A Level Biology - Chapter 11 - Energy Transfers in and between organisms

Biological Processes need Energy


Why do plants need energy?

- Photosynthesis
- Active transport (mineral uptake via root hair cells)
- DNA replication
- Cell division
- Protein synthesis

Why do animals need energy?

- Muscle contraction
- Maintenance of body temperature
- Active transport
- DNA replication
- Cell division
- Protein synthesis

Define Photosynthesis

- process in which energy from light is used to make glucose
- from H2O and CO2
- light energy is converted to chemical energy in the form of glucose

Define Respiration

- process of releasing energy (in the form of ATP) from glucose
- energy used to power all the biological processes in the cell
Two types:
aerobic respiration
(using oxygen):
- produces CO2, H2O and releases energy
anaerobic respiration
(without oxyge

Comment on ATP's role as the immediate source of energy in a cell

- cell can't access energy directly from glucose.
- ATP's phosphate groups contain chemical energy.
- ATP diffuses to the part of the cell that needs energy.
- formed in condensation reaction between ADP + Pi catalysed by ATP synthase
- hydrolysed back to

What are ATP's specific properties that make it a good energy source?

- releases a small, manageable amount of energy at a time ---> no energy wasted as heat.
- small, soluble molecule (can be easily transported around the cell)
- easily broken down, so energy can be released instantaneously
- can be quickly re-made.
- can

Define metabolic pathway

- series of small reactions controlled by enzymes
- i.e respiration and photosynthesis.

Define phosphorylation

- adding phosphate groups to a molecule
- i.e. ADP is phosphorylated to ATP

Define photophosphorylation.

- adding phosphate groups to a molecule using light

Define photolysis

- the splitting of a molecule using light energy.

Define photoionisation

- light energy 'excites' electrons in an atom / molecule
- giving them more energy causing them to be released
- release of electrons causes atom / molecule to become positively-charged ion

Define hydrolysis

- the splitting of a molecule involving the addition of water

Define decarboxylation

- the removal of CO2 from a molecule

Define dehydrogenation


Define redox reactions

- reactions involving both oxidation and reduction
- lost electrons
- lost hydrogen
- gained oxygen
- gained electrons
- gained hydrogen
- lost oxygen

What is a coenzyme & how does it work?

- a coenzyme is a molecule that aids the function of an enzyme
- transfer a chemical group from one molecule to another.
- NADP used in photosynthesis - transfers H from one molecule to another (reduces one molecule and oxidises another)



Describe chloroplasts (site of photosynthesis)

- flattened organelles surrounded by double membrane.
- Thylakoids (fluid-filled sacs) stacked up in the chloroplast intro structures called grana (singular = granum)
- linked together by bits of thylakoid membrane called lamella (singular = lamella)
- ph

Comment on photosynthetic pigments and photosystems

- chloroplasts contain photosynthetic pigments (chlorophylls A,B and carotene)
- these are coloured substances that absorb the light energy required for photosynthesis.
- found in thylakoid membranes attached to proteins, this is called a photosystem
- 2

Briefly summarise the Light-Dependent Reaction

1. Reaction requiring light , takes place in thylakoid membranes of the chloroplasts.
2. Light energy absorbed by chlorophyll and other photosynthetic pigments in the photosystems.
3. Light energy excites the electrons in the chlorophyll, leading to their

Briefly summarise the Light-Independent Reaction.

1. Calvin Cycle - doesn't directly use light energy, but does rely on the products of light-dependent reaction
2. Takes place in the stroma of the chloroplast
3. Here, the ATP and NADPH from light-dependent reaction supply energy and H necessary to make s

In the LDR, what is the energy from the photoionisation of chlorophyll used for?

1. Making ATP from ADP and Pi - photophosphorylation
2. Making reduced NADP (NADPH) from NADP
3. Photolysis of water - splitting of water into protons (H+ ions), electrons and oxygen.

Define electron carriers

- Proteins that transfer electrons linking photosystems

Define electron transport chain (ETC)

- a chain of proteins through which excited electrons flow
- formed by photosystems and electron carriers

What does Non-cyclic photophosphorylation produces?

- O2

Outline stage 1 of the LDR

Light energy excites electrons in chlorophyll
1. Light energy absorbed by chlorophyll in PSII
2. Light energy excited electrons in chlorophyll
3. These excited electrons move to a higher energy level
4. High-energy electrons are released from the chloro

Outline stage 2 of the LDR

Photolysis of water produces protons, electrons and O2
5. As excited electrons from chlorophyll leave PSII to move down they must be replaced.
6. Light energy splits water into protons (H+ ions), electrons and oxygen (photolysis).
- reaction: H2O ---> 2

Outline stage 3 of the LDR

Energy from the excited electrons makes ATP (chemiosmosis)
8. Excited electrons lose energy as they move down ETC.
9. This energy used to transport protons into thylakoid - thylakoid has a higher concentration of [H+] than stroma (forming a proton gradi

Outline stage 4 of the LDR

Energy from the excited electrons generates reduced NADP
12. Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level
13. Finally, electrons transferred to NADP, along with a proton from the stroma, to form reduc

Define chemiosmosis

- process of electrons flowing down an electron transport chain and creating a proton gradient across the membrane
- drives ATP synthesis
- described by chemiosmotic theory

Cyclic photophosphorylation only produces?


