Scientific Learning: Grade 8 Science

Leave a slice of bread in a damp, warm corner for a few days and something grows on it: gray-white fluff with tiny black dots. What is it? Where did it come from? Is it alive? You could guess. A scientist doesn’t stop at guessing. She looks closely, tests her guesses, researches what nobody has answered yet, and asks many people when the answer lies with them.

Those four ways of finding out are what this unit is about: observation, testing, research and survey. Before any of them, one more skill: staying safe, because a laboratory has flames, glass and chemicals, and a careless moment can hurt you or spoil your results.

Ways of learning science

Scientists learn about the world by doing things: observing, testing, doing surveys, carrying out project work and building models. Some of this happens inside a laboratory, and much of it outside, in a field, a forest, a river or a village. The facts, theories and rules of science all come out of work like this.

Every one of these activities is done safely and carefully. Safety protects you from accidents. Care protects your results: a test done in a hurry, with dirty test tubes or mixed-up labels, gives an answer that is simply wrong.

1.1 Precautions to be taken while performing experimental work in the science laboratory

A science laboratory (lab) is a special room for scientific study and experiments. It has the equipment and chemicals you need, and in it you study, observe, test and use the facts, objects and substances of science. It also has things that can hurt you: flames, hot glass, sharp tools and harmful chemicals. So every lab has safety rules, and most labs put up a notice with safety signs like the ones in Figure 1.1.

Figure 1.1 Safety signs you may see in a science laboratory. A blue circle tells you what to do; a red circle with a line across it tells you what not to do; a yellow triangle warns of a danger; a green sign shows the way to safety.

Work done carelessly, without these precautions, can cause accidents, and it can also spoil the results of observations, tests and experiments.

The safety rules

Each rule has a reason. Knowing the reason makes the rule easy to remember.

Rule	Why
a.Don’t handle materials carelessly.	Glass breaks, chemicals spill, and a mixed-up bottle can give a wrong result or a dangerous reaction.
b.Wear a mask, gloves and goggles when using harmful chemicals.	One splash of acid or alkali in the eye can blind you; the skin and lungs need protecting too.
c.Put on an apron or a lab coat.	It takes the splash instead of your skin and your school uniform, and comes off quickly.
d.Know where the emergency exit is.	In a fire there is no time to look for it.
e.Wash your hands with soap after the work.	Traces of chemicals and microbes stay on your hands and get into your mouth and eyes.
f.Don’t eat or drink in the lab.	Food can pick up chemicals from the bench or your hands.
g.Never taste chemicals, and don’t sniff them straight from the bottle.	Many lab chemicals are poisonous or burn the nose and throat.
h.No playing or teasing.	A push near a flame, or a bottle of acid, is how most school lab accidents happen.
i.Follow the method given by your teacher.	It has been worked out to be safe and to give a correct result.
j.Take special care with a burner and hot objects.	Hot glass looks exactly like cold glass.
k.Don’t put hot equipment straight on the table.	It can burn the table, crack the glass, or burn the next person who touches it. Put it on a heat-proof mat or a wire gauze.

And when something does go wrong, a spill, a cut or a burn, however small, tell your teacher at once. A small burn is cooled under cool running tap water for about 20 minutes.

This lab bench has seven things wrong with it. Tap each one you find.

0 of 7 found

An open bottle of alcohol next to a lit burner. Alcohol vapor catches fire easily. Keep flammable liquids closed and far from flames.Not found yet.
A bottle with no label. Nobody knows what is in it. Every bottle must be labeled; never use a chemical you can’t name.Not found yet.
A hot beaker standing straight on the wooden bench. It scorches the bench and may crack. Put hot glass on a heat-proof mat, and use tongs.Not found yet.
Food and a cup of tea on the bench. Food picks up chemicals from the bench and your hands. Never eat or drink in the lab.Not found yet.
An open bottle of acid at the very edge of the bench. One knock and it falls and splashes. Close bottles, and keep them well back from the edge.Not found yet.
A spill on the floor. Someone will slip, maybe holding glass. Tell the teacher and have spills cleaned up at once.Not found yet.
A school bag in front of the emergency exit. In a fire, people would trip over it in the rush. Keep bags out of the way and the exit clear.Not found yet.

Your friend has some chemical on her finger and wants to know what it is. What should she do?

Pick an answer to see why.

A reaction gives off harmful fumes. Where should it be done?

Pick an answer to see why.

