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what is the product of mitosis
chromatids decondensed
two separate nuclei
what is the difference between organs and tissue
organs have more functions than tissues
tissues made of cells, organs made of tissues
tissues are made up of the same type of specialised cell which carries out the same function whereas organs are made up of many different types of tissues
why do cells produced become smaller after each cell cycle in mitosis
- fewer organelles
- no time in G1 or G2 phase
- cytoplasm is divided to form new cells
how can you tell whether an electron image is of the golgi apparatus
- fluid-filled flattened sacs
- separate cisternae
- smooth membrane/ no ribosomes
- sacs are in stacks
describe the structure of the cell wall of the xylem
- lignin in rings in the cell wall
- cellulose molecules are held by hydrogen bonds
- presence of bordered pit
- presence of pectin in the cell wall
- xylem cell walls are contain lignin
cell wall of xylem vessel is made up of cellulose
why do people with emphysema require air with a higher concentration of oxygen than those without emphysema
- smaller surface area of alveoli with emphysema
- therefore need larger concentration gradient to maintain the rate of diffusion
how is glycogen produced
alpha glucose molecules joins together by 1,4 and 1,6-glycosidic bonds to form glycogen
via condensation reactions
why is glycogen suitable for its role
branches molecule for more rapid hydrolysis
glycogen is a compact molecule which means that more of it can fit in a smaller amount of space
insoluble-> no osmotic effect
why do people with CF have thicker mucus
- gene mutation causing a non-functioning CFTR protein channel
- chloride ions cant move out of epithelial cells
- accumulation of sodium and chloride ions in the cells which causes water to move out of the mucus by osmosis
why does the structure of arteries allow for it to maintain and withstand high pressures
- more collagen provides strength to withstand high pressure
- contraction of muscle allows constriction of lumen
- elastic fibres for elastic recoil
why did meselson and stahl accept the semi conservative replication model
- generation 1 has a single band which is halfway between 15N and 14N
- DNA has one strand containing 15N and one strand containing 15N
- in semi-conservative model further generations would have no band at 15N
compare and contras fibrous and globular proteins
both contain bonds such as disulphide bridges holding them together
both are chains of amino acids joined by peptide bonds
fibrous contains cross linkages whereas globular dont
both has a 3D structure
what does p^2 and q ^2 and 2pq represent in the hardy weinberg equation
p^2- homozygous dominant
q^2- homozygous recessive
2pq- heterozygous genotype
what is the effect of interbreeding on genetic diversity
would increase the genetic diversity
introduction of different alleles into the population
how can molecular phylogeny be used to determine relationships between organisms
sequencing bases in their DNA/ amino acids in proteins
the more similarities they have the more closely related they are
explain how preventing the shortening of spindle fibres effect mitosis
sister chromatids cant be separated
so chromosomes remain at the equator
how do you calculate tensile strength
force/ cross sectional area of the fibre
why does contamination of tissue cultures have to be avoided?
contaminants case disease of plant tissue
contaminants compete for nutrients
contaminants cause poor growth
why is a drug tested on animals and healthy volunteers?
testing on animals for toxicity
finding out how the drug is metabolised
how does lignin add to the strength of xylem tissue
lignin holds the fibres together and keeps fibres parallel
how does inbreeding lead to genetic defects?
