3.5 energy transfers in and between organisms Flashcards
fixation
- process by which gaseous CO2 is converted into sugars (e.g photosynthesis)
- endothermic process
- helps to regulate the conc of CO2 in atmospheres and oceans
- the carbon needed to synthesise all types of organic molecule are provided by this process
what are organic molecules
- all biological molecules that contain ‘C’
glucose uses in plants
F ats
O ils
S tarch
R esipiration
A mino acids
C ellulose
what are organisms that photosynthesise called
photoautotrophs/ producers
properties of ATP
- stores and releases only a small amount of energy at a time so no energy is wasted as heat
- small soluble molecule = can be transported about easily
- easily broken down so energy can be released instantaneously
- can make other molecules more reactive by transferring one of its phosphate groups to them
- can’t pass out of the cell so cell always has an immediate supply of energy
what is the compensation point
when rate of photosynthesis = rate of respiration ; there is no net gain or loss of carbohydrate
which plants reach the compensation point sooner
shade plants:
- they photosynthesise at lower light intensities which means they can photosynthesise even when it is becoming dark alongside respiration, which allows it to reach it’s compensation point sooner
what is the time a plant takes to reach the compensation point called
compensation period
components of chloroplasts
- thylakoids
- granum
- stroma
- double membrane
- photosynthetic pigments
thylakoids
- pigment containing flattened sacs
- site of light dependent reaction
granum
- stack of thylakoids
- grana stacks provide chloroplast with an increased SA (allows photosynthesis to occur in a limited space)
- all grana held together by inter-granal thylakoids (site of light dependent reaction)
stroma
- gel material containing enzymes
- second part of photosynthesis occurs here (light independent reaction)
- thylakoids embedded within stroma
double membrane in chloroplasts
- controls molecular traffic in and out of chloroplast
- inner membrane folded extensively to form thylakoids
photosynthetic pigments
- coloured biological compound
- present in chloroplasts and photosynthetic bacteria
2 types of pigments found in plants
- chlorophyll
- carotenoids
what light does chlorophyll reflect
green
what light do carotenoids reflect
orange, red or yellow light
location of photosynthetic pigments
- found in photosystems (I AND II) which are found in thylakoid membranes
photophosphorylation
addition of a phosphate group using energy from sunlight
photolysis
splitting of a molecule using energy from sunlight
photoionisation
loss of an electron due to absorption of light energy
chemiosmosis
movement of ions down a gradient across a semi-permeable membrane
3 main processes that take place in the light dependent reaction
- cyclic photophosphorylation
- non cyclic photophosphorylation
- photolysis of water
what does cyclic photophosphorylation include
photosystem 1
electron acceptor
electron transport chain
electron transport chain
cluster of proteins that transfer electrons through a membrane, allowing the energy they have to be gradually released and ultimately captured within ATP molecules
what happens in photoionisation in the light dependent reaction
- chlorophyll absorbs light
- electrons are lost/ chlorophyll becomes positively charged
process of cyclic photophosphorylation
- light hits photosystem 1 and excited 2 electrons
- electrons accepted by electron acceptor (leaves photosystem 1 electron deficient)
- electrons pass along electron transport chain (losing energy each time they’re carried on)
- the energy released is used to pump H+ ions from stroma into lumen creating an electrochemical gradient
- H+ ions now diffuse via chemiosmosis from the lumen through ATP synthase converting ADP + Pi into ATP
- electrons then pass back to photosystem I (cyclic) and process repeats
product of cyclic photophosphorylation
ATP - used in light independent reaction
difference between cyclic and non-cyclic photophosphorylation
cyclic = involves only photosystem I
non-cyclic = involves photosystem I and II
process of non cyclic photophosphorylation
- light hits photosystem II and excited 2 electrons
- electrons accepted by electron acceptor (leaves photosystem II electron deficient)
- electrons pass along electron transport chain (losing energy each time they’re carried on)
- energy released is used to make ATP from ADP + Pi
- light also hits photosystem I (exciting 2 electrons that pass on to an electron acceptor)
- to replace those electrons, photosystem I absorbs the 2 electrons originally from photosystem II