Outline the process of cyclic photophosphorylation

1. Only uses PSI - called cyclic as electrons from chlorophyll aren't passed onto NADP, but are instead passed back to PSI via electron carriers
2. Electrons are therefore recycled and can repeatedly flow through PSI.
3. Does NOT produce any NADPH / only

Where does the Calvin Cycle take place?

- Calvin Cycle takes place in the stroma of the chloroplasts

Draw the Calvin Cycle

Outline stage 1 of the Calvin Cycle

CO2 combined with RuBP
1. CO2 enters the leaf via stomata and diffuses into the stroma of the chloroplast
2. CO2 is combines with RuBP (5C), catalysed by the enzyme rubisco
3. This gives an unstable 6C carbon, which quickly breaks down into two molecule

Outline stage 2 of the Calvin Cycle

ATP and NADPH reduce GP to TP ---> organic substances
4. Hydrolysis of ATP (from LDR) provides energy to turn GP (3C) into Triose Phosphate [TP] (3C).
5. reaction also requires H+ ions, which come from NADPH (also from LDR). NADPH is recycled to NADP.

Outline stage 3 of the Calvin Cycle

RuBP is regenerated
7. 5/6 molecules of TP produced in the cycle are used to regenerate RuBP
8. Regenerating RuBP uses the rest of the ATP produced by the LDR

GP and TP can be converted to useful organic substances

1. Carbohydrates - hexose sugars (i.e. glucose) are made by joining two TP molecules together and larger carbohydrates (i.e. sucrose / starch / cellulose) are made by joining hexose sugars together in different ways
2. Lipids - made using glycerol, synthe

Justify why the Calvin Cycle needs to turn six times to make one hexose sugar

- 3 turns of cycle produces 6 molecules of TP, as 2 TP molecules are made for every CO2 molecule used
- 5/6 of these TP molecules are used to regenerate RuBP
- 3 turns - one TP molecule produced for hexose sugar
- Hexose sugar has 6C, so 2 x TP (3C) molec

What are the optimum conditions for photosynthesis - light?

1. High light intensity of a certain wavelength
- Light needed to provide energy for the LDR => higher intensity, more energy it provides
- Only certain wavelengths of light used for photosynthesis.
- Photosynthetic pigments chlorophyll A and B an caroten

What are the optimum conditions for photosynthesis - temperature?

2. Temperature around 25C:
- Photosynthesis involves enzymes (ATP synthase, rubisco, etc).
- If the temperature falls below 10C, the enzymes become inactive
- If the temperature is more than 45C enzymes start to denature.
- At high temperatures, stomata c

What are the optimum conditions for photosynthesis - carbon dioxide?

3. [CO2] at 0.4%
- CO2 makes up 0.04% of the gases in the atmosphere.
- Increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close

What are the optimum conditions for photosynthesis - water?

4. Constant supply of water:
- Too little water and photosynthesis has to stop
- Too much water and soils become waterlogged (reducing uptake of minerals such as Mg, necessary to make chlorophyll A).

List three of photosynthesis' limiting factors.

1. Light intensity
2. Temperature.
3. CO2 concentration

Outline how limiting factors limit the rate of photosynthesis.

- If any of these factors is too low / too high, it will limit the rate of photosynthesis.
- Even if the other two factors are at the perfect level, it won't make any difference to the rate as long another factor is at the wrong level

Draw a graph of rate of photosynthesis (y) against light intensity (x).

- A to B, rate increases with light intensity - therefore light intensity is limiting the rate of photosynthesis.
- At point B, the graph levels off as saturation point is reached ---> new limiting factor.

Draw a graph of rate of photosynthesis (y) against temperature (x).

- Increasing with temperature, until a point where graph levels off as something else becomes the limiting factor.
- Same general curve for each temperature, but higher temperatures ---> higher curve with slightly steeper gradient.

Draw a graph of rate of photosynthesis (y) against [CO2] (x).

- Increasing with [CO2], until a point where graph levels off as something else becomes the limiting factor.
- Same general curve for each [CO2], but higher [CO2] ---> higher curve with slightly steeper gradient.

What do growers do with information about limiting factors?

Growers use information about limiting factors to increase plant growth
- They try to create an environment with optimum conditions for photosynthesis, increasing growth, yield and profit.
- Either in glasshouse, or employ similar techniques in polytunnel

How can we manage [CO2] in a glasshouse?

- CO2 added to the air, by burning a small amount of propane in a CO2 generator.

How can we manage light intensity in a glasshouse?

- Light can get in through the glass.
- Lamps provide light at night-time.

How can we manage temperature in a glasshouse?

- Glasshouses trap heat energy from sunlight, which warms the air.
- Heaters and cooling systems can also be used to keep a constant optimum temperatures.
- Air circulation systems make sure the temperature is even throughout the glasshouse.



What are the two types of respiration?

- aerobic (requires O2)
- anaerobic (does not require O2)
- both produces ATP, anaerobic produces less
- both begin with the process of glycoloysis

Define glycolysis

1. Involves splitting one molecule of glucose (6C) into two smaller molecules of pyruvate (3C)
2. Process occurs in cytoplasm of cells
3. First stage of respiration for both aerobic & anaerobic respiration - does not require oxygen to take place (anaerobi

Outline the process of Glycolysis.

