3.5 Energy transfers in and between organisms

Photosynthesis

process by which plants use light energy to convert water and carbon dioxide into oxygen and high-energy carbohydrates such as sugars and starches

palisade mesophyll

photosynthetic tissue below the epidermis in a leaf contains chlorophyll

autotrophic nutrition

when an organism produces its own food & is the source of energy for all other living things

Photoautotrophs

Organisms that use light as a source of energy to synthesise organic substances.

Location of Light Dependent Reaction

thylakoid membrane

location of light independent reaction

stroma

Photosystem

A cluster of pigments embedded into a thylakoid membrane attached to proteins that absorbs light energy

granum (grana)

stacks of thylakoids

coenzyme

molecules that aid the function of an enzyme by transferring a chemical group from one molecule to another.

Leaf adaptations for photosynthesis

Thin - gases can readily diffuse

Stomata - gas exchange

Spongy mesophyll has air spaces - allow CO2 to diffuse

Large SA - more light absorption

Chloroplasts packed into upper palisade layer - elongated so more chloroplasts

Waxy cuticle is transparent

Waxy cuticle - reduces evaporation

Guard cells close when flaccid - water loss regulated

Rf equation

distance moved by substance/distance moved by solvent

light-dependent reactions

1. Photoionisation - light energy absorbed by chlorophyll to excite electron and release them
2. Energy is released from the electrons down the ETC
3. Energy is used for reducing NADP into NADPH, photolysis, produce ATP by photophosphorylation

cyclic photophosphorylation

involves PSI, electrons released not donated to NADP but returned to PSI. Only small amounts of ATP produced, no NADPH, no oxygen

non-cyclic photophosphorylation

involves PSI and PSII, lost energy is replaced by photolysis, lost energy is used for chemiosmosis which moves protons and synthesises ATP, reduces NADP

Light Independent Reactions (Calvin Cycle)

Uses ATP and NADPH to produce high energy sugars, takes place in the stroma of chloroplasts.


1. CO2 + RuBP + Rubisco = GP
2. GP + ATP + NADPH = TP
3. 1/6 TP = glucose, 5/6 TP = RuBP

investigating the Calvin cycle

Radioactively labelled CO2 - leaves exposed for different amount of times and removed for analysis

photosynthesis limiting factors

Temperature, light intensity, water, carbon dioxide or chlorophyll availability

inverse square law of photosynthesis

light intensity is directionally proportional to 1/distance(squared)

aerobic respiration

series of oxidation reactions that oxidise glucose, releasing carbon dioxide and water providing organisms with energy in the form of ATP

Glycolysis

1. glucose phosphorylated by 2 ATP into 2 triose phosphate, produces 2 ADP + Pi
2. triose phosphate is oxidised into pyruvate (X2), producing 2 NADH and 4ATP

Link reaction

Pyruvate actively transported into mitochondria


1. Decarboxylation removal of carbon group from pyruvate
2. Reduction as NADH is created as NAD+ is reduced, so pyruvate is oxidised into acetate
3. Coenzyme A attaches to acetate to form acetyl-CoA

Krebs cycle

1. Acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C)
2. Citrate (6C) is decarboxylated by 1 carbon dioxide and oxidised by 1 NAD (to form 1 NADH) into 5C
3. 5C is decarboxylated by 1 carbon dioxide and oxidised by 2 NAD (forms NADH) and 1 FAD (forms FADH) into 4C and produces 1 ATP molecule by substrate phosphorylation

electron transport chain

1. NADH and FADH oxidised and released hydrogen is split into protons and electrons
2. Electrons move done ETC losing energy at each carrier
3. lost energy used to pump protons into intermembrane space
4. electrochemical gradient formed
5. Chemiosmosis, as protons diffuse through ATP synthase 24 ATP are produced
6. Oxygen is the final electron acceptor - protons, electrons and oxygen combine to produce water

anaerobic respiration in animals

Respiration in the absence of oxygen


1. pyruvate is converted into lactic acid and NADH is oxidised back into NAD

anaerobic respiration in plants and microorganisms

pyruvate is decarboxylated and reduced by NADH into ethanol, produces CO2 and NAD

Ecosystem

A community of organisms and their abiotic environment in a given area

Producer

An organism that makes its own food

Biomass

The total mass of organic material, measured in a specific area over a set time period. This can be calculated in terms of dry mass or mass of carbon per given area.

