photosynthesis — a survival guide · both respiration and photosynthesis are taking place. in...

Photosynthesis —A survival guide

Pupil worksheets

Debbie Eldridge

Activity sheet

101 Pupil worksheets – Where does the wood come from?

Where doesthe woodcome from?

This is an extract from van Helmont’s diary…“I took an earthenware pot in which I put 200 poundsof earth that had dried in a furnace. I moistened it withrain water and implanted in it a trunk of a willow treeweighing 5 pounds. I planted it in the garden andcovered the earth with an iron lid punched with manyholes to allow rain water in. At length, after 5 years,the tree did weigh 169 pounds and 3 ounces. I againdried the earth in the vessel and found it weighedalmost 200 pounds (less about 2 ounces). Therefore164 pounds of wood, bark and roots arose out ofwater only.”

Draw a table showing the mass of the tree andsoil at the beginning and end of his experiment.

1. What was the change inmass of the tree?

2. What was the changein mass of the soil?

3. What did van Helmontconclude from his experiment?

4. Do you agree withhis conclusion?

5. What other explanations couldthere be for the results he found?

?

An experiment carriedout by Jean Baptiste vanHelmont (1580 – 1644)

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A class was askedwhether they agreedwith van Helmont’sconclusion. Here aresome of theirresponses:

I agree with vanHelmont. Onlythe water couldhave made thismuch difference.

Some of the tree mayhave grown fromminerals in the soil.

But I think thatplants make theirfood from sunlight…

van Helmont may nothave known aboutthe gases in the air.

Card 1A

Think about water.

• Is water a food source?• Would you survive on water alone?• Do we know how much water wasadded to the pot over the fiveyears?

• What should van Helmont havedone if he had wanted to provethat all this increase in mass wasfrom water?

• What measurements could hehave taken?

• Do you think van Helmont wascorrect to say that water aloneaccounted for the growth of thewillow tree? Try to summarise yourthoughts using some of the pointsabove to support your argument.

“Only the watercould have made thismuch difference...”

Card 1B

What is sunlight?

• Does sunlight have mass?• Living things are made of atoms.Are there any atoms in sunlight?

• Could sunlight contribute to theincrease in mass of the plant?

• Is sunlight needed for plantsto grow? What role do you think itmight have?

• Do you think it is correct to saythat plants make their food fromsunlight? Try to summarise yourthoughts using some of the pointsabove to support your argument.

But I think thatplants make theirfood from sunlight…

In groups, choose one of the cardsbelow and consider the questions andinformation on the card. After you havediscussed the questions and informationtry to come up with a summary of yourgroups’ thoughts.

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205 Pupil worksheets – The story of photosynthesis

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The storyof photosynthesis

Take a look at how plantsmake their food.

We know that the food plants madefrom photosynthesis are calledCARBOHYDRATES.

If we look at the word‘CARBOHYDRATE’we can tell quite a lot about it...

Carbohydrates contain the atomsCARBON, HYDROGEN andOXYGEN.

This carbohydrate (Fig 3) is calledglucose – it is a sugary substanceand you are probably very familiarwith its taste if you have eaten ordrunk any of the products opposite.

1. So, which part of the word carbohydrate means that itcontains carbon?

2. And which part of the word means that it containshydrogen?

3. Now, can you suggest what the letters ATE mean whenplaced on the end of a chemical name?

4. Figure 3 above is a chemical picture of one carbohydrate.Count how many carbon, hydrogen and oxygen atoms thismolecule has…

Card 1C

How much did the mass ofthe soil decrease over thefive years?

• Could this have contributed tothe growth of the plant? Howmuch?

• Can plants grow without soil?Look at the results of theinvestigation below on mungbeans: Mung bean seeds weregerminated and grown in twosolutions – one containing all theminerals found in soil, one withjust water (no minerals).The plants were grown forthe same time and in thesame conditions.

• Can plants grow withoutminerals?

• Do minerals have an effect?

• Do you think it is correct to saythat some of the tree came fromminerals in the soil? How muchcould the minerals havecontributed to growth?

Card 1D

What gases are in the air?

