KCSE PIVOT BIOLOGY

a) What is natural selection? (Theory put forward by Charles Darwin that explains that)÷ Nature selects for individuals that are well adapted to a particular environment; and against those that are less adapted; (2 mks) b) Discuss three examples of natural selection in action. 1.Melanic forms of peppered moths in Europe. There are two forms of peppered moths; white and black. Before industrialization, the tree trunks were white. Therefore the white peppered moths were were camouflaged. The black varieties were easily noticed and fed upon by predatory birds; the white forms therefore reproduced and increased in number. During industrialization, the smoke from industries coated tree trunks black. The black variety became camouflaged, reproduced and their population increased. The white varieties were easily noticed and fed upon by predators; their population reduced. 2. Resistance against drugs and antibiotics, where microorganisms are continually exposed to a certain dru

1. Comparative anatomy/taxonomy.  Members of a  phylum/group show  similarities. Organs  have similar  structure. These are organs that perform  the  same  function in different organisms such  as  the  digestive  system, urinary system, vertebrate  heart. Homologous  structures are  structures with the  same embryonic  origin but have  been modified to  perform different  and specific  functions. This phenomenon is called adaptive radiation. Structures in organism get modified as to suit the needs of the environment. They show a form  of  divergent evolution. Evolution in which organisms have the same ancestral origin but occupy different ecological environments hence their body structures get modified to suit the new environment. e.g.  the pentadactyl limb in vertebrates which has been modified  for racing in horse; swimming horse in whale and  flightwhale in bats and birds or beaks  of finches and  birds. Pentadactyl limb structure is based on five digits which suggest a common a

(a) - The root hairs grows between the soil particles surrounded by a film of water/soil solution; The sap   in the root hair has higher osmotic pressure than the soil solution; Water is drawn into the root hair    by osmosis; This dilutes the cell sap in epidermal cell; relative to the sap in the adjacent cortical    cells; Because of this, water moves into the adjacent cortical cells; until it reaches the xylem    vessels; Within the leaf cells; some water is used in the manufacture of food; and some vapourises   when the temperatures are high; gets into the intercellular air spaces; and diffuse out of the leaf;    through the stomatal opening; into the atmosphere; in a process called transpiration; (Total 17 mks)      (b) Mechanisms of translocation of manufactures food. - Active transport; - Mass flow; - Surface spreading; - Cytoplasmic streaming;(Any three correct points = 3 mks

a) Heart; blood capillaries; b) Varicose veins; thrombosis; arteriosclerosis; hypertension; First two c) Water is absorbed into the root hairs by osmosis; root hairs cell sap is hypertonic to the surrounding film of water; Root hair sap become dilute compared to adjacent cortex cells; hence set .osmotic pressure for water to move by osmosis; some water moves by cytoplasmic streaming; up to the endodermis; water then moves across the endodermis by active transport; to the root xylem; water xylem move to the plant by root pressure; capillarity; aadhesive and cohesive forces; and transpiration pull; The water then enters leaf cells by osmosis; then into the intercellular air spaces; of the spongy mesophyll layer; after is then lost to atmosphere by diffusion; through stoma; process called transpiration;

a) - xylem; - sclerenchyma; - collenchyma; b) - Protect inner delicate organs; - Site for muscle attachment; - Bring about locomotion; - Give body shape; - Provide support to the body; First 3 c) -Girdles comprise pectoral girdle; Pelvic girdle; -Pectoral girdle comprise the clavicle; and scapula; scapula has glenoid cavity; articulate with head of humerus; to form ball and socket joint; scapula has coracoids process; metacramion; acromion; spine; provide site for muscle attachment; Pelvic girdle comprise of 3 fused bones; -The two halves of pelvic girdle articulate at pubic symphysis; to offer support to upper parts of the body; - On either side of pelvic girdle are cup shaped acetabulum; articulate with femur; form ball and socket joint; - At the pubis is the obturator foramen; passage of blood vessels; on dorsal side the pelvic girdles have articular facets; articulate with sacrum of the axial skeleton; Total 22 (max 16)

■Has secretory glands / crypts of lieberkuln which secretes enzymes (maltase / sucrose / peptidase / lipase to complete digestion of lipids / sugar / proteins. ■Goblet cells secrete mucus which allows for smooth movement of food / protect wall of ileum from action of digestive enzymes. ■Very long to provide large surface area for absorption ■Highly folded / coiled to slow movement of food to allow more time for digestion / absorption / increase surface area for absorption. ■Has numerous villi which increase surface area for absorption / microvillus which further increase surface area for absorption. ■Ileum wall / villi have thin epithelium which is only one cell thick to reduce distance over which digested food has to diffuse. ■Villi are highly vasculised / have a rich network of blood capillaries for rapid transport from small intestines / maintain a steep concentration gradient. ■Villi have lacteals for absorption of fatty acids and glycerol ■Cells of ileum wall have

