topic 5 Flashcards
5.1
What’s cellular respiration?
- Where food’s broken down and energy from food molecules is transferred to ATP
- Cellular respiration yields ATP
- To be used as a source of energy for metabolic reactions
Equation?
balanced?
Glucose + oxygen –> carbon dioxide + water (+ATP)
C6H12O6 + 6O2 –> 6CO2 + 6H2O (+ATP)
Is respiration exothermic / endothermic ?
why?
- Exothermic
- It releases energy + generates heat
Uses of the ATP produced from cellular respiration?
- chemical reaction
- Metabolic reactions
- Movement
- Anabolism
- Cell division
Where does respiration occur?
- In mitochondria + sometimes cytoplasm of each cell of the body
When doing bond energy calculations how to calculate
1. energy required to break bonds in reactants?
2. energy released when bonds in products are made?
3. energy change?
- sum of energy in reactants
- sum of energy in products
- Energy change = Reactants - Products energy
Hydrolysis + synthesis of ATP + ADP ?
- ATP hydrolysed to ADP + Pi
- Using water
- Energy made available for cellular reactions.
- ATP synthesised from ADP + Pi
- Releases water
- Energy is obtained from respiration
Catabolism reactions
- Breaking down complex molecules to simpler ones
- Exergonic ( releases energy )
- Hydrolysis reactions
- Oxidation reactions
Anabolism reactions
- Building up ( synthesizing complex molecules from simpler ones )
- Endergonic ( takes in energy )
- Condensation
- Reduction reactions
What are the different stages involved in aerobic respiration?
● glycolysis (in the cytoplasm)
● link reaction (in mitochondrial matrix)
● Krebs cycle (in mitochondrial matrix)
● oxidative phosphorylation (in mitochondrial inner membrane)
5.2
Glycolysis:
- first stage of both aerobic + anaerobic
- occurs in cytoplasm
Stages of glycolysis:
- Glucose (6C)
(phosphorylated to glucose phosphate,
2ATP –> 2ADP = energy transferred to new molecule = making it highly reactive) - Glucose phosphate (6C)
(highly reactive = splits into 2 triose phosphate) - 2x Triose phosphate (3C)
(molecules oxidised to produce 2x pyruvate.
on EACH molecule: NAD–>NADH [reduced] + 2ADP –> 2ATP - 2x pyruvate (3C)
Products of glycolysis:
2x Pyruvate
Net gain of 2 ATP
2x NADH
5.3
Link reaction:
Occurs in mitochondrial matrix
Reaction that moves products of glycolysis (Pyruvate + NADH) into krebs cycle.
Pyruvate + NADH actively transported from cytoplasm into mitochondrial matrix - for krebs cycle
link reaction occurs 2x as there are 2 pyruvate
Stages of the Link reaction:
- Pyruvate (3C) x2
(-is oxidised to form acetate (2C) -loses H
-the NAD picks up lost H+ and becomes reduced =
NAD –> NADH + releases Co2) - Acetate (2C)
(Acetate combines with coenzyme A to form Acetyl Coenzyme A = Acetyl CoA) - Acetyl CoA (2C)
Products of the link reaction:
2 pyruvate + 2 NAD + 2 CoA –>
2x CO2
2x NADH
2x Acetyl CoA
Krebs cycle:
Occurs in mitochondrial matrix
In a series of Redox reactions , Krebs cycle generates reduced coenzymes (NADH + FADH) + ATP by substrate level phosphorylation + CO2 is lost.
Stages of the Krebs cycle:
- Acetyl CoA (2C) combines with a 4C compound to form 6C acid (citrate).
[the CoA is recycled back into the link reaction to bind to another acetate] - 6C citrate is broken down into a 5C acid
- NAD –> NADH (reduced)
- CO2 released - 5C acid is broken down into original 4C compound acid
- NAD –> NADH x2
- FAD–> FADH
- ATP released
- CO2 released - The 4C acid combines with another acetyl CoA + cycle repeats
Products of the krebs cycle:
pr cycle:
3x NADH (reduced NAD)
1x FADH (reduced FAD)
1x ATP
2x CO2
pr glucose molecule (as 2x pyruvate pr glucose):
6x NADH (reduced NAD)
2x FADH (reduced FAD)
2x ATP
4x CO2
5.4
Oxidative phosphorylation:
- occurs in inner mitochondrial membrane (cristae)
- involves electron transport chain
- movement of protons across inner mitochondrial membranes
- catalysed by ATP synthase
Stages of oxidative phosphorylation:
- The NADH + FADH from krebs cycle are oxidised + H+ atoms split into protons + electrons.