• Do the gases in the air havemass? (If you compare an emptyballoon and one filled with air youwill soon find out.)

• How could you show that thesegases have an effect onincreasing the mass of a plant?

• Look at the results of anexperiment that examined thegrowth of plants at three differentconcentrations of carbon dioxide.What does it tell you? Can gasesin the air affect growth? Whichgas is shown to have an effect inthese experiments?

van Helmont may nothave known aboutthe gases in the air

Total

Shoots

Roots

?

Some of the tree mayhave grown fromminerals in the soil

H

O

H

HH

HO

H

O

C

O

H

OC

C

C

H

O

CC

HH

H

H

Fig 1–All minerals

Fig 2–Water only

Dryweightp

erplant(g)

Average CO2concentration in parts per million (ppm)

0.06

0

0.12

0.18

0.24

1200 1600400 800

Fig 3–Carbohydrate molecular structure

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307 Pupil worksheets – Talk about...

Talkabout...

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206 Pupil worksheets – The story of photosynthesis

What atoms would still be missing?

If we had some water as well as thecarbon dioxide, what extra atomcould this supply?

Now, if you were a plantand you had to make thiscarbohydrate, what atoms areyou going to need and wherecould you get them from?

If we had some carbon dioxide(Fig 4), could we make carbohydratesfrom it?

OK – suppose we have thecarbon dioxide and some water(H2O) (Fig 5) – we would needto split the water up to releasethe hydrogen from it.

The process of splitting water intohydrogen and oxygen is verydifficult. However – with the help ofsunlight energy plants can split thewater and use the hydrogen tocombine with the carbon andoxygen from carbon dioxide.

When light energy is used tosplit water, there is a productleft over that is not needed.What is this product?

You may have come across thisidea before – it seems thatphotosynthesis not only results inthe production of carbohydratessuch as glucose, but also releasesoxygen into the air – which is agood thing as we will see later

We know that plants use sunlightenergy to split water (H2O) intohydrogen and oxygen.The hydrogen is added to thecarbon dioxide to makeCARBOHYDRATES.

The oxygen produced from thissplitting of water is released intoour atmosphere.

We summarise this using achemical equation:

6CO2 + 6H2O � C6H12O6 + O2carbon dioxide water carbohydrate oxygen

O

O

C

H O

H

H O

H

1. What do these products have in common?2. Are there any similarities and differencesbetween them?

?

Fig 4–Carbon dioxide (CO2) Fig 6–Water (H2O) & Sunlight

Fig 5–Water (H2O)

Activity sheet

409 Pupil worksheets – What sort of carbohydrates do plants make?

PlantPart of plantbeing tested

Iodinesolution

Schulze’sreagent

Activity sheet

408 Pupil worksheets – What sort of carbohydrates do plants make?

What sort of carbohydratesdo plants make?

If we want to find evidence ofglucose, starch and cellulose inplants, we can test for thesedifferent carbohydrates with iodinesolution (for starch), Benedict’sreagent (for sugars) and Schulze’sreagent (for cellulose).

Materials:Each group will need:• One white tile• A knife/scalpel• A pestle and mortar• One boiling tube• One small bottle of iodine solution• One small bottle of Benedict’sreagent

• Three samples of each plant e.g.onion, apple, grape, celery, potato

Materials to be shared:Access to a water bath set at 90oC

��HAZARDS: Take care with knives.Only the teacher should handleSchulze’s reagent.

To test for glucose you add Benedicts’ reagentand place in a water bath at 90oC for 5minutes. If glucose is present the colourchanges from blue to orange (sometimes ittakes a while and the colour looks a greenyellow as it is changing).To test for starch you add iodine solution.If starch is present the reddish brown iodinesolution changes to a blue black colour.To test for cellulose you add Schulze’sreagent. If cellulose is present it will turn apurple colour.

1. What did your results show?2. Remind yourself – where do the atomsthat make up these carbohydrates comefrom?

ExtensionTake small pieces of cotton wool/paper towelor packaging from an egg box. Place on awhite tile. Try adding iodine solution andShulze’s reagent to each. Where do theproducts come from? Can you explain yourobservations by thinking about how theseproducts are made.

