a-level biology questions

Describe ATPs specific properties that make it a good energy source?
1. It is a small, soluble molecule so it can be easily transported around the cell. 2. It is easily broken down so energy can be easily released instantaneously. 3. It can be quickly re-made. 4. Phosphorylates molecules. 5. Cant pass out of the cell
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What is photoionisation?
Where light energy excites electrons in a molecule, giving them more energy and causing them to be released.
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Carbohydrates produced by photosynthesis are not used straight away, what happens with them?
The carbohydrates are stored as starch grains in the stroma.
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Explain how light-dependent reactions shows that some of the energy from electrons released during photoionisation is conserved in the production of ATP and reduced NADP
Making ATP from ADP and inorganic phosphate. Making reduced NADP from NADP. Splitting water into protons, electrons and oxygen.
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What is chemiosmosis?
The process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis.
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What is cyclic photophosphorylation?
Only uses PS1. It is called cyclic because the electrons from the chlorophyll molecules are not passed onto NADP, but are passed back to PS1 via electron carriers. The process does not produce NADP or O2.
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At what wavelengths do ps1 and ps2 absorb best at?
Photosystem 1= 700nm Photosystem 2= 680nm
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How many turns of the calvin cycle are needed to produce 1 moleucle of TP?
3
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How many turns of the calvin cycle are needed to produce 1 hexose sugar?
6
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How much ATP and NADPH does 6 turns of the calvin cycle produce
18 ATP and 12 NADPH
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How are lipids and amino acids formed from the calvin cycle?
Lipids- Made using glycerol, which is synthesised from triose phosphate and fatty acids which are synthesised from GP. Amino acids- Made from GP.
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What are the optimum conditions for photosynthesis?
High light intensity of a certain wavelength- Light provides energy for light dependent reaction. Temperature around 25 degrees- enzymes inactive or denature if not. CO2 0.4%, any higher stomata close.
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Evaluate data relating to common agricultural practices used to overcome the effect of these limiting factors
Carbon dioxide concentration- Can be added to the air by burning propane. Light- Can get through the glass, lamps provide light at night timw. Temperature- Glasshouses trap heat energy from sunlight which warms the air.
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How do you calculate an rf value?
Distance travelled by spot/ Distance travelled by solvent
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How much ATP is produced in glycolysis?
4 ATP is produced, but 2 were used up. Net gain = 2
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What happens after glycolysis in anaerobic respiration?
The pyruvate produced in glycolysis is converted into ethanol (in plants and yeast) or lactate (in animals) using reduced NAD.
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Explain how ATP production can be affected by mitochondrial diseases?
They can affect proteins involved in oxidative phosphorylation or the Krebs cycle function, reducing ATP production. This may cause anaerobic respiration to increase to try make up ATP shortage. lots os lactate produced cause fatigue and weakness.
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How is dry mass measured?
A sample of the organism is dried in an oven set at a low temperature. The sample is then weighted at regular intervals. Once the mass becomes constant all the water has been removed.
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Describe how the chemical energy store in dry biomass can be estimated using calorimetry
A sample of dry biomass is burnt and the energy released is used to heat a known volume of water. 2. The change in temperature of the water is used to calculate the chemical energy of the dry biomass.
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What is gross primary production?
The total amount of chemical energy converted from light energy by plants, in a given area.
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How do you calculate net production of consumers?
N= I - (F + R) Where N is net production, I is chemical energy ingested in food, F is chemical energy lost in faces and urine, R is energy lost through respiration
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Explain the role of saprobionts in decomposition
Saprobionts feed on the dead plants and animals and on their waste products breaking them down. This allows important chemical elements in the remains to be recycled.
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Explain the role of mycorrhizae in facilitating the uptake of water and inorganic ions by plants
Mycorrhizae greatly increase the rate at which phosphorus can be assimilated.
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Describe the process of eutrophication?
1. Mineral ions leached from fertilised fields stimulate the rapid growth of algae. 2. Algae blocks light from reaching the plants below. 3. Plants die because cant photosynthesise. 4. Bacteria feed on dead plant matter. 5. Fish die
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Explain the phosphorus cycle?
1. Phosphate in rocks are released into the soil by weathering. 2. Phosphate ions are taken into the plants through the roots. 3. Phosphate ions are transferred through the food chain. 4. Phosphate ions are lost from the animals in waste products.
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Phosphorus cycle continued?
5. When plants + animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants. 6. Weathering of rocks releases phosphate ions into seas which is taken up.
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Explain how nutrients are lost when when crops are harvested?
1. Crops take in minerals from the soil as they grow. 2. When crops are harvested they are removed from the field where they are grown rather than being allowed to die + decompose there. This means mineral ions they contain are not returned to soil.
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What is a reflex?
A reflex is where the body responds to a stimulus without making a conscious decision to respond
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What is taxes? What is kinesis?
Taxes- The organism moves towards or away from a directional stimulus e.g. light. Kinesis- The organisms movement is affected by a non-directional stimulus e.g. humidity.
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Explain what happens when a pacinian corpuscle is stimulated?
1. When a pacinian corpuscle is stimulated, the lamellae are deformed and press on the sensory nerve ending. This causes the sensory neurones cell membrane to stretch, deforming the stretch-mediated sodium ion channels. The channels open.
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Explain the features of rod cells?
