Energy transfers Flashcards
light-dependent reaction
light is absorbed by chlorophyll and a water molecule is split (photolysis)
- takes place in thylakoid membrane
light-independent reaction
carbon dioxide is synthesised into useful organic compounds.
- takes place in stroma.
equation for photosynthesis
carbon dioxide + water -> glucose + oxygen
6CO2 + 6H2O -> C6H12O6 +6O2
Adaptations of plants for photosynthesis
- large surface area
- minimal overlapping to avoid blocking sunlight
- thin -> short diffusion distance
- transparent cuticle and epidermis to allow light through
- long narrow pier mesophyll cell packed with chloroplasts
- stomata for gas exchange
- stomata open and close in response to light intensity
Structure and role of chloroplasts
- large surface area of thylakoid membranes
- proteins in grant hold the chlorophyll in a very precise manner for maximum light absorption
- ATP synthase channels in grana membranes which catalyse production of ATP
- grana membranes have enzymes attached for ATP production.
Process of light-dependent reaction
- PSII
- chlorophyll absorbs light and excites the electrons. They leave and go to primary electron acceptor at higher energy state.
- Photolysis - splits water into hydrogen - protons + electrons, oxygen. Protons go to the proton pump and electrons replace the lost electrons in chlorophyll
- electrons move from higher energy state to lower energy state through the electron transfer chain.
- the ‘lost’ energy is used to pump protons from the stroma to the thylakoid. Accumulation of protons creates the proton gradient.
- PSI
- Charged protons move out through ATP synthase to create ATP (Chemiosmosis) and are taken up by NADP = reduced.
- Chlorophyll absorbs more light and electrons leave.
- Creates NADPH
Photolysis equation
2H2O -> 4H+ + 4e + O2
The main components in light dependent reaction that are needed are:
NADP, ADP, Pi, and water
Process of light independent reaction
CALVIN CYCLE
- CO2 diffuses into leaf, dissolved in water and diffuses into stroma of chloroplast
- It reacts with RuBP, catalysed by rubisco
- 2 glycerine 3-phosphate molecules are formed (GP)
- Reduced NADP reduces this into 2 triode phosphate (TP) using energy from ATP (GP->TP)
- The NADP is re-formed and goes back to light-dependent reaction to be reduced again.
- Some TP molecules are converted to organic substances for use of plant e.g. glucose.
- Most are used to regenerate RuBP using ATP from light-dependent reaction.
The stroma are adapted to carrying this reaction through:
- all needed enzymes are found in the stroma, which is membrane bound in the chloroplast
- stroma fluid surrounds the grana, so the products of light-dependent reaction are easily available.
- contains DNA and ribosomes so needed proteins are easily manufactured.
light compensation point
the point where the CO2 released during respiration equals that taken up during photosynthesis.
the rate of photosynthesis can be measured by
measuring the volume of oxygen produced by the apparatus.
- Ensure no air bubble.
- water bath to maintain constant temperature
- Potassium hydrogen carbonate collusion used to provide source of CO2.
- oxygen released by plant during photosynthesis collects in funnel end of capillary tube; drawn gently and measured.
- repeat 4-5 times
factors affecting photosynthesis.
- light intensity
- carbon dioxide concentration
- temperature
- water
respiration transfers energy stored in
complex organic molecules, such as glucose, to ATP by phosphorylation.
there are 2 types of respiration
- aerobic respiration - requires oxygen; produces water, carbon dioxide and many molecules of ATP
- anaerobic respiration - takes place in absence of oxygen, produces a small amount of ATP. In plants and fungi it also produces carbon dioxide and ethanol; animals produce lactate.
there are 4 stages in aerobic respiration;
- glycolysis - 6-carbon glucose split into 2 mols of 3-carbon pyruvate
- link reaction - 3-carbon pyruvate is oxidised into carbon dioxide and acetyl coenzyme A
- Krebs cycle - acetyl coenzyme A enters a cycle of redox reaction that produce ATP and a large number of electrons stored in reduced NAD and reduced FAD.
- oxidative phosphorylation - use of electrons, associated with reduced NAD and FAD, released from Krebs cycle to synthesise ATP with water as by-product.
respiration
the metabolic reaction where energy is released in the form of ATP from glucose.
