Topic 5: Energy transfers in and between organisms

structures of chloroplasts

thylakoid

grana (stack of thylakoids)

stroma

lamellae (joining grana together)

double membrane

DNA and starch grain

site of light **dependent** stage

thylakoid membrane

photolysis of water

water is split by light into protons, electrons, and oxygen

2H2O → 4H+ + 4e- O2

e- supply chlorophyll with more e-

e- and H+ taken by electron carrier: NADP

NADP is reduced to NADPH

O2 is a by-product: respiration or diffuses out as waste

H+

hydrogen ions or protons

photoionisation of chlorophyll

chlorophyll absorbs light which excites its electrons to higher energy levels

electrons are lost/removed from the chlorophyll

chlorophyll is photoionised/oxidised

electrons are taken by electron carrier (NADP); it is reduced

electrons undergo oxidation and reduction reactions down electron transport chain; releasing energy (ADP+Pi → ATP)

chemiosmotic theory

protons actively transported, by ATP, into thylakoid space

protons from photolysis and active transported protons create concentration gradient across thylakoid membrane

protons facilitatively diffuse out the membrane via ATP synthase channels/stalked granules; change shape of enzyme as pass through = catalyse formation of ATP

products of light dependent reaction

NADPH

ATP

site of light **independent** stage

stroma

light independent stage (summary)

RuBP + CO2 (+ Rubisco) → (6C intermediate) → 2 x GP (+ 2x ATP and 2 x NADPH) → 2 x TP (+ ATP) → 1C: to form hexose sugar and 5C: RuBP

light independent stage

RuBP (5 Carbon molecule) combines with CO2 catalysed by Rubisco enzyme into 2 x glycerate 3-phosphate (GP) (3C)

2x GP is reduced into 2 x triose phosphate (TP) (3C) using 2 x NADPH and 2 x ATP

5C out of the 6C of 2 x TP are used to regenerate RuBP using ATP (Pi used to regenerate RuBP too), the 6thC is used to form hexose sugars like glucose

how chloroplasts are adapted

fluid in stroma contains all enzymes to carry out reactions

stroma fluid surround grana, LDR products can readily diffuse in the stroma

contains DNA + ribosomes so it can quickly synthesise proteins (enzymes)

use of glucose

respiration

biomass

stored as starch

measuring rate of photosynthesis

photosynthometer

measure the volume of O2 released by plant

measure the volume of CO2 absorbed by plant

eg. aquatic plant with gas syringe connected.

structures of mitochondria

matrix

cristae

double membrane

intermembrane space

site of glycolysis

cytoplasm of cell

glycolysis

glucose to big to pass through chloroplast membrane, needs to be split


1. activate glucose by phosphorylation
2. splitting of phosphorylated glucose
3. oxidation of triose phosphate
4. production of ATP

glucose → pyruvate

activation of glucose by phosphorylation

glucose is phosphorylated to make 6C glucose phosphate

2 ATPs are used to supply phosphate groups

splitting of phosphorylated glucose

6C sugar phosphate breaks down to form 2 x 3C sugar phosphates: triose phosphate

oxidation of triose phosphate

triose phosphate is oxidised to pyruvate

hydrogen is removed from each triose phosphate molecule

hydrogens ‘passed’ to 2 x NAD molecules; they are reduced to NADH

production of ATP

2 ATP molecules made directly from the conversion of each triose phosphate into pyruvate, as phosphate groups are removed

= 4 ATP molecules made

reactants (in) and products (out) of glycolysis

in:

glucose, 2 x NAD, 2 x ATP

out:

2 x pyruvate, 2 x NADH, 4 x ATP (**net gain** of 2 ATP)

link reaction

pyruvate is **oxidised** to acetate, producing NADH and CO2

pyruvate (3C) + NAD → acetate (2C) + CO2 + NADH

acetate combines with coenzyme A producing acetylcoenzyme A

acetate (2C) + CoA → AcetylCoA

site of Krebs cycle (and link reaction)

matrix

Krebs cycle

AcetylCoA reacts with 4C molecule, releasing CoA and producing 6C molecule

AcetylCoA + 4C → CoA + 6C

series of oxidation-reduction reactions occur converting 6C molecule back into 4C producing:

2 x CO2

1 x ATP

3 x NADPH

1 x FADH2

site of oxidative phosphorylation

cristae membrane

oxidative phosphorylation

coenzymes NADH and FADH2 donate electrons

these pass along the electron transfer chain in a series of oxidation-reduction reactions

this releases energy (ATP) to actively transport protons across membrane, in to intermembrane space

these accumulate, create concentration gradient, facilitatively diffusing back (into matrix) through ATP synthase channels

oxygen is the **final acceptor** of electrons and protons to form water

anaerobic respiration in plants and microorganisms

glycolysis occurs as normal

glucose → 2 x pyruvate (net gain of 2 ATP and 2 NADH)

then, in order for glycolysis to continue, NADH must be oxidised (like in link reaction) into NAD

2 x pyruvate + 2 x NADH → 2 x NAD + 2 x **ethanol** + CO2

anaerobic respiration in animals

glycolysis occurs as normal

glucose → 2 x pyruvate (net gain of 2 ATP and 2 NADH)

each pyruvate molecule takes 2 H+ to form lactate and NAD

pyruvate + NADH → lactate + NAD

lactate/lactic acid

lactate must be removed (broken down by oxygen into carbon dioxide and water)

because it is toxic as it is acidic (inhibiting/denaturing enzymes)

causing muscle cramps and muscle fatigue

alternative respiratory substrates

lipids and amino acids can act in place of glucose/sugars

enter respiration in Krebs cycle, after being broken down into ‘parts’

heat energy waste during respiration

in general, greater the energy that is released, greater the energy ‘lost’ as heat (so less efficient)

so this is why electrons passed down a *series* of electron transfer carriers, rather than one “big jump/reaction”

less than 3% of sunlight usually converted into chemical energy, why?

