AQA A LEVEL BIOLOGY PAPER 2

air spaces between them = rapid diffusion, long and narrow and are packed with chloroplast the thin tissue of the leaf allows light to reach mesophyll

Name three advantages of mesophyll in the leaf

stroma in the fluid filled matrix

where does the LIR occur?

100 stacked discs of thylakoids

what is the grana?

chlorophyll absorbs light energy, excite electrons, move along carriers etc releasing energy, used to join ADP and pi to form ATP, photolysis of water produces protons electrons oxygen, NADP reduced by electrons

describe the light dependent reaction starting with Photolysis

electron is oxidised that reduces NADP, carries out series of redox reactions along the electron transport chain that is then accepted by oxygen that is the terminal electron receptor which oxidises NADPH back to NADP

describe the electron transport chain

contain both DNA and RNA so proteins can be manufactured quickly, thylakoid membrane has a large SA for rapid DF and a network of proteins in the Grana to maximise the absorbance of light

name three advantages of the structure of a chloraplast

CO2 combines 5 carbon ribulose-bi-phosphate to make 6 carbon molecule that is then catalysed by rubisco to create two 3 phosphate glycerate molecules that are then reduced via NADP and energy from ATP from LDR to triose phosphate that will eventually turn into glucose, NADP reformed and goes back to LDR

describe the process of the LIR

phosphorylated glucose is broken down in two 3 carbon molecules called pyruvate (happens in the matrix mitochondria

what is glycolysis and where does it happen?

pyruvate is decarboxylated and dehydrogenated to acetate NAD is reduced

what happens in the link reaction after Glycolysis?

acetyl coenzyme A combines with oxaloacetate to form citrate which is decarboxylated and dehydrogenated to form 5 carbon molecule which is then dehydrogenated and decarboxylated to form 4 carbon ATP made by substrate-level phosphorylation and FAD is reduced, oxalacetate is then regenerated to restart the cycle

what happens in the Krebs Cycle after the link reaction?

H+ from oxidized reduced NAD and FAD, splits into p and e travels down electron transport chain via oxidation-reduction reactions losing energy each carrier used pump p from matrix into intermembrane space creating high concentration forming electrochemical gradient move down into matrix by ATP synthase drives synthesis ATP chemiosmosis, Matriz end transport chain p,e, and o combine form water. o final electron acceptor.

what is oxidative phosphorylation?

hydrolysed to glycerol that is phosphorylated into into triose phosphate that becomes glucose and thus glycolysis can occur

how does the respiration of lipids occur?

where no oxygen is available to accept the H+ ion and so reduced NAD builds up and cannot take anymore H+ from Glyolysis thus pyruvate is now reduced and produces lactate and oxdidised NAD and produces ethanol in plants

what is anaerobic respiration?

the dry weight of the total mass of living material in a specific area at a given time

what is biomass?

gross primary production - respiratory losses = the chemical energy left

what is the calculation for net primary production? and what is it?

total chemical plant biomass

what is gross primary production?

net production = chemical energy of ingested plants - (energy lost in faeces + energy lost in respiration)

what is the calculation for net production?

nitrogen from atmosphere is fixed by nitrogen-fixing bacteria to ammonium ions via ammonification, also nitrogen from atmosphere is fixed by mutualistic bacteria to ammonium containing compounds, then fed on by saprobionts that causes ammonification, ammonium ions that undergo nitrification by nitrifying bacteria twice into nitrite and nitrate ions that are then absorbed by producers or lost to the atmosphere

describe the nitrogen cycle

phosphates from rocks are eroded into oceans and running water that is absorbed by plants and excreted into the soil via death that then taken up by water to form new rocks

describe the phosphorus cycle

algae build up on surface of water due to nitrogen from water that limits light to lower level plants that can no longer photosynthesise and die that are fed on by saprobiants that multiply and take up oxygen in the water so that O2 becomes the limiting factor and larger organsims die as a result that are also fed on by saprobiants that release toxins into the water

what is eutrophication?

natural = dead decomposing plants and artificial = mined from rocks t provides nutrients to plant

what is an example of a natural and artificial fertiliser?

the change of speed of direction in response to a stimulus

what is kinesis?

response to a stimulus where the direction is determined by the stimulus itself that is moving the entire organism away or towards

what is taxis?

the detectable change in the external or internal environment

what is a stimulus?

