2.1.6 - Cell Division and Cellular Organisation Flashcards
What is the cell cycle?
the sequence of events that takes place in a cell for its growth and division
What are the stages of the cell cycle?
Interphase -G1 -Synthesis -G2 Mitotic phase -mitosis -cytokinesis
What happens during the first growth phase (G1) of the cell cycle?
- proteins are produced
- organelles are replicated
- cell size increases
What happens during synthesis in the cell cycle?
the DNA is replicated in the nucleus
What does the G1 checkpoint check for?
- cell damage
- cell size
What happens during the second growth phase (G2) of the cell cycle?
cell continues to increase in size
What does the G2 checkpoint check for?
errors in replicated DNA
What happens in cytokinesis in the cell cycle?
cytoplasm divides in two (to produce two cells)
What is G0?
the phase where a cell leaves the cell cycle
Why might a cell leave the cell cycle (G0)?
- differentiation (cell becomes specialised so no longer needs to divide)
- DNA may be damaged (no longer viable)
- aging
What is mitosis?
nuclear division to produce two genetically identical daughter cells
What is mitosis needed for?
- growth
- tissue repair
- asexual reproduction
What are the stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens during prophase in mitosis?
- chromosomes coil and condense
- nucleus disappears (nuclear envelope disintegrates and nucleolus becomes less prominent)
- centrioles move to opposite sides of the cell and start to produce spindle fibres
What happens during metaphase in mitosis?
-spindle fibres continue to grow and attach to the centromeres of the chromosomes
-chromosomes are moved to line up on the metaphase plate (equator of the cell)
CHECKPOINT -> checks all chromosomes are attached to the spindle
What happens during anaphase in mitosis?
- centromeres divide, causing sister chromatids to separate
- spindle fibres contract (shorten), pulling chromatids to opposite poles of the cell
What happens during telophase in mitosis?
- chromatids reach the poles of the cell
- chromatids uncoil (become longer and thinner)
- nuclear envelope reforms around each group of chromosomes (forming two nuclei)
- nucleolus form
What is meiosis?
cell division where the nucleus divides twice, to produce 4 haploid daughter cells
What is a haploid cell?
a cell containing only a single set of chromosomes (half the normal amount)
-23 chromosomes in humans
What is a somatic cell?
a normal human cell containing 46 chromosomes (23 homologous chromosomes)
-diploid
What is a zygote?
a fertilised egg cell
-two gametes fused
What is a gamete?
a sex cell
- is haploid (has 23 chromosomes)
eg. egg, sperm cell
What is meiosis needed for?
- to produce gametes
- to half the number of chromosomes
- to create variation
How does meiosis create genetic variation?
- crossing over (homologous pairs of chromosomes swap) during prophase 1
- independent assortment (chromosomes from each pair are randomly allotted to daughter cells) in metaphase 1 and 2
What happens during prophase 1 in meiosis?
- chromosomes coil and condense
- nucleus disappears (nuclear envelope disintegrates and nucleolus becomes less prominent)
- homologous chromosomes pair up (forming bivalents)
- centrioles move to opposite sides of the cell and start to produce spindle fibres
- crossing over occurs
What happens during metaphase 1 in meiosis?
- spindle fibres continue to grow and attach to the centromeres of the chromosomes
- homologous pairs are lined up at metaphase plate (equator of the cell)
- independent assortment occurs
What happens during anaphase 1 in meiosis?
- spindle fibres contract
- chromosomes are pulled to poles (not pulled apart -unlike in mitosis)
What happens during telophase 1 in meiosis?
- chromosomes reach the poles of the cell
- chromosomes uncoil (become longer and thinner)
- nuclear envelope reforms around each group of chromosomes (forming two nuclei)
- nucleolus forms
What happens during prophase 2 in meiosis?
- chromosomes re-condense
- nucleus disappears (nuclear envelope disintegrates and nucleolus becomes less prominent)
- spindle fibres reform
- no crossing over occurs (unlike prophase 1)
What happens during metaphase 2 in meiosis?
- spindle fibres continue to grow and attach to the centromeres of the chromosomes
- chromosomes are lined up at metaphase plate (equator of the cell)
- independent assortment occurs again
What happens during anaphase 2 in meiosis?
- centromeres divide, causing sister chromatids to separate (like anaphase in mitosis)
- spindle fibres contract (shorten), pulling chromatids to opposite poles of the cell
What happens during telophase 2 in meiosis?
