Mitosis and Mieosis

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EdExcel Additional Science
Divide and Develop

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Mitosis
Each daughter cell has
the same number of
chromosomes and genetic
information as the parent
(“diploid”)

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Meiosis
Each daughter cell has half
the number of chromosomes
of the parent (“haploid”).

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Mitosis vs. Meiosis
Mitosis: Meiosis:
2. Used for growth and repair of 2. Used to produce gametes for
cells sexual reproduction
3. Used in asexual reproduction 3. Each daughter cell has half the
4. Cells with identical number of number of chromosomes of the
chromosomes and genetic parent
information are produced

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Cell Growth
There are three ways in which a cell might “grow”:
1) Cell division:
2) Cell expansion:
3) Cell specialisation:

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Measuring Growth
Dry mass vs. wet mass
Dry mass is a more accurate measure of mass but it involves
removing all the water from an organism, so wet mass is usually
used instead.
Mass Mass
Plant growth Animal growth

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Environmental differences
Clearly, not all differences are due to just our genes (“Nature
vs. Nurture”)…
Variation due to Variation due to Variation due to a
inheritance only environment only bit of both
For example, height is affected by our genes, our hormones
and our diet.

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5 Things needed for Growth in Plants
SUNLIGHT
Gives the plant energy
NUTRIENTS
Roots
absorb
these from
WATER the soil
Travels up
from the roots
CARBON DIOXIDE
Enters the leaf through small …and the right
holes on the underneath temperature

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Artificial Plant Hormones
Hormones can be used to help plant growth and the
development of fruit:
1) Auxin 2) Ethene
This hormone helps This hormone helps
fruit to develop fruit to ripen

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Performance-Enhancing Drugs
Reasons for taking
performance-enhancing
drugs

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Regeneration of Animals
Plants can easily grow new leaves or stems when one is cut off.
Animals find this much more difficult. Here are a few
exceptions:

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Stem cell research
Stem cells are cells that have not yet specialised:
These stem cells have the
potential to develop into
any kind of cell. The rest
of the embryo is
destroyed. Most of these
Embryo embryos come from
unused IVF treatments.
Egg and
sperm Cloned
embryos
The ethical issue:
Should these embryos be treated as humans?

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The Hayflick Limit
In 1965 I discovered that a human
cell can only divide around 52 times
before it shows signs of old age.
This is called “The Hayflick Limit”.
Stem cells and cancer cells have no
Hayflick limit.

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Making decisions
Some questions cannot be answered by science and need to be
considered on ethical grounds.
Factors that might influence a decision:
• Beliefs/religion
• What does “the right thing” mean?
• “Playing God”
• Risks – acceptable or unacceptable?
• Social and economic contexts

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Cloning Animals
Method 1 – “Embryo transplants”
A developing embryo is “split” before the cells specialise and
the identical embryos are implanted into host mothers.

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Selective breeding
I raise cows. Each type of
cow is good at a certain job.
The Friesian cow produces
large quantities of milk, the
Jersey cow produces very Friesian
nice milk and the Hereford
cow produces lot of beef.
Jersey
If, for example, I want lots
of milk I would only breed
Friesian cows with each
other – this is SELECTIVE
BREEDING.
Hereford

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Selective breeding vs. Cloning
Advantages Disadvantages
Cloning
Selective
breeding

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Selective breeding vs. Cloning
Advantages Disadvantages
1) Allows large 1) Causes reduced
numbers of numbers of alleles
organisms with good 2) Loss of variation
Cloning characteristics to could harm survival
be produced chances if the
2) Very efficient environment changes
1) Produced organisms 1) Causes reduced
with favoured numbers of alleles
characteristics
Selective 2) Loss of variation
2) Very efficient and could harm survival
breeding economically viable chances if the
environment changes

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Gene Therapy
Gene therapy is when a disease is treated by modifying a
person’s “genome” (genetic makeup). Consider the example of
cystic fibrosis, a disease causing lung problems:
The patient is anaesthetised
They inhale a “vector virus”
carrying a normal gene
The normal genes enter lung
cells
Patients feel better for
around 4 weeks
Gene therapy can also be used to treat breast cancer but it is
very expensive.

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“Designer Babies”
Should we be able to
“design” our children?

21. 04/01/12
Abortion
Should the abortion limit of
24 weeks be lowered to 18?