Cell Division Flashcards
What are the two main phases of eukaryotic cell cycle?
Interphase
Mitotic Phase
What 5 things are occurring during interphase?
1) DNA replicated and checked for errors in nucleus
2) Protein synthesis occurs in cytoplasm
3) Mitochondria grow and divide, increasing no. in cytoplasm
4) Chloroplasts grow and divide
5) Normal metabolic processes of cells occur
What are the 3 stages of interphase?
G1, S, G2
What happens in G1?
Organelles are replicating
Proteins being synthesised
Cell increases in size
What happens in S?
Synthesis phase- DNA is replicated in nucleus
What happens in G2?
Cell continues to increase in size
Energy stores are increased
Duplicated DNA is checked for errors
What are the 2 parts of the mitotic phase?
Mitosis- nucleus divides
Cytokinesis- the cytoplasm divides and two cells are produced
What is G0?
The phase of the cell cycle where a cell leaves the cycle either temporarily or permanently
What are main 3 reasons a cell leaves the cell cycle?
Differentiation
DNA or cell damage
Old age
What is the role of checkpoints in the cell cycle?
Control mechanisms of cell cycle. They monitor and verify whether the process has accurately occured
When does the G1 checkpoint occur? What does it check for?
End of G1 before S
Checks for: cell size, nutrients, growth factors, DNA damage
When does the G2 checkpoint occur? What does it check for?
End of G2 before mitosis
Checks for: cell size, DNA replication, DNA damage
When does spindle assembly checkpoint occur?
At the point in mitosis when all the chromosomes should be attached to spindles and been aligned
Why is mitosis important?
Growth of tissues
Replacement of damaged cells
Asexual Reproduction
Why do prokaryotic cells not divide by mitosis?
Don’t have a membrane bound nucleus or spindle fibres so divide by binary fission instead
Before mitosis occurs, DNA is replicated, how is this then arranged?
DNA replicated
2 identical sister chromatids joined by centromere
What is chromatin and what is its role?
Chromatin is a complex of DNA and histones
Helps to package DNA in a compact way that can fit inside the nucleus
What 5 things occur during prophase in mitosis?
1) Chromosomes coil and condense
2) Nucleolus disappears
3) Nuclear membrane starts to break down
4) Protein microtubules form the spindle
5) Centrioles migrate to opposite poles of the cell
What 2 things occur in metaphase in mitosis?
1) Chromosomes are moved by spindle fibres to the equator of the cell
2) Chromosomes line up on the metaphase plate
What 3 things occur in anaphase in mitosis?
1) Centromeres divide
2) Spindle fibres shorten
3) Sister chromatids are separated and pulled to opposite poles
What 4 things occur in telophase in mitosis?
1) Chromosomes reach poles
2) Nuclear envelope forms around each set of chromosomes
3) Chromosomes uncoil
4) Nucleolus reforms
What is cytokinesis?
The division of the cytoplasm to produce two new cells
Explain process of cytokinesis in animals
The cell-surface membrane is pulled inwards
Cleavage furrow formed
Cytoskeleton (actin filaments) pull close enough until fuses around the middle
Explain process of cytokinesis in plants
Vesicles travel along and assemble in the same place as metaphase plate
Vesicles fuse to each other and the cell membrane
Divides cell membrane in two
Cellulose is laid down between the new cell membrane to maintain shape
Give 3 adaptations of erythrocytes and explain how this helps them
Flattened Biconcave Shape- gives larger surface area to volume ratio
Don’t have nuclei- Space for other organelles and haemoglobin
Flexible- pass through narrow capillaries
Give 2 adaptations as neutrophils(white blood cell) and explain the role of these
Multi-lobed nucleus so can squeeze through small gaps to get to site of infection
Granular cytoplasm- contains lysosomes with enzymes to attack pathogens
Give 3 adaptations of sperm cells and explain the role of these
Flagella- for movement
Many mitochondria- provides energy for swimming
Acrosome- contains digestive enzymes to digest protective layer of the ovum, so egg can be fertilised
Give 5 adaptations of palisade cells and explain the role of these
Lots of chloroplasts- absorb large amounts of light
Rectangular box shape- packed tightly in a continuous layer
Thin walls-increase rate of diffusion of CO2
Large vacuole- maintain turgor pressure
Chloroplasts can move- absorb more light
Give an adaptation of a root hair cell and explain the role of this
Large long extensions which increases surface area of cell, maximising uptake of water and minerals from soil
Give 2 adaptations of guard cells/stoma and explain the role of these
Guard cells change shape and stoma close- to prevent further water loss from the plant
Cell wall of guard cell thicker on one side- doesn’t change shape symmetrically as volume changes
Define ‘tissue’
Tissue is made up of differentiated cells that have a specialised function or functions.
What are the 4 main categories of tissue in animals?
Nervous tissue
Epithelial tissue
Muscle tissue
Connective tissue
What are the adaptations of each of the 4 main categories of tissue?
