5. Energy Transfers

Question 1

Photosynthesis

Answer 1

process in which light energy is converted into chemical energy in the form of glucose, symbol equation is 6CO2 + 6H2O + light energy —> C6H12O6 + 6O2

Question 2

Chloroplast

Answer 2

organelle surrounded by a double membrane, thylakoids stacked into grana linked by lamellae providing a large surface area for the LDR, photosynthetic pigments which absorb light energy for the LDR, stroma containing enzymes for the LIR

Question 3

Light-dependent reaction

Answer 3

first stage of photosynthesis, occurs in thylakoid membranes of chloroplast, involves photoionisation, chemiosmosis and photolysis, produces ATP and NADPH for the LIDR

Question 4

Photoionisation

Answer 4

photosynthetic pigments (eg. chlorophyll) absorb light energy, exciting an electron which leaves the chlorophyll

Question 5

Chemiosmosis

Answer 5

electron moves along the electron transport chain, releasing energy which is used to actively transport H+ into the thylakoid, forming a proton gradient, H+ diffuse down their electrochemical gradient into the stroma through ATP synthase joining ATP + Pi —> ATP

Question 6

Photolysis

Answer 6

splitting of water producing H+, O2 and electrons, NADP picks up H+ and is reduced to NADPH

Question 7

Light-independent reaction

Answer 7

second stage of photosynthesis, occurs in stroma of chloroplast, involves the Calvin cycle, produces useful organic compounds (eg. glucose)

Question 8

Calvin cycle

Answer 8

CO2 combines with RuBP to form 2 molecules of GP, catalysed by the enzyme rubisco, both molecules of GP are reduced using 2ATP and 2NADPH to form 2 molecules of triose phosphate, most triose phosphate is regenerated into RuBP using energy from ATP, some triose phosphate is converted into useful organic compounds

Question 9

Effect of light intensity

Answer 9

increasing light intensity means more light energy for the LDR, increasing rate of photosynthesis, light must be correct wavelength as different pigments absorb different wavelengths of light

Question 10

Effect of temperature

Answer 10

increasing temperature means molecules have more kinetic energy, increasing rate of photosynthesis, beyond optimum enzymes denature, reducing rate

Question 11

Effect of CO2 concentration

Answer 11

increasing CO2 concentration means more GP generated, increasing rate of photosynthesis, beyond optimum stomata close, reducing rate

Question 12

Investigating photosynthetic pigments

Answer 12

add a spot of pigment onto the chromatography paper on the origin line, place the paper in solvent making sure solvent is below the origin line, remove before solvent reaches the top, calculate Rf value by dividing distance travelled by spot by distance travelled by solvent

Question 13

Respiration

Answer 13

process in which chemical energy released from glucose is used to make ATP, symbol equation for aerobic respiration is C6H12O6 + 6O2 —> 6CO2 + 6H2O

Question 14

Mitochondria

Answer 14

organelle surrounded by a double membrane, inner membrane folded into cristae providing a large surface area for oxidative phosphorylation, matrix containing enzymes for the link reaction and Krebs cycle

Question 15

Glycolysis

Answer 15

takes place in the cytoplasm, glucose is phosphorylated using ATP into 2 molecules of triose phosphate, triose phosphate is oxidised into pyruvate, NAD is reduced into NADH, yields 2 pyruvate 2NADH and 2ATP

Question 16

Link reaction

Answer 16

takes place in the mitochondria matrix, pyruvate is dehydrogenated and decarboxylated into acetate, acetate combines with coenzyme A to form acetyl coenzyme A, yields of 2 acetyl coenzyme A, 2CO2 and 2NADH (per glucose)

Question 17

Krebs cycle

Answer 17

takes place in the mitochondria matrix, acetyl coenzyme A combines with a 4C compound to form a 6C compound, coenzyme A is recycled, 6C compound is dehydrogenated and decarboxylated into a 4C compound, NAD is reduced to NADH, FAD is reduced to FADH, ATP undergoes substrate level phosphorylation, yields 3NADH, 2CO2, FADH, ATP (per cycle)

Question 18

Oxidative phosphorylation

Answer 18

takes place at the mitochondria cristae, NADH and FADH are oxidised releasing H+ and electrons, electrons moves along the electron transport chain, releasing energy which is used to actively transport H+ into the intermembrane space, forming a proton gradient, H+ diffuse down their electrochemical gradient into the matrix through ATP synthase joining ATP + Pi —> ATP, oxygen is the final electron acceptor (combines with H+ and electrons to form water)

