crop is destroyed by these pests annually. Pesticides increase the world food
supply.
(2) There are an estimated 300–500 million cases of malaria per year. The
majority of these occur in Africa. The vast majority of the estimated 1
million annual deaths from this disease occur among children and mainly
among poor African children. Malaria is often a disease of the poor,
impacting at least three times more greatly on the poor than any other
disease. Africa’s GDP would be up to $100 billion greater if malaria had
been eliminated years ago. Mosquitoes have been estimated to be
responsible for half of all human deaths due to transmission of disease.
Pesticides improve human health by destroying disease-carrying
organisms.(iii) Identify and discuss TWO negative effects of pesticide use. (2 points
maximum. 1 point for each correct negative effect and explanation.) (1) If a
pesticide is continually applied to a population of the pest species, most
susceptible individuals will be killed, leaving only resistant individuals. These
resistant individuals breed and multiply. Eventually a high proportion of the
individuals from that pest species are now resistant to the pesticide. We have
simply caused pest populations with a higher tolerance for poisons to survive
and breed. More toxic pesticides in turn are developed and utilized.
(2) Pesticides can accumulate in living organisms. An example of
accumulation is the uptake of a water-insoluble pesticide, such as
chlordane, by a creature living in water. Since this pesticide is stored in the
organism, the pesticide accumulates and increases over time. If this
organism is eaten by an organism higher in the food chain that can also
store this pesticide, levels can reach higher values in the higher organism
than is present in the water in which it lives. Levels in fish, for example,
can be tens to hundreds of thousands of times greater than ambient water
levels of the same pesticide. This type of accumulation is called
bioaccumulation. In this regard, it should be remembered that humans are
at the top of the food chain and so may be the most vulnerable to
bioaccumulation.(b) Discuss any TWO alternatives to the use of pesticides. (2 points maximum. 1
point for each correct alternative and explanation.) (1) When landscaping a yard
or planning a garden, choose plant varieties that are native to the region and