Nervous tissue- support transmission of electrical impulses
Epithelial tissue- cover body surfaces
Muscle tissue- adapted to contract
Connective tissue- adapted to hold tissues together
Give an adaptation of squamous epithelium. Give an example of where it is present.
Thin- due to being one cell thick- allows for rapid diffusion
In lining of lungs
Give two adaptations of ciliated epithelium. Give an example of where it is present.
Cilia present which sweep mucus away
Goblet cells also present, releasing mucus to trap pathogens
Present in trachea
What is cartilage adapted to prevent?
Prevents ends of bones from rubbing together and causing damage.
What is muscle tissue adapted to do?
Shorten and lengthen in order to move bones
What are 2 main tissues in plants? Give their main adaptation
Epidermis Tissue- adapted to cover plant surfaces
Vascular tissue- adapted for transport of water and nutrients
How is the epidermis of plant adapted for its function? (3 ways)
Single layer of closely packed cells covering the surfaces of plants
Covered in waterproof, waxy cuticle to reduce water loss
Stomata present in epidermis
How is the xylem tissue adapted for function, structurally?
Walls are strengthened by lignin which provides structural support for plants
Define ‘organ’
A collection of tissues that are adapted to perform a particular function in an organism
Define ‘organ system’
Each organ system working together in a coordinated manner to carry out major function.
What is the mitotic index a measure of?
A quantitative expression of the amount of cell division happening within a tissue
What is the equation for the mitotic index?
MI= number of cells with condensed chromosomes/ total number of cells x 100
Define diploid
Normal chromosome number, two chromosomes of each type one inherited from each parent
How many daughter cells does meiosis form?
4
Define haploid
Half of the chromosome number of parent cell
What type of division is meiosis?
Reduction Division
Define ‘homologous chromosomes’
Matching pair of chromosomes, one inherited from each parent.
What is an allele?
Different version of same gene
What occurs during Meiosis 1?
Reduction division, the homologous chromosomes are separated into two cells. Each intermediate cells contains only one full set of genes.
What occurs during Meiosis 2?
Similar to mitosis, pairs of chromatids are separated forming two more daughter cells. 4 haploid cells produced in total.
What 5 things occur during Prophase 1?
Chromosomes condense Nuclear envelope breaks down Nucleolus disappears Homologous chromosomes pair up (bivalents) Crossing over occurs- causing variation
What occurs during Metaphase 1?
Homologous pairs of chromosomes line up randomly along metaphase plate
The maternal or paternal chromosomes end up facing each pole- Independent Assortment
What occurs during Anaphase 1?
Spindle fibres form an attach to centromere
Crossing over that occurred in prophase, break off and rejoin and fuse. The fuse is called chiasmata.
Sister chromatids no longer identical
What 4 things occur during Telophase 1?
Chromosomes assemble at each pole
Chromosomes uncoil
Cell undergoes cytokinesis
Reduction in chromosomes from diploid to haploid
What 3 things occur during Prophase 2?
Chromosomes condense and become visible again
Nuclear envelope breaks down
Spindle fibres form
What happens during Metaphase 2?
Chromosomes assemble on metaphase plate
Due to crossing over there is more independent assortment, and so more genetic variation
What occurs during Anaphase 2?
Chromatids are pulled to the poles of the cell
What occurs during Telophase 2?
Chromatids assemble at poles Chromosomes uncoil and chromatin forms again Nuclear envelope forms Nucleolus forms Cytokinesis forms 4 daughter cells
What are stem cells?
Undifferentiated cells
What 3 things are stem cells necessary for?
Growth, Development, Tissue Repair
What is ‘potency’?
A stem cell’s ability to differentiate into different cell types
Define a ‘totipotent cell’. Give examples.
Stem cells that can differentiate into any cell type
Fertilised egg, zygote, cell in first few mitotic divisions
Define a ‘pluripotent cell’. Give examples.
Stem cells that can form all tissue types but not whole organisms.
Early embryos
Define a ‘multipotent cell’. Give examples.
Stems cells that can form a range of cells within a certain type of tissues
Haematopoietic cells in bone marrow
Where are all blood cells derived from?
Bone marrow
When does an embryo go from totipotent to pluripotenet?
At about 7 days when a mass of cells called blastocyst has formed
What are the advantages of harvesting stem cells from umbilical cords?
Plentiful supply
Invasive surgery not required
What are the sources of animal stem cells?
Embryonic stem cells
Tissue stem cells
What are the sources of plant stem cells?
Meristematic tissue found in all growing areas of pants
Give 7 areas of medicine where stems cells have the possibility to treat disease
Heart disease Type 1 diabetes Parkinson's disease Alzheimer's disease Macular Degeneration Birth defects Spinal injuries
Give 3 areas of science where stem cells are already used
Treatment of burns
Drug trials
Developmental biology
Why are there ethical issues surrounding stem cells?
Embryos are destroyed in process
People see it as murder
Religious views
