F4-F5 Biology Selected Topics (Essays).doc

8/14/2019 F4-F5 Biology Selected Topics (Essays).doc

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Biology - Sample Essays

Oxidation of lactic acid occurs mainly in the liver where a portion of it is oxidised to produceenergy while the remaining ones is converted into glycogen for storage in the muscle cells. heoxygen debt is paid off when all the lactic acid is removed. his happens through the increased

breathing rate after vigorous exercise. herefore, an oxygen debt is the amount of oxygen neededto remove lactic acid from the muscle cells.

Photosynthesis

Light Reaction#uring the light reaction, chlorophyll captures light energy which excites the electrons ofchlorophyll molecules to higher energy levels. In the excited state, the electrons leave thechlorophyll molecules. 0ight energy is also used to split the water molecules into hydrogen ionsand hydroxyl ions. his reaction is known as the photolysis of water.

2 H 2O 2 H ++ 2 OH !

"#ight an$ ch#orophy##%

he hydrogen ions then combine with the electrons released by the chlorophyllto form hydrogen atoms.

2 H ++2 e !2 H

he energy from the excited electrons is used to form energy1rich molecules of A ". At thesame time, each hydroxyl ion loses an electron to form a hydroxyl group. his electron is thenreceived by the chlorophyll.

2 OH !2 OH+2 e !

he hydroxyl groups then combine to form water and gaseous oxygen.

2 OH12H 2O+6O 2

Oxygen is released into the atmosphere and used for cellular respiration. he A " molecules provide energy while the hydrogen atoms provide reducing power for the dark reaction whichtakes place in the stroma.

&ark Reactionhe dark reaction is also known as the 2alvin cycle. It is light independent. #uring the dark

reaction, the hydrogen atoms are used to fix carbon dioxide in a series of reactions catalysed by photosynthetic en!ymes. he overall reaction results in the reduction of carbon dioxide intoglucose.

6CO 2+2 H6"CH 2O%+6H2O

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32%- O4 is a basic unit of glucose. 5ix units of it combine to form one molecule of glucose. heglucose monomers then undergo condensation to form starch which is temporarily stored asstarch grains in the chloroplast. he entire process can be represented by the following equation.

6H 2O+6CO 2C 6H 12O 6+6O 2

66666666666666666666666666666666666666666666666666666666666666666666666666666 6

&igestion

R'(inant7hen a cow feeds on grass, it partially chews the grass. his partially chewed food is swallowedinto the rumen, the largest compartment of the stomach. %ere, cellulose is broken down by thecellulose produced by symbiotic microorganisms such as bacteria and proto!oa. "art of the

breakdown products are absorbed by the bacteria and proto!oa, the rest by the cow. As the foodenters the reticulum, the cellulose undergoes further hydrolysis. he content of the reticulum,

called the cud, is then regurgitated bit by bit into the mouth to be thoroughly chewed again. his process helps soften and break down cellulose, making it more accessible to further microbialaction in other parts of the stomach. he cud is then re1swallowed and moves into the omasum.%ere, large particles of food are broken down into smaller pieces by peristalsis. 7ater isremoved from the cud. he food particles finally move into the abomasums, the true stomach ofthe cow. %ere, gastric 8uices containing digestive en!ymes complete the digestion of proteins andother food substances. he food then passes through the small intestine to be digested andabsorbed in the normal way.

Ro$entsIn rodents like squirrels, the caecum and appendix are enlarged to store the cellulose1producing

bacteria. he breakdown products pass through the alimentary canal twice. he faeces in the first batch are usually produced at night and are soft and watery. hose are eaten again to enable theanimals to absorb the products of bacterial breakdown as they pass through the alimentary canalfor the second time. he second batch of faeces becomes drier and harder. his adaptation allowssquirrels to recover the nutrients initially loss with the faeces.

