3.5 Energy Transfers in and between organisms Flashcards
What is the equation for photosynthesis?
6CO2 + 6H20 —-> C6H1206 + 6C02
What is photosynthesis?
Using light energy to make glucose
Occurs in plants and algae
What are adaptations of a plant for photosynthesis?
Leaf located near top of plant
Thin and wide = wider surface area, short diffusion pathway
Stomata for gas exchange
Air spaces - supports ease of gas-exchange
Palisade cells located near top of leaf
Large palisade cells are large = high S.A
Palisade contain many chloroplasts (site of photosynthesis)
Large Vacuole= pushes chloroplast to edge of cell closer
Structure of chloroplast?
Double membrane
Contains thylakoids
Granum
Thylakoids surrounded by stroma fluid
What is the light dependent reaction?
Stage of photosynthesis in which light energy is required to produce ATP and reduced NADP
Where does the light independent reaction take place?
The thylakoid membrane in the chloroplast
What are the products of the light independent reaction?
ATP, Reduced NADP and Oxygen (waste or respiration)
Describe photoionisation
- Chlorophyll (Photosystem) absorbs light energy which excited electrons to higher energy level
- Causes them to be released from the chlorophyll
Describe the production of ATP during the light dependent reaction
- Electrons travel down electron transfer chain from photosystem to photosystem, losing energy at each step
- Energy from this is used to transport/pump protons from stroma into the thylakoid
- This creates a proton gradient across the thylakoid membrane
- Proteins move by facilitated diffusion down the gradient into the stroma via ATP synthase embedded in thylakoid membrane
- Uses energy from this proton gradient to do photophosphorylation to make ATP: ADP + PI —> ATP
- Photolysis occurs and O2 given off as waste
- Electrons that are excited are transferred to NADP with a proton from photolysis to reduce NADP to form reduced NADP
What is photolysis?
The splitting of water using light energy
Describe the process of photolysis
Water splits to produce protons, electrons and oxygen
(2H20 —-> 02 + 4e- + 4H+)
Why does photolysis occur?
Electrons replace those lost from chlorophyll
How is reduced NADP formed?
In the second PS, the electrons are excited and transferred to NADP with a Proton from photolysis to reduce NADP and from reduced NADP
Describe the light independent stage?
- Involves the calvin cycle
- RuBP ( 5C) joins with CO2 to make 2X GP (3 Carbon)
- GP reduced to TP (3 Carbon)
Uses energy from ATP and hydrogen atom from reduced NADP - TP can be used to regenerate RuBP
- TP can be converted into useful organic substances eg. Glucose
What can TP produce as “useful organic substances”
Can produce hexose phosphates glucose, sucrose or cellulose
Fatty acids which join to form lipids for cell membranes
Production of amino acids for protein synthesis
Describe what is meant by Carbon Fixation within the Calvin Cycle
Carbon dioxide combines with RuBp
Uses enzyme Rubisco
Carbon has been fixed as it has been removed from external environment and is part of the cell
Name the limiting factors of Photosynthesis
Temperature, Light Intensity ,and Carbon Dioxide concentration
Effect of limiting Light on the calvin cycle?
RuBP decreases - being conveyed into GP but not reformed from TP
GP increases - not converted into TP but being formed from RuBP
Effect of limiting CO2 on the calvin cycle?
RuBP increases – not converted into GP (no CO2) but is being reformed from TP
GP decreases – not being formed from RuBP (no CO2) but being converted into TP
Effect of limiting Temperature on the Calvin cycle?
Increase = more Ek + More E-S complexes (rubisco)
Above Optimum= H bonds in tertiary structure break → active site changes shape → enzyme denatured + FEWER E-S Complexes
What is the compensation point in plants?
the point in the day (light intensity) when the CO2 taken in by photosynthesis equals the amount given out by respiration = no net gas exchange
How to measure the rate of photosynthesis?
measure amount of CO2 used or measure amount of O2 produced, in a certain time
How does a photosynthometer work?
measures amount of O2 produced
uses aquatic plants (e.g. elodea), as the O2 produced can be observed and collected
the plant is surrounded in sodium hydrogencarbonate solution (CO2 source)
the plant is kept in darkness before experiment runs (uses up all the O2 in the plant)
as the experiment runs, O2 will be produced, this will be collected in a capillary tube
the amount collected can be measured, this will be converted into a volume by multiplying length of oxygen bubble collected by πr2
volume of O2 collected can then be divided by time to calculate rate of photosynthesis
What does respiration produce?