Benedict’sreagent

Observations when Indicator added

Results table

Method:1. Collect three samples of each plant you

want to test. For each sample you collectthink about what part of the plant this hascome from. Onions for example are anunderground storage organ; apples are thefruit and celery is a leaf stalk. Fill in the firstcolumn of your results table to describewhich part of the plant you are testing.

2. Place two samples of each plant on awhite tile or other non absorbent surface.You may want to break the structure up alittle with a knife or scalpel.

3. Place the third in a pestle and mortar andgrind it up with a little water. Then place itinto a boiling tube and cover it withBenedict’s solution. Place this tube in awater bath set at 90oC and leave it for5 minutes while you carry out theother tests.

4. Go back to your first two samples on thewhite tile. Place a few drops of iodinesolution on one of the samples and askyour teacher to place a few drops ofSchulze’s reagent on the other. Leave fora few minutes so the indicator has timeto soak into the plant material.

5. Record your observations in theresults table.

?

Glucose and other sugars suchas sucrose and fructose aresoluble so need to be linkedtogether in long chains to makesubstances like starch andcellulose. Starch is useful forstoring sugar. Cellulose is usedto build plant cell walls.

Activity sheet

5a

11 Pupil worksheets – How can we show that plants use carbon dioxide?

You may wish to complete this table..

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510 Pupil worksheets – How can we show that plants use carbon dioxide?

How can we show thatplants use carbon dioxide?

We know that carbon dioxide is in the air but as it is aninvisible gas we need to use particular methods to detect it.Changes in carbon dioxide concentration can be detectedusing an indicator called hydrogencarbonate indicator.

Atmospheric air contains 0.04% carbon dioxide. When atmosphericair is bubbled through the indicator it is an orange red colour.However, if a plant is using carbon dioxide in photosynthesis it willremove carbon dioxide from the indicator and the indicator turns firsta deeper red and then more purple.

Materials:Each group will need:• Four transparent containers with lids• Three equal length sprigs of Cabomba or other pondweed• Hydrogencarbonate indicator sufficient to fill four containers• One lamp• One flat sided glass tank to act as a heat screen• A small piece of neutral density shading or a square of muslin –enough to surround one of the containers.

Method• Take four transparent containers that can be sealed easily.• Rinse the containers with a small amount of indicator.• Add a standard volume of indicator to each container and in threeof the containers, place equal length sprigs of pondweed e.g.Cabomba.

• Seal all the containers.• Take one containing pondweed and place it in a dark cupboard.• Take a second one containing pondweed and cover it withshading.This can be done using layers of muslin or if you want to knowexactly how much light you are cutting out you can use a neutraldensity filter.

• The remaining two containers (one with and one withoutpondweed), should be left uncovered.

• The containers (apart from the one in the dark) should then beplaced the same distance from a bright white light source.The experiment should be left until there is a noticeable changein colour (this maybe as little as one hour or as long as overnightdepending on the light intensity and how much pondweed thereis). Make sure the lamp will not cause overheating of your water.If the light is very powerful you could place a transparent screenbetween the light and the plant, or a flat sided container of coldwater to absorb the heat but not the light.

• When there is a noticeable change in colour in the indicator,remove the shading and compare the colours in the four containersto those in the picture above.

Results:(Either refer to your own results or look at the specimen results onthe PowerPoint.)

OR you might prefer to answer these questions:

1. Describe your observations.2. Link these observations with what you know about photosynthesis.3. Do they confirm what you set out to show in this experiment?4. What happened to the indicator when the pondweed was placed inthe dark?

5. What do you deduce from this?6. Can you think of any improvements to the method which you wouldcarry out if you had the time to repeat this experiment?

7. What colour would the indicator go if the plant is respiring andcarrying out photosynthesis at the same rate? Why?

8. Select the two times of the day that this is most likely to happen?NIGHT, DAWN, MID MORNING, LUNCHTIME, AFTERNOON, DUSK

Container

1

2

3

4

Cabombapresent

Yes

Yes

Yes

No

Colour ofindicator

Has thecarbondioxide in theindicatorincreased ordecreased? What does this tell you?

