Science, about class 8

Dev reads that the stomach has muscle tissue, lining tissue and nerve tissue. They work together to mix and break down food. What is the stomach?

1. AAn organ, because different tissues work together in it.
2. BA tissue, because it is made of cells.
3. CAn organ system, because it does a big job.
4. DAn organism, because it is alive.

Four plants are grown in a hot, dry place with no rain. Which plant loses water most slowly?

1. AA plant with wide, thin leaves
2. BA plant with drip tips on its leaves
3. CA plant with spines instead of wide leaves
4. DA plant with a thin, soft stem

Mei has a headache. Her cousin has tablets that a health worker gave him for his own illness. He says she can have one. What should Mei do?

1. ATake half a tablet, because a smaller dose is safer.
2. BTake one tablet, because medicine helps everyone.
3. CNot take it, and tell an adult who can ask a health worker.
4. DTake it if her cousin says it is safe.

After a baby is born, the umbilical cord is tied and cut. This does not hurt the baby. Why not?

1. AThe baby is still asleep from the birth.
2. BThe mother is given medicine that stops the baby feeling it.
3. CThe cord is hard and dry, like a nail.
4. DThe cord has no nerves, so it cannot feel pain.

Ravi puts 10 g of sugar into 200 mL of water in each of four cups. In which cup does the sugar disappear fastest?

1. AOne sugar lump in warm water, stirred
2. BSugar grains in cold water, not stirred
3. COne sugar lump in cold water, not stirred
4. DSugar grains in warm water, stirred

A chart gives the pH of four liquids. Liquid P is 2. Liquid Q is 7. Liquid R is 9. Liquid S is 13. Which is the strongest alkali?

1. ALiquid R
2. BLiquid S
3. CLiquid P
4. DLiquid Q

A dam holds back a deep lake. The wall of the dam is much thicker at the bottom than at the top. Why?

1. AThe water is deeper at the bottom, so it pushes harder on the wall.
2. BThere is more water at the top, so the push is bigger there.
3. CWater pushes only downwards, so the bottom takes all the push.
4. DThe water at the bottom is colder, so it pushes harder.

On a cold morning a small bird puffs up its feathers. Why does this keep it warmer?

1. APuffed feathers make heat of their own.
2. BPuffed feathers hold more still air, which passes heat on slowly.
3. CPuffed feathers are good conductors, so heat spreads round the body.
4. DPuffed feathers let cold air flow past the skin.

A machine makes a note of 30 000 Hz. Which of these can hear it?

1. AA dog and a bat, but not a person
2. BA person, a dog and a bat
3. COnly a bat
4. DA person and a dog, but not a bat

Ana has an electromagnet with a few turns of wire and 1 cell. She uses the same iron nail, wire and kind of cell. She joins the coil to the cells for only a few seconds. Which change makes it strongest?

1. AWind more turns, and keep one cell
2. BJoin more cells in a line, with the same turns
3. CKeep the coil, and take the iron nail out
4. DWind more turns, and join more cells in a line

Dev's family has a bare field on a slope. Each storm washes soil into the stream. Which plan helps most?

1. APlant grass or trees, so their roots hold the soil
2. BDig the soil over until it is loose and fine
3. CLeave the field bare, so the rain soaks in
4. DSpread sand over the field to make it heavy

At midday a stick 1 m tall casts a shadow 0.6 m long. At the same place and time, how long is the shadow of a pole 3 m tall?

1. A0.2 m
2. B1.8 m
3. C3.6 m
4. D5 m

An older boy at school asks Ravi to send him a picture of his private parts. He tells Ravi to keep it a secret. What should Ravi do?

1. ASend it, because the boy is a friend from school.
2. BSay no, and tell an adult he trusts about it.
3. CSend it, but only if the boy sends one first.
4. DSay no, and keep the secret so the boy is not in trouble.

On a cold night a family wants to warm a small room. They plan to burn charcoal in a pot, with the door and windows shut. Why is this dangerous?

1. ACharcoal gives no heat at all unless fresh air blows on it.
2. BThe fire uses up the carbon dioxide that people need to breathe.
3. CShort of air, it makes carbon monoxide, a poison gas.
4. DThe smoke turns the walls black, and that is hard to clean.

Ana's brother touches a broken heater and cannot let go of it. The heater is still switched on. What should Ana do first?

1. APull him away from the heater by his arm.
2. BThrow water over the heater to stop it.
3. CSwitch off the power if she safely can, and call for help.
4. DWait for him to let go, as the current soon stops.

Mei counts daisies in a meadow with 5 frames. Each frame covers 1 m². She places them at random. The counts are 6, 9, 4, 7 and 4 daisies. The meadow is 10 m by 8 m. About how many daisies are in the meadow?

Ana sits still and counts 17 beats at her wrist in 15 seconds. After skipping for a minute she counts 31 beats in 15 seconds. By how many beats per minute did her pulse rise? Skip only if you are well, and stop if you feel unwell.

Dev uses a plank on a log as a seesaw. The empty plank balances at its middle. A small sack of 30 N sits 40 cm from the pivot on the left. A sack of 24 N sits on the right. How far from the pivot must the 24 N sack sit for the plank to balance?

What is the density of the metal, in g/cm³?

Ravi sees a flash of lightning from indoors. Sound goes about 340 m/s in air. The storm is 2 380 m away. How many seconds pass between the flash and the thunder?

Each year a flood leaves a layer of silt about 5 mm thick on a river plain. A hole shows 42 cm of these layers. There are 10 mm in 1 cm. About how many years of floods made the layers?

A baby in the uterus does not breathe air. Explain how its waste carbon dioxide leaves its body.

A cook makes a sauce that is far too sour from lemon juice. He stirs in a pinch of baking soda. The sauce fizzes and tastes less sour. Explain what the baking soda did, and why he adds only a little at a time.

A pot of lentils needs 2 400 kJ of energy. A clay stove burning wood is about 30% efficient. Dry wood holds about 16 000 kJ in each kg. How many kg of wood does the stove need?

(a)How many seconds does a signal take to go from the Earth to Nila? [2 marks]

(b)Engineers send Nila a command, and Nila replies at once. How many minutes pass before the reply reaches the Earth? [2 marks]

(c)The controller wants to steer Nila with live pictures, like a toy car. Use your answer to part b to explain why she cannot do this. [2 marks]