NB => takes place in the cytoplasm; anaerobic process.
Stage 1 - Phosphorylation:
1. Glucose (6C) is phosphorylated using a phosphate from a molecule of ATP. Creates 1 molecule of glucose phosphate (6C) and one molecule of ADP.
2. ATP is then used to add

What happens to pyruvate in anaerobic respiration?

In plants & yeast:
- pyruvate is converted into ethanol
- reduced NAD converts ethanal into ethanol which regenerates oxidised NAD
In animals cells & some bacteria:
- pyruvate is converted into lactate
- this also uses reduced NAD which is regenerates oxi

What happens to pyruvate in aerobic respiration?

- actively transported into matrix of mitochondria for link reaction

Outline the link reaction

1. Pyruvate is deoxycarbolated ( one carbon removed from pyruvate in form of CO2)
2. Pyruvate is oxidised to form acetate and NAD is reduced to form NADH.
3. Acetate is combined with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA)
NB => no app is

How many times must the link reaction occur for each glucose molecule?

Link reaction occurs twice for every glucose molecule.
1. 2 molecules of pyruvate made for each glucose molecule entering glycolysis.
2. Link reaction and Krebs Cycle happen twice for every glucose molecule.
3. 2 molecules of acetyl CoA go into Krebs Cycl

Outline the Krebs Cycle

- Series of oxidation-reduction reactions which take place in matrix of mitochondria.
- Takes place once for every pyruvate, so goes around twice for every glucose molecule.
1. Acetyl CoA from the link reaction combines with a 4C molecule (oxaloacetate) t

Some products of the Krebs Cycle are used in oxidative phosphorylation.
List the products of the Krebs Cycle and outline where they go.

1 x coenzymeA ---> reused in next link reaction.
4C molecule (oxaloacetate) ---> regenerated for use in next Krebs Cycle.
2 x CO2 ---> released as waste product.
1 x ATP ---> used for energy
3 x NADH ---> oxidative phosphorylation.
1 x reduced FAD ---> ox

Define oxidative phosphorylation

- process where energy carried by electrons from reduced coenzymes (reduced NAD & reduced FAD) is used to make ATP
- involves electron transport chain (ETC) and chemiosmosis

Outline the process of oxidative phosphorylation

1. H atoms released from reduced NAD & reduced FAD a (oxidation) - H atoms split into protons (H+) and electrons (e-).
2. Electrons move down ETC (made up of electron carriers) losing energy at each carrier.
3. energy used by the electron carriers to acti

Calculate how much ATP can be made from one glucose molecule.

2 NADH ---> 2 x 2.5 => 5 ATP
Link Reaction (x2):
2NADH ---> 2 x 2.5 => 5 ATP
Krebs Cycle (x2):
6 NADH ---> 6 x 2.5 => 15 ATP
2 FADH2 ---> 2 x 1.5 => 3 ATP
Total => 32 ATP

How do mitochondrial diseases affect ATP production?

1. Affect the functioning of mitochondria - can affect how proteins involved in oxidative phosphorylation or the Krebs Cycle function, reducing ATP production.
2. May cause anaerobic respiration to increase in order to compensate for some of the ATP short

How can other respiratory substrates be used in aerobic respiration?

- Some products from the breakdown of other molecules:
- fatty acids from lipids
- amino acids from proteins
- can be converted into molecules that are able to enter the Krebs Cycle (usually converted to acetyl CoA)

Energy Transfers in Ecosystems


Define ecosystem

- All the organisms living in a particular area along with all the abiotic (non-living) conditions

Outline how energy is "produced" and transferred throughout an ecosystem

1. In an ecosystem there are
- organisms that make their own food - plants / algae, via photosynthesis
2. Some sugars produced during photosynthesis used in respiration, to release energy for growth
---> rest used to make other biological molecu

List 2 methods of measuring biomass

1. Using dry mass
2. Using a calorimeter

How can we measure biomass as dry mass?

- Measured in terms of the mass of carbon that an organism contains or the dry mass of its tissue per unit area per unit time
1. Dry mass is the mass of the organism with the water removed.
2. To measure dry mass, sample of the organism dried, often in an

How can we measure biomass using calorimeter.

- Can estimate the amount of chemical energy stored in biomass by burning biomass in a calorimeter.
=> heat given off tells you how much energy mass contained
1. Sample of dry biomass burnt and energy released to heat a known volume of water.
2. Temperatu

Define Gross Primary Production (GPP) + Units

- Total amount of chemical energy converted from light energy by plants in a given area, in a given time.
Units: kj / m2 / yr

Define Respiratory Loss (R) + Units

- (Approx 50% of) GPP lost to the environment as heat enegy when the plants respire, this is called respiratory loss (R)
Units: kj / m2 / yr.

Define Net Primary Production (NPP) + Units

- Remaining chemical energy - energy available to plant for growth and reproduction, i.e. energy stored in plant's biomass.
- Energy available to organisms at the next trophic level.
Units = kj / m2 / yr.

Give the equation for NPP.