A fume cupboard in a laboratory, a cabinet with a sliding glass front — **Figure 1.2** A fume cupboard. Its fan pulls air in through the opening at the front and out through a pipe at the top, carrying fumes away from the person working. Photo: Wikimedia Commons, Public domain

An old black-and-white photograph of Robert Bunsen, a seated man with side whiskers, in a dark coat — **Figure 1.3** Robert Bunsen (1811–1899). Photo: Franz Hanfstaengl, Public domain

1.2 Experimental work in science

An experiment is a planned piece of work in which we use science process skills, such as observing, investigating, testing and making models, to check a theory or a principle and draw a conclusion. If an experiment doesn’t give the result we wanted, we don’t give up: we find what went wrong and try another way. Experiments can be done in the lab or outside, and the safety rules apply everywhere.

Observation

A story from science

Mamta’s flower and Mamta’s caterpillar

Mamta was walking in a garden full of colorful flowers. In class she had learned the parts of a flower, so she picked one and took it apart slowly, one whorl at a time: first the green calyx (the sepals), then the colored corolla (the petals), then the androecium (the stamens, which make pollen) and last the gynoecium (the carpel: stigma, style and ovary). Seeing the four parts with her own eyes, she finally understood what had been taught.
On a leaf of the same plant, a caterpillar (jhusilkira) was eating. Mamta remembered that a caterpillar turns into a pupa and then into a butterfly, and decided to see it for herself. She carried the leaf home with the caterpillar on it, put it in a glass jar without closing the lid, and gave it soft leaves every day. After 15 to 16 days the caterpillar stopped eating and became a pupa. 13 to 14 days later, a yellow butterfly with black spots on its wings came out. Mamta told her friends and her science teacher, who explained that careful observations like hers are where science begins.

Observation is the process of experiencing an object, an event or a process very carefully, using our sense organs. We observe by seeing with the eyes, hearing with the ears, smelling with the nose, touching with the skin and tasting with the tongue (but never tasting anything in a lab). Where our senses aren’t enough, we use instruments: a hand lens or a microscope for tiny things, a telescope for distant ones, a thermometer for exact hotness.

Observation isn’t only for the lab. You can observe science at home and around your school, in a zoo, a botanical garden, a medicine factory or a telecom company. A good observation is planned:

Be clear what you will observe: which object, process or event.
Decide why: the purpose of the observation.
Decide how you will record and present what you see (notes, drawings, a table, photos).
Write a report afterwards.

Which of these is an observation?

Pick an answer to see why.

Activity

1.1: the structure of a fungus

Objective: to study the structure of a fungus.

You need: a piece of bread, water, forceps (or tongs), a glass slide, a coverslip, methylene blue (a stain) and a microscope.

Sprinkle some water on a piece of bread and keep it covered in a warm, damp place.
Sprinkle a little water on it every day.
After a few days a fungus (mold) grows on it. (One is a fungus; many are fungi.) Put a drop of methylene blue on a glass slide. With forceps, lift a few of the fungus’s threads into the drop, and lower a coverslip over it.
Look at it under the microscope.
Draw what you see in your practical file, and list the features of the fungus.

What you should see

Fine, branching, colorless threads with round black heads on tall stalks, as in Figure 1.4. The stain colors the threads blue so they are easier to see.

Figure 1.4 Black bread mold (Rhizopus). Its threads, the hyphae, together make the mycelium. Some run over the bread like runners (stolons); at their joints, root-like rhizoids grow into the bread and take in food. Upright stalks (sporangiophores) carry round sporangia, full of spores.

A microscope view of a thin stalk ending in a round dark head, the sporangium of bread mold — **Figure 1.5** A sporangium of bread mold on its stalk, seen through a microscope at 400 times. Photo: Arpitoon, CC0

Writing the report

After an observation, we write a report, so that others know exactly what we did and can check it. Reports can be laid out in different ways. The report of Activity 1.1 could look like this:

In short

Report: Observation of a fungus

Title: Observation of a fungus

Objective: to study the structure of a fungus

Materials used: bread, water, forceps, glass slide, coverslip, methylene blue, microscope

Method: A piece of bread was taken. A little water was sprinkled on it every day, and it was kept covered in a damp place. A fungus appeared on the bread after a few days. Some of its threads were placed in a drop of methylene blue on a glass slide with forceps, covered with a coverslip and observed under a microscope.

Result: These features were seen:

i.No green color (no chlorophyll) was seen in it.
ii.It was made of thin, branching threads (hyphae), together called the mycelium.
iii.Root-like threads (rhizoids) grew down into the bread, and stem-like threads (stolons) ran along it.
iv.Round sporangia were seen at the tips of long upright threads (sporangiophores).