Broad / wide / flat lamina; to provide large S.A; for absorption of CO2/sunlight; ■Thin; to ensure short distance for CO2 to reach photosynthetic cells/palisade/mesophyll; ■Guard cells/ presence of stomata; for efficient diffusion of CO2 into leaf/ oxygen out of leaf/gaseous exchange/ water vapour/ transpiration. ■Transparent cuticle/epidermal cells; for penetration of light; into palisade cells/ photosynthetic cells. ■Palisade cells contain many chloroplasts; to trap light (for photosynthesis); ■Chloroplasts have chlorophyll; for trapping light energy; ■Leaves have veins; Xylem to conduct water to photosynthetic cells; and phloem to translocate the photosynthates to other parts of the plant; ■Air spaces in spongy mesophyll; for gases to circulate/diffuse easily/ for CO2 to diffuse into palisade cells; ■Mosaic arrangement of leaves; enables all leaves to trap sunlight; ■Palisade cells are next to upper epidermis for maximum light absorption (by chloroplasts)

a) ■Agrochemical from neighboring farms causes eutrophication e.g. pesticides -Poison the fish and plants life (living organism) ■Siltation – reduce photosynthesis                - clog gills of fish                - causes turbidity ■Industrial wastes e.g lead, mercury (heavy metals) get fixed in the food chain that gets its way to man. ■Untreated sewage – causes eutrophication  - reduce oxygen in water. -causes decomoosition -causes diseases  -increases turbidity reducing light penetration ■Spilt oil from tankers or used oil from garage  -limits supply of oxygen to aquatic life  -covers stomata of plants  - clogging gills and feathers of bird ■Hot water – kills organism  -reduces concentration of oxygen.          b)-proper sanitation  -proper hygiene  -boiling drinking water  -avoid coming into contact with water bare footed  -draining stagnant water  -washing fruits with clean water  -proper cooking of food  -destroying the vectors  -proper storage o

Ileum> hepatic portal vein> liver> hepatic vein> inferior vena cava> vena cava> right auricle> right ventricle> pulmonary artery> lungs> pulmonary vein> left auricle> left ventricle> aorta> abdominal aorta> femoral artery> femoral arterioles> capillaries> ultrafiltration> tissue fluid> muscle cell. NB sequence of flow must be correct

i) White blood cells; – engulf; and destroy bacterial/pathogen; Produce antibodies; which neutralise bacterial toxins; Blood platelets; – Cause clotting; on fresh wounds preventing entry of bacteria into tissues prevent loss of blood water; and mineral salts;. ii) It is muscular/has cardiac muscles; which are myogenic (does not need nervous stimulation) to pump blood; It is supplied by vagus nerve which has sympathetic and parasympathetic nerves; which controls to rate of heart beat depending on body’s physiological requirements; It has triscupid; and bicuspid valves between atrium and ventricles which prevent back flow of the blood into the right and left ventricles respectively;. Presence of valvular tendons attached to the walls of ventricles and to the atria –ventricular walls; to prevent  atria-ventricular valves from turning inside out due to changes in the pressure in the ventricles. Heart is supplied by coronary artery; which supplies nutrients  and oxygen to the

Describe how xerophytic plants are structurally adapted to their habitat. Adaptation of xerophytes     These are plants which are adapted to withstand harsh environmental conditions like – low supply of water, high day temperatures, windy conditions and low humidity; all these conditions lead into excessive water loss by transpiration; they are therefore adapted by;     Structural adaptations:- Their leaves are modified into spines/thorn like structures to reduce surface area exposed for transpiration; Their stomata are sunken; and water vapour accumulate on the sunken depression; lowering water vapour concentration gradient; between the atmosphere and the sub-stomatal air spaces; this reduces the rate of transpiration; Leaves have thick waxy cuticles; to reduce cuticular transpiration; The number of stomata is reduced to minimal to reduce stomatal transpiration. Deep roots so as to reach and absorb water found in deeper layers in the soil; They have parenchyma cells