- electrons pass along electron transport chain
- this time, the energy released and electrons are used to reduce NADP to NADPH
products of non cyclic photophosphorylation
ATP and reduced NADPH
what happens in photolysis
water molecules are split by light energy
where does photolysis occur
thylakoid lumen
process of photolysis
- light energy hits a water molecule
- with aid of enzymes, the water is split into oxygen, H+ ions and electrons
- H+ ions reduce NADP which passes to the light-independent reaction
- electrons replace those lost from photosystem II in non cyclic photophosphorylation
- oxygen released as a waste gas
where does the light dependent reaction occur
thylakoids of chloroplasts
where does the light independent reaction occur
stroma of chloroplasts
process of light independent reaction
- carbon dioxide reacts with RuBP to form 2 molecules of GP (reaction catalysed by enzyme rubisco)
- GP is reduced by ATP and NADPH (from the light dependent reaction) into 2 molecules of TP
- some of the TP is used to build other carbohydrates and complex molecules
- most of the TP is recycled to regenerate RuBP
- for every molecule of glucose made, 5 molecule of RuBP is produced
products of the Calvin Cycle
NADP
ADP
Pi
what is the light independent reaction also known as
calvin cycle
what provides additional energy for the light independent reaction
hydrolysis of ATP
factors affecting rate of photosynthesis
light intensity
temperature
CO2
water
how does light intensity affect rate of photosynthesis
- only certain wavelengths of light are used for photosynthesis
- the higher the light intensity, the more energy it provides
what colour light does chlorophyll A absorb
red
what colour light does chlorophyll B absorb
blue/violet
what colour light does carotene absorb
orange
how does temperature affect rate of photosynthesis
- ideal temp = 25
- at high temps, stomata closes to avoid losing water = photosynthesis slows because less CO2 enters leaf
- because photosynthesis involves enzymes e.g rubisco, if the temperature is below 10, the enzymes become inactive. if temp is above 45, the enzymes start to denature
how does CO2 affect rate of photosynthesis
- CO2 makes up 0.04% of the gases in the atmosphere
- increasing this % up to 0.4%, gives a higher rate of photosynthesis, but any higher and the stomata start to close
how does water affect rate of photosynthesis
- too little water = photosynthesis stops
- too much water = soil becomes waterlogged
- reduces intake/uptake of minerals e.g magnesium
farming and plant growth
- farmers know factors that limit photosynthesis and therefore limit plant growth
- this means that they try to create an environment where plants are in optimum conditions which increases growth and yield
how do farmers manage conditions
- co2 conc: added to atmosphere e.g burning a small amount of propane
- light: glass allows light in
- temp: glasshouse trap heat energy
respiration
process whereby cells release energy from organic molecules
what is respiration
process by which organisms extract energy stored in complex molecules and use it to generate ATP
how much energy is released when ATP is hydrolysed to form ADP and inorganic phosphate
30.5kJ
why use ATP in a reaction
- ATP releases its energy instantly in a single reaction
- hydrolysis of ATP releases a small amount of energy, idea for fueling reactions in the body
types of respiration
- aerobic and anaerobic
where does respiration occur
- in all living cells
- eukaryotes = cytoplasm (early stage) and mitochondria (later stage)
- mitochondria
why is the mitochondria a useful place for respiration to occur
- highly folded inner membranes that hold key respiratory proteins and enzymes that make ATP
- provide an isolated environment: maintains optimum conditions for respiration
- have their own DNA and ribosomes = can manufacture own respiratory enzymes
4 stages in aerobic respiration
- glycolysis
- link reaction
- krebs cycle
- oxidative phosphorylation
what are coenzymes
molecules that aid function of an enzyme by transferring a chemical group from one molecule to another
conenzymes used in respiration
- NAD
- coenzyme A
- FAD
role of NAD and FAD
- transfer H from one molecule to another.
- can reduce (give hydrogen) or oxidise (take hydrogen) a molecule
role of coenzyme A
transfers acetate between molecules
where does glycolysis occur
- cell cytoplasm
is glycolysis an anerobic or aerobic process
anerobic
stage 1 of glycolysis
phosphorylation:
- glucose phosphorylated by 1 ATP molecule (forms 1 molecule of glucose -6-phosphate)
- G-6-P converted to fructose-1-phosphate.
