Energy transfers

What are the 4 stages of aerobic respiration?

1. Glycolysis

2. Link reaction

3. Krebs cycle

4. Oxidative phosphorylation

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?

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