IAA moves down a concentration gradient to the dark side of the shoot that then increases the growth of that side to increase more than that of the light side so the plant curves towards the light (phototrophism) ,in roots however, IAA inhibits growth and so builds up on the underside of the root so the plant can more on the top so that it bends towards gravity (gravitrophsim)

what is the base movement of IAA in plants and roots?

where the active transport of H+ ions from cytoplasm into the spaces in the cell wall casuing the cell wall to become more plastic

what is the acid growth hypothesis?

brain and spinal cord

What does the CNS consist of?

provides a voluntary/autonomic nervous system to provide a quick response with a thought process to avoid overloading the brain so that it can carryout other actions at the same time

what does the PNS do?

stimulus - receptor - sensory neurone - coordinator - motor neurone - effector - response

name the pathway of the detection of a stimulus

chemoreceptors detect change in PH from the increase of CO2 in the blood that sends a nerve impulse to the medulla oblongata, nerve impulse sent to SAN via the sympathetic nervous system that initiates a wave of excitation across the atria, causing it to contract, there is a short delay by non conducting tissue while the ventricles fill and then the AVN releases another wave of excitation down the Purkinje tissue and bundles of his to the apex of the heart that then contracts from the base up, the more impulse to SAN = faster contraction of the heart to increase the heart rate, opposite = reduced impulse via parasympathetic

Describe the cardiac cycle with reference to increase heart rate

Contraction within the muscle itself

What does myogenic mean?

Pressure in PC is transfixed to chemical energy from mechanical pressure that causes the stretch mediated sodium channels to become distorted and change shape to allow sodium to diffuse down a concentration gradient that causes the opening of more sodium ion channels to open on a neurone that stimulates the depolarisation of an axon as a threshold has been met of the micro voltage

Describe the generating of a action potential via the pacinian corpuscle

Receptors in eye that found at the periphery, Detect low intensity light, have low visual acuity, can't detect colour and have more than one linking to the same neurone

What are rods?

Found in fovea, detects colour, only one connected to the same neurone so multiple colours can be detected, detects high intensity light to produce rhodopsin

What is a cone?

Cell body, dendrons, axon, Schwann cell, myelin sheath and nodes of Ranvier

Name the six parts of a motor neurone?

Transport of hormones via blood plasma to target cells that is more slower and general

What is the hormonal system?

Transport of nervous impulses that is faster and in a more localised region

What is the nervous system?

Has a cell body in the middle of the axon that is a dorsal root ganglian

What is the distinguishable feature of a sensory neurone?

Long axon, cell body at the end, short den-trites

Distinguishable features of a motor neurone?

No threshold has been reached by stimulus so sodium potassium pump occurring where 3 molecules of sodium go in and 1 potassium goes out via active transport

Describe what is happening in resting potential?

Neurone begins to depolarise as a stimulus has reached the threshold so sodium voltage-gated channels open and an influx of sodium ions enters the neurone that further depolarises the neurone, and as more sodium draws in, more gates open until threshold has been reached and then begins action potential that repolarises the neurone by closing the sodium voltage gate channels and opening the potassium voltage gate channels until it has gone below resting potential where the refractory period occurs and no action potential can occur (sodium-potassium pump) then the process is repeated at each node of Ranvier until it reaches the synapse

Describe the process of a nervous impulse

The jumping of an action potential from node ranvier to node ranvier

What is saltatory conduction?

Diameter of a axon(larger = greater conductance), temperature (enzymes) and myelinated sheath (no myelin sheath = less saltatory conduction so less action potentials can occur along the same neurone = slower)

What affects the speed of a nervous impulse?

Temporal summation occurs when a high frequency of action potentials in the presynaptic neuron invokes postsynaptic potentials that summate with each other

What is temporal summation?

Spatial summation is a mechanism of invoking an action potential in a neuron with input from multiple presynaptic cells

What is spatial summation?