Co#onisation an$ )'ccession

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&e*inition92olonisation: is the process whereby living organisms move into a newly formed area which is

devoid of life.95uccession: is the gradual process by which one community changed its environment so that it

is replaced by another community.

angro,e )-a(phe pioneer species of a mangrove swamp are the 5onneratia sp and Avicennia sp. he presenceof these species gradually changes the physical environment of the habitat. he extensive rootsystems of these plants trap and collect sediments, including organic matters from decaying plant

parts. As time passes, the soil becomes more compact and firm. his condition favours thegrowth of the hi!ophora sp. ;radually, the hi!ophora sp replaces the pioneer species. heseeds of the hi!ophora sp show distinct viviparity. he prop root system of the hi!ophora sptraps silt and mud, creating a firmer soil structure overtime.

he ground becomes higher. As a result, the soil is drier because it is less submerged by seawater. he condition now becomes more suitable for another mangrove species, the &ruguierasp, which replaces the hi!ophora sp. he buttress root system of the &ruguiera sp forms loopswhich extend from the soil to trap more silt and mud. As more sediment is deposited, the shoreextends further to the sea. he old shore is now further away from the sea and is like terrestrialground. Over time, terrestrial plants like the nipah palm and "andanus sp begin to replace the&ruguiera sp. he gradual transition and succession from a mangrove swamp to a terrestrialforest and eventually to a tropical rainforest,which is a climax community, takes a long time.hat is why we need to conserve and preserve our mangrove forest.

Pon$5uccession in a disused pond begins with the growth of pioneer species such as phytoplankton,algae and submerged plants like the %ydrilla sp, 2abomba sp and $lodea sp. hese plants havespecial adaptive features which enable them to colonise the pond. heir fibrous roots penetratedeep into the soil to absorb nutrients and bind sand particles together. "lenty of sunlight

penetrates through the clear water to allow photosynthesis to take place. 7hen the pioneerspecies die and decompose, more organic nutrients are released into the pond. he organic matteris converted into humus at the pond base. he humus and soil which erode from the sides of the

pond are deposited on the base of the pond, making the pond shallower. he condition becomesmore unfavourable for submerged plants but more suitable for floating plants such as duckweeds30emna sp4, water hyacinths 3$ichornia sp4 and lotus plants 3


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which can live in water as well as on land, for example, sedges and cattails. he rhi!omes ofthese plants grow hori!ontally across the habitat. heir extensive roots bind the soil particlestogether and penetrate deeply to absorb more mineral salts. hese plants spread rapidly andcolonise the habitat, changing it. he emergent plants grow from the edge of the pond towardsthe middle of the pond as the pond becomes shallower. 7hen these plants die, their decomposed

remains add to the sediments on the base of the pond. his further reduces the depth of the pond.he condition of the pond now becomes more favourable for land plants like small herbaceousweeds, for example, Ageratum cony!oides, $uphorbia hirta and Oldentandia dichotoma. As time

passes, the land becomes drier and the pond dries up. 0and plants such as shrubs, bushes andwoody plants become more numerous. A primary forest emerges and eventually turns into atropical rainforest which is also known as a climax community.

Ce## &i,isionitosishe two ma8or phases mainly interphase and mitotic cell division also known as the / phase whichconsists of mitosis and cytokinesis begins and ends according to the cell cycle. /itosis begins withinterphase. Interphase is divided into three shorter stages, ;', 5 and ;-. In ;' phase, the cell synthesises

protein and new cytoplasmic organelles such as mitochondria and chloroplast. he chromosomes are notcondensed and appear as thread1like structures called chromatin. In 5 phase, however, synthesis of #


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cells undergo the same stages of mitosis as in animal cells, cytokinesis in plant cells us markedlydifferent. A cleavage furrow does not form. Instead, membrane enclosed vesicles fuse to form a cell plate.he cell plate grows outwards until itsedges fuse with the plasma membrane of the parent cell.


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undergoes mitosis three times to form eight haploid nuclei. hree of the eightnuclei migrate to one end of the cell to form antipodal cells. Another two nuclei,called the polar nuclei, move to the centre. One of the three nuclei nearest theopening of the ovule 3micropyle4 develops into an egg cell or female gamete,flanked by two synergid cells. he structure formed is known as the embryo sac.It is where the embryo will develop. he ovule, which eventually becomes aseed, now consists of the embryo sac and the surrounding integuments.9$ight cells have no cell walls= synergid cells provide nutrient and support to eggcell= integuments form protective layers around embryo sac.or(ation o* Po##en .'be3 4ygote an$ .rip#oi$ 5'c#e's"ollination is the process in which mature pollen grains from the anther are transferred to the stigma of a flower. A pollen grain on a stigma initiates thefertilisation process. he secretion of sucrose solution in the stigma stimulatesthe pollen grain to germinate and form a tube known as the pollen tube. he

