hsc science

8/13/2019 hsc science

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Senior Science

8.2 Water for Living

Section 1

Water is Essential


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Describing aqueous mixtures

, mi"ture consists of two or more substances that can be separated by physical means."amples

Dirty water a mi"ture of dirt and water the dirt can be separated by filtration.

/ugar solution a mi"ture of sugar and water the sugar can be separated byevaporating the water.

, li'uid solutionis a mi"ture in which a solid! li'uid or gas #the solute$ dissolves in a li'uidsubstance #the solvent$. , solution%

contains dissolved substances #particles$

and these particles are spread out evenly throughout the li'uid.

,lso!

0he particles are e"tremely small #cannot be seen with the naed eye$.

0he particles can remain suspended indefinitely.

0he particles cannot be separated by filtration

, solute is the substance that dissolves in the solvent.

, solvent is a li'uid in which the solute dissolves.

, solution where the solvent is water is called an a'ueous mi"ture.

, solute is soluble if it dissolves completely in a solvent

, substance is insoluble if it will not dissolve in a solvent.

If two li'uids mi" they are said to be miscible.

Notes Questions

1. Which of the following mi"tures are solutionsil and water Dirty water sea water air mayonnaise alcohol and water paint

2. "plain why a solution is a mi"ture.

3. /uggest a reason why the diagram opposite couldrepresent a solution.

+. 4opy and then complete the following table

Solute Solvent Solution

/alt water

/ugar! flavours and other 5 4oca cola

6eer

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8.2.1.i &erform a first-hand investigation to demonstrate the range of substances that willdissolve in water and to identify the solute and solvent in each case

Solutes an Solvents

!im 0o identify the solute and solvent in a range of substances that dissolve in water.

"is# !nal$sis

6efore any practical tas is performed! a ris analysis should be completed. 0his means anassessment of sources of ris needs to be made. 7actors to consider include physical!chemical and biological factors.

6 /ee 9umans at Wor /ection 1 for more details

%et&o

1. rganise the following e'uipment% : medium test tubes

test tube rac

solids #solutes$ - sodium chloride! &henolphthalein! iodine! copper sulfate!

polystyrene foam

li'uids #solvents$ - water! methylated spirits! acetone

/patula

2. ;i" small 'uantities of each of the solutes separately with each of the solvents.3. Determine if a solution is formed.+.


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:. 9ow many pieces of fruit will be used in this e"periment #1! 2! 3! =! 1* 5$

E. 9ow many times will the e"periment be repeated to get reliable data

8. 9ow does the e"perimenter now that all the water has been removed from the fruitDiscuss the se'uence% Weigh 9eat Weigh 9eat Weigh 9eat Weigh. 9ow

long would the se'uence be continued.

F. "plain why an oven could be used.

1*."plain why a weighing machine could be used.

11."plain why a scalpel or pin would be useful.

12.ame a container that would be acceptable to hold the fruit.

"is# anal$sis

/afe woring practices involve care to be taen

When using scalpels and pins.

6y wearing correct footwear in the laboratory.

6y being careful where bags are placed in the laboratory.

6y concentrating on the tas to be completed and reducing distraction.Write a sentence for 0W of the above safe woring practices.

0&e -roceure scaffol

0he procedure scaffold has three main parts%

1. ,n statement outlining the aim or -ur-oseof the investigation

(enerally a single sentence

2. %aterialsneeded for the investigation

0his may be a list.

0his may be left out in some cases.

3. !se'uence of steps in a logical orer.

&referably in point form

ne idea per point

umbers can be used to show 1st! 2nd3rdetc

0he order is usually important

Words such as now, next and after thiscan be used.

;any steps should begin with command words such as add, stir, and weigh.

0here is enough detail so that the investigation can be re-eate.

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Writeu- of aim 3 met&o

nce pre-planning occurs the draft method can be written and the e"periment performed.

1. 4eaing Write a heading for the investigation.

2. /re -lanning questions Write down a summary of the various ideas and issuesraised in response to the pre planning 'uestions above.

3. Write a draft method using the ?aboratory


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/art 5 /erforming t&e ex-eriment

Writeu- of results conclusion

1. &erform the investigation

>se your method or an edited version to perform the investigation.

2.


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7ses of ater in living t&ings

5loostream - ;ulticellular animals need

to transport materials around their bodies

eg digested food from the small intestine

urea from the liver @ idneys and carbon

dio"ide to the lungs. /ince water is a good

solvent it dissolves many substances lie

glucose! urea! salts! o"ygen and carbon

dio"ide. It is an ideal fluid for transporting

these substances. 6lood plasma is F*

water. 0he substances dissolve in the

water and are carried in solution around the

body. Water is also necessary for

substances to enter the bloodstream. gthe lung surface needs to be moist so that

o"ygen can dissolve and move across to

red blood cells.

