Unit 5- energy transfers in and between organisms

Where does LDR take place ?

In chloroplast of plant cell- in thylakoid membrane/grana

First stage of LDR- photolysis of water

Light energy is absorbed by chloropyll and splits water into oxygen, H+ and e-

What happens to the oxygen after photolysis?

Used for respiration or diffuses out of the leaf through the stomata

Second stage of LDR- photoionisation

Light energy is absorbed by the chlorophyll and results in electrons becoming excited

Energy level raises and electron leaves chlorophyll

Chloropyll has been ionised- lost an electron

Production of ATP in LDR

Electrons that gained energy and left chlorophyll move along electron carrier proteins embedded within thylakoid membrane

Redox reaction takes place each time it moves- taking energy from e- and uses it to make ATP

Chemiosmosis:

As electrons move along carrier proteins and release energy- used to pump protons/H+ ions across chloroplast membrane via active transport

Results in high conc of protons/H+ ions in thylakoid lumen- electrochemical gradient created

Protons pass through enzyme ATP synthase by facillitated diffusion- causes a change in shape- releasing energy to catalyse reaction to make ATP

Chemiosmosis: production of reduced NADP

Protons combine with co-enzyme NADP- becomes reduced NADP/NADPH (proton plus electron gives hydrogen atom)

Protons moving down conc gradient- chemiosmosis

Where does LIR take place?

In the stroma- contains enzyme RuBisCo- catalyses this reaction

Why does temp affect LIR?

It involves enzymes

LDR- isnt affected

LIR process:

* CO2 (has one carbon) reacts with RuBP (five carbons)- forms two molecules of GP (a 3 carbon compound, so 6 in total)
* GP is reduced to TP- using energy from ATP and accepting a H from reduced NADP- reduction reaction as GP gains a hydrogen
* 2 molecules of TP- one of carbon atoms is removed from cycle each time- 6 times- to be converted into useful organic substances
* To allow cycle to continue- have to regenerate RuBP with energy from ATP

Why do we say useful organic substances?

Glucose is the product- can form many things e.g monosaccharides

Limiting factors of LIR?

\-Temperature- enzyme controlled reaction

\-Co2 conc- one of the reactants entering calvin cycle

Limiting factors of LDR?

* Light intensity- for photolysis and photoionisation

What are agricultural practices to remove limiting factors for maximum photosynthesis?

* Growing plants under artificial lighting- maximum light intensity
* Heating green house to increase temp
* Burning fuel- release more co2

What do farmers need to consider using these techniques?

The extent that each technique is used needs to be considered in terms of profit

If extra growth from photosynthesis is minimal- wont be cost effective to pay for heating etc

Aerobic respiration- glycolosis (stage 1)- where?

The cytoplasm

Glycolysis process:

-Glucose (6 carbons) is phosphorylated to glucose phosphate- by hydrolysing 2 ATP to release phosphate

-Glucose phosphate is a high energy molecule- splits into 2 TPs (3 carbons)

-Both Tp molecules are oxidised as the co-enzyme NAD picks up a hydrogen from the TP- converted into NADH- TP molecules oxidised producing pyruvate (3 carbon)

-Oxidation of TP into pyruvate releases 2 molecules of ATP

What happens to the pyruvate at the end of glycolysis?

Transported into mitochondrial matrix for the next step

Aerobic respiration-the link reaction (stage 2)- where ?

Occurs in the mitochondrial matrix

The link reaction process:

-The pyruvate (3 carbons) made in glycolysis is oxidised- makes acetate (2 carbons)

-The hydrogen from pyruvate is picked up by enzyme NAD to make NADH

-1 stage where carbon dioxide is formed

-Acetate combines with co-enzyme A to produce- acetylcoenzyme A (2 carbon)- to enter next stage, Krebs cycle

3 products of link reaction:

-2 Acetyl CoA

-2 Co2 released

-2 reduced NAD

Aerobic respiration- the krebs cycle (stage 3)- where?

-Takes place in the mitochondrial matrix

Aerobic respiration- the krebs cycle process

-Acetyl CoA (2 carbons) produced in the link reaction reacts with a 4 carbon compound- producing 6 carbon compound

-Co enzyme A -released and re used in link reaction

-Lose 2 carbon dioxide- this stage produces ATP

-In a series of redox reaction the reduced co-enzymes FADH and NADH

Products produced per one krebs cycle?

-3 reduced NAD

-1 reduced FAD

-1 ATP

-2 Co2

(multiply by 2 for one gllucose molecule as there is 2 pyruvate in one)

Aerobic respiration- oxidative phosphorylation- where?

-Cristae- mitochondria inner membrane

What does OP stage involve?

-The most ATP is made

-The electron transfer chain

-Movement of protons across inner mitochondrial membranes

-Catalysed by ATP synthase

OP process:

-Reduced co-enzymes NAD and FAD in mitochondrial matrix split hydrogen atoms into H+ ions and electrons

-Electrons are passed along electron transport chain releasing energy which is used to transport H+ ions to the intermembrane space

-This creates an electrochemical gradient- build up of protons in intermembrane space

-H+ ions move down their conc gradient through ATP synthase by facilliated diffusion- this catalyses the phosphorlyation of ADP to make ATP

-The oxygen in matrix picks up electrons at end of chain and protons- creating water- it is called the terminal acceptor

Where does anaerobic respiration occur?