Precautions:

i.Forceps are sharp: use them carefully.
ii.Don’t let the fungus get into your mouth or eyes, and don’t breathe its spores in; wash your hands afterwards.

Figure 1.6 Three single-celled organisms: Amoeba, Euglena and Paramecium (not drawn to the same scale).

Scientific test

Observation alone can’t tell us everything. Looking at a liquid, you can’t tell whether it is an acid. From what we observe, we make a sensible guess, an inference (an assumption): “Lemon juice tastes sour, so it is probably an acid.” In science, such a guess that can be tested is called a hypothesis.

A test is a scientific procedure, done in or out of the lab, to check whether a hypothesis is true. A test is a kind of experiment. Before you start, be clear about:

what you are testing, and what your hypothesis is;
the purpose and the method, with the materials you need;
how you will present the results.

And, as always, write a report afterwards.

Activity

1.3: testing acids, bases and salts

Objective: to find out, with indicators, whether given substances are acids, bases or salts (neutral).

You need: lemon juice, soap water, salt water, red litmus paper, blue litmus paper and test tubes.

Put lemon juice, soap water and salt water in three separate test tubes.
Dip a strip of red litmus and a strip of blue litmus into the lemon juice, and see whether either changes color.
Do the same with the soap water and the salt water.
Record the results in a table in your practical file, and complete the conclusion.

Indicator	Lemon juice	Soap water	Salt water
Red litmus paper
Blue litmus paper

Choose a liquid, dip a red and a blue litmus strip in it, and then decide: acid, base or neutral?

It is:

Press Dip the strips to dip a red and a blue litmus strip into the liquid.

Look at the wet ends of the strips. Is the liquid an acid, a base, or neutral?

Right: blue litmus turned red and red stayed red. Only an acid does that.

Right: red litmus turned blue and blue stayed blue. Only a base does that.

Right: neither strip changed color, so the liquid is neutral.

Not quite. Look again: the blue strip turned red. That means an acid.

Not quite. Look again: the red strip turned blue. That means a base.

Not quite. Neither strip changed, so it is neither an acid nor a base: neutral.

Liquid	Red litmus	Blue litmus	You said
lemon juice	–	–	–
vinegar	–	–	–
soap water	–	–	–
limewater	–	–	–
salt water	–	–	–
sugar water	–	–	–

Here is how the report of Activity 1.3 could be written.

In short

Report: Test of acids, bases and salts

Title: Test of acids, bases and salts

Objective: to sort the given substances into acids, bases and salts with the help of indicators

Materials used: lemon juice, soap water, salt water, red and blue litmus paper, test tubes

Method: The three substances were put in three separate test tubes. Red and blue litmus papers were dipped into each in turn, and any change of color was observed.

Observations:

Indicator	Lemon juice	Soap water	Salt water
Red litmus paper	no change	turns blue	no change
Blue litmus paper	turns red	no change	no change

Conclusion: Lemon juice is an acid, as it turns blue litmus red. Soap water is a base, as it turns red litmus blue. Salt water is neutral (a salt solution), as neither litmus changed color.

A liquid turns red litmus blue and leaves blue litmus blue. What is it?

Pick an answer to see why.

1.3 Research work

Every piece of research begins with a question, or with curiosity. Research is an in-depth study to find the answer to a question that hasn’t been answered well enough yet. Every discovery ever made is the result of research like this.

Research needs patience. You follow a careful procedure, and you often fail. When you do, you find the weakness in your method, improve it, and try again.

Phases of research work

Research usually goes through these steps:

Goal setting: deciding exactly what you want to find out.
Making a hypothesis: a testable guess at the answer.
Choosing the method of collecting data.
Preparing the materials needed.
Collecting data.
Analyzing the data: putting it in tables and graphs and seeing what it shows.
Conclusion: answering the question, and saying whether the hypothesis was right.

How a research question is born

Samprit did exactly what a scientist should: he didn’t believe something just because he was told it. Figure 1.7 shows what Rusa was describing.

Figure 1.7 How fertilizer from fields harms a pond. Rain washes the fertilizer that plants don’t take up into the water; algae feed on it and spread over the surface; when they die, bacteria that rot them use up the oxygen in the water, and fish suffocate.

Activity

1.6: what affects the growth of algae?

Research question: What factors affect the growth of algae?

Objective: to find out the role of chemical fertilizer and of acid in the growth of algae.

