Flashcards in Cell Division, Diversity And Differentiation Deck (58):
In the cell cycle,
M is the ________
G, S are part of the ______
division phase (mitosis/meiosis)
What are checkpoints in the cell cycle for?
prevent uncontrolled division (lead to tumors), repair damage to DNA
What happens in the M phase of the cell cycle?
the checkpoint ensures that the cell is ready for mitosis
cell growth stops and mitosis occurs
What happens in the G₀ (gap 0) phase of the cell cycle?
apoptosis (programmed cell death)
What happens in the G₁ phase of the cell cycle?
growth phase, cell grows
checkpoint ensures ready to enter S phase
transcription of genes to RNA
What happens in the S (synthesis) phase of the cell cycle?
rapid phase (reduces mutation)
genes that are active in all cells replicate first
What happens in the G₂ phase of the cell cycle?
chemicals ensure the cell is ready for mitosis
stimulate proteins which make chromosomes condense to spindle
Mitosis prophase is when...
2 sister chromatids shorten, thicken as DNA coils, nuclear envelope breaks down,
centrioles move to poles,
cytoskeleton protein threads form spindle between centrioles
Mitosis metaphase is when..
chromatids attach to spindle threads in middle and are attached by their centromeres.
Mitosis anaphase is when...
chromatids are pulled apart, the centromere splits,
motor proteins pull chromatids in opposite directions to poles
they are now chromosomes
Mitosis telophase is when...
cytokinesis is when...
chromosomes reach the poles
nuclear envelope forms around the chromosomes
now there are 2 identical nuclei
the cytoplasm splits leading to 2 new daughter cells.
a type of nuclear division that results in the formation of gametes.
one set of chromosomes (23)
2 gamete nuclei fuse = ...
containing same genes, same place
same genes but different alleles (variants)
What happens in the S phase of interphase, in Meiosis?
chromosomes are duplicated as the DNA is replicated
now, each chromosome consists of 2 sister chromatids
in meiosis, chromosomes pair with homologous pair.
Meiosis prophase 1
chromatin condenses, supercoils
nuclear envelope breaks down
microtubules form from centrioles
chromosomes come together in homologous pairs, each member consists of 2 chromatids
crossing over occurs (non-sister chromatids wrap, swap sections, alleles shuffled)
Meiosis metaphase 1
line in middle, attach to spindle thread by centromere
independent assortment occurs (homologous pairs arranged randomly) = determines how pulled apart
Meiosis anaphase 1
pair of homologous chromosomes pulled apart by motor proteins
each chromosome has 2 chromatids
Meiosis telophase 1
nuclear envelope forms
cell divides by cytokinesis
then there's a short interphase when chromosomes uncoil (each chromosomes = 2 chromatids)
Meiosis prophase 2
nuclear envelope breaks down
chromosomes coil and condense
chromatids of each chromosomes are no longer identical
Meiosis metaphase 2
chromosomes attach by centromere to middle of the spindle
chromatids randomly arrange
Meiosis anaphase 2
chromatids pulled apart by motor proteins towards poles
chromatids randomly segregated
Meiosis telophase 2
nuclear envelope forms around each 4 haploid nuclei
2 cells now divide to give 4 haploid cells
How does Meiosis produce variation?
crossing over (prophase 1)
independent assortment (anaphase 1 and 2) or metaphase
random haploid gametes fuse
Why do organisms need specialised cells for particular functions?
Multicellular organisms are large so have a small SA to V ratio. This means that not all cells are in direct contact with the external environment.
undifferentiated cell, stem cell
stem cells become specialised into different types
genes switch on or off so that proportions of organelles differ, the shape of the cell changes, the contents of the cell changes.
How are erythrocytes (RBC) adapted to their function?
large SA:V because they are small (O₂ can diffuse and reach all regions of the cell)
biconcave shape (large SA:V)
flexible (change shape, easily travel through capillaries
organelles lost at differentiation (no nucleus, more space for haemoglobin molecules)
How are neutrophils adapted to their function?