Comment on the energy transfer between trophic levels

1. Consumers get energy by eating plant material or animals that have eaten plant material
2. Not all chemical energy stored in consumer's food is transferred to the next trophic level (only around 10%).
3. Firstly, not all food is eaten - plant roots / b

Give the equation for the net production (NP) of consumers.

N = I - (F + R).
N = Net production.
I = Chemical energy in ingested food.
F = Chemical energy lost in faeces and urine.
R = Energy lost through respiration.
Units: kj / m2 / yr.

How would we calculate the efficiency of energy transfer?

(NP / total energy received) x 100

How can food chains / food webs show how energy is transferred between organisms?

Food chains - show simple lines of energy transfer between trophic levels
Food webs - show many food chains in an ecosystem, and how they interact and overlap.
Decomposers (such as fungi) are also part of food webs - the break down dead or undigested mate

Farming practices aim to increase the efficiency of energy transfer (2 factors)

1. Reducing energy lost to other organisms.
2. Reducing energy lost through respiration.

Outline how simplifying the food web reduces the energy loss to other organisms.

- Pests reduce the productivity of crops by reducing the amount of energy available for crop growth - reduces energy available for human consumption
=> By removing food chains that don't involve humans, energy losses reduced and crop productivity increase

Outline how farmers can reduce respiratory losses to increase the efficiency of energy transfer

1. Can control conditions livestock is kept in ---> more energy used for growth and less is lost through respiration (decreasing activities that increase the rate of respiration):
- Animals kept in pens where movement is restricted.
- Pens often indoors a

Nutrient Cycles


Outline the role of fungi and bacteria (saprobionts) in nutrient recycling.

- In natural ecosystems (unchanged by human activity), nutrients are recycled through food webs
- Some microorganisms are saprobionts (a type of decomposer) - feed on remains of dead plants and animals and on their waste products (faeces / urine), breakin

Comment on the symbiotic relationships that some fungi form with plant roots

- these symbiotic relationships are called Mycorrhizae
- Fungi made up of long, thin strands called hyphae, connect to the plant's roots.
- Hyphae greatly increase the surface area of the plant's root system, helping the plant to absorb ions from the soil

Define saprobiotic nutrition

- the process of obtaining nutrients from dead organic matter using extracellular digestion

Comment on the necessity of the Nitrogen Cycle.

- Plants and animals need nitrogen for proteins and nucleic acids.
- Atmosphere is made up of 78% nitrogen but this cannot be used by animals
- They need bacteria to convert nitrogen in air to N-containing compounds.

Draw out the Nitrogen Cycle

Atmospheric Nitrogen (N2) ---> N-compounds in plants (nitrogen fixation)
---> N compounds in animals (feeding).
---> to NH3 (ammonification by saprobionts).
---> NH4+ -> Nitrites -> Nitrates (nitrification).
---> Atmospheric nitrogen (denitrification)

Outline the process of Nitrogen Fixation

1. N2 gas in atmosphere converted to N-containing compounds: ammonia (biological nitrogen fixation)
2. Carried out by bacteria found inside root nodules of leguminous plants i.e. Rhizobium
3. Bacteria form a mutualistic relationship with plants - they pro

Outline the process of Ammonification

1. Nitrogen compounds from dead organisms are turned into ammonia (NH3) by saprobionts, which goes on to form ammonium ions (NH4+)
2. Animal urine and faeces also contain N compounds ---> also turned into NH3 by saprobionts, which goes on to form NH4+ ion

Outline the process of Nitrification

1. ammonium ions in the soil are changed into N-compounds that can be used by plants
2. Nitrifying bacteria change ammonium ions into nitrites.
3. Other nitrifying bacteria called then turn nitrites into nitrates which can be used by plants.
(ammonium ion

Outline the process of Denitrification

1. Nitrates in soil converted into N2 gas by denitrifying bacteria - they use nitrates in the soil to carry out respiration and produce N2 gas
2. Happens under anaerobic conditions, i.e. waterlogged soils

Suggest other ways of getting Nitrogen into an ecosystem

1. Lightning - fixes atmospheric nitrogen
2. Artificial fertilisers - produced from atmospheric nitrogen on an industrial scale in the Haber process.

What is phosphorus used for?

- make biological molecules such as phospholipids, DNA and ATP

Draw out the phosphorus cycle

soil <- rock -> seas / lakes / rivers.
-> algae and other primary producers.
-> fish (feeding) -> birds (feeding).
-> guano (excretion).
-> soil -> plants -> animals (feeding).
-> decaying organisms -> soil.
-> faeces and urine -> soil
soil -> rock ->

Outline the processes of the Phosphorus Cycle

1. Phosphate ions in rocks released into soil by weathering
2. Phosphate ions absorbed through roots - mycorrhizae greatly increase the rate at which phosphorus can be assimilated
3. Phosphate ions transferred through the food chain as animals eat the pla

How are nutrients lost when crops are harvested?

1. Crops take in minerals from the soil as they grow and use them to build their tissues
2. When crops are harvested - they can no longer die and decompose in the field in which they were grown ---> mineral ions they contain not returned to soil by decomp

What is the role of fertilisers? Outline the differences between artifical and natural fertilisers.


What are the environmental issues related to fertiliser use?

