Biology Questions and Answers Form 4 – High School Biology Exams Q & A
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 offspring
ii) List some characteristics which are inherited
size
height/length
colour/type
shape
yield
iii)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 diseases
b) i) Explain the meaning of the following terms
Heredity
the resemblance among individuals related by descent
transmission of traits from parents to offspring
Trait
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 characteristic
Chromosomes
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 histosones
DNA
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 synthesis
ii) 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 species
ii) State the causes of variation in organisms
random assortment of genes during meiosis
crossing over
fertilization
doubling of chromosome numbers(mutation)
environmental conditions
iii) 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 intermediates
iv) Explain the following terms
Acquired 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 reproduction
Genotype
genetic constitution of an individual/genetic makeup
Phenotype
characteristics of an individual observed or discernible by other means i.e. observable character
Dominant gene (character)
expressed in the phenotype when homozygous or heterozygous
Recessive gene
only expressed in homozygous state
Homozygous
when two alleles are identical e.g. LL,ll
Heterozygous
when two alleles are different at a particular locus e.g. Ll
F1 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 generation
d) 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 cross
iii) 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 dominance
i) 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 dominance
In 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 individual
OR
a cross between individual(organism) of unknown genotype with a homozygous recessive individual
ii) State the importance of a test cross in genetics
helps in determining the genetic constitution/genotype of an organism
iii) What are multiple alleles?
a set of more than two alleles that may determine a character
example is blood group which can be determined by any two of three alleles i.e. A,B and O
iv) 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 BO
ii) Explain the inheritance of Rhesus factor (Rh) in human beings
in humans blood is either Rh positive or Rh negative
people 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 homozygous
recessive the result is as shown below
Let 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 y
chromosome
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 below
g) 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 sex
iii) What is meant by the term sex linkage?
genes are located on the sex chromosome
they are transmitted along with those that determine sex
iv) Name the sex-linked traits in humans
colour blindness
haemophilia
Hairy ears. pinna, nose
Baldness
Duchene muscular dystrophy (DMD) muscular wasting
v) Give an example of a sex linked trait in humans on:
Y Chromosome
tuft of hair sprouting from pinna/baldness
X Chromosome
colour blindness/haemophilia
vi) 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 XhX
Work out the genotypes of the offspring
h) i) What is mutation?
sudden change in the structure of DNA at a particular locus/chromosome/ gene
ii) 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/colchicines
iii)State the factors that may cause mutation
these are chemicals and radiations
Radiations Effects
X-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
Formaldehyde
iv) State the characteristics of mutations
arise suddenly
are unpredictable
random
generally rare
may breed true
some are desirable while others are lethal
v) Explain chromosomal mutation
– Change in nature, structure or number of chromosomes
vi) Explain how the following types of chromosomal mutations occur
Duplication
a section of a chromosome is repeated/replicates
therefore genes are repeated
Inversion
occurs when chromatids break at 2 places and when rejoining the middle piece rotates and joins in an inverted position
Deletion
portion of a chromosome is left out after it breaks off
alters number and sequence of genes
Translocation
occurs when a section of a chromatid breaks off and becomes attached to another chromatid of another chromosome
Non-disjuntion
Failure of homologous chromosomes/sister chromatids to separate/segregate during meiosis
Polyploidy
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 diseases
vii) What are gene mutations?
an alteration in the structure of a gene
i) Explain how the following occur during gene mutation
Deletion
some bases/nucleotides of a gene are removed
Inversion
the order of some bases/nucleotides of a gene is reversed
Insertion
addition of a base between two existing bases
Substitution
a portion of a gene is replaced by a new portion
ii) Name the disorders in humans caused by gene mutation
albinism
sickle cell anaemia
achondroplasia/chondordystorphic dwarfism
haemophilia
colour blindness
phenylketonuria
I. State the practical applications of genetics
i. Breeding programmes (research)
high yielding/hybrid vigour/heterosis
resistance to diseases
resistance to drought/salinity
early maturing
ii. Genetic engineering
genetic manipulation to produce desired characteristics
iii. Law
– legal questions of paternity knowledge of blood groups or blood transfusion
iv) Genetic counseling
aimed at reducing harmful traits e.g. albinism, congenital idiots, colour blindness e.t.c
v) 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 forms
iii) What is special creation?
maintains that the whole universe and all living organisms came into being due to the act of a supernatural being
b) Discuss the various kinds of evidence for evolution
i) Fossils
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 horse
ii) 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/physiology
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 ancestry
iv) 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 drift
as 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/convergence
Examples
marsupials in Australia
llama, jaguar, panther in S. America
lion, camel in Africa
I tiger in Asia
vi) 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 ancestry
c) 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
– 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
Stimulus
A change in the environment of organism which causes change in organism’s activity
Response
– 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
ii) What causes tactic responses?