You need: pond water with algae in it, three glass bottles of the same size, a little chemical fertilizer, vinegar (an acid), labels.

Bring water containing algae from a nearby pond.
Pour an equal amount into each of the three bottles, so that each is half full.
Add nothing to the first bottle. Add a little chemical fertilizer to the second, and a little vinegar to the third. Label each bottle.
Keep all three side by side in the same place, and observe the growth of algae every five days.
After 15 to 20 days, write a conclusion from the results. Use a table like this:

Date	Growth of algae in bottle 1 (pond water)	Growth of algae in bottle 2 (with fertilizer)	Growth of algae in bottle 3 (with vinegar)

Figure 1.8 The algae experiment after about 15 days. Bottle 1 (pond water only) is lightly green; bottle 2 (with fertilizer) is much greener; in bottle 3 (with vinegar) the algae have died and settled.

The report of the research could be written like this.

In short

Report: Effects of chemical fertilizer and acid on the growth of algae

Research title: Effects of chemical fertilizer and acid on the growth of algae

Objective: to find out the role of chemical fertilizer and acid in the growth of algae

Materials used: pond water containing algae, three glass bottles, chemical fertilizer, vinegar

Method: Water containing algae was brought from a nearby pond. Three bottles were half filled with equal amounts of it. The first was left as it was and labeled “pond water”. A little chemical fertilizer was added to the second, labeled “water with chemical fertilizer”. A little vinegar was added to the third, labeled “water with vinegar”. The bottles were observed every five days.

Observations:

Date	Bottle 1 (pond water)	Bottle 2 (with fertilizer)	Bottle 3 (with vinegar)
At the start	a little algae	about the same as bottle 1	about the same as bottle 1
After 15–20 days	the algae grew a little	the algae grew much faster than in bottle 1	the algae began to die

Conclusion: Chemical fertilizer helps algae grow (a positive role), while acid harms their growth (a negative role).

Bright green algae coating the rocks and coloring the water along a lake shore — **Figure 1.9** An **algal bloom** on Lake Erie, in the USA, fed by fertilizer washed off farms. The same thing happens, on a smaller scale, in ponds and lakes in Nepal that receive farm runoff and sewage. Photo: NOAA Great Lakes Environmental Research Laboratory, CC BY-SA 2.0

Activity

1.7: black or white?

Which absorbs more heat from sunlight, a black surface or a white one? Do a short piece of research and present a report with your conclusion to the class.
A way to do it: take two identical bottles (or tins). Cover one with black paper and the other with white paper. Fill both with the same amount of water from the same jug, measure the starting temperature, and leave them side by side in the sun. Measure the temperature of each every 10 minutes for half an hour.

What you should see

The water in the black bottle warms up faster and ends up hotter. A black surface absorbs most of the light that falls on it and turns it into heat; a white surface reflects most of it. That is why we feel hotter in a black shirt on a sunny day, and why the tubes or panels of the solar water heaters on Nepal’s roofs are black.

In Activity 1.7, which of these must be kept the same for the two bottles?

Pick an answer to see why.

1.4 Survey

Some questions can’t be answered in a lab at all. How do the families in your ward get rid of their rubbish? How many students in your school walk to school? The answers are with people, so you go and ask them.

A survey is the process of collecting data on a topic or a problem directly from the people or places concerned, and drawing a conclusion from it. The ways of collecting the data are the tools of a survey:

a questionnaire: a printed list of questions that people answer;
an interview: asking questions face to face and noting the answers;
a discussion: talking with a group, such as the mothers’ group of a tole;
observation: seeing for yourself, for example counting the bins in a street.

The data are analyzed, a conclusion is drawn, and often a solution to the problem is suggested. A survey usually follows these steps:

Choosing the objective.
Choosing the method (tool) of collecting data.
Collecting the data.
Analyzing the data.
Drawing a conclusion.

After a survey, a report is written: the title, the purpose of the study, the tools used, the analysis of the data, and finally the conclusions and suggestions.

A sample survey report

In short

Report: A study of solid waste management in a village of Kathmandu

Background: The village surveyed is a culturally rich place in the inner city of Kathmandu, with many temples, monasteries and old monuments. People there live by business, office jobs and farming. With modern ways of living, solid waste has become a problem. This survey studied how the people manage the waste that comes out of their houses each day. Its findings may also help manage waste in other places.
Objective: to study solid waste management in the study area.
Method of collecting data: A questionnaire on solid waste management was prepared (Annex 1), and 50 households were surveyed with it.
Analysis of data: 50 percent of the houses put all their waste into the municipality’s vehicle without separating biodegradable and non-biodegradable waste. 30 percent separated the biodegradable waste and made compost from it. The remaining 20 percent made compost from the biodegradable waste and used the non-biodegradable waste to make other things. The results are shown in the bar diagram, Figure 1.10.
Conclusion: Recycling and reusing solid waste has started in the area, but half the houses still don’t separate their waste.