- 2nd ATP molecule phosphorylates fructose-1-phosphate forming hexose-1,6-biphosphate
stage 2 of glycolysis
splitting sugar:
- hexose-1,6-biphosphate split into 2 triose-phosphate (TP) molecules
stage 3 of glycolysis
production of ATP:
- dehydrogenase enzymes remove 2 H atoms from each sugar - forming 1 NADH for each TP (NAD = H acceptor)
- each sugar also produces 1 ATP (substrate level phosphorylation)
- TP converted into pyruvate by enzyme action (also regenerates molecule of ATP)
products of glycolysis
glucose -> 2 pyruvate + 2 ATP + 2NADH
net gain of ATP in glycolysis
2
limiting factor to rate of glycolysis
supply of NAD
purpose of link reaction
- allows pyruvate to enter aerobic respiratory pathway
where does link reaction occur
- mitochondrial matrix
- means that pyruvate produced in cytoplasm must be actively transported into mitochondria before reaction can begin
link reaction process
- pyruvate reacts with coenzyme A -> acetyl CoA
- CO2 + H2 released in process
- H2 reduces 1 molecule of NAD+ (forms NADH)
- sugar molecule now only has 2 carbons
yield of link reaction
- 2NADH + 2CO2
- (glycolysis releases 2 molecules of pyruvate which means link reactions happens twice)
where does Krebs occur
mitochondrial matrix
process of Krebs cycle
- acetate removed from acetyl CoA
- acetate combines with oxaloacetate (4C) to form citrate (6C)
- citrate decarboxylated = releases 1 CO2 AND dehydrogenated, releases 2 H+ atoms (reduce NAD+ -> NADH + H+)
- citrate now is a ‘5 carbon compound’
- 5C compound decarboxylated -> releases 2 H+ atoms again (reduces NAD+ -> NADH + H+) AND releases another CO2
- 4 carbon compound formed (lost C)
- 4 C.C -> another 4 C.C (regenerates 1 molecule of ATP - substrate level phosphorylation: for energy)
- 4 C.C -> ANOTHER 4 C.C - releases 2 H+ atoms: de(reduces FAD+ -> FADH2 + C.C)
- final 4 C.C intermediate converted into oxaloacetate through dehydrogenation: produces another molecule of NADH + H+
products of Krebs cycle
- 4 x CO2 (decarboxylation)
- 6 x NADH (redox)
- 2 x FADH2 (redox)
- 2 x ATP (substrate level phosphorylation)
- all products doubled because Krebs Cycle happens twice (produces 2 acetyl CoA)
oxidative phosphorylation
- NADH oxidised by 1st protein in ETC
- produces a H+ proton and NAD along with 2e- that bind to the protein
- e- passed between ETC proteins in a series of redox reactions
- as they travel down the chain they lose energy
- some of the energy is used to pump H+ ions from the matrix into the intermembrane space; rest lost as heat
- inner mitochondrial membrane impermeable to H+ ions
- and so conc. gradient forms
- H+ ions move down their conc. gradient, into matrix using protein channels
- protein channels associated with ATP synthase, which phosphorylates one ADP for each H+ ion passing through it, forming ATP
- use of energy in a chemical gradient to generate ATP by flow of H+ ions through ATP synthase (chemiosmosis)
- final protein in etc, donates a pair of e- to an oxygen atom.