pollen tube grows through the tissues of the style into the ovule. #uring thegrowth of pollen tube, the generative nucleus divides by mitosis to form twomale gamete nuclei. he male nuclei follow the tube nucleus down the pollentube. 7hen the pollen tube reaches the ovary, it penetrates the ovule throughthe micropyle. he tube nucleus disintegrates and the tip of the tube bursts,leaving the passage for the male nuclei to enter the embryo sac.#ouble fertilisation, which is unique for angiosperms, occurs within the ovule.his process involves the union of the two male gametes nuclei with differentnuclei of the embryo sac. One male gamete nucleus fuses with the egg nucleus,forming a diploid !ygote 3-n4. he other male gamete nucleus fuses with the two

polar nuclei, forming a triploid nucleus 3+n4. he division of the tripod nucleuswill give rise to the endosperm, the food1storing tissue of the seed. he synergidcells and the antipodal cell will degenerates.

.he Ly(phatic )yste(or(ation an$ Co(position o* nterstitia# #'i$

&lood that enters the arterial end of the capillaries is under high pressure.his is because the blood capillaries have a smaller diameter than the arteriolesand arteries. his blood pressure causes fluid to leak continuously from the blood

plasma into the spaces between the cells. his fluid is known as interstitial fluid.he interstitial fluid fills the spaces between the cells and constantly bathes thecells. he exchange of substances between the blood capillaries and the bodycells occurs in the interstitial fluid.


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at the venous end allows fluid to re1enter the blood capillaries.

&yna(ic cosyste(5itrogen Cyc#eo build proteins, plants need the element nitrogen. he nitrogen gas inthe atmosphere is about E D but plants are not able to utili!e the nitrogen. hisis because the nitrogen has to be fixed before it can be absorbed by the plants.

sually, inadequate stretching and muscle fatiguelead to abnormalities in the mechanisms that control muscle contractions.

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'sc'#ar &ystrophy/uscular dystrophy is caused by the progressive degeneration andweakening of the skeletal muscles that control movement. he body musclesgradually become weak as they are replaced by fibrous tissue. his disease iscaused by a mutated gene in the @ chromosome and mainly affects boys. At

present, there is no cure for muscular dystrophy.

OsteoporosisOsteoporosis is a common bone disorder which causes the bones to

become thinner, more brittle and more porous. It is a common disease amongelderly women. he loss of bone mass normally begins after the age of +) yearsand accelerates greatly after the age of C( years. It particularly affects womenafter menopause, when changes in hormone levels 3especially oestrogen level4reduce bone strength. #uring the course of an individual?s life, the body needs

phosphate and calcium to build bones. If the dietary intake of these minerals isnot sufficient, or if the body does not absorb enough of these minerals from thediet, bone production and bone tissue will suffer, resulting in brittle and fragile

bones. hese bones are easily sub8ected to fracture. he loss of bone massoccurs gradually over an extended period of time. /ost people are not evenaware that they have osteoporosis until a bone is fractured because there are nosymptoms or early signs of osteoporosis. 5ymptoms that manifest over the yearsinclude fractures of the vertebrae, wrists or hips= a reduction in height over timeand a stooped posture. Osteoporosis can be prevented by taking adequateamounts of calcium, phosphorus and vitamin #. egular exercise can alsoreduce the likelihood of bone fractures and help reduce bone mineral loss.Although there is no cure for osteoporosis, medications can slow down the lossof bone mineral.

ArthritisArthritis refers to a group of skeletal disorders that involve inflammationof the 8oint. he 8oints become swollen, stiff and painful. One form of arthritis isosteoarthritis. Osteoarthritis is part of the ageing process caused by the wear and tear of the cartilage between the bones inside certain 8oints. he ageing

process may also result in a decreased production of the synovial fluid in the 8oints. he patient usually suffers from a painful and stiff knee which restrictsdaily activities like walking and climbing stairs. If treatment fails to relieve pain,a surgeon can replace the damaged 8oints with artificial ones made of plastic or metal.

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Respiration Circ'#ationH'(an Respiratory )yste(#uring inhalation, the external intercostals muscles contract while theinternal intercostals muscles relax. his action causes the ribcage to moveupwards and outwards. At the same time, the diaphragm muscles contract. hediaphragm lowers and flattens. hese two actions cause the volume of thethoracic cavity to increase, and the pressure of the thoracic cavity decreases.%igher atmospheric pressure on the outside forces the air to enter the lungs.#uring exhalation, the external intercostals muscles relax while the internalintercostals muscles contract. his action causes the rib cage to movedownwards and inwards. At the same time, the diaphragm muscles relax. hediaphragm curves upwards 3dome1shaped4. hese two actions cause the volumeof the thoracic cavity to decrease, and the pressure of the thoracic cavityincreases. %igher atmospheric pressure inside the lungs forces the ait out of thelungs.

