science

Plastics that have strong covalent bonds have high melting points, are rigid

Plastics that have weak intermolecular forces have low melting points, can be stretched easily

Gore-tex lets water vapour escape but prevents water coming in.

We can dispose of plastics 3 ways:

1.Landfill sites: wastes resources, get filled easily, most plastics are non-biodegradable

2.Burning plastics: produces air pollution, produces carbon dioxide,

3.Recycling: time consuming, saves resources

If the angle of incidence is above the critical angle, light is totally internally reflected.

If the angle of incidence is below the critical angle,light is refracted away from the normal.

If the angle of incidence is equal to the critical angle, light travels along glass-air boundary.

Digital signal has two states e.g on/off 1/2

Analogue signal varies continuosly in amplitude/ frequency

Multiplexing:when 2 or more digital signals are sent down the same optical fibre at the same time.

1.Name features and examples of a.stimulants b. depressants

2.How does smoking cause coughing?

3. How does carbon monoxide in cigarettes affect the body?

4, How does tar in cigarettes affect the body?

5. Name some a.short term and b. long term effects of alcohol.

1a.increase amount of transmission substance released at synapses e.g caffeine, nictine, ecstasy

b. block amount of transmitter substance released at synapses e.g alcohol, solvents, temazepam

2.Smoking damages cilla. So cilla cant remove mucus, tar, dirt from lungs which leads to a "smoker's cough". Coughing damages alveoli and can cause emphysema

3. Carbon monoxide combines with haemoglobin in red blood cells. Prevents oxygen being carried by red blood calls to respiring cells.

4. Tar contains chemicals that irritants and carcinogens.

5a.lack of balance, poor judgemant, blurred vision

b. cirrhosis-liver damage, brain damage

Homeostasis is the maintenance of a constant internal environment.

If you have too much sugar in blood, insulin changes glucose into glycogen

If you don't have enough sugar, glucagon changes glycogen back into glucose

Oestrogen: stimulates repair of uterus wall and thickening of uterus lining

Progesterone:maintains uterus lining

Cooking is a chemical change. The texture and taste of food changes when it is cooked, and cooking helps to kill harmful microbes

Cooking causes the protein molecules to change shape. It is called denaturing and is irreversible.

Decomposition of baking powder:

Food additives:

Antioxidants-stop food reacting with oxygen

Food colours-improve appearance

Food enhancers-bring out flavour.

Emulsifiers-mix ingredients (water and oil) there are two ends: hydrophobic and hydrophilic.

Hydrophilic is polar and bonds to polar water molecules.

Hydrophobic is non-polar and bonds to the non polar oil molecules.

Bonding holds oil and water molecules together

payback time (years) = cost of installation (£) ÷ savings per year in fuel costs (£)

efficiency = useful energy output ÷ useful energy input