Glycolysis
the initial stage of both types of respiration. Occurs in cytoplasm and is the process by which a hexose sugar, usually glucose, is split into 2 mols of 3-carbon mol pyruvate.
glycolysis is divided into 4 stages:
- Phosphorylation of glucose to glucose phosphate: 2 phosphate mols added to glucose to make it more reactive, they come from the hydrolysis of 2 ATP mols. Lowers activation energy for enzyme-controlled.
- splitting of phosphorylated phosphate: glucose split into 2 triodes phosphate (3C).
- oxidation of triode phosphate: hydrogen removed from TP (glycerine 3 phosphate) and transferred to NAD to form reduced NAD.
- production of ATP: diode phosphate is converted into pyruvate and 2 ATP molecules are regenerated from ADP in the process.
glucose -> glucose phosphate -> triode phosphate -> pyruvate
link reaction
- pyruvate oxidised to acetate and loses a carbon dioxide molecules and hydrogen ions that form reduced NAD.
- Acetate combines with coenzyme A to produce acetyl coenzyme A.
pyruvate + NAD + CoA –> acetyl CoA + reduced NAD + CO2.
krebs cycle
- 2-carbon acetyl coenzyme A from link reaction combines with 4-carbon mol to produce 6 carbon mol.
- in a series of reactions this 6 carbon mol loses carbon dioxide and hydrogen to give 4 carbon mol and single mol of ATP produced as a result of substrate-level phosphorylation.
- 4 carbon mol can now combine with new molecule of acetyl coenzyme A to begin the cycle begin.
krebs and link reaction produce
- reduced coenzymes NAD and FAD
- one mol of ATP
- 3 carbon dioxides.
coenzymes
not enzymes, they’re molecules that some enzymes require in order to function. They play a major role in photosynthesis and respiration, where they carry hydrogen atoms from one molecule to another.
NAD - respiration
FAD - krebs cycle
NADP - photosynthesis
oxidative phosphorylation
- hydrogen atoms produced during glycolysis and Krebs cycle combine with coenzymes NAD and FAD.
- reduced NAD and FAD donate the electrons of hydrogen atoms they are carrying to first mol in ETC.
- electrons pass along chain of electron transfer carrier mols in a series of oxidation-reduction reactions. As electrons flow along the chain, energy they release causes active transport of protons across inter mitochondrial membrane and into inter-membranal space.
- protons accumulate inter-membranal space before they diffuse back into mitochondrial matrix through ATP synthase channels embedded in inner mitochondrial membrane.
- at end of chain the electrons combine with these protons and oxygen to form water. Oxygen is therefore the final acceptor of electrons in ETC.
there are 2 types of anaerobic respiration in eukaryotes:
- plants: pyruvate converted to ethanol and CO2.
- animals: pyruvate converted to lactate.
production of ethanol in plants and some microorganisms
pyruvate + reduced NAD –> ethanol + CO2 + oxidised NAD
- pyruvate loses CO2 and accepts protons from reduced NAD to produce ethanol.
production of lactate in animals
pyruvate + reduced NAD –> lactate + oxidised NAD.
- at some point the lactate is oxidised back to pyruvate. Lactate acid is toxic and causes muscle fatigue so it is important to be removed.
glycolysis takes place in the
cytoplasm
Krebs cycle takes place in the
mitochondrial matrix
electron transport chain occurs in the
mitochondria.
Biomass can be measured in terms of
mass of carbon or dry mass of tissue per given area.
- measured in g or kg per metre (kg m -2)
the chemical energy store in dry biomass can be estimated using
calorimetry (burning dry sample in pure oxygen in sealed container)
gross primary production (GPP) is
the chemical energy store in plant biomass, in a given area or volume.
Net primary production (NPP) is
the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account
equation for Net primary production
NPP = GPP - R
R = respiratory losses to environment.
net production of consumers (N) equation
N = I - (F+R)
I - chemical energy stored in ingested food
F - chemical energy transferred to environment
R - respiratory energy transferred to environment
primary or secondary productivity is the
rate of primary or secondary production, measured as biomass in one area and time
farming practices and energy efficiency
in farming, energy can be wasted in a number of ways between trophic levels, so farmers must find ways to reduce wasteful energy transfers, and maximise the amount if energy transferred between trophic levels
animals –> reduce waster through respiratory energy by:
- reducing movement which can be controversial (e.g. battery farming)
- heating enclosures
plants –> reduce energy waste by:
- simplifying food webs by use of pesticides
- reducing competition by removing weeds
- using fertilisers to keep the soil nutrient rich
calculating efficiency
percentage efficiency = energy in higher trophic level / energy in lower trophic level x 100
nitrogen is present in biological molecules such as
amino acids, proteins, and nucleic acids.
