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
i 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
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 DNA has 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
i 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.
(c) OCR 2011 GCSE Science A
No comments:
Post a Comment