2.1.6 Diversity Flashcards
Describe the role of mitosis in fragmentation
- produces many cells
- cells are genetically identical
What does the cell cycle consist of?
G1, S phase, G2, Mitosis, cytokinesis
What processes take place during G1?
cells grow and increase in size
organelles replicate
protein synthesis
What is the role of the G1 checkpoint?
Cell size?
DNA damage?
What processes take place in S phase?
DNA replicates (each chromosome contains 2 sister chromatids)
rapid phase
What processes take place in G2?
cells grow once again
synthesis of proteins to be used in mitosis
What is the role of the G2 checkpoint?
DNA replication error?
damage is tried to be repaired
What occurs in mitosis?
nuclear division
prophase, metaphase, anaphase, telophase
What is the role of the metaphase checkpoint?
ensures spindle fibre is formed and chromosomes are split properly, to make sure each cell gets an even number of chromosomes.
What is cytokinesis?
cytoplasm splits
What are the positive and negative regulators?
negative: p53 tumour suppressor gene involved in initiating apoptosis (cell death)
positive: CDK, cyclin, allow cells to move forward
What occurs in G0?
cell leaves cell cycle, not preparing to divide
either because of cell differentiation, DNA damage (apoptosis), or senescent cells (maximum number of divisions)
some cells e.g epithelial cells don’t have this phase, and some cells e.g. neurones remain here forever or a very long time
What are 3 reasons for why mitosis is important?
asexual reproduction: amoeba, some plants do by forming new plantlets on ends of stolons; fungi such as yeastsby budding; aphids may produce eggs.
growth: producing more cells that are genetically identical to eachother
tissue repair: growth factors secreted by platelets, white blood cells + damaged blood vessel walls = stimulate smooth muscle and endothelial cells to repair damaged blood vessels
What happens in prophase?
chromatin condenses into chromosomes and they shortern and thicken as DNA supercoils -become visible
nuclear envelope breaks down
centriole divides and move to opposite poles of the cell
spindle fibres form
in plants, these are formed from the cytoplasm
What happens in metaphase?
pairs of chromatids (chromosomes) attach to spindle fibres at equator region, attached by their centromeres
chromatids on either side of the mitotic plate
What happens in anaphase?
centromere of each pair of chromatids (each chromosome) splits
spindle fibres shorten and motor proteins pull chromatids to opp poles and turn into V shape
What happens in telophase?
separated chromosomes reach poles
new nuclear envelope forms around each set of chromosomes
Chromosomes unwind into chromatin
Spindle fibres disappear.
What happens in cytokinesis? (mitosis)
Animal cells: plasma membrane folds inwards and ‘nips in’ the cytoplasm to form membrane down the middle until it splits into two new cells. Microfilaments pull in surface membrane creating a furrow.
plant cells: end plate forms + new plasma membrane +cellulose material are laid down on either side along this end plate
What is the end result of mitosis?
two new daughter cells are formed. they are genetically identical to each other and to parent cell (parent cell before interphase)
What is chromatin?
*A complex of nucleic acids (e.g. DNA or RNA) and proteins (e.g. histones), which condenses to form a chromosome during cell division
What are chromosomes?
*A condensed structure of the DNA double helix
What is chromatid?
a chromosome that has been replicated to form two identical halves, in preparation for cell division.
What is a centriole?
bundle of microtubules that form the spindle fibres
What is a centrosome?
Area of cytoplasm where centriole is
What is a centromere?
The region on the chromatids which attach to the spindle fibre
What is the significance of meiosis in life cycles?
inc genetic variation -> increases chance of survival when environment changes as some will be better adapted than others
occurs in diploid germ cells to produce haploid gametes (maintains chromosome number by halving no. of chromosomes in gametes)
What are homologous chromosomes?
a pair of matching chromosomes, one maternal and one paternal, containing the same genes at the same loci.
