K.C.S.E Online Revision

Biology Questions and Answers Form 2

KCSE Revision Questions and Answers

Biology Notes Form 2

1. a) i) Define transportMovement of substances from one pan of the body to another

ii) Explain the necessity of transport in plants and animalsmake nutrients move from one point to anothermovement of respiratory gases i.e. oxygen and carbon IV oxideelimination of metabolic wastesmovement of hormonesmovement of watermovement of saltsmovement of enzymes

b) i) Describe the structure and function of root hairroot hairs are found near the root tipthey are cells with elongated finger-like projections which are in contact with soil particlesthey are permeable to water and mineral salts hence are used to absorb Water and mineral saltsThere large number offers a large surface area for absorption of water and mineral salts.

ii) State ways in which the root hairs are adapted to their functionsthe root hair is long/narrow/numerous to increase surface area for absorption of water and mineral saltsmany mitochondria in cytoplasm to supply energy for active transport of mineral saltsare thin walled to speed up rate of absorption of Water and mineral salts

c) i) Compare the internal structure of a dicotyledonous root and a monocotyledonous root

Monocot root

ii) State the similarities and differences between a dicotyledonous and monocotyledonous root

Similaritiesboth used for anchorage and absorption of water and mineral saltsboth have root hairs, epidermis, pericycle, cortex, endodermis and vascular bundles(xylem and phloem)both may be used to store food/storage organs


Monocotyledonousphloem and xylem are arranged in ring form alternatelypith present

Dicotyledonousphloem lies between radial rays of central xylem(star shaped)pith absent

iii) Compare the internal structure of a monocotyledonous and dicotyledonous stem

Monocotyledonous stem

Dicotyledonous stem

i) Give the similarities and differences between a monocotyledonous and dicotyledonous stem

Similaritiesboth are used for protectionboth conduct water, salts and foodboth have epidermis, cortex, pericycle and vascular bundles


Monocotyledonousvascular bundles are many and scatteredsome have hollow pith or pith is absentno cambium layer therefore cannotundergo secondary growth verylittle cortex

Dicotyledonousvascular bundles are few and arranged in a concentric ring near the epidermispith large and well developed

State the differences between the internal structure of a root and a stem.no cambium layer therefore cannotundergo secondary growthvery little cortexpresence of cambium thereforeundergoes secondary growthcortex has several layers of cells

c) i) Name the transport structures of a flowering plantxylem vessels and tracheids transport water and mineral salts from the soilPhloem vessels translocate manufactured food from leaves to other parts of the body

ii) State the ways in which xylem vessels are adapted to their functionlignified/thickened to prevent collapsingnarrow to facilitate capillaryno cross walls for continuous flow/column of waterhave bordered pits for lateral movement of water

a) i) Why do flowering plants need water?photosynthesistransportturgidity w h helps in plant supportsolvent i.e. medium for chemical reactionscooling effect during transpirationseed germination

ii) Describe the movement of water from the soil to the leaves of a tall plantSoil water exists as a thin film in the soil, between soil particlesthe concentration of cell sap of root hair is greater than that of the surrounding solution in the soil, thus drawing the Water molecules across the cell wall and cell membrane into the root hair by osmosiswater drawn into the root hair cell dilutes the cell sap making it less concentrated than that in the adjacent cortex cells of the rootdue to osmotic gradient water moves from the root hair cells into the cortex by osmosis, from cell to cell by osmosis, across the endodermis by active transport into xylem vessels of the root that conduct water into xylem vessels of the stem into xylem vessels of the leaves

StemOnce in the stem water moves up the plant aided by the narrowness of the xylem vessels (capillary), root pressure, attraction of water molecules to each other (cohesion).Attraction of water molecules to the Walls (adhesion) from the stem water enters the xylem of leaveswater moves in the xylem vessels of the stem in a continuous (uninterrupted) water column up to the tree leaves

Leavesonce in the leaves water moves into the mesophyll cells by osmosis as water vaporizes from the spongy mesophyll cells their sap becomes more concentrated than the adjacent cells as the result water flows into the cell from other surrounding cells which in turn takes in water from xylem vessels within the leaf veins this creates a pull(suction force) called transpiration pull that pulls a stream of water from xylem vessels in the stem and roots .The transpiration pull maintains a continuous column of water from the roots to the leaves.

iii) Name the process by which mineral salts enter into a plantactive transportdiffusion

i) Explain the forces that make water and mineral salts move through a plantmineral salts are taken up due to diffusion because of the concentration gradient between the mineral ions in sap and those in soil solutionactive transport involves energy in form of ATP due to respiration which forces mineral salts through a plant against a concentration gradientwater moves by osmosis through a semi-permeable membrane of root hairs and between cells of stemin stem water moves by cohesion(attraction of water molecules to each other)it also moves by adhesion(attraction of water molecules to walls)capillarity is due to narrowness of xylem vesselstranspiration pull occurs When Water vapour evaporates from sub-stomatal chambers into the airroot pressure is a force that pushes Water up the stem from the roots and causes guttation /exudation

ii) Explain the uptake of mineral salts by plantsplants require mineral salts for metabolism and proper functioning of their bodiesmineral salts are taken up from the soil into the root hairs in form of solution by activetransport which requires energyactive transport involves substances called carriers taken up together with water and are then carried to the stems and leavesthe main process involved in uptake and movement of mineral salts is active transport

b) i) What is transpiration?loss of water from plant to the atmosphere

ii) Name the sites through which transpiration takes place in a plantstomata (stomatal transpiration)lenticels (lenticular transpiration)cuticle(cuticular transpiration)

iii) State the importance of transpiration to plantscooling the planttransport of watertransport of mineral saltsexcretion of excess Water from plants

excess transpiration causes wilting

i) Explain the structural factors that affect the rate of transpiration in plantsnumber of stomata i.e. the more the stomata the higher the rate and vice versaturgidity of the guard cells which control the opening and closing of stomata when they are open transpiration rate is highsize of leaves where the larger the surface area the higher the rate of transpirationleaf fall leads to lower rate of transpiration and also drying of leaves reduces rate of transpirationThin cuticle reduces distance through Which water vaporizes hence increase transpiration rate. Absence of cuticle also increase rate of transpiration

ii) Explain the environmental factors that affect rate of transpiration in plantshigh temperature increases rate of transpiration and low temperature reduces the ratehumidity when high increases rate and when low reduces the ratetranspiration rate is higher in moving air (wind) than in still airhigh light intensity increases internal temperature hence higher rate of evaporation leading to higher rate of transpirationavailability of water in the soil leads to more absorption hence more loss to the atmosphereatmospheric pressure when high leads to more evaporation and when low leads to low rate evaporation of water

iii) State the structural differences between xylem vessels and sieve tubessieve tubes have cross wall while xylem vessels have nonexylem vessels are lignified while sieve tubes are notSieve tubes have cytoplasm elements while xylem vessels have none.