– caused by unidirectional stimulus
– usually doesn’t involve growth
– response is either positive or negative
– named according to source of stimulus
– e.g phototaxis, aerotaxis, chemotaxis
iii) State the importance of tactic response to:
Members of kingdom protista
– move towards favorable environment/move away from unfavorable environment
Euglena when they swim towards the source of light
– phototaxis
– sperms when they swim towards the ovum
– chemotaxis
v) State the advantages of tactic responses to organisms
– to avoid unfavorable environment/injurious stimuli
– escape from predators
– to seek favorable environment
– to seek for food/prey
c) i) Define the term tropism
– growth movement of plants in response to external unilateral/unidirectional stimuli
ii) Explain the various types of tropism in plants
Phototropism
– growth movements of plant shoots in response to unilateral sources of light
– the tip of the shoots produce auxins down the shoot
– light causes auxins to migrate to outer side/darker side causing growth on the side away from light hence growth curvature towards source of light roots are negatively phototrophic
Geotropism
– response of roots/pans of a plant to the direction of force of gravity
– auxins grow towards the direction of force of gravity causing positive geotropism in roots while shoot grows away from force of gravity (negatively geotrophic)
Thimotropism/Haptotropism
– growth response of plant when in contact with an object
– contact with support causes migration of auxins to outer side causing faster growth on the side away from contact surface
– this causes tendrils/stem to twin around a support
Hydrotropism
– growth movement of roots in response to unilateral source of water/moisture
– the root grows towards the source of water/ positively hydrotropic while leaves are negatively hydrotropic
chemostropism
– growth movement of parts of plant to unilateral source of chemicals
– the chemicals form a gradient between two regions e.g. pollen tube growing towards the ovary through the style
iii) State the ways in which tropisms are important to plants
– expose leaves/shoots in positions for maximum absorption of sunlight for photosynthesis
– enables roots of plants to seek/look/search for water
– enables plant stems/tendrils to obtain mechanical support especially those that lack woody stems.
– enables roots to grow deep into the soil for anchorage
– enables pollen tube grow to embryo sac to facilitate fertilization
iv) Explain the differences between tropic and tactic responses
Tropism
-growth curvature in response
-slow
-influenced by hormones
Taxes
-locomotory response
-fast
-external influence
d) The diagram below represents growing seedlings which were subjected to unilateral light at the beginning of an experiment
i) State the results of P, Q and R after S days
– P will bend/grow towards light
– Q will remain straight/have little or no growth
– R will remain/grow straight/grow upwards
ii) Account for your results in (i) above
P- Growth substance/growth hormone/IAA/auxin are produced by the stem tip
– they move (downwards and get distributed) to the side away from light where they cause rapid/more growth/cell division/elongation that results in bending
Q- Source of auxin has been removed
R- The auxins cannot be affected by light because the tip has been covered
iii) If the tin foil were removed from the tip of seedling R, what results would be observed after two days
– it will bend/grow towards light
iv) State the expected results after 3 day is if the box were removed
– all seedlings will grow straight/upwards
e) In an experiment to investigate a certain aspect of plant response, a seedling was placed horizontally as shown in diagram I below. After seven days the appearance of the seedling was as shown in diagram 2
Account for the curvature of the shoot and root after the seven days
i) Shoot
– auxins accumulate on the lower side of the seedling due to gravity
– high concentration of auxins in shoot stimulates faster growth causing more elongation on the lower side than the upper side hence curvature occurs upwards
ii) Root
– the high concentration of auxins inhibits growth hence the upper side with less auxins grows faster than the lower side therefore the curvature occurs downwards
f) What is etiolation?