What happens before meiosis?
each chromosome duplicated as DNA replicated, so each chromosome now has 2 sister chromatids.
What happens in prophase I in meiosis?
chromatin condenses into chromosomes and each one supercoils.
nuclear envelope breaks down
spindle threads of tubulin protein form from centriole in animal cells
chromosomes come together in their homologous pairs
crossing over- non sister chromatids wrap around eachother and may swap sections so alleles are shuffled.
What happens in metaphase 1 of meiosis?
pairs of homologous chromosomes attach along equator of spindle, each by their centromere.
pairs arranged randomly (i.e. its random which member of each pair faces which pole = INDEPENDENT ASSORTMENT -> determines how they’ll segregate in anaphase
What happens in anaphase 1?
members of each pair are pulled apart by motor proteins that drag them along the tubulin threads of the spindle
centromeres don’t divide
results in chromosomes have swapped areas + allele shuffling
What happens in telophase 1?
most animal cells: 2 new nuclear envelopes around each set of chromosomes, then divides by cytokinesis
plant: anaphase 1 -> prophase 2
half number of chromosomes each with 2 chromatids
What happens in prophase II?
nuclear envelope breaks down
chromatin coil and condense into chromosomes (each have 2 chromatids)
chromatids no longer identical - still sister chromatids though as said in an exam question
new spindles form, at 90 degree angle to previous spindle fibre
What happens in metaphase II?
chromosomes attach by their centromeres to equator of spindle
chromatids of each = arranged randomly (which side they’re on is random) = more independent assortment, will determine how they separate in anaphase
What happens in anaphase II?
centromeres divide
chromatids of each chromosome pulled apart to opp poles by motor proteins
What happens in telophase II?
nuclear envelopes form around each set of chromatids (haploid nuclei)
spindle fibres break down
animals: 2 cells now divide (cytokinesis) to give 4 haploid cells
plants: tetrad of 4 haploid cells is formed
How does meiosis produce genetic variation?
crossing over in prophase I shuffles alleles (new combo of alleles) - amount of variation depends on distance between crossover points
independent assortment of homologous chromosomes in metaphase I = large number of possible allele combinations in each resulting cell.
(also independent assortment of chromatids in metaphase II)
random fusion of gametes - many allelle combinations, they aren’t genetically identical
How can mutations cause genetic variation?
changes DNA base sequence, DNA checks might not recognise damage, diffs in protein structure and function
Multicellular eukaryotic organisms start as ———
(all genes in its genome are able to be expressed) = a ———
After several mitotic divisions, an —– forms, containing many ——– cells
undifferentiated zygote cell
stem cell
embryo
undifferentiated embryonic stem
Cells differentiate as certain genes are switched off and othergenes may be expressed more so that: —–
proportions of organelles may differ
shape of cell changes
some of contents of cell changes
= SPECIALISED CELL
How are erythrocytes specialised to carry out their function?
function: carry oxygen from lungs to respiring tissues
biconcave shape: increases SA:V ratio (more O2 can diffuse)
few organelles: provides more space for many haemoglobin molecules
small: large SA:V ratio and short diffusion distance, allows them to change shape so they can move in narrow capillaries
Where are the stem cells that eventually differentiate into erythrocytes found?
bone marrow
How are neutrophils specialised to carry out their function?
function: ingest invading pathogens, usually bacteria and fungi, by phagocytosis (non specific immune response)
flexible shape: can move through blood vessels easily and change shape
granular cytoplasm, with lysosomes: digestive enzymes
multilobed nucleus (flexible nuclear membrane): allows for greater flexibility
specific receptors: can identify and bind to antigens on pathogens
nucleus, ER, ribosomes: can synthesise toxic chemicals that kill pathoegens as well as enzymes
attracted to site of infection by chemotaxis
Where are the stem cells that eventually differentiate into neutrophils found?
bone marrow
How are spermatozoa specialised to carry out their function?