ATP
What are the two types of respiration?
Aerobic and Anaerobic
What are the four stages of aerobic respiration?
Glycolysis
Link Reaction
Krebs cycle
Electron transport chain
What is glycolysis?
The first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm and is an anaerobic process
Describe the stages of glycolysis
- Phosphorylation of glucose to glucose phosphate = using inorganic phosphate from 2 ATP
- Hydrolysed to 2x TP (triose phosphate)
- 2x TP → oxidised to 2x pyruvate
- 2 NAD reduced and 4 ATP regenerated
- Net production of 2 ATP
If the respiration is only anaerobic, what can pyruvate be converted to?
Ethanol
Lactate
Using reduced NAD
Describe what happens after glycolysis if no oxygen is present?
Pyruvate converted to lactate or ethanol
Oxidising reduced NAD → NAD regenerated
GLYCOLYSIS CAN CONTINUE WHICH NEEDS NAD
Why is anaerobic respiration much more inefficient than aerobic respiration?
ATP yield is much lower.
Majority of ATP formed in oxidative phosphorylation which anaerobic respiration cannot meet.
What happens after glycolysis if oxygen is present?
Pyruvate is actively transported into the mitochondrial matrix
Then continues into the stages of respiration
Describe the link reaction?
Occurs in the mitochondrial matrix
Pyruvate oxidised and decarboxylated → acetate
Produces CO2 and NADH
Acetate combines with coenzyme A → acetyl coenzyme A
What are the net number of each product in the link reaction
Acetyl CoA = 2
CO2 = 2
Reduced NAD = 2
Describe the krebs cycle
- Acetyl CoA reacts with 4-carbon molecule (oxaloacetate), producing a 6-carbon molecule
- Coenzyme A is released
- Series of oxidation-reduction reactions 4C molecule is regenerated ( 6C→5C→4C)
- NADH and FADH generated as CO2 is lost ( decarboxylation and dehydrogenation)
- ATP produced by substrate level phosphorylation
Describe the stage of oxidative phosphorylation
- NADH and FADH release the hydrogen atoms
- H+ build up in the matrix
- Electrons transferred down the ETC by redox reactions
- Energy lost from electron carriers used to actively transport protons from matrix to intermembrane space
- H+ build up in the intermembrane space, then diffuse back via ATP synthase into matrix
- Releasing energy to generate ATP from ADP + Pi
- Electrons from ETC and proton from matric react to form water
- Oxygen therefore is the final electron acceptor
Why is oxygen needed for the production of ATP on the cristae of the mitochondrion?
Terminal electron acceptor
ETC releases energy for the formation of most ATP
If no O2 = electrons cannot be passed along ETC
Krebs and Link stop as NAD and FAD, cannot be produced
What are the respiratory substrates?
Carbohydrates are turned into glucose
Proteins, excess amino turned into intermediate in krebs cycle
Lipids, provided fatty acids and glycerol → fatty acids become acetyl coenzyme A and glycerol becomes TP
How is biomass transferred between Autotrophs and heterotrophs?
Through trophic levels in a food web
Which ways can biomass be measured in?
Mass of Carbon
Dry mass of tissue per given area
How can we measure biomass using dry mass method?
- Sample dried in oven set at low temp
- Sample reweighed at regular intervals
- All water removed when mass remains constant
- Mass of C taken to be 50% of dry mass
Give the units for biomass?
g or kgm-2
How can we estimate the chemical energy within biomass?
Using Calorimetry:
1. Sample of dry biomass burnt
2. Energy is released used to heat a known volume of water
3. Change in temp of water used to calculate the chemical energy
What is the Gross Primary Production?
The chemical energy store in plant biomass, in a given area or volume
What is Net Primary Production (NPP)?
The chemical energy stored in a plant biomass after the respiratory losses to the environment have been taken into account
What is the formula used to represent the NPP?
NPP= GPP-R
What is the NPP available for?
Plant growth
Reproduction
Other trophic levels in ecosystem
What formula is used to work out the net production of consumers?
N=I-(F+R)
I= chemical energy store in ingested food
F= the chemical energy lost to the environment in faces and urine
R= the respiratory losses to the environment
What are the units for the rates of productivity?
kJ ha-1 year-1
Why do we use ha-1 year-1 within the units for rates of productivity?
ha-1 : standardises results so different environments can be compared
Per year: more representative as takes into account the effect of seasonal variation on biomass so environments can be compared
What is primary and secondary productivity?
