2.6 Cell Division Flashcards
What are the three main stages of the cell cycle?
- Interphase
- Mitosis
- Cytokinesis
What are the three stages of interphase?
G1- First growth stage
S- Synthesis phase
G2- Second growth stage
What are the features of G1?
- Cellular contents apart from the chromosomes are duplicated
What are the features of S phase?
Each of the chromosomes is duplicated
What are the features of G2?
- Duplicated chromosomes checked for errors
- Any errors are repaired or replaced
What are the overall features of interphase?
- DNA is replicated and checked for errors
- Protein synthesis
- Mitochondria and chloroplast grow and divide
- Normal metabolic functions occur
What is G0?
- Where a cell moves out of the cell cycle
Why do cells enter G0?
- Differentiation- cell becomes specialised so can no longer divide
- DNA has become damaged- Division may no longer be viable
- Age of organism- Leads to more resting cells which links to age related diseases
What are checkpoints in the cell cycle?
Control the mechanisms of the cell and verify if the processes have been conducted in correctly.
What is vital so that identical daughter cells are produced?
- DNA is replicated correctly
- Chromosomes are in correct position for mitosis
- Cell grows to correct size before it divides
What is mitosis?
Formation of two genetically identical daughter cells from an original cell
How organisms grow
What is the order of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What is a centromere?
The point the chromatids are connected to in a chromosome
What is the difference between a chromatid and a chromosome
A chromatid is one half of a replicated chromosome whereas a chromosome consists of DNA wrapped around proteins.
What happens in prophase?
- Chromosomes: Coil up,shorten, thicken and take up stain more
- Centriole divides
-Nucleolus becomes less obvious then shrinks and disappears - Centrioles migrate to opposite poles
- CROSSING OVER DOES NOT HAPPEN IN MITOSIS
What happens in metaphase?
- Each centrioles is at a pole and produces spindle fibres
- Each centromere is attached to a pole
- Chromosomes are pulled to the equator
What happens in anaphase?
- Spindle fibres contract
- Centromere divides
- Chromatids are pulled to opposite poles
- Each half of the cell receives one chromatid
What happens in telophase?
- Chromatids reach the poles
- Begin to uncoil and become less distinct
- Nuclear envelope starts to reform
- Chromatids now chromosomes again
What happens in cytokinesis in Mitosis?
- Cell divides
- Genetically identical daughter cells
What is a homologous pair of chromosomes?
Pair of chromosomes that have the same genes in the same location
What are sister chromatids?
Chromatids joined by a centromere
What happens in Prophase 1?
Chromosomes condense
Nuclear envelope disintegrates
Spindle fibres begin to form
Homologous chromosomes pair up forming a tetrad
Crossing over occurs
What is crossing over?
Where homologous chromosomes align and cross over at the chiasmata where genetic information is swapped
What happens in Metaphase 1?
- Chromosomes line up on the equator
- Spindle fibres attach to the centromeres
- Independent assortment occur
What is Independent assortment?
- Maternal and paternal chromosomes can be on either side of the equator
- Tetrad position is independent of all chromosomes
What happens in Anaphase 1?
- Homologous chromosomes are pulled by the spindle fibres,one pair to each pole
-They are not pulled apart (still consist of 2 chromatid) - Causes genetic variation
What is Telophase 1?
- Nuclear envelope reforms
- Chromosomes uncoil
- Cell undergoes cytokinesis
- Each cell contains half the original number of chromosomes - Consists of 2 chromatids
What happens in prophase 2?
-Beginning of second division
- Chromosomes recondense
- Nuclear envelope breaks down
- Spindle fibres reform
What happens in Metaphase 2?
Chromosomes are lined up on the equator by the spindle fibres
Independent assortment happens agan
What happens in Anaphase 2?
- Centromeres divide
- Chromatids are split apart by spindle fibres
- Chromatids move to opposite poles of the cells- Chromatids are randomly segregated
What happens in Telophase 2?
- Chromatids uncoil
- Nuclear envelopes reform
- Cell undergoes cytokinesis
How does meiosis cause genetic variation?
- During prophase 1 crossing over occurs
- During metaphase 1 independent assortment leads to a random distribution of maternal and paternal chromosomes
- During metaphase 2 independent assortment happens again
- Random fusion of gametes at fertilisation
What is the definition of a tissue?
A collection of differentiated cells that have specialised functions
What is the definition of an organ?
A collection of tissues adapted for a particular function
What are the adaptations of Erythrocytes?
- Flattened bi-concave shape to increase SA:V
- No nucleus- increases space for haemoglobin
- flexible to fit through capillaries
What adaptations do Neutrophils have?
- Multilobed nucleus to squeeze through small gaps
- Granular cytoplasm with lots of lysosomes
What adaptations do sperm cells have?
- Flagellum makes them capable of movement
- Many mitochondria for energy
- Acrosome contains digestive enzymes to penetrate ovum
What adaptations do palisade cells have?
- Lots of chloroplasts
- Thin cell wall increasing the rate of diffusion of CO2
- Chloroplasts can move within cytoplasm
What adaptations do root hair cells have?
- Long extensions to increase surface area
What adaptations does squamous epithelium have?
- flat cells which make it up- only one cell thick
- Allows for rapid diffusion
What adaptations do ciliated epithelium have?
- CIlia which beat in waves
- Found in trachea and oviducts
- Goblet cells which release mucus
What are the adaptations of cartilage?
- Found in ear,nose and end of bones
- Contains elastin and collagen
What are the features of epidermis?
- Thin layer of cells
- Usually covered by a waxy cuticle
- Allow CO2,O and H20 ro diffuse into or out of the cell
What are the features of xylem?
- Type of vascular tissue
- Composed of vessel elements which are elongated dead cells
- Walls of cells are strengthened by lignin which provides structural support
What are the features of phloem?
- Type of vascular tissue
- Transports a lot of sucrose
- Composed of sieve tube cells seperated by sieve plates
What are stem cells?
Undifferentiated cells
What problems can the division of stem cells cause?
- Not enough division = Cells and tissues arent placed quickly enough
- Too much division-= Tumours
What does Stem cell potency mean?
- The ability to differentiate into different cells
What does totipotent mean?
A stem cell can differentiate into any type of cell (Blastocyst)
What does pluripotent mean?
- Can form all types of tissue but not all organisms (embryo)
What does multipotent mean?
Stem cells can only form certain types of tissue (blood stem cells etc.)
What is the benefit of being multicellular?
- Can make use of resources more efficiently
Why do red blood cells need to be produced regularly?
- Short lifespan
How are tissue stem cells recovered?
- Bone marrow
- Umbilical cords
Where are plant stem cells found?
Wherever growth occurs (usually tips)
What are the main objections to using embryonic stem cells?
- Results in destruction of embryos
- Religious objectyions of interfering wiith life
- Moral objections due to ‘murder’
What are the issues of using stem cells from umbillical cords?
- They are multipotent not pluripotent
