1. a) Homologous structures have a common embryonic origin but are modified to
Perform different functions; while analogous structures have different embryonic origin but are
modified to perform similar functions;
b) Nictitating membrane; post anal tail; body hair;
2. a) Pentadactyl limb structure of mammals; beaks of birds; feet of birds;
b) – Missing links between fossils because some parts or whole organisms were not fossilized
– Some parts were distorted during fossilization hence may give wrong impression
of structures;
– Some structures have been destructed by geological activities;
3. Camouflage is the conceal/ element of identity of an organism by resembling the color
of the environment while mimicry is the imitation of non- living organisms to conceal identity
4. Light energy splits water molecules; into hydrogen ions and oxygen atoms;
5. (a) Caecum/ Rumen/ pauch;
(b) Closes to prevent food from moving up the oesophagus;
6. (a) – the soft bodied organisms fail to fossilize;
– Human activities interfere with fossilization;
Earth movements e.g. volcanic eruptions interfere with fossilization; (mark any first2 pts
(b) – They resembled from neck downwards;
-They walked upright;
– The shape of the skull suggested they were able to speak;
7. a i)vestigial structures are those structures that have ceased to be functional over along
period of time and hence reduced in sizes
ii)-appendix;
-caecum
-coccyx or tail/tail bone;
– Nictitating membrane/semi – lunar fold at the corner of the eye;
-ear muscles
– Body hair;
b) Disease causing organism mutates; and became resistant;
8. Struggle for existence –environmental pressure on the population in order to survive;
Survival for the fittest-advantageous variations an individual possesses to make it survive;
9. Secretion of antidiuretic hormone; rearbsorption of salts at the loop of Henle;
10. -Divergent evolution refers to a situation where by organisms that are believed to have
had a common ancestral origin have homologous structures which have been modified to suit different environments;
11. a) Allows survival of organisms with better qualities / traits / characteristics; eliminates
organisms with unfavorable characteristics/ traits;
b) Divergent;
12. Evidence does not support Larmarks theory
Acquired characteristics are not inherited/;
Inherited characteristics are found in reproductive cells ;
13. (a) Vestigial structures
(i) Are those structures that have ceased to be functional over a long period of time hence
reduced in size;
(ii) Appendix/coccyx/tail/ nictitating membrane semilun fold at the corner of the
eye/caecum/ear muscles, body hairs;
(b) Disease causing micro-organisms mutate and become resistant;
14. a) The gradual emergence of complex life forms from pre-existing simple forms over along
period of time ;
b) Nature selects those organisms with structures that are well adapted to survival in
the environment. These structures are passed to their offspring; organisms with structures
that are poorly adapted perish ;
15. The insecticide kills most of the insects when introduced; those that survive; give rise to a new
generation of flies that are resistant to insecticide.
16. – Most organisms especially soft-bodied ones do not form fossils;
– Most fossils have not yet been discovered;
– Exposed fossils are usually destroyed by physical and chemical weathering;
– Earth movements e.g. volcanicity, earthquakes, tsunami do destroy fossils;
– Most animals are prayed upon;
17. -Fossil records/paleontology ;
-Comparative anatomy/taxonomy;
-Comparative embryology;
-Geographical distribution;
-Cell biology;
-Comparative cellulogy/immunology; (award 1st three 3mks)
18. Nature selects organisms that are well adapted and allows them to survive: but rejects those that are poorly adapted they perish/die/become eliminated;
19. (a) The genotype of an organism is not changed by characteristics acquired during the
life/ phenotypically acquired characteristics do not affect the genotype of an individual
(b) – Missing links (due to decomp0osing of savaged form)
– Distortion of parts (some parts were flattened);
– Geographical activities (e.g. earthquake, faulting, erosion) (any 2)
20. (a) White flowers.
(b) The white flowers were fewer that is the ratio of ¼ of the total flowers.