% offulllight

100%

0%

100%

Here is a reminder ofsome information youmight find useful...

Green plants and algaeuse up carbon dioxide– removing it from theindicator as they carryout photosynthesis.BUT…

They also producecarbon dioxide as theyrespire – and all livingthings respire ALL THETIME.

?

Results table

� Increasing CO2 in indicator Decreasing CO2 in indicator�Atmospheric level of CO2

Activity sheet

5b

13 Pupil worksheets – Matching cards excersise

Activity sheet

5b


Matchingcards excersise

Select the correct colour that theindicator will go in each container

Select thecorrectexplanationfor each ofthe colourchanges

Contents of container

Hydrogencarbonate indicatorand pondweed, placed 20 cmaway from a lamp.

Hydrogencarbonate indicatorand pondweed, surrounded bya thin layer of shading, placed20 cm away from a lamp.

Hydrogencarbonate indicatorand pondweed surrounded by athicker layer of shading, placed20 cm away from a lamp.

Hydrogencarbonate indicatorand pondweed placed in acupboard.

Colour ofindicator

Both respiration and photosynthesis are takingplace. In this case, the pondweed is using up morecarbon dioxide in photosynthesis than it isproducing in respiration.

Both respiration and photosynthesis are takingplace. In this case, the pondweed is using up thesame amount of carbon dioxide in photosynthesisas it is producing in respiration.

Both respiration and photosynthesis are takingplace. In this case, the pondweed is using up lesscarbon dioxide in photosynthesis than it isproducing in respiration.

Respiration is taking place in the pondweed. It isn’tusing up any carbon dioxide in photosynthesis; it isonly producing it in respiration.

Explanation






Colour ofindicator

Purple

Red

Orange

Yellow

Explanation

Results table

Results table

Explanations• Both respiration and photosynthesis aretaking place. In this case, the pondweedis using up less carbon dioxide inphotosynthesis than it is producingin respiration.

• Both respiration and photosynthesis aretaking place. In this case, the pondweedis using up the same amount of carbondioxide in photosynthesis as it is producingin respiration.

• Respiration is taking place in the pondweed.It isn’t using up any carbon dioxide inphotosynthesis; it is only producing itin respiration.

• Both respiration and photosynthesis aretaking place. In this case, the pondweedis using up more carbon dioxide inphotosynthesis than it is producingin respiration.



Activity sheet

5c

Hydrogencarbonate indicatorsolution changes colour whenthe amount of carbon dioxidedissolved in it changes.The table opposite showsdetails of these colour changes.

The tubes were left in bright sunlight for two hours

1. What would be the colour of the indicatorsolution in tube A?

2. Name the process taking place in the cellsof plant which causes this colour change.

3. The colour of the indicator in tube B did notchange. Explain why.

4. Tube C is wrapped to keep the light out.The indicator changed to yellow.Explain why.

5. Why was it necessary to include tube D inthe experiment?

6. Colour is a qualitative change and cannoteasily be measured. Can you design anexperiment using this indicator to work outhow fast different plants photosynthesise?

Colour ofindicatorsolution

Red

Yellow

Purple

Amount of carbon dioxidedissolved in indicator

Same amount of carbondioxide as in the air

More carbon dioxide than inthe air

Less carbon dioxide than inthe air

A

Pondweed Small snails &pondweed

Pondweed Indicator only

B C D

Activity sheet

5b


Use arrows to join up the correct colourthat the indicator will go with the correctexplanation to each of the contents






Colour ofindicator

Red Respiration is taking place in the pondweed. It isn’tusing up any carbon dioxide in photosynthesis; it isonly producing it in respiration.

Both respiration and photosynthesis are taking place.In this case, the pondweed is using up more carbondioxide in photosynthesis than it is producing inrespiration.

Both respiration and photosynthesis are taking place.In this case, the pondweed is using up less carbondioxide in photosynthesis than it is producing inrespiration.

Both respiration and photosynthesis are taking place.In this case, the pondweed is using up the same amountof carbon dioxide in photosynthesis as it is producing inrespiration.

Orange

Yellow

Purple

Explanation

?