'ells - Water is essential for all the cells reactions. ;any

of these reactions only occur when the two reacting

substances are dissolved #in water$. 7or e"ample seeds

will not germinate without a certain amount of water in theseed. ,lso! within the cell! water is still necessary for

transport and moves substances around the cell. JIn plant

cells! water is necessary in maing the cell turgid #stiff$.

When the vacuoles of plant cells are full of water! they

cause the cells to push against the cell walls.K

0rans-iration Stream - ;ulticellular plants need totransport materials around their bodies. /alts and

other nutrients are absorbed by the roots and

delivered to the leaves via the transpiration stream.

0his is only possible because these substances are

soluble in water. JWater is also essential for

photosynthesis.K

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Notes Questions

E. "esearc& What is a cell

8. What is the main substance in cells

F. 9ow much water would there be in a living organism that weighed 1**g

1*.Why do cells need water

11.Water has a number of properties that contribute to maing it an important molecule for

living organisms.

12.What type of atoms #elements$ mae up a water molecule

13.Why is water a polar molecule

1+.What causes water molecules to be cohesive #stic together$

1=.What type of substances will dissolve in water

1:."esearc& What is the bloodstream1E.ame three substances transported around the body.

18.Why can blood transport many of these substances

1F.Why is water essential for chemical reactions in cells

2*."esearc& What is the transpiration stream

21.ame one substance transported by the transpiration stream.

8.2.1.c Discuss ways in which plants optimise water uptae

8.2.1.d Discuss ways! using e"amples! that plants reduce water loss such as 0hic outer coating #cuticle$ on leaves sing the information below! answer the following

1. Discuss ways in which plants optimise water uptae.

2. Discuss ways! using e"amples! that plants reduce water loss

It may be necessary to do further research to write a complete discussion.

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In plants! water moves from the soil! into the root! through the stem! then the leaves andfinally into the air via stomata.

n a hot day! a large tree absorbs hundreds of litres of water from the soil. Lery little of thisis used for photosynthesis. ;ost #FF$ is evaporated from the leaves.

Water absorption occurs via the root hairs. 0he root hairs greatly increase the surface area in

contact with water bearing soil.

0he 2ndcolumn needs to be reorganised to match the 1stcolumn./lant feature "eason for -lant feature

"tensive root systems


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8.2.1.iii &erform a first-hand investigation to identify adaptations of some plants that assistin reducing water loss

8.2.1.iv (ather! process and analyse information to identify the different ways in which a

range of terrestrial animals reduce water loss

8.2.1.e Discuss ways! using e"amples! that animals reduce water loss such as% e"crete uric acid instead of urea nocturnal behaviour reduced activity lying in the shade burrowing underground

Writing t&e met&o of a first&an investigation

In order to write a valid! e"perimental method! certain principles of e"perimental design needto be nown.

W&$ o ex-eriments9 When planning a first-hand investigation the following principlesshould be considered.

, first-hand investigation is designed to discover ne information.

"perimenters are interested in the trut&.

0he e"periment must be able to be re-eateby other scientists.

1. utline the information that was discovered in the e"periment to determine the amount ofwater present in a variety of fruits! vegetables and meat.

2. Identify 0W reasons why this e"periment could be repeated.

0&e riting genre 0o communicate the objectivityof the e"periment the tradition is to neveruse the words BIC or BWC. It is normal to write inpast tenseusing complete sentences.

Writing t&e met&o 0he method is a description of steps to be followed and thematerials used. When writing the method the following topics should be considered.

: :ariables; ;roups' 'ontrol% %easurements! !ctivityN NumberS Safety

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: :ariables

In an e"periment the effect of one variable on another is investigated.

0he ine-enent variable is the variable deliberately changed by the

e"perimenter.

0he e-enent variableis the variable that could change because of the change

in the independent variable.

'ontrolle variables 0he dependent variable and the independent variable canchange. ,ll other variables are ept the same throughout the e"periment theseare called the controlle variables.

3. In this investigation on water content%

aK Identify the independent variable )1 mar#*

bK Identify the dependent variable )1 mar#*

cK ame 2 variables that could have been controlled. )2 m#s*

; ;roups

;rou-soccur because the independent variable is changed for different groups.

0he only difference between the groups at the start of the e"periment is the

difference in the independent variable. In all other aspects the groups are thesame.

+. 9ow many groups are there in the water content investigation

' 'ontrol

0here are two t$-esof groups the 'ontrol ;rou-and the Ex-erimental ;rou-. 0he control is the reference against which e"perimental groups are compared.

0he control allows the e"perimenter to determine if the changes made to the

e"perimental group actually cause the dependent variable to change.

5. Outline the purpose of a control.

6. Is there a control in this experiment?

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M Measurements

0here are two types of measurement

Qualitative< 0his measurement does not involve numbers. It uses words to

compare eg green! greener more! less slower! faster

Quantitative< 0his measurement involves numbers. 0hey should be

carefully measured. rrors should be recorded and considered in the

Discussion section of the ?aboratory


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1+. Identify 0W+safe woring practices re'uired for this investigation.L

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