closely related animals mated with each other
inbreeding depression
increased chance of homozygous recessive genotypes for genetic defects
how are breeding programmes at zoos designed to reduce the risk of inbreeding
exchange of gametes between zoos
ivf
studbooks
selection of unrelated mates
exchange of animals between zoos
what is the structure of lipids
only contains carbon, hydrogen and oxygen
fatty acids and glycerol joined by ester bonds
how do you answer questions that give you ranges
smaller range -> more reliable
ranges overlap -> no significant difference
work out the maximum and minimum for each value if given ranges
how do you increase validity
name controlled variables
how is species richness counted
count the number of species in a known are using a quadrat
why odes biodiversity need to be maintained
loss of biodiversity means there are fewer species
loss of endemic species leads to extinction
some species havent been discovered and may be useful
why is little genetic diversity bad
no selective advantage when the environment changes
less likely to survive
increases the risk of extinction
why is increased genetic diversity good
greater chance of survival as higher chance of having beneficial alleles
increased mating with genetically different individuals
different individuals decreases inbreeding
how does the use of hardy weinberg equation allow us to see if evolution has occurred
identify changes in the allele frequency over time
if allele frequency has changed then evolution has occured
if theres no migration
what is species evenness
relative abundance of each species
describe the process of semi conservative replication
DNA helicase breaks H bonds between bases-. forms 2 strands
original strand acts as template and complementary base bairing occurs between free floating DNA Nucleotides and template strand
nucleotides join by condensation reactions catalysed by DNA polymerase
H bonds form between bases on original and new strand
describe the experiment meselson and stahl used to show that DNA replicates semi-conservitavely
2 samples of bacteria grown- one in nutrient broth containing light nitrogen and other in heavy nitrogen
as bacteria reproduced -> took up nitrogen
sample of DNA taken and spun in centrifuge
DNA from heavy settled lower down than light
the bacteria grown in heavy were taken out and put in broth only containing light and left for one round of replication
another DNA sample taken and spun in centrifuge
DNA settled in the middle showing that DNA contained a mixture of heavy and light nitrogen which shows the DNA replicated semi-conservatively
recall info on amniocentesis
carried out at 15-20 weeks
sample of amniotic fluid taken using fine needle
analyses foetal cell DNA
1% chance of miscarriage
results arent available until 2-3 weeks later
recall info on chorionic villus sampling
carried out 11-14 weeks
earlier decision can be made so less traumatic
sample taken from chorionic villi
done via abdomen or catheter
1-2% chance of miscarriage
initial results available in a few days
what happens in prophase
chromosomes condense
centrioles move to opposite ends of the cell
spindle fibres form
nuclear envelope breaks down
what happens in anaphase
centromeres divide seperating sister chromatids
spindle fibres contract pulling chromatids to opposite ends
what happens in telophase
chromatids decondense
nuclear envelope reforms
2 nuclei
what are activators
factors that increase the rate of transcription
they help RNA polymerase bind to DNA and begin transcription
what are repressors
prevent RNA polymerase from binding and stop transcription
what is an operon
a section of DNA that contains a cluster of structural genes that are transcribed together as well as control elements and sometimes a regulatory gene
what is a structural gene
code for useful proteins e.g enzymes
what are control elements
include a promoter and and operator
what is a promoter
a DNA sequence located before the structural genes that RNA polymerase binds to
what is an operator
a DNA sequence that transcription factors bind to
what is a regulatory gene
codes for an activator or repressor
what is the lac operon in E. coli
E. coli can respire used lactose if glucose is unavailable
the genes that produce the enzymes needed to respire lactose are found on the lac operon
it has 3 structural genes- lacZ, lacY, lacA which produces proteins that help bacteria digest lactose including beta-galactosidase and lactose permease
what happens in the lac operon when lactose isnt present
regulatory gene produces lac repressor which is a transcription factor that binds to the operator when no lactose isnt present
blocks transcription because RNA polymerase cant bind to promoter
what happens in the lac operon when lactose is present
lactose binds to repressor
changes repressors shape
lac repressor can no longer bind to operator site
RNA polymerase can begin transcription of the structural genes
what happens when theres increased methylation
how does histone modification affect gene expression
how does histone modification affect gene expression
how can epigenetic changes be passed on
what is monogenic and polygenic
what is the role of oncogenes
they code for protein that stimulate the transition from one stage in the cell cycle to the next
DNA mutation of epigenetic changes in these genes can lead to the cycle being continually active - may cause excessive cell division
what is the role of tumour suppressor genes
they produce proteins that stop the cell cycle e.g p53
inhibits G1 to S transition
if this gene becomes inactive theres no brake on the cell cycle - continuous division
