Cell Division Flashcards
What happens in G1 phase of interphase?
Growth phase:
- Protein synthesis
- Cell increases in size
- Organelles replicate
What happens in S phase in interphase?
Synthesis phase:
- DNA is replicated in the nucleus
What happens in G2 phase of interphase?
Second growth phase:
- Cell continues to increase in size
- Duplicated DNA is checked for errors
What happens in G0 phase?
The cell leaves the cycle either temporarily or permanently
What happens in the mitotic phase?
- Mitosis (nucleus divides)
- Cytokinesis (cytoplasm divides)
Why might a cell leave the cycle?
- Differentiation: A cell that becomes specialised is no longer able to divide
- The DNA of a cell may be damaged
- As you age, the number of these cells in your body increases: linked to age related diseases such as cancer and arthritis
A few types of cells that enter G0 can be stimulated to go back into the cycle, e.g. lymphocytes in an immune response
What happens at the G1 checkpoint?
End of G1 phase:
- Cell size
- Nutrients
- Growth factors
- DNA damage
What happens at the G2 checkpoint?
End of G2 phase:
- Cell size
- DNA replication
- DNA damage
What happens at the spindle assembly checkpoint?
Point in mitosis:
- Chromosomes attached to spindle
What is mitosis necessary for?
- Growth
- Replacement
- Repair of tissues in multicellular organisms
- Asexual reproduction
What happens in prophase?
- Chromatin fibres coil & condense = chromosomes
- Nucleolus disappears
- Nuclear envelope disappears
- Spindle formation begins
What happens in metaphase?
Chromosomes line up on the equator
What happens in anaphase?
- Centromeres divide
- Chromatids are separated and pulled to opposite poles
What happens in telophase?
- Chromatids have reached poles = chromosomes
- The 2 new sets of chromosomes assemble at each pole
- Nuclear envelope reforms
- Chromosomes uncoil
- Nucleolus is formed
- Cytokinesis begins
Describe cytokinesis in animals
- A cleavage furrow forms around the middle of the cell
- The cell-surface membrane is pulled inwards by the cytoskeleton until close enough to fuse around middle, forming 2 cells
Describe cytokinesis in plants
- Vesicles from Golgi assemble on equator
- Vesicles fuse with each other and membrane, dividing cell into 2
- New cell wall forms along the new sections of membrane
What are alleles?
Different versions of the same gene
What happens in P1 in meiosis?
- Chromosomes condense
- Nucleolus disappears
- Nuclear envelope disappears
- Spindle formation begins
- Homologous chromosomes pair up, forming bivalents
What can occur in P1 that causes genetic variation?
- Crossing over, when bivalents get chromatids entangled and genetic material is transferred between them
What is chiasmata?
The points at which crossing over occurs (chromatids break and rejoin?)
What happens in M1 in meiosis?
- Homologous pairs of chromosomes line up on the equator
What happens in A1 of meiosis?
- Homologous chromosomes are pulled to opposite poles and chromatids stay joined together
- Any potential chiasmata on recombinant chromatids are also pulled apart
What can occur in M1 that causes genetic variation?
- Independent assortment, when the orientation of each homologous pair is random. It can result in many different combinations of alleles facing the poles
What happens in T1 of meiosis?
- Chromosomes assemble at each pole
- Nuclear membrane reforms
- Chromosomes uncoil
- Undergoes cytokinesis
What happens in P2 of meiosis?
- Chromosomes condenses and become visible
- Nuclear envelope breaks down
- Spindle formation begins
What happens in M2 of meiosis?
- Individual chromosomes assemble on equator (like mitosis)
- Independent assortment occurs
What happens in A2 of meiosis?
- Chromatids of individual chromosomes are pulled to opposite poles after division of centromeres (like mitosis)
What happens in T2 of meiosis?