a) Two functions of the placenta - serves for the exchange of materials between the mother and the foetus. - Serves as endocrine organ- forms source of progesterone  hormone which is  important in female reproduction. b) The role of hormones in the human menstrual cycle the menstrual cycle begins on the very first day of the menstrual flow. pituitary gland starts to secrete follicle stimulating hormone (FSH) The FSH causes development of a Graafian follicle in the ovary. It also stimulates the walls of the follicle/tissues of the ovary to start secreting oestrogen. Oestrogen causes repair and healing of the uterine wall.  It also stimulates the pituitary gland to secrete the lutenising hormone (LH)  LH stimulates the final maturation of the Graafian follicle and ovulation. Following ovulation, LH causes remains of the Graafina follicle to re-organize into a corpus luteum. LH stimulates the corpus luteum to secrete the hormone progesterone. Progesterone causes the lining of

 a) i) - Gradual developmental change of species of organisms from simple forms of life into complex ones over a long period of time. -Or  Emerging of new forms of life from pre-existing ones gradually, over a long period of time. ii) - Homologous structures – structures of common/similar embryonic origin but modified to perform different functions. - Analogous structures- structures of different embryonic origin modified to perform similar functions. b) Fossil/paleontological evidence these are remains of organisms preserved in naturally occurring material like sedimentary rocks for many years. They show morphological changes of organism over a long period of time egskull of man and leg of horse. Comparative anatomy/taxonomy Members of a given phylum/group show similarities Such organisms have similar structures or organs performing the same functions eg digestive system, urinary system and nervous system. Homologous structures have the same embryological origin but perfo

Follicle stimulating hormone (FHS); is secreted from the anterior lobe of the pituitary gland just after menstruation;  It causes Graafian follicle to grow in the ovary; FSH also stimulates tissues of the ovary to produce oestrogen; Oestrogen; brings about healing and repair of endometrium; destroyed during menstruation; Accumulation of oestrogen; stimulates pituitary gland produce Luteinising hormone (LH); Luteinising hormone (LH); stimulates maturation of graafian follicle; The mature graafian follicle releases an ovum into funnel shaped part of the ovary;  This is known as ovulation; LH also brings about changing of graafian follicle into corpus luteum; LH then stimulates corpus luteum to secrete progesterone; Progesterone; stimulates thickening of the endometrium and increases blood supply to the endometrium; in preparation for implantation. When fertilization has taken place, progesterone levels increase and this inhibits secretion of FSH; hence no more gr

The pinna;- is funnel shaped to trap sound waves; cartilaginous to maintain the funnel shape; collects and directs sound waves into the external auditory meatus ear; The external auditory canal; - a tube connected to the pinna that directs sound waves from the pinna to the eardrum lining the auditory canal; has hair that trap foreign particles; The canal contains wax-secreting cells; and hair which traps dust particles; and pathogenic bacteria hence prevent them from getting into the ear; The eardrum; - has a thin tough membrane; that easily vibrates when hit by sound waves; transferring them into vibrations. The ear ossiscles; - they act like a layer and they easily move forward and backward to amplify sound vibrations that hit them; The suspensory ligaments; - suspends the ear ossicles and prevents excessive vibration that would otherwise damage the inner parts of the ear; The eustachian tube - it connects the middle ear with the pharynx; and it equalises air pressure between

KCSE BIOLOGY SYLLABUS FORM 1 . 1. Introduction to Biology     Definition of Biology     Branches of Biology     Importance of Biology     Characteristics of living organisms     Comparison between plants and animals 2. CLASSIFICATION 1     Review and use of magnifying lens     External features of plants and animals     Necessity and significance of classification     Major units of classification( naming)     Kingdoms     Discussion of Binomial nomenclature 3. THE CELL     Definition of cell     Structure and functions of parts of a light microscope     Use and care of the light microscope     Cell structure and functions as seen under microscope     Preparation of temporary slides of plant cells     Estimation of cell size     Cell specialization, tissues, organs, and organ systems.     Practical activities     1. Observe, identify, draw and state the functions of parts of the light microscope     2. Prepare and observe temporary slides of plant ce

Characteristics Of Living Organisms In order to identify living organisms, scientists listed 8 characteristics which all living organisms have: 1. Nutrition: Taking in foods which are organic substances and mineral ions, containing raw materials and energy for growth and tissue repair, absorbing and assimilating them. 2. Excretion: Removal from organisms of toxic materials, the waste products of metabolism and substances in excess. 3. Respiration: Chemical reactions that break down nutrient molecules in living cells to release energy. 4. Sensitivity/Irritability The ability to detect or sense changes in the environment and to make appropriate  responses. 5. Reproduction: Progresses that existing organisms  make more of the same kind of organism. 6. Growth and Development The permanent increase in size and dry mass by an increase in number of cells, cell size, or both; Physical and chemical modifications in organisms that improves ability to function.