Fertilization Fertilization activates the egg Activation of the egg triggers embryonic development.
B5 Growth and Development Year 11 2013. Development Egg to child Development.
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Transcript of B5 Growth and Development Year 11 2013. Development Egg to child Development.
![Page 1: B5 Growth and Development Year 11 2013. Development Egg to child Development.](https://reader030.fdocuments.net/reader030/viewer/2022032802/56649dff5503460f94ae873d/html5/thumbnails/1.jpg)
B5 Growth and Development
Year 11 2013
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Development
• Egg to child• Development
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Big Changes
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Francesco Redi
• 1668• ‘Appeared’
• Did experiments with flies to show:
• Flies lay eggs• Hatch into maggots• Maggots into pupae• Re-organise into fly
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Specialised cells
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Plant Systems
• Specialised cells• Tissues• Organs• Plant
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Body systems
• Specialised cells• Tissues• Organs• Body Systems
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Zygote
• All body cells from one original cells
• Fertilised egg• Instructions in DNA to
make all different tissues
• List as many different types of tissues as possible
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Egg to embryo
• Sperm and egg cell• Fertilisation• Zygote• Division of cells by
mitosis• Embryo• 100 cells – becomes
specialised• 2months main organs
have formed - foetus
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Identical Twins
• Embryo – 8cells• Clones• Cells which are identical
and unspecialised• Embryonic stem cells
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Meristem cells
• Stems grow taller• Roots get longer• Stems get wider
• New cells at tips of roots and shoots
• Rings of dividing cells in stems and roots to increase thickness - meristems
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Stem Cells
• Why can’t we replace whole organs?
• Plants keep some unspecialised meristem cells all their lives, so when leaves are picked they can grow back.
• The same can happen in newts
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Meristems make more plants...
• Cuttings – roots or leaves from a plant
• Rooting powder – plant hormones, cause meristem cells to develop into root cells
• Genetically identical clones
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Plants cannot move....
• So the conditions in the soil may affect it and it may die
• Phototropism – growing towards light
• Higher concentrations of plant hormones cause shoot cells to grow faster on the shady side.
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Chromosomes contain genes..
• Nucleus contains chromosomes
• Long molecule of DNA• 1M in each nucleus• 30,00 genes• Each gene codes for a
protein• 23 pairs of
chromosomes
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Cells grow and divide
• Before a cell divides it needs to make copies of its organelles and chromosomes
• Mitosis• Reproduce asexually
using mitosis• Clones
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Gametes
• Males make many, swim or are carried
• Females have large gametes that stay in one place
• Sperm in testes• Egg cells in ovaries
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Meiosis
• Gametes have half the chromosomes of a normal cell
• Sperm cell fertilises egg cell; nuclei fuse; full set of 46 chromosomes
• Gametes made by meiosis
• All different – show genetic variation
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Discoveries in DNA
• 1865 Gregor Mendel’s work on pea plants
• 1940’s Erwin Chargaff discovers a pattern in the bases of DNA
• 1951 Linus Pauling and Robert Corey show proteins have a helix structure
• 1952-3 Rosalind Franklin and Maurice Wilkins x-ray diffraction of DNA
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Crick and Watson - 1953
• Published paper in Nature
• Brought together all the work done on DNA so far.
• Used it to work out the double helix structure of DNA
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Bases
• A- Adenine• T – Thymine• C – Cytosine• G – Guanine• Base pairing – A
always with T and C always with G.
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DNA Info
• DNA copies itself• Weak bonds split
between bases• Two strands formed
from free bases in cell
• New chains identical to original
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DNA to Proteins
• How amino acids are arranged determines the shape and structure of proteins
• About 20 different amino acids
• Crick 1961 worked out that triplet codes make amino acids. 64 possible codes, so some have more than one code
• Codes for start and stop
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Where in the cell?
• DNA in nucleus contains code for proteins
• Proteins made on ribosomes in cytoplasm
• mRNA travels out of nuclear pores and into cytoplasm
• One strand• Uracil used instead of
Thymine to pair with Adenine
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Structural Proteins
Protein Found in... PropertyKeratin Hair, nails, skin Strong and
insolubleElastin Skin Springy
Collagen Skin, bone, tendons, ligaments
Tough and not very stretchy
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Functional Proteins
• Essential for chemical reactions which take place in our bodies• Enzymes• Antibodies
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Link between genes and proteins
• All cells from zygote• Begin to specialise• By controlling what
proteins a cell makes, genes control how a cell develops
• Each cell has a copy of ALL genes, however some differentiate – genetic switches
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Gene Switching
• Each gene controls a protein. One per protein
• Approx 20-25,000 genes• Not all genes are active,
some switched off• Eg in a hair cell or
salivary gland cell
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Gene switching in embryos• Early embryo made entirely of
embryonic stem cells• Unspecialised up to 8 cell stage• All genes switched on• As the embryo grows, genes
switch off as cells become specialised
• In adults there is regular replacement of worn out cells. These can only develop into cells of a particular organ, so some genes must be switched off.
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Stem Cells
• Treatment of some diseases/replacement of damaged tissue
• Stem cells come from early embryos, umbilical cord blood and adults.
• Embryonic stem cells most useful as unspecialised.
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Cloning
• Therapeutic cloning• Tissues do not match• Remove nucleus of
zygote and replace with patient’s body cell nucleus.
• Adults – bone marrow, harvest for storage
• Claudia Castillo