- The electrons are passed along the electron transport chain (proteins embedded in inner mitochondrial membrane)
- Each time an electron moves to next protein in the ETC, it releases enough energy to transfer a proton (hydrogen) to intermembrane space.
- Results in an electrochemical gradient due to build up of the protons in intermembrane space.
- Protons move down this electrochemical gradient (through facilitated diffusion) through the ATP synthase = allows for chemiosmosis
- This catalyses phosphorylation of ADP to form ATP
- Oxygen is a terminal electron acceptor = pick up the electrons at end of ETC + binds with H+ to form water H2O
Why is Oxygen important in respiration?
- Oxygen is a terminal electron acceptor = pick up the electrons at end of ETC + binds with H+ to form water H2O
- if O2 didn’t pick up those E- = no more E- would be able to move across ETC = no energy released = protons wouldn’t transfer across to intermembrane space = no gradient build up = ATP wouldn’t be synthesised
5.5
Anaerobic respiration?
- occurs in absence of O2 to produce limited yield of ATP
- occurs in cytoplasm only
- different products in mammals vs plants + microbes
Anaerobic respiration in mammals:
- Pyruvate produced in glycolysis is reduced to form Lactate ( by getting H+ from NADH which is oxidised into NAD)
- The oxidised NAD is reused in glycolysis = to ensure more ATP is continued to be produced for anaerobic respiration.
Pyruvate (3C) —> Lactate (reduced = +H)
[ NADH –> NAD ] (oxidised = - H)
Anaerobic respiration in plant (+ microbes)
- Pyruvate produced in glycolysis is reduced to form Ethanol + Carbon dioxide
(By getting H+ from NADH which is oxidised into NAD) - The oxidised NAD is reused in glycolysis = to ensure more ATP is continued to be produced for anaerobic respiration.
Pyruvate (3C) —> Ethanol + CO2 (reduced = +H)
[ NADH –> NAD ] (oxidised = - H)
Why does lactate (by-product of anaerobic respiration) affect mammalian muscle contraction?
Lactate = acidic = results in muscle fatigue.
can’t respire anaerobically forever as acidic pH will denature enzymes etc
What is the disadvantage of producing ethanol during anaerobic respiration?
Dissolves cell membranes so cells die when concentration is above 12%
Compare the ATP yields per molecule of hexose glucose sugar from aerobic + anaerobic respiration:
Aerobic ≈ 38 molecules of ATP in ideal conditions
Anaerobic = 2 molecules from glycolysis
Core practical 9: investigating aerobic or anaerobic respiration using a respirometer
- Pressure changes in the boiling tube due to CO2 production (anaerobic experiments) or O2 consumption (aerobic experiments) cause a drop of coloured liquid to move.
- Sodium hydroxide =Absorbs CO2 so that there is a net decrease in pressure as O2 is consumed
5.6 [photosynthetic pigments]
Photosynthesis?
- Reaction in which light energy is used to split apart the strong bonds in water molecules in a process of photolysis in order to combine hydrogen with carbon dioxide to produce fuel in the form of glucose
- Autotrophic organisms make energy-containing compound out of CO2 + water by photosynthesis
Equation?
Carbon dioxide + Water –> Glucose + Oxygen
6Co2 + 6H20 --> C6H12O6 + 6O2
Absorption spectrum ?
Action spectrum ?
Absorption Spectrum:
- The range of different wavelengths of light that a photosynthetic pigment absorbs
Action Spectrum:
- The rate of photosynthesis at different wavelength of light absorbed
- How much photosynthesis occurs at different wavelight of light
Why do Chloroplasts contain different photosynthetic pigments ?
Chloroplasts contain different photosynthetic pigments (eg chlorophyll a + chlorophyll b) which absorb different wavelengths of light
- This means that more light can be absorbed in total = increases rate of photosynthesis
Examples of different photosynthetic pigments:
- Chlorophyll a [alpha] = (blue-green)
- Chlorophyll b [beta] = (yellow-green)
- Carotenoids:
- Carotene (orange)
- Xanthophyll (yellow)
- Phaeophytin (grey) = breakdown product of the other photosynthetic pigments
CORE PRACTICAL 10: Investigate the effects of different wavelengths of light on the rate of photosynthesis
METHOD ?