A#,eo#i aseo's :change;aseous exchange happens between the alveolus and the bloodcapillaries through diffusion. he oxygen concentration or partial pressure of oxygen, "O- in the alveolus is higher than the blood capillaries. &lood capillariescarry carbon dioxide from body cells to the alveolus. 5o, it has a higher partial

pressure of carbon dioxide, "2O- compared to the air in the alveolus. 2arbondioxide diffuses into the alveolus and then it is breathed out through the nose or mouth. Oxygen diffuses into the blood capillaries from the lungs and combineswith haemoglobin to form oxyhaemoglobin. %aemoglobin is the red pigment in&2. Oxygen in the form of oxyhaemoglobin is carried to the cells and tissues.Oxyhaemoglobin is unstable so it will breakdown into haemoglobin and oxygen

when it reaches the cell or tissue with lower "O-.2arbon dioxide is given out by cell as waste products of cellular respiration. hiscarbon dioxide is transported out of the cell by a few means. ED of themdissolve in blood plasma, -+D of them binds with haemoglobin to formcarbaminohaemoglobin, a type of multiple amino while E)D of them are carriedwith bicarbonate ions.2O- %-OJ%-2O+J% %2O+19with the presence of carbonic anhydrase3%2O+4&lood plasmaJlungsJnose 3%2O+J2O- %-O4

.he Reg'#atory echanis( o* Carbon &io:i$e Content in the 7o$y#uring vigorous exercise, partial pressure of carbon dioxide increases as

there is active cellular respiration. 2arbon dioxide reacts with water to formcarbonic acid. he higher carbon dioxide concentration level in the blood resultsin a drop in the p% value of the blood and tissue fluid 3cerebrospinal fluid4

bathing the brain.2O- %-OJ% %2O+1his drop of p% is detected by the receptors include the central chemoreceptorslocated in the medulla oblongata and the perisheral chemoreceptors which aresensitive to both the carbon dioxide content and the p% of the blood. he

perispheral chemoreceptors are the aortic bodies found within the aortic bodies

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chromosomes produce gamates with four equally possible combinations of the chromosomes.

iii< Ran$o( *erti#isation$ach gamete has a unique set of combination of genes. A male gametecan fertilise any of the female gametes. he fertilisation between a malegamete and a female gamete occurs randomly. As a result, each !ygote isunique. 7ith random fertilisation, variations occur in the offspring.

Repro$'ction or(ation o* $entica# .-insIdentical twins are formed when the ball of cells from a fertilised ovumsplits into two embryos. Only one sperm and one ovum are involved in the

process of fertilisation. he two embryos develop into two separate foetuses inthe uterus. $ach foetus has its own umbilical cord but shares the same placenta.5ince the twins originate from one embryo, they are, therefore, identical in everyaspect. hey are born the same sex.or(ation o* raterna# .-ins "5on!i$entica# .-ins%

raternal twins are formed when two ova are released at the same time,one from each ovary. $ach ovum is then fertilised by a sperm. As a result, two!ygotes are formed and develop into two separate embryos. $ach embryo has itsown placenta and umbilical cord. hey are genetically un1identical thus havingdifferent physique and may or may not varies in sex.)ia(ese .-ins5iamese twins are identical twins which did not separate completelyduring embryonic development.


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'nction o* P#acenta ts A$,antages"lacenta takes over the 8ob of corpus luteum to constantly produceoestrogen and progesterone to maintain the thick, blood1enriched endometriumthroughout the pregnancy. he placenta is the site of the exchange of nutrients,respiratory gases and wastes between the foetus and its mother. he placenta isconnected to the foetus by the umbilical cord. >mbilical cord is a tube with oneumbilical vein and two umbilical arteries. he umbilical arteries carrydeoxygenated blood from the foetus to the placenta while the umbilical veincarries oxygenated blood from the placenta to the foetus.


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body temperature is high is prevented as high basal body temperature give asign that the process of ovulation is happening on that particular day.

