Model Answers P2 Flashcards
Succession
• Pioneer species colonises an area with hostile conditions
• This leads to changes in the abiotic factors
• The conditions become less hostile
• Other species are able to colonise the area
• Conditions continue to change and become less hostile and new organisms outcompete the pioneer species increasing biodiversity
• Eventually conditions become favourable to a climax community
• The climax community has stable abiotic factors, stable populations, stable communities
Energy losses between trophic levels in Consumers
• Energy is not transferred between consumers because:
1. Some parts aren’t eaten (bones)
2. Some parts are eaten and are not absorbed (faeces)
3. Some parts are eaten, absorbed but excreted (urine)
4. Some biomass us broken down in respiration (temp regulation/movement)
Energy losses in plant GPP
• Sunlight is not converted to biomass because:
1. Some light is the wrong wavelength (e.g. green)
2. Some doesn’t hit a chlorophyll molecule/transmitted
3. Most light is reflected by other molecules in the atmosphere
4. Other limiting factors may be involved
Biomass
• Dry mass of carbon in a organisms in a particular area
• A sample of organism is dried.
• The sample is then weighed at regular intervals (e.g. every day) • Until the mass remains constant
Increasing Productivity on Farms
• Food chains/webs are simplified (pests are removed)
• Respiration of livestock is reduced (movement limited, temperature regulated)
Nitrogen cycle
• Nitrogen gas in the air is converted into ammonia in the soil by nitrogen fixing bacteria
• Some nitrogen fixing bacteria in leguminous plant root nodules have a mutualistic relationship with
plants and convert nitrogen gas to ammonia then nitrates directly
• Nitrates in the soil are absorbed by plant roots and converted to nitrogen containing compounds e.g. amino acids and DNA
• Nitrogen containing compounds in plants may be absorbed when eaten by consumers
• Proteins from waste and dead material are broken down/hydrolysed to ammonia in soil by enzymes
released by saprobionts during ammonification
• Ammonia in the soil is oxidised to nitrites, then nitrates, by nitrifying bacteria in the soil in aerobic conditions. These nitrates can be absorbed by the plants
• If the soil is waterlogged, the lack of oxygen leads to denitrification where nitrates are converted back to gaseous nitrogen by denitrifying bacteria
Optimising nitrogen cycle
• Using crop rotation to plant leguminous plants – these will replenish nitrates in the soil
• Using crop rotation to replenish soil nutrients
• Ploughing aerates soil to ensure more oxidised ammonia→nitrates in
nitrification
• Preventing waterlogging reduces anaerobic conditions so less denitrification occurs
• Selective breeding can be used to optimise growing conditions
• Fertilisers can be added to increase concentration of minerals e.g. nitrates
Phosphorus cycle
• Plants absorb phosphorous form the soil
• Consumers eat the plants and absorb phosphorous
• Dead and waste (faeces etc.) material is decomposed releasing phosphorous into the soil
• Runoff from farm fertiliser means excess phosphorous enters bodies of water (lakes/rivers etc.)
• Phosphorous sediment in water is uplifted forming rocks on the surface
• Weathering releases phosphorous from the rock into the water and soil
• Leeching of phosphorous from soil/weathered rock causes phosphorous to enter the water
Eutrophication
• Excess nitrates runoff into bodies of water
• Excess growth of algae/Algal bloom forms on the surface of water • Reduced light so aquatic plants die
• Saprobionts respire aerobically while decomposing dead matter
• Less oxygen for fish and other organisms so they die
LDR
• In photoionisation, light excites the electrons in chlorophyll II and they move to carrier proteins in the thylakoid membrane.
• The electrons are replaced by the e- produced by splitting water (photolysis), which also produces oxygen and H+.
• Electrons move along carrier proteins in a series of redox reactions losing energy as they go. This is used to pump H+ into the thylakoid space creating a chemiosmotic gradient.
• H+ move down the gradient through ATP synthase during photophosphorylation producing ATP from ADP+Pi
• The electrons are donated to chlorophyll I and more are excited by light, travelling along another ETC until they reduce NADP to NADPH with H+ from photolysis.
