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Didn't you notice Ammu's doubt? Didn'tyou also have this doubt?

What may happen to the proteins in ourfood?

Analyse the given description, forminferences about this and record it in theScience diary.

Synthesis of Urea

Aminoacids are formed due to the breakdown of proteins. These aminoacids are utilizedfor the synthesis of new proteins necessary for body building, enzymes and many othersubstances. During these reactions, many byproducts are formed. Many of these arewaste materials which are harmful to the body. Ammonia is a major waste product formedin this way. It is very much harmful to the body. The ammonia formed in the cells diffuses

Sir, then whathappens to theproteins in our

food?

You know thatthe carbohydrate and

lipids of the food we takein are converted to

carbondioxide and water atthe end of metabolism

liberating energy, and it isthis energy that is utilized

for life activities andgrowth....

Std. XBiology

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into the blood and the blood carries it to the liver. In the liver, with the help of enzymes,it combines with CO2 and water, and is converted to a substance called urea.

NH3+ CO2+H2O → Urea

The formation of urea, known as Urea cycle, takes place in a cyclic manner in severalsteps. Urea is a relatively less toxic substance which is highly soluble in water. Ureaformed in the liver is transferred to blood from where it is eliminated through urine.

Like urea, other byproducts ofmetabolism such as carbondioxide, water,etc., also, in excess in the body adverselyaffect homeostasis. These are to beremoved from the body to avoid such asituation. How are carbondioxide andwater removed from the body? List theorgans which facilitate this.

� Skin� ...................................................................�

Urine, the main excretory material in thebody, contains mainly water, urea andsalts.

Let us plan an experiment to test thepresence of urea in urine.

Using the given description conduct anexperiment with your friends, and recordthe findings in the Science diary.

Experiment

Add 2 or 3 drops of phenolphthalein to 5ml of urine. Observe the colour change.Add the enzyme urease into this. Observethe colour change again.

Planning

Aim

..................................................................

Materials required

..................................................................

Procedure

.....................................................................

Observation

..................................................................

Inference

..................................................................

..................................................................

IndicationPhenolphthalein + Urea → milk colour

Urea + Urease → Red colour

How is urine formed from blood?

Which is the organ that helps this ?

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Analysing the given description and Figure 4.1, prepare notes on the structure, position,size, etc., of this organ.

.....................................................................................................................

In order to know how kidneys filter and remove impurities from blood, their internalstructure is to be understood. Analyse Fig. 4.2, complete the given illustration andpresent it in the class room.

Fig - 4.1. Kidneys and associated parts

thoracic cavity

adrenal gland

kidney

vertebral column

ureter

urinary bladder

urethra

abdominal cavity

Kidneys

Kidneys are the organs which purify blood by eliminating impurities in the form of urine.There is a pair of kidneys in human beings. They are seen against the posterior musclesof the abdominal cavity in the lumbar region, on either side of the vertebral column.

They are bean-shaped and are about 11cm long, 5cm broad and 3 cm thick. Eachkidney is dark red in colour and weighs about 150g and is covered by a rigid but softmembrane. Blood reaches the kidneys from the heart at high pressure, through therenal artery and returns through the renal vein. About 1100mL. of blood passes throughthe kidneys per minute.

Urea, salts, excess amount of medicines taken into the body, vitamins and other harmfulsubstances that reach the body are filtered and removed from the blood by the kidneys.

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Position, size, shape

$

Functions

$

Major blood vessels and theirfunctions

$

Internal structure,main parts

$

Each kidney has about twelve lakhs of micro filters inside. These are the nephrons.Nephrons are the basic functional units of kidney. Analysing Figure 4.3, draw inferencesabout how nephrons are arranged inside the kidney.

Fig - 4.2. Longitudinal section of kidney

Cortex

The outer part where lakhs ofmicro filters are seen

Medulla

The inner part where longtubes of the filters are seen

Pyramid

The part to which the collectingducts of micro filters open

Renal artery

The vessel which carriesblood to the kidney

Pelvis

The part to which urine flowsfrom the filters

Ureter

The vessel which carries urinefrom the kidney to the urinarybladder

Renal vein

The vessel which carries bloodfrom the kidney

Kidneys

Fig - 4.3. The arrangement of nephrons in the kidney nephron

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Fig - 4.4. Structure of a nephron

GlomerulusInside the kidney the renalartery breaks up into minutecapillary networks which looklike a bundle of threads. Eachbundle is called glomerulus.Minute pores are present onits walls which effect ultrafiltration.

Renal tubule

The vessel connecting theBowman’s capsule and thecollecting duct. The reabsorptionof essential substances andelimination of certain wastematerials take place.

Urine

afferent vessel efferent vessel

Fig - 4.5. Ultrafiltration

Glomerular filtrate

Contains water, glucose, amino acids, ions ofSodium, Potassium and Calcium, vitamins,urea, uric acid, creatinine, etc.

UltrafiltrationHow might kidneys be filtering out the excretory wastes in the blood? What might bethe adaptations facilitating this ? Using the indicators, analyse Figures 4.4 and 4.5.

