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Biology - Differences Between Organisms (AQA Syllabus A)

In GCSE Science, students will look at genetic variation and its control. This is the first of four quizzes on the subject and it look in particular at the differences that can be found between organisms of the same species. This is partly genetic variation, such as eye colour, but also environmental variation, caused by things such as diet.

There are not only differences between different species of plants and animals but also between individual organisms of the same species. These differences are due partly to the information they have inherited from their parents and partly to the different environments in which the individuals live and grow.

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The information that results in plants and animals having similar characteristics to their parents is carried by genes, which are passed on in the sex cells (gametes) from which the offspring develop. Different genes control the development of different characteristics of an organism. Many genes are needed to carry all the genetic information for a whole organism.

Genes make up the chromosomes of an organism and are contained in the nucleus of each cell. In the gametes, the nucleus contains only half of the number of chromosomes required for the complete organism. When the male and female gametes come together, their nucleii fuse and the fertilised cell (zygote) contains a full set of chromosomes and can develop into and adult animal or mature plant.

Since half of the information for the new individual comes from the male gamete and half from the female, there are many similarities to, but some differences from, the parents. This difference between organisms of the same species is called variation.

Sometimes this variation creates a feature in a plant or animal that enables it to compete better. If that is the case, the organism will breed successfully and the new feature is likely to be passed on to the next generation. This is how evolution takes place.

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  1. Gametes contain only half the number of chromosomes other types of cells have, therefore they are what?
    Diploid cells contain a full set of chromosomes
  2. Which of the following is correct in order of decreasing size?
    A lot of candidates mix up the size of chromosomes and genes, genes are small parts of chromosomes
  3. Which of the following could account for body mass?
    Genes can give one organism a greater body mass than another but environmental factors like diet can create differences too
  4. Environmental variation can be caused by which of the following?
    Climate and light intensity can create environmental variation in both plants and animals e.g. plants grow more slowly in a cold climate and hair goes lighter in strong sunlight
  5. Eye colour is an example of which of the following?
    Discontinuous variation can only have certain values
  6. What causes inherited variation?
    Inherited variation means that the offspring resemble their parents but not exactly
  7. Eye colour can be changed using coloured contact lenses. Eye colour is an example of what?
    True eye colour is controlled by genes. Exactly which ones are involved is not yet known
  8. Why is plotting a line graph of foot length more appropriate than using a bar chart?
    Continuous variation is variation that has no limit on the value that can occur within a population. A line graph is used to represent continuous variation. Had the question been about foot (shoe) size rather than foot length, the answer would have been a histogram. Foot (shoe) sizes have only certain values
  9. Genes are part of what?
    A gene is a section of DNA, which carries coding for the cell to make a particular protein. These proteins combine to make more complex chemicals like amino acids and enzymes, needed for the organism to function
  10. A group of students carried out a survey into the blood groups. What would be the most appropriate way to show the data?
    Blood groups are an example of discontinuous variation. You could use a pie chart but the usual scientific way of showing ths type of data is to plot it on a histogram because it is easier to see small differences. Pie charts are better if you convert your results to percentages

Author: Kev Woodward

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