5. Energy Transfer In & Between Organisms Flashcards
General adaptations of the leaf for photosynthesis
- Large SA to absorb as much light as possible
- Arrangement of leaves to minimise overlapping (avoids shading)
- Transparent cuticle & epidermis to let light through to the mesophyll cells below
- Long narrow upper mesophyll cells packed with chloroplasts to collect sunlight
- Many air spaces in lower mesophyll layer for rapid diffusion in the (g) phase of co2 and h2O
- Network of xylem to carry h2O to leaf cells and phloem to carry sugars produced away
What is the overall equation for photosynthesis
6CO2 + 6H2O ———> C6H12O6 + 6O2
. light
What are the 3 main stages to photosynthesis
- Capturing of light energy (chlorophyll)
- Light-dependant reaction (splitting of water)
- Light independent reaction (reduction of co2)
What are the 2 purposes for the energy from the capture of light in the LD reaction of photosynthesis
- to add an inorganic phosphate (Pi) molecule to ADP making ATP. Process known as photophosphorylation
- to split water into H+ ions (protons) and OH- ions. Process known as photolysis
Explain briefly how ATP is made (photosynthesis: LD stage)
Chlorophyll molecule absorbs light = energy of pair of electrons is boosted= they move to a higher energy level
Results in chlorophyll molecule becoming ionised (photoionisation)
Electrons are taken up and passed along a number of electron carriers (forms a transfer chain) in a series of oxidation&reduction reactions
Each new carrier is at a slightly lower energy level so the electrons lose energy
Some of this energy is used to combine Pi with ADP to make ATP
Which theory describes and explains the precise mechanism by which ATP is produced in the LD reaction?
Chemiosmotic theory
Step by step process of the mechanism for the production of ATP in the LD stage (chemiosmotic theory)
- Protons are pumped from the stroma into each thylakoid using proton pumps in the thylakoid membrane
- Photolysis of water also produces protons which increases their conc inside the thylakoid space
- A conc gradient is created & maintained across the thylakoid membrane (high conc of protons inside thylakoid space, low conc in stroma)
- Protons pass through ATP synthase protein channels and as they do cause changes to the structure of the enzyme which then catalyses the combination of ADP with Pi to form ATP
Where does the energy used to drive the process of pumping protons into the thylakoids come from
Energy from electrons released when water molecules are split by light (photolysis)
Why is the photolysis of water necessary
Loss of electrons when light strikes chlorophyll molecule leaves it short of electrons. If the chlorophyll molecule is to continue absorbing light energy, these electrons must be replaced.
Replacement electrons are provided from photolysis
Protons are also produced
What is the equation for photolysis of water
2H2O ———> 4H+ + 4e- + O2
Describe and explain the role of protons produced from the photolysis of water (LD stage)
- Protons are passed out of the thylakoid space through ATP synthase channels and are taken up by an electron carrier called NADP
- By taking up the protons NADP becomes reduced. (Allows transport of hydrogen into light independant reaction)
- The reduced NADP is important because it is a further potential source of chemical energy to the plant.
- The oxygen by-product is either used for respiration or diffuses out of the leaf as a waste product of photosynthesis
How are chloroplasts structurally adapted for capturing sunlight and carrying out the LD reaction of photosynthesis
- Thylakoid membranes provide a large SA for attachment of chrlophyll, electron carriers and enzymes used in the LD reaction
- Network of proteins in grana hold chlorophyll in a precise manner for max absorption of light
- Granal membranes have ATP synthase channels within them and are selectively permeable which allows proton gradient to be established
- Chloroplasts contain both DNA & ribosomes so they can quickly & easily manufacture some of the proteins involved in the LD reaction
What are the products of the LD reaction (ATP and reduced NADP) used for in the second stage of photosynthesis?
To reduce glycerate 3-phosphate
What does the Calvin cycle refer to
The second stage of photosynthesis : Light independent reaction that takes place within the stroma of the chloroplasts
Give the step by step process of the Calvin cycle
- CO2 reacts with the 5 carbon compound ribulose biphosphate (RuBP), a reaction catalysed by an enzyme known as rubisco
- This reaction produces two molecules of the 3-carbon, glycerate 3-phosphate (GP)
- Reduced NADP, produced in the LD reaction, is used to reduce GP to triose phosphate (TP) using energy supplied by ATP
- The NADP is re-formed and returned to the LD reaction to be reduced again by accepting more protons - Some TP molecules are converted to organic substances that the plant needs (eg. starch cellulose lipids glucose amino acids & nucleotides)
- Most TP molecules are used to regenerate ribulose bisphosphate using ATP from the LD reaction
How is the chloroplast adapted to carry out the LID reaction of photosynthesis
- fluid of stroma contains all enzymes needed to carry out the LID reaction.
- The stroma fluid surrounds the grans so the products of the LD reaction in the grana can readily diffuse into the stroma
- Contains both DNA & ribosomes so it can quickly & easily manufacture some of the proteins involved in the LID reaction
Define the law of limiting factors
At any given moment the rate of physiological process is limited by the factor that is at its least favourable value
What does compensation point mean
The point at which the volume of o2 produced & co2 absorbed in photosynthesis is exactly balanced by the o2 absorbed & co2 produced by cellular respiration
What is the effect of temperature on the rate of photosynthesis
Provided that other factors are not limiting, the rate of photosynthesis increases in direct proportion to the temperature
Above optimum temperature, the rate falls steeply
How does CO2 concentration affect the rate of photosynthesis
No photosynthesis at very low levels
At low - fairly low concentrations, the rate is positively correlated with CO2
At very high concentrations the rate reaches a plateau
CO2 affects enzyme activity, in particular the enzyme that catalyses the combination of ribulose bisphosphate with co2 in the LID reaction
How does light intensity affect the rate of photosynthesis 
At low – medium light intensities, the rate is directly proportional to light intensity
At high light intensity the rate reaches a plateau
What are the 2 different forms of cellular respiration ?
Aerobic respiration
Anaerobic respiration
What 4 stages make up aerobic respiration ?
Where do they take place ?
Glycolysis - cytoplasm
Link reaction - mitochondrial matrix
Kerbs cycle - mitochondrial matrix
Oxidative phosphorylation - inner mitochondrial membrane
Describe in simple terms what happens in glycolysis
The splitting of the 6-carbon glucose molecules into x2 3-carbon pyruvate molecules
Describe in simple terms what happens in the link reaction
The 3-carbon pyruvate molecules enter into a series of reactions which lead to the formation of acetylcoenzyme A, a 2-carbon molecule
Describe in simple terms what happens in the Krebs cycle
The introduction of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of NADH & FADH
Describe in simple terms what happens in oxidative phosphorylation
The use of the electrons, associated with NADH & FADH, released from the Krebs cycle, to synthesise ATP. Water is produced as a by-product
Give the step by step process of glycolysis
- Glucose is phosphorylated to glucose phosphate. Phosphate molecules come from the hydrolysis of x2 ATP molecules to ADP
- Each glucose phosphate is split into x2 triose phosphate molecules
- Oxidation of triose phosphate. Hydrogen is removed and transferred to NAD to form NADH
- Production of ATP. Enzyme controlled reactions convert each triose phosphate into a pyruvate molecule. Each time x2 ATP is regenerated from ADP
What is the overall yield from one molecule of glucose undergoing glycolysis ?
- x2 ATP
- x2 NADH
- x2 molecules of pyruvate