Figure 1.10 The results of the waste survey of 50 houses, as a bar diagram. The height of each bar is the percentage of houses.

Annex 1: Survey questionnaire

What do you do with the solid waste that comes out of your house?
- a.Give it to a waste collection agency.
- b.Manage some of it at home and give the rest to a waste collection agency.
- c.Manage all of it at home.

What do you do with biodegradable waste?
- a.Make compost from it.
- b.Throw it on the road or in the river.
- c.Give it to the waste collectors.

What do you do with non-biodegradable waste?
- a.Use it to make other things.
- b.Collect it and give it to a collection agency.
- c.Burn or bury it.

Four ways of finding out

You want to know whether the farmers of your district use more chemical fertilizer or more organic manure. Which method suits best?

Pick an answer to see why.

Exercise

1. Choose the correct answer

a. What is the process of experiencing an object, event or process carefully through the sense organs?

Pick an answer to see why.

b. Which method is suitable to find out whether the farmers of a region use more chemical or more organic fertilizer?

Pick an answer to see why.

c. Which of these would you stop your friend from doing in the laboratory?

Pick an answer to see why.

d. What should be done when carrying out a chemical reaction that produces fumes?

Pick an answer to see why.

e. Which is the first step of a scientific study?

Pick an answer to see why.

2. Differentiate between

Observation and test

Answer

Observation	Test
Experiencing an object, event or process carefully with the sense organs (and instruments).	A set procedure to check whether a hypothesis is true.
It tells us what something is like or what happens.	It tells us whether our guess about it is right.
It usually comes first, and gives rise to a hypothesis.	It comes after a hypothesis has been made.
e.g. looking at bread mold under a microscope	e.g. dipping litmus paper in lemon juice to see if it is an acid

Research and survey

Answer

Research	Survey
An in-depth study to answer a question or a curiosity.	Collecting data on a topic directly from people or places, and drawing a conclusion.
Starts with a hypothesis, which it tests.	Usually needs no hypothesis; it finds out how things are.
Data often come from experiments, done in or out of the lab.	Data come from questionnaires, interviews, discussions and observation.
e.g. finding the effect of fertilizer on algae	e.g. finding how 50 households manage their waste

3. Give reasons

Precautions should be taken while doing experimental work.

Answer

A laboratory has flames, hot and breakable glass, sharp tools and harmful chemicals. Without precautions these can cause accidents: burns, cuts, poisoning or injured eyes. Precautions also keep the results correct: clean apparatus, the right method and careful handling stop mistakes that would give a wrong answer.

A report is prepared after an experiment or a survey.

Answer

A report records what was done, how, what was found and what it means. It lets other people learn from the work, check it, and repeat it to see if they get the same result; it also keeps a record for the future. Results that are never written down are soon forgotten and can’t be checked.

Observation is the first step in scientific learning.

Answer

Every scientific study starts with noticing something: an event, a change, a pattern. That observation raises a question (“why did that happen?”), and the question leads to a hypothesis, a test and a conclusion. Without an observation, there is nothing to explain and nothing to test.

4. Answer these questions

What is observation?

Answer

Observation is the process of experiencing an object, an event or a process very carefully, using the sense organs (eyes, ears, nose, skin, and, outside the lab, tongue), helped where needed by instruments such as a hand lens, microscope or thermometer.

What is the importance of observation in scientific work?

Answer

It is the first step of a scientific study: it raises the questions that science tries to answer.
It gives the facts (data) on which hypotheses, tests and conclusions are built.
It is how the result of every experiment is seen and recorded.
It lets us learn directly about nature and check what we read, as Mamta did with the flower and the caterpillar.

What is done in scientific work when there is not enough information from observation?

Answer

From the observation, we make a sensible guess, a hypothesis, and then carry out a test (an experiment) to check whether it is true. For example, sourness suggests lemon juice is an acid, but a litmus test is needed to be sure. For bigger questions, a research study or a survey is done.

What precautions should be taken while carrying out a scientific experiment?

