Flashcards - Topic 2 Cell division and growth - Edexcel Biology GCSE
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
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
25 = 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
What can doctors determine from percentile charts? (3)
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 than in younger animals as growth stops 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? (2)
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