Function: fertilise egg cells
Acrosome: specialised lysosome where enzymes are released to digest protective covering of ovum
many mitochondria in neck; ATP provides energy for undulipodium to move
nucleus (haploid): sperm and egg can combine resulting in a cell with 46 chromosomes
long and thin: can move easily
Where are sperm made?
testicles
How are ciliated and squamous epithelial cells specialised to carry out their function?
squamous epithelial cells: flattened in shape, very thin, fit together tightly. rapid diffusion (due to short distance) of gases at alveoli or blood vessels
ciliated epithelial cells: hair like structures which beat to move mucus + trapped pathogens from lungs/ in airways, or, to move egg from ovary to uterus
How are palisade cells specialised to carry out their function?
function: carry out photosynthesis in leaves
long + cylindrical: pack together closely, but with a little space so CO2 in these air spaces diffuses into cells
well developed cytoskeleton: move chroroplasts nearer to upper surface of leaf when sun = low, but further down when sun = high.
large number of chloroplasts: organelles that carry out photosynthesis, so can absorb maximum light
large vacuole: chloroplasts positioned nearer to edge of cell, reducing diffusion distance
How do guard cells carry out their function?
function: regulate opening and closing of stomatal pores for gas exchange in lower epidermis of leaves
1.sunlight used to produce ATP
2.K+ ions from surrounding epidermal cells are actively transported into guard cells
3.lowers water potential of guard cells so water enters by osmosis
4. tips - cell wall more flexible, and inner walls are thicker (more rigid). swelling occurs, tips bulge, and a gap forms
5.stomata open = air can enter spaces within layer of cells beneath palisade layer
How are root hair cells specialised to perform their function?
hair like projection:greatly inc SA for absorption of water and mineral ions. ions lower water potential so water follows by osmosis.
special carrier proteins: for active transport
many mitochondria: produce ATP needed
Define tissue
group of similar cells working together to perform a specific function/ set of functions
Epithelial tissue: examples, function and characteristics.
examples: skin, cavities of gut and airways, blood vessels, walls of organs, alveoli
function: lines free surfaces in the body - protection, absorption, filtration, excretion and secreiton
characteristics: form continuous sheets.
no blood vessels: recieve nutrients by diffusion from underlying connective tissue
short cell cycles to replace worn/damaged tissue
smooth, cilia or microvilli, squamous
Connective tissue: examples, function and characteristics.
Examples: blood, bone, tendons, ligaments, skin
Function: holds structures together and provides support
Characteristics: consists of a non living extracellular matrix w/proteins (collagen and elastin) and polysaccharides (e.g. hyaluronic acid which traps water). This enables it to withstand forces and separates the living cells.
What is a special type of connective tissue?
cartilage
What are immature cartilage cells called? Once the matrix is synthesised, what happens?
chondroblasts
mature, less active chondrocytes
Where is hyaline cartilage found?
joins ribs to sternum, nose, trachea, larynx
What is fibrous cartilage?
discs between vertebrae in spine and in the knee joint
What is the elastic cartilage?
outer ear (pinna), epiglottis
Muscle tissue: Examples, function, characteristics
examples: connected to bones by tendons, walls of heart, walls of small intestne, blood vessels, uterus, urinary tracts
function: made from cells that can contract and cause movement. skeletal: cause bones to move, packaged by sheets of connective tissue, protects internal organs. cardiac: allows heart to beat and pump blood. smooth: propels substances along tracts, constricts airways, maintaining blood pressure and flow of air
characteristics: many blood vessels (get as much O2 as possible), elongated and contain myofilaments (actin and myosin) which allow tissue to contract.
