part 3 Flashcards
What effect does stomatal opening have on heat stress on a plant?
It cools the plant/reduces the temperature. Water leaves the stomata and evaporates, reducing the temperature of the plant.
What effect does ABA have on the stomata?
ABA (from leaf and root cells) causes stomatal closing by activating changes in ionic concentration of guard cells, reducing water potential and turgor of cells and closing stomata.
State three chemical defences against herbivory (attack by insects).
Tannins, alkaloids, Terpenoids.
State three physical defences against herbivory.
Thorns, barbs, spikes, spiny leaves, fibrous and inedible tissue, hairy leaves, stings.
How do tannins prevent herbivory?
Bitter taste to deter animals and toxic to insects (inactivate digestive enzymes in insect saliva).
How do alkaloids prevent herbivory?
Bitter tasting and sometimes poisonous.
What is the name for a chemical made by an organism which affects the behaviour of other members of the same species?
Pheromones.
Plants do not have pheromones, what do they have instead?
Volatile Organic Chemicals (VOCs) produced by plants, which act between themselves and other organisms.
Give an example of a plant that produces a VOC and describe its action.
Cabbages, under attack from cabbage white butterfly caterpillars, produce VOCs to attract the wasp Cotesia glomerata. The wasp lays eggs in caterpillar eggs, killing them. The VOCs deter the female cabbage white butterfly from laying more eggs on the plant.
How does the plant, mimosa pudica, protect itself against herbivory?
Contains alkaloids and the stem has sharp prickles, but if leaves are touched, they fold down and collapse, dislodging insects and scaring off larger animals. Caused by movement of potassium ions and changes in water potential of the cells.
Describe the functions of positive phototropism and positive geotropism.
Positive phototropism - plant shoots grow towards light which enables them to carry out the light dependent reaction of photosynthesis. Positive geotropism - roots grow downwards into the soil, giving them anchorage and enabling them to obtain water and mineral ions.
What will happen if a shoot is grown in light, shining from one side?
It will grow towards the light/positive phototropism.
If a shoot is exposed to light from one side, where will auxin be found within the shoot?
There will be less auxin on the light side and a greater concentration of auxin on the shady side. Auxin migrates laterally away from the light.
What effect does auxin have on the cells in a shoot?
It causes cell elongation and growth on the dark side so the shoot bends away from the shaded side and towards the light.
What is etiolation?
When plants are grown in the dark or partial darkness, producing rapid growth upwards. Plants are tall, thin and pale.
Which hormones cause longer internodes in plants grown in the dark?
Gibberellins.
What slow-rotating piece of equipment can be used to demonstrate geotropism in the lab?
Clinostat.
What would you expect to observe if germinating beans are grown on a clinostat over a few days?
The roots will curl as they try to grow ‘downwards’.
What would you expect to observe if a potted plant shoot is grown on a clinostat over a few days?
The shoot will grow horizontally outwards from the pot.
Which plant hormone is involved in fruit ripening?
Ethene.
Which plant hormone is involved in encouraging root growth?
Auxins.
Which plant hormone(s) is/are involved in delaying senescence?
In leaves - cytokinins; in citrus fruits - gibberellins.
Which plant hormone is involved in preventing the ageing of ripened fruit?
Cytokinins.
What hormone is used in rooting powder?
Auxin.
What are climacteric fruits?
Fruits that continue to ripen after harvesting e.g. bananas, avocados, tomatoes, mangoes.
Why are climacteric fruits harvested before they are ripe?
The unripe fruit is hard and much less easily damaged during transport than the ripe fruit.
How are auxins used as weedkillers?
They cause rapid and unsustainable growth in the dicot weeds so they die.
Is photosynthesis endothermic or exothermic? What does that mean?
Endothermic - overall reaction takes in energy.
State the overall chemical equation of photosynthesis.
6CO2 + 6H2O –> C6H12O6 + 6O2.
What is chemiosmosis?