.echno#ogy in ai$ o* n*erti#ityInfertility will not be a problem as the technology improves. his is

because there are many methods that can aid infertility in both men andwomen. Artificial Insemination 3Intro1uterine insemination4 can be used for malethat has low sperm count. his is done by collecting the man?s sperm over a

period of time so that the sperm count will be high enough for fertilisation. hewife can be inseminated with the husband?s sperms or sperms from the sperm

bank. he sperms are in8ected directly into the fallopian tube. 5ometimes, thewoman is inseminated with sperms obtained from the sperm bank. A sperm bank is a special laboratory that stores sperms in liquid nitrogen at a temperature of 1' Bo2. 5perms from the donors are collected, fro!en and kept in a sperm bank.he genetic biodata of each donor are kept meticulously, so that a womanwishing to conceive can use the sperm bank to obtain the sperms she wants.In some cases, another woman can be used as a surrogate mother as somefemales are unable to give birth or even to get pregnant. he sperms and ovaare contributed by the parents. he sperms can also be obtained from a sperm

bank and the ova from the surrogate mother. $ither sperms or an embryo istransferred to the uterus of the surrogate mother. he surrogate mother then

becomes pregnant and the foetus develops in her uterus until birth. In vitrofertilisation, another method of fertilisation that occurs in a controlledenvironment of a laboratory outside the human body. his method is used whenthe fallopian tubes are blocked, thus preventing fertilisation by the sperms. Afine laparoscope is used to remove mature ova from the ovary. he ova are then

placed in glassware with culture solution to mature. hen, concentrated spermsfrom the father are added. he sperms and ova fuse and develop into embryos.After two to four days, when the embryos are selected and inserted into theuterus through the cervix for implantation on the uterine wall. If the procedure is

successful, the implantation embryos will develop into a healthy baby or healthy babies. &abies conceived in this method are sometimes called test1tube babies.2ouples can also use ova from donors.

)per(atogenesis5permatogenesis occurs in the germinal epithelium of the seminiferoustubules. he primodial germ cell in the germinal epithelium cells 3-n4 divides bymitosis to produce spermatogonia 3-n4 3spermatogonium sing.4. Onespermatogonium 3-n4 grows in si!e to become a primary spermatocyte 3-n4.$ach primary spermatocyte 3-n4 undergoes meiosis I to produce two secondaryspermatocytes. $ach secondary spermatocyte 3n4 completes meiosis II to

produce spermatids 3n4. In the process of spermiogenesis, each spermatid

differentiates 3matures4 into a spermato!oaFsperm 3spermato!oon sing.4.

OogenesisOogenesis occurs in the germinal epithelium of the ovary before birth andis regulated by hormones. he primodial germ cell in the germinal epitheliumcells 3-n4 divide by mitosis to produce oogonia 3-n4 3oogonium sing.4. heoogonium 3-n4 grows in si!e to become a primary oocyte 3-n4. $ach primaryoocyte 3-n4 undergoes meiosis but stops at prophase I of meiosis I. /eiosisresumes at puberty to produce a larger secondary oocyte 3n4 and a smaller first

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polar body. he secondary oocyte 3n4 undergoes meiosis II and stops atmetaphase II. he first polar body completes meiosis II to form two polar bodies 3n4. At this stage, the secondary oocyte, together with the layers of follicle sellsaround it, is now called a secondary follicle. he secondary oocyte starts to growin the follicle. he secondary follicle increases in si!e and matures to form thegraafian follicle. At intervals of approximately - days, the graafian folliclemerges with the wall of the ovary. he ovarian wall and the graafian follicle thenrupture, releasing the secondary oocyte or egg into the fallopian tube. his

process is known as ovulation. If the secondary oocyte is fertilised by a sperm,meiosis II will be completed to form two haploid cells of unequal si!e. he larger cell is ovum while the other is a polar body. he nuclei of the sperm cell and theovum then fuse to form a diploid !ygote 3-n4. his means a primary oocyteultimately give rise to a single haploid ovum and three haploid polar bodies. All

polar bodies will degenerates. After ovulation, the follicle cells left in the ovaryform a corpus luteum. If there is no fertilisation, the corpus luteum willdegenerates after a few days. he cycle formation of the graafian follicle,ovulation and the corpus luteum is known as the ovarian cycle.