Results table


Evening

Late morning

17 Pupil worksheets – Investigating photosynthesis in a broad bean plant

Activity sheet

7Investigatingphotosynthesis ina broad bean plant

A broad bean plant was placedin a tall chamber with a datalogging probe (Fig 7) to detect theconcentration of carbon dioxide(parts per million).

The aim of the experiment wasto record the changes in carbondioxide over a prolonged periodwhen the plant was exposed to arange of light treatments. We couldthen relate this to changes in thephotosynthetic rate of the plant.

Examine the graph above showingthe changes in carbon dioxide levelsopposite. Study it carefully to try tounderstand what is happening.Use the questions after the graphs tohelp you analyse the graphs in detail.

For the first 1000 seconds of theexperiment the carbon dioxide probewas left in atmospheric air.1. Describe the general trend in

concentration of carbon dioxideduring this period.

The probe was then placed insidethe transparent sealed containerwithout any plant inside. (A)2. How can you tell that the probe

was now in a sealed container?Are the values more or lessconsistent than when it was leftin the atmosphere?

The broad bean plant was thenplaced in the container but at thisstage there were no external lightson and the area was quite shaded.3. What happens to the level of

carbon dioxide?4. What does this tell you about the

ability of the broad bean tophotosynthesise at low lightintensities?

At 2400 seconds a bright light wasswitched on. (B)5. What begins to happen almost

immediately?6. What process is causing this

change?

At 3000 seconds the plant inthe container was completelysurrounded with black paperand the light switched off. (C)At 4000 seconds the blackpaper was removed but nolights switched on in the lab. (D)7. Is there any difference between

the slope of the graph over twotime periods?

8. How could you get the carbondioxide levels to remain relativelystable within the container?

9. The soil in the pot containingthe bean plant was surroundedby a plastic bag. If therewere organisms in the soil;how might this have affectedthe results?

10. If you were repeating thisexperiment can you think of waysyou could alter the design of theexperiment to provide better datathan is shown here?

If you have access to a data loggerand probe for carbon dioxide youmay wish to set up this experimentyourselves. If you do, remember thelight intensity in a lab is only a smallfraction of natural light and you willneed a bright light source to see theresults of photosynthesis.

Time interval (seconds)

Broad bean placed in sealed container

Light turned on

Light turned off, black paper added

Black paper removed

End of experiment

0

0

400

600

500

300

200

100

800

700

2000 30001000 4000 5000 6000 7000

Carbo

ndioxidelevels(ppm

)

16 Pupil worksheets – Gas exchange at different times of the day

Activity sheet

6Gas exchange atdifferent timesof the day

1. Can you draw a set of picturesto show what type of gasses aplant takes in and gives out,and how much, duringdifferent times of the day?One of the pictures has beendone for you.

Dawn

Midnight

?

Afternoon

A

A

B

B

C

C

D

D

E

E

Fig 7–Broad bean plant and logging probe

carbon dioxide oxygen

19 Pupil worksheets – Measuring photosynthesis by oxygen evolution

Place your Cabomba in front of a bright lightsource and let the plant equilibrate for fiveminutes. (You may want to place a flat sidedcontainer of water between the measuringcylinder and the lamp to prevent the water in themeasuring cylinder heating up.) Count thebubbles produced in 30 seconds. Repeat thereading twice more and record your results in atable. Move the measuring cylinder so that it isdifferent distances from the light source and letequilibrate again. Repeat the experiment until youhave enough results to show a pattern. (Fig 11 & 12)

Activity sheet

8Cut the stem of the Cabombasprig at an angle under thesurface of the liquid. This cutend must remain in the liquidor an air lock may form.You should be able to observebubbles of gas rising fromthe cut. (Fig 10)


Where does thewood come from?

Activity sheet

8Measuring photosynthesisby oxygen evolution

In this experiment you are going to use theaquatic plant Cabomba to observe bubbles ofoxygen which are released as the plant carriesout photosynthesis. These bubbles can becounted and the rate of bubbling can give youan indication of the rate of photosynthesis.If we alter the light intensity, does the rate ofbubbling vary?