iv) State the adaptations of plants which enable them to reduce water lossthick waxy cuticlereduced leaf size/thorns/spinesshedding of leavesSunken stomata. Water vapour accumulates in the depression of stomata lowering the water vapour concentration gradient leading to lower rate of evaporationrolling of leaves

v) State the factors that cause increase in the rate of transpiration from leavesincreased light intensitylow relative humiditytemperature

vi) Explain how drooping of leaves on a hot sunny day is advantageous to a plantreduces surface area exposed to sun reducing cuticular transpiration

c) Explain how aquatic and terrestrial plants are adapted to deal with problems of transpiration

a. Mesophytesthey grow in soils with enough waterwater loss is perfectly balanced by absorption of more from the soilno special adaptations

b. Xerophytesthey grow in dry conditionsroot grow very deep to absorb watersucculent/fleshy leaves to store waterfew stomata which are sunkenthickened waxy cuticleleaves are hairy and often foldingsome leaves are needle-like/spines or scalesleaf surfaces are reduced i.e. small leavesall these adaptations are to reduce water loss

c. Hydrophytesplants that grow in waterpresence of sclereidsleaves are broadleaves have many stomata on upper side only (none on the lower surface)some leaves float on waterabsence or reduced leaf cuticlelarge air spacessome leaves are submergedpoorly developed or reduced vascular bundles

d) i) What is translocationtransfer of manufactured food substances to the parts where they are required

ii) Name the tissue which is responsible for translocation of manufactured food in flowering plantsphloem tissue

iii) Name the processes that bring about the translocation of manufactured foodactive transportDiffusionMass flowCytoplasmic streaming

iv) Draw a labeled diagram to represent phloem tissue

ii) State the functions of the labbeled structures cytoplasmic strandstranslocation

Companion cell

supply nutrients to sieve tube elementsupply energy for translocationregulates activities of tube cells/elements

Sieve tubes elementconduct food down the stem

iii) name the compounds that are translocated in phloemsugarsamino acidshormones e.g auxinsoils/lipidsresinsvitamins

Describe an experiment you would carry out in order to demonstrate that phloem transports manufactured food substances in a plant

a. Ringing experimentcut a ring in the bark including the phloem from the stem of a woody plantphloem is found next to or just beneath the barkobserve daily for some time(more than three weeks)a swelling of the bark appears above the ringthis is due to accumulation of food from leavesthe bark of a second similar plant is removed carefully leaving the phloem intacta swelling does not appear

ii) Use the radio-active tracersplant is exposed to carbon containing radio-active carbon C14C14 is found in the end products of photosynthesisIt is finally detected in phloemC14 is found to move in both directions

iii) Collecting exudate from stylets of aphidsaphids feed on certain plant phloem using their styletsaphid mouth parts are dissected using a sharp razorexudes from the mouth parts are collected and then analyzedsucrose is found to be a major component of the exudatesthis proves that phloem translocates manufactured food substances

e) Describe an experiment you would carry out to demonstrate that xylem transports water

i. Eithercut a stem of a young plant or twig of a tree under wateror else uproot a young herbaceous plant and wash the soil gentlyput some water in a beaker and add a dye i.e. eosin or red ink and place the cut stem or young plant in a beakerleave for time e. g. between 20 minutes and one hourcut a thin section of stem or leafmount it on a slide and examine under a microscopeobserve and note the distribution of the dye or inkthe dye appears only in the xylem vessels

ii. ORuse radio-active tracers, C14 in form of carbonring a plant then put it in a container containing radio-active phosphorous solutionThe radio-active phosphorus is later detected in the leaves.

2. a) i)List the components of animal transport systemssystem of blood vessels in which materials are circulated round the bodyblood, a fluid medium which contains dissolved substances and cellsthe heart, a pumping mechanism which keeps blood in circulation

ii) Distinguish between closed and open circulatory systemsclosed system has blood vessels through which blood moves eg vertebratesopen system has no blood vessels hence blood is in direct contact with tissues e. g arthropoda

iii) What are the advantages of the closed circulatory system over open circulatory system?Closed system has continuous vessels hence able to generate high pressureCirculates blood over longer distanceCirculates blood at a faster rateEfficient transport of nutrients and waste productsAnimals are more active

iv) Distinguish between single circulatory system and double circulatory system Single circulatoryblood passes through the heart once in a complete circuit of the bodyDouble circulationblood enters the heart twice in a complete circulationPulmonary circulation from the heart to lungs and backSystemic circulation from the heart to body systems and back

b) i) Describe the general layout of the transport system in mammalsblood which is a fluid tissue of the body carrying food substances, oxygen, carbon IV oxide and metabolic wastes

arteries which are elastic tubes carrying blood from the heart to cellsveins which are blood vessels carrying blood away from the cells to the heartcapillaries which are extremely numerous and are microscopic channels connecting arteries to veins

ii) Describe the structure and function of the mammalian heartthe heart is a four-chambered hollow muscle located in the thoracic cavityit consists of two small receiving chambers, the atria(auricles) and two larger pumping chambers, the auriclesthe left ventricles is the most powerful and has the thickest wallsthis is because it is the chamber which pumps blood throughout the bodyeach time it contracts, blood is forced out into the elastic arteries(aorta)blood moves on to the capillariesfrom capillaries blood moves to veins and back to the heart through the vena cavafrom vena cava it enters into right auricle which contracts and pumps blood into the right ventricleright ventricle pumps blood into the lungs through the pulmonary arteryblood releases carbon IV oxide to lungs and picks oxygen then returns to left auricleleft auricle pumps blood into left ventricleleft ventricle then pumps blood into the aorta and into arteries, starting the process all over againboth auricles contract simultaneously while both

iii) Explain how the mammalian heart is adapted to performing its functionsthe heart is made of muscles that contract and relax synchronously without requiring nervous stimulationnerve supply however, determine contraction strength and frequencythe heart is divided into four chambersThe right atrium is connected to the right auricle. It receives blood from the whole body.The blood is pumped from the left atrium to the right ventricleTo avoid flow back into the right atrium, a valve is present between the two chambers

