energy transfer in and between organisms Flashcards
Location of light dependent reaction
Thylakoid membranes of chloroplast
Location of light independent reaction
Stroma of chloroplast
Thylakoid membranes
Folded membranes containing photosynthetic proteins (chlorophyll)
embedded with transmembrane electron carrier proteins involved in the LDRs
Chlorophyll
Located in proteins on thylakoid membranes
mix of coloured proteins that absorb light
different proportions of each pigment lead to different colours on leaves
Light-dependent reaction (LDR)
First stage of photosynthesis occurs in thylakoid membranes uses light energy and water to create ATP and reduced NADP for LIR
involves photoionisation of chlorophyll, photolysis and chemiosmosis
Advantage of many pigments
Each pigment absorbs a different wavelength of visible light
many pigments maximises spectrum of visible light absorbed
maximum light energy taken in so more photoionisation and higher rate of photosynthesis
Photolysis
Light energy absorbed by chlorophyll splits water into oxygen, H+ and e-
H20 –> 1/2 O2 + 2e- + 2H+
Products of photolysis
H+
Picked up by NADP to form
reduced NADP for LIR
e-
passed along chain of
electron carrier proteins
oxygen
used in respiration or diffuses out leaf via stomata
Chemiosmosis
Electrons that gained energy move along a series of electron carriers in thylakoid membrane release energy as they go along which pumps proteins across thylakoid membrane electrochemical gradient made protons pass back across via ATP synthase enzyme producing ATP down their conc. gradient
Photoionisation of chlorophyll
Light energy absorbed by chlorophyll excites electrons so they move to a higher energy level and leave chlorophyll some of the energy released is used to make ATP and reduced NADP
What happens to protons after chemiosmosis
Combine with co-enzyme NADP to become reduced NADP reduced NADP used in LIR
Products of LDR
ATP (used in LIR)
reduced NADP (used in LIR) oxygen (used in respiration / diffuses out stomata)
Light independent reaction (LIR)
Calvin cycle
uses CO2, reduced NADP and ATP to form hexose sugar occurs in stroma which contains the enzyme Rubisco temperature-sensitive
RuBP
Ribulose Bisphosphate
5-carbon molecule
GP
Glycerate-3-phosphate
3-carbon molecule
TP
Triose phosphate
3-carbon molecule
Producing hexose sugar in LIR
Takes 6 cycles
glucose can join to form disaccharides (sucrose) or polysaccharides (cellulose) can be converted to glycerol to combine with fatty acids to make lipids
Limiting factor
A factor which, if increased, the rate of the overall reaction also increases
Limiting factors of photosynthesis
Light intensity
CO2 concentration
temperature
How light intensity limits photosynthesis
If reduced, levels of ATP and reduced NADP would fall
LDR limited - less photolysis and
photoionisation
GP cannot be reduced to triose phosphate in LIR
How temperature limits photosynthesis
LIR inhibited - enzyme controlled (Rubisco)
up to optimum, more collisions and E-S complexes
above optimum, H-bonds in tertiary structure break, active site changes shape - denatured
How CO2 concentration limits photosynthesis
If reduced, LIR inhibited
less CO2 to combine with RuBP to form GP
less GP reduced to TP
less TP converted to hexose and RuBP regenerated
Products of LIR
Hexose sugar
NADP - used in LDR
Agricultural practices to maximise plant growth
Growing plants under artificial lighting to maximise light intensity
heating in greenhouse to increase temperature
burning fuel to release CO2
Benefit of agricultural practices for plant growth
Faster production of glucose -> faster respiration
more ATP to provide energy for growth e.g. cell division + protein synthesis
higher yields so more profit
Stages of aerobic respiration
1) Glycolysis
2) Link reaction
3) Krebs cycle
4) Oxidative phosphorylation
Location of glycolysis
Cytoplasm
Glycolysis
Substrate level phosphorylation
- 2 ATP molecules add 2 phosphate groups to glucose glucose phosphate splits into two triose phosphate (3C) molecules
both TP molecules are oxidised (reducing NAD) to form 2 pyruvate molecules (3C) releases 4 ATP molecules
Coenzymes
A molecule which aids / assists an enzyme
NAD and FAD in respiration both gain hydrogen to form reduced NAD (NADH) and reduced FAD (FADH)
NADP in photosynthesis gains hydrogen to form reduced NADP (NADPH)
Products of glycolysis
Net gain of 2 ATP
2 reduced NAD
2 pyruvate molecules
How many ATP molecules does glycolysis produce
2 ATP molecules used to phosphorylate glycose to glucose phosphate
