Unit 2.1 Producing New Cells Flashcards
Cell division (mitosis)
A single cell copies all its DNA and divides into 2 identical daughter cells.
Used to increase the number of cells in an organism.
Essential for growth and repair of tissues.
Diploid
Body cells have 2 sets of chromosomes (one from each parent) so are said to be diploid.
The diploid number of chromosomes in human cells is 46.
Chromosome complement
How many chromosomes there are in a cell.
There are 46 in a human cell.
Haploid
Gametes contain one set of chromosomes (one from each pair) and are said to be haploid.
The haploid number of chromosomes in human gametes is 23.
Replicated chromosome
A chromosome that has been copied before mitosis occurs.
Chromosomes must be copied so that new cells have a complete set of chromosomes containing the same DNA as the parent cell.
Replicated chromosomes are ‘X’ shaped and are made of 2 chromatids held together by a centromere.
The 2 chromatids are separated during mitosis, when the centromere splits.
Centromere
Holds the 2 chromatids together in a replicated chromosome.
Stages of mitosis
DNA is replicated and organised into chromosomes.
Chromosomes appear as they shorten and thicken, and the nuclear membrane breaks down.
Chromosomes line up on the equator of the cell and attach to spindle fibres.
Spindle fibres shorten, splitting the centromere and pulling the chromatids to opposite poles of the cell.
The chromosomes gather at the poles forming 2 new nuclei, with nuclear membranes.
The cytoplasm divides.
Equator
An imaginary line along the misddle of a cell.
Replicated chromosomes line up here during mitosis.
Spindle fibres
Used to separate daughter chromatids during mitosis.
Chromatid
Replicated chromosomes are made of 2 daughter chromatids.
Chromatids are the 2 copies of the original DNA, which are separate during mitosis.
Chromatids are held together by a centromere.
Meristem
The region of a plant where mitosis occurs.
Meristems are found at the root and shoot tip.
They are made of small, actively dividing, unspecialised cells.
These cells differentiate to form the specialised cell types found in plants.
Stem cells
Unspecialised cells found in animals.
They are able to self-renew (copy themselves) and can develop into specialised cells.
Stem cells are used for growth and repair - all new body cells are produced from stem cells.
Embryonic stem cells
Early embryos are made of a ball of embryonic stem cells.
They are able to copy themselves, and then can specialise into any type of cell needed to build a body.
Tissue (adult) stem cells
Found throughout the body, throughout life.
Produce a limited range of cell types.
Used for growth, repair and renewal of cells in the tissues where they are found.
eg. bone marrow cells can only produce new blood cells.
Therapeutic use of stem cells
Stem cells can be used to repair damaged or diseased organs or tissues by replacing cells.
Stem cells can be removed from embryos/adult tissues and can be cultured (grown) in a lab before being transplanted.
They can be used to produce new skin for skin grafts, and for producing new cells for corneal grafts (onto the eye).
Research use of stem cells
Stem cells can be used to study cell processes, and to study how diseases such as cancer develop.
They can also be used for drug testing.
Potential use of stem cells
How stem cells could be used in the future, eg. to replace damaged cells in organs such as the brain or heart.
Could be used to cure diseases such as heart disease, MS or Parkinson’s disease.
Arguments in favour of the use of stem cells
They could be used to treat many diseases; the embryos used are ‘spare’ after IVF treatment and would be destroyed anyway; they can only be used up to 14 days old, so are not fully formed people.
Arguments against the use of stem cells
Use of embryonic stem cells involves destruction of an embryo, which is a potential human life. Many people object on religious/moral grounds, and argue that it is unnatural.
Specialised cells
Multicellular organisms are made of many specialised cells, which are adapted to carry out a particular function.
Stem cells differentiate and turn into specialised cells.
Examples of specialised cells include red blood cells, guard cells, root hair cells and neurons.
Tissues
Specialised cells which group together to carry out a particular function. eg. muscle tissue is made of specialised muscle cells.
4 main types of human body tissues
Epithelial (lining); connective (eg. tendons); muscle and nerve.
Examples of plant tissues
Palisade and spongy mesophyll, xylem, phloem.
Organs
Structures which are made of different tissues working together to carry out a particular function.
Organs can be made of several different types of tissue eg. the heart = muscle + connective tissue.
Organ systems
Groups of organs that work together to carry out related functions eg. digestive system, nervous system