the tricuspid valveThe right ventricle pumps blood to the lungsThis is facilitated by the presence of pulmonary arteryA valve is also present to avoid blood flowing back from the pulmonary artery to the right ventricleBlood from the lungs enters the heart through the pulmonary vein into the left atrium.When the left atrium contracts, blood flows into the left ventricleBlood will not flow back into the left atrium because of the presence of bicuspid valve(mitral)The left ventricle is connected with the aorta and when it contracts, blood flows into the aorta for distribution into the whole bodyThe heart muscle surrounding the left ventricle is thicker than that surrounding the right ventricle to be able to generate enough pressure to push blood to the whole bodyA pace-maker is present in the heart muscle to initiate and synchronise contractions.For the heart muscle to be well nourished and be provided with enough oxygen and carbon IV oxide removal, it is supplied with blood by the coronary arteries and drained by the coronary veins

iv) Explain why blood leaving the lungs may not be fully oxygenatedunder ventilation of the lungsblockage of alveoli (air sacs)high cardiac frequency i.e. high rate of pumping of blood in the heart

e) Describe the structure and functions of the blood vessels

i. Arteriescarry away blood from the heartcarry oxygenated blood except pulmonary artery which takes blood from the heart to lungs for oxygenhave thick, muscular wallsare elastichave narrow lumenall these adaptations are required to withstand high pressure caused by heartbeat

ii. Capillarieslink arterioles and venules to arteries and veinssmall in diameter to increase pressure resistance for materials to filter outthin walled as they consist of a single layer of cells to allow diffusion of substances e.g leucocytes to tissuesthin walled to allow presence of intercellular spaceslarge number i.e. numerous to provide a large surface area for exchange of materialshave sphincter muscles at the junction of the arterioles and capillaries to control movement of blood into themlie close to the body for easy exchange of materials

iii. Veinscarry blood back to the heartall carry deoxygenated blood except pulmonary vein that carries blood from the heart to lungshave thinner Walls than arterieshave valves to prevent back flow of bloodhave wide lumen

b) i) State the ways in which the composition of blood in the pulmonary arterioles differs from that in the pulmonary venules

pulmonary arteriolesdeoxygenatedhigh carbon iv oxidelow oxygenmore nutrients

pulmonary venulesoxygenatedlow carbon iv oxidehigh oxygenless nutrients

ii) Give the reasons why pressure of blood is greater in the arterioles than I the veins of mammalsblood is pumped to the arteries by the heart at high pressureblood pressure in veins is reduced by capillary resistancearteries have narrow lumen which maintains high pressure/veins have wide lumen which reduces pressurearteries have more/thicker muscular walls which generate pressure/veins have less/thinner muscular walls which reduce pressure

iii) Name the common heart diseases in humansthrombosisantheromaarteriosclerosisvaricose veinscerebral vascular thrombosis

c) i) State the functions of mammalian bloodtransport of substancesdefense against diseasesclottingtemperature regulation

ii) Describe how mammalian blood components carry out their functions Plasmatransport dissolved food substances like glucose, amino acids, fatty acids and glycerol from small intestines to liver and other body tissuestransports hormones, enzymes from secretory glands to tissues when requiredtransports carbon IV oxide to lungs and urea from tissues to the kidneysdistributes heatbathes the tissues allowing for exchange of materialscontains protein fibrinogen and pro-thrombin which take part in blood clotting

Red blood cells (Erythrocytes)transports oxygen from the lungs to body tissues in form of haemoglobintransport carbon IV oxide from body tissues to the lungs in form of bicarbonates

White blood cells (leucocytes)engulf foreign bodiesproduce antibodies for defense against diseaseproduce antitoxins which neutralize bacterial toxins

Blood platelets (thrombocytes)produce an enzyme called thrombokinase/thromboplastin necessary for blood clottingprevents loss of blood, water and mineral salts

iii) State the Ways in which the red blood cells are adapted to their functionsmany per unit volume hence carry more oxygen and carbon IV oxidebiconcave in shape to provide large surface area for absorption of oxygen and carbon IV oxideabsence of nucleolus hence more haemoglobin to carry sufficient oxygen and carbon IV oxidealter shape to be able to pass through the narrow lumen of capillaries to deliver or supply oxygen and carry away carbon IV oxidehave haemoglobin with high affinity for uptake of oxygen and carbon IV oxide

iv) State the structural differences between a red blood cell and a white blood cell.

Red blood cellshas hemoglobinsmaller sizelacks nucleus

White blood cellsnot pigmentedlarger sizenucleated

v) State the functional differences between a red blood cell and a White blood cell

Red blood cellTransports oxygen and carbon IV oxide

White blood cellProtects body against harmful pathogens

How does the heart increase blood flow to some parts of the body during exercisestronger contractionsfaster contractions/heartbeat

Explain how oxygen and carbon Iv oxide are transported in the blood

Oxygenoxygen concentration is higher in lungs(alveoli) that in bloodoxygen in the alveoli dissolves in the film of moisture and diffuses through thin epithelial and capillary walls into plasma and red blood cellsthe oxygen combines with haemoglobin to form oxyhaemoglobinblood then becomes oxygenatedblood from lungs then travels to all body tissues where the oxyhaemoglobin breaks down to form oxygen and haemoglobinhaemoglobin is transported back to the lungs to collect more oxygen while the oxygen in capillaries diffuses into body cells for respirationrespiration produces carbon IV oxide

Carbon IV oxidecarbon IV oxide produced during respiration diffuses out of cells into blood plasma and red blood cells due to concentration gradientcarbon IV oxide and water fonn carbonic acid carbamino compounds with haemoglobinin the presence of carboxyl anhydrase enzyme, hydrogen carbonate is carried in blood to the lungsin the lungs the hydrogen carbonate dissociates to liberate carbon IV oxide which diffuses into alveolar cavity due to concentration gradientfrom alveolar space carbon IV oxide is expelled during expiration

