B5 (Biology): Growth and Development

This section shows links to revision materials Biology B5 - Growth and Development.

Overview of Module

Genetic technologies are at the cutting edge of contemporary science. Research into proteomics, stem cell technology and cellular growth control is at the forefront of modern medical science. Knowledge and understanding of these areas promise powerful applications to benefit both present and future generations.

The first topic explains plant and animal development, comparing and contrasting the development of

unspecialised cells. The ability of plant meristems to regenerate whole plants is considered, including

the effect of plant hormones on their development.

The second topic looks at how the structure of DNAallows cells to be accurately copied. Key stages in the cell cycle are identified, and cell division by mitosis and meiosis compared.

The final topic describes the process of protein synthesis, following the one-gene-one-protein hypothesis.

Topics (see below for more detail)

• B5.1 How do organisms develop? - Embryo development; cell specialisation in plants and animals; plant growth responses
• B5.2 How does an organism produce new cells? - Main processes of the cell cycle; comparisons of mitosis and meiosis
• B5.3 How do genes control growth and development within the cell? - Structure of genetic code and mechanism for protein synthesis

B5.1 How do organisms develop?

1. recall that cells in multicellular organisms can be specialised to do particular jobs

2. recall that groups of specialised cells are called tissues, and groups of tissues form organs

3. recall that a fertilised egg cell (zygote) divides by mitosis to form an embryo

4. recall that in a human embryo up to (and including) the eight cell stage, all the cells are identical (embryonic stem cells) and could produce any type of cell required by the organism

5. understand that after the eight cell stage, most of the embryo cells become specialised and form different types of tissue

6. understand that some cells (adult stem cells) remain unspecialised and can become specialised, at a later stage, to become many, but not all, types of cell required by the organism

7. understand that in plants, only cells within special regions called meristems are mitotically active

8. understand that the new cells produced from plant meristems are unspecialised and can develop into any kind of plant cell

9. understand that unspecialised plant cells can become specialised to form different types of tissue (including xylem and phloem) within organs (including flowers, leaves, stems and roots)

10. understand that the presence of meristems (as sources of unspecialised cells) allows the production of clones of a plant from cuttings, and that this may be done to reproduce a plant with desirable features

11. understand that a cut stem from a plant can develop roots and then grow into a complete plant which is a clone of the parent, and that rooting can be promoted by the presence of plant hormones (auxins)

12. understand that the growth and development of plants is also affected by the environment, e.g. phototropism

13. understand how phototropism increases the plant’s chance of survival

14. explain phototropism in terms of the effect of light on the distribution of auxin in a shoot tip.

B5.2 How does an organism produce new cells?

1. recall that cell division by mitosis produces two new cells that are genetically identical to each other and to the parent cell

2. describe the main processes of the cell cycle:

• a. cell growth during which:
  • numbers of organelles increase
  • the chromosomes are copied when the two strands of each DNA molecule separate and new strands form alongside them
• b. mitosis during which:
  • copies of the chromosomes separate
  • the nucleus divides

NOTE: Candidates are not expected to recall intermediate stages of mitosis

3. recall that meiosis is a type of cell division that produces gametes

4. understand why, in meiosis, it is important that the cells produced only contain half the chromosome number of the parent cell. NOTE: Candidates are not expected to recall intermediate stages of meiosis

5. understand that a zygote contains a set of chromosomes from each parent.

B5.3 How do genes control growth and development within the cell?

1. recall that DNAhas a double helix structure

2. recall that both strands of the DNA molecule are made up of four different bases which always pair up in the same way:A with T, and C with G

3. understand that the order of bases in a gene is the genetic code for the production of a protein

4. explain how the order of bases in a gene is the code for building up amino acids in the correct order to make a particular protein

NOTE: Candidates are not expected to recall details of nucleotide structure, transcription or translation

5. recall that the genetic code is in the cell nucleus of animal and plant cells but proteins are produced in the cell cytoplasm

6. understand that genes do not leave the nucleus but a copy of the gene (messenger RNA) is produced to carry the genetic code to the cytoplasm

7. understand that although all body cells in an organism contain the same genes, many genes in a particular cell are not active (switched off) because the cell only produces the specific proteins it needs

8. understand that in specialised cells only the genes needed for the cell can be switched on, but in embryonic stem cells any gene can be switched on during development to produce any type of specialised cell

9. understand that adult stem cells and embryonic stem cells have the potential to produce cells needed to replace damaged tissues

10. understand that ethical decisions need to be taken when using embryonic stem cells and that this work is subject to Government regulation

11. understand that, in carefully controlled conditions of mammalian cloning, it is possible to reactivate (switch on) inactive genes in the nucleus of a body cell to form cells of all tissue types.