Cell Division and Growth Flashcards
What is the cell cycle?
● A series of events that take place in a cell
involving cell growth, DNA replication and
cell division
● It is described as the lifecycle of a cell
State the three stages of the cell cycle
Stage 1 - interphase
Stage 2 - mitosis
Stage 3 - cytokinesis
What is interphase?
The longest stage of the cell cycle that
involves cell growth, the synthesis of
new organelles and DNA replication
What does DNA replication involve?
● Double helix ‘unzips’ exposing two strands
● DNA bases align next to complementary bases on
the DNA strands
● Complementary base pairs join
● Two identical DNA molecules formed
What is a chromosome?
A linear DNA molecule tightly coiled
around proteins
What happens to chromosomes during DNA
replication?
The DNA in the ‘arm’ of each
chromosome (chromatid) is
replicated.
What is mitosis?
A form of cell division that produces two
diploid ‘daughter’ cells, both genetically
identical to the parent cell
Why is mitosis important in organisms?
● Asexual reproduction
● Growth
● Repair of damaged cells
● Cell replacement
State the four stages of mitosis
● Prophase
● Metaphase
● Anaphase
● Telophase
Outline prophase
● DNA condenses, chromosomes become visible
● Nuclear membrane disappears
-spindle fibres form
Outline metaphase
● Chromosomes line up along the cell equator
Outline anaphase
● Spindle fibres attach to each chromosome
● ‘Arms’ of each chromosome pulled to opposite poles
● Chromatids separated
Outline telophase
● Nucleus of the cell divides
● New membrane forms around each set of
chromosomes
What does cytokinesis involve?
● Division of the cell membrane and cytoplasm
● Two genetically identical ‘daughter’ cells
produced
A cell divides by mitosis once every 2 minutes.
Calculate the number of identical cells present after
10 minutes
10 ÷ 2 = 5
5 cell divisions have taken place
2^5 = 32 cells
What is cancer?
● Non-communicable disease
● Uncontrolled cell division (due to damaged DNA) results
in the formation of a primary tumour
● Tumour cells break off and spread to other tissues
forming secondary tumours
What are percentile charts?
● A chart used to monitor growth
● Measurements (e.g. fetal length or head
circumference) can be compared to the expected
values at a certain age
What does the 95th percentile mean?
95% of measurements will be below the
value of the 95th percentile
How do percentile charts demonstrate how you are growing?
● Slower growth than normal (below the bottom line)
● Faster growth than normal (above the top line)
● Abnormal growth (irregular growth patterns)
Describe growth in animals
● Cell division occurs in all body cells.
● It occurs at a slower rate in adults that in younger animals as growth stops in adulthood and cell division is only required for replacement and repair.
● Most cells differentiate at an early stage and become
specialised.
● Some adult stem cells retain their ability to differentiate.
Describe growth in plants
● Cell division can only occur in meristematic tissue.
● The rate of cell division remains the same throughout a plant’s life.
● Meristematic stem cells can differentiate into any cell type for as long as the plant lives
● Cell elongation occurs in all cells. Cells expand and enlarge enabling growth of the plant.
What are stem cells?
Cells that are unspecialised and capable
of differentiating into a range of different
cell types
What is meant by ‘differentiation’?
● The process by which stem cells become
specialised (have a specific function)
● Some genes switch on or off, determining cell
type
Why is cell differentiation important?
It enables the formation of specialised
tissues with specific functions e.g.
muscle tissue.
What are embryonic stem cells?
Stem cells found in very early embryos
that are unspecialised and capable of
differentiating into any cell type
What is the function of embryonic stem cells?
Enable the growth and development of
tissues in human embryos
What are adult stem cells?
Stem cells that can differentiate into a
limited range of cell types e.g. bone
marrow stem cells
What is the primary function of adult stem cells?
Replacement of dead cells e.g.
replacement of red blood cells which
only live for 120 days
Where are stem cells found in plants?
Meristems
Where is meristem tissue found?
In regions of the plant where cells are
continuously dividing e.g. root tips, shoot
tips
What are meristematic stem cells?
Stem cells found in meristems that are
unspecialised and capable of
differentiating into any cell type during
the life of a plant
How can stem cells be used in medicine?
● Stem cells collected
● Stem cells stimulated to differentiate into specific
cell types e.g. heart muscle cells
● Specialised cells transplanted into the patient
● Used to treat damage or disease e.g. heart disease
Where can embryonic stem cells be collected from?
2
● Donor stem cells removed from embryos
grown in vitro
● Patient’s own stem cells removed from the
umbilical blood before birth
What are the benefits of using stem cells in
medicine? (4)
● Treat damage or disease e.g. heart disease, type 1 diabetes
● Treat diseases that would otherwise be untreatable
● Used in scientific research
● Growing organs for transplants
What are the risks of stem cell use in medicine? (6)
● Transplanted stem cells could cause tumours
● Finding suitable stem cell donors is a difficult task
● Stem cells may be rejected by the body (immunosuppressants taken)
● Potential side effects
● Long term risks of using stem cells unknown
● Stem cells may become contaminated during preparation and when
transplanted transmit infections to the patient, making them sicker
What are the ethical issues related to the use of
stem cells in medicine?
● The embryos that were used to provide stem cells
are destroyed which is seen as unethical and a
waste of potential human life
● May lead to the reproductive cloning of humans