Movement (diffusion) of protons across ATP synthase down the electrochemical gradient to generate ATP.
In chemiosmosis, where does the energy to pump protons come from?
Energy given off by an electron passing down the first electron transport chain in the light-dependent reaction.
Chemiosmosis allows the transformation of ADP into ATP. This process in photosynthesis is known as?
Photophosphorylation.
During photosynthesis, what is pumped across the membrane and into the thylakoid space of the chloroplast?
Hydrogen ions.
What pumps the hydrogen ions into the thylakoid space?
A cytochrome complex (electron carrier).
Where does chemiosmosis occur?
Along the membrane.
What is grana?
Stacks of thylakoids that contain photosynthetic pigments.
What is the stroma and its function?
The fluid enclosed in the chloroplast; site of light-independent stage.
What is the structure that connects grana together?
Intergranal lamella.
Describe the structure of a photosystem.
A light-harvesting complex that channels light towards a reaction centre (containing a primary pigment called chlorophyll a); accessory pigments channel photons towards the reaction centre.
Name one primary pigment and 3 accessory pigments.
Primary - chlorophyll A; accessory - xanthophylls, carotenoids, chlorophyll b.
Describe the differences between photosystem I and photosystem II.
PSI contains chlorophyll a that absorbs light at a peak of 700nm (P700). PSII contains chlorophyll a that absorbs light at a peak of 680 nm. Electrons are excited to a higher energy level in PSI than PSII.
Describe the light absorption of carotenoids, xanthophylls and chlorophylls.
Carotenoids absorb blue light; xanthophylls absorb blue and green light; chlorophylls absorb blue and red light.
In which part of the chloroplast does the light-dependent reaction take place?
Thylakoid membrane.
In which part of the chloroplast does the light-independent reaction take place?
Stroma.
Suggest why the Rf values of some pigments show a range rather than a single figure.
There are different types of these, with slightly different molecular masses/sizes of molecules/solubilities in the solvent.
Rf values for the different pigments differ according to the solvent used. Suggest why this is the case.
The molecules of pigment will have different solubilities in different solvents.
What 4 processes occur in the light-dependent reaction?
Light harvesting at the photosystems; photolysis of water; photophosphorylation (production of ATP in the presence of light); formation of reduced NADP.
Outline the role of water in photosynthesis.
Electron donor; source of protons/hydrogen ions; source of by-product, oxygen; keeps cells turgid so they can function (all metabolic reactions need to be in solution).
Suggest why a lack of iron in soil may reduce growth in plants.
Iron is needed for electron carriers in the chain (on thylakoid membranes) and for ferredoxin. A reduction of electron carriers could reduce rate of photosynthesis.
What is photolysis and where exactly does it take place?
The enzyme-catalysed splitting of water molecules, in the presence of light. It takes place in PSII on thylakoid membranes of chloroplasts.
Describe the differences between non-cyclic and cyclic photophosphorylation.
NC - involves PSI and PSII; produces ATP, oxygen and reduced NADP (NADP is final electron acceptor). C - involves PSI only; produces ATP only as electrons are recycled back to PSI and NADP is not reduced.
Describe how a proton gradient develops between the thylakoid lumen and the stroma.
Energy from electrons moving through chain of electron carriers is used to actively pump protons across the thylakoid membrane into the thylakoid lumen.
Describe the purpose of the proton gradient.
Protons can diffuse down their gradient through ATP synthase channels (using proton motive force), causing ADP to combine with inorganic phosphate to form ATP.
Describe what happens to protons that have moved through ATP synthase.
They are accepted along with electrons from the electron transport chain, by NADP. This is facilitated by NADP reductase (NADP has been reduced to NADPH).
Describe how an electron moves through the electron transport chain.
A photon excites an electron from PSII, the electron rising to a higher energy level and getting accepted by an electron acceptor. This energy level is unstable so the electron moves through a chain of electron carrier proteins, losing energy as it moves (this energy is transferred to pump protons). It is accepted by chlorophyll a in PSI and re-excited by another photon of light to a higher energy level than before.