Most carbon IV oxide is transported from tissues to lungs within the red blood cells and not in the blood plasma. Give the advantages of this mode of transport.PH of blood is not altered/homeostasis is maintainedWithin the red blood cell is an enzyme, carbonic anhyrase which helps in fast loading(combining) and offloading of carbon (iv) oxide

d) i) what is blood clotting?process in which blood components clump together to prevent loss of blood from an injured/cut vessel

ii) Name a protein, vitamin, an enzyme and a mineral element involved in blood clottingProtein — fibrinogen/prothrombinVitamin – k/quinineEnzyme — thrombokinase/thromboplatin/thrombinMineral element — calcium

iii) describe the blood clotting processenzyme thromboplastin produced in the platelets of damaged tissues converts plasmaprotein prothrombin into thrombin in the presence of calcium ionsthrombin converts another plasma protein fibrogen into fibrin in the presence of vitamin Kfibrin is insolublefibrin forms fibres which form a meshwork that forms a clotprothrombin thromboplastin thrombincalcium ionFibrinogen thrombin fibrin clotvitamin K

iv) State the role of blood clotting on woundsprevents blood/body fluids from being lostconserves water and saltsprevents entry of microorganisms/pathogensregulates body temperatureenables wound to heal faster

v) Explain why blood flowing in blood vessels does not normally clotPresence of anticoagulant in bloode) i. list the major types of human blood groupsO, with neither B nor A antigenAB, with both A and B antigensA, with type A antigenB, with type B antigen

iii. Explain the meaning of :

Universal donora person who can donate blood to any other blood group without agglutination/clumpingthis is usually blood group Ohowever this person cannot receive blood from other blood groups except group O

Universal recipientcan receive blood from all blood groups without agglutinationthis is usually blood group ABhowever, can only donate blood to group AB

iii) What is the difference between rhesus positive and Rhesus negative blood samples?rhesus positive blood has the Rhesus (Rh) antigenrhesus negative lacks the Rhesus antigen

vi) What is blood transfusion?Introduction of blood from one person to another

v) Under what conditions would blood transfusion be necessary in people?during accidentsduring surgery in hospitalsbleeding mothers when giving birth

vi) How can low blood volume be brought back to normal?transfusiontaking fluidseating iron rich food/taking iron tablets

How may excessive bleeding result in death?Anaemia/low blood volume/loss of iron/low red blood cells count/low haemoglobin leading to low oxygen, loss of nutrients and dehydration.

State the precautions that must be taken before blood transfusionblood must be disease freesterilized equipment must be usedblood of the recipient and that of the donor must b compatible to both ABO and rhesus factorFresh blood must be used.

j) i) What is immunity?Resistance to disease by organisms

ii) Distinguish between natural and acquired immunitynatural immunity is inherited/transmitted from parent to offspring/inborn/innateAcquired immunity is developed after suffering from a disease or through vaccination.

iii) What are allergic reactions?Excessive sensitivity and reaction of an individual to certain substances in environment e.g. dust, pollen, perfumes, smoke etc.

vi) How does an allergic reaction occur?the substances act as antigensan antigen-antibody reaction occurs on surface of cellsthe cells release a substance called histaminethe histamine causes irritation, itching and may stimulate nasal discharge

ii) State the role of vaccination against certain diseasesprotect body against infectious diseasesprevent spread/transmission of certain diseasesdiseases for which vaccination is given include tuberculosis, poliomylitis,measles,whooping cough, diphtheria

3. a) i) What is gaseous exchange?The continuous exchange of oxygen and carbon Iv oxide between the organism and environment

ii) Why is gaseous exchange important to organisms?to supply oxygen necessary for energy productionto remove carbon IV oxide produced during respirationTo remove Water vapour.

b) i) name the structure used for gaseous exchange by plantsstomatal pores/stomatalenticelscuticlepneumatophores

ii) Briefly describe the structure of stomataare minute pores found in leaf epidermiseach consists of a slit-like openingEach is bordered by two large, bean-shaped guard cells.Guard cells contain chloroplasts, unlike the other epidermal cells which enable photosynthesis to occurInner walls of guard cells are thicker than the outer cells

iii) State the factors which affect stomatal openingwater which when low stomata close and when high stomata keeps openlight as stomata open in bright light and close in darknesstemperature

iv) Name the theories suggesting the mechanism of opening and closing of stomatainterconversion of starch and sugarpH theorymineral ion concentration

v) Describe the mechanism of opening and closing of stomatastomata close at night and open during daytimeThis comes about due to changes in turgidity as a result of pH changes in guard cells.In the dark carbon dioxide accumulates in the intercellular spacesThis raises concentration of carbonic acidThe pH drops (pH lowered)Enzymes convert sugar into starch in guard cellsOsmotic pressure in guard cells is loweredWater moves out of guard cells by osmosis making cells lose turgidity hence become flaccidThe stomata closeDuring day time there is photosynthesis hence the production of sugar, carbon IV oxide concentration is lowered, pH increases, guard cells become turgid causing stomata to open.During the day potassium ions concentrate in guard cells, raising their osmotic pressure and causes then to openIn the night the concentration of potassium ions decreases increasing osmotic pressure in guard cells therefore causes stomata to open.

i) What is the advantage of having stomata open during daytime and having them closed at night?opening in the daytime allows diffusion of carbon IV into the leaf for photosynthesis to take place and allows diffusion of oxygen out of the leaftranspiration also takes place, thus cooling the leaf and facilitating uptake of water and mineral slatsClosing in the night is to conserve water in the plant especially when there is not enough water available in the soil.

c) i) State the ways in which leaves of plants are adapted to gaseous exchangepresence of stomata for faster gaseous exchangeintercellular spaces/air spaces in the leaf for movement/circulation of airfilm of moisture around the surface of cells for easy diffusionbroad/flattened shape to increase surface areathin lamina to reduce distance of diffusionexposed to air for easy diffusion

ii) Describe how gaseous exchange takes place in terrestrial plantsGaseous exchange takes place in spongy mesophyllDuring the day air diffuses into large air spaces of spongy mesophyll through stomataThe carbon iv oxide in the air diffuses into the photosynthesis oxygen is producedSome of the oxygen diffuses out of the leaf through stomataDuring the night air diffuses out of air spaces of spongy mesophyllThe air dissolves into film of moistureThe oxygen in the air diffuses into cells and is used in respiration during which carbon iv oxide is producedThe carbon iv oxide diffuses out of the leaf through stomata due to diffusion/concentration gradientAt night carbon iv oxide accumulates in the leaf since photosynthesis does not take placeSome gaseous exchange also takes place through cuticleGaseous exchange occurs through epidermis of young leaves and stemsThe cork cells at lenticels are loosely packedGaseous exchange takes place between cork and atmosphere within the loosely packed cell

iii) State the ways in which floating leaves of aquatic plants are adapted to gaseous exchangestomata found only on upper dermis to allow efficient gaseous exchangepresence to aerenchyma tissues/large air spaces to enable it float/buoyancy/storage of airabsence of cuticle to enhance gaseous exchange

iv) How is aerenchyma tissue adapted to its function?has large airspaces which store gases/for gaseous exchange/buoyancy

v) Explain stomatal distribution in plants of different habitatsland plants have their stomata mainly on the lower side to reduce water loss but if on both sides then upper side has very fewwater plants, floaters, have stomata on upper side to enhance water lossin dry areas, plants have leaves with sunken stomata to reduce water loss by transpirationPlants in wet areas have stomata equally distributed on both sides.

