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what is the inhibition of enzymes?
slows the rate of an enzyme-controlled reaction by preventing binding of the substrate to the active site of the enzyme
what is a competitive inhibitor?
inhibitors resemble shape of enzyme so they can bind to the active site of the enzyme, forming an enzyme-inhibitor complex
enzyme-inhibitor complex remains intact - inhibitors not acted upon
inhibitor molecules are displaced from active sites and become less likely to reattach if the concentration of the substrate is increased
what is a non-competitive inhibitor?
inhibitors attach to allosteric site and changes shape of the enzyme active site
active site is no longer complementary to substrate molecules
non-competitive inhibition is permanent
adding substrate does not dislodge inhibitor
not competing for active site
what is end-product inhibition?
product of a late reaction in the series inhibits the enzyme controlling an earlier reaction
as product molecules accumulate, the steps in their production are switched off
why is the initial rate of an enzyme-controlled reaction measured?
the rate of reaction is high and the initial rate is the only point during the reaction when concentration of reactants and products is known
what is cell theory?
cells are the smallest unit of living organisms
all cells are derived from the division of other, pre-existing cells
within cells are the sites of all chemical reactions of life (metabolism)
what is a gram positive wall structure in bacteria?
thick walls of peptidoglycan
wall becomes purple when stained by crystal violet - stain is retained
what is a gram negative wall structure in bacteria?
thin walls of peptidoglycan with an additional outer membrane
high lipid content of this outer membrane prevents the crystal violet stain from being retained by the cell wall - bacteria do not become purple
why are gram negative bacteria antibiotic resistant?
outer, lipid-rich membrane of gram negative bacteria is relatively impermeable to antibiotics, such as penicillin
what happens in the first 3-4 days after fertilisation?
the zygote moves down the oviduct via ciliary action and arrives in the uterus
what happens once the zygote is in the uterus?
mitosis and cell division occurs (cleavage division) and this results in new cells called blastomeres
as more cleavage divisions occur the blastomeres become smaller
after 4 days the zygote is a solid ball of blastomeres
what happens between 4-7 days after fertilisation>
the ball of blastomeres forms into a blastocyst - a hollow ball of cells
outer layer of cells called trophoblasts
fluid filled blastocoel
what happens to inner cell mass and trophoblasts?
inner cell mass will become the embryo
trophoblasts are destined to become a membrane which nourished the embryo and fetus
analogous structures
resemble each other in function but differ in fundamental structure
homologous structure
structures built to a common plan but adapted for different purposes
classification
Kingdom
Phylum
Class
Order
Family
Genus
Species
how is a new scheme of classification developed?
extremophiles are discovered
species of bacteria that survive and prosper in extremely hostile environments
microorganisms have cells that can be identified as prokaryote, but larger RNA molecules present in those ribosomes were discovered to be different from those of previously known bacteria
new evolutionary relationships - led to a new scheme of classification
each domain shares a distinctive, unique pattern of ribosomal RNA
simpson’s index of biodiversity
diversity of species present in a habitat can be measured by using the simpson diversity index
N = total number of organisms of all species found
n = number of individuals of each species
what is species richness and why is it not a complete measure of biodiversity of a habitat?
total number of different species within a given area or community
species richness is not a complete measure of biodiversity of a habitat because abundance of each species present is not required
what is the first stage of atherosclerosis development?
endothelial damage
what happens in endothelial damage?
artery walls develop strands of yellow fat deposited under the endothelium
builds up from certain lipoproteins and from cholesterol that may be circulating in the blood
damage causes white blood cells (macrophages) to invade the fatty streaks where they begin to take up cholesterol from low density lipoproteins and develop fibrous connective tissue forming an atheroma
what is the second stage of atherosclerosis development?
raised blood pressure
what happens in the raised blood pressure stage of atherosclerosis development?
deposits impede blood flow and contribute to raised blood pressure
thickening of artery walls leads to loss of elasticity, which also contributed to raised blood pressure
in the coronary arteries reduction of blood flow impairs oxygenation of cardiac muscle fibres
leads to angina - chest pains
what is the third stage of atherosclerosis development?
lesion formation and an inflammatory response
what happens in lesion formation and an inflammatory response?