(ingest invading pathogens)
twice the size of RBS
attracted to infection sites by chemotaxis
ingest by phagocytosis
How are spermatozoa adapted to their function?
many mitochondria (aerobic respiration, ATP for undulipodium to move)
small, long, thin (move easily)
enzymes released from acrosome (head) = lysosome (digest covering of ovum and allow entry)
head contains haploid male gamete nucleus and little cytoplasm
How are epithelial cells adapted to their function? (lining tissue in alveoli, capillaries)
squamous epithelial cells (flattened)
many have cilia
How are palisade cells adapted?
long, cylindrical (pack closely)
small spaces between (air circulate)
large vacuole (chloroplasts near top so reduce diffusion distance for CO₂)
many chloroplasts (for photosynthesis)
cytoskeleton threads, motor proteins (move chloroplasts to upper surface
How are guard cells adapted? (in lower epidermis [outer layer of cells covering organism])
light energy used to produce ATP
ATP transports potassium ions to guard cells (lowers water potential so water enters from other cells by osmosis)
cells swell and stoma enlarges
stomata opens to let air enter spaces within layer of cells below palisade
gaseous exchange occurs, CO₂ into palisade (photosynthesis)
O₂ out palisade, out stomata
How are root hair cells adapted? (epidermal cells)
hair-like projections (increases SA to absorb from soil)
mineral ions actively transported into cells (lower water P so water follows)
carrier proteins in plasma membrane (actively transports mineral ions
produce ATP (for active transport)
What are the 4 main animal tissue types?
What are epithelial tissues, their function and structure?
covers and lines surfaces
cells close, continuous sheets
no blood vessels
receive nutrients from diffusion from tissue fluid
short cell cycles
protection, absorption, filtration, excretion, secretion
What are connective tissues for, and structure?
has non-living extra cellular matrix containing proteins and polysaccharides
matrix separates living cells within tissue and enables it to withstand forces like weight
e.g. blood bone, cartilage
________ _____ in cartilage are called _____________
What happens when chondroblasts divide by mitosis?
secrete extracellular matrix
matrix synthesised and chondroblasts becomes mature, less active chondrocytes which maintain the matrix
What are the 3 types of cartilage?
What is Hyaline cartilage?
it forms embryonic skeletons
covers ends of long bones in adults
joins ribs to sternum
trachea (c-shaped rings)
larynx (voice box)
What is Fibrous cartilage?
occurs in discs between vertebrae in the backbone
and knee joint
What is Elastic cartilage?
makes up outer ear (pinna) and epiglottis (flap that closes over larynx when swallow)
Tell me about muscle tissues, Anna.
cells specialised to contract and cause movement
well vascularised (blood vessels)
fibres are elongated
contain myofilaments that allow muscle tissue to contract
3 muscle tissues?
skeletal muscle - packaged by connective tissue sheets, joined to bones by tendons, cause movement
cardiac muscle - walls of heart, allow to beat and pump blood
smooth muscle - walls of intestine, blood vessels, uterus, urinary tracts, propels substances along these tracts
Epidermal plant tissues (equivalent to epithelial in animals)
lack chloroplasts (apart from guard cells)
some contain waxy substance that forms cuticle (in dry environments)
Vascular plant tissues
transport (xylem, phloem)
xylem transports water and minerals from roots to plant
phloem sieve tubes transfer products of photosynthesis from leaves to plant
Meristematic plant tissues
contain stem cells (meristem)
from this tissue, all plant tissues are derived
at root, shoot tips, cambium of vascular bundle (these areas called meristems)
cells in meristems have thin walls, little cellulose, no chloroplasts, not large vacuole, divide by mitosis so differentiate.
What happens when most cells mature?
develop large vacuole, rigid cell wall so can't divide
new cells arise at meristems by mitosis
How do cambium cells differentiate into xylem vessels?
lignin (woody substance) deposits in cell wall to reinforce it and make waterproof, but also kills cells
end of cells break down so xylem forms in columns with wide lumen.
How do cambium cells differentiate into phloem sieve tubes?
lose most organelles, sieve plates develop between them
How do cambium cells differentiate into companion cells?
retain organelles, continue metabolic functions, provide ATP for active loading of sugars into sieve tubes
Nervous system + Endocrine system
nutrition to provide ATP and materials for growth and repair
transport to and from cells
breathing, gaseous exchange
excretion and osmoregulation
protect against pathogens
communication, control and coordination
(skin, hair, nails) waterproof, protection, temp regulating
(skeleton, skeletal muscles) support, protection, move
(lymph nodes and vessels)transports fluids back to circulatory system, resists infection
undifferentiated cell capable of becoming any type
What are 4 sources of stem cells?
embryonic stem cells (formed when zygote begins to divide)
adult stem cells (developed in tissues) (blood, brain, bone) like repair system
induced pluripotent stem cells (iPS cells) (in labs by reprogramming differentiated cells to switch on key genes so become undifferentiated)