d) i) List the types of respiratory surfaces of animalscell membrane in unicellular organisms e. g. amoebagills in fishtracheal systemskin, buccal cavity and lungs in amphibianslings in mammals

ii) State the characteristics of respiratory surfaces in animalsmoist thin walled/thin membrane/thin surfaceHighly/richly vascularised/numerous blood vessels/Well supplied with blood vessels.Large surface area

iii) Describe gaseous exchange in protozoaexample is amoebasmall and have large surface areaoxygen diffuses into the organism and carbon IV oxide diffuses out into Watersimple diffusion of gases is enough to meet its respiratory requirements

e) i) Make a labeled drawing of a fish gill

ii) How is a fish gill adapted to its function?large surface area due to many filamentsextensive vascularisation due to capillaries, for gaseous exchangethin filaments to facilitate diffusion of gasespresence of rakers to filter solid particlesgill bar is bony, hard and firm to support the filaments and rakers and for attachment of filaments and rakers

iii) Discuss gaseous exchange in bony fishexample is tilapiathe mouth opens and the floor of the mouth is lowered so that the volume in the mouth is increased and pressure is loweredwater then enters into the mouth cavitythe mouth is closed and the floor of the mouth raised so that the volume is reduced this raises the pressure, forcing water over gills and out through the operculumAs water passes over the gills oxygen diffuses due to concentration gradient (partial pressure) into the blood stream.In the body tissues, carbon IV oxide diffuses into the blood (due to concentration gradient, and is transported to the gills and diffuses out into the water.

iv) What is counter-flow system?Where water in which the fish lives flows in opposite direction across the gill.

vi) What is the advantage of counter-flow system?maintains a diffusion gradient so that there is maximum uptake of oxygenoxygen continues diffusing into blood and carbon iv oxide into Water

f) i) Describe the mechanism of gaseous exchange in terrestrial insectsexample is cockroachair in the atmosphere contains oxygenair is drawn into the body of the insect through the spiracles due to movement of abdominal musclesthese movements cause the opening of spiraclesair moves through the trachea to tracheolesoxygen moves from the tracheoles into body cells by diffusion due to concentration gradientcarbon iv oxide in the tissues diffuses into tracheoles due to concentration gradientFrom tracheoles carbon IV oxide moves into trachea and out through the spiracles into the air.

ii) State how traceholes are adapted to gaseous exchangethin walls of tracheolesmoist surfacelarge surface area due to numerous tracheoles

g) i) What is breathing?Any process which speeds up the rate of gaseous exchange between an animal and its surrounding.

ii) Name the structures in humans that are used in gaseous exchangenoselarynxepiglottistrachealungspleural membranepleural cavitydiaphragm muscles

iii) Describe the mechanism of gaseous exchange in a mammal

Breathing inexternal intercostals muscles contract while internal intercostals muscles relax, raising then ribcage upwards and outwardsmuscles of the diaphragm contract hence it flattensthe volume of the thoracic cavity increases while pressure decreaseshigher air pressure in the atmosphere forces air into lungs through the nose

Breathing outexternal intercostals muscles relax while internal intercostals muscles contract, moving the ribcage downwards and inwardsmuscles of the diaphragm relax hence the diaphragm assumes dome shapethe volume of the thoracic cavity decreases while pressure increasesthe higher pressure forces air out of the lungs through the nose

iv) Explain how mammalian lungs are adapted to gaseous exchangelarge number of alveoli that increase surface areamoist inner surface of alveoli for dissolving oxygen/gases to facilitate exchange of gasesthrough alveolar cavities and bloodthin walls of alveoli to allow efficient/faster diffusion of gasesrich capillary/blood supply on alveolar surface to transport oxygen away from the lungs and carbon IV oxide to the lungs

v) Name the features of alveoli that adapt them to their functionhave large surface area/spherical shapednumerous/many to increase surface areaone cell thickmoist surface for air to diffusehighly vascularised/numerous capillaries

vii) How is the trachea of a mammal suited to its function?has a ring of cartilage which keeps it open at all timescilia that move mucus/particles to the top of the trachea i.e. into larynx for removalmucus to trap dust, solid particles and microorganismshollow for passage of air

viii) State the advantages of breathing through the nose rather than through the mouthnose has hairs to filter solid particlesit has mucus lining to trap dust particlesthe nose has cells sensitive to smell for survivalit warms the air before it reaches the lungs

ix) Give the conditions under which the carbon iv oxide level rises above normal in mammalian bloodvigorous exerciseemotions/stressdisease infection

x) Explain the physiological changes that occur in the body to lower the carbon iv oxide level back to normal when it risesheartbeat/cardiac frequency increases to pump blood faster carbon iv oxide from the tissues and supply more oxygenventilation rate/rate and depth of breathing increases to take more oxygen and remove carbon iv oxide from the lungsarterioles to take in more oxygen and remove carbon iv oxide from the lungsarterioles dilate leading to faster flow of blood to and from body tissues

h) i)Describe the factors which control the rate of breathing in humansbreathing movements usually occur unconsciouslyit is controlled by the medulla oblongata part of the brain situated at the breathing centremedullar oblongata is in the brainrespiratory centre transmits impulses to the diaphragm through phrenic nervescarbon iv oxide concentration in the blood determines the breathing rateif carbon iv oxide is less, the brain is triggered to decrease breathing ratecardiac frequency decreases and the arterioles constricttherefore carbon iv oxide level is raisedthis brings back to normal level of breathing and carbon iv oxide level increases/is morethe brain is triggered to increase breathing ratecardiac frequency is increasedthere is vasodilation of arteriolescarbon iv oxide level fallstherefore the normal level is attained and carbon iv oxide is removed faster

ii) Name the respirator diseasesasthmabronchitiswhooping coughpneumoniatuberculosis

