2.1.6 Cell Division, Cell Diversity And Cellular Organisation Flashcards
Describe the cell cycle
Interphase (G1, S, G2)
Mitotic phase (mitosis, cytokinesis)
What processes occur during G1
Proteins that synthesise organelles are produced
Organelles replicate
Cell increases in size
What processes occur during S phase
DNA is replicated in nucleus
What processes occur during G2
Cell increases in size
Energy stores increased
Duplicated DNA checked for errors
What processes occur during mitosis phase of the cell cycle
Nucleus divides
What processes occur during cytokinesis phase of the cell cycle
Cytoplasm divides and 2 cells are produced
Name the checkpoints in the cell cycle
G1 checkpoint
G2 checkpoint
Spindle assembly checkpoint
What is the G1 checkpoint for
End of G1 phase
Checks cell size, nutrients, growth factors, DNA damage
What is the G2 checkpoint for
End of G2 phase
Checks cell size, DNA replication and damage
What’s the spindle assembly checkpoint for
Checks for chromosome attachment to spindles, during mitosis
Mitosis can’t proceed until checkpoint is passed
Order of phases in mitosis
Prophase
Metaphase
Anaphase
Telophase
Describe the events in prophase in mitosis
Chromatin fibres coil and condense to form chromosomes
Nucleolus disappears
Nuclear membrane breaks down
Spindle fibres form linking poles of cell
(Centrioles go to poles of cell in animal cells and some plant cells)
Spindle fibres attach to areas on centromeres and move chromosomes to centre of cells
Describe the events in metaphase in mitosis
Chromosomes moved by spindle fibres to form plane in centre of cell (metaphase plate) and held in position
Describe the events in anaphase in mitosis
Centromeres divide
Sister chromatids separated, pulled to opposite poles of cell by shortening spindle fibres
Describe the events in telophase in mitosis
Chromatids reached the poles, chromosomes
Sets of chromosomes assemble at each pole, nuclear envelope reforms around them
Chromosomes start to uncoil, nucleolus forms
How does cytokinesis occur in animal cells in mitosis
Cleavage furrow forms around middle of cell
Cell-surface membrane pulled inwards by cytoskeleton until close enough to fuse around the middle, forms 2 cells
How does cytokinesis occur in plant cells in mitosis
Cleavage furrow can’t form due to cell walls
Vesicles from Golgi assemble in same place as metaphase plate
Vesicles fuse with eachother and cell-surface membrane, divides cell in 2
New sections of cell wall form along new sections of membrane
Why is mitosis important in life cycles
Necessary when daughter cells have to be identical: growth, replacement, repair of tissues
Necessary for asexual reproduction
What is meiosis I
Reduction division
Pairs of homologous chromosomes separated into 2 cells
Haploid cells created
What is meiosis II
Pairs of chromatids in each cell separated forming 2 cells, 4 haploid daughter cells produced
Describe the events of prophase 1 in meiosis I
Chromosomes condense, nuclear envelope breaks down, nucleolus disappears
Spindle formation begins
Homologous chromosomes pair up, form bivalents
Crossing over occurs
Describe the events of metaphase 1 in meiosis I
Homologous pairs of chromosomes assemble along metaphase plate
Independent assortment of orientation of each homologous pair results in genetic variation
Describe the events of anaphase 1 in meiosis I
Homologous chromosomes pulled to opposite poles, chromatids stay joined together
Sections of DNA on sister chromatids break off and rejoin at chiasmata, genes exchanged between chromatids
Sister chromatids no longer identical, genetic variation arises
Describe the events of telophase 1 in meiosis I
Chromosomes assemble at each pole and nuclear membrane reforms, chromosome uncoil
Cell undergoes cytokinesis and divides into 2 cells, 2 haploid cells created
Describe the events of prophase 2 in meiosis II
Chromosomes condense and become visible
Nuclear envelope breaks down, spindle formation begins
Describe the events of metaphase 2 in meiosis II
Individual chromosomes assemble on metaphase plate
Due to crossing over, chromatids no longer identical, independent assortment of chromatids occurs
Genetic variation occurs
Describe the events of anaphase 2 in meiosis II
Chromatids of individual chromosomes are pulled to opposite poles after division of centromeres
