Growth and development Flashcards
What are the cells in a multicellular organism like?
Specialised to do a job.
What are cells of the same typed grouped into?
Tissues
Different tissues that are grouped together, and work together, are called?
Organs
What tissues would you find in the heart?
Muscle, epithelial, blood and nervous tissue.
What is epithelial tissue?
Lining and covering tissue, eg the skin, the lining of the gut
What does an organism begin life as?
A zygote
What is a zygote?
A fertilised egg
How does a zygote divide?
By Mitosis
What does the cell division in the zygote produce?
An embryo
What are the cells up to the eight cell stage of the embryo?
Embryonic stem cells.
What is special about embryonic stem cells?
They could become any cell of the human body.
How do the cells in the eight cell stage of the embryo differ from each other?
They don’t.
What is the process of cell specialisation called?
Differentiation.
Do adults still have stem cells?
Yes, they have adult stem cells.
What is the difference between embryonic stem cells and adult stem cells?
Adult stem cells can only develop into a limited number of cell types, eg. bone marrow cells into different types of blood cell.
In a specialised cell, which genes are switched on?
Only the ones it needs.
In embryonic stem cells, which genes are switched on?
It can switch any genes on. (21st century answer)
What specialised plant tissues form?
Xylem, phloem, etc
What does the xylem do?
Transports water and mineral salts.
What does the phloem do?
Transports the products of photosynthesis
What organs does a plant have?
eg leaves, flowers, stems, roots
Where in the plant would you find unspecialised cells?
In areas called the meristems.
What is special about cells in the meristems?
They are unspecialised
What happens when a cell divides in the meristem?
One of the daughter cells can specialise, the other stays as a meristematic cell.
Where does cell division happen in plants?
Only in the meristems
How is plant growth produced?
By division of meristem cells, followed by the enlargement of one of the daughter cells.
How can you clone a plant?
By placing the cut end of a shoot in water or soil.
Where would the roots grow if you place the cut end of the shoot in water or soil?
From the base of the stem
Which plants are propagated using cuttings?
Garden plant; house plants; some food plants
What is the advantage of propagation by cuttings?
The new plants are genetically identical to the original plant, with all the same desirable features (clones); it enables seedless mutations to be propagated.
How can you encourage root growth in cuttings?
By using plant hormones (sold as “rooting powder”)
How else could you clone plants?
You could use tissue culture, where a small piece of tissue is placed on agar jelly containing nutrients and plant hormones, where each one will grow into a tiny plantlet.
What are the plant hormones in rooting powder called?
Auxins
What is the effect of auxins?
They encourage cell division and enlargement.
What is plant growth and development affected by?
Environment
What is a plant’s response to light called?
Phototopism
Plants grow towards light, this is called?
Positive phototropism
Why is positive phototropism good for plants?
They need light for photosynthesis, so growing towards the light increases their chances of survival
Where is auxin produced?
In the growing tip of plant shoots.
What happens to auxin when one side of the shoot is in shade?
It is distributed to the shaded side.
What is the effect of the auxin when there is more on the shaded side?
There is more growth on the shaded side, so the plant grows towards the light.
What is mitosis?
The cell division that takes place in an organism to produce growth or repair.
What is the result of mitosis?
Two identical daughter cells, clones.
What must happen before mitosis?
The DNA in each chromosome is copied, leaving each chromosome doubled up.
What is the cell cycle?
cell growth; mitosis
What happens during the cell growth phase of the cell cycle?
The cell increases in size; it increases the number of organelles; the DNA in each chromosome is copied
What happens during the mitosis phase of the cell cycle?
The stands of each double chromosome separate and two nuclei are formed, making two identical daughter cells.
What is the type of cell division that forms the gametes?
Meiosis
What is the posh word for sex cells?
Gametes.
What are the gametes in flowering plants?
Pollen; eggs
What are the gametes in animals?
Eggs and sperm.
How many chromosomes in a human gamete?
23
How many chromosomes in a human big toe cell?
46
How many chromosomes in a human zygote?
46
What is the mechanism of meiosis?
The cell copies the chromosomes, and divides, producing two daughter cells. These divide again, this time without copying the chromosomes, this produces sex cells with half the normal number of chromosomes.
Why is meiosis needed for sex cells, why not just use mitosis?
The zygote would contain twice the number of chromosomes of the normal cell - 92 in the human
What is a chromosome made of?
A DNA molecule.
What is the shape of the DNA molecule?
A double helix.
What are the units of DNA called?
Bases
How many bases (in DNA)?
Four
What are the bases?
ATCG
How do the bases pair up?
A with T, C with G
What does the order of the bases in a chromosome do?
It makes up the genetic code, which tells the cell how to make the amino acids, and how to arrange them into proteins.
Where is the DNA found in plant and animal cells?
In the nucleus
DNA gives the instructions for?
protein synthesis
Where does protein synthesis happen?
In the cytoplasm
Where do the genes stay in the cell?
In the nucleus
How do the instructions for protein synthesis get into the cytoplasm?
Messenger RNA copies the DNA (so the DNA has to separate), and carries the instructions into the cytoplasm
Where are proteins assembled?
On organelles in the cytoplasm called ribosomes.
How does the genes code for an amino acid?
A code of three bases (called a triplet pair) codes for each amino acid.
What does transfer RNA do? (tRNA)
It ferries amino acids to the ribosomes
Why are some genes switched off in the cell?
The cell only makes the proteins that it needs.
What are the cells in the embryo like, up to the eight cell stage?
They are identical embryonic stem cells.
What happens to the cells after the eight cell stage of the embryo?
They start to differentiate,
What happens to the protein synthesis in the specialised cells?
They start synthesising specialised proteins.
What happens to the shape and structure as the cell differentiates?
It usually changes.
Which genes can be switched on in embryonic stem cells?
Any
What do embryonic stem cells have the potential to do?
Replace damaged tissues.
What do adult stem cells have the potential to do?
Replace a limited range of damaged tissue.
Why does using embryonic stem cells raise ethical questions?
The embryo is destroyed.
What do some people believe about embryos that have been created?
That they have a right to life.
Where do embryonic stem cells come from?
Embryos that are surplus from IVF.
How are people likely to react to the idea of embryos being created with the intention of destroying them?
It would be very controversial, and there would be protests.
What regulates work with stem cells?
The Government, via laws.
How are some of the ethical issues of working with embryonic stem cells overcome?
Therapeutic cloning.
How is therapeutic cloning done?
Replacing the nucleus of an egg with the nucleus of a body cell, then stimulating the egg to make it divide to produce an embryo.
Why would therapeutic cloning be better, ethically?
There is no fertilisation, and the belief, for some religions, is that human life starts at fertilisation.
What happens to the embryo produced by therapeutic cloning?
It is destroyed when the stem cells are harvested.
Why is therapeutic cloning better, medically?
The cell is genetically identical to the patient, so will not be attacked by the immune system.
What does therapeutic cloning do to inactive genes?
They have been reactivated.
What is the hope of therapeutic cloning?
That all cell types will be able to be formed.
