B5 Growth and Development
- Created by: emchown
- Created on: 09-03-15 17:19
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- B5
- Group of specialised cells = tissue. Group of tisses = organ.
- Mitosis
- Process where cell divides to prodice 2 new identical cells,
- Cells for growth and reapir and rplace old tissues
- Fertilisation
- Egg id fertilised by Sperm to produce a Zygote.
- Zygote divides to form a cluster of cells called an Embryo.
- Up to (and including) the 8 cell stage, cells are identical and unspecialised (Embryonic Stem Cells)
- Zygote divides to form a cluster of cells called an Embryo.
- @ 16 cell stage, most cells begin to specialise, form different types of tissue.
- Although genes in the cells are the same, they are subtley diff.
- @ 16 cell stage, most cells begin to specialise, form different types of tissue.
- Differences define what functions the cells have.
- Some cells stay unspecialised (Adult Stem Cells). Can become specialed at later stage but cannot become any type of cell
- Egg id fertilised by Sperm to produce a Zygote.
- Mitosis and Growth
- Can only take place when cells are ready to divide, so cells go through a cell cycle.
- Cell Cycle
- 1) Growth Stage (G1) - cell gets bigger, number of organelles increase.
- 2) Synthesis Stage (S) - where DNA is copied
- 3) - Very short growth stage (G2)
- 4) Mitosis phase (M)
- Both new cells need all DNA and organelles to function properly.
- Number of organelles needs to increase and DNA has to be copied.
- Chromosomes are copied when two strands of each DNA molecule seperate and new strands form along side.
- Number of organelles needs to increase and DNA has to be copied.
- Plant Meristems
- Similar to stem cells in animals
- Only cells inside of Meristems can divide repeatedly (mitotically active)
- They are found in shoots and roots (apical - higher and longer) and stems (lateral - increased girth)
- They are unspecialled and can develop into any kind of cell. eg. xylem, Phloem and organs
- Xylem and Phloem
- Xylem
- Made from specialled cells.
- Transports water and mineral salts from roots to stem and leaves
- Helps replace water lost during transportationand photosynthesis
- Phloem
- Made from specialled cells
- Transports dissolved food made by photosynthesis for respiration or storage
- Xylem
- Xylem and Phloem
- When a stems deliberately cut, hormones can be added that send messages to meristems to start to produce roots
- It will grow into clone of parent plant
- Main hormone used is Auxin
- It affects cell division @ tip of shoot.
- Just under tip, cells grow in presence of auxins
- Phototropism
- A response by a plant to light
- Plants survival depends on photosynthesis
- Plants will grow towards light source to be able to photosynthesise
- How it works
- Cells furthest away from the light source grpw more due to auxin being sensitive to light
- Its produced at the shoot tip and migrates down the shoot
- Light source shines at an angle - auxin facing the light moves to shaded side
- Concentration of side furthest away from light increases
- Cells there elongate and shot bends toward the light
- Charles Darwin
- Experiments to show role played by plant hormones produced in shoot tip
- If tip of shoot removed or covered, shoot grows up as if light wasnt there
- If covered by transparent cap, it grows towards the light
- Cylinder around stem and tip exposed - grows towards light
- Experiment proves it is a substance produced in tip that cause cells in shoot to grow
- Meiosis
- Only takes place in ovaries and testes
- Produces gametes for sexual reproduction
- Gametes contain half the no. of chromosomes of parent cell. Fuse together - full number
- 1) Cell with 2 pairs of chromosomes
- 2) Each chromosome replicates itself
- 3) Chromosomes part an dmove to opposite sides with their 'copies'
- 4) Cell divides for first time
- 5) Copies seperate and second cell division takes place.
- 6) Four gametes are now produced with half no. chromosomes
- DNA
- It's a nucleic acid, found in the nucleus and has a double helix form.
- Structure was found out by Watson and Crick.
- DNA molecule has bases connected together (rungs on a ladder).
- The bases are always in pairs, A and T, G and C.
- The bases are always in pairs, A and T, G and C.
- Base Pairs
- DNA stored in and never leaves the nucleus
- It has a sequence of genes that code for protiens.
- Protiens are made in the cytoplasm of a cell so there's a mechanism to transfer info in genes to cytoplasm
- Protiens are made in the cytoplasm of a cell so there's a mechanism to transfer info in genes to cytoplasm
- DNA molecules too large to leave cell
- Relevant section of DNA 'unzipped'
- Instructions copied onto mRNA which can pass through the nuclear membrane
- Instructions are carried to the ribosomes in the cytoplasm which follow instructions to make specific protiens
- Instructions copied onto mRNA which can pass through the nuclear membrane
- Relevant section of DNA 'unzipped'
- Relevant section of DNA 'unzipped'
- Instructions copied onto mRNA which can pass through the nuclear membrane
- Instructions are carried to the ribosomes in the cytoplasm which follow instructions to make specific protiens
- Instructions copied onto mRNA which can pass through the nuclear membrane
- Order of bases determines what protien is made.
- Gene Switching
- A gene codes for one specific protien
- All body cells contain exactly the same genes
- All cells produce protiens for growth and respiration
- Certain genes (making cell membrane and ribosomes) will be switched on in all cells
- Genes that are not needed will be switched off
- Certain genes (making cell membrane and ribosomes) will be switched on in all cells
- Certain genes (making cell membrane and ribosomes) will be switched on in all cells
- Genes that are not needed will be switched off
- When a stem cell become specialised, genes for proteins specific to new cell type will be switched on
- Any gene in an embryonic stem cell could be switched on
- Ethical Decisions
- To produce large no. of stem cells, you need to clone cells from embryos.
- Stem cells collected when embryos made up of 150 cells.
- Rest of the embryo destroyed
- Rest of the embryo destroyed
- Unused embryos from IVF used for research
- Should embryos be classed as people? Murder?
- Left over from IVF - never grow into human?
- Research carried out as long as consent from parents
- Government regulates and makes laws on these matters.
- Mammalian Cloning
- Dolly the Sheep first to be cloned from adult skin cells
- Illegal to clone human in this way
- Dolly the Sheep first to be cloned from adult skin cells
- Take specialised cell and reactivate inactive genes - making new specialised cell type
- Gives potential to grow new tissue that is genetically the same as patient
- Tissue will not be rejected by immune system of patient
- Patient doesnt have to take expensive cocktail of drugs
- Such drugs can affect patients immune system and can stop it fighting disease
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