2.1.6 Cell division, cell diversity and cellular organisation Flashcards
What happens during stage G1 of interphase?
(Growth stage 1)
- Cellular contents (mitochondria, chloroplasts) are duplicated
- Cell increases in size
What happens during stage S of interphase?
(Synthesis stage)
Chromosomes are duplicated in nucleus
What happens during stage G2 of interphase?
(Growth stage 2)
- Cell continues to increase in size
- Energy stores increased
- Chromosomes checked for repairs
What happens during stage G0 of interphase?
(Resting state)
Cell leaves cycle temporarily or permanently
Why does cell enter stage G0 of interphase?
- Differentitation
- Damage to DNA
What are checkpoints in interphase?
Requirements that have to be fulfilled before the next stage can begin
What is checked for in the checkpoints of interphase?
- Cell size
- DNA damage
- DNA replication without error
- Nutrient availablity
- Chromosome attachment to spindle
What are the three checkpoints of interphase?
- G1 checkpoint
- G2 checkpoint
- Spindle assembly checkpoint
How many daughter cells are produced from mitosis?
Two genetically identical diploid cells
How many daughter cells are produced from meiosis?
Four genetically different haploid cells
What is mitosis important for?
- Growth and repair
- Asexual reproduction
In terms of n what are the changes in chromosome number before, during and after for mitosis?
2n -> 4n -> 2n
What type of division is meiosis known as?
Reduction division
What are homologous chromosomes?
Matching sets of chromosomes where each one has the same genes at the same position (loci)
What are alleles?
Different versions of the same gene (located in the same positions)
What happens during meiosis I?
Homologous chromosomes are separated into two different cells
What happens during meiosis II?
Pairs of chromatids in each daughter cell are separated to form four cells in total (similar to mitosis)
When does crossing over occur in meiosis?
Prophase 1
What is crossing over?
Homologous chromosomes pair up and form bivalents (occurs when chromatids entangle)
What is independent assortment?
Orientation of homologous pair at equator is random and independent so different combinations of alleles face the poles
When does independent assortment occur in meiosis?
Metaphase 1 and metaphase 2
What results in genetic variation in meiosis?
Crossing over and independent assortment
What is an organ?
Collection of tissues adapted to perform a particular function
What is an organ system?
Composed of several organs working together to carry out a major function e.g. cardiovascular system
What are stem cells?
Undifferentiated cells with the potential to differentiate into any specialised cell
What are totipotent stem cells?
- Can differentiate into ANY type of cell
- Can produce a whole organism
- E.g. zygote
What are pluripotent stem cells?
- Can form all tissue types
- BUT NOT whole organisms
- Present in early embryos
What are multipotent stem cells?
- Can only form a range of cells within a certain type of tissue tissue
- E.g. stem cells in bone marrow can form different blood cells
Why do erythrocytes and neutrophils need to be constantly replaced?
They have short life spans (red blood cell has no nucleus so cannot multiply)
What are the sources of animal stem cells?
- Embryonic stem cells (totipotent)
- Tissue stem cells: bone marrow and umbilical cord (both multipotent)
When do embryonic stem cells enter the pluripotent stage?
After seven days, when mass of cells (blastocyst) has formed
What is the source of stem cells in plants?
Meristematic tissue (pluripotent)
- Found in the apical meristems (tips of shoots and roots)
- Found in the vascular cambium (these differentiate into cells needed in xylem and phloem)
What are the uses of stem cells?
- Repairing damaged tissue
- Treating neurological conditions e.g. Alzheimer’s and Parkinson’s
In terms of n what are the changes in chromosome number before, during and after for meiosis?
2n -> 4n -> 2n -> n
