groups/Rh factor reveal some phylogenic relationship among organisms/common ancestryiv) Geographical distribution 
  • organisms differ in various geographical regions
  • present continents are thought to have been a large land mass joined
  • together/pangea/Eurasia/Gondwanaland
  • present continents drifted apart from one land mass/continental driftas a result of continental drift isolation of organisms occurred bring about different patterns of evolution 
  • organisms in each continent evolved along different lines hence emergence of new species/divergence/convergenceExamples 
  • marsupials in Australia
  • llama, jaguar, panther in S. America
  • lion, camel in Africa
  • I tiger in Asiavi) Cell biology (cytology) 
  • structures and functioning of cells are similar
  • occurrence of organelles e.g. mitochondria in all cells/both plant and animal cells
  • these point at a common ancestryc) i) State the evolutionary characteristics that adopt human beings to the environment– Brain

    – Eyes

    – Upright posture/bipedal locomotion

    – prehensible arm/hand

    – Speech

    ii) State the ways in which Homo sapiens differs from Homo habilis

    Biology Questions and Answers Form 4

  • standing upright/erect posture
  • intellectual capacity/higher thinking capacity/bigger brain/higher brain capacity
  • communication through language/speechd) i) Explain Larmarck’s theory of evolution– Inheritance of acquired characteristics/environment induces production of a favorable trait which is then inherited

    ii) Explain why Lamarck’s theory of evolution is not accepted by biologists today

    – evidence does not support Lamarck’s theory

    – acquired characteristics are not inherited/inherited characteristics are found in reproductive cells only

    iii) Explain Darwin’s theory of evolution

    – inheritance of genetically acquired characteristics

    – a character happens to appear spontaneously which gives advantage to an organism therefore adapted then inherited through natural selection

    e) i) What is natural selection?

    – Organisms with certain characteristics are favoured by the environment

    Such organisms tend to survive and produce viable offspring

    Others not favored are eliminated from subsequent generations

    ii) With examples, explain how natural selection takes place

    – organism with certain characteristics are favored by their environment

    – such organisms tend to survive and produce viable offspring

    – others not favored are eliminated from subsequent generations

    – as the environmental conditions change the survival value of a character may alter with time so that characteristics which were favored may no longer have advantage and other characters may then become favorable

    – if a favorable character is inherited, then offspring produce generations which are better adapted to survive in a population

    – more offspring are produced than can survive which results in struggle for survival – the fittest survive

    iii) State the advantages of natural selection to organisms

    – assist to eliminate disadvantageous characteristics/perpetuates advantageous characteristics

    – allows better adapted organisms to survive adverse changes in the environment/less adapted organisms are eliminated

    iv) State the ways in which sexual reproduction is important in the evolution of plants and animals

    – brings about useful variations/desirable characters

    – variations make offspring better adapted for survival/more resistant to diseases

    – may lead to origin of new species


    v) Explain the significance of mutation in evolution

    – Mutation bring about variation which can be inherited

    – Some of these variations are advantageous to the organism

    – Others are disadvantageous

    – The advantageous variations favour the organism to compete better in the struggle for survival

    – This results into a more adapted organism to its environment or new species/varieties

    – Those with disadvantageous characters will be discriminated against therefore eliminated from the population/death/perish

    vi) Plain why it is only mutations in genes of gametes that influence evolution

    – gametes form the new offspring

    vii) How would you prove that evolution is still taking place?

    – resistance of organism to antibiotics, pesticides and drugs

    – new varieties of bacteria are resistant to certain antibiotics such as penicillin

    – houseflies and mosquitoes are resistant to DDT

    vii) Explain why some bacteria develop resistance to a drug after they have bee subjected to it for some time

    – bacteria mutates/develops a new strain/chemical composition is altered hence is able to produce enzymes/chemicals which degrade the drug rendering it non-susceptible to the drug

    – the new strain is favoured by selection pressure natural selection

    f) How has industrial melaninism i.e. peppered moth contributed towards the mechanism of evolution

    – This is an example of natural selection

    – The peppered moth exists in two distinct forms, the speckled white form (normal form) and a melanic form (the black/dark)

    – They usually rest on leaves and barks of trees that offer camouflage for protection

    – Originally the “speckled white” form predominated the unpolluted area of England

    – This colouration offered protection against predatory birds

    – Due to industrial pollution tree barks have blackened with soot

    – The white form underwent mutation

    – A black variety/mutant emerged suddenly by mutation

    – It had selective advantage over the white forms that were predated upon in the industrial areas

    – The speckled white form is abundant in areas without soot/smoke

    3. a) i) Define irritability, stimulus and response irritability

    -also called sensitivity

    – Responsiveness to change in environment


    A change in the environment of organism which causes change in organism’s activity


    – change in activity of an organism caused by a stimulus

    ii) State importance of irritability to living organisms

    – Adjusting to environmental conditions. Sensitive/defect/responding

    iii) List the examples of external stimuli to organisms

    – air/oxygen (aero)

    – light(photo)

    – osmotic pressure (osmo)

    – current (Rheo)

    – chemical concentration (chemo)

    – \water/moisture (hydro)

    – Touch/contact (hapto/thigmo)

    – Gravity/soil (geo)

    – Temperature (thermo)

    b) i) What are tactic responses?

    – response in which whole organism or its motile parts move e. g. gamete


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Biology Questions and Answers Form 4