section 5: energy transfer in and between organisms

Question 1

chemiosmosis (process in light dependent reaction of photosynthesis and OP of respiration)

Answer 1

• protons are pumped from the stroma using protein carriers in the thylakoid membrane called proton pumps
• the energy to drive this process comes from electrons released when water molecules are split by light - photolysis
• the photolysis of water also produces protons that further increases their concentration in the thylakoid
• this creates and maintains a concentration gradient of protons between the thylakoid and stroma
• the protons cross the thylakoid membrane through ATP synthase channel proteins/ stalked granules and as they pass through it causes change to the structure of the enzyme which catalysed the combination of ADP with inorganic phosphate to form ATP

Question 2

photolysis of water (photosynthesis)

Answer 2

when a chlorophyll molecule absorbs light and loses electrons it is now oxidised and must replace these electrons: these are provided when water molecules are split - photolysis

• the electrons produced from this go back to the chlorophyll molecule - reducing it
• the oxygen is a by product which is either used in respiration or diffuses out
• the protons are taken up by NADP and produces reduced NADP, which then goes on to the light independent reaction

Question 3

where does the light-dependent reaction take place?

Answer 3

in the thylakoid membrane

Question 4

what are the advantages of the light dependent reaction taking place in the thylakoid membranes?

Answer 4

• thylakoid membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes for LDR
• a network of proteins in the grana hold the chlorophyll to allow maximum absorption of sunlight
• granal membranes have ATP synthase channels and are selectively permeable

Question 5

what is the process of making ATP in the light dependent reaction?

Answer 5

• photosynthetic pigments absorb light energy which excites an electron that then leaves the chlorophyll molecule
• this is called photoionisation because the chlorophyll molecule lost it’s negative charge in the electron and so now it is positively charged/ionised
• the electrons are then taken up by an electron carrier and they move down the electron transport chain through a series of oxidation and reduction reactions
• they lose energy as they move to each electron carrier and some of this energy is used to combine a phosphate ion with ADP to make ATP

Question 6

where does the light independent reaction take place?

Answer 6

in the stroma of the chloroplast

Question 7

what is an oxidation reaction?

Answer 7

• loss of hydrogen
• loss of electrons
• gain of oxygen
• energy given out

Question 8

what is a reduction reaction?

Answer 8

• gain of hydrogen
• gain of electrons
• loss of oxygen
• energy taken in

Question 9

what are the advantages of the light-independent reaction taking place in the stroma?

Answer 9

• the fluid of the stroma contains all the enzymes needed to carry out the LDR
• the stroma fluid surrounds the grana and so the products of the LDR in the grana can readily diffuse into the stroma

Question 10

the process of the calvin cycle (photosynthesis)

Answer 10

1. first step involves CO2 combining with the 5C compound ribulose biphosphate (RuBP)
2. this reaction is catalysed by the enzyme RuBisCo
3. RuBP is now carboxylated which forms the unstable 6C compound
4. this 6C compound then immediately breaks down to form 2 molecules of glycerine-3-phophate (GP)
5. after CO2 has been fixed, GP is reduced to form triose-phophate (TP), GP is reduced using hydrogen atoms from the reduced NADP formed in the LDR (which can then return to the LDR)
6. the ADP made in the LDR is also used to form 2 ADP molecules
7. TP can be used to form organic molecules such as glucose or amino acids
8. but 10/12 of the TP molecules are used to regenerate the RuBP molecules

Question 11

what are coenzymes?

Answer 11

molecules that some enzymes require in order to function
- not actually enzymes
- important in photosynthesis and respiration to carry hydrogen between molecules
examples include NAD, FAD and NADP

Question 12

what is the process of glycolysis? (respiration)

Answer 12

1. it starts with glucose which is made more reactive by the addition of 2 phosphate molecules (phosphorylation) - the phosphate molecules come from the hydrolysis of 2 ATP molecules to ADP
2. the phosphorylated glucose is then split into two 3C molecules - triode phosphate
3. hydrogen is removed from each of the two TP molecules and transferred to a hydrogen carrier - NAD which forms reduced NAD (NADH)
4. enzyme-controlled reactions convert each TP into another 3C molecule called pyruvate, during this process 2 molecules of ATP are regenerated from ADP

Question 13

where does glycolysis take place?

Answer 13

in the cytoplasm of mitochindria

Question 14

what is the net yield of glycolysis

Answer 14

2 ATP
2 reduced NAD
2 pyruvate

Question 15

what is the process of the link reaction? (respiration)

Answer 15

1. pyruvate is decarboxylated, and dehydrogenated, meaning it loses a CO2 molecule and 2 hydrogen atoms, is oxidised into acetate
2. the 2C acetate then combines with a molecule called coenzyme A, to produce a compound called acetyl coenzyme A

Question 16

what is the net yield from the link reaction (2 pyruvates)?

Answer 16

• 2 acetyl coenzyme A (goes to krebs)
• 2 carbon dioxide (released as waste)
• 2 reduced NAD (goes to oxidative phosphorylation)

Question 17

where does the link reaction take place?

Answer 17

in the matrix of the mitochondria

Question 18

where does the krebs cycle take place?

