Biology OCR, B5

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What are groups of specialised cells called?
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What do group of tissues form?
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What is special about human embryo cells up to the eight cell stage?
all the cells are identical (embryonic stem cells) and can produce any type of cell required by the organism
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What happens to embryos after the eight cell stage?
most of the embryo cells become specialised and form different types of tissue
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What cells remain unspecialised?
adult stem cells but can become specialised at a later stage to become many, but not all, types of cell required by the organism
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What parts of a plant are mitotically active? (divide to produce new cells)
only cells within special regions called meristems
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What is special about the new cells produced by plant meristems?
they are unspecialised and can develop into any kind of plant cell
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What are types of tissues in a plant?
xylem and phloem
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What are types of organs within a plant?
flowers, leaves, stems and roots
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What does the presence of meristems (as sources of unspecialised cells) allow?
the production of clones of a plant from cuttings, which can be used to reproduce a plant with desirable features
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How can a plant cutting produce a clone?
a cut from a plant can develop roots and then grow into a complete plant which is a clone of the parent. Rooting can be promoted by the presence of plant hormones (auxins)
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What are auxins and where are they produced?
Auxins are plant hormones that make some parts of a plant stem grow faster than others. The result is that the plant stem bends towards the light. Auxin is produced in the tip of growing shoots. If the tips are removed, phototropism cannot take place
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What is phototropism?
the growth of a plant in the direction of it's light source
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Why do plants bend towards their light source?
the light destroys the auxins on that side of the stem and so on the shaded side of the plant, there are more auxins encouraging growth and the plant bends towards the light for photosynthesis
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What happens when a plant's shoot tip is covered?
light cannot break down the auxin, so phototropism cannot occur
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What does cell division by mitosis produce?
two new cells that are genetically identical to each other and to the parent cell
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What are the main processes of the cell cycle?
Cell growth, which increases the number of organelles and chromosomes are copied when the two strands of each DNA molecule separate and new strands from alongside them. Next mitosis occurs and copies of the chromosome separate and the nucleus divides
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What is meiosis?
a type of cell division that produces gametes
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What does a zygote contain?
a set of chromosomes from each parent
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Why is it important in meiosis for the cells to contain half the chromosome number of the parent cell?
so the gametes can combine during sex to form a zygote with a full set of chromosomes (46 chromosomes, 23 from each gamete)
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What is the structure of DNA?
DNA has a double helix structure
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What are the bases in DNA and which ones pair together?
DNA molecules are made up of four different bases, which always pair up in the same way: A with T and C with G
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What is the order of bases in a gene?
the genetic code for the production of a protein
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What does the order of bases in a gene build?
build up amino acids in the correct order for a particular protein
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Where is genetic code found in the cell?
the nucleus of plant and animal cells
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Where are proteins produced?
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How do genes get transferred from the nucleus to cytoplasm?
genes do not leave the nucleus but a copy of the gene (messenger RNA) is produced to carry the genetic code to the cytoplasm
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Whey are many genes in a particular cell not active (switched off)?
because the cell only produces the specific proteins it needs
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What genes are switched on and off in specialised cells and embryonic stem cells?
in specialised cells only the genes needed for the cell can be switched on, but in embryonic stem cells any gene can be switched on during development to produce any type of specialised cell
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What have adult and embryonic stem cells have the potential to do?
the potential to produce cells needed to replace damaged tissues
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What can reactivating inactive genes in the nucleus of a cell do?
it can form cells of all tissue types
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Card 2


What do group of tissues form?



Card 3


What is special about human embryo cells up to the eight cell stage?


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Card 4


What happens to embryos after the eight cell stage?


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Card 5


What cells remain unspecialised?


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Just your average kid

Really good, was a great help!

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