B5 Flashcards
What does an organism being multicellular mean?
They have cells that are specialised to do different jobs
What is an organ?
A combination of various tissue working together
Organs combine to create…
systems e.g. the circulatory system, the digestive system
Describe the stages of a human developing from gametes
A sperm fertilises an egg creating a zygote
The Zygote goes through mitosis until it forms an embryo
After 8 weeks the embryo becomes a fetus
Up to what stage in development is an embryo made of only embryonic stem cells?
The eight cell stage, up to this point the cells are identical and can become any cell they want to
Where are adult stem cells found?
Mainly in bone marrow and the brain
Adult stem cells are unspecialised but cannot become any cell like embryonic stem cells
What do unspecialised plant cells form?
Transport tissue such as xylem and pholem
What is xylem and what does it do?
It is 1 of 2 types of transport tissue in plants
It carries water and salt minerals (that have been obtained by osmosis or active transport) and take them to other parts of the plant
What is phloem and what does it do?
It is 1 of 2 types of transport tissue in plants
It carries sucrose and proteins between the leaves and and other parts of the plant
Where are meristems found and what do they do?
They are found in places such as the tips of shoots, in the stem, in side buds and the roots
They are made up of unspecialised cells that can become anything as the plant grows
They are the only type of cells in plant that divide
What happens when a meristem splits?
One of the daughter cells remains as a meristematic cell and the other becomes a specialised cell
How can plants be cloned?
Through using cuttings
Tissue culture
Explain how cutting of plants can be used to clone them
A part of the plant that contains meristems is cut off and replanted and it will begin to grow a plant genetically identical to the one it was cut from. Root growth from the cutting in stimulated by plant hormones in the soil they are planted in
Explain tissue culture cloning
A small piece of tissue is put in age jelly containing nutrients and plant hormones
They then grow into small plants that can be grown into full sized plants
What is auxin?
A plant hormone that promotes the growth of plant tissue by increasing cell division and enlargement
What is tropism?
An organisms response to a stimulus
Phototropism is…
a response to the direction of light
Why does phototropism happen in plants?
As plants rely on light for photosynthesis so growth towards a light source increases a plants change of survival
How is auxin involved in a plant growing towards light?
If the plant is only being hit by sunlight on 1 side, auxin will grow on the shaded side of the plant. This stimulates greater cell growth in this side causing the plant to curve towards the light
What is the function of mitosis?
For growth and repair of cells
What happens during mitosis?
Each chromosome in the cell is copied, so there are two sets of DNA
They then align along the centre of the cell and then it splits
What does mitosis result in?
Two daughter cells that are identical to the mother cell it came from and each other
Each cell has 23 pair of chromosomes in them
What is the function of meiosis?
To creates gametes
What happens during meiosis?
Each chromosome in the cell is copied, so there are two sets of DNA
The cell and then it splits, and then slips agin
What does meiosis result in?
Four unique cells that are nothing like the mother cell or like each other
Each cell has 23 single chromosomes
What are chromosomes?
Thread like structures found in the nucleus
Made from a DNA molecule
Are grouped in pairs (humans have 23 pair)
Describe the shape of a DNA strand
A double helix
What is DNA made up of?
Bases that pair up to join the two DNA strands
A and T join and C and G join
These bases make up genetic codes for protein synthesis to make the proteins we are built up of
As DNA is unable to leave the nucleus, what takes the information to make proteins?
mRNA
Its bases are the same as DNA except is uses U instead of T
How are proteins made?
A DNA strand unwinds and unzips itself
A complementary strand of mRNA creates a complimentary strand
The mRNA then leaves the nucleus and goes to a ribosome
The ribosome read the bases
Each three bases creates a codon that codes for 1 amino acids
Amino acids exist in the cytoplasm and transfer RNA (tRNA) then collects the amino acids and they are then bound together at the ribosome
Why do specialised cells have some genes ‘switched off’?
These genes are not required for these cells to function e.g. a heart cell doesn’t need the gene for eye colour switched on
In what state are the genes in embryonic stem cells?
They are all ‘switched on’ allowing them to become any cell
Why are there issue around using using embryonic stem cells?
When embryonic stem cells are taken, the embryo is destroyed
Some people believe that embryos have a right to life when they are conceived, even though the majority are the surplus from IVF treatment
Also creating embryo just for research and therapy is even more controversial
Why is therapeutic cloning suggested as an alternative to the use of embryonic stem cells?
It does not require fertilisation but does still destroy the embryo produced
What is the process involved in therapeutic cloning?
The nucleus of a regular cell is extracted and the nucleus of an egg cell is also extracted
The nucleus from the body cell is placed inside the egg cell and the egg cell then begin to split
This creates embryonic stem cells with the same genetics as the person and can be used for a variety of treatment
Are the cells made from therapeutic cloning exactly like stem cells?
There has not been enough testing of the cells to see if they can become any cell