Explain why chloroplasts in guard cells only contain PSI.
Produces ATP which actively pumps potassium ions into the cell, lowering the water potential so water follows by osmosis. This causes the guard cell to become turgid and the stoma to open.
Describe the differences in the fate of electrons released from chlorophyll in both non-cyclic and cyclic photophosphorylation.
Cyclic - pass via electron carriers back to PSI (little ATP generated); Non-cyclic - from PSII, pass via electron transport chain to PSI, PSI electrons accepted by NADP.
What is RuBisCo and its function?
Ribulose bisphosphate carboxylase/oxidase; an enzyme found in the stroma that catalyses carbon fixation (CO2 + RuBP –> GP).
Suggest why there are always only low levels of RuBP in the stroma of chloroplasts.
It is being continually regenerated and then combined with CO2.
Describe the role of carbon dioxide in the Calvin cycle.
Combines with 5C-RuBP to form a 6C intermediate. This is unstable and so breaks into 2 x 3C-GP molecules. This reaction is catalysed by RuBisCO.
Describe the conversion of GP into TP in the Calvin cycle.
3C-GP is converted into 3C-TP using ATP and the H atom from reduced NADP.
Describe how RuBP is regenerated in the Calvin cycle.
5/6 of TP is converted back into RuBP through reshuffling of the arrangement of carbon atoms. This conversion also uses ATP (RuP –> RuBP).
Describe the fate of triose phosphate.
1/6 leaves the Calvin cycle and is converted into sucrose, starch, cellulose, amino acids, glycerol, fatty acids, some is respired in glycolysis. The other 5/6 is used to regenerate RuBP.
State 2 products of the light dependent reaction used in the Calvin cycle.
ATP and reduced NADP.
Describe how plants respond to water stress. Explain how this affects their ability to photosynthesise.
Stomata close to prevent transpiration, which reduces gaseous exchange so not enough CO2 for photosynthesis. Plasmolysed cells cannot function as enzymes cannot work. Reduced water availability for photosynthesis – as source of electrons and protons.
Describe the effects of reducing the light intensity on the Calvin cycle.
Light dependent reaction cannot occur, so less ATP/NADPH; less GP –> TP; TP levels fall and GP accumulates; if TP levels fall then RuBP cannot be regenerated.
Describe the effects of reducing carbon dioxide levels in the Calvin cycle.
RuBP cannot accept it and RuBP accumulates; GP cannot be made; TP cannot be made.
Name all three enzymes involved in photosynthesis and their functions.
ATP synthase (allows chemiosmosis to occur to join ADP and Pi together to make ATP); NADP reductase (joins NADP with H+ and e- to make reduced NADP); RuBisCo (catalyses carbon fixation - CO2 + RuBP –> GP).
Describe what is meant by the term compensation point.
When the rate of photosynthesis is equal to the rate of respiration. This is when there is no net gain or loss of carbohydrate.
Define ‘limiting factor’.
A factor that limits the rate of reaction when in short supply.
Name three factors that affect photosynthetic rate.
Temperature; Carbon dioxide concentration; Light intensity.
Why does increasing light intensity also increase photosynthetic rate?
More energy absorbed by photosystems to excite electrons, so more electrons undergo ETC to generate proton gradient for more ATP production and reduced NADP production.
Why does more carbon dioxide increase photosynthetic rate?
Higher rate of carbon fixation at Calvin cycle for more GP and TP production.
Describe and explain how temperature affects photosynthetic rate.
At lower temp, enzymes are inactive hence low PS rate. As temp increases, enzymes and substrates gain KE and hence higher rate of ESC formation, so higher PS rate. At higher temp, enzymes become denatured hence PS rate decreases.
What is ATP synthesised from?
ADP + inorganic phosphate (P).
Name three biological processes that require the use of ATP.