LIR
• CO2 is fixed, combining with RuBP using the enzyme Rubisco
• This produces two glycerate-3-phosphate (GP)
• GP is reduced to Triose phosphate (TP)
• Using energy from ATP and reduced NADP
• TP can be regenerated to RuBP using energy from ATP,
• 1C from TP is converted into organic molecules e.g. glucose, amino acids, glycerol
Glycolysis
• In the cytoplasm
• Phosphorylation of glucose using ATP to make it more reactive;
• Lysis of the phosphorylated glucose intermediate to form Triose Phosphate
• Oxidation from TP to pyruvate by losing H+ and e-
• Net gain of 2 ATP;
• NAD reduced/NADH formed
Link reaction
• In the mitochondrial matrix
• Pyruvate is oxidised using coenzyme A • CO2 released
• NAD is reduced
• Acetyl CoA is formed
Krebs cycle
• Acetyl CoA reacts with a 4C acceptor molecule
• The 6C intermediate is decarboxylated and oxidised,
removing CO2 and reducing NAD
• The resulting 5C intermediate is also decarboxylated and oxidised removing CO2 and reducing 2xNAD, reducing FAD and generating 1x ATP in a series of REDOX reactions.
• Until the original 4C acceptor is formed again.
Oxidative phosphorylation
• FADH and NADH are oxidised and lose e- and H+
• The e- are passed from carrier protein to carrier protein in the mitochondria inner
membrane in a series of redox reactions
• This releases energy
• The energy is used to pump H+ through the membrane into the inner membrane space building a chemiosmotic gradient
• H+ moves back through the membrane through ATP synthase
• ADP+Pi→ATP
• Oxygen is the terminal electron acceptor forming water
Anaerobic respiration in mammals
In Mammals
• Pyruvate is reduced to lactate • NADH is oxidised during this
process
• This prevents NAD running out and allows ATP to continue being made in glycolysis
Anaerobic respiration in yeast
In yeast
• Pyruvate is reduced to ethanal then ethanol
• NADH is oxidised during this process
• CO2 is produced
• This prevents NAD running out and allows ATP to continue being made in glycolysis
Taxis
• In invertebrates
• Movement in a direction
• Movement toward (positive) or away (negative) from stimulus
• So organisms can survive and reproduce
• E.g. chemotaxis, phototaxis,
Kinesis
• In invertebrates
• Directionless movement
• Movement isn’t in a direction
• Usually, to do with rate of turning
• Increased rate of turning leads to an organism remaining in favourable conditions
• So organisms can survive and reproduce
How does IAA impact cell elongation in roots
- IAA produced in the tip
- IAA diffuses down the root
- IAA accumulates/moves to the base of the root (due to gravity)
- IAA inhibits elongation in root
- Root elongates downwards
How does IAA impact cell elongation in the shoots
Shoots (when sunlight from one direction)
1. IAA produced in tip
2. IAA diffuses down the shoot
3. IAA accumulates/moves to the shaded side
4. Leading to cell elongation
5. Shoot elongates toward the light
Pacinian corpuscle
• Pressure is applied and the lamella is deformed
• Stretch mediated sodium ion channels open
• Na+ diffuse into axon
• Leading to depolarisation and action potential if threshold is exceeded
Convergence in rod cells
• Rods are found around the outside of the retina, away from the fovea
• Light stimulus triggers depolarisation in the rod cells
• Many rods converge and are connected to a single sensory neurone
• Depolarisation undergoes (spatial) summation to trigger an action potential
• In low light there is enough light to lead to action potential
• However, this reduces visual acuity
Acuity in Cone Cells
• Cone cells are located in the fovea (behind the retina to maximise light stimulus)
• Every cone cell is connected to a single sensory neurone (no convergence)
• Each cone sends a single impulse to the brain
• With high visual acuity
• Three types of cones detect three different wavelengths of light
Control of heart rate/initiating a heart beat
• Sino Atrial Node initiates a wave of electrical impulses across both atria causing them to contract
• Non-conductive tissue prevents impulse going straight to ventricle
• Atrio Ventricular Node delay impulse so ventricles can fill
• AV Node sends wave of electrical impulses down Bundle of His
• Ventricles contract from bottom up.
What happens if CO2 (pH)increased
• pH in blood lowers
• Chemoreceptors detect it
• CO2 needs to be removed
• Sensory neurone takes more impulses to medulla
• Medulla sends more impulses along the sympathetic
nerve
• Sympathetic nerve causes SAN to increase
• Heart rate increases
What happens if the CO2 (pH) decreases?
• pH in blood increases
• Chemoreceptors detect it
• Sensory neurone takes more impulses to medulla
• Medulla sends more impulses along the parasympathetic
nerve
• Parasympathetic nerve causes SAN to decrease
• Heart rate decreases
What happens if the blood pressure increases?
• Baroreceptors detect pressure increase
• Too high pressure can damage artery walls, so needs to be
restored
• Sensory neurone takes more impulses to medulla
• Medulla sends more impulses along the parasympathetic
nerve
• parasympathetic nerve causes SAN to decrease
• Heart rate decreases