where the smooth lining breaks down, the circulating blood is exposed to the fatty, fibrous despotits
lesions are known as atheromatous plaques
further deposition occurs as cholesterol and triglycerides accumulate, and smooth muscle fibres and collage fibres proliferate in the plaque
blood platelets collect at the exposed, roughened surface
platelets release factors that trigger inflammation - blood clotting
a thrombus may form - a blood clot within the vessel
embolus if it breaks free and is circulated in the bloodstream
what causes a myocardial infarction (heart attack)?
if an embolus is swept into a small artery or arteriole that is narrower than the diameter of the clot, a blockage will be caused
if a coronary artery is blocked, the heart muscle will be starved of oxygen and glucose
what causes a stroke and what is the effect?
a stroke occurs when an embolus blocks an artery in the brain
neurones affected will die within minutes
body functions controlled by that region will be lost
what causes an anuerysm?
in artery walls which have been weakened by atherosclerosis, the remaining layers may be stretched and bulged under the pressure of the blood pulses
aneurysm - ballooning of the wall
may burst at any time
why do plants have a simple gas exchange system?
plants have low metabolic rates and low rates of gaseous exchange
plants do not move and do not have to maintain a high body temperature
what are lenticels and what do they do?
tiny patches of very loosely packed cells
many air spaces which allow direct diffusion to and from tissues beneath
where is the highest rate of gas exchange in a plant?
the leaves to supply carbon dioxide for photosynthesis
how do guard cells alter size of stomata?
using turgor pressure
turgid = curved shape opens stomata
flaccid = pore closes
how do gases travel through a leaf?
carbon dioxide dissolves in water films surrounding spongy mesophyll cells and can then freely diffuse through the cell surface membrane into the photosynthesising tissues
oxygen diffuses outward by the same route
what is a barrier to gas exchange in insects?
insect exoskeleton is made of chitin, which is impermeable
what are insect tracheae?
branching network of fine tubes supported by rings of chitin
prevents collapse under pressure changes
allows tracheae to be flexible
what are spiracles?
connect tracheae to outside atmosphere
8 small holes on each side of the abdominal segments
2 more pairs of spiracles on thorax
spiracles are opened and closed by small muscles
fine hairs prevent entry of small particles that could block the tracheoles
how are tracheoles adapted to gas exchange?
thin walls to allow diffusion into and out of cells
gases move down their concentration gradients
what effect does opening and closing spiracles have?
opening and closing of certain spiracles ensures fresh flow of air through the main tracheae
closing spiracles at times when gas exchange is slow helps conserve water
movements of the abdomen compresses and expands the tubes, flushing air through them much faster
why are xylem vessels dead and empty?
creates wide lumen for unrestricted water flow
why do the end walls of the xylem vessels break down?
creates long, continuous tube for water transport
why are the cell walls of xylem vessels lignified?
prevents vessels collapsing when contents are under tension
why are xylem vessels lignified with rings, spirals, and in a reticulate manner?
allows vessels to be flexible, preventing breakage as the stem moves
why do xylem vessels have pits?
water and ions can be transferred to all parts of the plants
areas of cell wall that lack lignin and so allow lateral transport
what are xylem tracheids?
narrow, short vessels with tapered ends
main water carrying tissue in less advanced plant species
sloping end walls break down with lignification
what are xylem parenchyma cells?
typical plant cells with no thickening
found among vessels and tracheids
living tissue
what are xylem fibres?
narrow, highly thickened dead cells with only a small lumen
similar to fibres found elsewhere in the plant
cannot transport water
used for support
why do sieve tubes in phloem have limited peripheral cytoplasm and organelles?
creates space for sugar transport through the cell
why do end walls form sieve plates with sieve pores in phloem?
form direct connections for transport
why are companion cells and sieve tubes connected by plasmodesmata in phloem?
enables the sieve tubes to stay alive without nucleus and with very limited cytoplasm
what are companion cells?
dense cytoplasm and many organelles
carry out cellular functions enabling the sieve tubes to stay alive and transport materials
what are sieve tubes?
elongated living cells with specialised structure
lose nuclei and cytoplasm is restricted to very thin peripheral layer with few organelles during development
connected to companion cells through plasmodesmata
what is the mass-flow hypothesis?