- Place a piece of pondweed in a beaker of water
- Cover 1 side of the beaker with the aluminium foil to block out the light
- Cover the other side of the beaker with one of the light filters
- Add half a spatula of sodium hydrogencarbonate to the water to provide CO2
- Leave for 5 minutes
- Place the bench lamp a set distance from the beaker
- Set up the photosynthometer + Leave for 5 minutes
- Record the volume of gas produced during this time
- Replace the filter with another colour of filter + repeat experiment
Findings ?
● Volume of gas produced (assumed to be oxygen) is proportional to rate of photosynthesis
● The greatest volume of gas will be produced when there is no filter used = as all wavelengths of light can be absorbed
● All filters will decrease volume of gas, but a green filter will decrease it the most because chloroplasts don’t absorb much green light - it is mostly reflected, which is why chloroplasts appear to be green
CORE PRACTICAL 11: Investigate the presence of different chloroplast pigments using chromatography
METHOD?
- Draw line in pencil around 1cm above the bottom of the filter paper used. Do not use a pen as the ink will obscure the results.
- Cut a section of leaf + place in a mortar. Add 20 drops of propanone + use the pestle to grind up the leaf sample + release the pigments
- Use a capillary tube to extract some of the pigment + blot it onto the centre of the pencil line drawn. Allow to dry + then blot again
- Suspend the paper in the solvent so that the level of the liquid does not lie above the pencil line + leave the paper for approximately 10 minutes/until the solvent has run up the paper to near the top
- Remove the paper from the solvent + draw a pencil line marking where the solvent moved up to.
=The pigment should have separated out + there should
be different spots on the paper at different heights above the pencil line - Calculate the Rf value for each spot
=distance travelled by solute / distance travelled by solvent
Findings ?
● Pigments that travel further up the paper will have a higher Rf value
-Rf values should be compared to the Rf known values in database to identify pigment. (make sure they use the same solvent + are for paper chromatography =these variables will make results differ)
- Factors that affect the rate of mobility:
-
Affinity- pigments have different affinities to the chromatography paper
=those with lower affinities will travel further up the paper - Solubility- pigments that are more soluble travel faster up the paper + will end up closer to the top at the solvent front
5.7 [ photosynthesis]
Chloroplast are sight of photosynthesis.
Describe the structure of chloroplasts
● Chloroplasts contain stacks of thylakoid , stacked up to form structures = grana
-which contain the photosynthetic pigments like chlorophyll
-These are arranged as photosystems ( l + ll )
● Chloroplasts contain stroma = the fluid surrounding the grana
-Stroma contains all of the enzymes required for the light-independent stage of photosynthesis
● Each granum is connected together by pieces of thylakoid membrane called lamella
● Double membrane = chloroplast envelope
(+ 3rd internal membrane system = thylakoid membrane)
Photosynthesis got 2 stages:
- Light dependent stage
- Occurs on the thylakoid membranes of the chloroplasts
-split water molecules (photolysis) - Photon of light hits chlorophyll molecule in thylakoid membranes = energy transferred to electrons = excited + move to higher energy level in thylakoid membranes + leaves chlorophyll molecule
- Picked up by an electron carrier to take part in cyclical or non-cyclical phosphorylation
cyclic photophosphorylation ?
- A photon of light hits a chlorophyll molecule in photosystem 1
- Electrons are excited + leave chlorophyll molecule
- Electrons taken up by an electron acceptor
- Electrons passed along an electron transport chain (ETC) from 1 electron carrier to the next = produces ATP from ADP + Pi
- Electron return to Photosystem I in chlorophyll + can be excited again in same way
Non-Cyclic Phosphorylation ?
- Photon of light hits chlorophyll in Photosystem II
- Electrons are excited + leave chlorophyll molecule
- Electrons taken up by electron acceptor + passed along an ETC chain to Photosystem I chlorophyll = ATP produced from ADP + Pi (Energy is released)
- Photolysis occurs: Splitting of water (using light energy) into hydrogen + hydroxide ions (to reduce NADP) + electrons to replace lost electrons in Photosystem II chlorophyll = restored to original state + ready to be excited again
- Electrons in PSI are also being excited by light + lost to an electron acceptor
- Electrons are carried down ETC + taken up by the electron acceptor NADP
- The NADP also takes up H+ ion from dissociated water to form reduced NADP
- Hydroxide ions react together to form water + oxygen
What are the NADPH + ATP produced during non-cyclic photophosphorylation used for ?