Bowman's capsule

Bowman’s capsule is adouble-walled cuplikecovering surroundingthe glomerulus. Helpsto collect glomerularfiltrate formed as aresult of ultra filtration.

Collecting duct

Urine is collected fromthe nephron. It opensout into the pelvis.

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Indicators� Is there any difference in size between

afferent and efferent vessels? Howdoes this difference affect the flow ofblood?

� What is the advantage of the breakingup of the afferent vessel into veryminute capillaries inside the Bowman’scapsule?

� Will there be any difference in thepressure of blood in the glomerulus inrelation to the afferent and efferentvessels? If yes, what is the reason?

� What is the necessity of micropores onthe capillary wall?

You have observed the picture of ultrafiltration and the components of theglomerular filtrate.

� What are the components of theglomerular filtrate?

� What may be the reason for the absenceof RBC and protein in the glomerularfiltrate?

Now you have learnt the composition ofthe glomerular filtrate. About 127 mL ofglomerular filtrate is formed per minute.If the whole of the glomerular filtrate istransformed into urine, a person wouldhave to expel about 180 litres of urine perday. Does this happen? How much urinedoes an individual expel in a day, on anaverage?

Record your guess.

.....................................................................

Is it now clear that all of the glomerularfiltrate is not converted to urine? Whathappens to the remaining glomerularfilterate?

Many components of the glomerular

filterate including water and glucose areessential for the body. While glomerularfiltrate flows through the renal tubule,these components are reabsorbed atdifferent parts of the tubule. Along withthis, certain substances which are notuseful to the body are discharged into theglomerular filtrate. Around 126 mL ofglomerular filtrate is reabsorbed and theremaining portion becomes urine. Thisreaches the ureter through the collectingduct. Subsequently, it is storedtemporarily in the urinary bladdersituated at the lower part of the abdominalcavity. As and when the bladder fills, theurge to urinate occurs and urine isexpelled through the urethra.

Components of UrineYou know that urine contains water, ureaetc.

What are the other components of urine?

You have learnt that human beings excreteon an average 1.5 litres of urine per day.Is there any difference in this quantity dueto the changes in climate? If so, what maybe the reason?

.....................................................................

}Water 96%

Urea 2%

Salts and other substances

NaCl, KCl, Creatinine,Uric acid,Salts of Phosphorus,Calcium, etc.

The pale yellow colour of urine is due to thepigment called urochrome formed as a resultof the break down of haemoglobin.

2%

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Table - 4.1

Observe Illustration 4.1., analyse the conditions causing changes in the quantity ofurine, and the mechanisms which make this possible and form inferences.

.....................................................................................................................

Secretion of

ADH decreases

Secretion of

ADH increases

Illustration - 4.1.

When kidneys failUnhealthy habits and life style influence the health of kidneys to a great extent. Kidneysmay fail due to several reasons and life itself may be in danger.

Read the details given in Table 4.1., gather more information and prepare a pamphleton diseases of the kidneys, their symptoms, reasons, etc.

Is there any means to sustain life of anindividual whose kidneys fail to function?

Have you heard of dialysis?

What is dialysis?

It is the process of purification of the blood

by filtering out impurities from it usingcomplex machinery. Dialysis is conductedwhen both the kidneys fail. ObserveIllustration 4.2 and identify the stages ofdialysis and record it in the Science diary.

Rainyseason/winter

Nephritis

Chronic renal failure

Kidney stone

Quantity ofurine

increases

Quantity ofurine

decreasesSummer

Dark coloured and turbid urine,backpain and fever, swelling of theface, ankles and feet.

Anaemia, weight loss, giddiness,vomiting, etc.Urea and other excretory wastes arenot filtered out, but retained in theblood itself.

Pain in the lower abdomen, urinaryblock, backpain, giddiness andvomiting.

Streptococcus infection, infection ofurinary bladder, Autoimmunedeficiency syndrome, etc.

Various types of renal diseases,diabetes, hypertension, etc.

Calcium oxalate, calciumphosphate etc., get sedimented inthe kidney and ureter as grains.

Disease Major Symptoms Reasons

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Kidney TransplantationGiven below are the contents of a poster pasted on the wall of a Primary Health Centre.Using this, discuss the significance and limitations of kidney donation and record thedetails in the Science diary. Collect more information and pictures of kidney donationand display them on the bulletin board.

Donate kidneys...... Share life......

• Kidney transplantation becomes necessary in a condition in which boththe kidneys completely fail beyond treatment.

• The kidney of a healthy individual who dies in an accident (deceaseddonor) or that of a healthy person (living donor) can be donated.

• Whatever be the category of donor, the blood groups of the donor andthe recipient must be compatible.

• It is a functional kidney that is transplanted from the donor to therecipient. Kidney transplantation is successful only when the recipient’sbody completely accepts the kidney.

4. Purified blood is passedback to vein

3. Artificial kidney (filters the bloodand separates excretory wastes )

Dialysingfluid

2. The chemical substance calledheparin is mixed with blood to preventcoagulation

1. The blood containing high amountof excretory wastes is collected fromthe artery

Illustration - 4.2. Dialysis

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Organ Excretory Materials Method of Elimination

Table - 4.2.