pressure differences that drive fluid movement are generated in different part of the plant
sugars dissolve in cytoplasm, causing a lowered water potential
water enters cells by osmosis and builds up a high hydrostatic pressure
source area
sugars are used up rapidly in respiration or converted to starch in other parts of the plant
starch is insoluble and forms starch grains - no osmotic effect
removal of dissolved sugar raises water potential and water flows out of the cell, forming a region of low hydrostatic pressure - sink area
pressure difference forces sugars in sieve tubes at source and induces mass-flow through the phloem towards the sink
remaining fluid in the sink returned to source through xylem vessels
what are the strengths of the mass-flow hypothesis?
possible to measure gradients suggested and show they are present
when pierced by insect mouthparts, the contents of sieve tubes flow out, showing them to be under pressure
model links phloem and xylem systems in plausible way
what are the weaknesses of the mass-flow hypothesis?
organic solutes move around the plant in different directions, not just to the lowest pressure sinks
sieve tubes and companion cells are living tissue and do not work if killed off - model does not explain why
starch grains found in many areas of the plant, not just the sinks
model suggests passive process but phloem have a higher metabolic rate than most other plant tissues
what are other features not explained by the mass-flow hypothesis model?
sugars need to be ‘loaded’ into sieve tubes - not explained
why sieve tubes contain phloem protein strands
purpose of sieve plates - hindrance to mass flow
how do fish obtain oxygen?
from water with internal gills
four pairs of gills supported by a bony arch
each gill has two rows of gill filaments in a V shape
filaments are very thin structures carrying rows of thin-walled gill plates on both surfaces
what does the operculum do?
protects gills and is partly responsible for maintaining continuous flow of water over them
tough, muscular flap of skin
how does water flow into the mouth of a fish?
as the mouth opens the floor of the buccal cavity is lowered and the operculum is closed tight against the body
increase in volume decreases pressure, compared with pressure outside, so water flows in
how does water flow out of the mouth of a fish?
contracting muscles in operculum cause it to bulge outwards, increasing the volume of the opercular cavity
decreases pressure and water flow across the gills
mouth closes and floor of the buccal cavity is raised
forces more water across the gills
increases pressure behind the operculum until it exceeds the pressure outside
forces operculum open and allows water to flow out
what is the counter-current mechanism?
as water passes over the gills, blood flows in the opposite direction
allows fish to remove 80-90% of dissolved oxygen from the water
maintains concentration gradient along the whole length of the blood-water boundary
only 50% of available oxygen would be transferred without counter-current mechanism
water potential
a measure of the tendency for water to pass from one place to another - in and out of a cell
what is the water potential equation?
water potential = turgor pressure + osmotic potential
osmotic potential
greater negative water potential is caused by the solutes dissolved in it
osmotic potential will always have a negative value
increased water potential of a solution caused by the solutes dissolved in it
how is liquid culture used?
flask that enables maintenance of large surface area in contact with the air
agitated or stirred
provided with sterile air when culturing aerobic microorganisms
what are the advantages of liquid culture?
ensures culture does not die, so active cells are always available
allows harvesting of any useful metabolism products from the microorganisms
what are the advantages of solid culture?
addition of a gelling agent to a liquid medium makes it solidify
little risk of spillage, useful for storing microorganisms
petri dishes provide a large surface area for growth and gas exchange with the air in the dish
in a petri dish individual cells inoculated onto the surface of the agar develop into a visible colony, allowing isolation and identification of the microorganisms from a mixed inoculum
in a glass flat-sided bottle or test tube, a greater depth of agar is provided than in a petri dish
reduces risk of dehydration and salt crystallisation
batch culture
inoculation of microorganisms into a sterile container with a fixed volume of growth medium
continuous culture
inoculation of microorganisms in a sterile container containing liquid growth medium
periodically some culture is replaced with fresh sterile medium
broad spectrum media
culture media containing basic nutrients needed by most microorganisms for growth
selective media
will only allow the growth of a few or one species of microorganisms
used in diagnostic work in laboratories
suppress growth of other bacteria
serial dilutions
repeated dilution, by a constant dilution factor, of an original solution or microbial culture
dilute sample from population until a countable number of microorganisms are present
multiple count by dilution factor to obtain estimate of number of cells in the undiluted culture
what is a haemocytometer used for?
determine a serial dilution with a number of cells that enables you to count bacterial cells accurately, yet contains sufficient cells for it to be a representative sample
what are the rules for a haemocytometer direct count?