Parental phenotype white flowers white flowers
Parental genotypes r r x v r
Gametes
(c) A cross between unknown genotype with a homozygous recessive/double recessive genotype
(d) – Low mental capability
- Short/stubby fingers
- Slit eyes
21. (a) Emergence of new life forms//species//organisms; from pre-existing forms gradually
over a long period of time;
(b) Fossil records//Palaeontology;
These are remains of organisms preserved in some naturally occurring materials e.g. sedimentary rocks for many years; They give direct evidence of the type of organisms that existed at a certain geological time//show a gradual increase in complexity/morphological changes of organisms over a long period of time e.g. skull of man
Geographical distribution;
present continents are thought to have been a large land mass joined together; continental drift led to isolation that lead to different patterns of evolution; e.g. camels of Africa resemble the Ilamas of S. America// tiger of Asia resemble jaguars of S. America // unique Marsupials of Australia;
(accept any valid example)
Comparative Embryology;
Vertebrate embryos show morphological similarities in their early development; suggesting these organisms have a common origin; Accept – embryos of mammals /reptiles/ amphibians compared to show the similarities;
Cell Biology// Cytology;
Occurrence of cell organelles e.g. Mitochondria
Cytoplasm nucleus// Accept any correct organelle; point towards a common ancestor;
Comparative serology;
Analysis of blood proteins and antigens / Rh factor/ blood group /haemoglobin reveal phylogenetic blood group/haemoglobin reveal phylogenetic relationships; Those species that are more close phylogenetically related contain more similar blood protein;// Antigen-antibody reactions/serological tests/experiments with serum reveal some phylogenetic relationship depending on the level of precipitation.
Comparative anatomy/taxonomy;
- Members of a phylum show similarities indicating common ancestry; These organisms have similar functions e.g. presence of digestive, urinary, nervous systems e.t.c;
- Homologous structures like pentadactyl limbs in different animals like monkey and rats have similar borne arrangement hence same origin but modified to perform different functions// adaptive radiation//divergent evolution; vestigial organs//coccyx Appendix;
- Analogous structures like wings of birds and wings of insects with different embryonic origin but perform same function//convergent evolution; (maximum 18mks)
N/B- Mention of each evidence 1mk each
- It is muscular//Has cardiac muscles which are myogenic;//capapble of contracting and relaxing without nervous stimulation to ensure the heart beat without stopping;
- Supplied by vagus and sympathetic nerves; which control the rate of heart beat depending on body’s physiological requirement;
- Has tricuspid and bicuspid valves//arteria ventricular valves; to prevent back flow of blood into wrong directions;
- Has semi lunar valves at the base of pulmonary artery and aorta; to prevent back flow of blood into right and left ventricles respectively;
- Presence of valve tendons attached to the walls //arteria ventricular walls; prevent arteria ventricular valves // tricuspid and bicuspid valves from turning inside out;
- Supplied by coronary artery; to supply food and oxygen t the cardiac muscles for their pumping action;
- Coronary vein; draws away metabolic wastes;
- Heart is enclosed by pericardial membrane; which secrete fluids which lubricates//reduces friction on the walls as it pumps;
- Pericardial membrane is lined with a layer of fat to act as shock absorber; hold the heart in position; checks over dilation of the heart;
- The heart is divided into two by (artria ventricular) septum; which prevents mixing of oxygenated and deoxygenated blood;
- The sino-artria node// pace maker; initiates a wave of excitation leading to contraction and relaxation of cardiac muscles;
- The artria –ventricular node; in the heart spread out waves of excitation through out the heart
The structure tied to function wrong function cancel the mark of the structure. Correct structure minus function do not qualify for a mark
22. (a) Nature or the environment selects those individuals that are sufficiently adapted; and rejects
those that are not adapted;
(b) Adaptation by natural selection.
– Individuals of the same species show variations.