Active transport, endocytosis, DNA replication.
What is a catabolic reaction?
Occurs within a cell. Large molecules are broken into smaller molecules.
What is an anabolic reaction?
Small molecules are combined into larger molecules.
What is glycolysis?
The first stage of respiration, glucose is converted into pyruvate.
What is NAD?
A coenzyme (nicotinamide adenine dinucleotide) Reduced NAD carries protons and electrons to the cristae.
What is phosphorylation in glycolysis?
Where glucose has 2 phosphate groups attached to form hexose bisphosphate using 2 molecules of ATP.
What is hexose bisphosphate split into during glycolysis?
2 molecules of triose phosphate.
What is triose phosphate converted into during the oxidation stage of glycolysis?
Pyruvate.
How many carbons are found in a molecule of pyruvate?
3.
Which molecule accepts the hydrogen atoms from triose phosphate when it is oxidised?
NAD.
What are the products of glycolysis for every molecule of glucose?
2 x pyruvate, 2 molecules of ATP, two reduced NAD.
What is the net gain of ATP in glycolysis?
2 (four are made but two are used).
Why is glycolysis an anaerobic process?
It occurs in the cytoplasm without the need for oxygen.
What is the cristae?
The inner highly folded mitochondrial membrane.
What is the mitochondrial matrix?
Fluid filled inner part of the mitochondria.
What is the average length of a mitochondrion?
2-5 micrometers.
Where does the link reaction occur in the mitochondria?
The mitochondrial matrix.
What is the name of the two coenzymes found in the mitochondria?
NAD & FAD.
Where is the electron transport chain found in the mitochondria?
The cristae of the inner membrane.
What is the cristae?
the inner highly folded mitochondrial membrane
What is the mitochondrial matrix?
fluid filled inner part of the mitochondria
What is the average length of mitochondrion?
2-5 micromiters
Where does the link reaction occur in the mitochondria?
the mitochondrial matrix
What is the name of the two coenzymes found in the mitochondria?
NAD & FAD
Where is the electron transport chain found in the mitochondria?
The cristae of the inner membrane
What is the name of the enzyme found in the cristae of the enzyme that synthesises ATP?
ATPsynthase
What is decarboxylation?
removal of a carboxyl group from a substrate molecule
What is dehydrogenation?
the removal of a hydrogen atom from a substrate molecule
What is substrate level phosphorylation?
production of ATP from ADP and P during glycolysis and the Krebs cycle
Why is pyruvate said to be decarboxylated and dehydrogenated during the link reaction?
The pyruvate loses a molecule of carbon dioxide and reduces NAD to become acetyl
What does the acetyl group in the link reaction join with before entering the Krebs cycle?
Coenzyme A
Explain how 1 molecule of glucose is formed into two molecules of acetyl coenzyme A
Glycolysis then the link reaction summary
What molecule enters the Krebs cycle?
Acetyl CoA
How many carbons are found in a molecule of acetyl CoA?
2
What molecule does acetyl CoA join to in the Krebs cycle?
oxaloacetate
How many carbons does citrate contain?
6
What two molecules combine together to form citrate in the Krebs cycle?
Oxaloacetate and acetyl CoA
What happens to citrate in the Krebs cycle?
It is decarboxylated and dehydrogenated into a 5C compound
What happens to the 5C compound in the Krebs cycle?
It is decarboxylated and dehydrogenated into a 4C compound
Where does substrate level phosphorylation occur in the Krebs cycle?
The 4C molecule combines temporarily with coenzyme A to produce a molecule of ATP
What are the products of one turn of the Krebs cycle?
3 reduced NAD, 1 reduced FAD, 2 molecules of CO2 and 1 molecule of ATP
What is the final stage of aerobic respiration called?
oxidative phosphorylation
Define chemiosmosis
the flow of protons, down their concentration gradient, across a membrane, through channel associated with ATP synthase
What is oxidative phosphorylation?
the formation of ATP using energy released from the ETC and in the presence of oxygen.