-Rod cells are very sensitive to light. This is because many rods join 1 neurone. - Rods give low visual acuity because many rods join the same neurone, which means light from 2 points close together cant be told apart.
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Explain the features of cone cells?
- Cones are less sensitive to light. This is becasue 1 cone joins 1 neurone so it takes more light to reach threshold. -High visual acuity because cones are close together + 1 cone joins 1 neurone.
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What is hyperpolarisation?
Potassium ion channels are slow to close so there is a slight overshoot where too many potassium ions diffuse out of the neurone. The potential difference becomes more negative than the resting potential.
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What is the purpose of the refractory period acting as a time delay between one action potential and the next?
- Action potentials do not overlap, but pass along as discrete impulses. - There is a limit to the frequency at which nerve impulses can be transmitted. - Action potentials are unidirectional
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What are the 3 factors that affect the speed of conduction of action potentials?
Myelination/ Axon diameter/ Temperature
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What is a synapse? What is a neuromuscular junction?
1. The junction between a neurone and another neurone. 2. A synapse between a motor neurone and muscle cell
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What is summation?
Summation is where the effect of neurotransmitter released from many neurones is added together.
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What is spatial summation?
1. Many neurones connect to 1 neurone. 2. The small amount of neurotransmitter released from each of these neurones can be enough altogether to reach the threshold in the post synaptic neurone and trigger an action potential.
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What is temporal summation?
Temporal summation is where 2 or more nerve impulses arrive in quick succession from the same presynaptic neurone. This makes an action potential more likely because more neurotransmitter is released into the synaptic cleft.
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What attaches bones to bones? What attaches muscles to bones?
Muscles to bones= Tendons Bones to Bones= Ligaments
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What is the function of transverse tubules?
They help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre.
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What is the function of the sarcoplasmic reticulum?
The sarcoplasmic reticulum stores and releases calcium ions that are needed for muscle contraction.
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What is positive feedback?
Positive feedback mechanisms amilify a change from the normal level. Positive feedback takes body temperature further away from the normal level.
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Explain how adrenaline and glucagon act via a second messenger?
1. The receptors for adrenaline and glucagon have specific tertiary structures. Adrenaline + glucagon bind to their receptors and activate an enzyme called adenylate cyclase. This converts ATP into a second messnger called cAMP. cAMP activates PK.
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What are the 3 functions of the refractory period?
1. Action potentials do not overlap, but pass along as discrete impulses. 2. There is a limit to the frequency at which nerve impulses can be transmitted. 3. Action potentials are unidirectional
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How does axon diameter affect the speed of conduction of action potentials?
Bigger diameters have less resistance to the flow of ions so with less resistance depolarisation reaches other parts of the neurone cell membrane quicker.
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Give 5 ways drugs can affect the action of neurotransmitters at synapses?
1. Same shape as neurotransmitters. 2. Block receptors. 3. Inhibit the enzyme that breks down neurotransmitters. 4. Stimulate the release of neurotransmitters. 5. Inhibit the release of neurotransmitters
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The hardy weinberg prediction is only correct under what conditions?
It has to be a large population/ No immigration/ No emmigration/ No mutations/ No natural selection
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Describe how alterations to tumour suppressor genes can lead to the development of tumours?
Increased methylation of tumour suppressor genes. Mutation. Tumour suppresor gens are not transcribed. Uncontrollable cell division.
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Describe how you would determine the mean percentage cover for beach grass on a sand dune?
1. Method of randomly determining position using random number generator. 2. Large number of quadrats. 3. Divide total percentage cover by number of quadrats.
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Suggest appropriate units for gross productivity?
Unit of energy per year
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Explain the decrease in gross productivity as the woodland matures?
1. Less light 2. Reduced photosynthesis
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Suggest what the scientists should have done during the drying process to be sure that all of the water had been removed from the plant samples.
1. Weigh samples at intervals during drying; 2. To see if weighings became constant (by 3 days).
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Describe another process carried out by microorganisms which adds ammonium ions to soil.
amino acids broken down (to ammonium ions by saprobionts
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Suggest two ways in which crop rotation may lead to high crop yields.
(Different crops use) different minerals. (Different crops have) different pests
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Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration.?
Regenerates / produces NAD. (NAD used) in glycolysis.
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In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this.
(Pyruvate used) in aerobic respiration
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What happens if carbon dioxide concentration is above 0.4 or temperature is above 25 degrees?
The stomata close to avoid losing too much water. Enzymes may denature for high temperatures.
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What other respiratory substrates can be used in aerobic respiration?
Fatty acids from lipids. Amino acids from proteins.
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What is biomass?
The chemical energy stored in a plant
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How can biomass be measured?
Mass of carbon per given area
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Describe how the chemical energy store in dry biomass can be estimated using calorimetry
1. A sample of dry biomass is burnt and the energy released is used to heat a known volume of water. 2. The change in temperature of the water is used to calculate the chemical energy of the dry biomass.