Setting up the CabombaYou will need:• 250 cm3 measuring cylinder or a measuring cylinderthat is just longer than your Cabomba sprig

• Cabomba sprig• 400 cm3 1% solution of sodium hydrogencarbonate.

Fill the measuring cylinder with a 1% sodiumhydrogen carbonate solution. (Fig 9)

Cup your hand around the Cabomba sprig andgently flatten the fronds against the central stemCarefully lower the flattened Cabomba intomeasuring cylinder, tip of sprig lowermost, andhold the end of the stem against the glass withyour finger. (Fig 8)

Fig 8

Fig 9 Fig 11

Fig 10

Fig 12

21 Pupil worksheets – Early earth

Activity sheet

9Earlyearth

Oxygen first appeared on the surface of the Earthwhen the first photosynthetic cyanobacteria (blue/greenalgae) developed the ability to split water moleculesusing the sun’s energy. The oxygen did not build up inthe atmosphere for a long time, since it was absorbedby rocks such as iron that could be easily oxidized(rusted). To this day, most of the oxygen produced overtime is locked up in the ancient rock formations found inancient sedimentary rock.

It was not until ~1 billion years ago that the reservoirsof rock became oxidized and the free oxygen stayed inthe air.

When free oxygen began to build up in the atmosphere,it formed two gases new to Earth. One was molecularoxygen (O2), and oxygen opened a door to the evolutionof whole new life forms. The other was ozone (O3), a gasthat forms high in Earth’s atmosphere and acts as a sortof global sunscreen. This protects the Earth’s surfacefrom the most harmful UV radiation. One of the amazingthings about life on Earth is that, by producing oxygen,the earliest organisms created conditions that enabledsubsequent, more complex forms of life to thrive.

But how did plants make the transition to land?To invade the land plants had to prevent drying outand develop ways to reproduce. In water they wereable to just dump their gametes (reproductive cells),into the water. On land, that doesn’t work.

Lichens are believed to have been amongst the firstphotosynthetic organisms to exist on land. A lichenis not a single organism but a combination of twoorganisms that live together intimately. A fungus canteam up with photosynthetic organisms likecyanobacteria or green algae to form lichens.These organisms can live without rain for months,providing protection for photosynthetic organisms,which produce oxygen and release it into theatmosphere.

The first independent land plants were the mossesand liverworts that grow close to the ground, absorbingwater and nutrients directly through their cells. Forthese plants to reproduce on land they needed to bein a wet environment where they could rely on a filmof water through which their gametes could swim.

Millions of years later plants have evolved the ability to liveand reproduce on land. These seed plants ‘package’ themale gamete in a pollen grain – an ingenious solution thatfrees themselves from the need for water to get thereproductive cells together.

* 1st paragraph adapted from “How the Scum of the Earth led to Advanced life”by Robert Roy Britt

(Fig 13 & 14 © John Bebbington FRPS)


Activity sheet

8

Extension:Light intensity decreases withdistance from a light source, butthe relationship is not linear.The light intensity decreases quiterapidly as distance is increased.The relationship is:

Light intensity is proportional to1d2

where d = distance

This means that at 5 cm from thelight source the intensity is 1/25 ofthe intensity at 1 cm and the lightintensity at 10 cm is 1/100 of theintensity at 1 cm. If you plot numberof bubbles against the light intensity,you may get a more meaningfulrelationship.

1. What are the input, outcome and controlledvariables in this experiment?

2. Describe the pattern shown by your graph(s).3. What is the relationship between the variables?4. Can you explain the pattern shown by the graphusing your understanding of photosynthesis?

5. Is the pattern shown in your graph what youexpected or were some of your resultsunexpected?

6. If you had any unexpected results, were they justa ‘one-off’ (a random error) or did all of therepeats give the same result? (This gives you anindication of how reliable your results were).

7. Were there any ways you could have improvedthis experiment? Were they all the same sizebubbles? Could you think of a way of measuringthe volume of gas given off?