4. a) i) Define respirationthe oxidation/breakdown of food within cells to release energy

ii) Explain the significance of respiration in living organismsit yields energy (ATP)this energy enables organisms to move, grow, excrete and reproduce

iii) Where does respiration take place?in the mitochondria

b) i) Draw and label a mitochondrion

ii) State the most important function of mitochondriato produce Adenosine triphosphate (ATP) which is the energy source of the Whole cell

iii) Give the functions of the labeled parts

Outer membranecontrols what enters and What leaves mitochondrion

Cristaealso called inner membraneincrease surface are for attachment of enzymesthis is Where cellular oxidation reactions occur

Matrixenzymes are located hereother reactions occur here

c) Explain the roles of enzymes in respirationthey catalyse reactions i.e. speed up respiration

d) i) What is aerobic respirationrespiration in the presence of oxygen

ii) Give a word equation for aerobic respirationglucose + oxygen – Water + carbon iv oxide + energy

iii) What are the end products of aerobic respiration?energycarbon iv oxidewater

e) i) What is anaerobic respirationoccurs in the absence of oxygen e. g. yeast and certain bacteria release energy in the absence of oxygen

ii) What are obligate anaerobes?are completely independent of oxygen

iii) What are facultative anaerobes?can survive both in the presence and absence of oxygen also called partial anaerobes

iv) State the Word equation representing anaerobic respiration in plantsGlucose ethanol + carbon (iv) oxide + energy

v) Name the end products of anaerobic respiration in plantsalcohol/ethanolcarbon iv oxideenergy

g) i) Give a word equation of anaerobic respiration in animals

Glucose —> lactic acid + energy

ii) Name the end products of respiration in animals when there is insufficient oxygen supplylactic acidenergy

iii) Why is there a high rate of lactic acid production during exercise?the demand for oxygen is more than supply leading to anaerobic respiration

iv) Why does lactic acid level reduce after exercise?lactic acid is oxidized to form carbon iv oxide and watersome is converted to glucosesome is converted into glycogen

v) State why accumulation of lactic acid during vigorous exercise lead to an increase in heartbeatlactic acid is poisonous to tissues and must be removedto increase supply of oxygen to tissues

State the economic importance of anaerobic respirationbrewing of alcoholbiogas productioncompost manure formationsilage formationbaking breadproduction of dairy productsfermentation of milksewage treatmentFermentation of tea in industries.

What is oxygen debt?amount of oxygen required to convert accumulated lactic acid to water, carbon IV oxide and energy

h) i) What is respiratory quotient(RQ)?ration of carbon IV oxide produced to oxygen consumed

RQ = volume of CO2 produced

volume of oxygen consumed

ii) Why are respiratory quotient importanttheir calculation assists in identifying the kind of substrate being used in respiration

iii) Name the respiratory substratescarbohydratesfatsproteins

iv) Why does anaerobic respiration of a given substrate yield a smaller amount of energy than aerobic respiration?Some energy locked up in intermediate products like ethanol in plants and lactic acid in animalssubstrate is completely oxidized in aerobic respiration

iv) Explain the disadvantages of anaerobic respirationLess energy produced in anaerobic respiration since food is partially oxidized while inaerobic respiration food is completely oxidized.Some metabolic wastes accumulate in cells affecting cellular functionsEthanol produced in plants poisons the tissues while lactic acid produced in animalscauses muscle fatigue/muscle cramp and may stop muscle contractionSuch intermediate wastes are not produced in aerobic respiration

v) Mention the types of experiments carried out for respirationgerminating seeds which yield energy in form of heatanimals produced heat when they respireyeast cells respire to produce heat

5. a) i) Define the following terms

Excretionthe process by which organisms get rid of waste products which result from chemical process which occur in living cells

Secretionthe process by which organisms produce substances which are useful to the body, by glands

Egestionremoval of indigestive materials from the body

Homeostasismaintenance of constant internal environment

ii) Explain Why excretion is necessary in plants and animals

-products of excretion are usually harmful while some are toxic

– if allowed to accumulate in the cells they would destroy tissues and interfere with normal metabolism

– They are therefore removed through excretion

b) i) Describe how excretion takes place in green plantscarbon IV oxide, oxygen and water diffuse through the stomata, lenticels and hydathodessome toxic wastes are convened into non-toxic substancesthese are deposited in certain tissues of the plant or stored in aging stmcturesresins and tannins are exuded through the bark of stem or lost during leaf fall

ii) Why do plants lack complex excretory structures like those of animals?plants have lower rates of metabolismplants excrete non-poisonous products derived from carbohydrate metabolism unlike animals which produce toxic wastes derived from protein metabolismplants re-use some of their wastes like nitrogenous wastes used in protein synthesisplants store waste products in roots, fruits and leaves

ii) State the excretory products of plants and some of their uses to humanscaffeine from tea and coffee is used in medicine and as a stimulant which is harmful to humansquinine used for treating malariacocaine derived from leaves of cocoa plant used as a stimulant by addicts or as a local anesthesia, also causes damage to the brain, may cause addiction if not well used and is an illegal drugTannins derived from barks of acacia (wattle bark) trees are used to make ink and tanning (softening) of leather.Nicotine got from leaves of tobacco plant stimulates the central nervous, may cause addiction if much is used or consumed. It is used to make cigarettes, cigars and is poisonous. It is a precursor of lung cancerCannabis sative(bhang) is used to make drugsGum derived from glues is used for sticking substances and making certain jelliesRubber, a product of latex, got from rubber plant is sued to make tyres and synthetic fibresMorphine from opium poppy plant is a narcotic and illegal drug as it causes addictionKhat and miraa are used as stimulantsColchicines used in inducing polyploidy, cancer therapy, treatment of gouts in small quantitiesPapain used as meat tenderizer

c) i) Describe excretion in unicellular organisms

-examples are amoeba and paramecium

-They have to remove waste products such as carbon IV oxide and nitrogenous substances e. g urea and ammonia