– phenomenon exhibited by plants when grown in darkness
– such plants are pale yellow due to absence of chlorophyll, have small leaves, long stems/hypocotyle and slender stems
– plants exhibit etiolation to reach light/obtain light
– this is a survival response
4. a) i) What is coordination in animals
– The linking together of all physiological activities that occur in the body so that they take place at the night time and in the correct place
ii) Name the main systems for coordination in animals
– Nervous system/sensory system
– Endocrine (hormonal system)
iii) List the components of the mammalian sensory system
– Central nervous system (CNS), brain & spinal cord
– Peripheral nervous system (PNS) cranial and spinal nerves
– Sense organs
– Autonomic nervous system (ANS) nerve fibers and ganglia
iv).Explain the terms receptors, conductors and effectors
– Receptors are structures that detect stimuli i.e. sense organs
– Conductors transmit impulses from receptors to effectors e. g. neurons
– Effectors are the responding parts e.g. muscles, glands
v) What are the functions of the central nervous system?
– provides a fast means of communication between receptors and effectors
– coordinates the activities of the body
vi) State the differences between somatic and autonomic systems of peripheral nervous system
– Somatic is concerned with controlling the conscious or voluntary actions of the body i.e. skin, bones, joints and skeletal muscles
– the autonomic (automatic) nervous system controls involuntary actions of internal organs, digestive system, blood vessels, cardiac muscles and glandular products.
b) i) What is a neurone?
the basic unit of the nervous system
also called nerve cell
conducts impulses
include monitor sensory and relay neurons
ii) Name the parts of a typical neurone and state the functions of each part
cell body/centron contains nucleus and cytoplasm
axon transmits impulses away from cell body
dendrites relays impulses across adjacent neurons
myelin sheath insulates axon and speeds up transmission of impulses
schwan cells forms myelin sheath and aid in nutrition and regeneration of axon
node of ranvier occur between schwan cells, where axon is not covered, speeds up impulse transmission
nissils granules contain mitochondria that provide cell body with energy for metabolic process
i) Describe the structure and function of a motor neurone
motor neurone relays impulses from CNS (brain/spinal cord) to effectors ( muscles/glands)
ii) Describe the structure and of sensory neurone
sensory neurone relays receptors (sense organs) to CNS
iii) State structural differences between motor and sensory neurons
Cell body in motor neurone is terminal (at the end) and inside central nervous system.
Cell body in sensory neurone is terminal but has axon at both ends (bipolar)
iv) Describe the structure and function of a relay neurone
also called intermediate/internucial/associate/connector/interneurone
locate inside central nervous system and spinal code
usually lack myelin sheath
c) State the function of the major parts of the human brain
i) Cerebrum
called forebrain
occupies most of the brain
consists of four lobes each with specific function
temporal lobe controls taste smell hearing learning and memory
partial lobe controls sensory output and touch
occipital lobe controls vision, motor output and speech
frontal lobe controls personality, learning thought and speech
also has parts called thalamus and hypothalamus
thalamus helps to sort sensory information
hypothalamus controls hunger, heartbeat body temperature and aggression
ii) Mid brain
quite small in humans
relay centre for audio and visual information
also involves in some sight, hearing and orientation responses
i) Hind brain
consists of cellebral and medulla oblongata
cerebellum is responsible for coordinating impulses, posture and balance, motor coordination and muscle tone
an automatic response to an external stimulus e. g. sneezing or Withdrawing hand from a hot object
ii) Describe a reflex action that will lead to the Withdrawal of a hand from a hot object
Receptors in the skin respond to stimuli. Arestimulated
an impulse is transmitted through the sensory neurone, across a synapse to the central nervous system (White matter), through the relay neurone into grey matter, then to the motor neurone and finally to the effect muscle which contracts
the hand is then withdrawn
iii) Explain how an impulse is transmitted across the synapse (gap)
impulse initiates release of transmitter substance acetylcholine at the end of the sensory neurone
acetylcholine diffuses across the synapse and generates an impulse in the next neurone
ii) Briefly describe the transmission of a nervous impulse across a neuro-muscular junction
impulse arrives at synoptic knob and causes vesicle to move to the pre-synaptic membrane
vesicle discharges transmitter substance into synaptic cleft
transmitter substance/acetylcholine diffuses across the cleft and attaches to post-synaptic membrane
the membrane is depolarized, generating the action potential
iii) What are the functions of a synapse?
allows transmission of nerve impulses from neurone to neurone
ensures nerve impulses travel in only one direction W
in the brain they store information/memory
b) i) What is a conditioned reflex?