Answer

Follow the method given by the teacher, and do experiments only when the teacher is present.
Wear a lab coat; wear goggles, gloves and a mask with harmful chemicals.
Never taste chemicals, and never sniff them directly: waft the air towards your nose.
Take care with burners and hot objects; put hot apparatus on a heat-proof mat, not on the table.
Do experiments that give off fumes in a fume cupboard.
Know where the emergency exit is, and tell the teacher about any accident at once.
Wash your hands with soap after the work.

List the things that should and should not be done while working in the laboratory.

Answer

Do	Don’t
wear a lab coat, and goggles and gloves with harmful chemicals	eat or drink in the lab
follow the given method	taste chemicals or sniff them directly
know where the emergency exit is	play, run or tease
take care with burners and hot objects	put hot apparatus straight on the table
tell the teacher about any accident	handle materials carelessly
wash your hands after the work	leave a burner burning with nobody watching

What should we pay attention to while doing research?

Answer

Begin with a clear question and goal, and make a testable hypothesis.
Choose a suitable method of collecting data, and prepare the materials.
Change only one thing at a time and keep everything else the same, with a control to compare with.
Collect data carefully and honestly, and repeat measurements.
Analyze the data before drawing a conclusion, and accept the result even if it doesn’t match your guess.
Be patient: if it fails, find the weakness, improve it and try again.
Follow the safety rules, and write a report at the end.

In what conditions is a survey conducted?

Answer

A survey is done when the information we need is with people or spread across many places, and can’t be found in a laboratory: for example, how households manage waste, which crops farmers grow, or how families preserve food. It is also used to understand a problem in a community and find a solution to it.

What is meant by survey tools? Give examples.

Answer

Survey tools are the methods used to collect data in a survey. Examples:

Questionnaire: a list of written questions, as in the waste survey of 50 houses.
Interview: asking people questions face to face and recording their answers.
Discussion: talking with a group, such as farmers or a mothers’ group.
Observation: seeing and counting for yourself, such as how many houses have compost pits.

Elina wants to study whether green plants need sunlight. Suggest a clear method for her.

Hint

A plant that gets light makes food (starch) in its leaves. Iodine turns starch blue-black.

Answer

Hypothesis: green plants need sunlight to make food.
Method:

Keep a potted plant in a dark room for two days, so that the starch already in its leaves is used up.
Cover part of one leaf, on both sides, with a strip of black paper held by clips.
Put the plant in bright sunlight for 5–6 hours.
Pick the leaf and remove the paper. With the teacher, dip the leaf in boiling water for a minute, then warm it in alcohol in a water bath (never over a flame) until it turns pale, and rinse it in water.
Spread it on a dish and add a few drops of iodine solution.

Result: the part that got sunlight turns blue-black (starch was made there); the covered part stays brown (no starch).

Conclusion: green plants need sunlight to make their food.

The covered part of the same leaf is the control: everything about it (the plant, the water, the air) is the same, except the light. A simpler version: grow two similar plants with the same soil and water, one in the sun and one in a dark cupboard, and compare them after a week.

The science teacher is absent, and Grade 8 has to do a practical class on plant and animal cells. Prepare a worksheet for it.

Answer

Worksheet: Observing plant and animal cells

Objective: to observe plant cells (onion peel) and animal cells (cheek cells) under a microscope, and compare them.

Materials: an onion, forceps, a clean toothpick, glass slides, coverslips, a dropper, water, iodine solution (or safranin), methylene blue, blotting paper, a microscope.

Method (plant cells):

Peel the thin, transparent skin from the inside of an onion scale with forceps.
Spread it flat in a drop of water on a slide; add a drop of iodine solution.
Lower a coverslip at an angle so no air bubbles are trapped; soak up extra liquid with blotting paper.
Look under the microscope, first at low power, then at high power.

Method (animal cells):

Gently scrape the inside of your own cheek with the flat end of a clean toothpick.
Spread the scraping in a drop of water on a slide, add a drop of methylene blue, and cover with a coverslip.
Look under the microscope.

Observation: draw two cells of each, and label the cell wall, cell membrane, cytoplasm, nucleus and vacuole wherever you see them.

Part	Onion cell	Cheek cell
Cell wall
Shape
Large vacuole
Nucleus

Questions: Which cell has a cell wall? Which has a regular shape? Why do we stain the cells?

Precautions: use only your own toothpick and throw it away after use; handle slides and coverslips carefully (they break); don’t taste or splash the stains; wash your hands at the end.

Worksheet to print (PDF, 4 pages) Answer key for teachers

Practice every question in the book, and keep track of the ones you miss →