OCR 21st Century

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OCR 21st Century
B5 Growth and Development
M Barker Shirebrook Academy
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B5.1 How do organisms develop?
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Cell specialisation
During the development of a multi-celled organism
cells differentiate to form specialised cells
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Cells, tissues, organs and systems
Basically, all living things are made up of cells
A group of CELLS makes up a TISSUE
A group of TISSUES makes up an ORGAN
A group of ORGANS makes up a SYSTEM
A group of SYSTEMS make up an ORGANISM
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Another example
Heres another example in humans
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Fertilisation
The human egg and sperm cell (GAMETES) contain
23 chromosomes each and are created by meiosis.
When fertilisation happens the gametes fuse
together to make a single cell called a ZYGOTE.
The zygote has 46 chromosomes (23 pairs) and
continues to grow through mitosis.
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Embryos
When the zygote grows all of the initial cells
are identical (up to the 8-cell stage). These
are called embryonic stem cells. From this
stage on the cells grow through mitosis and start
to specialise.
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Adult Stem Cells
It is also possible to have adult stem cells
these are unspecialised cells that can become
specialised later (but they cant form ALL types
of cell)
Adult stem cells can be found in places like bone
marrow.
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Plant Growth Introduction
Plants grow due to their cells dividing through
mitosis. The cells then specialise into root
hair cells, palisade cells etc. Unlike animals,
plants continue to grow for the rest of their
lives.
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Plant Growth - Meristems
Plant growth occurs in areas called meristems.
These meristems are mitotically active
Cells from the meristem behave like stem cells
they can develop into any kind of cell. Cloned
plants can be produced from these cells.
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Cloning Plants by tissue culture
1) Scrape of a few cells from the desired plant
2) Place the scrapings in hormones (auxin) and
nutrients
3) 2 weeks later you should have lots of
genetically identical plants
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Plant Hormones
The growth of roots and shoots is controlled by
hormones
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Some Definitions
Shoots grow towards light (positive phototropism)
and against gravity (negative geotropism). Roots
grow away from light (negative phototropism) and
in the direction of gravity (positive geotropism).
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B5.2 How does an organism produce new cells?
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Cell growth 1 - Mitosis
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Cell growth 2 - Meiosis
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Mitosis vs. Meiosis

• Mitosis
• Used for growth and repair of cells
• Used in asexual reproduction
• Cells with identical number of chromosomes and
  genetic information are produced (clones)

• Meiosis
• Used to produce haploid gametes for sexual
  reproduction
• Each daughter cell has half the number of
  chromosomes of the parent

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Fertilisation Revision
The human egg and sperm cell (GAMETES) contain
23 chromosomes each and are created by meiosis.
When fertilisation happens the gametes fuse
together to make a single cell called a ZYGOTE.
The zygote has 46 chromosomes (23 pairs) and
continues to grow through mitosis.
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B5.3 How do Genes control growth?
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Genes, Chromosomes and DNA
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How genes work - DNA
Some facts - DNA has a double ______
structure - This contains instructions on what a
cell does, how the organism should work etc -
The instructions are in the form of a ______ -
The code is made up from the four ____ that hold
the strands together with hydrogen bonds A
always pairs with T and C with G - The bases
represent the order in which _____ acids are
assembled to make specific ________
Words helix, amino, code, bases, proteins
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Making proteins
1) DNA unravels and a copy of one strand is
made
2) The strand copy is made to produce RNA
3) The copy (with its code) then moves towards
the ribosome
4) The ribosome decodes the code which tells
the ribosome how to make the protein
In other words, genes do NOT leave the nucleus
but a copy of the gene (the mRNA) carries the
genetic code to the cytoplasm.
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Adult Stem Cells
Cells inside an organism contain the same genes.
So how can cells specialise if they have the same
genes and make the same proteins?
The reason is that many of the genes in the
nucleus are switched off so that the cell only
produces the proteins it needs.
It is possible to switch on different genes to
make the cell produce different proteins this
is the basis of stem cell research.
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Stem cell research
As well as adult stem cells from bone marrow,
stem cells can also come from...
These stem cells have the potential to develop
into any kind of cell. The rest of the embryo is
destroyed. Most of these embryos come from
unused IVF treatments.
Embryo
Egg and sperm
Cloned embryos
The ethical issue Should these embryos be
treated as humans?
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Cloning Animals
Heres how Dolly the sheep was cloned
It is possible to switch on inactive genes in
the nucleus of a body cell to form cells of all
tissue types. Are cloning and stem cell research
the way forward???