- Chromatids assemble at poles (like mitosis)
- Chromosomes uncoil = chromatin
- Nuclear envelope reforms
- Nucleolus becomes visible
- Cytokinesis = 4 haploid daughter cells, genetically different from each other
Give 3 specialised animal cells
- Erythrocytes
- Neutrophils
- Sperm cells
How are erythrocytes specialised to carry out their function?
- Flattened biconcave shape - increases SA:V ratio
- No nuclei & not many other organelles - increases space available for haemoglobin
- Flexible - squeeze through narrow capillaries
How are neutrophils specialised to carry out their function?
- Multi-lobed nucleus - squeeze through small gaps to get to site of infections
- Granular cytoplasm contains many lysosomes
How are sperm cells specialised to carry out their function?
- Flagellum - movement
- Mitochondria - supply energy needed to swim
- Acrosome on head - contains digestive enzymes that digest protective layers around ovum
Give 3 examples of specialised plant cells
1- Palisade cells
2- Root hair cells
3- Guard cells
How are palisade cells specialised to carry out their function?
- Chloroplasts - absorb large amounts of light for PHS
- Chloroplasts can move within cytoplasm - absorb more light
- Rectangular shape - closely pack together to form a continuous layer
- Thin cell walls - increases rate of diffusion of CO2
- Large vacuole - maintain turgor pressure
How are root hair cells specialised to carry out their function?
- Long extensions (root hairs) - increase SA to maximise uptake of water and minerals from soil
How are guard cells specialised to carry out their function?
- Can open and close depending on whether they lose or gain water
- Cell wall thicker on one side - cell doesn’t change shape symmetrically as its volume changes
Give 4 examples of specialised animal tissues
- Squamous epithelium
- Ciliated epithelium
- Cartilage
- Muscle
How is squamous epithelium specialised to carry out its function?
- Thin - 1 cell thick to allow rapid diffusion
How is ciliated epithelium specialised to carry out its function?
- Cilia - move together to move substances
- Goblet cells - release mucus to trap any unwanted particles present in the air
How is cartilage specialised to carry out its function?
- Contains elastin and collagen
- Prevents ends of bones rubbing together
What is muscle?
A tissue that needs to be able to contract in order to move bones
Give 3 examples of specialised plant tissue
- Epidermis
- Xylem tissue
- Phloem tissue
How is the epidermis specialised to carry out its function?
- Covered by a waxy, waterproof cuticle - reduce water loss
- Stomata present- allow CO2, water vapour and O2 in/out
How is xylem tissue specialised to carry out its function?
- Lignin - structural support
How is phloem tissue specialised to carry out its function?
- Sieve tube cells -perforated end so cytoplasm connects from one cell to the next
What is an organ?
A collection of tissues that are adapted to perform a particular function in an organism
What is an organ system?
Composed of a number of organs working together to carry out a major function in the body
What is differentiation?
The process of a cell becoming specialised
What are stem cells?
Undifferentiated cells that have the potential to becomes a type of specialised cell
What is potency?
A stem cell’s ability to differentiate into different cell types
What is totipotent?
- Can differentiate into any type of cell (embryo)
What is pluripotent?
- Can form all tissue types but not whole organisms
- They are present in early embryos
What is multipotent?
- Can only form a range of cells within a certain type of tissue (adult)
Where are blood cells derived from?
Stem cells in the bone marrow
What are the 2 types of stem cells?
- Embryonic
- Tissue/adult
What are embryonic stem cells?
- Present at a very early stage of embryo development
- Totipotent
- After 7 days, a mass of cells form (blastocyst) and then they are in a pluripotent state
What are adult stem cells?
- Present throughout life from birth
- Found in places like bone marrow
- Multipotent
Where are stem cells found in plants?
Meristematic tissue (meristems)
Where is meristematic tissue found?
Wherever growth is occuring in plants
Give 3 examples of potential stem cell uses
1- Heart disease
2- Type 1 diabetes
3- Spinal injuries
Give 3 ethics points on using stem cells
- Destruction of embryos
- Religious objections
- Moral objections
