A2 level biology

• Describe the factors that affect rate of photosynthesis Carbon dioxideLightTemperature (for enzymes)In commercial greenhouses we control these factors to an optimum to maximise yield potential
• Describe the parts of the light independent stage of photosynthesis Carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of GP - this reaction is catalysed by the enzyme rubiscoATP and reduced NADP from the light-dependent reaction are used to reduce GP to triose phosphateSome of the triose phosphate is used to regenerate RuBP in the Calvin cycleSome of the triose phosphate is converted to useful organic substances
• Describe how the light dependent stage aids the light independent stage Uses reduced NADP from the light dependent reaction to form a simple sugarsThe hydrolysis of ATP provides the additional energy for this reaction
• Describe the chemiosmotic theory Energy transferred during ETC is used to actively pump protons from the stroma into the thylakoidA proton gradient is established and protons then diffuse down their concentration gradient into the stroma via the enzyme ATP synthaseThe energy transferred by the movement of protons is used to phosphorylate ADP to form ATP
• Describe the parts of the light dependent stage of photosynthesis Chlorophyll absorbs light energy which leads to the photoionisation of chlorophyll in PS1 (photosystem 1) - this causes electrons to be released and promoted to a higher energy levelThe electrons are passed from one carrier to another in the ETC at decreasing energy levels which causes energy to be releasedThis energy is then used via the chemiosmotic theory to add phosphate to ADP to form ATP - photophosphorylationThe released electrons are then accepted by NADP to form reduced NADPPhotolysis (breaking) of water produces protons electrons and oxygen
• Extra useful notes for aerobic respiration Other respiratory substrates besides glucose include the breakdown products of lipids and amino acids which enter the Krebs cycle to produce ATP and reduced coenzymesThe Link reaction and the Krebs cycle occur twice per glucose molecule as two pyruvate molecules are produced in glycolysisThe net produwon'tn of ATP in aerobic respiration is 38 8 during glycolysis (which occurs twice) so 16 in total + 24 in Krebs cycle (you won't need to recall this but its helpful to know just in case)
• Describe the oxidative phosphorylation This is essentially the Chemiosmotic Theory in action during aerobic respiration so use‎‎‎ ‎‎‎‎‎‎the same notes
• Describe the Krebs cycle (stage 3 of aerobic respiration) Series of oxidation-reduction reactions occursGenerates reduced coenzymes and ATP by substrate-level phosphorylation (essentially direct formation of ATP from ADP and Pi using energy from the chemical processes occurring)Carbon dioxide is lost during krebs cycle
• Describe the link reaction (stage 2 of aerobic respiration) Pyruvate is oxidised to acetate producing reduced NAD in the processAcetate combines with coenzyme A in the link reaction to produce acetylcoenzyme AAcetylcoenzyme A reacts with a four-carbon molecule releasing coenzyme A and producing a six-carbon molecule that enters the Krebs cycle
• Describe the difference with what happens to pyruvate in aerobic and anaerobic respiration If respiration is only anaerobic pyruvate can be converted to ethanol or lactate using reduced NAD. The oxidised NAD produced in this way can be used in further glycolysisIf respiration is aerobic pyruvate from glycolysis enters the mitochondrial matrix by active transport
• Describe what happens during glycolysis Phosphorylation of glucose using ATPProduction of triose phosphateOxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD
• Describe the need for respiration To produce ATPATP is used for:Active transportSynthesis reactions e.g. protein/DNA synthesisMuscle contractionCell divisionLight independent reactions of photosynthesisFirst stage of glycolysis (see following notes)
• State the formula for efficiency of energy transfer
• State the formula for net production of consumers ( N)
• State the formula for NPP
• Define NPP (Net primary production) The chemical energy store in plant biomass after respiratory losses to the environment ‎‏‏‎have been taken into account - this is essentially the energy available to other trophic ‏‏‎ ‎levels in the ecosystem such as herbivores and decomposers Note: NPP N and GPP are measured in kJ m^-2 yr^-1
• Define GPP (Gross primary production) Chemical energy store in plant biomass in a given area or volume in a given time
• Describe how you could estimate the chemical energy store in dry biomass Estimated by calorimetry A known mass of a sample of biomass is completely burnt so that all the energy released is used to heat a known volume of waterThe increase in the temperature of the water is then used to calculate the chemical energy of the biomassTo calculate the chemical energy stored you need to know that 4.2 joules of energy is required to raise the temperature of 1 cm^3 (1g) of water 1 degree celcius
• Describe how you could measure the biomass of plant material Heat all the plant material (removed from a known area) at regular intervals at a constant temperature until the mass is constantDivide the dry mass by the area from which the plant material was removed
• Define the term biomass and it's units Measured in terms of mass of carbon or dry mass of tissue per given area in a given timeTypical units for biomass could be kgm^-2yr^-1 or gm^-2yr^-1 depending on the plants (or animals) being investigated
• Describe how biomass is formed In any ecosystem plants synthesise organic compounds from atmospheric or aquatic carbon dioxide.Most of the sugars synthesised by plants are used by the plant as respiratory substrates.The rest are used to make other groups of biological molecules. These biological molecules form the biomass of the plants.