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Describe how net primary production is available for plant growth and reproduction. It is also available to other trophic levels in the ecosystem, such as herbivores and decomposers ?
NPP is the energy available to the plant for growth and reproduction. It is also the energy available to organisms at the next stage in the food chain . These include herbivores and decomposers.
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Explain how production is affected by farming practices designed to increase the efficiency of energy transfer by simplifying food webs to reduce energy losses to non-human food chains
Farmers can reduce pest numbers. Insecticides kill insect pests that eat and damage crops. Less biomass is lost from crops so NPP is greater. Biological agents e.g. parasites eat pests.
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Explain how production is affected by farming practices designed to increase the efficiency of energy transfer by reducing respiratory losses within a human food chain?
1. Animals kept in pens where their movement is restricted. 2. The pens are indoors and kept warm, so less energy is wasted by generating body heat.
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What are the benefits of increasing NPP and the efficiency of energy transfer to humans?
1. Moor food can be produced in a shorter space of time usually at a lower cost. 2. However raises ethical issues restricts natural behaviour causes animals pain and distress.
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Explain the role of saprobionts in decomposition?
Saprobionts feed on the remains of dead plants and animals and on their waste products breaking them down. This allows important chemical elements in the remains to be recycled.
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Describe saprobiotic nutrition?
Saprobionts secrete enzymes and digest their food externally, then absorb the nutrients they need. During this process organic molecules are broken down into inorganic ions. Obtain nutrients.
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What is the role of hyphae?
1. Increase the SA of the plants root system, helping the plant to absorb ions fromthe soil that are usually scarce. 2. Increase the uptake of water by the plant.
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Explain the use of natural and artificial fertilisers to replace the nitrates and phosphates lost by harvesting plants and removing livestock
Artificial fertilisers= contain pure chemicals. Natural fertilisers= manure, composted vegetables.
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Why is the leaching of phosphates less likely than the leaching of nitrates?
Phosphates are less soluble in water.
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Describe how in flowering plants, specific growth factors move from growing regions to other tissues, where they regulate growth in response to directional stimuli
High concentrations of auxin inhibit growth in roots.
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Where does IAA increase in gravitropism?
IAA concentration increases on the lower side- cells elongate so the shoot grows upwards.
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Describe how photoreceptors convert light into an electrical impulse?
1. Light enters the eye, hits photoreceptors and is absorbed by light sensitive optical pigments. 2. Light bleaches the pigments casuing a chemical change + altering the membrane permeability to sodium ions
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What is the role of the bundle of His?
The bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity between the ventricles to the apex of the heart.
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What is the role of the purkyne tissue?
The purkyne tissue carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously from the bottom up.
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Compare transmission across a cholinergic synapse and across a neuromuscular junction
1. The post synaptic membrane has lots of folds that form clefts. These clefts store the enzyme that break down Ach. 2. Has more receptors. 3. Ach is always excitatory at a neuromuscular junction.
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Recall the importance of maintaining a stable blood glucose concentration in terms of availability of respiratory substrate and of the water potential of blood
If blood glucose concentration is too high the water potential of the blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis. This can cuase cells to shrivel up and die.
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Recall how possession of separate mechanisms involving negative feedback controls departures in different directions from original state, giving a greater degree of control
Only 1 negative feedback mechanism means a slower response + less control. you can only turn it on or off. Multiple mechanims means you can actively increase or decrease a level so it returns to normal.
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Recall the factors that influence blood glucose concentration
Healthy balanced diet, exercise, losing weight
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Why do people with diabetes have a different urine colour?
The kidneys cant reabsorb all of the glucose so some of it is excreted in the urine.
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When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why.
Water potential of blood will decrease; 2. Water moves from osmoreceptor into blood by osmosis.
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If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why.
Glucose in filtrate lowers water potential Lower Ψ gradient. Less water is reabsorbed.
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What is genetic drift?
1. Individuals within a population show variation. 2. By chance the allele for 1 genotype is passed on more often. 3. number of individuals with allele increases. 4. reproductive isolation and speciation.
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Explain why genetic drift is important only in small populations
Chance has a gretaer influence . In a large popualtion any chance variations will even out.
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Explain how in eukaryotes and some prokaryotes, translation of the mRNA produced from target genes can be inhibited by RNA interference (RNAi)
siRNA associates with proteins and unwinds. SiRNA binds to the target mRNA. The proteins associated with the siRNA cut the mRNA into fragments . Fragments move to a processing body to be degraded.
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What are promoter regions?
DNA sequences that tell the enzyme RNA polymerase when to start producing mRNA.
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Other cards in this set

Card 2

Front

What is photoionisation?

Back

Where light energy excites electrons in a molecule, giving them more energy and causing them to be released.

Card 3

Front

Carbohydrates produced by photosynthesis are not used straight away, what happens with them?

Back

Preview of the front of card 3

Card 4

Front

Explain how light-dependent reactions shows that some of the energy from electrons released during photoionisation is conserved in the production of ATP and reduced NADP

Back

Preview of the front of card 4

Card 5

Front

What is chemiosmosis?

Back

Preview of the front of card 5
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