Where does oxidative phosphorylation take place?
in the mitochondria
What is the electron transport chain?
A chain of electron carrier proteins that contain an Fe ion. As electrons pass along the chain, some of the energy is used to pump protons across the inner mitochondrial membrane.
What is the name of the enzyme embedded in the cristae that is involved in oxidative phosphorylation?
ATP synthase
Which two coenzymes deliver hydrogen atoms to the ETC?
Reduced NAD & reduced FAD
How do reduced NAD & FAD release the hydrogen atoms they are carrying at the ETC?
They are reoxidised
What happens to the hydrogen atoms released at the ETC?
They are split into protons and electrons
When electrons are released at the ETC from reduced NAD and FAD, what is their fate?
They are passed along the chain of electron carriers. They are finally accepted by oxygen which helps to form water.
Where are protons pumped into by the ETC?
The intermembrane space
What forms when protons are pumped into the intermembrane space?
A proton gradient
What is the source of potential energy in the intermembrane space?
The proton gradient accumulates and creates a chemiosmotic potential also known as the proton motive force. The energy is used to generate ATP.
As protons flow from the high concentration inside the intermembrane space, why must they flow through ATP synthase?
The protons cannot easily flow through the lipid bilayer of the mitochondrial membranes.
How does the flow of protons cause ATP to be formed?
The protons cause a conformational change in the ATP synthase which allows ADP and Pi to combine to form ATP.
What is the final electron acceptor?
oxygen
How is water formed during oxidative phosphorylation?
Oxygen accepts the electrons and combines with protons from chemiosmosis to form water
Which stage of photosynthesis also involves chemiosmosis?
Photophosphorylation in the light dependent reaction
How many ATP can be formed from a molecule of reduced NAD?
3 ATP (2.5)
How many ATP can be formed from a molecule of reduced FAD?
2 ATP (1.5)
How many molecules of ATP can be formed from glycolysis by 1 molecule of glucose?
2
How many molecules of ATP can be formed from the link reaction by 1 molecule of glucose?
0
How many molecules of ATP can be formed from the Krebs cycle by 1 molecule of glucose?
2
How many molecules of ATP can be formed from oxidative phosphorylation by 1 molecule of glucose?
28
What is the total yield of ATP from one molecule of glucose during aerobic respiration?
32
Why is the theoretical yield of 32 ATP per glucose molecule rarely achieved?
Some ATP is used, some protons may leak through the mitochondrial membrane
Why is the pH of the intermembrane space lower than the mitochondrial matrix and the cytoplasm?
There is an accumulation of protons.
What are the two metabolic pathways used by eukaryotic cells to reoxidise NAD?
Ethanol fermentation and lactate fermentation
Which stage of respiration is the same for both aerobic and anaerobic respiration? Why?
Glycolysis, it occurs in the cytoplasm
In ethanol fermentation, what enzyme decarboxylates pyruvate into ethanal?
pyruvate decarboxylase
The enzyme pyruvate decarboxylase converts pyruvate into what during ethanol fermentation in yeast?
ethanal
Which enzyme is used to help ethanal accept hydrogen from reduced NAD in ethanol fermentation in yeast?
ethanol dehydrogenase
Why is yeast described as a facultative anaerobe?
It can respire aerobically or anaerobically depending on the environment
Write out the two steps involved in ethanol fermentation
- Pyruvate –> Ethanal + CO2; 2. Ethanal + H+ from reduced NAD –> Ethanol
What is the name of the enzyme that allows pyruvate to accept hydrogen from reduced NAD in lactate fermentation?
lactate dehydrogenase
Write out the equation for formation of lactate in anaerobic respiration in eukaryotic cells
Pyruvate + H+ from reduced NAD –> lactate
What is the fate of lactate?
It is moved to the liver where it is either converted back into pyruvate or it is recycled to glucose and oxygen
Lactate and ethanol fermentation do not produce any ATP. Suggest how these processes still allow the production of some ATP.
