Energy Transfers

Describe photoionisation during LDR (2 marks)

• chlorophyll absorbs light energy which excites electrons

• electrons are released from chlorophyll

Describe phoyolysis of water in LDR (2 marks)

• water splits to produce protons, electrons and oxygen

• electrons replace those lost from chlorophyll

Describe what happenes after photoionisaiton (5 marks)

• electrons move along electron transfer chain releasing energy

• this energy is used to actively pump protons from stroma into thylakoid

• protons move by facilitated diffusion down Electrochemical gradient into stroma via ATP synthase

• Energy used to join ADP and Pi to form ATP

• NADP accepts a proton and an electron to become NADPH

Describe the light independent reaction of photosynthesis (4 marks)

• CO2 reacts with RuBP which is catalysed by rubisco

• forms 2 gp molecules which is reduced into triose phosphate using reduced NADP and ATP

• some TP is used to form organic substances

• some tp is used to reform RuBP to continue the cycle

Describe how Light intensity affects photosynthesis (2 marks)

• as light intensity increases Rate increases because LDR reaction increases meaning more ATP and reduced NADP is produced

• at a certain light intensity, rate stop increasing because another factor (temp/co2) is limiting it

Describe and explain how CO2 concentration affects photosynthesis (2 marks)

• As CO2 concentration increases rat3 increases because more CO2 reacts with RuBP to form more GP so more TP is formed so more RuBP and organic substances are made/regenerated

• At a certain concentration, rate stops increasing because another factor (light, temp) is limiting it

Describe the role of the enzyme dehydrogenase in photosynthesis (1 mark)

• catalyses the reduction of NADP in the LDR

Describe the process of glycolysis (respiration) (2 marks)

• glucose phosphorylated into glucose phosphate using inorganic phosphates from 2 ATP

• splits into ×2 triose phosphate which is then oxidised to ×2 pyruvare. 3 NADH whilst 4 ATP is regenerated (net gain of 2)

Explain what happens after glycolysis if respiration is anarobic

• pyruvate is converted into lactate or ethanol

• reduced NAD is oxidised regenerating NAD so glycolysis can continue so more ATP is produced

Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration (2 marks)

• only glycloysis is involved which produces little ATP

• No oxidative phosphorylation which forms majority of ATP

Describe the link reaction (3 marks)

• pyruvate is then actively transported into the mitochondrial matrix

• pyruvate oxidised to acetate which produces Co2 and reduced NAD

• acetate combine with coenzyme A forming Acetyl coenzymeA

Describe the Krebs cycle (2 marks)

• Acetyl coenzyme A reacts with a 4 Carbon molecule releasing coenzyme A and producing a 6 carbon molecule that enters the kreb cycle

• series of oxidation-reduction reactions causes the 4 carbon molecule to be regenerated and 2 co2 is lost, NAD and FAD is reduced and phosphorylation producing ATP

Describe the process of oxidative phosphorylation (4 marks)

• Reduced NAD/FAD oxidised to release protons and electrons

• electrons transfered down electron transfer chain by redox Reactions

• energy released by electrons used in production of ATP. Protons is actively pumped from the matrix into intermembrane slace and diffuses into matrix down an Electrochemical gradient via ATP synthase. This releases energy to synthese ATP from ADP and Pi

• In matrix at the end of the ETC, oxygen is the final electron acceptor so protons electrons and oxygen combines to form water

Describe how biomass is formed on plants (3 marks)

• during photosynthesis, plants make organic compounds

• most sugars created are used for respiration

• rest are used to make other groups of biological molecules which form biomass

How can biomass be measured (1mark)

• mass of dry mass of tissue in a given area

Describe how features of calorimeter enable valid measuremanr of heat energy released (3 marks)

• stirrer - distributes heat energy evenly

• insulation - reduces heat loss and gain

• water - has a high specific heat capacity

what is gpp and npp and the equation (3 marks)