– These diffuse from the body surface into the surrounding Water

– Diffusion is due to large surface area

ii) List excretory organs and products of mammalskidney excretes urea, water and saltsskin excretes Water, slats and urealungs excrete carbon IV oxide and waterliver excretes bile salts

d)i) Draw and label a mammalian skin

ii) Explain how the mammalian skin is adapted to its functions

the skin is made up of dermis and epidermis

Epidermisit is made up of three layersthe outermost layer, comified layer is made up of dead cells that prevent entry of microorganisms, prevent physical damage and dessicationgranular layer made of living cells gives rise to cornified layermalpighian layer is made up of actively dividing cells that give rise to new epidermal cells/granular layer it contains melanin that protects the body against ultra violet rays(radiations)

Dermishas several componentsHas sweat gland which produce sweat through sweat pores on the skin and the sweat evaporates cooling the body by lowering body temperature. When it is cold, no sweat is produced, conserving watersweat contains water, sodium chloride, uric acid and urea hence the skin acts as an excretory organHas hair. The hair stands erect to trap air when temperature is low to reduce loss/insulation. It lies flat to allow heat loss when temperature is high.Has nerve endings which are sensitive to stimuli such as heat, cold, pain, pressure and touchHas subcutaneous fat/adipose fat that insulates the body against heat lossHas arteries and capillaries (blood vessels) that supply food and oxygen and remove excretory products. Arterioles vasodilate when temperatures are high to lose heat by radiation, and convention. Arterioles constrict when temperatures are low to conserve heat i.e. reduce heat lossHas sebaceous glands which secrete sebum, and antiseptic and water repellant that prevents drying and cracking the skin by making the skin supple

e) What is the role of lungs in excretion?during respiration oxygen is used up in the body cells to produce energycarbon IV oxide is produced as a by-productthe carbon IV oxide must be eliminated from the bodyelimination is through the lungsalso, water vapour is formed and must be removedthis removal is through the lungsthe lung is therefore considered as an excretory organ as it removes carbon IV oxide and water vapour which are by-products of respiration

f) State the functions of the liver

i. Excretionin this function the liver is aided by the kidneydeamination i.e. excess amino acids converted into urea and uric acid which is transported to skin and kidney for removaldetoxification where harmful substances are converted into harmless ones in the liver and transported to kidneys for removalbreakdown of worn out blood cells and haemoglobin and the residue excreted through thekidney to give urine a yellow tingeBreakdown of sex hormones after they have performed their function and the wasted arereleased through the kidney and bile.

ii) Homeostasisregulation of blood glucosethe normal amount of glucose in blood is about 90mg/ 100increase in blood sugar is detected by cells of the pancreas which secrete insulininsulin stimulates the liver to convert excess glucose to glycogenfurther excess glucose is converted to fats until the normal blood sugar level is attainedExcess glucose is oxidized to carbon IV oxide, water and energy. Excess glucose is also used in respirationdecrease in blood sugar level below normal level is detected by the pancreas, which secretes glucagon which stimulates the liver to convert glycogen to glucose until the normal sugar level is attainedfats, amino acids are converted to glucoseit also leads to reduced oxidation of glucose

Deaminationexcess amino acids are deaminated by the removal of amino groupthe amino group is converted to ammoniaammonia combines with carbon IV oxide to form ureaurea is excreted in urine through the kidneyDetoxificationpoisonous substances are converted to less harmful compoundsThermal regulationmaintenance of body temperatureheat is generated in the liver by chemical activitiesthe heat is distributed

g) i) Draw a labeled diagram of mammalian nephrone

ii) Describe how the human kidney functionsthe afferent arterioles, which is a branch of the renal artery, supplies blood to the glomerulusthe afferent arteriole has a wider diameter than the efferent arteriolethis difference in diameter of afferent and efferent vessels causes high pressure leading to ultra filtrationthe walls of the blood capillaries are one cell thick hence glucose, amino acids, vitamins,hormones, salts, cratinine, urea and water filter into Bowman’s capsule to form glomerular filtratewhite blood cells, red blood cells, plasma proteins (such as globulin) and platelets are too large to pass through the capillary walls hence remain in blood capillarythe filtrate flows into proximal convoluted tubule where amino acids, vitamins and all glucose are selectively reabsorbed back into the blood streammany mitochondria provide energy for reabsorption of these substances against a concentration gradient by active transportthe glomerular filtrate flows into the loop of Henlewater in the descending loop moves by osmosis into the blood capillariessodium chloride is actively pumped from the ascending arm of the loop of Henle into the blood capillariesthe glomerular filatrate flows into the distal convoluted tubulewater and salts are reabsorbed from distal convoluted tubule into blood capillariesthe glomerular filtrate flows into collecting tubule (duct) from where more Water is reabsorbed into blood streamantiduretic hormone influences the amount of Water reabsorbed depending on osmotic pressure of bloodthe glomerular filtrate from collecting duct, now referred to as urine, is emptied into pelvis and ureter into bladder and out of body through urethraurine consists of excess water, slats and nitrogenous wastes

iii) State the adaptations of proximal convoluted tubule to its functionfolded to increase surface area for absorption thin epithelium to reduce distance of diffusion micro-villi on innerlining to increase surface area for absorption folded to reduce speed of flow for efficient absorption numerous mitochondira to provide energy for reabsorption dense capillary network to transport reabsorbed products

iv) Name the common kidney diseasesnephritiskidney stones(renal calculicystitisoedemakidney failure

6. a) i) Why is homeostatic control necessary?this provides a constant internal environment so that the cells of the body have the optimum (best) condition for their survival

ii) What is internal environment?immediate surrounding of body cellsrefers to tissue fluid within an organism

b) i) Why is constant body temperature maintained by mammals?most enzymes in the body function within a narrow range of temperaturehigh temperature denatures enzymeslow temperature inactivates and inhibits enzymes

ii) Explain the advantage gained by possessing a constant body temperatureanimals remain active despite fluctuations in environmental temperaturehigher chances of survival in various environments ie they colonize various environmentschemical processes in their body continues at an optimum rate

iii) How do mammals regulate body temperature?the body temperature of a mammal is kept constantto maintain this temperature the mammal must be able to balance its heat loss against the heat gainbody temperature is controlled by the hypothalamus, a specialized part of the brainchanges in the temperature within the body and the surrounding are detected by the hypothalamus it transmits impulses to the skin and the blood stream in response to temperature changes hypothalamus acts as a thermostat for the bodya mammal loses heat by breathing out, urine, feaces, skin by radiation and by evaporation of sweat.A mammal generates heat by the activity of its muscles, by general metabolism in respiration, or chemical activitiesIn hot conditions the hypothalamus stimulates responses that increase heat loss from the body hence lowering the body temperatureSuch responses include sweating, vasodilation, keeping its hair flat on the surface of skin and reduction of metabolic rateIn cold conditions the hypothalamus stimulates responses that generate heat gain in the body and reduce heat loss to the environmentSuch responses include shivering, vasoconstriction, raising its hair to trap a layer of air around the skin because still air is a good insulator of heat and by generation of heat by increasing metabolic rate.

