Cell Divison Flashcards
what are the phases of the cell cycle
interphase, M phase and cytokinesis
describe the processes occuring in interphase
G1 phase- cell grows and new organelles and proteins are made
G1 checkpoint- cell checks chemicals needed for replication are present and check for any DNA damage
S phase- cell replicates its DNA ready to divide
G2 phase- cell keeps growing and proteins needed for cell division are made
G2 checkpoint- cell undergoes apoptosis if DNA has been damaged but if not cell undergoes mitosis
what is the structure of chromosomes in mitosis
chromosomes made up of two strands joined by a centromere, separate strands are called chromatids, called sister chromatids if two strands on the same chromosome
what are the four stages of mitosis
prophase, metaphase, anaphase, telophase
describe what happens during prophase
chromosomes condense, centrioles move to opposite end of cell forming the spindle, nuclear enveloped breaks down
describe what happens during metaphase
chromosomes line up in the middle of the cell and become attached to spindle by centromere
describe what happens during anaphase
centromeres divide, separating each pair of sister chromatids, spindles contract and pull chromatids to opposite ends of the cell
describe what happens during telophase
chromatids reach opposite poles on the spindle, uncoil and become long and thin, called chromosomes again, nuclear envelope forms around each new group of chromosomes, two nuclei present
describe what happens during cytokinesis
cytoplasm divides, cleavage furrow forms, two daughter cells produced which are genetically identical to each other
why is mitosis necessary for organisms
allows growth and repair, some organisms reproduce asexually
what are zygotes
two gametes joined together through fertilisation
what is a diploid cell
cell containing two of each chromosome (one from mum and one from dad)
what are pairs of matching chromosomes called
homologous chromosomes
what type of cells are haploid cells
gametes (only one copy of each chromosome)
what is meiosis
type of cell division that occurs in reproductive organs to produce gametes, produce genetically different cells because each new cell ends up with a different combination of chromosomes
what occurs during prophase 1 of meiosis
chromosomes condense, homologous chromosomes pair up, crossing over occurs, centrioles move to opposite ends of the cell forming spindle fibre, nuclear envelope breaks down
what occurs during metaphase 1 of meiosis
homologous pairs line up across the centre of the cell and attach to spindle fibres by their centromeres
what occurs during anaphase 1 of meiosis
spindles contract, pulling pairs apart so one chromosome goes to each end of the cell
what occurs during telophase 1 of meiosis
nuclear envelope forms around each group of chromosomes, cytokinesis occurs and two haploid cells are produced
what occurs during meiosis 2
same as meiosis 1 but with half the number of chromosomes, in anaphase 2 sister chromatids are separated, each new daughter cell inherits one chromatid from each chromosome, four haploid cells are produced
how does crossing over cause genetic variation
during prophase 1 homologous pairs of chromosomes pair up, chromatids twist around each other and bits of the chromatid switch over, causing a different combination of alleles but same genes
how does independent assortment cause genetic variation
when homologous pairs are lined up in metaphase 1 and then separated in anaphase 1 its completely random which chromosome from each pair end up in which daughter cell
what are stem cells
unspecialised cells which can develop into any type of cell
what type of disease could be treated with stem cells
type 1 diabetes, alzeiheimers, parkinson’s and heart disease
how are erythrocytes specialised
biconcave shape provides large surface area for gas exchange, no nucleus so more room for haemoglobin
how are neutrophils specialised
flexible shape allowing them to engulf foreign particles, many lysosomes containing digestive enzymes to breakdown pathogens
epithelial cells
ciliated epithelia have cilia to beat particles awa, others have microvilli which increase surface area
squamous epithelia are very thin to allow efficient diffusion of gases
how are sperm cells specialised
have a flagellum so they can swim to the egg, lots of mitochondria to provide energy to swim, acrosome contains digestive enzymes to enable the sperm to penetrate the surface of the egg
how are palisade mesophyll cells specialised
contain many chloroplasts, walls are thin so CO2 can diffuse easily into the cell
how are root hair cells specialised
have a large surface area, permeable cell wall, cytoplasm contains lots of mitochondria for active transport
how are guard cells specialised
in light take up water to become turgid, their thin outer walls and thickened inner walls forced them to bend outwards opening the stomata
define the term tissue
group of cells that are specialised to work together to carry out a particular function
how is squamous epithelial tissue specialised and where it is found
thin exchange surface for diffusion, found in many places including alveoli in the lungs
where is ciliated epithelium found
found on surfaces where things need to be used like the trachea where cilia wave mucus along
what are the three types of muscle tissue and what is its basic structure
bundles of elongated cells called muscle fibres
smooth, cardiac and skeletal
describe cartilage
type of connection time tissue, formed when cells called chrondoblasts secrete extracellular matrix
describe the role and basic structure of xylem tissue
transports water and supports the plant, contains hollow xylem vessels made up of which are dead
describe the structure and role of phloem tissue
transports sugar around the plant, arranged in tubes made up of sieve cells and companion cells and some ordinary plant cells
define the term organ
a group of different tissues that work together to perform a particular function
give two examples of organs, one for plants and one for animals
lungs and leaf
erythrocytes and and neutrophils are derived from stem cells from where
bone marrow
xylem and phloem are produced from stem cells found where
meristems