It’s also present as nitrogen gas in the atmosphere (NH2), ammonia (NH3), ammonium ions (NH4+), nitrates (NO3-), and nitrates (NO2-).
There are 4 main stages in the nitrogen cycle
ammonification, nitrification, nitrogen fixation, and denitrification.
ammonification
production of ammonia from organic nitrogen containing compounds like urea, nucleic acid, vitamins. Saprobiotic organisms release ammonia which forms ammonium ions in the soil.
nitrification
conversion of ammonium ions to nitrate ions, an oxidation reaction that releases energy. Carried out by nitrifying bacteria; oxidise ammonium ions -> nitrite ions - > nitrate ions. Requires oxygen so more air space is more efficient.
nitrogen fixation
formation of nitrogen containing compounds from nitrogen gas. Occurs by:
- free-living nitrogen-fixing bacteria: reduce nitrogen gas to ammonia and make amino acids. Nitrogen-rich compounds are released when they die.
- mutualistic nitrogen-fixing bacteria: live on roots. They obtain carbohydrates from plant and give amino acids.
denitrification.
the conversion of nitrogen-containing compounds into nitrogen gas. This occurs when there is an increase in anaerobic denitrifying bacteria due to lower oxygen levels. A balance needs to be kept otherwise plants can’t use nitrogen.
saprobionts
decomposers (often bacteria) that release phosphates, ammonia and ammonium ions.
nitrifying bacteria
bacteria that oxidise ammonium ions to nitrites, and nitrites to nitrates.
denitrifying bacteria
use nitrates to respire anaerobically and release nitrogen gas.
phosphorus is present in biological molecules such as
ATP, nucleic acids and some proteins.
It is a component of bones and shells.
phosphate ions (PO4 3-) are present in cells and are involved in metabolic processes.
Phosphates are also present in rocks, oceans, lakes, and soil.
Mycorrhizae
associations between certain types of fungi and the roots of the vast majority of plants.
The fungi act like extensions of the plants root system and vastly increase the total surface area for the absorption of water and minerals.
The mycorrhizae acts like a sponge and holds water and minerals in neighbourhood of roots.
This enables the plants to better resist drought and take up inorganic ions more readily.
The mycorrhizae plays a part in nutrient cycles by
improving the uptake of relatively scarce ions such as phosphate ions.
the mycorrhizal relationship between plants and fungi is a
mutualistic one.
The plants benefits from improved water and inorganic ion uptake while the fungus receives organic compounds such s sugars and amino acids from the plant.
there are 2 types of fertilisers
natural organic - remains of animals and plant waste
artificial inorganic - mined from rocks, converted and blended minerals.
Fertilisers increase productivity through minerals they provide e.g. nitrogen
- component of amino acids, ATP and nucleotides
- needed for growth and plants likely to grow faster, taller and have a greater leaf areas when it is present, increasing rate of photosynthesis and crop productivity.
overuse of nitrogen-containing fertilisers
- reduced species diversity
- leaching
- eutrophication
reduced species diversity
nitrogen-rich soil promotes growth of other rapidly growing species, outcompeting other species and causing them to die, resulting in lower species diversity.
leaching
rainwater causes removal of soluble nutrients, and they end up in waterways. This results in high conc of nutrients in drinking water which can prevent efficient O2 transport in babies and link to stomach cancer. Also results in eutrophication.
eutrophication
normal nitrate conc are limiting factor for algal growth in lakes. When leaching results in higher concs, algae grow on surface of water, causing algae to absorb sunlight, so light is limiting factors for plants underneath (die). Saprobiotic bacteria grow (aerobic, resulting in higher demand of O2). O2 conc decreases, nitrate ion conc increases. O2 low levels result in death of aerobic organisms. Population of anaerobic organisms increases; they further break down decaying organisms releasing more nitrates and toxic wastes like hydrogen sulphide which makes water putrid.