Both processes allow glycolysis to continue which has a net gain of 2 ATP
What is a respiratory substrate?
an organic substance that can be oxidised by respiration, releasing energy to make ATP
How can glycerol be used as a respiratory substrate?
It is converted to triose phosphate and then respired
How are fatty acids used as respiratory substrates?
They combine with acetyl CoA and enter the Krebs cycle
How are proteins used as respiratory substrates?
Different amino acids can enter different stages of aerobic respiration e.g. serine can be converted into pyruvate
Which respiratory substrate can be converted into acetate and enter the Krebs cycle via the link reaction?
fatty acids
Which molecule can be deaminated and the rest of the molecule enters the Krebs cycle directly?
amino acids
Why do lipids have the highest mean energy value per gram?
Lipids contain large chains of hydrocarbons which are a source of protons
What is the formula for the respiratory quotient?
CO2 produced/ O2 consumed
What is the RQ value for glucose?
1
What is the RQ value for fatty acids?
0.7
What is the RQ value for proteins?
0.8
What does an RQ value of over 1 suggest?
Anaerobic respiration is taking place
In an investigation into respiration, the RQ value was calculated as 0.82. Suggest which respiratory substrate was being used.
Protein
In an investigation into respiration, the RQ value was calculated as 0.99. Suggest which respiratory substrate was being used.
Glucose
In an investigation into respiration, the RQ value was calculated as 0.70. Suggest which respiratory substrate was being used.
Fatty acids
In an investigation into respiration, the RQ value was found to be 2.3. Suggest what can be deduced from these findings?
Anaerobic respiration has occurred
What is a mutation?
A random change to the genetic material.
What is a gene mutation?
A random change to base sequence of a gene.
What is a mutagen?
A substance or radiation that can cause a mutation.
What is a triplet?
A set of the 3 bases in DNA.
What is a point mutation?
A substitution of one DNA nucleotide for another, changing the triplet.
What are the 3 types of point mutation?
Silent, missense, nonsense
What is a silent point mutation?
A change to the DNA base triplet sequence that has no effect on the amino acid sequence in a protein.
What is a missense point mutation?
A change to the DNA base triplet sequence that leads to a change in the amino acid sequence in a protein.
What is a nonsense point mutation?
A change to the DNA base triplet sequence resulting in a termination triplet that leads to a truncated protein.
What is an indel mutation?
Insertion or deletion of one DNA nucleotide causing a frameshift.
What is a frameshift?
A change to every DNA base triplet downstream of an indel mutation.
Give an example of chromosome mutations.
Deletion / duplication / translocation / inversion
What is translocation in chromosome mutations?
A section of a chromosome breaks off and joins another non-homologous chromosome
What is inversion in chromosome mutations?
A section of a chromosome breaks off and is reversed before joining back onto the chromosome
What is the main example of gene expression control in prokaryotic cells?
lac operon
What is the function of the enzyme lactose permease?
Allows lactose to enter a bacterial cell.
What is the function of the enzyme beta-galactosidase?
Hydrolyses lactose into glucose and galactose.
What are the 4 components of the lac operon?
promoter, operator, lacZ structural gene, lacY structural gene
What is a structural gene?
A gene that codes for a functional protein.
What is a regulatory gene?
A gene that codes for a transcription factor which initiates/inhibits transcription of structural genes
What does the gene lacI code for?
Repressor protein
What does the gene lacZ code for?
Beta-galactosidase
What does the gene lacY code for?
Lactose permease
Where does the repressor protein bind in the lac operon?
Operator
Where does RNA polymerase bind in the lac operon?
Promoter
What is the inducer for the lac operon?
Lactose
What is the effect of lactose on the repressor protein?
Binds to the repressor protein, altering its shape and preventing it from binding to the operator region of the lac operon.
What conditions are necessary for the lac operon to be switched off?
Glucose present, lactose absent
