Year 2 Model Answers Flashcards
Describe predator-prey relationships
Predator populations peaks after prey population
Prey population increases due to low numbers of predators
more food for predators so numbers increase
increased predation reduces number of prey
number of predators decreases due to lack of food / starvation;
Describe 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
Why are there are energy losses between trophic levels in consumers?
Energy is not transferred between consumers because:
Some parts aren’t eaten (bones) and some parts are eaten and are not absorbed (faeces)
Some parts are eaten, absorbed but excreted (urine)
Some biomass us broken down and lost as heat in respiration (temp regulation/movement)
Why don’t plants convert energy from light to GPP?
Sunlight is not converted to biomass because:
Some light is the wrong wavelength (e.g. green)
Some doesn’t hit a chlorophyll molecule/transmitted
Most light is reflected by other molecules in the atmosphere
Other limiting factors may be involved
What is Biomass?
Dry mass of carbon in a organisms in a particular area
How do farmers increase productivity?
Food chains/webs are simplified (pests are removed)
Respiration of livestock is reduced (movement limited, temperature regulated)
How is Biomass determined?
A sample of organism is dried.
The sample is then weighed at regular intervals (e.g. every day)
Until the mass remains constant
Describe the 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
Describe ways the Nitrogen Cycle is Optimised
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
Describe the Phosphorous 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
Describe 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 less photosynthesis
Saprobionts respire aerobically while decomposing dead matter
Less oxygen for fish and other organisms to respire so they die
Describe the Light Dependent Reaction
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.
Describe the Light Independent Reaction
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
Describe 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
Describe the Link Reaction
In the mitochondrial matrix
Pyruvate is oxidised using coenzyme A
CO2 released
NAD is reduced
Acetyl CoA is formed
Describe the 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.
Describe 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
Describe Anaerobic Respiration 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
Describe Anaerobic Respiration 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
Describe 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,
Describe 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 affect the shoots?
IAA produced in tip
IAA diffuses down the shoot
IAA accumulates/moves to the shaded side
Leading to cell elongation
Shoot elongates toward the light
How does IAA affect the 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
Describe how the Pacinian corpuscle works
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
Describe 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
Describe 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
Describe the electrical control of heart rate
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.
Describe how heart rate responds when CO2 increases
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
Describe how heart rate responds when CO2 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
Describe how heart rate responds when blood pressure decreases
Baroreceptors detect pressure increase
Too low pressure means not enough oxygen etc. will get to cells
Sensory neurone takes more impulses to medulla
Medulla sends more impulses along the sympathetic nerve
sympathetic nerve causes SAN to increase
Heart rate increases
Describe how heart rate responds when 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