Actions;o#'ntary Actions o* the )ke#eta# 'sc#esGoluntary actions such as walking and talking are under conscious control.Goluntary control of the skeletal muscles is governed by the cerebral cortex of the cerebrum. he pathway of the transmission in voluntary actions is as follows.7hen the door bell rings, the receptors in the ear pick up the ringing of thedoorbell. he receptors trigger nerve impulses in the afferent neurones. henerve impulses pass from the afferent neurones to the interneurones in the

brain. he brain interprets the nerve impulses from many interneurones that thedoorbell is ringing. he brain also decides that the door should be opened. romthe interneurones, nerve impulses are transmitted to the efferent neurones andthen to the muscles. he muscles in the arm carry out the response and open

the door.

n,o#'ntary Actions o* the )ke#eta# 'sc#es= .he Re*#e: ArcInvoluntary actions that involve skeletal muscles allow an immediateaction that does not require conscious effort. In such circumstances when theresponses to stimuli are involuntary, they are called reflexes.A sharp pin pierces the skin causing the sensory receptors in the skin togenerate impulses. he nerve impulses are transmitted along an afferentneurone towards the spinal cord. In the spinal cord, the nerve impulses aretransmitted from the afferent neurone to an interneurone. rom theinterneurone, the nerve impulses are transmitted to an efferent neurone. heefferent neurone carries the nerve impulses from the spinal cord to the effectors

3muscle tissue4 so that the pin can be pulled out from the skin immediately.

)pecia# Case= >nee!?erk "pate##ar re*#e:%Hnee18erk only involves the simplest neural circuit because it involves onlytwo kinds of neurones: the afferent neurone and the efferent neurone. he reflexhammer hits a tendon that connects the quadriceps muscle in the thigh to a

bone in the lower leg. As the hammer strikes the knee, the force stretches thequadriceps muscles and stimulates the stretch receptors in the muscles,triggering nerve impulses. Afferent neurones transmit the information to the

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efferent neurones in the spinal cord. he efferent neurones transmit thisinformation to the quadriceps muscles, and the muscle contracts, 8erking the legforward.)ynapseshe transmission of information is by no means electrical but chemical in nature.7hen the nerve impulse reaches the end of the presynaptic end of the neurone,it will stimulate the release of chemicals named neurotransmitters in thesynaptic vesicles. he synaptic vesicles then fuse with the cell membrane,releasing the neurotransmitters through exocytosis. he neurotransmitters thencross the synapse where they may be accepted by the next neurone at aspecialised site called a receptor. he neurotransmitters then fuse with thereceptor thus transmitting the nerve impulse to the next neurone. Gesiclescontaining the neurotransmitters are only in the presynaptic end and thereceptors are only on the postsynaptic end, therefore the synapse ensures thatthe flow of impulses in one direction only.

&iseases Re#ate$ to 5er,o's )yste(i< A#@hei(er s &isease

nder secretion during growing years retards bone growth, resulting in acondition known as dwarfism. he organs of the person often fail to growand the si!e of the body is like that of a child. oday, geneticallyengineered growth hormones can be given to children with the deficiency

in growth hormone and successfully induce growth, allowing the childrento attain normal height.ii< .hyro:ineOver secretion causes an increase in the metabolic rate of the body.2ommon symptoms include excessive sweating, heat intolerance,increased bowel movements, nervousness, rapid heart rate and weightloss. 5ometimes, the thyroid gland can grow and enlarges two or threetimes its normal si!e, a condition known as goitre. One causes of goitre isiodine deficiency. In this situation, the thyroid gland cannot synthesise

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and release enough thyroxine 3throxine contains iodine4. As a result, itenlarges in response to excess stimulation from the pituitary gland.>nder secretion during childhood can cause severe mental retardation, acondition known as cretinism. In adulthood, it causes myxedema. A personwith myxedema has a slow heart rate, low body temperature, highsensitivity to cold, general lethargy and a tendency to gain weight easily.A lack of iodine in the diet also reduces the production of thyroxine.

iii< ns'#inOver secretion of insulin can lead to hypoglycaemia, an abnormally lowlevel of glucose in the blood. 5ome of the symptoms of hypoglycaemia arefatigue, insomnia, mental confusion, nervousness, mood swings, faintingspells and headache. 5evere hypoglycaemia can lead to convulsions andunconsciousness.>nder secretion of insulin can lead to diabetes mellitus. #iabetes mellitusis a chronic condition associated with abnormally high levels of sugar 3glucose4 in the blood. "eople with diabetes either do not produce enoughinsulin or cannot use the insulin that their body produce. As a result,glucose builds up in the bloodstream. A person with diabetes mellitusexperiences an increase in frequency of urination, excessive thirst,numbness or burning sensation in the feet, ankles and legs, blurred or

poor vision, fatigue, and slow healing of wounds. 0arge quantities of human insulin are now produced by genetically engineered bacteria."atients are usually in8ected with this commercially prepared insulin.

