Everyday Science Mixed Quiz 2: Body, Chemistry and Environment, WBPSC Clerkship GS

Pure water is neutral, so its pH at 25°C is exactly 7. Below 7 a solution is acidic and above 7 it is basic. Lemon juice is acidic (pH about 2) while lime water is basic (pH near 12).

About 78% of dry air is nitrogen. Oxygen is about 21%, argon about 0.9% and carbon dioxide only about 0.04%. Many pick oxygen because we breathe it, but nitrogen is the largest part.

O negative red cells carry no A, B or Rh antigen, so the recipient's antibodies do not attack them and the blood can be given to anyone. AB positive can receive from all, so it is the universal recipient.

Haemoglobin is the iron-containing protein of red blood cells; it carries oxygen and makes blood red. Chlorophyll is the green pigment of plants, melanin colours the skin and carotene gives carrots their orange.

A fuse wire is connected in series. When too much current flows, it heats up and melts, breaking the circuit and saving the appliance. So it must have a low melting point; an alloy of lead and tin is commonly used.

Rusting is an oxidation in which iron combines with oxygen and water or moisture to form hydrated iron oxide. Without either one, iron does not rust. That is why paint, oil or a zinc coating is used to keep iron away from air and water.

Baking soda is sodium hydrogencarbonate (NaHCO3). On heating or with an acid it releases carbon dioxide, which makes cakes and breads rise. Sodium carbonate is washing soda (Na2CO3) and sodium hydroxide is caustic soda.

Loss of water vapour through the tiny pores of leaves, the stomata, is called transpiration. It cools the plant and keeps water moving up from the roots. Respiration breaks food down for energy, photosynthesis makes food and osmosis is movement of water across a membrane.

A barometer measures air pressure. An anemometer measures wind speed, a hygrometer measures humidity and an ammeter measures electric current. A sudden fall in a mercury barometer suggests stormy weather.

The SI unit of resistance is the ohm, symbol Ω. The volt is the unit of potential difference, the ampere of current and the watt of power. By Ohm's law $V = I \times R$, so resistance $R = \frac{V}{I}$.

Diamond is a form of carbon in which every atom is strongly bonded to four others, making it the hardest natural substance. Graphite, another form of carbon, is soft and slippery and is used in pencil leads.

Dry ice is solid carbon dioxide. It does not melt into a liquid but turns straight into gas, a change called sublimation. It is at about −78°C, so it is used to keep food cold.

Insulin is secreted by the beta cells of the pancreas and lowers blood glucose. Its shortage causes diabetes mellitus. The thyroid secretes thyroxine and the adrenal gland secretes adrenaline.

Polio is caused by the poliovirus. Malaria is caused by the protozoan Plasmodium, while tuberculosis and cholera are caused by the bacteria Mycobacterium and Vibrio cholerae. Antibiotics work on bacterial diseases, not on viral ones.

The ozone layer in the stratosphere absorbs most of the Sun's harmful ultraviolet rays, which can cause skin cancer and eye disease. Chlorofluorocarbons (CFCs) damage the ozone layer.

Mercury (Hg) is the only metal that is liquid at ordinary room temperature, with a melting point of about −39°C. Lithium, aluminium and copper are solid. Mercury is used in barometers and thermometers, but it is poisonous.

CNG is mainly methane (CH4), the chief component of natural gas. It pollutes less than petrol or diesel. The main constituents of LPG are propane and butane, while biogas is also mostly methane.

The thyroid gland uses iodine to make thyroxine. Without iodine the gland swells, which is called goitre; that is why iodised salt is advised. Rickets comes from lack of vitamin D, scurvy from vitamin C and anaemia mainly from iron.

An adult human body has 206 bones. A newborn has roughly 270–300, but some fuse as the child grows. The longest bone is the femur of the thigh and the smallest is the stapes of the ear.