A response caused by a unilateral stimulus (associated stimulus) which substitutes the normal stimulus
ii) Explain a conditioned reflex
it is automatic
it involves the spinal cord
it is usually learned e. g. writing, cycling, dancing
it involves the interaction of highly specialized centers of the brain with a large number of neurone necessary to bring about conditioning
example is experiments carried out by Pavlov using dogs
iii) Compare a simple reflex action with a conditioned reflex
c) i) What are endocrine glands?
ductless glands that produce hormones in animals
hormones are chemical substances which help to coordinate the functions of the body
ii) State the functions of hormones in animals
regulate growth and development
control behavior during breeding
proper functioning of cells
regulate metabolic activities
iii) Name the main endocrine glands, their secretions and functions in the human body
Gland: Thyroid
Hormone:
Thyroxine
Function:
increases the rate of metabolism
Gland: Parathyroid
Hormone:
Parathyroid hormone
Function:
regulates calcium and phosphate levels
Gland: Pituitary
Hormone:
growth hormone
Function:
regulates growth of the body
gonadotrophic hormone
Function:
stimulates the growth of male and female organs
lactogenic hormone (prolactine)
Function:
stimulates secretion of milk after child birth
thyrotropic hormone( TSH)
Function:
proper functioning of thyroid glands/thyroxine production
adrenocorthicotropic hormone (ACTH)
Function:
stimulate release of adrenal cortex hormone
oxytocine hormone
Function:
regulates blood pressure
stimulates smooth muscles
stimulates contraction of uterus during child birth
aids flow of milk from mammary glands
follicle stimulating hormone (FSH)
Function:
causes maturition of egg in females
stimulates sperm production in male
Vasopressin (ADH) antidiuretic hormone
Function:
regulates water balance by kidney
Gland: adrenal
adrenaline (epinephrine hormone)
Function:
for emergency
prepares body to cope up with stress
aldosterone hormone
Function:
maintain balance of salt and water in blood
cortisone hormone
Function:
break down the stored proteins to amino acids
aids in the break down of adipose tissue
regulates sugar levels in the blood
prevents inflammation
sex hormone
Function:
supplements sex hormones produced by gonads
promotes development of sexual characteristics
Gland: Pancreas
Hormone:
insulin
Function:
regulates levels of sugar in blood
enables liver to store sugars
glucagon
Function:
regulates levels of sugar in blood
Gland: ovaries
Hormone:
oestrogenFunction:
causes secondary sexual characteristics in female
prepares the uterus for pregnancy
progesteroneFunction:
growth of mucus lining of uterus
maintains the uterus during pregnancy
Gland:testes
Hormone:
androgen testosterone
Function:
causes secondary sexual characteristics in male
Gland: stomach cells
Hormone:
gastrin
Function:
stimulates release of gastric juice
Gland:intestinal cells
Hormone:
secretin
Function:
stimulates secretion of pancreatic juice
iv) Give the differences between nervous and endocrine (hormonal) communication
nervous
response confined to effector organs( localized target)
speed of response is rapid
nervous impulse through nerve/nerve cells/neurons
duration of response is short
speed of transmission is rapid
transmission is electrical
hormonal(endocrine)
response more widespread (various targets)
response less rapid
hormones transferred through blood
persistent for long
speed of transmission is slower
transmission is chemical
v) State the effects of over secretion and under secretion of adrenaline and thyroxine in humans
g) i) Define the following terms
Drug
a substance that causes a change in body function
Drug abuse
indiscriminate use of drugs without minding their side effects
misuse or wrong use of drugs
ii) State the types of drugs, examples and side effects
Sedatives
also called depressant
a drug that decreases the action of the central nervous system
reduce anxiety, and tension, induce sleep and act as muscle relaxants
when abused they cause withdrawal effects such as anxiety, delirium and death
includes barbiturates, other sedatives, tranquilizers and alcohol
Pain-killers
suppress centers of pain in the brain
Hallucinogens
given to people with hallucination or mentally ill patients to calm then down
when abused they lead to a feeling of confusion, agitation, depression and violent behavior that can lead to murder or suicide
examples include valium, LSD, bhang, narcotics and cannabis
Stimulants
drugs that temporarily increase the action of the central nervous system
they create a feeling of alertness, wakefulness, a sense of self confidence and well being
used to decrease fatigue and mild depression
when abused they cause feelings of persecution, hallucination and addiction
include amphetamines, cocaine, caffeine, miraa and nicotine
iii) State the general effects of drug abuse on human health
damage to body organs e. g. liver cirrhosis
drug addiction
impaired judgment resulting in clumsiness
socio-economic problems e. g. crime, loss of jobs, divorce, prostitution, HIV/AIDS
may cause poor health
h) i) List the special sense organs in mammals and the major function of each
– Eye for sight
– Ear for hearing and balance
– Nose for smell
– Skin for touch, temperature detection, pain detection
iii) How is the human eye adapted to its function?