Describe the events of telophase 2 in meiosis II
Chromatids assemble at poles
Chromosomes uncoil, nuclear envelope reforms, nucleolus becomes visible
Cytokinesis results in divisions of cells, 4 daughter cells in total
Haploid due to reductive division
Genetically different
What’s the importance of meiosis in life cycles
Used for sexual reproduction due to haploid cells created, gametes formed
Genetic variation created due to independent assortment and crossing over
How are erythrocytes adapted for their function
Flattened biconcave shape, increases SA:V, essential for transporting oxygen around the body
Enucleated, increases space for haemoglobin which carries oxygen
Flexible to squeeze through narrow capillaries
How are neutrophils adapted for their function
Multi-lobed nucleus, easier to squeeze through small gaps to get to site of infection
Granular cytoplasm contains lots of lysosomes that contain enzymes to attack pathogens
How are sperm cells adapted to their function
Flagellum to provide movement, many mitochondria to supply energy to swim
Acrosome on head of sperm contains digestive enzymes, released to digest protective layers around ovum and allow sperm to penetrate which leads to fertilisation
How are palisade cells adapted to their function
Rectangular shape, can be closely packed to form continuous layer
Thin cell walls, increases rate of diffusion of CO2
Large vacuole to maintain turgor pressure
Chloroplasts can move in cytoplasm to absorb more light
How are root hair cells adapted to their function
Long extensions (root hairs), increase SA of cell, maximises uptake of water and minerals from the soil
How are guard cells adapted to their function
When they lose water and become swollen due to osmotic forces, shape changes and stoma closes to prevent water loss
Cell wall thicker on one side so cell does not change shape symmetrically as volume changes
What is the order of the levels of organisation in multicellular organisms
Specialised cells
Tissues
Organs
Organ systems
Whole organism
Definition of a tissue
Collection of differentiated cells with a specialised function
How is squamous epithelium adapted for its function
Very thin due to flat cells that make it up and because its one cell thick
Used for rapid diffusion (lining of lungs)
How is ciliated epithelium adapted for its function
Hair-like structures called cilia on one surface that move rhythmically
Goblet cells present to release mucus
Lines trachea and causes mucus containing bacteria etc to be swept away from lungs
Function of cartilage
Connective tissue
In outer ear, nose, in between and at ends of bones
Firm but flexible
Prevents bones rubbing together and causing damage
Function of muscle
Tissue that contracts to move bones
Function of xylem tissue
Vascular tissue Responsible for transport of water and minerals throughout plants
Function of phloem tissue
Vascular tissue responsible for transport of organic nutrients (sucrose) from source to sink
Definition of an organ
Collection of tissues adapted to perform a particular function in an organism
Definition of an organ system
Number of organs working together to carry out a major function in the body
What is a stem cell
Undifferentiated cell
What does totipotent mean
Stem cells can differentiate into any type of cell
Eg fertilised egg, zygote
What does pluripotent mean
Stem cells that can form all types of tissue but not whole organisms
Present in early embryo
What does multipotent mean
Stem cells that can only form a range of cells within a type of tissue
List sources of animal stem cells
Embryonic stem cells: very early stage of embryonic development, totipotent, after 7 days the blastocyst forms and the cells are pluripotent until birth
Adult stem cells: from birth, in bone marrow, multipotent
Neutrophils and RBC produced from bone marrow
Plant stem cell source
Present in meristems, found wherever growth is occurring in plants (roots and shoots)
Also found in vascular cambium (between xylem and phloem), cells differentiate into cells present in xylem and phloem tissue
Pluripotent cells
Uses of stem cells in medicine
Potential uses: Repair of damaged tissues (eg following a heart attack); treatment of neurological conditions
Successful uses: treatment of burns; research into developmental biology
