Biology - Competition (AQA Syllabus A)

As a part of GCSE Science, students will look at interdependence and adaptation. This is the first of three quizzes on the topic and it looks in particular at inter-species and intra-species competition for resources such as food, water, space and a mate.

Organisms are well adapted to survive in their normal environment. Population size depends on a variety of factors including competition, predation, disease and human influences. Both plants and animals compete for the resources in their habitat. There are two types of competition; inter-species (different types of animal competing for the same resources) and intra-species (animals of the same type competing for resources).

Animals compete for food, water, territory and (intra-species only) mates. Natural selection reduces inter-species competition to a degree as it reinforces behavioural adaptations like feeding at different times of day, eating different types of food or feeding at different heights where there are trees. This means that two or more species can occupy the same territory and competition will only be for water.

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Plants make their own food by the process of photosynthesis. This happens in the chloroplasts where chlorophyll turns water and carbon dioxide into sugars. These sugars are either stored as starches or used for respiration to keep the plant alive. So plants don't need to compete for food. But they still need water and light for the process of photosynthesis and must compete for those. They also need mineral salts that are found dissolved in the water in the soil which is one reason they compete for space to grow as well.

So every habitat has its own unique set of organisms living there. These are the ones who compete successfully for the resources. If something changes in the environment, population numbers will change and a species that can no longer compete will disappear from the habitat.

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  1. When the grey squirrel was introduced to parks in Britain in the 1870s, the numbers of the native red squirrels decreased. Why?
    This quiz is about competition so there are only two answers that could be correct. Since Britain only occasionally suffers from drought, the most likely explanation is food. Always apply this sort of logic when answering questions
  2. Human beings live all over the world. This means that we must compete with plants and animals. What are we competing for?
    Humans are very successful mammals. We need space for building and farming and water for drinking and for growing our food
  3. Some students grew some radish seeds. The instructions said they needed to be planted 2cm apart. In the experiment, they planted some 0.5cm apart, some 1cm apart and some at the correct distance. They observed that the closer the seeds were planted ...
    When the seeds germinated, they were competing for light and so they grew taller. After a week, they were competing for water and nutrients. Because they were planted too close, there was not enough of either to go round so their growth slowed down
  4. Working together can give organisms an advantage in competition. What is this called?
    There are many examples of this e.g. leguminous plants, lichen, buffalo and oxpecker birds, cleaner fish and sharks
  5. What happens to plants and animals that are unsuccessful in competing for resources?
    Unsuccessful organisms become weaker and weaker. Animals are forced to move somewhere else or face death
  6. Ladybirds feed on insects called aphids. What happens when the number of aphids increases?
    There is less competition for food so more ladybirds survive
  7. Lions live in groups (prides). The dominant male lions sometimes chase some of the male cubs away as they approach sexual maturity, making them leave the pride. Why do you think this is?
    This tends to only happen when their father starts to lose out to intruder males attempting to mate with the females of his pride. The clue to the correct answer lies in the question - males chasing away males is almost certain to be about mating
  8. Which of the following best describes the population curve for a predator-prey relationship?
    When the number of prey drop, the predators will not start to decline straight away. Although competition for food is greater, it takes a while before the predators starve to death or move somewhere else to find food
  9. The Forestry Commission have planted lots of trees in Scotland, often in quite wet and boggy countryside. These trees are mainly Sitka spruce, which are evergreen and are planted close together. Which of the following might explain why there are not many plants growing on the forest floor?
    Whilst all of these could seem like a reasonable answer, there is plenty of water as the trees are planted in wet and boggy areas. There are always seeds in the soil so very soon after ploughing, the plants will regrow. Tree roots spread out in all directions but there is still plenty of space for plants adapted to live in poor quality thin soils. The trees are planted very close together which cuts out a lot of the light reaching the forest floor. Very few plants can survive permanently low light levels as they can't photosynthesise properly in such conditions
  10. In North America, the lynx is an animal that feeds on hares. Which of the following features of the hare will not help it run away before a lynx can get close enough to catch it.
    Competition is also about competing to escape! Hares that are better at escaping will live longer and have more offspring. The senses of hearing, sight and smell make a good early warning system

Author: Kev Woodward

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