paper 1 revision

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?

1. artery walls develop strands of yellow fat deposited under the endothelium


1. builds up from certain lipoproteins and from cholesterol that may be circulating in the blood
2. 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?

1. deposits impede blood flow and contribute to raised blood pressure
2. thickening of artery walls leads to loss of elasticity, which also contributed to raised blood pressure
3. in the coronary arteries reduction of blood flow impairs oxygenation of cardiac muscle fibres


1. 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?

1. where the smooth lining breaks down, the circulating blood is exposed to the fatty, fibrous despotits


1. lesions are known as atheromatous plaques
2. further deposition occurs as cholesterol and triglycerides accumulate, and smooth muscle fibres and collage fibres proliferate in the plaque
3. blood platelets collect at the exposed, roughened surface


1. platelets release factors that trigger inflammation - blood clotting
4. a thrombus may form - a blood clot within the vessel


1. 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


1. dilute sample from population until a countable number of microorganisms are present
2. 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?

1. find dry mass of sterile filtration membrane
2. filter known volume of liquid culture
3. heat filter membrane in oven at 100oC until mass is constant
4. subtract mass of sterile filter membrane from final mass
5. calculate mass of cells per unit volume of culture

what is the method for an indirect count measuring turbidity?

1. place serial dilution sample into curettes
2. place curettes into colorimeter and pass light through it
3. measure absorbance or transmission of contents of cuvette
4. 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?

1. produce a serial dilution
2. pipette a small, known volume of each dilution onto a petri dish
3. use l-shape glass rod to gently spread pipettes suspension of bacterial cells over whole surface of agar
4. 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