Transmitter released that attaches to chloride ion protein channels on the post synaptic neurone, the channels open and chloride ions move into the post synaptic neurone by FDF, binding of neurotransmitter = K+ channels to open and release potassium in synapse so the potential decreases that causes hypolarisation so AP will not occur as sodium not present

How does synaptic inhibition occur?

Combine multiple impulses at the same synapse so Brain is not overloaded with info + can stimulate multiple impulses in different neurones at the same time

What are the functions of a synapse?

Calcium ions open because of AP that move into synaptic knob via FDF, this causes vesicles to fuse with the presynaptic neurone membrane that release acetylcholine into the synaptic cleft, acetylcholine then binds to protein receptors on the sodium ion channels on the post synaptic neurone that diffuse across a concentration gradient that causes a influx of sodium ions in the post synaptic neurone that causes an AP, acetylcholine then broken by acetylcholinerase into choline and Ethanoic acid and diffuses back across the synaptic cleft but does not cause an action potential in the pre synaptic neurone as it is not in its acetylcholine form

Describe the transmission across a cholinegenic synapse?

Calcium ions from sarcoplasmic reticulum causes by AP diffuse into muscle via concentration gradient that then causes tropomyosin to move that exposes the binding site of the actin filament, an ADP molecule then attaches to the myosin head that causes it to form a cross bridge with actin filament binding site, the actin filament is then pulled by the myosin head changing shape/angle that releases ADP, ATP then allows the myosin head to detach from the actin filament that is then broken by ATPase which provides the energy for myosin head to change back to its original shape and the process is repeated

Describe how the contraction of skeletal muscles work?

Sliding filament theory

What is the theory behind skeletal muscle contraction called?

The distance between two Z lines

What is the sarcomere?

Stay the same

What happens to the a-bands during muscle contraction?

Decreases in size

What happens to the H-zone and I band during the skeletal muscle contraction?

Calcium reabsorbed by the sarcoplamsic reticulum that causes the tropmysoin to be blocked again

How does the muscle relax?

Pair of muscles where one relaxes and the other contracts

What are antagonistic muscles?

Numerous mitochondria, large store of myoglobin, rich supply of blood vessels and contract slowly

What are the features of a slow twitch muscle fibre?

Thicker, more myosin filaments, high concentration of glucose, higher concentration of enzymes and store of phosphocreatine to rapidly gain ATP from ADP

What are the features of a fast twitch muscle fibre?

Water potential decreases in the osmoreceptors in hypothalamus that stimulates an nerve impulse to be sent to the posterior pituitary gland which releases ADH that fuses with CSM of the distal tubule and collecting tubule to activate phosphorylase that fuses the vesicles containing aquaporins to fuse with the membrane of the collecting duct and distal conveluted tubule to make them more permeable so that more water is held within the body

Describe osmoregulation

Adrenaline binds to proteins on CSM of liver that causes the channel to change shape and release adenyl Cyclades which converts ATP to cyclic AMP (secondary messenger model) that binds to kinase and activates it which catalysed the reaction of glycogen to glucose

Describe the process of adrenaline in homeostasis

Production of glucose from sources other than that of carbohydrates

What is gluconeogenesis?

Breakdown of glycogen into glucose

What is glyconeolysis?

Conversion of glucose to glycogen

What is glycogenesis?

Diet

What factor affects blood glucose concentration?

Islets of Langerhans

Where are B cells and A cells produced?

Released by A cells, detects fall in blood glucose concentration, activates enzymes for gluconeogenesis and glyconeolysis

What does glucagon do?

Binds to protein receptors on the pancreas liver membrane that causes it to change shape vesicles fuse with the membrane containing transport channels, this activates cyclic amp as a second messenger to activate enzymes that undergo glycogenolysis or gluconeogenesis

How does adrenaline affect blood glucose concentration?

when water potential of the blood is too low detection by receptors hypothalamus which then sends a signal to the pituitary gland to secrete more ADH increasing the permeability through the recruitment of aquaporins opening channels in the DCT and collecting duct more water is absorbed by osmosis down a water potential gradient

Explain the role of ADH if the production of concentrated urine

Mechanism that returns a change in the internal environment back to its optimum state

What is negative feedback?

Enhancing of an effect created by its own influence

What is positive feedback?