- NADPH + ATP produced during non-cyclic photophosphorylation used in the light-independent reactions (calvin cycle) to make glucose
How does chemiosmosis produce ATP in the Light dependent stage ?
-⬆conc of H+ inside thylakoid
- energy generated as e- travel down ETC
- moves the H+ ions down electrochemical gradient
- from thylakoid space –> stroma (+ binds to NADP –> NADPH)
- through ATP synthase
= ATP synthase catalyses ADP + Pi –> ATP
Photolysis of water :
- Splitting of water (H2O) using light energy absorbed by chlorophyll into hydrogen + electrons
- H20 –> 1/2O2 + 2e- + 2H+
How + where is reduced NADP produced in Light dependent stage ?
+ what does NADP act as ?
NADP + 2H+ + 2e- –> NADPH
- in stroma of chloroplast
- NADP acts as the final electron acceptor of the electron transfer chain
Where does light-dependent reaction take place?
Where does the light-independent reaction take place ?
-
Light-dependent reaction:
- On the thylakoids of chloroplast -
Light-independent reaction:
- In the stroma of chloroplast
The light-independent stage :
- Final stage of photosynthesis (in stroma)
- which uses ATP (source of energy) + reduced NADP (reducing power) to produce glucose
- consists of series of reactions known as the Calvin cycle
Calvin cycle
3 main stages:
- Carbon fixation
- Reduction
- Regeneration
Calvin cycle :
- Carbon fixation: [as CO2 is said to be fixed]
- CO2 (from air) combines with 5C Ribulose bisphosphate (RuBP) in chloroplast to produce an unstable 6C compound
- Catalysed by RUBISCO enzyme
- Reduction:
- 6C very unstable = immediately splits into two molecules of glycerate 3-phosphate (GP), a 3-carbon compound
- GP is then reduced (Hydrogen added) into glyceraldehyde 3-phosphate (GALP), a 3-carbon sugar
- using hydrogen comes from 2x NADPH + energy from 2x ATP [both from the light-dependent reaction]
- Regeneration:
- Most of the GALP passes through series of steps to replace the RuBP needed in 1st step with ATP
- Some GALP molecules used to make glucose, which is then converted to essential organic compounds such as polysaccharides, lipids, amino acids + nucleic acids
How does the light-independent reaction result in the production of useful organic substances?
uses of GALP ?
- GALP acts as raw material when 1C leaves the cycle to produce monosaccharides, amino acids & other biological molecules
- some GALP feeds into glycolysis + krebs cycle as fuel to provide energy through ATP
Roles of ATP & NADPH in the light-independent reaction:
ATP:
- reduction of GP to GALP TP
- provides phosphate group to convert RuP into RuBP
NADPH:
- coenzyme transports electrons needed for reduction of GP to GALP TP
alternatve routes:
- most plants fix carbon divride divecty into 3-c compords = called C3 plants
- other plants produce 4-C compounds to minimise photorespiration → C4 plants
- CAM plants fix carbon at night so that stomata co remain closed in the dark to mininise water loss but Still have enough CO2
What’s a limiting factor ?
What are the limiting factors for photosynthesis ?
- A factor that determines maximum rate of a reaction, even if other factors change to become more favourable
- CO2
- Light intensity
- Temperature
- magnesium levels (maintain normal functioning of chlorophyll)
- Carbon dioxide as a limiting factor:
- if there is not enough carbon dioxide available = it cannot be fixed in the Calvin cycle
- This means light-independent stage (Calvin cycle) cannot proceed at its maximum rate
- Light intensity as a limiting factor:
- amount of light affects the amount of chlorophyll which is excited
- this determines the amount of ATP + NADPH produced
- this determines the rate of reactions in the light-independent stage
- Temperature as a limiting factor:
- many of the reactions in the LD and LI (Calvin) stages are controlled by enzymes = sensitive to temp
- if the temperative is too high / too low + even if other conditions are suitable reactions will not be at their maximum rate = enzymes may denature
Adaptations EG?
- growing in height for sunlight
- spreading leaves into a mosaic pattern
- developing large leaves
- seed dispersal methods mean baby plants do not grow in the shade of their parents