conjunctiva is thin/transparent/tough to allow light to pass through/to protect the eye Sclerotic layer is made up of (collagen) fibers/fibrous. It maintains shape of the eyeball/protects the eye
cornea is transparent/curved thus refracts light rays/allows light to pass through
Choroid is a layer of tissue with black pigment/dark pigment. Prevents internal reflection of light in the eye/contains blood vessels that supply oxygen/nutrients/remove (metabolic) wastes from the eye
retina has cones/rods for bright colour vision/low light vision
yellow spot has a high concentration of cones for accurate vision/visual acuity
Blind spot has no cones and rods. Place where optic nerve leaves/enters the eye
optic nerve has (sensory) nerve fibers for transmission of impulses to the brain (for interpretation)
Lens is biconvex/made up of elastic material/transparent. Adjust focus on far or near objects allow light to pass through/for refraction of light rays
ciliary body is made up of muscle fibers glandular which contract/relax to change shape
suspensory ligaments are inelastic to hold lens in position/attach it to ciliary body
iris(is the coloured part of the eye it) has radial and circular muscles which control size of pupil
pupil is the small hole at the centre of iris through which light passes into the eye
aqueous humor is a fluid through which oxygen/nutrients pass to the comea/lens/maintains shape of the eyeball/refracts light rays
vitreous humor is a fluid which maintains shape of eye/refracts light rays
iii) What is accommodation of the eye?
ability of the eye to adjust to bring an image from a near or far object into sharp focus on the retina
iv) Explain how an eye viewing a near object adjusts to viewing a far object
ciliary muscles relax
suspensory ligaments become taut/tight
lens decreases curvature/becomes thinner
radial muscles relax
circular muscles contract
size of pupil decreases to reduce amount of light
v) What changes occur in the eye if it changes from observing an object at a distance to one at a closer range?
– ciliary muscles contract
– Tension in suspensory ligaments reduces/relaxes slackens
– Lens bulges/thickens/increases curvature
– Radial muscles contract
– Circular muscles relax
– Size of pupil becomes large to allow in more light.
viii) State the changes which would take place in the eye if a person in a dark room had lights switched on
circular muscles contract and radial muscles relax
pupil becomes small to allow less light into the eye
ix) Explain how the eye forms an image
the mammalian eye works like a camera
light rays enter the cornea pass through the pupil, aqueous humor, lens and vireous humor
light rays are refracted by the aqueous and humor and lenses
finally light falls on the retina to form an image
the image is real and invened and smaller than object, back to front/reversed
Retina forms a fine image when light rays reach it.
x) Name the defects of the eye and state how they can be corrected
Short sight (Myopia)
eye cannot focus on far objects
image is formed in front of the retina because light rays converge in front of retina
the lens is too thick, curve and eyeball too long
corrected by wearing concave/biconcave/lenses
these lenses diverge light rays onto retina
Long sight (Hypermetropia)
eye lenses are unable to focus because they are flat, thin and weak hence unable to focus image on the retina
they are unable to accommodate/change the focal length
near image is formed behind the retina but a distant one is correctly focused on the retina
corrected by wearing convex/biconvex/converging lenses
Presbyopia
occurs in old age hence called old sight
caused due to loss of elasticity of lenses, weakness of ciliary muscles hence lack of focus of light rays
this causes long sight
corrected by wearing biconvex/convex/converging lenses
Squinting
eyeballs are uncoordinated/do not turn at the same time
eye muscles move in different directions
this makes accommodation and focusing difficult
corrected through surgery
Astigmatism
surface of cornea is uneven
leads to weak focus of light raise on retina
corrected by using cylindrical lenses/lenses with combined curvature
xi) State the advantages of having two eyes in human beings
stereoscopic vision
gives a wider angle of binocular vision
if one is damaged human is not blinded
i) What are the functions of the human ear?
hearing
maintaining body balance and posture
iv) How are the structures of the human ear suited to perform the function of hearing?