1. Excess fertiliser in soils can lead to leaching into the waterways.
2. This can lead to eutrophication.
3. Leaching is more likely if fertiliser applied just before heavy rainfall.
4. Leaching of phosphates is less likely as phosphates are less water-s

Define leaching


Define Eutrophication


Outline the process of Eutrophication.

1. Naturally low [nitrate] in lakes and rivers - limiting factor.
2. As [nitrate] increases as a result of leaching, no longer a limiting factor for growth of plants and algae ---> populations grow.
3. Algae grow mostly at the surface, the upper layers of

Name the three methods by which ATP can be produced

- Photo-phosphorylation (light energy absorbed by chlorophyll is stored in bond between ADP and Pi)
- Oxidative phosphorylation (ATP generated through hydrolysis of respiratory substrate)
- Substrate level phosphorylation (phosphate added directly to ADP

What is the equation for photosynthesis?

6CO2 + 6H2O --> C6H12O6 + 6O2

How are leaves adapted to carry out photosynthesis? (6)

- Long, narrow mesophyll packed with chloroplasts under which spongy mesophyll has air spaces for efficient gas exchange
- Thin to shorten diffusion distance
- Large surface area across which sunlight can be absorbed
- Transparent cuticle which can transm

What are the three main stages of photosynthesis?

- Chlorophyll absorbs light energy from the sun
- Light dependent reaction- in which light energy is converted into chemical energy (ATP)
- Light independent reaction- in which carbon is fixed into organic molecules

Approximately how large are chloroplasts and what kind of membrane do they have?

Approximately 1um wide and 2-10um long. They have a double membrane

What are the grana and the stroma and which process takes place in each?

- The grana are stacks of thylakoids, which contain chlorophyll, where the L-D reaction takes place. They may be connected to other by intergranal lamellae
- The stroma is a fluid filled matrix where L-Ind reaction takes place (also contains starch granul

How are chloroplasts adapted to carry out photosynthesis? (3)

- Thylakoid membranes provide large SA for insertion of carrier proteins, enzymes and chlorophyll (held in a way which allows for max light absorption)
- Have ATP synthase channels embedded in thylakoid membranes
- Contain own DNA/RNA for manufacture of e

What occurs during the light dependent reaction?

- Chlorophyll absorbs light energy from the sun, exciting electrons in PII
- Two electrons are emitted/released and taken up by electron carriers in the thylakoid membrane
- They are transferred in redox reactions, losing energy at each stage of the trans

Why is the energy loss at each stage of the electron transfer (due to gradually lowering energy levels) important?

To provide energy which can be used to phosphorylate ADP with Pi to form ATP (energy conserved in unstable bond which is created)

What is the process by which the synthesis of ATP is enabled and how does int occur?

Chemiosmosis- during which protons are pumped against concentration gradient from the stroma into the thylakoids (which have high concentration H+ from photolysis) and diffuse back into the stroma through ATP synthase channels. This alters it's shape allo

What else might the light energy hitting the chloroplast be used for?

The photolysis of water in which it is split up into H+, H- and oxygen (lost to environment as a waste gas)

What happens to the protons/electrons which are emitted during photolysis?

Protons are used in the reduction of NADP whilst electrons are accepted by PII to replace those lost due to excitation

What are the 3 processes which are ultimately made possible by the L-D reaction?

- Synthesis of ATP
- Reduction of NADP
- Photolysis

What are the three main stages of the light-independent reaction (Calvin cycle)?

- Carbon fixation
- Reduction
- Regeneration

What occurs during carbon fixation?

CO2 reacts with RuBP (catalysed by rubisco) to form 2 molecules of glycerate 3 phosphate (GP)

How is GP reduced?

(2) Reduced NADP and (2) ATP used to reduce (2) GP to triose phosphate (TP)

What is most of the TP used for and how much is converted into useful; substances?

In 5/6 cycles TP is used to regenerate RuBP (5C molecule) however in 1/6 cycles it is converted into a useful organic substance

Explain why it takes 6 turns of the cycle to produce 1 molecule of glucose

2 TP needed per glucose, 2 generated per cycle but only 1/6 cycles leads to organic molecules being produced

What factors might limit photosynthesis and why?

- Light- if light intensity increases, energy absorbed increases, increasing rate of L-D reaction
- CO2- CO2 often limits photosynthesis since optimum > atmospheric. More CO2 = more reacting with RuBP and also affects ribulose activity
- Temperature- Spee

Roughly how efficient is respiration and what is it's equation (aerobic)?

Approx 40% efficient - Glucose + O2 > CO2 and H20

Name the two types of anaerobic respiration and give their equations

- Ethanol fermentation- Glucose > Ethanol + CO2
- Lactate fermentation- Glucose > Lactate

What occurs during glycolysis (which takes place anaerobically in cytoplasm and is common to all organisms)?

- Glucose is phosphorylated (requires 2 ATP) to form glucose phosphate making it more reactive
- It is then split into 2 TP
- TP is then oxidised by NAD (1 per molecule) to pyruvate in enzyme catalysed reactions generating ATP

What is the net gain per glucose molecule?

2 ATP, 2 NADH, 2 pyruvate

What are the next three stages which occur only in aerobic respiration?

- Link reaction
- Krebs cycle
- Oxidative phosphorylation

What occurs during the link reaction?

