Class 8 Science worksheets, free, one for each strand

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1. 1) Metal - it conducts heat and electricity well and is malleable. The exception among metals is mercury, which is liquid at room temperature.
2. 2) Non-metal - it is dull and brittle, and breaks into pieces when hammered rather than flattening.
3. 3) Metal - it is sonorous, malleable and a good conductor. It is also the metal most obviously affected by rusting.
4. 4) Non-metal, and the exception to the rule that non-metals are dull - iodine is lustrous.
5. 5) Metal, and the exception to the rule that metals are solid at room temperature.
6. 6) Non-metal, and the exception to the rule that non-metals do not conduct electricity - graphite does, which is why it is used in electrodes.
7. 7) Metal. It is malleable and conducts heat and electricity well.
8. 8) Non-metal. It is brittle, dull and a poor conductor.
9. 9) Metal. It is lustrous, ductile and the best conductor of electricity.
10. 10) Non-metal. It is a gas at room temperature and does not conduct.
11. 11) Metal. It is lustrous when freshly cut and conducts electricity, though it is soft enough to cut with a knife.
12. 12) Non-metal. It is a very hard non-metal and does not conduct electricity, unlike graphite.

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1. 1) Yes. Iron sulphate + copper. Iron is more reactive than copper, so it displaces it. The blue solution turns pale green and a reddish-brown deposit forms on the nail.
2. 2) No reaction. Copper is less reactive than iron, so it cannot displace iron from its salt. The solution stays as it was.
3. 3) Yes. Zinc sulphate + copper. Zinc is more reactive than copper, so the blue colour fades and copper is deposited.
4. 4) Yes. Zinc sulphate + hydrogen. Bubbles of hydrogen gas are given off, and the gas burns with a pop when a lighted splint is brought near.
5. 5) Yes. Copper is more reactive than silver: copper + silver nitrate → copper nitrate + silver.
6. 6) No. Silver is less reactive than copper, so it cannot displace it.
7. 7) Yes. Magnesium is more reactive than zinc: magnesium + zinc sulphate → magnesium sulphate + zinc.
8. 8) Yes. Iron + hydrochloric acid → iron chloride + hydrogen.
9. 9) No. Copper is below hydrogen in the reactivity series, so it does not displace hydrogen from an acid.
10. 10) No. Zinc is less reactive than magnesium, so no reaction takes place.

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1. 1) A fuel, a supply of air to provide oxygen, and heat to reach the ignition temperature. Water works by bringing the temperature below the ignition temperature and by cutting off the air.
2. 2) Oil floats on water, so the burning oil spreads instead of going out. Water conducts electricity, so using it on an electrical fire risks a shock. Carbon dioxide is used instead, because it is heavier than air and smothers the fire without conducting.
3. 3) The outermost blue zone, because combustion there is complete - the fuel meets enough oxygen to burn fully. The inner yellow zone glows brightly but burns only partly, and the dark innermost zone is unburnt vapour.
4. 4) Because it has not reached its ignition temperature. Striking it produces heat by friction, and that heat takes the chemical on the head above its ignition temperature.
5. 5) The amount of heat produced by burning one kilogram of a fuel completely, measured in kilojoules per kilogram. A fuel with a higher calorific value gives more heat for the same mass, which is one of the things that makes a fuel worth using.
6. 6) Because the supply of air is cut off. Combustion needs oxygen, and once the oxygen inside the glass is used up the flame dies.
7. 7) The lowest temperature at which a substance catches fire. Below it, the substance will not burn however long it is heated by a spark.
8. 8) Because carbon dioxide is heavier than air and does not support combustion. It forms a blanket over the fire, cutting off the oxygen supply.
9. 9) Because a flame is produced only by substances that vaporise on heating. Wax vaporises and the vapour burns as a flame, while coal burns as a glowing solid.
10. 10) Because it can set light to clothing or other objects it passes, and a fire in a crowded space traps people. It is a hazard even if it looks small.
11. 11) Because it has a high calorific value, burns cleanly without much smoke or ash, and is easy to store and transport as a liquid under pressure.

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1. 1) The nucleus. It controls the cell's activities and carries the genetic material.
2. 2) The cell wall. It is rigid, gives the plant cell its fixed shape, and lies outside the cell membrane.
3. 3) The cytoplasm. It holds the other cell organelles and is where many cell activities take place.
4. 4) The chloroplast. It contains chlorophyll and is where photosynthesis happens.
5. 5) The vacuole. It stores water and dissolved substances and helps keep the cell firm.
6. 6) The cell membrane. It is selectively permeable, so it lets some substances through and keeps others out.
7. 7) The mitochondria. They release energy during respiration, which is why they are called the powerhouse of the cell.
8. 8) The chromosomes. They carry the genes that pass characteristics from one generation to the next.
9. 9) The nucleolus. It lies inside the nucleus and takes part in making ribosomes.
10. 10) The ribosome. It builds proteins from the instructions the cell gives it.
11. 11) The chromoplasts. They contain coloured pigments other than green.

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1. 1) Lactobacillus - a bacterium.
2. 2) Yeast - a fungus. It carries out fermentation, producing carbon dioxide which makes the dough rise.
3. 3) Rhizobium - a bacterium. It lives in the root nodules of legumes and converts atmospheric nitrogen into a form the plant can use.
4. 4) Plasmodium - a protozoan, carried by the female Anopheles mosquito.
5. 5) A bacterium. Tuberculosis is a communicable bacterial disease.
6. 6) Penicillium - a fungus, from which Alexander Fleming obtained penicillin.
7. 7) A virus. Viruses reproduce only inside a living host cell.
8. 8) A bacterium (Vibrio cholerae). It spreads mainly through contaminated water.
9. 9) A fungus. It grows on the skin and is spread by contact.
10. 10) A virus, carried by the Aedes mosquito, which acts as the carrier rather than the cause.
11. 11) Bacteria and fungi. They multiply on exposed food and break it down.
12. 12) A fungus. It attacks the wheat plant and reduces the crop.

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1. 1) Because microorganisms need moisture to grow. Salt and sugar draw water out of the food and out of the microbes themselves, so they cannot multiply and the food does not spoil.
2. 2) The milk is heated to about 70°C for around fifteen to thirty seconds and then chilled quickly. The heating kills the microorganisms present, and the quick cooling prevents any that survive from multiplying again.
3. 3) Because Rhizobium bacteria in their root nodules fix atmospheric nitrogen into the soil. That restores nitrogen the previous crop removed, so less fertiliser is needed for the next one.
4. 4) Because a plant cell has a rigid cell wall outside its cell membrane, which holds the shape. An animal cell has only the flexible cell membrane, so its shape can change.
5. 5) Because a cold is caused by a virus, and antibiotics act on bacteria rather than viruses. Taking them unnecessarily also helps bacteria become resistant to them, which makes them less useful when they are genuinely needed.
6. 6) Because bacteria multiply much faster in warm conditions. The higher temperature speeds up their growth, so the milk sours sooner.
7. 7) Because a vaccine works by making the body produce antibodies in advance. Those antibodies are then ready if the real disease-causing microbe ever arrives.
8. 8) Because plants and animals cannot use nitrogen gas directly. It has to be converted into compounds such as nitrates before a plant can take it in and make protein.
9. 9) A plant cell has a rigid cell wall, chloroplasts and a large central vacuole; an animal cell has none of these and only a cell membrane around it.
10. 10) Because mould spores are present in the air and need warmth, moisture and food to grow. Damp bread provides all three.
11. 11) Because bacteria and fungi act as decomposers. They break down dead matter and return its nutrients to the soil, where plants can use them again.