– The variations are caused by genes that can be passed on from parents to the off springs
(inherited);
– Some of these variation become more suitable or favorable or advantageous in the prevailing
environmental conditions;
– Because organisms usually produce more off springs than the environment can support;
competition for resources sets in;
– This leads to struggle for existence;
– Individuals with more favorable characteristics/ adaptations/ gene mutation have better chance
of survival in the struggle;
– Hence they reach reproductive age, reproduce and pass on favorable characteristics to the off spring;
– Those with less favorable characteristics or adaptations fail to reach sexual maturity; they die young;
– Examples of natural selection include- malarial parasite/plasmodium which has developed
strains that are resistant to anti-malarial drugs;
– Sickle cell trait; the homozygous die young and the heterozygous are resistant to malaria.
(c) – Convergent evolution.
– This is a phenomenon where structures from different embryonic origins are modified
to perform the same function. E.g. wings of birds and those of insects, eyes of human
beings and those of octopuses;
– Divergent evolution.
– This is a phenomenon where one basic structural form is modified to give rise to various
different forms which perform different functions. E.g. pentadactyl limbs of vertebrates,
shapes of beaks in birds;
(d) Evidences to show that evolution has taken place. (Any 4)
i) Fossil records.√
ii) Comparative anatomy. .√
iii) Comparative embryology. .√
iv) Geographical distribution (continental drift).√
v) Vestigial organs.√
vi) Cell biology. √
(i) Fossils records;
Fossils are remains of dead organisms preserved naturally. They indicate that organisms have evolved from simple life forms to most complex forms. Fossils of human beings indicate that the modern human being has a highly developed brain and uses speech for communication unlike the early human being. Of horses show that the modern horse is 1.5 m high, lives in dry grassland, teeth are adapted for chewing and it stands on one digit whose distal end is converted into hoof.
(ii) Comparative Anatomy;
This involves comparing the form and structure of different organisms.Some groups
organisms show basic structural similarities suggesting common or related ancestry
showing divergent evolution.
Other groups of organisms show morphological similarities but are found to have different
ancestry showing convergent evolution;
(iii) Vestigial Organs;
Some structures have ceased to be functional and have reduced in size; such structures are called vestigial structures. Examples include the appendix and the tail in human beings; reduced wings in flightless birds, nictitating membranes in mammalian eyes and lack of visible limbs in pythons.
(iv) Geographical distribution;
– Its believed that long ago the land was one mass which later drifted apart to form the current continents. This is called the continental drift.
– Regions with similar climatic conditions and lie in the same latitude have flora and fauna that are not identical. This indicates that they have evolved differently; e.g. Amazon forest of South America has long tailed monkeys, panthers and jaguars while similar African forests have short tailed monkeys, leopards and
cheetahs.
(v) Comparative embryology;
Studies show that embryos of fish, birds, amphibians, reptiles and mammals are morphologically similar during the early stages of development but with time they develop and change to look like their parents;
(vi) Cell biology;
– Cells of higher organisms show basic similarities in their structure and function; e.g. the presence of cell membranes and organelles such as mitochondria, ribosomses and golgi bodies.
– Higher plant cells have cellulose cell walls, chloroplasts and starch showing evolution from a common ancestry.
– The blood pigment, haemoglobin is common in vertebrates and invertebrates.
23. a) organic evolution is the process by which changes in the genetic composition occur in
response to environmental changes *RCH*
b) within the population some individual posses the gene for resistance to the antibiotic or it develops the genes by mutation ; such genes lead to production of enzyme which neutralize the antibiotic; the resistance forms survive the antibiotic hence transmit their advantages genes to their offspring; thus a new population of resistance strains is established(e mergence of new species(speciation)
c) fossil records;
-remains of ancestral forms that were accidentally preserved in some naturally
occurring
materials
-they give direct evidence of the type of animals and plants that existed at a certain
geological agp
-the fossils records also show gradual increases in complexity of organism over time
e.g. evolution of man
-by comparing fossils of different organism its possible to tell the phylogenic
relationship between the organism
c) Gene for red colour and white colour in flowers are co dominant/ equal dominance/ none
is dominant/ recessive