-In the cytoplasm and the absence of oxygen

Anaerobic respiration in animals

-The pyruvate produced in glycolysis is reduced (gains hydrogen from NADH) to form lactate

-This oxidises NAD so that it can be re used in glycolysis ensuring more ATP is continued to be produced

Anaerobic respiration in plants and microbes

-Same as anaerobic but ethanol and Co2 is prodcued instead of lactate.

Why are plants known as the producers in a food web?

-They produce their own carbohydrates using co2 in atmosphere and or water

What is biomass?

The mass of living material of the organism

It is what is left over after the loss of energy between trophic levels in a food web due to excretion and respiration

How is the amount of biomass measured?

-In terms of mass of carbon or dry mass of tissue per given area

-Chemical energy store in dry biomass can be measured using calorimetry

What is productivity?

The rate at which something is produced-depends on the abiotic and biotic factors- quantified using GPP and NPP

What is gross primary production?

-The chemical energy store in plant biomass, in a given area or volume. So the total energy entering the food chain from photosynthesis

What is net primary production?

-The chemical energy store in plant biomass taking into account the energy that will be lost due to respiration

-GPP - R

-Its the energy left over that is available to the plant to create new biomass and therefore available to the next trophic level in a food web

What ecosystem would have high prodcutivity levels?

Rainforest

How to calculate the net production of consumers in e.g animals

N = I - F + R

I- chemical energy store in ingested in food

F- the chemical energy lost to the environment in faeces and urine

R- respiratory losses

How is the rate of primary and secondary production measured

-Measured as biomass in a given area in a given time e.g KJ ha-1 year-1

Why is the unit per unit area used

-To standardize the results to enable environments to be compared- it takes into account that different environments will vary in size

Per year used why?

-Takes into account the impact seasons will have on rain, light and heat-provides an annual average to allow fair comparisons between environemtn

How to calculate the effieciency of energy transfers?

energy available after transfer'/energy available before the transfer x 100

The nitrogen cycle: nitrogen fixation- step 1

-Nitrogen fixing bacteria convert atmospheric nitrogen to ammonium ions

-There either free-living in the soil or have a symbiotic relationship with leguminous plants e.g beans as they live in their root nodules

Step 2 - ammonification

-Organic nitrogen from decomposition of proteins, urea etc are converted to ammonium ions which are released into the soil

-This is carried out by saprobionts- these digest waste extracellularly

Step 3 - nitrification

-ammonium ions producd by ammonification and nf in soil are oxidised to nitrites then nitrates- carried out by nitrifying bacteria- TWO stage oxidation reaction

Step 4 -Denitrification

-Converts nitrogen in compounds back to nitrogen gas-loosing nitrogen

-Not useful as nitrogen gas cannot be absorbed by plants

-Carried about by anaerobic dentrigying bacteria-often why farmers aerate their soil

What is the phosphorus cycle used for?

Essential to form DNA, ATP and pbs

The phosphorus cycle:

-Plants absorb the phosphate ions from oceans etc by active transport

-Animals eat the plants- use ions to synthesise organic materials

-Animals excretion containing phosphate ions enter oceans etc again

-Excretion and decompisition- excretion meaning that the phosphate ions from waste and remains- guano in their excretion and is rich in phosphorus

-Guano, bones etc will erode- releasing phosphate ions back

-Some guano may go through deposition- forms phosphate ions in rocks

-Rocks will erode and returns PI back- also addition of fertillers mean it will run off into oceans

-Sedimentation- build of sediment to create rocks, contains phosphate ions.

What is the use of fertilisers?

to replace the nitrates and phosphates ions lost when plants are harvested and removed from nutrient cycles as crops

What are natural fertillers?

-dead and decaying remains of plants and animals as well as animal wastes e.g manure

What are artificial fertilisers?

Inorganic chemicals which are synthesised?

Pros of natural fertillisers?

-They are cheap/free if farmer owns animals

Cons of natural fertillisers?

-The exact minerals and proportions cannot be controlled

Pros of artificial fertillisers?

-They are chemicals created to contain exact proportions of minerals

Cons of artifical fertilllers?

-Soluble in water- more likely to leach into rivers-has negative impact on environment

-Could also be seen as advantage- minerals are easily absorbed

What is leaching?

When water soluble compounds are washed away into rivers or ponds

Impact of leaching?

Eutrophication

Describe eutrophication

-Nitrates leached from soil stimulate algae growth in pond- algae bloom

-This blanket of algae on surface of water blocks sunlight

-As a result plants below cannot photosynthesise and plants will die

-bacteria in water feed and respire on the dead plant matter

-This results in increased bacteria- respiring now and using up the oxygen within the water

-eventually plants and animals in water will die due to lack of dissolved oxygen in water