- Pyruvate is actively transported from cytoplasm into matrix
- Pyruvate is oxidised by NAD (becomes NADH) which dehydrogenates it (dehydrogenase- removing H-) and decarboxylates it (decarboxylate- removing CO2) to form acetate
- Acetate picked up by coen

What is the net gain per glucose in the link reaction?

2 acetyl CoA, 2 NADH, 2 CO2

What occurs during the Krebs cycle?

- Acetyl CoA reacts with 4C molecule to form 6C molecule (releases CoA which goes back to link reaction)
- This 6C molecule is oxidised to a 4C one, by NAD/FAD (which are reduced), being dehydrogenated and decarboxylated
- 1 ATP is produced through substr

What is the net gain per glucose in the Krebs cycle?

2 ATP, 4 CO2, 6 NADH, 2 FADH2

Why is the Krebs cycle important?

- Breaks large molecules into smaller ones
- Regenerates 4C molecules react with acetyl coA which would accumulate
- Produces H- for oxidative phosphorylationlation

What occurs during oxidative phosphorylation (via ETC on inner mitochondrial membrane)?

- Reduced coenzymes transfer electrons to the first electron carrier in the ETC, reducing the protein.
-Electrons passed down the chain in a series of redox reactions with energy released at each stage of the transfer (since each carrier is at a slightly

How does O2 act as the terminal electron acceptor and why is this critical?

O2 combines with H+ (provided by reduced co-enzmes and located in the inter-membrane space) and H- to form water.
Without it electron transfer down the chain would stop and life would not be able to continue

What are two alternative respiratory substrates and how are they used in aerobic respiration?

- Amino acids are deaminated by the liver to form organic acids for use in the Krebs cycle
- Lipids are hydrolysed to glycerol (which can be phosphorylated to form TP in glycolysis) and fatty acids (which are broken down in the matrix to form acetyl fragm

What occurs during anaerobic respiration?

ATP is generated only through glycolysis with the pyruvate accepting hydrogen from NADH (which previously reduced glucose to pyruvate)

Why is it crucial to oxidise NADH? (2)

- NAD is regenerated
- Prevents a build up occurring

How is lactate (a toxic acid) broken down?

It is oxidised by cells in the liver (20% goes back into aerobic respiration whilst the rest is converted into glycogen in the liver)

What do animals use organic molecules for?

As respiratory substrates and to make other biological molecules e.g protein, nucleic acids which form their biomass

What is biomass (the means by which energy is transferred between organisms - g/m2) and how can it be estimated?

Dry mass/mass of carbon in a given area over a given time

What is a producer?

A photosynthetic organism which manufactures it's own organic substances using light energy

Why is energy transfer more efficient between primary and secondary consumers than producers and consumers?

Cellulose is more difficult to digest (so more biomass excreted) than proteins and fats

How is energy transfer through an ecosystem expressed and what stages can this be divided into?

Using food chains (or more complex foods webs) in which organisms are grouped into trophic levels and arrows represent energy flow

What is gross primary production (GPP)?

The chemical energy store in plant biomass in given area in given time (kJ/Ha/year)

Give the equation for net primary production (energy store after respiratory losses have been taken into account)

NPP = GPP - Respiratory losses to environment

What is the net production of consumers?

Energy converted into a consumer's biomass
N = Ingested energy - respiratory losses- energy lost to environment in faeces/ urine

What are the advantages of biological control methods vs pesticides (artificial)?

Biological = specific to pest, reproduce themselves (continuous), pests don't develop resistance, don't spread chemicals
Pesticides = more easily controlled, eradicate pest completely

Alongside simplifying food webs, how do farmers reduce respiratory losses to the environment?

- Limiting movement
- Maintaining high temperatures
- Giving organisms highly digestible food
(growth rate can also be increased through selective breeding or steroids)

Why is the nitrogen cycle important?

Nitrogen ions are very soluble so often leach bout of soil leading to low concentrations left for active transport into roots

What are the 4 main stages of the nitrogen cycle?

- Nitrogen fixation
- Ammonification
- Nitrification
- Denitrification

What occurs during nitrogen fixation and what 2 types of bacteria carry it out?

N2 converted into NH3 by micro-organisms (requires great deal of energy). Carried out by:
- Free living nitrogen fixing bacteria (reduce gaseous N2 to NH3 to use to make aas releasing NH4+ when they die/decay)
- Mutualistic nitrogen fixing bacteria (e.g r

What occurs during ammonification?

Ammonia is produced from the decomposition, by saprobionts, of N containing organic molecules e.g aa's, proteins etc forming NH4+ in the soil

What occurs during nitrification?

Conversion of NH4+ to NO3- by nitrifying bacteria (releases chemical energy for respiration- chemoautotrophs) Involves the oxidisation of ammonium to nitrite ions (NO2-) followed by nitrate ions (NO3-)

What occurs during denitrification?

Denitrifying bacteria convert nitrates in the soil to N2 gas. It occurs when soil becomes waterlogged and anaerobic bacteria thrive.

Why is phosphorus important?

Needed for use in ATP, DNA and phospholipids

What occurs during the phosphorus cycle?