Pinna is funnel shaped allows collection of sound waves and channels them down the auditory canal/auditory mateus
auditory canal is a tube that concentrates and directs sound waves to tympanic membrane/tympanum/eardrum
Eardrum is thin and tight. It sets into vibration/vibrates/converts sound waves into vibrations
the vibrations are transmitted to the ear ossicles/malleus, incus and stapes that amplify the sound vibrations
the vibrations are then transmitted to the fennestra ovalis/oval window
Oval window is a membrane which amplifies/transmits vibrations to the fluids (perilymph and endolymph) then to cochlea.
The cochlea is coiled to occupy a small space and accommodate a large number of sensory cells
The sensory cells/hairs (in the cochlea) are set into vibrations/stimulated producing nerve
impulses in the auditory nerve
Impulses in the auditory nerve are transmitted to the brain for interpretation for hearing
Eustachian tube connects the inner ear to the throat. It equalizes air pressure in the middle ear with the atmospheric air pressure (in outer ear)
Fennestra rotundus/round window dissipates/discharges/discards vibrations from inner ear to middle ear
iii) Explain how the structure of the human ear performs the function of balancing
there are three semi-circular canals/utriculus/succulus/vestibular apparatus arranged in planes at right angles to each other
at the end of each canal is a swelling called ampulla which contains receptors
the movement of the head causes movement of the fluid/endolymph in at least one canal
the fluid movement causes stimulation of the receptors/sensory hairs
sensory impulses are generated
the auditory nerve transmits the impulses to the brain for interpretation for the position of body/posture/balance
iv) State what would happen if the auditory nerve was completely damaged
deafness
loss of body balance
impulse not transmitted to the brain
5. a) i) What is support?
to support is to carry part of the weight/mass of an organism
ii) What is locomotion?
progressive change in the position of an organism
iii) State the importance of support systems in living organisms
they provide a framework for the body of organisms and help to determine their shape
provide land animals with means for support to their weights against gravity
organs are attached to the skeleton for support and stability to avoid entanglement and crushing each other
they protect very important and delicate organs whether inside or outside the body e. g. eyes, heart
in large plants the rigid trunks of trees support the greater mass of leaves and fruits
iv) State the importance of locomotion in animals
in search of food
Search for mates
escaping predators
b) i) Name the tissues in higher plants that provide mechanical support
Sclerenchyma
collenchyma (not lignified)
xylem/tracheids and vessels
ii) State the importance of support in plants
exposing the surface area of leaf to sunlight for photosynthesis
ensure flowers are exposed to pollination agents
expose fruits and seeds to agents of dispersal
to resist breakages due to their own weight and that of other organisms
for proper transport and translocation of materials
iii) Name the types of plant stems
herbaceous e.g. shrubs
woody e. g. trees
weak stems in creepers, twining plants and plants bearing tendrils
iv) Name the tissues in plants that are strengthened with lignin
sclerenchyma
xylem vessels/tracheids/xylem
v) What makes young herbaceous plants remain upright?
turgidity
presence of collenchyma
vi) State the ways by which plants compensate for lack of ability to move from one place to another
ability to pollinate
response to nastic and tropic movement
ability to exploit localized nutrients
ability to disperse seed or fruit propagation
c) i) Explain the Ways in which erect posture is maintained in a Weak herbaceous stem
– This is the function of turgidity and presence of collencyma
Cells take in water and become turgid
ii) Explain how support in plants is achieved
Turgor pressure due to absorption of water keeps cells firm hence hold herbaceous plants upright
collenchyma and clerenchyma tissues are closely packed in stem and roots to provide support
inelastic cuticle on epidermis is covered by a waxy layer hence keeping shape of plant and setting inward pressure against turgid cells and this causes a force to hold plant upright
xylem vessels and tracheids are lignified to provide support to stems, roots and leaves
climbing plants obtain mechanical support from other plants and objects
they have climbing structures like tendrils which hold on to other objects
d) i) Give the reasons why support is necessary in animals
for attachment of muscles
For attachment of other body organs
to protect delicate body organs
to maintain body shape/form
to enable movement/locomotion
ii) Why is movement necessary in animals?
