Exam practice

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	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

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 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.

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.

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.

• 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.

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.

• 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.

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

• 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.

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.

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.

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

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

1. Keep a potted plant in a dark room for two days, so that the starch already in its leaves is used up.
2. Cover part of one leaf, on both sides, with a strip of black paper held by clips.
3. Put the plant in bright sunlight for 5–6 hours.
4. 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.
5. 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.

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):

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

Method (animal cells):

1. Gently scrape the inside of your own cheek with the flat end of a clean toothpick.
2. Spread the scraping in a drop of water on a slide, add a drop of methylene blue, and cover with a coverslip.
3. 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.