Revision Part 4 – final section Cell division – the differences MITOSISMEIOSIS Diploid cells /...
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Transcript of Revision Part 4 – final section Cell division – the differences MITOSISMEIOSIS Diploid cells /...
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Revision
Part 4 – final section
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Cell division – the differences
MITOSIS MEIOSISDiploid cells / 2n Haploid cells / n (1)
Produces identical cells Produces different cells
Involves 1 cell division 2 cell divisions
Makes 2 daughter cells Makes 4 daughter cells
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Sperm adaptations• Acrosome - contains
enzymes to digest the egg cell membrane
• Tail – many mitochondria in cells to release energy.
WHY
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ENZYMES
DIGESTS EGG MEMBRANE / PENETRATE / GET INSIDE THE EGG
RESPIRATION
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MITOSIS – DIPLOID CELLS (46 CHROMOSOMES)MEIOSIS – HAPLOID CELLS (23 CHROMOSOMES)
MITOSIS – IDENTICAL CELLSMEIOSIS – DIFFERENT CELLS
MITOSIS – 1 CELL DIVISIONSMEIOSIS – 2 CELL DIVISIONS
MITOSIS 2 DAUGHTER CELLSMEIOSIS 4 DAUGHTER CELLS
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DNA fingerprinting
• Isolate blood of cell sample
• Extract DNA
• Use restriction enzymes to fragment the DNA
• Place DNA fragments on gel
• Apply and separate fragments using an electric current (electrophoresis)
• Banding of DNA fingerprint can be matched.
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DNA is cut into fragments
DNA FRAGMENTS SEPARATED / ELECTRIC CURRENT APPLIED / ELECTROPHORESIS
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3
CAT GAG ACT
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Plant cells and growth
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ChloroplastsCell Wall
Vacuole
Cell Membrane
Nucleus
Cytoplasm
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Growth
• Plant• Most growth is due to
cells elongating (growing longer) not dividing
• Cell division only normally occurs at the tips of shoots and roots
• Many cells never lose the ability to differentiate
• Animal• Growth is due to cells
dividing• Cell division occurs all
over the body• Most animal cells lose the
ability to differentiate very early on
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Plant hormones
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How Does This Plant Know to Send Its Shoots ‘Up’ and Its
Roots ‘Down’?
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Response in plants • Tropism – plant growth in response to a
stimulus
• Growth towards the stimulus is a positive tropism and growth away is a negative tropism e.g. shoots are positively phototropic but negatively geotropic
Stimulus Tropism
Light Phototropism
Gravity Geotropism
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Artificial Use of Hormones
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Artificial Use of HormonesFarmers use Artificial Hormones to increase their yield and to organise ripening times to suit their convenience
There are 3 main types:
• Rooting Compound
• Ripening Hormone
• Selective Weed killers
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Auxin is made in the tip or top of plantThe tip is covered so it doesn’t receive lightAuxin levels are equal on both sidesBoth sides grow at the same rate
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The Big Picture
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Human growth – typical questions ? Graph analysis?
• Put the stages of human growth in the correct order, starting with the earliest:– Adulthood (maturity)– Childhood– Infancy– Old age– Adolescence (puberty)
• What stage of growth are you in?
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Mutations
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What is a mutation?
• A mutation is a permanent change in the DNA sequence of a gene. Sometimes mutations in DNA can cause changes in the way a cell behaves. This is because genes contain the instructions necessary for a cell to work. If some of the instructions to the cell are wrong, then the cell may not know what it is supposed to do!
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How does it happen?
• There are two ways in which DNA can become mutated:
• Mutations can be inherited. This means that if a parent has a mutation in his or her DNA, then the mutation is passed on to his or her children. e.g. Down’s syndrome
• Mutations can be acquired. This happens when environmental agents damage DNA, (X rays, radiation, chemicals, chance), or when mistakes occur when a cell copies its DNA prior to cell division.
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Selective Breeding Produces:-
• New Varieties Of Organisms
• Animals & Plants With Increased Yields
•How? – animals / plants with the desired characteristic are selected to be bred
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Selective Breeding
Advantages Disadvantages
– Produces an organism with the right characteristics for that function
– A more efficient and economically viable process in farming & horticulture
• Loss of variation which reduces the species’ ability to respond to environmental change
• Reduces the number of alleles available for further selection
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What is a stem cell?
• An undifferentiated cell, it has not yet specialised and can turn into different cells or tissues.
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Adult Cloning
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Cloning
• Clones are genetically identical. They have the same DNA as the original animal or plant. Identical twins are natural clones – they have the same DNA.
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Cloning cows – embryo transplants
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Embryo transplantation• Sperm is collected from the prize bull;
• A prize cow is artificially inseminated with the sperm.
• When the fertilised egg divides into an eight-cell embryo it is collected and split into four two-celled embryos.
• Each embryo is implanted into a surrogate cow where it grows into a calf.
• All the calves will be genetically identical to each other but not to their parents.
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How Dolly was made
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Nuclear transfer
• Egg cell taken from sheep A and the nucleus is removed.
• An udder cell is taken from sheep B and the nucleus is removed.
• The nucleus from sheep B is put into the egg cell of sheep A.
• The egg cell is put into a sheep to grow.• The cell grows into a clone of sheep B (where the
nucleus containing the genetic information came from
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• The importance of cloning– Organ supply for humans– Cloning of human embryos to provide stem cells
• Risks– Low success rate– Moral / ethical issues– Complications / early death of clones
• Benefits– Cloned pigs could make up a shortage in
transplant organs– Diseases could be cured using embryonic stem
cells
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Cloning plants
• Produces exact genetic copies of themselves without involving another plant.
• Gardeners can take cuttings.• Why is it easier to clone a plant instead of
an animal?
Plant cells keep their ability to differentiate
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Plants that can do it by themselves?
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Commercial cloning
• Choose the plant based on the characteristics you want
• Remove a small amount of tissue from the parent plant. You need a tiny amount, this can be removed from several points to give several clones, if possible take the tissue from fast-growing root and shoot tips
• The tissue is grown in a medium containing nutrients and growth hormones. All of this is done in aseptic conditions to prevent growth of microbes.
• As the tissues produce shoots and roots they can be moved to potting compost to carry on growing.
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Pros and cons
• You know pretty much the characteristics of the plant since it’s genetically identical to the parent
• Mass-produce plants that are hard to grow from scratch
• A change in the environment or a disease could affect all of the plants
• Lack of genetic variation
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