iv. Anti$i'retic hor(one "A&H%Over secretion of A#% can results in high retention of water in the

body.>nder secretion of A#% can result in a disorder known as diabetesinsipidus. As a result, the person excretes a large amount of urine. "eople

with diabetes insipidus are thirsty all the time. hey often want to drink liquids frequently. his is because so much water is lost in the urine= the

person may die of dehydration if deprived of water for even a day.

>i$ney ts 'nction + the or(ation o* BrineHidney is situated in the dorsal wall of the abdomen. It has three main

parts that are the outer cortex, inner medulla and the pelvis. $ach kidneyconsists of numerous tubular units that are called nephrons. Hidney is needed toremove toxic waste products from our body. Hidney involved in theosmoregulation to keep the osmotic concentration of the blood constant byremoving excess water and salts. It regulates the p% of the blood by controllingthe removal of hydrogen ions. It also controls the blood volume.

he formation of urine depends on the nephrones through three processes:i< B#tra *i#trationhe afferent arteriole which has a bigger diameter than that of theefferent arteriole sends blood to the glomerulus. he blood is now under relatively high pressure and ultra filtration takes place in the &owman?scapsule. he filtrate which filters into the &owman?s capsule consists of small molecules, water, glucose, amino acids, urea and mineral salts. hefiltrate does not contain blood cells or plasma proteins. hese componentsremain in the glomerular capillaries as they are too large. he filtrate then

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goes down the proximal convoluted tubule for reabsorption.

ii< Reabsorptioneabsorption takes place in the proximal convoluted tubule, loop of %enle, distal convoluted tubule and collecting duct. At the proximalconvoluted tubule, about B(D of the water in the glomerular filtrate3water, urea, glucose, amino acids and salts such as sodium ions4 isabsorbed back into the surrounding blood capillaries by osmosis. All theglucose, amino acids, vitamins and some salts are reabsorbed by activetransport. >rea is not reabsorbed. As the filtrate 3water, salt and urea4

passes along the loop of %enle, about -)D of the water and some saltsare reabsorbed into the blood capillaries. At the distal convoluted tubuleand collecting duct, the amount of water and salts that are reabsorbedinto the blood capillaries depends on the content of water and salt in the

blood. eabsorption of water and salts is regulated by the endocrinesystem.

iii< )ecretion5ecretion takes place in the distal convoluted tubule. Along the tubule,waste products such as urea, uric acid and ammonia are pumped out of the blood capillaries into the distal convoluted tubule by active transport.his process is called secretion. 5ome drugs and toxic substances aresecreted by simple diffusion. he final glomerular filtrate which remains inthe collecting duct is called urine 3 BD of water, -.(D nitrogenous

products such as urea, uric acid, ammonia and cretinine, '.(D salts andother trace elements such as bile pigments4. rom the collecting ducts,urine is channelled into the pelvis and carried out of the kidney by theureter to the urinary bladder before it is excreted through the urethra.

Ho(eostasis%omeostasis is the regulation of the physical and chemical factors in theinternal environment to maintain a constant internal environment.Os(oreg'#ationOsmoregulation is the regulation of salt and water balance in the body tomaintain the blood osmotic pressure. It is controlled by two hormones mainlyAntidiuretic %ormone 3A#%4 and aldosterone.7hen the osmotic pressure increases, it is detected by the osmoreceptors in thehypothalamus.


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#'coreg'#ationhe normal blood glucose level is )mg in '))cm+ of blood. 7hen the

blood glucose level increases, the change is detected by the L1cells of the Isletsof 0ongerhans. his stimulates the pancreas to secrete insulin. ;lucose isconverted into glycogen for temporal storage. ;lycogen is converted into lipid to

be stored under the adipose tissues. "art of the glucose is used as therespiration of glucose increases. he blood glucose level declines back tonormal.7hen the blood glucose level decreases, the change is detected by the M1cells of the Islets of 0ongerhans. his stimulates the pancreas to secrete glucagon. 0ipidis converted back to glycogen while glycogen is converted back to glucose. he

blood glucose level rises back to normal.