- this is also the final proton acceptor and so binds with H+ ions in the matrix to form water
- donation of e- to oxygen molecule releases enough energy to pump another H+ ion across the membrane
- then used to phosphorylate a further ADP-> ATP
- FADH2 also oxidised by etc however it interacts with 2nd protein in chain
- means it causes less H+ ions to be pumped across the membrane than NADH and so it generates less ATP
what happens if oxygen is absent in aerobic respiration
- oxygen can’t act as a final electron acceptor at the end of oxidate phosphorylation
- conc. of protons increase in the matrix and reduces proton gradient in inner mitochondrial matrix
- reduced NAD and reduced FAD unable to unload H atoms and can’t be re oxidised
- krebs and link reaction stop
- glycolysis still occurs, but the NADH generated in conversion of TP-> pyruvate has to be re oxidised so that glycolysis can continue
- reduced co-enzyme molecules can’t be reoxidised at etc and so there needs to be an alternative pathway to operate this
2 pathways to re oxidise NADH
- ethanol fermentation pathway; fungi, yeast, plants
- lactate fermentation pathway; mammals
where does anaerobic respiration occur
in cytoplasm
ethanol fermentation process
- pyruvate converted into ethanal; releases one molecule of carbon dioxide
- ethanal gets converted into ethanol; when NADH is converted into NAD, it loses 2 H atoms which is used to convert ethanal -> ethanol
where does lactate fermentation occur
in mammalian muscle tissue
lactate fermentation process
pyruvate converted into lactate using hydrogens from converting reduced NAD -> NAD
- lactate produced in muscles is carried away from muscles in the blood to the liver
- when more oxygen is available, the lactate can either: convert into pyruvate (enters Krebs via link reaction) OR be recycled into glucose and glycogen
- if lactate is not removed, the pH would be lowered and inhibit action of many enzymes involved in glycolysis and muscle contraction.
equation for efficiency
actual energy/theoretical energy x 100
how are nutrients recycled within natural ecosystems
nitrogen cycle
phosphorus cycle
what do saprobionts do
- secrete enzymes externally onto dead organisms/waste products
- breaks down the biological molecules
- absorb some of the nutrients
why are saprobionts important
- type of decomposer and recycle important nutrients in ecosystems
what is extracellular digestion
enzymes are secreted onto the food and it is digested externally
role of mycorrhizae
- hyphae connect to plant roots and increase the surface area
- helps plants absorb more ions from the soil/take up more water
what are mycorrhizae
- fungi that have formed a symbiotic relationship (mutually beneficial) with plant roots
- made up of long thin strands which connect to plant roots (hyphae)
what do mycorrhizae get out of their symbiotic relationship with plant roots
- obtain organic compounds from the plant e.g glucose
why is nitrogen important in living organisms
- DNA
- RNA
- ATP
- proteins e.g antibodies, enzymes, hormones
stages of nitrogen cycle
- nitrogen fixation
- decomposition
- ammonification
- nitrification
- denitrification
nitrogen fixation
- nitrogen fixing bacteria convert nitrogen into ammonia
- forms ammonium ions which plants use
ammonification
- nitrogen compounds from dead organisms/waste products, are converted to ammonia by saprobionts
nitrification
ammonium ions in the soil oxidised to nitrites and nitrates by nitrifying bacteria
denitrification
- nitrates in the soil are converted to nitrogen gas by denitrifying bacteria e.g anaerobic conditions
how else can nitrogen get into ecosystems
- lightning (forms nitrogen oxides from nitrogen)
- artificial fertilisers (haber process)
why is phosphorus important to plants and animals
phospholipids; cell membranes
DNA
ATP
how do phosphate ions initially enter ecosystems
- phosphorous in rocks dissolves in oceans
stages of phosphorus cycle
- phosphate ions released into soil from rocks
- plants taken up ions through roots
- ions transferred through food chains and lost as waste/death
- decomposition
how are nutrients lost from ecosystems
- harvested crops/animals are removed from fields
- mineral ions not returned to the soil by decomposition of plants/waste by saprobionts
what do fertilisers do
- replace lost minerals so more energy from ecosystems can be used for growth
examples of natural fertiliser
- organic matter; manure, compost, crop residues
what do artificial fertilisers consist of
pure chemicals as powders of pellets
what is leaching
water soluble compounds in the soil drain into aquatic ecosystems
what is eutrophication
- the addition of extra nutrients such as nitrate/phosphate ions to aquatic ecosystems
when is leaching most likely
- when artificial fertilisers are applied just before heavy rainfall
why is leaching less likely with organic fertilisers
- the ions are contained in biological molecules which need to be decomposed by saprobionts before plants can absorb them
stages of eutrophication
- nitrate ions leached from soil into water sources e.g ponds/rivers
- stimulate rapid growth of algal bloom
- large amounts of algal bloom block light from reaching plants below
- plants cannot photosynthesise in the water and die
- saprobionts respire aerobically, so they carry out decomposition on dead plants; and use oxygen
- reduces oxygen concentration in water
- fish and other organisms die as well due to lack of oxygen
