Revision

Part 4 – final section

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

Sperm adaptations• Acrosome - contains

enzymes to digest the egg cell membrane

• Tail – many mitochondria in cells to release energy.

WHY

ENZYMES

DIGESTS EGG MEMBRANE / PENETRATE / GET INSIDE THE EGG

RESPIRATION

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

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.

 

DNA is cut into fragments

DNA FRAGMENTS SEPARATED / ELECTRIC CURRENT APPLIED / ELECTROPHORESIS

3

CAT GAG ACT

Plant cells and growth

ChloroplastsCell Wall

Vacuole

Cell Membrane

Nucleus

Cytoplasm

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

Plant hormones

How Does This Plant Know to Send Its Shoots ‘Up’ and Its

Roots ‘Down’?

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

Artificial Use of Hormones

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

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

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?

Mutations

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!

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.

Selective Breeding Produces:-

• New Varieties Of Organisms

• Animals & Plants With Increased Yields

•How? – animals / plants with the desired characteristic are selected to be bred

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

What is a stem cell?

• An undifferentiated cell, it has not yet specialised and can turn into different cells or tissues.

Adult Cloning

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.

Cloning cows – embryo transplants

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.

 

How Dolly was made

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

• 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

Plants that can do it by themselves?

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.

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