Why can some plants pollinate themselves and others need to be pollinated by insects? Plants need to make seeds to reproduce and to do that many plants have to transfer pollen to and from one another. Pollen is usually produced by the male part of the flower, but sometimes it is produced by the male flower. In order to reproduce, the egg-containing ovules of the flower have to be fertilised by pollen. Plants pass pollen around in several ways. One is with the help of the wind. Plants also depend on insects for help. The most common pollinators are flying insects, but crawling and hopping insects, snails, bats and hummingbirds can also do the job. For example, bees go from flower to flower gathering nectar. As they go to work, pollen collects on their hairs. When they fly to another flower for nectar, the pollen is rubbed off. One thing that keeps a plant healthy and helps it to survive is genetic diversity - different strengths passed along through its genes to cope with different situations. The only way to get genetic diver sity is from other plants of the same kind. Some plants can fertilise or pollinate themselves. It is not much of a problem as the male and female parts of these plants are in the same flower. Botanists say many of the plants that fertilise themselves have been selected for that ability by humans, which is what agriculture is all about. In agriculture, plants are developed through selective breeding and do not have to depend on pollinators being in the vicinity. Farmers have generally selected for a lack of diversity, mainly because it is easier to grow a crop if all the plants are about the same height and can be harvested at the same time. Self-fertilising plants can be found in the wild though. They often evolved in extreme climates such as in the desert. Since insects are only present when there is enough moisture, the plants decided to take care of reproduction themselves. However, these plants also have diversity. Some stray pollen will oc casionally be passed along by the wind or a wandering insect and give the plant a little added diversity. Why do people get addicted to drugs? There are two types of drug dependency. One is psychological, the other physical. These two types of dependency happen when a person uses a drug over and over again. If a drug changes a person's mood or behaviour, it can lead to them becoming dependent. Experts say that some people are prone to become dependent on drugs more easily than other people. If a person becomes physically dependent on a drug and stops taking the drug, there will be a lot of bad reactions, and the person may feel really ill for a while.