• Describe what happens in eutrophication Leaching and runoff of inorganic fertilisers so increased concentration of nitrates and phosphates in lakeAlgal bloom on surface of water which means there is no light for plants on water bed so can’t photosynthesiseDeath of plants so large quantities of decaying organic matter and therefore Increased numbers of aerobic saprobiontsAerobic bacteria fish and invertebrates die as dissolved oxygen is used up by saprobionts and they cannot respireCauses a reduction in species diversity
• Describe the issue of leeching due to use of fertilisers Large amounts of fertilisers can be washed away (leached) into rivers and lakesThis may result in eutrophication. (see on the next page)This is particularly the case when fertilisers are overused
• Describe the difference between artificial and natural fertilisers Natural Fertilisers – includes dead and decaying remains of plants and animals manure and bone meal. As they decay mineral ions are released which are taken up by crop plantsArtificial Fertilisers – contain a mixture of inorganic compounds of nitrogen phosphorous and potassium (NPK)
• Describe the use of fertilisers To replace nutrients removed by the growth and harvesting of crops and feeding
• Describe the role of mycorrhizae Phosphorus in the form of phosphate ions is taken in through the roots of plantsSome fungi form symbiotic or mutualistic (where both organisms benefit) relationships with plant roots - these relationships are known as mycorrhizaeThe fungi consists of hyphae – long thin strands which connect with the plant roots and extend into the soil to increase the surface area for absorption of water and of ions such as phosphateIn return the fungi receive organic compounds such as glucose produced by the plant during photosynthesis
• Draw a simplified diagram of the nitrogen cycle
• Describe the role of denitrifying bacteria Convert nitrates back into atmospheric nitrogen which then continues the cycle
• Describe the role of saprobionants in ammonification Saprobiotic microorganisms cause decay and break down animal and plant proteins into ammonia which forms ammonium ions in the soilThese ammonium ions will then form ammonia via ammonification
• Describe the role of nitrifying bacteria Oxidise ammonia and ammonium ions in the soil into nitrites and then nitratesNitrates are absorbed by plant roots by active transport and provide the source of nitrogen for the synthesis of proteins and nucleic acids
• Describe the role of nitrogen fixing bacteria Live free in the soil and ‘fix’ nitrogen into ammonia/ammonium compounds
• Describe the role of saprobiotic microorganisms in decomposition Used to break down the proteins in animals to form organic residues in soil that can be‎ ‏‏recycled
• Draw a simplified diagram of the nitrogen cycle
• Describe phototropism in plants Cells in the tip of the shoot/root produce IAAIAA diffuses down the shoot/rootIAA moves to shaded side of the shoot/rootIn shoots this stimulates cell elongation whereas in roots it inhibits cell elongationSo shoots bend towards light whereas roots bend away from light
• Describe how heart rate is controlled Baroreceptors detect a [fall / rise] in blood pressure and/or chemoreceptors detect a [rise / fall] in blood CO2 concentration or [fall / rise] in blood pHThis sends impulses to the medulla / cardiac control centre which send more frequent impulses to SAN along the [sympathetic (increases heart rate) / parasympathetic (decreases)] neuronesSo [more / less] frequent impulses are sent from the SAN to / from the AVN so the cardiac muscle contracts [more / less] frequentlySo heart rate [increases / decreases]
• Describe the locations of chemoreceptors and pressure receptors Chemoreceptors and pressure receptors are located in the aorta and carotid arteries
• Describe the Myogenic stimulation of the heart Sinoatrial node (SAN) acts as pacemaker - sends regular waves of electrical activity across the atria causing it to contract simultaneouslyNon-conducting tissue between atria/ventricles prevents impulse passing directly to the ventricles preventing immediate contraction of ventriclesWaves of electrical activity reach the atrioventricular node (AVN) which delays the impulse allowing the atria to fully contract and empty before ventricles contractAVN sends a wave of electrical activity down the bundle of His which branches into Purkyne tissue and causes the ventricles to contract simultaneously from the base up
• Describe the differences in colour vision for rods and cones Rods only allow monochromatic vision (black and white)There is only one type of rod that only contains one pigmentCones allow colour vision3 types of cones; red blue and greenWith different optical pigments → absorb different wavelengthsStimulation of different combinations/proportions of cones gives a range of colour perception
• Describe the differences in visual acuity for rods and cones Rods give lower visual acuitySeveral rods are connected to a single neuroneSeveral rods send a single set of impulses to the brain (therefore it cannot distinguish between separate sources of light)Cones give higher visual acuityEach cone is connected to a single neuroneCones send separate (sets of) impulses to the brain (so can distinguish between 2 separate sources of light)
• Describe the differences in sensitivity to light for rods and cones Rods are more sensitive to lightSeveral rods are connected to a single neurone Spatial summation is required to reach/overcome threshold to generate an action impulseCones are less sensitive to lightEach cone connected to a single neuroneNo spatial summation