Cells and Organisms
The soil in a tropical rain forest is always warm and wet. The soil in a woodland in northern Europe is often cold and sometimes dry.
In which of these places would you expect dead leaves from the trees to decay more quickly?
Why?
Leaves decay faster in a tropical rain forest, because micro-organisms grow faster when it is warm and wet.
Why does oiling the axles of a bicycle make the bicycle move easily?
Dry ice 'disappears' when placed in the open. Which change of state is being exhibited here?
Sublimation
Which property of metals is used in foils?
Malleability
After bread dough has been kneaded, it is left in a warm place for a while, to allow the dough to rise.
Why does it take time for the dough to rise?
The yeast steadily produces carbon dioxide as it respires. Time is needed to allow it to produce enough carbon dioxide to make the dough rise.
Why does the wax not freeze at the top of a candle?
The heat on top of the candle makes it melt.
Harry was attending an interview on aviation. When asked about the material used to make air crafts, he answered Sodium. He was asked to leave immediately.
Why?
Sodium burns on exposure to air! Aluminium is used to construct the bodies of air crafts as it is strong yet light.
Why can't antibiotics cure a cold?
Colds are caused by a virus. Antibiotics only kill bacteria. They do not kill viruses.
True or False -
Astronauts are weightless in space.
False. They have mass and minimal gravitational force acting on them due to which they have weight.
Balloons can be twisted into shapes.
Why?
Potassium is stored in kerosene. Why?
If an amoeba had a cell like a plant cell, it would not be able to move or feed in the way it does.
Explain why.
Plant cells have cell walls, which are stiff. The cell would not be able to move easily, and it would not be able to flow around smaller organisms.
A 100 kg block of wood is traveling with a constant velocity on ice. What is its normal force?
1000 N.
Force = Mass * Gravitational Force
True or False -
Mothballs sublime.
True.
Mercury is a metal. What's unusual about it?
It is liquid at room temperature; all other metals are solids at room temperature
The pH of milk is often about 6.7 while that of yogurt is about 4.5.
Explain what causes this change in pH, as milk is changed to yogurt.
The bacteria change sugar in the milk to lactic acid. Acids have a low pH.
Bob is inside a vacuum room in which a ball weighing 300 KG and a feather weighing 50 g is released from the same height. Both the objects hit the surface of the ground at the same time.
Identify the error in these statements.
How can Bob survive in a vacuum room?
What eventually happens if energy is continually removed from a liquid?
It freezes.
Why is Helium used in balloons?
Helium is lighter (less dense) than air so the balloons float in the air.