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B5 Revision
Growth & Development…read more

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DNA - Making
~DNA is a double helix of paired bases.
~DNA molecules contain code to make all the proteins in
your body.
~DNA has two strands, made up of lots of small groups
called nucleotides.
~These contain bases - Adenine, Cytosine, Guanine and
~DNA controls the production of proteins in a cell.
~A gene is a section that has code for only one protein,
they make proteins by joining amino acids together in a
particular order.
~Each set of 3 bases codes for 1 amino acid
~DNA determines which genes are on or off, and so which
proteins the cell produces, which determines the cell type.
~Proteins are made in cell cytoplasm by organelles called
~DNA is found in cell nucleus, cell gets info from DNA to
ribosomes - copy is made using RNA molecules.
~RNA is similar to DNA but shorter and only a single
~RNA is the messenger between DNA in the nucleus and
RNA in the cytoplasm.…read more

Slide 3

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Cell Division - Mitosis
~New cells are needed for growth and repair.
~The cells in the body divide to produce more cells to grow and
replace damaged cells.
~This happens in humans plants and other animals.
~First the cell physically grows and duplicates its contents.
~The cell copies everything so when it splits the two new cells
contain the right information.
~The number of organelles increases during cell growth.
~The chromosomes are copied, so that the cell has two copies of its
~Molecule of DNA splits.
~Bases on free floating nucleotides pair up with matching bases on
the DNA.
~Cross links form between the old DNA strands and the nucleotides
are joined together.
~It then splits into two by Mitosis.
~The cell has two copies of its DNA spread out in long strings.
~Before the cell divides, the DNA forms X-Shaped chromosomes.
Each arm of a chromosome is an exact duplicate of the other.
~The chromosomes then line up at the centre of the cell and cell
fibers pull them apart. The two arms of each chromosome go to
opposite ends of the cell.
~Membranes form around each of the sets of chromosomes. These
become the nuclei of the two new cells.
~Lastly the cytoplasm divides and you are left with 2 new cells
containing the exact same DNA.…read more

Slide 4

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Cell Division -
~Cells in reproductive organs divide by meiosis to
form sperm or egg cells. (Gametes)
~These have half the usual number of chromosomes,
because the egg and sperm combine to form a
~Gametes only have one copy of each chromosome,
23 when they combine they have 46.
~Gametes are produced by Meiosis, it involves two
~It duplicates its DNA just like mitosis.
~First division - the chromosome pairs line up in the
centre of the cell.
~The pairs are pulled apart, so each new cell only
has one copy of each chromosome, some of the
father's and mother's chromosomes go into each
new cell.
~Second division - the chromosomes line up in the
centre of the cell, like mitosis the arms of the
chromosomes are pulled apart.
~You get 4 gametes each with only 23
~After two gametes join at fertilisation the zygote
grows by repeatedly dividing by mitosis.…read more

Slide 5

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Development From
A Single Cell
~Cells in an early embryo can turn into any type of cell.
~A fertilised egg divides by mitosis to produce a bundle of
cells, the embryo of the new organism.
~Embryonic stem cells are un differentiated this means
they are able to divide to produce any type of specialised
~Stem cells may be able to help to cure many diseases.
~Adults stem cells are already used to cure diseases and
make new tissues for the body.
~Embryonic stem cells can be extracted from very early
human embryos, these could then be controlled to
differentiate into specific cells to replace faulty cells in
sick people.
~Cloning could also be used to make stem cells.
~Human adult cell cloning could also be used to produce
tissues for disease sufferers that wouldn`t be rejected by
the sufferer's immune system.
~A cloned embryo is created that is genetically identical
to the sufferer. If the conditions are right inactive genes
are reactivated and an embryo grows.
~Embryonic stem cells that can become any cell in the
body are then extracted from it.…read more

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Growth In Plants
~Animals stop growing, plants can grow continuously.
~Animals grow when they are young and stop when
they reach full grown, plants can grow continuously.
~Meristems contain plant stem cells.
~Some plant tissues contain unspecialised cells that are
able to divide and form any cel type in the plant, they
can divide to create any type of cell.
~Clones of plants can be produced from cuttings.
~Cuttings will contain unspecialised meristem cells
which can differentiate to make any plant cell.
~Phototropism is movement in response to light.
~Some parts of a plant such as roots and shoots can
move in response to light, shoots grow towards the
light to adsorb sunlight and roots grow away from
sunlight to adsorb nutrients and water from the soil.
(Positive and Negative Phototropism)
~Auxins are plant growth hormones.
~Auxins are chemicals that control growth near the tips
of shoots and roots.
~Auxins help cutting grow into a complete plant.
~If you add auxins to plant cutting they will produce
roots rapidly and start growing newly.…read more

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