Biogeochem - Chapter 2: Carbon cycle and primary production

Question 1

What is photosynthesis?

Answer 1

uses light (photons) as an energy source. (light reaction)

the growth and production of organic matter (biosynthesis). (dark reaction)

Question 2

What is the photosynthesis light reaction?

Answer 2

• the use of light energy is known as phototrophy
• light is used to oxidise a substrate (eg water, hydrogen sulphide) and gain activated electrons and ATP

Question 3

what is the photosynthesis dark reaction?

Answer 3

the use of the stored energy (ATP) and electrons (gained during light reaction) to fix (reduce) the CO2 to produce organic matter

Question 4

what happens in the light reaction?

Answer 4

light (energy) is converted into chemical energy in the form of energy rich compounds (ATP)

Question 5

what happens in the dark reaction?

Answer 5

the ATP are reacting (releasing their stored chemical energy) to help form organic compounds of CO2, a process that requires energy as organic compounds contain more chemical energy than CO2

Question 6

what is primary production?

Answer 6

the process in which living organisms create organic matter (biomass) from carbon dioxide

Question 7

Anoxygenic phototrophic bacteria definition

(eg green and purple sulphur bacteria)

Answer 7

anoxygenic phototrophic bacteria are bacteria that can perform photosynthesis using light energy, but unlike plants and some other photosynthetic organisms, they do not produce oxygen as a byproduct of this process.

They are anerobic

Question 8

what photosynthetic pigment (or compound) do anoxygenic phototrophic bacteria use?

Answer 8

bacteriochlorophyll

they use H2S (which requires less light energy to be oxidised than water) which is oxidised to elemental sulphur and sulphate

Question 9

2 groups of Anoxygenic phototrophic bacteria

Answer 9

Purple sulphur bacteria

Green sulphur bacteria
- super sensitive to oxygen… if its present they die
- they are the most efficient organism on the planet

Question 10

what are oxygenic phototrophic organisms

Answer 10

organisms that can perform photosynthesis using light energy and produce oxygen as a byproduct of this process. This group includes plants, algae, and cyanobacteria (eg anabaena)

Question 11

characteristics of oxygenic phototrophic organisms

Answer 11

• Main pigment of oxygenic phototrophs is chlorophyll a
• Able to capture more energy than the anoxygenic phototrophic bacteria

Question 12

Whats the greatest depth you can find oxygen in soils

Answer 12

can only find it 2cm deep into the soils at a maximum as consumption is so high

Question 13

What are the major differences between marine and terrestrial primary production?

Answer 13

The biomass turnover and the amount of standing stock (the biomass present in an ecosystem at any given time).

Aquatic systems have a very high primary production, but most of it is consumed very quickly ( –> microbial loop) hence the have a low standing stock.

terrestrial systems have a similar turnover of biomass, but this is usually soft biomass (leaves and fresh shoots).

Question 14

What is gross productivity?

Answer 14

the organic carbon produced in an ecosystem

Question 15

What are the conditions required for positive net productivity to occur?

(X > Y…)

Answer 15

the gross productivity (amount of organic carbon produced in an ecosystem) mut be higher than the respiration (consumption)

Question 16

what can primary production be limited by?

Answer 16

Primary production can be limited by the amount of nutrients available

can also be limited by light energy

Question 17

What is the law of minimum?

Answer 17

It states that growth is controlled by the scarcest resource (limiting factor)

this can be energy, water or nutrients (eg minerals in plants or carbon substrate in bacteria or animals)

Question 18

What is the Redfield ratio

Answer 18

C106 N16 P1

it is the ratio of carbon : nitrogen : phosphorus which is nearly constant throughout the worlds oceans, in both phytoplankton biomass and in dissolved nutrient pools.

