2.1.6 Cell division, cell diversity and cellular organisation COMPLETE Flashcards
Structure of a chromosome
- Tips are the Telomere
- Centre held together by a centromere
- Protein is wound around histones
The cell cycle order
- Interphase
- Prophase
- Metaphase
- Anaphase
- Telophase
Proper meteors always telephone
Interphase
Mitosis
DNA is uncoiled and not visible
DNA replication occurs
Cell size increases so more cytoplasm, organelles and chloroplast
Prophase
Mitosis
Chromosomes becomes visible as they shorten and thicken.
Centrioles move towards the opposite poles
Microtubules develop
Nuclear envelope breakdown
Metaphase
Mitosis
Chromosomes line up at the equator
centrioles reach the two poles
Spindle fibres attach to the centromeres and pulls to arrange them
Anaphase
Mitosis
Chromatids pull apart to opposite ends of the cell
The centromeres divide and spindle fibres contract and shorten to pull them apart
Centromere leads
Telophase
Mitosis
Nuclear envelope reforms around chromosomes as the chromatids have now reached the poles.
The nucleus reappears and the chromosomes uncoil to form chromatin
Cytokinesis
Cytoplasm divides into two each containing a full set of chromosomes
ANIMALS: Furrows a cleavage by starting at the edge
PLANT: Forms a cell plate and starts from the middle
Importance of Mitosis
- Asexual reproduction
- Growth of multicellular organisms
- Repair to replace damaged cells
- Replace the blood cells broken down in the liver
Purpose of Checkpoints
- Prevent uncontrolled division
- Detect and repair damage to DNA
- Ensure cycle doesn’t reverse
- DNA only copied once
G2 Checkpoint
Checks cell size, DNA replication and that theres no damage
G1 Checkpoint
Checks cell size, Nutrients, Growth factors, DNA damage
G0 Checkpoint
Resting phase where cells leave permanently or temporarily
Cell differentiation to specialise them
Check for DNA damage
Lymphocytes can start dividing again and re enter cycle
Mitosis in Plants
Takes place in the meristem regions, just behind the root tips and shoot tips, the cambium and in the buds.
No centrioles present just the cell plate
Mitosis in Yeast Cells
Known as Budding
The nucleus divides by mitosis and the cell swells on one side creating an uneven distribution of cytoplasm.
The cell wall forms and so do two genetically identical cells
Mitosis in Prokaryote Cells
Known as binary fission
The cell grows to its limit then DNA begins to replicate
The two loops of DNA are pulled to opposite ends of the cell
This divides into two cells and a new wall forms
Stem Cells
Undifferentiated Cells that can differentiate into specialised ones
Totipotent Cell
Has the potential to develop into any type of cell found in the human body
Pluripotent Cell
Stem cells that develop the 3 primary germ layers
Multipotent cells
Thy can develop into more than one cell type, limited to adult stem cells and cord blood cells
Sources of animal stem cells
Embryonic Stem Cells
Adult Stem Cells
Uses of Stem Cells
- Cellular Medicines such as diabetes treatment
- To understand how our bodies work
- Test drug efficiency
- Therapies to replace damaged cells
Differentiation
Cells become specialised to perform a particular function.
Erythrocytes
Produced in the bone marrow
Only contain haemoglobin
Have a biconcave disk shape
Neutrophils
Destroy bacteria and other foreign materials by phagocytosis.
Produced in bone marrow
Contain lots of lysosomes
Squamous Epithelial Cells
Thin flat cells that lie inside blood vessels to reduce friction
Ciliated Epithelium Cells
Column Shaped with lots of cilia and mitochondria
Found in the trachea, bronchi, bronchioles
Sperm Cells
Small long thin shape with a flagellum containing microtubules for movement
Mitochondria for energy
Acrosome on the tip specialised to breakdown the outside of an egg.
Palisade Cells
Long thin walls
Contains lots chloroplasts for photosynthesis
Root hair cells
Hair line projection with thin cell walls
Found near the tips of roots
Increases the SA
Aids the absorption of water and minerals
Guard Cells
Contain chloroplasts and open during the day to let CO2 into the leaves
DEFINITION- Tissues
Collection of Cells specialised to work together to perform a particular function
DEFINITION- Organs
Collection of tissues working together to perform a particular function
DEFINITION- Organ System
Organs working together to perform a life function
Examples of Tissues
Cartilage
Muscle
Xylem
Phloem
Leaf Structure
- Cuticle
- Upper Epidermis
- Palisade Mesophyll layer
- Spongy Mesophyll Layer
- Stroma
- Guard Cells
- Vascular bundle
Prophase I Early
Meiosis
Chromosomes condense, supercoil and become visible
The nucleus disappears and the envelope breakdown
Centrioles migrate to the poles and form spindle fibres
Prophase I Late
Meiosis
Homologous chromosome pairs form bivalent pairs
Recombination occurs and chromosomes are crossed over at points called the chiasmata
Metaphase I
Meiosis
The bivalents randomly line up at the equator
Independent Assortment takes place
Spindle fibres attach onto the centromeres
Anaphase I
Meiosis
The homologous chromosomes are pulled apart by spindle fibres.
The chiasmata are pulled apart as they separate
Centromeres do not divide
Telophase I
Meiosis
In animal cells the nuclear envelope reforms
Cytokinesis may occur and the cell might split
Prophase II
Meiosis
Chromosomes re condense, each consisting of two nucleotides
Nuclear envelope goes
Centrioles replicate and spindle fibres develop perpendicular to the last ones
Metaphase II
Meiosis
Chromosomes randomly line up at the equator and theres independent assortment of the chromatids
Spindle fibres attach to the centromere
Anaphase II
Meiosis
Chromosomes are pulled apart by spindle fibres
Centromere divides to allow chromosome to split
Pulled to the poles
Telophase II
Meiosis
Chromatids reach the poles and re condenses
The nuclear envelope reforms forming a separate nuclei
Cytokinesis
Meiosis
Cytoplasm splits forming four non identical daughter cells with half of each parent cell
1 diploid -> 1 Haploid
Causes of Variation
Crossing Over
Independent Assortment
Random Fertilisation
Mutation
Crossing over
Occurs in prophase 1
Alleles are switched at the chiasmata producing q different combination for each chromatid
Independent Assortment
Metaphase 1
Bivalents randomly line up so paternal and maternal are jumbled. This means a combination of both chromosomes could be in the gamete produced,
Metaphase 2
Chromatids orientate randomly so after crossing over they’re not identical
Random Fertilisation
Any one of the 300 million of the genetically different sperm could fertilise the egg
Mutation
During Interphase when DNA is replicated, mutation may occur