8. Predict what would happen to the numberof bubbles if you increased the power ofthe light bulb.

Distance fromlight source (cm) Test 2 Test 3

Mean number ofbubblesTest 1

Number of bubblesreleased in 30 seconds

Results table

Plot a graph to show how thenumber of bubbles is affectedas distance from the lightsource is changed.

?

Fig 13–Grasses Fig 14–Moss(Rhizocarpon geographicum)

Fig 15–Liverworts

Fig 16–Red banded rock

Look at any stagnant pond and you’ll be able toimagine early Earth. Green scum. Most scientistsbelieve it’s the way things were back before theplanet had enough oxygen to allow more complexlife forms to evolve. For the first billion and ahalf years (4.0 – 2.5 billion years ago. 1 billion =1000 million), Earth’s atmosphere contained nofree oxygen, and therefore earth's oceanscontained no dissolved oxygen. Your scummyancestors had the planet to themselves up toabout 2.2 billion years ago. These single-celledorganisms were the only things that couldsurvive without access to oxygen. But thenthings changed...

Activity sheet

1023 Pupil worksheets – What are chloroplasts?

What arechloroplasts?

Information:Chloroplasts are small green‘bodies’ in some plant cellswhich enable the plant to‘capture’ sunlight energy.

The chloroplast is filled with a greenpigment called chlorophyll. If youimagine an oblong shaped boiledsweet with a filling…the sweet islike the chloroplast and the filling isthe chloro“phyll”

Looking at chloroplasts:• Select a plant which has a verythin leaf such as Elodea or simplemoss leaves.

• Place a single leaf on amicroscope slide, add a drop ofwater and a cover slip.

• Look at the leaf down amicroscope and see if you canidentify the small greenchloroplasts.

• If you have difficulty seeing thechloroplasts, look at the cells atthe edge where the leaf is verythin.

If you look very carefully you maybe able to see the chloroplastsmoving around within the cell.Your teacher may show you a videoclip of this effect.

22 Pupil worksheets – Early earth

Activity sheet

9Look at the graphbelow which shows thechanges in the earth’satmosphere since itformed over 4.5 billionyears ago

1. There was no ozone when life first appeared. Why was the formation of ozone not possible at this stage?2. Life is thought to have evolved underwater. Why do you think the conditions were better there?3. Primitive life started producing oxygen 3 billion years ago and yet the graph shows that oxygen levels startedto increase significantly less than 1 billion years ago. What does the text suggest is the explanation for this?

4. What was the major adaptation that plants had to achieve in order to be able to live on land?5. The graph shows that about 0.3 billion years ago the oxygen level may have risen as high as about 27% andthen it dropped back to its present 20% What would you think the plant life would have been like at this time?

6. Apparently forest fires were common about 0.3 billion years ago and charcoal remains are evidence of this.What would this have done to the oxygen and carbon dioxide levels?

4

5

10

15

20

25

30

Billions of yearsbefore present

Stacks of chlorophyll pigmentStarch grains

Oxygenlevel/percent

3 2 1 Present

1 billion = 1000 million

Earth Formed

Oldest surviving rock

First linving things (bacteria)

First red rocks containing Fe3+

Limestone becomes morecommon after this time

?

Limestone becomesvery common after this time

First land plants

Fig 17–Chloroplasts clustered around the edges ofthe leaf cells

Fig 18–Chloroplasts in the guard cells from thelower leaf surface

25 Pupil worksheets – Can we show that only the green parts of the leaf do not produce starch in photosynthesis?


24 Pupil worksheets – What are chloroplasts?

Activity sheet

11Can we show that only the greenparts of the leaf produce starchin photosynthesis?

We know that the plant converts thesimple sugars made in photosynthesisinto starch for storage. Why don’t welook to see if there is any starch in thenon-green areas of the leaf?

Try this practicalactivity:

Materials:Each group will need:• Beakers 1 x 250 cm3

and 1 x 100cm3

• Bunsen burner• Tripod• Gauze• Boiling tube plus holder• Forceps• Ethanol (~25cm3 )*• White tile• Iodine solution indropping bottle

• A leaf from a variegatedplant which has beenilluminated for 24 hours

* To be given out byteacher

�Hazard:Ethanol is highlyflammable and must notbe placed near a flame.When the leaf has been inboiling water for a minute,it is essential that theBunsen burner is switchedoff before you collect theethanol.