some sunlight misses the leaves entirely

only certain wavelengths of light are absorbed by chlorophyll

sunlight reflected from the surface of the leaves

sunlight misses the chlorophyll

only small % of the light energy absorbed by the chlorophyll is stored as biomass, why?

photosynthesis is inefficient (approx. 2% efficient) - energy is lost as electrons are passed on

energy lost by respiration

GPP

gross primary production

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

measured in kJ ha^-1 year^-1 (eg.)

NPP

net primary production

= chemical energy stored in plant biomass after respiratory losses to the environment have been taken into account

GPP equation

NPP = GPP - R

R = respiratory losses to environment

what is NPP used for

plant growth and reproduction

available to other trophic levels in ecosystem ie. herbivores and decomposers

not all energy in biomass of plants can be transferred by consumers, why?

not all parts of plant can be eaten

not all parts eaten can be digested (lost in faeces instead)

heat energy lost due to respiration

% of energy transferred between consumers is low, why?

heat energy lost due to respiration

movement/muscle contractions

faeces

net production of consumers (N) equation

N = I - (F + R)

I = represents chemical energy in **i**ngested food

F = energy lost due to **f**aeces and urine

R = **r**espiratory losses due to environment

what happens to energy in faeces/dead organisms

energy is transferred to decomposers

used in growth of decomposers

used in respiration of decomposers

released as heat

efficiency of transfers to consumers

efficiency of transfers to consumers greater than transfers to producers (photosynthesis about 2% efficient)

efficiency lower in older animals

carnivores use more of their food than herbivores

biomass

total mass of living material in a specific area at a given time

measured in terms of mass of carbon/dry mass of tissue per given area (units: g m^-2)

can be estimated using calorimetry

increasing efficiency of energy transfer

simplifying food webs

reduce respiratory losses (leads to intensive rearing)

intensive rearing

controlling the conditions of how the animals live

stop them moving; supplying them with antibiotics for disease; keeping them warm = all reduces their energy losses due to heat etc

slaughtered while growing

fed controlled diet (max proportion of food digestible)

genetically selected for high productivity

biological compounds containing phosphorus

ATP, NADP, GP, TP, RuBP, phospholipids, nucleic acid

phosphorus cycle

exist as phosphate ions in sedimentary rocks

weathering and erosion dissolves ions, absorbed by plants for biomass

animals eat plants (then excrete)

death of animals: saprobionts break down animal/plant

phosphorus enters rivers and oceans by run off and leaching

phosphorus in water then goes to form rocks again, sedimentation (back to start of cycle)

biological molecules containing nitrogen

amino acids/proteins, ATP, ADP, NAD, NADP, nucleic acid, urea

main nitrogen cycle

1. plants and animals **die/excrete**

biological molecules containing nitrogen in the ground


2. **saprobiotic nutrition and ammonification**

saprobionts converts biological molecules into ammonia

ammonia is then converted into ammonium ions


3. **nitrification** by nitrifying bacteria

ammonium ions is oxidised into nitrite ions (by bacteria)

nitrite ions is oxidised into nitrate ions; nitrate ions are absorbed by plants (cycle repeats)

side cycle of nitrogen cycle

if there is no water draining in soil, this creates an anaerobic environment/low O2 for the bacteria

**denitrifying bacteria** then uses nitrate ions (as final acceptor of electrons/protons) producing nitrogen gas; released into atmosphere

this is why fields must be ploughed, as now the nitrates is ‘out’ of the cycle for plants

nitrogen gas is converted back into nitrogen compounds by nitrogen fixing bacteria (**nitrogen fixation**)

either, free living nitrogen fixing bacteria or mutualistic nitrogen fixing bacteria

saprobionts in decomposition

microorganisms/saprobionts

secrete enzymes (extra-cellular digestion)

absorb products of digestion/smaller molecules

respiration produces CO2

mycorrhizae

= association between fungi and roots; mutualistic/symbiotic relationship

fungi helps plant by extending the surface area of the roots for uptake of ions and water

roots help fungi by obtaining organic compounds like glucose from the plant

how is phosphorus cycle different to nitrogen cycle

phosphorus cycle has no atmospheric stage, phosphorus is not found in the atmosphere

fertilisers

natural or artificial fertilisers replace nitrates and phosphates lost by harvesting plants and removing livestock

natural = dead/decaying remains of plants/animals

artificial = mined from rocks then converted to different forms

fertilisers: reduce species diversity

nitrogen rich soils favour growth of grasses, nettles, and other rapidly growing species

outcompeting many species

leaching

rain will dissolve soluble nutrients such as nitrates carrying them deep into soil beyond reach of plants, or enter the streams/lakes

may cause illness if drinking water or eutrophication

eutrophication

run off/leaching of nutrients/nitrates

leads to increase growth of algae

competition of light

death of algae/plants

increase (food supply) decomposers (which respire)

respiration uses up oxygen

fish/animals die due to lack of oxygen (used by decomposers)

= lower species diversity and putrid water (toxic and heavily nitrated)