4 molecules generated in oxidation of TP to pyruvate net gain 2 ATP molecules
Location of the link reaction
Mitochondrial matrix
Link reaction
Reduced NAD and pyruvate are actively transported to matrix
pyruvate is oxidised to acetate (forming reduced NAD)
carbon removed and CO2 forms
acetate combines with coenzyme A to form acetylcoenzyme A (2C)
Products of the link reaction per glucose molecule
2 acetylcoenzyme A molecules 2 carbon dioxide molecules released
2 reduced NAD molecules
Mitochondria structure
Double membrane with inner membrane folded into cristae enzymes in matrix
Location of the Krebs cycle
Mitochondrial matrix
Krebs cycle
Acetylcoenzyme A combines with 4C molecule to produce a 6C molecule - enters cycle oxidation-reduction reactions
Location of oxidative
phosphorylation
Cristae of mitochondria
Products of the Krebs cycle per glucose
8 reduced coenzymes
6 reduced NAD
2 reduced FAD
2 ATP
4 carbon dioxide
Role of reduced coenzymes in oxidative phosphorylation
Accumulate in mitochondrial matrix, where they release their protons (H+) and electrons (e-)
regenerate NAD and FAD to be used in glycolysis/ link reaction / Krebs cycle
Role of electrons in oxidative phosphorylation
Electrons pass down series of electron carrier proteins, losing energy as they move
energy released actively transports H+ from mitochondrial matrix to inter- membranal space electrochemical gradient generated
How is ATP made in oxidative
phosphorylation
Protons move down electrochemical gradient back into matrix via ATP synthase ATP created
movement of H+ is chemiosmosis
Role of oxygen in oxidative phosphorylation
Oxygen is the final electron acceptor in electron transport chain
oxygen combines with protons and electrons to form water enables the electron transport chain to continue
How would lack of oxygen affect respiration
Electrons can’t be passed along the electron transport chain
the Krebs cycle and link reaction stop because NAD and FAD (converted from reduced NAD/FAD as they release their H atoms for the ETC), cannot be produced
Oxidation
Loss of electrons
when a molecule loses hydrogen
Location of anaerobic respiration
Cytoplasm
glycolysis only source of ATP
Reduction
Gain of electrons
a reaction where a molecule gains hydrogen
Anaerobic respiration animals
Pyruvate produced in glycolysis is reduced to form lactate pyruvate gains hydrogen from reduced NAD
reduced NAD oxidised to NAD so can be reused in glycolysis
2 ATP produced
Anaerobic respiration in plants & microbes
Pyruvate produced in glycolysis is reduced to form ethanol and CO2
pyruvate gains hydrogen from reduced NAD
reduced NAD oxidised to NAD so can be reused in glycolysis
2 ATP produced
Other respiratory substances
Fatty acids and amino acids can enter the Krebs cycle for continued ATP synthesis
Lipids as respiratory substances
Glycerol from lipid hydrolysis converted to acetylcoenzyme A can enter the Krebs cycle
Producers
Plants
produce their own carbohydrates from carbon dioxide (autotrophs)
start of a food web
Consumers
Heterotrophs that cannot synthesise their own energy obtain chemical energy through eating
Energy transfer between trophic levels
Biomass and its stored energy is transferred through trophic levels very inefficiently
most energy is lost due to respiration and excretion
Proteins as respiratory substances
Amino acids from protein hydrolysis can be converted to intermediates within Krebs cycle
Biomass
Measured in terms of:
mass of carbon
dry mass of tissue per given area
Calorimetry
Laboratory method used to estimate chemical energy stored in dry biomass
How is dry mass of tissue estimated
Sample of organism dried in oven below 100C (avoiding combustion + loss of biomass) sample reweighed at regular intervals
all water removed when mass constant
Why is dry mass a representative measure of biomass
Water content in tissues varies heating until constant mass allows standardisation of measurements
for comparison
Calorimetry method
Sample of dry biomass is burnt energy released used to heat known volume of water
change in temperature of water used to calculate chemical energy
Net primary production
Chemical energy stored in plant biomass after respiratory losses available for plant growth and reproduction - create biomass available to other trophic levels
Gross primary production
Chemical energy stored in plant biomass, in a given area / volume
total energy resulting from photosynthesis
Calculating net primary production
NPP = GPP - R
R = respiratory losses to the environment
Calculating net production of consumers (N)