iv) Why does body temperature of a healthy person rise up to 37 C on a hot humid day?sweat evaporation is reduced hence cooling is less therefore more heat is retained in the body causing temperature to rise

v) Name the structures in the human body that detect external temperature changestemperature receptors (end bulb corpuscles e. g. bulb of Krause (warmth) and organ of Ruffinni (cold)heat (thermal) receptors

vi) State the advantages that organisms with small surface area to volume ratio experience over those with largerheat loss slow hence their body temperature can increase to intolerable levelsHeat gain from surrounding slower hence may remain inactive for a long time.Need specialized and complex transport system and also gaseous exchange system

Explain why individuals with smaller sizes require more energy per unit body weight than those with larger sizes.surface area to volume ratio is higher in smaller individuals than larger ones, therefore smaller heat is lost faster by smaller ones than larger onesthey therefore require more energy per unit body weight to maintain body temperature

c) i) What is the meaning of osmoregulation?mechanism which regulates osmotic pressure of internal environment of an organismthe regulation/maintenance of salt/solute-water balance of an internal environment

ii) State the importance of osmoregulationMaintenance of constant level of water and slats (osmotic pressure) for optimum/suitable conditions for metabolism suitable for cellular functions

iii) State the ways by which desert mammals conserve water fewer glomeruli longer loop of Henleexcretion of dry feaces or concentrated urinehump for fat to be metabolized to give metabolic water for usenocturnal, burrowing, aestivate or hibernatesweat glands few or absentmore ADH (vasopressin)

iv) Explain why some desert animals excrete uric acid rather than Wateruric acid is less toxic than ammonia, hence elimination of uric acid requires less waterthan ammonia therefore more water conserveduric acid being less toxic is safer to excrete where there is less water/desert

v) Explain why eating a meal with too much salt leads to production of a small volume of concentrated urinethe concentration of salts in the blood rises leading to production of more ADH hence higher rate of water reabsorption by kidney tubules

vi) Explain how marine fish regulate their osmotic pressureswallow plenty of sea water to increase amount of water in the bodyhave chloride excretory cells in their gills to remove excess saltseliminate nitrogenous wastes in form of trimethalamine oxide which requires little water for eliminationfew/small glomeruli thus slow filtration rate in the kidneysretain nitrogenous wastes in form of urea to raise osmotic pressure of body fluids

d) i) What is the biological significance of maintaining a relatively constant sugar level in a human body?body cells are surrounded by tissue fluids that are isotonic/same osmotic pressure as cytoplasmif sugar level is high/hypertonic, cell will lose water by osmosis to the surrounding, thus increasing the concentration of the contentsthis changes the physiology of the cellif the blood sugar is lower than the normal, the cytoplasm gains water by osmosis,diluting the cell contents, thus altering the physiology of the cell

ii) Discuss the role of the following hormones in blood sugar control

Insulininsulin is produced when there is increase in blood sugar concentrationit converts glucose to glycogen which is in the liver or muscle thus lowering sugar level

Glucagonwhen glucose level decreases glucagon is produced, which causes the breakdown of glycogen to glucose thus raising blood sugar level

e) Explain the part played by antidiuretic hormone in homeostasisProduced when there is less water (high osmotic pressure above normal level of salt concentration) in the blood.It acts on kidney tubules (nephron) thus increasing water reabsorption from tubules to the blood stream, thus restoring osmotic pressureWhen there is more water(lower osmotic pressure) or decreased salt concentration in blood, little or no ADH is produced, less water reabsorbed hence water loss in urine (more dilute urine) hence raising the osmotic pressure in body fluids/blood

f) What is the role of blood clotting in homeostasis?when a blood vessel is cut, there is exposure of blood platelets to the airthis triggers fibrinogen to be converted to fibrinthe fibrin forms a clot that prevents body fluids e. g. blood from being losttherefore the clot conserves water and salts in the body

g) Describe the role of the following hormones in homeostasis

i. Aldosteroneconcerned with regulation of ionic balancesecreted by the cortex of adrenal glandsit increases sodium ion uptake by the gut and promotes the reabsorption of sodium ions (and therefore water) in the kidneys)this is accompanied by elimination of potassium ionsthis raises the overall level of sodium and lowers the overall level of potassium in the bloodas sodium ions are absorbed in the blood, chlorine ions follow so as to neutralize the effect of sodium ionsthe production of aldosterone is regulated by the concentration of sodium ions which has an inhibiting effect, and a fall in sodium ions has a stimulating effect on the adrenal cortexthe flow of aldosterone is stimulated by the adreno-cortic-tropic hormone (ACTH) produced in the anterior of the pituitary gland however, the main method of control is dependent on the fact that adrenal cortex itself is somehow sensitive to the relative concentration of potassium and sodium in the blood

ii. Adrenalineproduced by adrenal glandsin high concentrations, it increases hydrolysis of glycogen and increases blood sugarit is usually released in emergency cases to increase glucose level for respirationthis releases energy for the emergency

h) i) Distinguish between diabetes mellitus and diabetes insipidusdiabetes mellitus is a condition resulting from insufficient production of insulin causing hyperglucaemia and presence of glucose in urinediabetes insipidus is a condition whereby less or no antidiuretic hormone is secreted hence a high volume of water is passed out in urine in a condition called diuresis

ii) How can high blood sugar level in a person be controlled?administer insulin

iii) Why does glucose not normally appear in urine even though it is filtered in the mammalian Bowman’s capsule?glucose molecules are actively reabsorbed in the proximal convoluted tubules

iv) When is glycogen which is stored in the liver converted into glucose and released into the blood?after activity/when blood sugar (glucose) falls below normalwhen glucagonstimulates the liver/when glucagon is producedafter strenuous/vigorous activityduring starvation

v) How would one find out from a sample of urine whether a person is suffering from diabetes mellitus?test or react urine in Benedict’s solutionpositive result i.e. orange or red precipitatePositive result is an indication of diabetes mellitus