The rate of primary and secondary production measured as biomass in one area and time respectively.
How can farming practices increase efficiency of energy transfer regarding crops?
Simplifying food webs to reduce biomass losses:
Herbicides → kill weeds so less competition = more energy to create a biomass
Fungicides → reduction of fungal infections → more energy to create biomass
Pesticides → reduce loss of biomass
Fertilisers to keep soil nutrient rich (more growth = more biomass)
How can farming practices increase energy transfer efficiency of energy transfer regarding animals/livestock ?
- Reduction of respiratory losses:
- Restrict their movement
- Keep warm - Slaughter animals while young:
- Most of energy is used for growth - Selective breeding
- To produce breeds with higher growth rates - Treated with antibiotics to prevent loss of energy due to pathogens
Describe simply the sequence of the nutrient cycle
Nutrients taken up by producer
Then incorporates them into complex organic molecules
Producer is eaten and nutrients passed to consumer down food chain
When organism die, complex molecules broken down by saprobionts = decomposition
Inorganic ion is released
Describe nitrification
Ammonium ions → nitrites→ nitrates
Oxidation by nitrifying bacteria (need oxygen)
Nitrates can be
absorbed using active transport
Describe Denitrification
Nitrates in the soil turn into Nitrogen gas by denitrifying bacteria (anaerobically - less oxygen)
Describe nitrogen fixation
Nitrogen gas (N2) converted to nitrogen containing compounds (exp. ammonia)
By nitrogen-fixing bacteria (free living or ‘mutualistic’ (living in nodules on roots of plants))
Why is the nitrogen cycle important?
Used by plants/animals to make proteins/nucleic acids (assimilated) → GROWTH
What is the role of saprobionts during nutrient cycles?
Decomposers (often bacteria) the release phosphates, ammonia and ammonium ions
What is the role of Mycorrhizae during nutrient cycles?
Fungi that grow in association with plant roots, and improve the plant’s uptake of water and inorganic ions
What is the role of nitrifying bacteria in the nutrient cycle?
Bacteria that oxidise ammonium ions to nitrites, and nitrites to nitrates
What is the role of denitrifying bacteria in the nutrient cycle ?
Uses nitrates to respire anaerobically and release nitrogen gas
What is the role of nitrogen-fixing bacteria?
Found in soil or mutualistic with plants. Both reduce N2 (gas) to ammonia
Describe the phosphorus cycle
- Phosphate ions in rocks are released by erosion/weathering
- Taken into plants by roots and in their biomass:
- Dna,rna, phospholipids ( and NADP and RuBP)
- Rate of absorption increased by mycorrhizae - Ions transferred through food chain
- Some lost from animals in water and death where they are decomposed by saprobionts releasing into the soil
How can phosphate be found in the sea due to cycle?
Weathering of rocks releases ion into seas, lakes and rivers
Taken up by aquatic producers
Passed along food chain to birds
Waste products from birds return ions to soil
Why are fertilisers needed?
Replaces lost nutrients from ecosystem when crops are harvested or livestock removes → lost to their biomass incorporating it
——> improve THE EFFICIENCY OF ENERGY TRANSFER
What are the properties of artificial fertilisers?
- Inorganic
- Contain pure chemicals e.g. ammonium nitrate as powders / pellets
- Inorganic substances more water soluble so larger quantities washed away, impacting the
environment
What are the properties of natural fertilisers?
- Organic
- E.g. manure, compost, sewage
- Cheaper / free but exact nutrients cannot be
controlled
What is leaching?
Excess ions can be washed into rivers or lakes causing pollution
Describe Eutrophication
- Rapid growth of algae in ponds and rivers (algal bloom)
- Algae blocks light, preventing it from reaching plants below
- Death of the plants below as they cannot photosynthesise
- Aerobically respiring saprobionts decompose the dead plant
matter, reducing oxygen concentration of water - Leading to death of aquatic organisms due to lack of dissolved
oxygen for aerobic respiration
Why is leaching less likely with natural fertilisers?
- Nitrogen / phosphorous contained in organic molecules
- Organic molecules less soluble in water so less likely to be washed away and need to be decomposed by saprobionts before being released
How can fertilisers reduce species diversity?
Favour fast growing plants e.g. grass / nettles
–> slower-growing plants lose out less organisms who feed off them