enables animals to search for food
enables animals to search for shelter
enables animals to escape predators/harmful conditions
enables animals to Search for water
enables animals to search for mates
enables animals to search for breeding sites
e) i) Name the organ used for support by animals
– Skeleton
ii) Name the different types of skeletons in animals, giving an example of an animal for each type of skeleton named
exoskeleton e.g. arthropoda (crab, insect)
endoskeleton e. g. chordata (cat, fish)
iii) State the difference between exoskeleton and endoskeleton
endoskeleton is a rigid framework covered by body tissues of an animal
exoskeleton is a rigid framework found on the surface of an animal
iv) State the advantages of having an exoskeleton
supports/protects delicate inner parts
water proof/prevents drying up of body
provided surface for muscle attachment
v) Explain the importance of having an endoskeleton
support the body
give body its shape
protect delicate organs e. g. skull, brain, ribs
used in locomotion e.g. bones serve as levers
red blood cells are formed in bone marrow
minerals are stored in bones e. g. calcium and phosphorus
f) i) Explain how a fish is adapted to living in Water
streamlined body for easy movement in water
swim bladder controls depth of swimming
fins for movement, balance, direction and stability,
gills for gaseous exchange in water
presence of lateral line to sense vibrations
scales provide protection .
colour which offers camouflage against predators
ii) Explain how a finned fish is adapted, to locomotion in Water
streamlined body to reduce resistance/friction )to swim smoothly)
the vertebral column consists of a series of vertebrae held together loosely so that it is flexible
myotomes/muscles associated with vertebral column produce movement
the sideways and backwards thrust of the tail and body against water results in resistance of water pushing the fish sideways and forwards in a direction opposed to thrust
heat not flexible so as to maintain forward thrust
presence of fins help in propulsion/balance/paired fins (pectoral and pelvic) for controlling pitch and slow down movement/unpaired fins (dorsal, ventral, anal) for yawing and rolling (caudal) for swimming/propulsion and steering/change of direction
presence of swim bladder to make fish buoyant
scales tip towards the back to provide smooth surface
body covered with mucus to reduce friction
flattened surface for easy floating
g) i) Name the main parts of the vertebral column giving the types of bones found in each part
Axial skeleton
forms the main axis of the body
formed by the skull, sternum, ribs and vertebrae
Appendicular skeleton
composed of limbs and girdles
the forelimbs are connected to the trunk by the pectoral girdles (shoulder bones)
hind limbs are connected to the pelvic girdle (hips)
bones are scapular, clavicle, humerus, ulna, femur, tibia, fibula, metacarpals, carpals, tarsals, metatarsals, phalanges, ilium, ischium and pubis
ii) What are the vertebrae?
bones of the vertebral column
iii) State the functions of the vertebral column
gives flexibility
absorbs shock
protects spinal cord
supports weight of body
provide surface for muscle attachment
between the vertebrae are soft discs which offer cushioning called interverterbral discs
iv) State the general characteristics of vertebrae
have solid structure called centrum to support weight of body
has transverse process lateral to centrum for muscle attachment
neural spine is dorsal to centrum and provides surface area for muscle attachment
neural canal a passage for spinal cord and offers protection to it
has facets for articulation with other vertebrae
neural arch encloses neural canal
v) Name the bones of the vertebral column
– Cervical vertebra
— Thoracic vertebra
– Lumbar vertebra
– Sacral vertebra
– Caudal vertebra
vi) Describe how the various vertebrae are adapted to their functions
Bone:
skull
Structure:
cranium and jaw bones
made of several bones joined together
large box called cranium and smaller paired boxes for eyes, ears, nose, jaw
has large hole called foramen magnum for passage of spinal cord
Function:
attachment of jaws
protect brain and other delicate parts
Bone:
cervical region Atlas (first cervical)
Structure:
ring shaped
no centrum
broad flat transverse processes
vertebraterial canal for passage of vertebra artery
facet for articulation of condyles of skull
Function:
protects the spinal cord
attachment of muscles
allow nodding of head
Bone:
axis (second cervical)
Structure:
adontoid peg projects from centrum
large flattened neural spine
vertebraterial canal
small transverse process
Function:
allows the head to rotate
protects the spinal cord
provides surface for muscle attachment
Bone:
cervical (others) Structure:
short neural spine
branched transverse process for neck muscles
vertebraterial canal
wide neural canal
Function:
supports weight of the head
protects the spinal cord