include any cell that touches or overlaps the middle of the three lines at the top and right-hand side
do not include any cell that touches or overlaps the middle of the three lines at the bottom and left-hand side
what is the method for an indirect count measuring dry mass?
find dry mass of sterile filtration membrane
filter known volume of liquid culture
heat filter membrane in oven at 100oC until mass is constant
subtract mass of sterile filter membrane from final mass
calculate mass of cells per unit volume of culture
what is the method for an indirect count measuring turbidity?
place serial dilution sample into curettes
place curettes into colorimeter and pass light through it
measure absorbance or transmission of contents of cuvette
more bacteria = more absorbance, less transmission
what are the disadvantages of measuring turbidity?
can only be used in liquid cultures
cannot distinguish between dead cells and living cells
calibration curve must be produced to calibrate measurements
what is the method for a viable count using spread plates?
produce a serial dilution
pipette a small, known volume of each dilution onto a petri dish
use l-shape glass rod to gently spread pipettes suspension of bacterial cells over whole surface of agar
each visible colony can be counted
what happens in atrial systole?
the atrium contracts
blood is pushed into the ventricles by contraction of the walls of the atrium
this contraction prevents backflow by blocking off the veins that brought the blood to the heart
what happens in atrial diastole?
the atrium relaxes
what happens in ventricular systole?
ventricle contracts - forceful
high pressure slams shut the atrioventricular valve and opens the semilunar valves, forcing blood into the aorta
a pulse is generated
what happens in ventricular diastole?
relaxation of the ventricles
each contraction of cardiac muscle is followed by relaxation and elastic recoil
p-wave
atrial depolarisation (atrial systole)
qrs wave
ventricular depolarisation (ventricular systole)
t wave
ventricular repolarisation (ventricular diastole)
phagocytes
monocytes, neutrophils
ingest bacteria or cell fragments
eosinophils
stimulate allergic responses and histamine production
lymphocytes
form antibodies
what happens if oxygen is absent in respiration?
if oxygen is the final hydrogen acceptor, then without it the carriers of oxidative phosphorylation will all become reduced and the flow of electrons and protons will cease
supply of NAD+ will be halted and the kerbs cycle will also come to a stop
with only glycolysis operating, there is a net gain of 2 ATP compared with about 38 ATP from full aerobic respiration
pyruvic acid, the end product of glycolysis, begins to accumulate
what happens when pyruvate accumulates in animal cells?
lactic acid is formed
pyruvate act as the acceptor fro reduced NAD
what happens when pyruvate accumulates in plant cells?
ethanal acts as the acceptor
ethanol is formed
what is the effect of lactate?
inhibits muscle contractions as lactate concentration rises
stiffness in muscles
how is lactate broken down?
slowly transported to the liver where it is converted back to sugars and used in glycolysis
what effect does ethanol have in plants?
most plant cells cannot metabolise ethanol and as its concentration rises they are ten killed by its toxic effects
what can ethanol be used for?
alcohol
important raw material for the chemical industry
excellent fuel
glycolysis
linear series of reactions in which a six-carbon sugar is broken down to two molecules of the three-carbon pyruvate ion
what happens in phosphorylation?
glucose is activated with ATP, forms a six carbon sugar with two phosphate groups attached (called fructose biphosphate)
two molecules of ATP are consumed per molecule of glucose
what happens in lysis?
fructose biphosphate is split, forming two molecules of a three-carbon sugar (called glycerine-3-phosphate (GP))
how is NAD+ involved in glycolysis?
oxidation of GP occurs by removal of hydrogen
NAD+, a coenzyme, accepts hydrogen ions and electrons
NAD is reduced to form NADH and H+ ions
what happens during ATP formation in glycolysis?
occurs twice in glycolysis, by which each triose phosphate molecule is converted to pyruvate
as two molecules of GP are converted to pyruvate, four molecules of ATP are synthesised
net gain of two ATPs in glycolysis - 2 ATPs are used to phosphorylate glucose
what happens in the link reaction?
pyruvate diffuses into the matrix of the mitochondria as it forms, and is metabolised there
pyruvate is decarboxylated by the removal of carbon dioxide, and is oxidised by the removal of hydrogen
reduced NAD is formed
an acetyl group is formed, which is combined with a coenzyme to form acetyl coenzyme A
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