Question 19

List some macronutrients

Answer 19

C, N, P, S, Mg, Ca

Carbon
Nitrogen
Phosphorus
Sulphur
Magnesium
Calcium

Question 20

List some trace elements (micronutrients)

Answer 20

Mn, Co, Ni, W, Zn, Se, B, Mo, Cu

Manganese
Cobalt
Nickel
Tungsten
Zinc
Selenium
Boron
Molybdenum
Copper

Question 21

What is the modified redfield ratio for diatoms?

Answer 21

C : Si : N : P
106 : 15 : 16 : 1

Question 22

What impact on cell division does phosphorus have if it is a limiting factor?

Answer 22

Phosphorus is required to synthesise new nucleic acids and membrane lipids during cell division. If it is not present, the cells cannot divide

Question 23

What is phytoplankton usually limited by? And what nutrient limits freshwater and marine environments

Answer 23

Typically limited by N, P or Fe but sometimes micronutrients such as Ni or Mn

In freshwater ecosystems, it is typically limited by P.

In marine environments, it is usually N (nitrate) that is limiting or sometimes Fe

Question 24

Strategies to overcome nutrient limitation

Answer 24

• Accumulation of nutrients when available
• feeding on bacteria or insects (carnivorous plants)
• a range of bacteria (including cyanobacteria) can fix atmospheric nitrogen and produce NH3
• a number of eukaryotic algae and plants live in close association with nitrogen-fixing bacteria (which convert N2 from the air to ammonium)
• some microorganisms (fungi) can excrete siderophores that have an extremely high affinity to metals (trace elements like Fe). Trees usually live in symbiosis with fungi which are used to capture metals for the tree

Question 25

What do nitrogen fixing bacteria convert

Answer 25

They convert N2 from the air to ammonium

Question 26

Why do trees and fungi live in symbiosis?

Answer 26

Fungi can excrete siderophores which have an extremely high affinity to metals (trace elements like Fe). Trees capture metals from the Fungi for the tree

Question 27

What factor prevents phytoplankton from growing

Answer 27

Nutrient limitation of N, P and other nutrients like Fe

Question 28

State the processes of the microbial loop

Answer 28

• phytoplankton produce organic matter under N & P limited conditions
• the organic matter produced contains CO2 and H2O (no limiting nutrients), eg carbohydrates like glucose and small organic acids like starch
• intracellular starch deposits fill up causing phytoplankton to excrete the freshly created organic matter (exudates)
• exudates stimulate the remineralisation of organic matter (eg zooplankton faecal pellets or detritus) and releases important nutrients (CO2, N and P)
• these then become available for phytoplankton to use

Question 29

Where does most of the primary production remineralisation occur?

(ie where in water column)

Answer 29

In the euphotic layer

this means that most of the important nutrients to the deep water is limited

Question 30

Role/impact of viruses in the marine ecosystem

Answer 30

Virus attack can lead to the complete collapse of a phytoplankton bloom within a few days. As the release of new viruses requires the host cell to lyse, this appears to be a very efficient way to create detritus and (via microbial loop), recycle nutrients

Question 31

What is ‘sloppy feeding’

Answer 31

Sloppy feeding describes the production of detritus during the ingestion of food by herbivorous and carnivorous animals (plankton to top predators)

Question 32

What happens if detritus is not available?

(hint - phytoplankton exudates/microbial loop)

Answer 32

Phytoplankton thus cannot grow due to N and P limitation and produce organic matter and excrete exudates

The exudates then keep the bacterioplankton alive

Question 33

what happens when detritus becomes available

(hint - how bacterioplankton and phytoplankton interact)

Answer 33

The bacterioplankton degrade the detritus.

They are not starving as they use the energy bound in the detritus. This releases inorganic nutrients enabling the phytoplankton to grow (not releasing exudates)

Question 34

When do bacterioplankton rely on exudates over detritus?

Answer 34

When the detritus is consumed and the nutrients are depleted, the phytoplankton is nutrient deprived and will start to produce exudates supporting bacterioplankton