Transcript Chromosomes Genes and DNA

Cell Division-measuring growth
• How would you measure growth?
Write your answers on pupil white boards
Cell Division-measuring growth
• Two methods to measure growth are
height and mass.
• Other measurements of growth are
cell length; number of cells; dry mass
• Dry mass is the mass of the organism
after all the water content is removed. It
is found by drying in an incubator until
there is a constant mass.
Measurements of growth
Method
Advantages
Disadvantages
Cell length
Easy to measure under a microscope
Often irregular shape
No reference to number of
cells
Number of cells
Good indication of overall size
Difficult to count them all
Doesn’t take into account the
size of cells
Dry mass
Accurate indication of growth
Time consuming
Organism or part (e.g. leaf) is
killed in process
Questions
• Jane is 20 years old and has had her height and
mass measured at regular intervals over one
year. Suggest why her mass showed greater
variability than her height.
• Suggest why organisms need to be dried until
there is a constant mass.
• Explain why dry mass is likely to be a more
accurate measurement of plant growth than
mass without drying.
Mitosis
• It is important that when cells divide during
growth that the new (daughter) cells
produced have the same genetic make up as
the original (parent) cell- they are clones of
the parent cell.
• This means that they have the same number
and type of genes and chromosomes as the
parent cell.
• This type of cell division is known as mitosis.
 Chromosomes make an identical copy of
themselves before the cell divides.
The copies are called chromatids and are
held together at the centromere.
centromere
chromatid
chromosome
chromosome
Mitosis
Mitosis is the type of cell division used in
1. Growth
2. Replacing worn out cells
3. Repairing damaged tissue.
3. Chromatids in
2. Chromatids line each chromosome
up along the centre separate & are
(equator) of the
pulled to opposite
cell
spindle
ends of thebycell
by
fibres
spindle fibres
1. Each
chromosome
replicates into
2 identical
chromatids
held together
at the centromere
4. Once chromatids reach
the opposite ends the cell
divides in 2
5. The 2 new cells
contain exactly the
same chromosomes as
each other and the
parent cell
Mitosis Hand jive-start at 23
seconds
• You tube hand jive
Asexual Reproduction in
Plants
• This produces genetically identical
offspring.
• Cells from the parent plant reproduce
identical copies of themselves.
• An example is strawberry runners
producing new plants.
• Because the new plants are genetically
identical to the parent they are called
clones.
Propagation of Strawberry Plants
New strawberry plants
developing from buds on
the runner. Each plant is
genetically identical to the
parent.
Parent
plant
The runner provides food reserves that allow
the new plants to become established.
Taking Cuttings
• The use of cuttings is a form of cloning that is
often carried out by gardeners to make larger
numbers of identical plants
Taking Cuttings
Cut a section with
a few leaves
Dip cutting into
compound that
contains hormones
to stimulate root
growth
Place in
compost until
established
Activity
• Take your own plant cuttings from a
geranium plant and pot them up!
• Think about what apparatus you will need
and plan how you will carry this out.
Tissue Culture
• This is a type of cloning that
can be carried out all year
round in a lab.
• It must be carried out by
scientists in sterile
conditions producing disease
free varieties
• This is used to conserve very
rare plants, e.g. orchids
sterilise in dilute bleach
to kill bacteria & fungi
containing
glucose for respiration
N to make amino acids
Control temperature & pH
Advantages of Plant cloning
• Only plants with desirable qualities are
produced.
• It is a quick process producing lots of
plants
Disadvantages of Plant cloning
• The lack of variation means that all
plants may be equally susceptible to
disease or have other weaknesses.
Twitter-see booklet
Cancer
Cancer is produced by
uncontrolled cell division.
Some causes of cancer
• UV radiation- this is produced from the
sun or sunbeds and causes skin cancer.
• Chemicals in cigarette smoke namely TAR
can cause lung cancer.
• Viruses eg Human papilloma virus which
can cause cervical cancer.
Skin Cancer
A cancer causing virus
DNA
Abnormal cells:
•may vary in size
•may have several nuclei
•may be unspecialised in shape and function
•may have irregular, thickened and enlarged
nuclear membranes
•may contain chromosomes that stick
together
Cancer cells
grow in clumps called
TUMOURS
Benign tumours
•Enclosed in a capsule and don’t invade
surrounding tissue
•Remain in one place
•Resemble the tissue from which they arise
Malignant Cancer
Malignant tumour
Lymphatic
vessel
Blood vessel
Malignant cells
Malignant tumours
•Can grow into the surrounding tissue
•Cells may break off from the main tumour
and spread around the body.
•Do not resemble cells around them.
•Are arranged in a haphazard irregular
fashion
The cells of a malignant tumour can be
carried to other parts of the body in the
blood or lymphatic systems
THEREFORE
The cancer can spread and new tumours
can grow in different parts of the body
The importance of detecting cancer
early
• If a cancer is detected early the tumour will
be smaller and will have caused less
damage to the body.
• It is also important to detect a malignant
tumour before it spreads to other parts of
the body.
• Therefore early detection improves survival
rates.
Screening programmes
• These programmes aim to identify the cancer
before it spreads too far.
• These are available to detect breast,
cervical, skin and testicular cancer.
Treating Cancer
• Once cancer has been identified there are a
number of treatment options:
• Surgery-cancer is removed from the body
• Radiotherapy
• Chemotherapy
Meiosis
• Meiosis is another type of cell division
• It occurs in the testes and ovaries to
produce sperm and eggs(gametes).
• The purpose of meiosis is to produce
gametes with half the number of
chromosomes of all the other cells in the
body.
• As meiosis halves the chromosome numbers
in the daughter cells it is also known as
reduction division.
• Most human cells have 46 chromosomes
arranged in 23 pairs.
• Sperm and eggs produced by meiosis have
only 23 chromosomes.
• It is not just any 23 chromosomes from the 46
but one chromosome from each pair that
passes to the sperm or egg.
What are the possible different chromosome combinations?
• It could be either chromosome of a particular
pair that passes into the sperm or egg. So
there are millions of potential chromosome
combinations 223 possibilities.
• This random independent assortment of
chromosomes in meiosis at gamete
formation gives unique gametes helps
produce variation in offspring.
Haploid and diploid
• The chromosome number in the gametes is
termed the haploid number (23 in
humans).
• The normal number in and organism is
termed the diploid number (46 in humans).
• Therefore fertilisation restores the diploid
number in the offspring and combines the
different arrangements of chromosomes
produced during meiosis.
Mrs Monroe’s Hand Signals
• Mitosis and meiosis
Design a Poster to illustrate
differences between mitosis and
meiosis
Tracking test