Calculate the percentage decrease in chlamydia cases between age groups 20-24 and 25-29. Give your answer to two significant figures.
Describe how the spread of STIs, such as chlamydia, can be controlled.
State the name of the female reproductive organ that produces oestrogen.
Describe what oestrogen does during puberty.
Complete the statements about drug resistance and genetic variation by supplying a suitable word or phrase in each space. Bacteria can be killed by drugs called [BLANK]. The appearance of strains of bacteria that are resistant to these drugs is an example of [BLANK] selection. Resistant strains of bacteria have gene mutations that allow them to survive drug treatment. Gene mutations are caused by random changes in the [BLANK] of bases in DNA and lead to the production of new [BLANK] in the bacteria. Mutation rates can be raised by [BLANK] radiation and some chemicals. In animals and plants, another source of genetic variation is a type of nuclear division called [BLANK].