What are features of epidermal tissue in plants?
flattened cells that form a protective covering over leaves, stems and roots
lack chloroplasts apart from guard cells
som have walls with waxy substance = cuticle, to reduce water loss
What are the functions of vascular tissue in plants?
transport, present in vascular bundles
xylem: H2O + minerals, roots to plant
phloem: transfers mainly sucrose in solution from leaves to roots, flowers and growing shoots (or vise versa)
What are features of meristematic tissue in plants?
contains stem cells
in roots, shoot tips, cambium of vascular bundles
cells: thin walls, no chloroplasts, no large vacuole, can divide by mitosis.
new cells arise from these undifferentiated cells, since as plant cells mature, they develop a vacuole and rigid structure, preventing them from dividing
Where does phloem and xylem originate from?
cambium cells
How is xylem made?
lignin deposited in cambium cell walls to reinforce them
ends of cells break down so xylem forms continuous colums with wide lumens
How is phloem made?
sieve tubes lose most of their organelles and sieve plates develop between them
companion cells: retain cell organelles, provide ATP for pumping of sugars into sieve tubes.
What are the 4 main plant organs and their functions?
leaf: photosynthesis
root: anchoring, absorption of mineral ions and water, storage
stem: support, transportation of water minerals and sucrose
flower: sexual reproduction
Define organ
collection of tissues, working together to perform the same function
What are stem cells?
undifferentiated cells that can continually divide by mitosis and become specialised; for growth and repair
what does totipotent mean?
can divide and differentiate into any type of cell in the human body. occur only for a limited time in early mammalian embryos.
what does pluripotent mean?
can differentiate into almost any type of cell (except placenta). Found in embryos
What does multipotent mean?
can differentiate into a limited number of cell types. found in mature mammals
What does unipotent mean?
can only differentiate into 1 type of cell
What are the sources of stem cells?
embyronic stem cells: mostly pluripotent - present in an early embryo when zygote begins to divide. Ethical concerns depending on when life is thought to begin - might be killing embryo
umbilical cord blood contains multipotent stem cells
adult stem cells found in developed tissues. renewing source of multipotent undifferentiated cells
induced pluripotent cells: created from adult unipotent cells. reprogrammed by switching key genes on using transcriptional factors. adult can give permission.
How can stem cells be used in bone-marrow transplants?
stem cells from healthy bone marrow used to:
treat blood diseases (sickle cell anaemia and leukaemia) +
immune system ones (SCID).
Also used to restore patient’s blood system after cancer treatment
How can stem cells be used in drug research?
new drugs can be tested first on tissues made from stem cells rather than animals
How can stem cells be used in developmental biology?
can study how stem cells develop to make particular cell types and learn how each cell type functions and see what goes wrong when there are diseases
How could type I diabetes be treated?
programming iPS cells to bcome pancreatic beta cells
How could liver disease be treated?
triggering bone marrow stem cells to develop into hepatocytes
How could Alzheimer and Parkinsons disease be treated?
triggering stem cells to become nerve tissue
How can stem cells be used in regenerative medicine?
patient’s cells obtained, reprogrammed to become iPS, used to make a bioscaffold of an organ which can be directed to grow into a specific organ and implanted = no need for immunosuppressant drugs
What other issues may stem cells be able to treat?
arthritis, burns, vision and hearing loss, muscular dystrophy and heart disease
Which statement explains the significance of mitosis in the development of whole organisms?
A Mitosis can be controlled at certain points in development, which will change body plans.
B Sex cells are produced by mitosis, which allows new organisms to be produced.
C Mitosis limits the total number of cells in an organism, which will change its shape.
D Budding in yeast is an example of mitosis, producing new multicellular organisms.
A
Which of the following, A to D, is an incorrect statement about blood cells?
A Erythrocytes and neutrophils are derived from the same stem cells,
B Erythrocytes develop large numbers of ribosomes early in their differentiation
C The majority of organelles in red blood cells are broken down by hydrolysis
D Neutrophils undergo mutation during differentiation.
D
Before the division of the nucleus of a cell, the genetic material must replicate. Explain why this is essential.
cells, genetically identical / have same DNA ; so both (daughter) cells receive a full, copy/ same / correct number of chromosomes