Calorimetry

estimates amount of chemical energy stored in a sample.

Sample is burned which releases energy that heats up water, thermometer records temperature change.

primary productivity

rate at which plants convert sunlight into chemical energy, measured usually in KJ per metre squared per year.

Gross Primary Productivity (GPP)

chemical energy stored in plant biomass in a given area at a given time

Net Primary Productivity (NPP)

the energy captured minus the energy respired by producers, GPP-R

Consumers

heterotrophs that feed on living organisms by ingestion for nutrition

energy pyramid

Shows the amount of energy passed from one trophic level to another. On average, 10% is passed on. Most energy consumed contributes to maintaining homeostasis, respiration, growth and reproduction.

food chain

single pathway of energy transfer

food web

a system of interlocking and interdependent food chains.

Net production in consumers equation

N \= I - (F + R)

Efficiency of energy transfer

the efficiency of energy transfer between trophic levels is calculated using: %= net production of trophic level / net production of previous trophic level X 100

fertiliser

A substance added to soil to enhance the growth of plants.

fungicide

substance that kills fungi or inhibits their growth, prevents infection

pesticide

A chemical intended to kill insects and other organisms that damage crops. Can cause persistence - lasts as damaging chemical for long time, bioaccumulation - build up of pesticide in a food chain.

herbicide

substance that kills plants such as weeds to reduce competition. Either broad spectrum or selective

organic fertiliser

made from animal faeces, compost, crop residue or sewage sludge

inorganic fertilizer

mined or synthetically manufactured mineral supplements such as nitrate, phosphate, potassium ions that can be detrimental as leach out and cause eutrophication

animal farming adaptations to increase efficiency

1. simplify food chains
2. reduce energy lost by respiration by: restricting movements, indoor pens to maintain temperature
3. Digestible feed so less lost as faeces

carbon cycle

1. CO2 in atmosphere
2. Photosynthesis uses CO2 to produce complex carbon compounds
3. Animals eat plants and ingest carbon
4. Both animals and plants respire releasing CO2
5. Animals and plants decay releasing CO2
6. Some form fossil fuels which can be burned and release CO2

nitrogen cycle

1. Nitrogen fixation - nitrogen fixing bacteria reduce nitrogen gas into ammonia and ammonium ions, found in root nodules of legume plants that form symbiotic relationships as provide nitrogen for sugars
2. Ammonification - detritivores digest solid material and expose cellulose and lignin. Saprophytes extracellularly digest proteins in detritus to form ammonia and ammonium ions
3. Nitrification - nitrifying bacteria oxidise ammonia into nitrites then nitrates.
4. Denitrification- denitrifying bacteria converts nitrate back into nitrogen gas for the atmosphere

Myccorhizae

fungi that form symbiotic relationships with plant roots, have long thin strands called hyphae that increase root SA so able to absorb scarce ions from soil

phosphorus cycle

1. Phosphate released from weathering rocks
2. Phosphate ions taken up by plants, mycorrhizae assist
3. Phosphate passed through food chains
4. Phosphate ions lost in waste
5. saprophytes breakdown organic matter and release phosphate in soil
6. Phosphate released from weathering rocks also goes into water where aquatic organisms use
7. seabird waste guano also returns high amounts of phosphate to soil

Leaching and Eutrophication

1. Rainwater dissolves soluble nutrients in inorganic fertilisers and washed into bodies of water - leaching
2. High nitrate levels in water can prevent efficient oxygen transport in babies and is linked to stomach cancer
3. Leads to eutrophication where nutrients in water leads to algae blooming which blocks sunlight from other plants so cant photosynthesise and die. Lack of oxygen as not produced in photosynthesis and decomposing bacteria use oxygen to breakdown plants via respiration. Results in death of ecosystem as low levels of oxygen cannot support life