- chromatids reach the poles of the cell
- chromatids uncoil (become longer and thinner)
- nuclear envelope reforms around each group of chromosomes (forming two nuclei)
- nucleolus forms
What is crossing over?
when homologous pairs of chromosomes swap parts of genetic material
- chromatids twist around eachother and break
- same genes/different alleles get swapped
- occurs during prophase 1 in meiosis
What is independent assortment?
the fact that the position of each bivalent is independent to all the other chromosomes
- maternal/paternal chromosomes can be on either side of the equator
- occurs during metaphase 1 and 2 in meiosis
What is a homologous chromosome?
a matching pair of chromosomes (one from each parent)
What is a bivalent?
a pair of homologous chromosomes
How does cytokinesis happen in animal cells?
- constriction from edges of cell
- cytoskeleton pulls membrane inwards
How does cytokinesis happen in plant cells?
-vesicles line up along centre and fuse to develop a cell plate, which becomes a cell wall
What are erythrocytes, their role and their adaptions?
red blood cells
- transport oxygen around the body
- flattened biconcave shape (increases SA:V)
- no nuclei + few organelles (more space for haemoglobin)
- flexible (can squeeze through narrow capillaries)
What are neutrophils, their role and their adaptions?
type of phagocyte (type of white blood cells)
- engulf and destroy pathogens
- multi-lobed nucleus (can squeeze through gaps to get to infection sites)
- granular cytoplasm containing lysosomes (have enzymes that attack pathogens)
What are sperm cells, their role and their adaptions?
male gametes
- tail/flagellum (used for movement -energy for movement is provided by lots of mitochondria)
- acrosome (on sperm’s head) contains digestive enzymes (used to digest protective layers around the egg to allow fertilisation)
What are palisade cells, their role and their adaptions?
plant cells present in the mesophyll
- chloroplasts (absorb lots of sunlight for photosynthesis)
- regular shape (pack closely together in rows)
- large vacuole (maintains turgor pressure)
What are root hair cells, their role and their adaptions?
cells present on surfaces of roots, near the tips
-long extensions/hairs (increase SA to maximise uptake of minerals and water from the soil
What are guard cells, their role and their adaptions?
found on the surfaces of leaves in pairs, which form small holes called stomata (which allow carbon dioxide to enter plant)
- when they loose water, they become less swollen and change shape (causes stomata to close to prevent water loss)
- cell wall is thicker on one side (cell doesn’t change shape symmetrically when volume changes)
What is the squamous epithelium, its role and its adaptions?
tissue present where rapid diffusion across a surface is essential (eg. lung linings)
- made up of specialised squamous epithelial cells
- very thin (made up of single layer of flat cells -increases rate of diffusion)
What is the ciliated epithelium, its role and its adaptions?
- made up of ciliated epithelial cells which have cilia (hair like structures which move in a rhythmic way)
- goblet cells are also present (release mucus to trap unwanted particles -eg. pathogens, dust, etc)
What is cartilage, its role and its adaptions?
connective tissue found in outer ear, nose, between bones
- prevents bones from rubbing and causing damage
- contains elastin and collagen fibres
- firm and flexible
- made up of chondrocyte cells embedded in a matrix
What is muscle, its role and its adaptions?
tissue that contracts in order to move body parts
-different types of muscle fibres (eg. skeletal fibres -contain myofibrils containing contractile proteins)
What is the epidermis, its role and its adaptions?
tissue covering surfaces of plants made up of closely packed cells
- covered by waxy cuticle (reduces water loss)
- stomata (gaseous exchange)
What is the xylem, its role and its adaptions?
vascular tissue responsible for transporting water and minerals through plants
- made up of vessel elements (elongated dead cells)
- lignin (strengthens walls of dead cells to provide support)
What is the phloem, its role and its adaptions?
vascular tissue responsible for transporting assimilates (organic substances eg. sucrose) throughout a plant
-composed of sieve tube elements separated by sieve plates
What are stem cells?
undifferentiated cells which can differentiate into any specialised cell
What is potency?
the ability that stem cells have to differentiate into different cells
What does totipotent mean?
can differentiate into any cell
What does pluripotent mean?
can differentiate all tissue types (but not a whole organism)
What does multipotent mean?
can only differentiate into a range of cells (within a certain type of tissues)
What sources are there for stem cells?
- embryotic stem cells (toti/pluripotent)
- adult tissue stem cells (multipotent)
- meristem tissue (pluripotent)
What potential uses are there for stem cells?
- repair of damaged tissues
- treatment of neurological conditions (eg. Alzheimer’s and Parkinson’s)
- research into developmental biology.
What are the benefits of being a multicellular organism?
- can make use of resources more efficiently
- cells are adapted to different roles (different shapes/sizes + different organelles)
