Edexcel Biology 2105, also Additional Science 2103

Unit B2

Topic 2 — Divide and Develop

Understanding how living things grow helps us to understand and treat medical problems arising at birth or later in life.

Cells replicate by mitosis and gametes are produced by meiosis. Cells are differentiated to specific functions. In animals this differentiation arises from stem cells, but this ability is lost at an early stage. Scientists are beginning to understand the medical potential of stem cells. This can be compared with plant growth, where regeneration and virtually continual growth is common. The more we can understand plant growth the more we will be able to produce the quantity of food the world requires. Consideration is given to the limiting factors affecting plant growth and distribution, which can be investigated practically.

There is ample opportunity to discuss ethical issues associated with growth and development and genetic modification, as well as giving consideration to the potential of gene therapy.

Guidance for students

Have you ever wondered?

Why don’t I keep on growing forever?
Why do scientists want to modify cows?
What is a stem cell and why do scientists think it is so valuable?
Why do plants need hormones?
Why have the International Olympics Committee (IOC) banned certain chemicals?
How does scientific knowledge contribute to decisions regarding the termination of pregnancies?
How can gene therapy help treat cancer sufferers?
Why do ‘weeds’ always grow in the most awkward places?

Learning objectives
  • Organisms grow by cell division, elongation and differentiation of cells.
  • Plants and animals are different and this results in different patterns of growth and development.
  • There is a variety of environmental factors that will influence the growth and distribution of
  • plants.
  • Human intervention can manipulate the outcome of reproduction.
    •

    Glossary

    You will be expected to be able to recall, explain, describe and use appropriately the following words and phrases:

    cancer cell embryo hormones regeneration
    cell division foetus inheritance selective breeding
    chromosomes gametes meiosis species
    continuous variable genes mitosis sperm
    differentiation genetic modification nucleus stem cell
    diploid growth nutrient termination
    elongation haploid ovum  
    auxins discontinuous variation nuclear transfer
    pedigree analysis phototropism steroids


    Information for teachers

    ICT is an integral part of the way science works, and students should be given opportunities to experience and explore its use. It is expected that ICT will be used where it enhances the learning and teaching of science and helps to make scientific concepts easier to understand.

    Some of the learning outcomes have been written deliberately in order to promote discussion and expression of opinion. Where contentious, unresolved or other scientific issues are discussed, it is expected that students will be exposed to the facts, evidence and opinions from all sides of the argument.

    Learning outcomes

    Learning outcomes, words or statements in bold indicate that this content is designated for Higher tier students only.

    Students will be assessed on their ability to:

    • describe mitosis as the division of a cell to produce two nuclei with identical sets of chromosomes, for growth or replacement B2 2.1
    • describe meiosis as the division of a cell to produce four haploid nuclei with sets of chromosomes that are not genetically identical to produce gametes eg sperm and ovum B2 2.2
    • explain the differences between mitosis and meiosis B2 2.3
    • discuss the meaning of growth, in terms of increase in size; length; wet mass; dry mass B2 2.4
    • demonstrate understanding of how cell division, elongation and differentiation contribute to the growth and development of an organism B2 2.5
    • explore the scientific evidence for the potential of stem cell research B2 2.6
    • demonstrate understanding that cells have a limit to the number of divisions they undergo, the Hayflick limit; stem cells and cancer cells have no Hayflick limit B2 2.7
    • demonstrate understanding that stem cells in the embryo can differentiate into all other types of cells, but that cells lose this ability as the animal matures B2 2.8
    • explore the scientific evidence that contributes to the decision regarding the legality and age of termination of a foetus B2 2.9
    • explore the phenomenon that organisms have a size range for that particular species: height in humans is a continuous variable, influenced by a number of genes, hormones and nutrition B2 2.10
    • discuss the factors affecting the growth and distribution of plants, including:
    – nutrients
    – light
    – temperature
    – carbon dioxide
    – oxygen
    – plant ‘hormones’
    		 B2 2.11
    • interpret data on how environmental factors affect the distribution of plants B2 2.12
    • discuss fruit initiation in plants and how it can be manipulated with artificial hormones B2 2.13
    • discuss regeneration in animals (including spiders, worms and reptiles) and why it is relatively rare B2 2.14
    • explore the evidence that selective breeding (artificial selection) can be used to:
    - improve the quality of milk from cattle
    - increase the number of offspring in sheep
    - increase the yield from dwarf wheat and other cereal crops
    		 B2 2.15
    • discuss the ethics and health concerns of using growth factors to enhance performance in sport B2 2.16
    • demonstrate an understanding of the stages in the production of cloned mammals, including Dolly the sheep:
    - the replacement of the nucleus in an egg cell with a diploid nucleus from a mature cell (nuclear transfer)
    - stimulation of the diploid nucleus to divide
    		 B2 2.17
    • discuss the potential benefits and ethical dilemmas posed by advances in genetic modification B2 2.18


    NOW DROPPED
    • explain the potential of gene therapy for the relief of symptoms of inherited diseases such as cancer B2 2.19
    • discuss whether gene therapy would prevent diseases being passed on to the next generation. B2 2.20