- Phosphate ions in rock deposits are dissolved by weathering/erosion ready for absorption by plants
- Ions incorporated into biomass of the plant and passed on to consumer when eaten
- Excess ions excreted/ released when animal dies and is decomposed by

What is the name of the fungi which exist in a mutualistic relationship with roots (especially useful for absorption of PO4 which is in short supply) and how do they benefit the plant?

Mycorrhizae (maximise SA for absorption due to extensions called hyphae) which obtain organic compounds from plant whilst providing it with mineral ions/water

How can inorganic ions (lost due to grazing livestock/harvesting plants) be replaced/ maintained in the soil? (4)

- Using fertilisers
- Aerating soil by ploughing fields (this prevents denitrification and improves ammonification by aerobic nitrifying bacteria)
- Planting nitrogen fixing crops
- Planting different crops with different requirements for nutrients/pests

Where do natural and artificial fertilisers come from and why are they important?

- Natural = manure/slurry which are decaying remains of organisms
- Artificial = mixed from deposits of ions/rocks
Both provide mineral ions increasing rate of photosynthesis/providing ions for use in organic compounds e.g nucleic acids, amino acids etc w

Name one other way in which efficiency of agricultural practices can be improved

Through selective breeding/ genetic modification to grow crops with increased growth rate, which are resistant to drought/pests/weed killer or have enhanced nutritional status

What are the 3 main environmental issues which accompany use of fertilisers?

- Leaching (nutrients removed from soil when they are dissolved by rainwater potentially polluting water and killing aquatic life/ poisoning drinking water)
- Eutrophication (nutrients in watercourses increase due to leaching of fertilisers/human sewage p

How does eutrophication ultimately lead to death of aquatic life?

- Leaching increases concentration of nitrate ions in the water
- This leads to increased growth of plants such as algae on the surface of the water - 'algal bloom'
- Mass of algae shades plants in the water below it preventing light from reaching them an

What can oxidation mean?

-Loss of electrons
-Loss of hydrogen
-Gain of oxygen
-Energy release

What can reduction mean?

-Gain of electrons
-Gain of hydrogen
-Loss of oxygen
-Energy absorption

What do photosynthetic pigments do?

Absorb and funnel light to the chloroplast

What is photoionisation?

The light energy from the sun excites the magnesium and increases the energy of the chlorophyll until electrons are released from the magnesium in the chlorophyll

How many electrons are released in photoionisation?

2 electrons

What is photolysis?

This is the break down of water via sunlight

What are the products of photolysis? and what is the equation?

Hydrogen, oxygen, electrons.
H2O-> 2H+ + 2e- + 1/2O2

What is the electron transport system?

Series of electron carriers arranged at progressively lower levels

What are the reaction terms for the chlorophyll and electron carrier in the electron transport system?

Chlorophyll= Has been oxidised (as it has lost electrons)
Carrier= has been reduced (as it has gained electrons)

How is the energy lost in the electron transport system used?

It is used to synthesise ATP (photophosphorylation)

What is photophosphorylation?

Adding a phosphate to a molecule using light

What are the 2 ways the thylakoid gains H+ ions?

-The photolysis of water releases 2 hydrogen molecules which become H+ ions
-The electron transport system releases energy during transfer which powers H+ ion pumps

What enzyme is used to form ATP?

ATP synthase

How is ATP synthase powered?

The H+ ions in the thylakoid have to move through the enzyme into the stroma by diffusion. The H+ ions then then give the enzyme energy as they move out

How is NADPH formed?

The electron carrier takes in electrons from the electron transport chain and the H+ ions in the stroma. The Hydrogen atoms then bind to the NADP and reduce it to form NADPH.

What are protons?

H+ ions

How is oxygen formed in the light dependent reaction of photosynthesis?

During photolysis half of an oxygen molecule is formed, it will then pair up and move out of the thylakoid.

4 ways in which the Calvin cycle is different to the light dependent reaction

-Doesn't need light
-Enzyme controlled metabolic pathways
-Happens on the Stroma
-Continues at night as it uses the ATP and NADPH remaining in the stroma

What does the Calvin Cycle produce?


What does the light dependent reaction produce?


How is GP formed? What is the term for the process?

Carbon dioxide reacts with RuBP and catalysed by Rubisco to create an unstable molecule which splits into 2 GP
Also known as Carbon fixation

How many carbon atoms does RuBP have?


What is rubisco?

An enzyme in the Calvin cycle which bonds RuBP and CO2

How is TP formed? What is the term for the process?

The GP is reduced using the hydrogen atoms from the NADPH, so it then becomes NADP
ATP also gives energy to the GP and a phosphate group, so it then becomes ADP
Also known as Reduction

What does the majority of TP do? (Calvin cycle)

Regenerate to become RuBP using ATP

What does some of the TP do? (Calvin cycle)

Synthesise organic molecules such as glucose

How many Calvin cycles does it take to make one glucose?


What is the law of limiting factors?

At any given moment, the rate of a physiological process is limited by the factor that is at its least favourable value.

What are the three limiting factors in photosynthesis?

-Light intensity
-Carbon dioxide

Why is temperature a limiting factor of photosynthesis?

It increases kinetic energy for more collisions and ESC with rubisco but higher temperatures can break hydrogen bonds and denature the enzyme

Why is carbon dioxide a limiting factor of photosynthesis?