• npp - chemical energy store in plants biomass after respiratory losses

• gpp - chemical energy store in plants biomass in a given area and time

• NPP = GPP - R

Explain the importance of NPP in ecosystems (2 marks)

• NPP is available for plant growth and reproduction

• NPP is also available to other trophic levels in the ecosystem

Explain why most light falling on producers is not used in photosynthesis (3 marks)

• Light is reflected/ wrong wavelength

• Light misses chlorophyll

• CO2/temperature are limiting factors

State the formula for net production of consumers (1 mark)

N = I - (F + R)

• I = chemical energy store in indigested food

• F = chemical energy lost in faces and urine

• R = chemical energy lost due to respiration

Explain why energy transfers between trophic levels are inefficient (4 marks)

• Heat energy is lost via respiration

• Energy lost via parts of organism that isnt eaten

• Energy lost via food not digested

• Energy lost via excretion

Explain how livestock farming practices increase energy transfer efficiency (4 marks)

Reducing respiratory losses by;

• restricting movement and keeping animals warm so less heat energy lost from respiration

• Slaughter animals whilst still growing/young as most of their energy is used for youth

• Treat with antibiotics so prevents loss of energy due to pathogens.

• selective breeding to produce breeds with higher growth rate

Explain the role of saprobionts in recycling chemical elements (2 marks)

• decompose organic compounds in dead matter by secreting enzymes for extracellular digestion

• absorb soluble needed nutrients and releases mineral ions

Explain the meaning and role of mycorrhizae (4 marks)

mycorrhizae = symbotic association between fungi and plant roots

• fungi increase surface area of root system

• to increase rate of absorption of water and mineral ions

• in return, fungi receive organic compounds

Describe the role of bacteria in nitrogen fixation (1 mark)

• nitrogen fixing bacteria converts nitrogen gas into ammonia which then forms ammonium ions by breaking the triple bond between 2 nitrogen atoms

Describe the role of bacteria in ammonification (1 mark)

• nitrogen containing substances from dead organisms are broken down and converted into ammonia which forms ammonium ions in the soil by saprobionts

Describe the role of bacteria in nitrificaiton (1 mark)

• Ammonium ions are then converted into nitrite and then into nitrates via a 2 step Oxidation reaction by nitrifying bacteria in aerobic conditions

Describe the role of bacteria in denitrification (1 mark)

• nitrates in the soil are then converted back into nitrogen gas by denitrifying bacteria

Suggest why ploughing/aerating soil increases its fertility (2 marks)

• more ammonium converted into nitrile and nitrate/more nitrification

• less nitrate converted into nitrogen gas/less denitrification

Describe the phosphate cycle (5 marks)

• Phosphate Ions in rock are released into the ocean by weathering

• phosphate Ions are then taken up by producers and added to their biomass (rate of absorption increased by mycorrhizae)

• phosphate ions transfer through food chain

• some phosphate Ions lost from animals via waste products

• saprobionts decompose organic compounds in dead organisms releasing phosphate ions

Explain why fertilisers are used (2 marks)

• to replace nitrate/phosphate lost when plants are harvested and livestock are removed

• improves efficency of energy transfer

Describe the difference between natural and artificial fertilisers (3 marks)

Natural:

• organic

• ions released during decomposition by saprobionts

Artifical:

• contains inorganic compounds of nitrogen phosphorus and potassium

Explain the advantage of using natural fertilisers over Artifical fertilizers (2 marks)

• less water soluble so less leaching

• organic molecules require breaking down by saprobionts so slow release of ions

Explain the key environmental impacts when using fertilisers (2 marks)

• phosphate/nitrates dissolve in water which leads to leeching of nutrients into lakes

• this causes eutrophication

Explain the process of eutrophication (4 marks)

• rapid growth of algae in pond so light blocked

• so submerged plants die as they cant photosynthesise

• so saprobionts decompose dead plant matter using oxygen in aerobic respiration

• so less oxygen for fish to aerobically respire leading to their deaths