Live practice

1. False: both a and b occur in the second set.
2. True.
3. False: \(2\) is missing from the second set.
4. True.
5. False: \(a\), rather than the set \(\{a\}\), is an element.
6. True: the first set is \(\{2,4\}\), and both divide 36.

• They remain in the environment for long periods and occupy landfill space.
• Plastics can block drains, pollute soil and water, and injure or kill animals through ingestion and entanglement.
• Burning them may release toxic smoke and greenhouse gases.
• Persistent poisonous chemicals may enter food chains and undergo biological magnification.
• Some waste fragments into microplastics that are difficult to remove.

Field lines are concentric circles in planes perpendicular to the wire, centred on it; direction follows the right-hand thumb rule.

For parallel resistors, conductances add.

In parallel, total resistance is slightly below the smallest branch.

Starlight passes through continually changing layers of air with different temperatures and refractive indices. Atmospheric refraction therefore causes rapid variations in apparent direction and intensity. A star is effectively a point source, so these fluctuations are noticeable as twinkling.

A concave lens has negative focal length: \(f=-2\) m.

The vas deferens carries sperm in the male reproductive system. Ovary, uterus and fallopian tube are female organs.

Insulin from pancreatic beta cells promotes uptake and storage of glucose, lowering blood glucose. In diabetes, insulin may be absent or insufficient, so glucose remains abnormally high. Injected insulin replaces the deficiency and helps maintain a safe concentration. It is a protein and would be digested if swallowed.

The heart pumps blood. Arteries carry blood away from the heart under pressure; veins return it and contain valves; capillaries permit exchange with tissues. Blood transports gases, nutrients, hormones, heat and wastes and provides defence/clotting. Lymph returns tissue fluid, absorbs intestinal fats and participates in immunity.

Ethane has six C-H bonds and one C-C bond. Total covalent bonds \(=6+1=7\).