Increasing carbon dioxide increases the amount of GP produced using rubisco but it can reach a saturation point where increasing it anymore has no affect on the rate of photosynthesis

Why is light intensity a limiting factor?

Light intensity contributes to photolysis and photoionisation but there is the light compensation point where light intensity no longer has an affect

What is photorespiration?

Process in which the rubisco enzyme binds with oxygen instead of carbon dioxide to form a different product

When can photorespiration occur?

At low carbon dioxide concentrations or at higher temperatures when rubisco's active site has changed to become less specific towards carbon dioxide

Two methods of measuring photosynthesis

Photosynthometer and lollipop apparatus

How does a photosynthometer work?

Pond weed is placed in a tube with light shining on it, the pond weed produces oxygen bubbles which are collected by a capillary tube and fed into a syringe where it can be measured

How does the lollipop apparatus work?

Algae is grown in the lollipop, radioactive C14 is then added to the algae
At intervals the valve is opened for the algae to be dropped in boiling methanol where it dies
the algae compounds can then be seperated by two-way chromatography

How do you control light intensity in an experiment?

-Keep the distance from the lamp and pond weed the same
-Same wattage of lamp
-Keep in a dark room to exclude other light sources

How do you control temperature in an experiment?

-Use a temperature controlled water bath
-Use water bath in front of lamp to stop excess heat or an LED

How do you control carbon dioxide in an experiment?

-Add the same concentration of sodium hydrogen carbonate to water

What is the compensation point?

When the rate of photosynthesis and rate of respiration are the same

What is a photosystem?

Combination of protein and pigment in thylakoid membrane

An example of a coenzyme


What do the electrons do to NADP?

Reduces the H+ ions to hydrogen atoms which the reduce NADP to NADPH

What are the differences between aerobic and anaerobic respiration?

-Aerobic uses oxygen whereas anaerobic doesn't
-More glucose is broken down in aerobic respiration to anaerobic
-Aeorbic produces Water, CO2 and energy but anaerobic produces lactate in animals and ethanol and CO2 in plants and fungi

What are the 4 stages of aerobic respiration?

1. Glycolysis
2. Link reaction
3. Krebs cycle
4. Oxidative phosphorylation

What is the main purpose of glycolysis?

Convert one molecule of glucose into two molecules of pyruvate

What is the process for glycolysis?

-The glucose is phosphorylised by 2 ATP which become ADP
-This turns the glucose into hexose bisphosphate which is split into two molecules of triose phosphate (TP)
-The TP is then oxidised and 2 hydrogen ions leave the system which NAD takes to become NA

What is the net gain of ATP in glycolysis?


What is chemiosmosis?

The movement of H+ ions down a concentration gradient out of the thylakoid through ATP which power the enzyme to catalyse the combination of ADP + Pi to ATP

Explain the process of the link reaction

-The pyruvate from glycolysis is firstly decarboxylated and CO2 is released
-It is then oxidised and hydrogen is released from the pyruvate and taken up by the NAD to become NADH
-This forms acetate
-Coenzyme A is then added to form acetyl coenzyme A (CoA

Explain the process of the Krebs Cycle

-Acetyl CoA combines with a 4 carbon compound (oxaloacetate), CoA then goes to the link reaction
-This forms a 6 carbon compound (citrate) which is then decarboxylated and dehydrogenation as NAD takes the hydogen to form NADH
-This forms a 5 carbon compou

How is coenzyme A used after the Kreb cycle?

Returns to the link reaction to be used again

How is the 3 NADH and 1 FADH used after the Kreb cycle?

Oxadative phosphorylation

Whats is substrate-level phosphorylation?

When an inorganic phosphate ion moves directly from one molecule to another

Explain the process of alcohol fermentation (Anaerobic respiration)

Pyruvate is firstly decarboxylated to ethanal, and then then reduced by NADH to become ethanol

Explain the process of lactate fermentation (Anaerobic respiration)

Pyruvate is reduced by NADH to lactate

What type of fermentation occurs in yeast and plants?

alcoholic fermentation

What type of fermentation occurs in humans?

lactic acid/lactate fermentation

How does anaerobic respiration make ATP?

The NAD that is needed in glycolysis is reduced in the process to NADH
Fermentation will oxidise the NADH to become NAD again which can continue the process of glycolysis which produces ATP through substrate-level phosphorylation

Examples of using aerobic respiration

-Aquatic animals use it when on long dives
-Mammalian birth

What is an advantage of lactate being produced?

It can be oxidised to pyruvate which can be used in aerobic respiration, for this to happen though it needs to be moved to the liver

What is a disadvantage of lactate being produced?

It is acidic and when in the muscles it can causes cramp and fatigue as the low pH can denature the proteins and enzymes

Where does substrate level phosphorylation occur?

glycolysis and krebs cycle

Where does oxidative phosphorylation occur?

inner mitochondrial membrane (cristae)

What is the main function of oxidative phosphorylation

-Produce ATP and H2O

Explain the process of oxidative phosphorylation

-NADH and FADH from the Kreb cycle are oxidised and the hydrogen atoms released split into 2e- and a H+ ion
-The 2e- enters the electron transport chain and releases energy by oxidation reactions as it moves from one acceptor to another
-This ETC powers t

What is the total ATP produced from one glucose molecule in aerobic respiration?