Live practice

The natural divisors of 6 are \(1,2,3,6\); its prime divisors are \(2,3\). The distinct letters of MATHEMATICS are \(M,A,T,H,E,I,C,S\), and the odd natural numbers below 10 are \(1,3,5,7,9\).

Ozone is a molecule containing three oxygen atoms, \(\mathrm{O_3}\). In the stratosphere it forms a protective layer that absorbs much of the Sun's harmful ultraviolet radiation. This protects living organisms from DNA damage, skin cancer and eye damage and also protects crops, plankton and other organisms. Near ground level, however, ozone is a pollutant and can damage respiratory tissues and plants. Thus its effect depends on where it occurs.

Draw several straight, parallel, equally spaced lines with arrowheads all in the same direction. Parallelism gives constant direction and equal spacing indicates constant magnitude.

Using \(W=VQ\):

The cornea and lens focus a real inverted image on the light-sensitive retina.

For a real inverted image, \(m=-3\). With \(u=-10\) cm and \(m=-\frac{v}{u}\):

The negative sign places the real image in front of the mirror.

Females are XX and produce ova carrying only X. Males are XY and produce approximately equal numbers of X-bearing and Y-bearing sperm. Fertilisation by an X sperm gives XX (female); fertilisation by a Y sperm gives XY (male). Thus the sperm, and therefore the father, determines chromosomal sex with roughly equal probability.

It produces many plants rapidly and preserves desirable parental characters because offspring are clones. It is useful for seedless plants or those with poor seed viability, such as banana, sugarcane and rose. Vegetatively produced plants often mature and flower sooner than seedlings.

Plant hormones are chemical messengers made in small quantities in one region and transported or acting locally to coordinate growth, development and responses. Auxin, gibberellin and cytokinin mainly promote growth; abscisic acid generally inhibits growth and supports stress responses.

• Carbon dioxide enters from air through stomata.
• Water is absorbed from soil by roots and transported through xylem.
• Light energy comes from the Sun and is trapped by chlorophyll.
• Chlorophyll is present in chloroplasts of green cells.
• Minerals needed to build chlorophyll and enzymes are absorbed from soil.