Answer 18

in the matrix of the mitochondria

Question 19

what is the process of the krebs cycle? (respiration)

Answer 19

1. oxaloacetate (4C) combines with acetyl coenzyme A (2C) to produce citric acid (6C)
2. coenzyme A goes back to the link reaction
3. the 6C citrate loses CO2 and hydrogen
4. the hydrogen reduces NAD
5. 5C compound is formed
6. 5C molecule is converted into a 4C molecule
7. decarboxylation and dehydrogenation occur which forms 1 reduced FAD and 2 reduced NAD
8. ATP is produced
9. the 4C oxaloacetate then joins with acetyl coenzyme A and the whole cycle starts again

Question 20

how many times does the krebs cycle occur per glucose molecules?

Answer 20

2 times

Question 21

what are the products of the krebs cycle?

Answer 21

• 3 reduced NAD
• 1 reduced FAD
• 1 molecule of ATP
• 2 CO2

Question 22

what is the process of oxidative phosphorylation? (respiration)

Answer 22

1. hydrogen atoms from glycolysis and krebs cycle join with coenzymes FAD and NAD
2. reduced NAD and FAD donate the electrons of the hydrogen atoms they are carrying to the first electron carrier molecule
3. electrons pass along the ETC in a series of oxidation reduction reactions
4. as the electrons flow along the chain, the energy they release cases the active transport of proteins across the inner mitochondrial membrane into the inner membranal space
5. the protons accumulate in the inner membranal space and then diffuse back into the matrix through ATP synthase channels
6. at the end of the chain the electrons combine with these protons and oxygen, forming water
7. oxygen is therefore the final acceptor of electrons

Question 23

why is oxygen required in oxidative phosphorylation?

Answer 23

to be the final acceptor of electrons

Question 24

where does oxidative phosphorylation take place?

Answer 24

in the cristae of the mitochondria - because the enzymes and proteins that OP needs are found here

Question 25

how are proteins used as an alternative respiratory substrate?

Answer 25

1. proteins are first hydrolysed into amino acids
2. then they are deaminated (amino group is removed)
3. they then enter the repertory pathway at different points depending on their number of carbons
   3C are converted to pyruvate and 4C or 5C are converted to intermediates in Krebs Cycle

Question 26

how are lipids used as alternative respiratory substrates?

Answer 26

1. are hydrolysed into glycerol and fatty acids
2. glycerol is phosphorylated
3. converted to TP
4. the TP is then converted to pyruvate and enters the link reaction and then Krebs
5. the fatty acids are hydrolysed into 2C fragments which are converted into acetyl coenzyme A
6. then this also joins the Krebs cycle

Question 27

what is the process of anaerobic respiration in animals?

Answer 27

the lactate-fermentation pathway

• used to re-oxidise the NADH
• in this pathway the pyruvate molecules accept the hydrogen atoms
• pyruvate becomes lactate
• this reaction is catalysed by the enzyme lactate dehydrogenase
• the oxidised NAD can return to accept more hydrogen atoms during glycolysis

Question 28

what happens to the lactate after it is produced

Answer 28

• lactate is acidic so therefore must be removed as it can affect the pH in the blood and therefore affect the functioning of enzymes
• lactate is transported to the liver where it can be converted back to pyruvate when there is more oxygen available

Question 29

how does anaerobic respiration occur in plants and fungi?

Answer 29

• the ethanol- fermentation pathway to re-oxidise NADH
• the pyruvate produced from glycolysis is decarboxylated and converted to ethanal
• this reaction is catalysed by the enzyme pyruvate dehydrogenase
• the ethanal then accepts the hydrogen atoms from the reduced NAD to produce ethanol and oxidised NAD
• this reaction is catalysed by ethanol dehydrogenase

Question 30

ecosystem

Answer 30

all of the living (biotic) and non-living (abiotic) components of a particular area

Question 31

biomass

Answer 31

the total mass of living material, normally measured in a specific area or over a period of time

Question 32

food chains

Answer 32

describe the feeding relationships between organisms, each stage of the chain is a trophic level

Question 33

food webs

Answer 33

more accurate representation of of feeding relationships, many food chains may link together to form webs as animals do not rely on one food source

Question 34

producers

Answer 34

photosynthetic organisms that obtain their energy from photosynthesis of sunlight

Question 35

consumers

Answer 35

organisms that feed on other organisms, do not produce their own food: can be primary, secondary etc.

Question 36

decomposers

Answer 36

when producers/consumers die, the energy they contain is accessed by decomposers that will break down larger molecules into smaller, simpler components which are recycled and taken up by plants

Question 37

saprobionts

Answer 37

a microorganism - type of decomposer that feeds on the remains of dead plants and animals and breaks them down which is important for the recycling of chemical elements such as nitrogen and phospherus

Question 38

what is a mycorrhizae relationship?

Answer 38

when some fungi form symbiotic relationship with the roots of plants

• the fungi are made up of long, thin strands called hyphae which connect to the plants roots
• they increase the surface area and help the plant to take up water and ions
• and in return the fungi get organic compounds such as glucose from the plant

Question 39

what is leaching?

Answer 39

when too much fertiliser is applied and therefore it may be washed into waterways
can lead to eutrophication
the leaching of phosphates is less likely than of nitrates because phosphates are less soluble in water

Question 40

what is eutrophication?

Answer 40

1. mineral ions are leached into lakes and rivers and stimulate rapid growth of algae
2. large amounts of algae block light from reaching plants below
3. eventually plants die as they are unable to photosynthesise enough
4. bacteria feed on dead plant matter, the increase in the amount of bacteria reduces the oxygen concentration
5. fish and other aquatic organisms die because there isn’t enough dissolved oxygen