Download B5 Growth and Development

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B5 Growth and
Development
OCR
st
21
M Barker
Shirebrook Academy
Century
B5.1 How do organisms develop?
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Cell specialisation
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During the
development of a
multi-celled organism
cells differentiate to
form specialised cells:
Ciliated
epithelial cell
White blood cell
Nerve cell
(neurone)
Egg cell (ovum)
Cells, tissues, organs and systems
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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
Another example
Here’s another example in humans:
Muscle cells
Muscle tissue
Organ
System
Organism
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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
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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.
Adult Stem Cells
It is also possible to
have adult stem cells –
these are unspecialised
cells that can become
specialised later (but
they can’t form ALL
types of cell)
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Adult stem cells can be
found in places like
bone marrow.
Ciliated
epithelial cell
White blood cell
Nerve cell
(neurone)
Egg cell (ovum)
Plant Growth Introduction
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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.
Plant Growth - Meristems
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Plant growth occurs in areas called meristems. These
meristems are “mitotically active”:
This meristem causes the
plant to grow upwards.
This meristem causes the
plant to grow in width.
Cells from the meristem behave like
stem cells – they can develop into
any kind of cell. Cloned plants can
be produced from these cells.
Cloning Plants by tissue culture
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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
Plant Hormones
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The growth of roots and shoots is controlled by hormones:
In the shoots the hormone
auxin is “destroyed” by
light, so the shoot will bend
towards the light as the
cells on the shaded side
grow quickest.
In the roots hormones slow
down growth of the cells in
the lower region, which
makes the root bend down.
Some Definitions
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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).
B5.2 How does an organism produce
new cells?
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Cell growth 1 - Mitosis
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The chromosomes are
copied…
Each daughter cell has
the same number of
chromosomes and genetic
information as the parent
– it’s a “clone”.
The nucleus
divides…
The
chromosomes
separate…
Cell growth 2 - Meiosis
Each daughter cell has half
the number of chromosomes
of the parent.
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Mitosis:
1.
Mitosis vs. Meiosis
Used for growth and repair of
cells
2. Used in asexual reproduction
3. Cells with identical number of
chromosomes and genetic
information are produced
(“clones”)
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Meiosis:
1.
Used to produce haploid
gametes for sexual
reproduction
2. Each daughter cell has half the
number of chromosomes of the
parent
During meiosis copies
of the genetic
information are made
and then the cell
divides twice to form
four daughter cells.
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?
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
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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.
Adult Stem Cells
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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.
Stem cell research
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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?
Cloning Animals
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Here’s how Dolly the sheep was cloned:
Clone
It is possible to “switch on” inactive genes in the nucleus of a
Host mothers
body cell to form cells of all tissue types. Are cloning and
stem cell research the way forward???