Rental artery, Afferent arteriole, Glomerulus, efferent arteriole, Bowman capsule, proximal conveluted tubule, descending limb of loop of henle, ascending limb of loop of henle, distal conveluted tubule, collecting duct

What is pathway of the nephron?

Inorganic ions, glucose, amino acids, vitamins nitrogenous waste and some hormones

What is in the filtrate?

Vasodilation, vasoconstriction and easing blood pressure

What effects the rate of glomerular filtration?

Hydrostatic pressure squeeze out small molecules filtrate from basement membrane in glomerulus into the Bowmans capsule via ultrafiltration barriers consisting of podocytes that allow the filtrate to pass beneath them but stop any larger molecules like blood cells and proteins from entering the capsule

How is glomerular filtrate formed?

Sodium actively transported out into blood capillaries that diffuses down concentration gradient in lumen to epithelial cells via facilitated diffusion through carrier proteins that also co-transport all valuable ions so that they can be reabsorbed by PCT (85% of reabsorption occurs in PCT)

Describe the process of the reabsorption of glucose and water in the proximal convoluted tubule

Sodium diffuses out of ascending limb into interstitial space between ascending and descending, sodium moves into descending limb and water moves out of it into blood capillaries, thus as filtrate moves through loop of henle it lowers its water potential until it reaches the bottom of the ascending limb that where sodium diffuses out and so water potential increases, then there's a higher water potential gradient in the interstitial space between ascending and collecting duct so water moves out of collecting duct into blood vessels

How is the gradient of sodium maintained in the loop of henle?

Always ensures there is a water potential gradient that rates out water from the tubule so water will move out of the filtrate

What does the countercurrent multiplier do?

Glucose phosphorylated using a phosphate from ATP, the ATP is then used to add another phosphate forming heroes biphosphate that is then split into 2 triose phosphates that is oxidised forming Pyruvate molecules

What is phosphorylation?

That anything above critical value is due to chance and so is significantly different and measures the difference between two means

Most important thing to remember about Chi-squared or T-test

When one allele masks another

What is epistasis?

Two characteristics determined by two different genes located on different chromosomes are inherited

What is dihybrid inheritance?

Two genes on the same autosome

What is autosomal linkage?

When there is a small population that is likely to express only one set of alleles and genes and so are also effect more easily by mutations

What is genetic drift?

Study of interrelationship between organisms and their environment

What is ecology?

Temperature and light

Name two abiotic factors

Intra = same species and inter = different species

What is the difffenrce between intraspecific and interspecific competition?

Predators eat prey, prey numbers decrease, less resources = predators decrease so prey can then repopulate, more food = more predators and so on

Cycle of predation

Systematic sampling

What would you use a belt transact for?

Gradual change along a shore/line

What Does systematic sampling measure?

Estimated population size = total in first sample X total in second sample divided by number of marked recaptured

What is the calculation for mark release recapture?

Pioneer species reproduce a-sexually in inhabitable environment as they germinate rapidly and are photosynthetic, this then forms moss from dead lichens leaving nutrients in the soil, rocks erode causing more nutrients to build up in soil, produce grass/shrubs and trees from nutrients as environment becomes more hospitable and also environment is changed so more adapted to others species than current one, reaches the climax community

Describe the process of succession starting from pioneer species

Where life is suddenly altered and climax is reached a lot quicker as less stages needed than primary succession because nutrients and organisms already available

What is secondary succession?

Economic, personal, ethical, cultural, aesthetic and management of succession

What are the main reasons for conserving a habitat?

Random, DNA rep, radiation and chemicals and mutagenic agents

What are the causes of mutation?

Groups of bases detach and reattach at different places

What is inverse mutation?

Bases separate from one strand and are inserted into a different one

What is translocation mutation?

No one cell can provide best conditions from for everything so having a range of them can cover all different conditions = multicellular

What is the importance of cell differentiation?

Cells that turn into any cells that only creates proteins for specific functions

What is totipotency?

Undifferentiated dividing cells that occur in adult animal tissues + need to be constantly replaced

What are stem cells?

Differentiate into single type of cell

What does unipotent?

Specialised cells

What are pluripotent cells?