Activity sheet

10

Chloroplasts absorb light energy and enable the plantto use this to build carbohydrates such as starch.In many high power images of chloroplasts we cansee the starch grains (see diagram and previous page).

The plant is able to export these carbohydrates toother parts of the plant where starch grains build up.For example a potato tuber stores starch grains – soalthough it has no chloroplasts to make carbohydrates– they are packaged up and stored there.

Looking at the starch grains storedin a potato tuber:• Take a small section of potato tissue and cut avery thin slice onto a white tile.

• Take approximately 1cm2 of thinnest tissue andplace it on a microscope slide.

• Add one or two drops of iodine solution.• Place a cover slip over the potato tissue.• Examine it under the microscope.

You may see that some of the starch grains are verylarge and some quite small. The starch grains in thechloroplasts in the figure on the previous page arevery small but remember the potato tuber is the mainstorage organ so we might expect large grains to buildup here.

Variegated plants such as these only have chloroplastsin some of the leaf cells.

1. Which cells of the leafwould you expect toshow evidence ofstarch grains if youleft this plant in thelight for a few hours?

2. How would youexpect the growthrate of a plant withvariegated leaves tocompare to a normaltotally green plant?Can you explain whyyou think this?

?

Fig 19–Potato slice

Fig 20–Starch grains X700 magnification

© John Bebbington FRPS

Activity sheet

0Where does thewood come from?

26 Pupil worksheets – Can we show that only the green parts of the leaf do not produce starch in photosynthesis?

Activity sheet

12a

Bringingit alltogether

In each of the bubbles pupils putdetails of a practical or activity thatthey have completed which illustrates/demonstrates this part of the reaction.

Activity sheet

11

Method1. Take a variegated plant which has been under bright

light for 24 hours and remove one of the leaves.2. Make a sketch of the leaf showing approximately

where the green and non green areas are.3. Half fill a 250 cm3 beaker with water and bring it to

the boil using a Bunsen burner, tripod and gauze.4. Place the leaf in the boiling water for one minute to

get rid of the waxy coating on the leaf.5. Turn off the Bunsen burner (see hazard above).6. Collect a boiling tube and place the leaf from the

boiling water into the tube using forceps.7. Your teacher will pour ethanol into the tube until

about one third full.8. Place the boiling tube with ethanol and the leaf

inside the beaker of hot water and leave for 5 –10minutes. The ethanol will remove the colour from theleaf because the chlorophyll is soluble in the ethanol.When we remove the leaf it should have lost thegreen colour and you will see the ethanol hasturned green.

9. Pour off the ethanol into a clean beaker and placethe leaf back in the hot water to rinse off the ethanoland soften the leaf.

10. Lay the leaf out on a white tile and “flood” the leafwith iodine solution.

11. Pour off the excess iodine solution and examine theleaf carefully to see where the starch is. Record yourobservations by sketching the leaf again after staining.

1. Why is the leaf placed in boiling water?2. Why is the leaf placed in ethanol?3. Why is the leaf placed back in the water after ithas been in ethanol?

4. Why is iodine solution added to the leaf?

Conclusion:Look at the two sketches you have made ofthe variegated leaf.Where is there evidence of starch?Where is there no starch?What does this suggest?

Extension:In the past some scientists have been able to create‘pictures’ in a leaf, The pictures are formed in starch byilluminating a leaf through a negative placed in a slideprojector (This picture is a print on which a questionwas superimposed)

Can you explain why we see this image?

CO2 + H2O O2 + GlucoseLight

Chlorophyll

?

27 Pupil worksheets – Bringing it all together

28 Pupil worksheets – Words for concept mapping


Activity sheet

12b

Words forconceptmapping

Chlorophyll

Carbohydrate

Glucose

Respiration

Starch grains

Carbon dioxide

Photosynthesis

Iodine solution

Light energy

Water

StarchStarch

Sugar Oxygen

Chloroplast

Cellulose

photosynthesis — a survival guide · both respiration and photosynthesis are taking place. in...

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