neck muscle attachment
Bone:
Thoracid
Structure:
long backwards pointing neural spine
transverse process that points sideways
facets for articulation of ribs
notch for spinal nerves to pass through
Function:
forms ribcage
articulation with one end of rib
protects the spinal cord
muscle attachment
Bone:
lumbar
Structure:
short neural spine
long transverse process towards abdomen
large centrum
extra processes e.g prezygapophysis, hypapophysis, anapophysis,metapophysis
Function:
protects organs of the abdomen
supports the upper part of the body
protects the spinal cord
muscle attachment
Bone:
sacral
Structure:
fused bones to form sacrum
well developed transverse processes of first vertebra
vertebraterial canal
short neural spine
Function:
protects the alimentary canal
attachment of hip girdle
protects the spinal cord
muscle attachment
Bone:
Rib
Structure:
long
flattened
attached to sternum from front
Function:
protects internal organs
muscle attachment
vii) Describe the bones that form the appendicular skeleton
Bone:
pectoral girdle (scapular shoulder bone)
Structure:
broad i,e flattened blade
glenoid cavity to articulate with humerous
metacronium/acromion for muscle attachment
hard to provide support
socket with cartilage/smooth surface to reduce friction
Function:
support muscle attachment
articulate with humerous
Bone:
Humerous
Structure:
long shaft for muscle attachment
round head to articulate with glenoid cavity
trachlea for articulation with ulna
olecranon fosa to prevent arm bending the other way
Function:
movement
muscle attachment
Bone:
Ulna and radius
Structure:
ulna longer and on side of little finger
has sigmoid notch and olecranon process to form hinge joint with humerous
radius is smaller and lies along thumb side and does not join ulna
allows articulation with wrist bone
Function:
movement
muscle attachment
Bone:
pelvic girdle (hip bone)
Structure:
composed of three fused bones ilium, ischium, pubis
upper end fused to sacrum
lower end has acetabalum for articulation with femur
has abturator
Function:
movement
muscle attachment
support
absorbs pressure exerted by ground when animals move
Bone:
Femur
Structure:
rounded head to fit in acetabalum of pelvis
projections called trochanter for attachment of thigh muscles
condyles at lower end for articulation with tibi
patella that covers knee and prevent leg from bending backwards
Function:
movement
muscle attachment
Bone:
tibia and fibula
Structure:
tibia is longer than fibula
tibia is outer bone and fibula is inner bone
tibia lies on the side of large toe
fibula is fussed to tibia on (outer side)
Function:
movement
muscle attachment
6. a) What is a joint?
the point where bones meet
ii) State the functions of joints
provide a point of articulation between bones
iii) Name the main types of joints
immovable joints e.g. skull, pelvic girdles and sacrum
slightly movable joints e. g. between vertebrae
Freely movable joints e. g. knee, elbow
iv) Give the features of movable joints
ends of bones covered with articular cartilage
ends bound by capsules of ligaments
have joint cavity filled with lubricating fluid called synovial fluid secreted by synovial membrane
they are called synovial joints
b) Describe the synovial joints
iv) Ball and socket
allow movement in all planes /directions i.e. 360°
rounded end of bone fits into a rounded/cavity in another bone
e.g. shoulder joint and hip joint
v) Hinge joint
convex surface of one bone fits into the concave surface of another bone
this allows movement in only one plane/direction 180°
e.g. elbow joint and knee joint
vi) Pivot joint
allows rotation e. g. where atlas pivots on olecranon process of axis
c) i) What is synovial fluid?
lubricating fluid produced by synovial membrane at movable joints
ii) State the functions of synovial fluid
absorbs shock
reduces friction/ gives lubrication
nourishment
distributes pressure
d) Explain the following terms
v) Ligament
connective tissue joining one bone to another
vi) Cartilage
supporting soft tissue found at joints
they cushion the bones and absorb shock
vii) Tendon
tissue that connects muscle to bones
7. Muscles
e) i) What is a muscle?
fleshy part of body
composed of long cells enclosed in a sheath
specialized cells capable of contracting
ii) State the functions of muscles
cover the skeleton
provide shape
contract and relax to enable body to move
f) Describe the structure and function of various types of muscles
i) skeletal muscles
also called voluntary/striated/stripped muscles
they are attached to skeleton
they consist of striated, multinucleated, ling fibers and are cylindrical shaped
found on legs, arms, eyes, neck where they cause movement
ii) Involuntary muscles
also called smooth/visceral/unstriated/unstripped
their movement is not controlled by the will
they are unstriated, nucleated, short fibred and spindle shaped
are found in alimentary canal, blood vessels, secretory glands, other tubular visceral
