Energy transfers

What are the 4 stages of aerobic respiration?

1. Glycolysis

2. Link reaction

3. Krebs cycle

4. Oxidative phosphorylation

What are the 2 stages of photosynthesis?

• Light dependent reaction (LDR)

• Light independent reaction (LIR)

Where do the 2 photosynthesis stages occur in plants?

Light dependent reaction: thylakoids of chloroplasts

Light independent reaction: stroma of chloroplasts

What is the purpose of the LDR?

To convert light energy into chemical energy (ATP and NADPH)

What are the 4 stages of the LDR?

1. Photolysis

2. Photoionisation of chlorophyll

3. Chemiosmosis

4. Production of ATP and reduced NADP

What happens during photolysis?

• Light energy is absorbed by chlorophyll ad splits water into oxygen, H+ and e-

• The H+ is picked up by NADP to form NADPH

• The e- are passed along a chain of electron carrier proteins

• The oxygen is either used for respiration or diffuses out of the leaf through the stomata

What happens during photoionisation?

• Light energy is absorbed by chlorophyll

• This energy causes 2 electrons to become excited and raise up to a higher energy level to leave chlorophyll

• Therefore the chlorophyll has been ionised by light

• Some of the energy from the released electrons is used to make ATP and NADPH in chemiosmosis

What happens during chemiosmosis and how does this lead to the production of ATP and reduction of NADP?

• The electrons that gained energy and left the chlorophyll move along a series of proteins embedded within the thylakoid membrane (ETC)

• As they move along, they release energy and some is used to pump protons from stroma into thylakoid - creating a proton gradient

• Protons then diffuse back into stroma via the channel protein ATP synthase - results in production of ATP

• In the stroma, the protons, as well as electrons, combine with the co-enzyme NADP to form NADPH

Whats another name for the LIR?

The Calvin Cycle

Where does the Calvin Cycle occur?

In the stroma

Name the 3 stages in the Calvin Cycle

1. Carbon fixation

2. Reduction

3. Regeneration

What happens during carbon fixation in the Carbon Cycle?

CO2 reacts with ribulose biphosphate (RuBP), catalysed by the enzyme rubisco to form 2 molecules of glycerate 3-phosphate (GP)

What happen during reduction in the Calvin Cycle?

• 2x GP are reduced to 2x triose phosphate (TP)

• This requires 2x NADPH and 2x ATP

• Forms 2x NADP and 2x ADP

What are the 3 steps of glycolysis?

What’s the net gain?

1. Phosphorylation of glucose to glucose phosphate, using ATP

2. The production of triose phosphate

3. Oxidation of triose phosphate to produce pyruvate

   Net gain (per glucose):

   2x reduced NAD

   2x ATP

   2x pyruvate

How does pyruvate from glycolysis enter the mitochondria?

Via active transport

Where does glycolysis take place?

In the cytoplasm

What are the 4 steps of the link reaction?

What’s the net gain?

1. Pyruvate is oxidised to acetate, forms CO2

2. NAD picks up the hydrogen and becomes reduced NAD

3. Acetate combines with coenzyme A to produce acetylcoenzyme A

   Net gain (per pyruvate):

   1x CO2

   1x reduced NAD

   1x acetyl coA

Where does the link reaction take place?

In the mitochondrial matrix

Give a summary equation for the link reaction

pyruvate + NAD + CoA → acetyl CoA + NADH + CO2

What are the 2 steps of the Krebs Cycle?

What’s the net gain?

1. Acetyl Co-A reacts with oxaloacetate (4 carbon molecule)

   This releases coenzyme A and produces citrate (6 carbon molecule) that enters the Krebs cycle

2. A series of redox reactions occur

   Net gain (per acetyl Co-A):

   2x CO2

   1x ATP

   1x FADH

   3X NADH

How do plants use the sugar that they synthesise?

Most of the sugars are used as respiratory substances

The rest are used to make other groups of biological molecules - these form the biomass of plants

What is biomass?

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

What are the units for biomass?

When an area is being sampled: gm-2

When a volume is being sampled: gm-3

Biomass can be measured in terms of what?

Mass of carbon or dry mass of tissue per given area

What method can be used to measure the chemical energy store in dry biomass?

Calorimetry

What is GPP?

Gross primary production is the chemical energy store in plant biomass, in a given area or volume. It is the total energy resulting from photosynthesis.

What is NPP?

Net primary production is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account

Give the equation relating GPP and NPP

NPP = GPP - R

Where R represents respiratory losses

What is NPP available for?

Plant growth, reproduction and for other trophic levels in the ecosystem

How can the net production of consumers be calculated?

N = I - (F+R)

• I: chemical energy stored in ingested food

• F: energy lost as faeces and urine

• R: respiratory losses

Why does biomass decrease along a food chain?

• Energy lost in urine and faeces

• Some of the organism is not consumed

• Energy lost to surroundings as heat

What is primary and secondary productivity?

Primary productivity: the rate at which energy is converted by producers into biomass

Secondary productivity: the rate at which consumers convert the chemical energy in their food into biomass

What are the units for rates of productivity?

kJha-1year-1

• kJ is the unit for energy

• ha-1 is per unit area to standardize the results to enable environments to be compared

• year-1 is per year to take into account the impact seasons will have on rain, light and heat. Provides an annual average to allow fair comparisons

Outline 4 farming practices used to increase the efficiency of energy transfer

• Exclusion of predators

• Artificial heating

• Restriction of movement

• Feeding is controlled

What is a pyramid of biomass?

Diagram that shows the biomass at each trophic level

Why is a pyramid of biomass preferable to a pyramid of numbers?

Shape of pyramid of numbers may be skewed since a small number of producers can support many consumers

Why can’t organisms use nitrogen directly from the atmosphere?

N2 is very stable due to strong covalent triple bond

Which biological molecules contain nitrogen?

Proteins, ATP and nucleic acids

What are the 5 key processes in the nitrogen cycle?

1. Saprobiotic nutrition and microbes

2. Ammonification

3. Nitrification

4. Nitrogen fixation

5. Denitrification