.her(oreg'#ationhermoregulation is the regulation of body temperature. 7hen the bodytemperature increases to a value higher than +Eo2, it is detected by thethermoreceptors in the hypothalamus.


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root. he upper side of the root grows faster than the lower side. he young rootcurves and grows downwards, showing positive geotropism. Auxins move awayfrom the light, accumulate in the shaded side.Loco(otionAntagonistic 'sc#esAntagonistic muscles are a pair of muscles which work together to allowcoordinated movements of the skeletal 8oints. his means that when one musclecontracts, the other relaxes.

7en$ing )traightening o* the Ar(7hen the biceps contract, the triceps relaxes. he biceps becomes shorter and thicker while the triceps becomes longer and thinner. his exerts a pullingforce transmitted to the radius through the tendons. As a result, the radius is

pulled upward and the arm is bended. he elastic ligaments that held the radius,ulna and the humerus together enable the radius and ulna to be pulled upward,

bending the arms from the elbow. 7hen the triceps contract, the biceps relaxes.


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of the fins help in controlling the direction as well as the stability of fish in thewater.

7ir$he antagonistic actions of the strong muscles enable the bird to flap itswings up and down. 7hen the pectorial ma8or 3in4 contracts and the pectorialminor 3out4 relax, the wings flapped downwards. 7hen the pectorial minor 3out4contracts and the pectorial ma8or 3in4 relaxes, the wings goes up.

rasshopper rog;rasshopper has strong muscular hind legs that are the flexor 3in4 and theextensor 3out4 muscle to enable them to 8ump. A flexor muscle controls forwardleg movement while the extensor controls the backward movement. &efore

8umping, the hind leg is folded in the shape of alphabet N, the flexor musclecontracts while the extensor relaxes. 7hen the extensor muscle contracts andthe flexor muscle relax, the hind leg will straighten quickly resulting in a lift andthe grasshopper 8umps forward and upward.o land, the forelegs are extended forward to absorb the landing shock. he hindlegs are then folded again. or walking, the grasshopper uses three legs to movewhile the other three labelled @ are used to support the body.rog has locomotion almost identical to grasshopper. It also has long, big andstrong muscular hind legs. he contraction of the femur muscles result instraightening of the leg quickly. he feet push the ground causing the frog to

8ump upward and outward. #uring landing, the front legs are extended first toabsorb the landing shock. At the same time, the hind legs are folded again intoits N shape.

Respiration ish7hen a fish inhales, its mouth opens and the buccal cavity is lowered. As

this occurs, the operculum closes and the opercular cavity becomes bigger. hisresulted into a lower pressure in the buccal cavity. 7ater is then drowned into itsmouth along with dissolved oxygen.7hen a fish exhales, its mouth closes, raising the floor of the buccal cavity. Awater flows through the lamellae, respiratory gases are exchanged between

blood capillaries and water. As this occurs, the opercular cavity becomessmaller. he high pressure in the buccal cavity forces the operculum to openallowing water to flow out.

rasshopperInsects inhale and exhale through the rhythmic contraction and expansionof their abdominal muscles. he body movements and the contractions of the

abdominal muscles speed up the rate of diffusion of gases from the tracheaeinto the body cells. 7hen an insect inhales, the abdominal muscles relax and thespiracles open. Air pressure inside the tracheae decreases and air is drawn in.7hen an insect exhales, the abdominal muscles contract. he increased air

pressure forces air out through the spiracles. he spiracle system with itsnetwork of small tubes allows oxygen to be absorbed directly from theatmosphere into the body cells. herefore, there is no circulatory system ininsects.

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rog7hen a frog inhales, it breathes in through its nostrils. he bucco1pharyngealfloor is lowered and fresh air is drawn in. At the same time, its glottiscloses and stae air remains in the lungs. Afterwards, the glottis will open. Itsnostrils are then closed and the bucco1pharyngeal floor is raised. his causeshigh air pressure which forces air into its lungs thus, expanding them.7hen a frog exhales, its lung muscles contract, expelling air from its lungs. Afrog does this by the abdominal pressure and elasticity of the lungs. 5ome of the9 illing in air: nostrils open, glottis closed, floor of the mouth lowers9 orce air in: nostrils closed, glottis open, floor of the mouth rises9$xpiration: nostrils open, glottis open, lung contracts

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F4-F5 Biology Selected Topics (Essays).doc