N = I - (F + R)
I = chemical energy store in ingested food
F = chemical energy store in faeces / urine
R = respiratory losses
Units of productivity rates
kJ Ha-1 year-1
kJ is the unit for energy
Why is productivity measured per area
Per hectare (for example) is used because environments vary in size
standardises results so environments can be compared
Why is productivity measured per year
More representative of productivity
takes into account effects of seasonal variation (temperature) on biomass environments can be compared with a standardised amount of time
Why is energy transfer inefficient from sun -> producer
Wrong wavelength of light - not absorbed by chlorophyll
light strikes non- photosynthetic region (bark) light reflected by clouds / dust lost as heat
Farming practices to increase energy transfer for crops
Simplifying food webs to reduce energy / biomass
herbicides kill weeks -> less competition
fungicides reduce fungal infections
results in more energy used to create biomass
fertilisers such as nitrates to promote growth
Why is energy transfer inefficient after producers
Respiratory loss - energy used for metabolism (active transport)
lost as heat
not all plant / animal eaten (bones)
some food undigested (faeces)
Saprobionts
Feed on remains of dead organisms and their waste products (faeces / urea) and break down organic molecules secrete enzymes for extracellular digestion
Farming practices to increase energy transfer for animals
Reducing respiratory losses (more energy to make biomass)
restrict movement
keep warm
slaughter animal when young (most energy used for growth) selective breeding to produce breeds with higher growth rates
Mycorrhizae
Symbiotic relationship between fungi and roots of plants
fungi act as extensions of roots increase surface area of system - increasing rate of absorption mutualistic relationship as plants supply fungi with carbohydrates
Importance of nitrogen to organisms
Used to create
amino acids / proteins
DNA
RNA
ATP
Nitrogen cycle stages
Nitrogen fixation
nitrification
denitrification
ammonification
Nitrogen fixation
Nitrogen fixing bacteria break triple bond between two nitrogen atoms in nitrogen gas fix this nitrogen into ammonium ions
Nitrogen fixing bacteria
Fix nitrogen gas into
ammonium ions
free living in soil
or form mutualistic relationship on root nodules of leguminous plants
give plants N in exchange for carbohydrates
Nitrification
Ammonium ions in soil are oxidised to nitrite ions nitrite ions are oxidised to nitrate ions
by nitrifying bacteria
Denitrification
Returns nitrogen in compounds back into nitrogen gas in atmosphere
by anaerobic denitrifying bacteria
Ammonification
Proteins / urea / DNA can be decomposed in dead matter and waste by saprobionts
return ammonium ions to soil - saprobiotic nutrition
Importance of phosphorius
Used to create:
DNA
RNA
ATP
phospholipid bilayers
RuBP / GP/ TP
Fertilisers
Replace nutrients (nitrates and phosphates) lost from an ecosystem’s nutrient cycle when
crops are harvested
livestock removed
can be natural (manure) or artificial (inorganic chemicals)
Natural fertilisers advantages
Cheaper than artificial fertilisers
often free if farmer has own
animals - recycle manure organic molecules have to be broken down first by saprobionts so leaching less likely
Artificial fertilisers advantages
Contain pure chemicals in exact proportions
more water-soluble, so more ions dissolve in water surrounding soil.
higher absorption
Natural fertilisers disadvantages
Exact minerals and proportions
cannot be controlled
Artificial fertilisers disadvantages
High solubility means larger quantities can leach away with rain
risking eutrophication reduce species diversity as favour plants with higher growth rates e.g., nettles
Leaching
When water-soluble compounds are washed away into rivers / ponds
for nitrogen fertilisers, this can lead to eutrophication
Eutrophication
When nitrates leached from fields stimulate growth of algae algal bloom
can lead to death of aquatic organisms
How does eutrophication lead to death of aquatic organisms?
Algal bloom creates blanket surface of water blocking light plants cannot photosynthesize and die
aerobic bacteria feed and respire on dead plant matter eventually, aquatic organisms die due to lack of dissolved oxygen in water
Mutualistic relationships
A type of symbiotic relationship where all species involved benefit from their interactions
Role of saprobionts in nitrogen cycle
They use enzymes to decompose proteins/DNA/RNA/urea
releasing ammonium ions