Question 19

Anaerobic respiration

Answer 19

respiration in the absence of oxygen, only involves glycolysis so yields a smaller amount of ATP

Question 20

Anaerobic glycolysis

Answer 20

takes place in the cytoplasm, glucose is phosphorylated using ATP into 2 molecules of triose phosphate, triose phosphate is oxidised into pyruvate, NAD is reduced into NADH, pyruvate is reduced using NADH into lactate (animals) or ethanol and carbon dioxide (plants/yeast), NAD is regenerated so glycolysis can continue

Question 21

Investigating respiration

Answer 21

place yeast in respirometer, in aerobic respiration oxygen is consumed (and carbon dioxide is absorbed) so pressure and volume of air decreases and bubble moves towards yeast, in anaerobic respiration carbon dioxide is produced so pressure and volume of air increases and bubble moves away from yeast

Question 22

Biomass

Answer 22

amount of chemical energy stored in an organism, measured in terms of dry mass or mass of carbon

Question 23

Estimating dry mass

Answer 23

weigh sample, heat sample in oven, reweigh at regular intervals until mass remains constant

Question 24

Estimating chemical energy in biomass

Answer 24

burn sample completely in calorimeter, energy released is used to heat a known volume of water, calculate the change in temperature of the water to estimate chemical energy

Question 25

Gross primary production

Answer 25

total amount of chemical energy made by producers in photosynthesis, measured in J m^2 yr^1

Question 26

Net primary production

Answer 26

amount of chemical energy a producer stores as biomass after respiratory losses (NPP=GPP-R), measured in J m^2 yr^1

Question 27

Net production

Answer 27

amount of chemical energy a consumer stores as biomass after respiratory losses and excretion (N=I-(R+F)), measured in J m^2 yr^1

Question 28

Tropic levels

Answer 28

each of the stages in a food chain, as you move up the food chain energy transfer between tropic levels becomes slightly more efficient

Question 29

Energy transfer efficiency

Answer 29

calculated by dividing net production of current tropic level by net production of previous tropic level and multiplying by 100

Question 30

Why energy transfer is inefficient

Answer 30

wrong wavelength of light, light reflected, energy lost as heat, respiratory loss (metabolism), not all plant/animal eaten (bones), not all plant/animal digested (faeces)

Question 31

Improving efficiency of energy transfer

Answer 31

simplifying food webs (remove pests and direct competition), fertilisers, reducing respiratory loss (restrict movement and keep warm), slaughter when young, selective breeding

Question 32

Saprobionts

Answer 32

feed on the remains of dead organic matter and their waste and break them down, secrete enzymes for extracellular digestion, absorbing the nutrients they need

Question 33

Mycorrhizae

Answer 33

fungi made from long thin strands (hyphae) that form a symbiotic relationship with plants by increasing surface area of the roots, mutualistic relationship as fungi help plant absorb water and mineral ions in return for carbohydrates

Question 34

Nitrogen fixation

Answer 34

nitrogen fixing bacteria in the root nodules of legumous plants convert nitrogen gas into ammonium ions

Question 35

Ammonification

Answer 35

saprobionts convert nitrogen compounds (eg. proteins) into ammonium ions

Question 36

Nitrification

Answer 36

nitrifying bacteria oxidise ammonium ions into nitrites then into nitrates

Question 37

Denitrification

Answer 37

anaerobic denitrifying bacteria convert nitrates into nitrogen gas

Question 38

Phosphorus cycle

Answer 38

phosphate ions in rocks are released into the soil by weathering and taken into the plants through the roots, animals eat the plants, animals excrete phosphate ions in waste products, plants and animals die, sapriobionts digest dead organic matter, releasing phosphate ions into the soil for assimilation by plants

Question 39

Fertilisers

Answer 39

replace nutrients lost when crops are harvested, can be natural (manure) or artificial (inorganic chemicals)

Question 40

Natural fertilisers

Answer 40

cheaper, aerate soil, consume less energy, less leaching as organic molecules have to be broken down first by saprobionts

Question 41

Artificial fertilisers

Answer 41

contain pure chemicals in exact proportions, more water-soluble so higher absorption by plants

Question 42

Leaching

Answer 42

when water soluble compounds are washed away into waterways by rain, can lead to eutrophication

Question 43

Eutrophication

Answer 43

mineral ions leached into fresh water causing algal bloom to form, algal bloom blocks sunlight from reaching aquatic plants below, aquatic plants can’t photosynthesise so die, saprobionts digest dead organic plant matter, respiring aerobically, fish die due to lack of oxygen