Excretory Organs

Fig - 4.6Lungs

Fig - 4.8

Skin

Other Excretory Organs in the BodyYou have learnt that the lungs, liver and skin are the other organs which eliminateexcretory materials formed in the body. What are the wastes that they expel? How dothey function? Analyse the figures and notes given below ( 4.6 to 4.8) and completeTable 4.2.

Like human beings, other animals also have systems to remove wastes formed asmetabolic byproducts. But depending on the peculiarities of the circumstances in whichthey live, they are diverse in structure. Analyse the given description and compare theexcretory organs, excretory materials, mechanisms of excretion, etc., of other organisms.Find out the similarities and differences, and the main reasons thereof and record themin the Science diary.

Fig - 4.7

Liver

The carbon dioxide formedas a result of metabolicactivities is collected andexpelled from the bodyalong with water vapour.

The waste managementplant that maintainshomeostasis by detoxifyingmost of the toxins thatreach the blood. Liver doesnot directly eliminateexcretory materials.

The sweat glands in the skin expelwater and wastes like urea and uricacid through sweat. Sweat contains99% water and 1% salts and othersubstances.

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Nn{Xw 4.13

Fig - 4.12.

Malpighian tubuleFig - 4.11.

Fig - 4.10.

Nephridia

contractile vacuole

Fig - 4.9.

Fig - 4.13.

Amoeba

There are no excretory organs in amoeba which is a unicellularorganism. But this function is performed with the help of contractilevacuoles. Excess water that reaches the body is also expelledthrough the contractile vacuole.

Excretion in Other Organisms

Earthworm

Nephridia are the excretory organs in earthworm.They separate water, nitrogenous wastes, etc.,from the body cavity and expel them through thepores on the body surface.

Insects

The excretory organs of insects are known asMalpighian tubules. They are minute tubesspread out in the body fluid that fills the bodycavity and open out into the alimentary canal.Malpighian tubules separate impurities from thebody fluid and carry them to the alimentary canal,from where they are expelled.

Fish

The major excretory material in fish is ammonia, which isexcreted directly into water through the kidneys.

Frog

Kidneys are the organs of excretion in frogs too. In tadpoles whichare fully aquatic, ammonia is the excretory material. But when tadpolemetamorphose into frog, instead of ammonia, urea is eliminated asthe excretory material.

Reptiles and Birds

Uric acid is the excretory material in birdsand reptiles. It is solid or semisolid in formand insoluble in water. This minimises theloss of water through excretion. Kidneysare the excretory organs in them too.Fig - 4.14. Fig - 4.15.

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Fig - 4.16.

Do Plants Excrete ?Did you notice the question? Read the description given below, observe the plantsaround you carefully, discuss the findings with friends, and present them in the class.

Excretion in Plants

In plants too there are mechanisms to eliminate excretory materials formed as a result ofmetabolic reactions. In plants there is no specific excretory system as in animals. Thequantity of wastes formed in plants is also very low compared to that in animals. Themain reason for this is said to be the lesser rate of activity in plants when compared toanimals. The excess oxygen produced as a byproduct of photosynthesis is eliminatedthrough stomata. Carbon dioxide formed as a result of cell respiration is also expelledthrough the stomata.

From the soil plants absorb more water than required. This excess water is expelledthrough stomata and hydathodes. Hydathodes are minute pores at the tip of the leavesof plants of the grass species to eliminate water. Water is expelled as vapour through thestomata, and as droplets through the hydathode.

Certain excretory products reach the older xylem vessels in the stem and accumulatethere. This activity has a significant role in the gradual formation of heart wood.

Shedding of leaves is another mechanism for the elimination of excretory products inplants. Plants reabsorb the essential components from leaves as they ripen and fall.Therefore in the falling leaves, excretory materials will be the major content.

You have learnt that in order to maintain homeostasis, organisms keep the internalenvironment free of wastes. If so, shouldn’t we conserve our external environment forthe wellbeing of nature and its countless species of living beings? Observe Figure 4.16.

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Have you come across such heaps ofwaste?

What impacts do this bring about?

Enlist them.

�

�

Does your school premises get dirty likethis?

If so, by what all means does it get dirty?

Enlist them.

� The leftover of lunch, packing leavesetc.

�

�

Shouldn’t we put an end to suchpollution? How?

By group activity, form an action plan toeliminate such heaps of waste . Afterpresenting it in the class room, implementit collectively for the welfare of the public.Be a model to society.

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A B

Follow up Activities1. Observe the figure.

2. Given below is the last part of the pamphlet about kidney diseases, prepared bySajin.

Our health habits and life style, to a great extent, influence the health of thekidneys. And due to many reasons, the kidneys are damaged, sometimes evenendangering life itself. By taking necessary precautions, the kidneys can beretained healthy to a certain extent.

Suggest any four precautions and complete the pamphlet3. Prepare 2 slogans for the awareness rally organized by the Environment Club of

your school as part of the waste disposal scheme.

a. Label the parts termed A and B.b. What difference has occurred in the structure of A and B?c. How will this affect the function of the kidneys?