Lecture 1: Introduction

Question 1

Describe Autotrophs. Where do they get their carbon from?

Answer 1

Autotrophs can synthesise energy-containing organic molecules, from inorganic sources, using basic energy sources such as sunlight. They get their carbon from inorganic forms such as CO2.

Question 2

Describe Heterotrophs.

Answer 2

Cannot synthesis their own food, so rely on other organisms for nutrition - from which they also acquire a reduced volume of carbon.

Question 3

Define biomass,

Answer 3

The total weight of all living organisms.

Question 4

Define Productivity.

Answer 4

The rate of carbon fixed from CO2 to organic material in an area.

Question 5

What is the difference between net and gross photosynthesis?

Answer 5

Gross photosynthesis is the total rate of CO2 fixation, whilst net photosynthesis is this value - CO2 released in respiration.

Question 6

Describe soluble organic molecules compared to soluble inorganic molecules.

Answer 6

Soluble organic - Excretory / breakdown products
Soluble inorganic - Chemical or biological derivation (DIC = carbon dioxide, bicarbonate anions, carbonic acid, carbonate)

Question 7

Describe insoluble organic and insoluble inorganic molecules.

Answer 7

Insoluble organic - Living or dead biomass

Insoluble inorganic - non biological particles

Question 8

In nutrient cycling, describe the respective roles of Autotrophic microbes and Heterotrophic bacteria in terms of uptake and conversion.

Answer 8

Autotrophs uptake inorganic matter, whilst Heterotrophs uptake organic and inorganic matter after which it is converted to particulate organic biomass.

Question 9

Nutrients are cycled through the food chain, but describe how they are released back into the environment.

Answer 9

Released as either dissolved organic forms, or dissolved inorganic forms (REMINERALIZATION)

Question 10

Give the equation for the carbon cycle.

Answer 10

CO2 + H20 organic carbon + O2

Question 11

By which process do funghi contribute to the carbon cycle?

Answer 11

They respire, as they are decomposers

Question 12

What is the largest store of carbon in the carbon cycle?

Answer 12

Rock 70,000,000 GtC

Question 13

Describe the difference between DIN and DON.

Answer 13

DIN = gas (N2), anion (NO3-, N02-) or cation NH4+
DON = A heterogenous group of organic compounds, ranging from well defined constituents such as urea and amino acids, to more complex compounds such as humic and fulvic acids.

Question 14

What does the following equation represent?

N2 + 8H —> NH3 + H2

Answer 14

Nitrogen fixation

Question 15

What is the chemical conversion that occurs in denitrification and nitrification?

Answer 15

De = NH4+ ---> NO3 - 
Nitri = NO3- ---> N2

Question 16

What type of nitrogen is converted to ammonia in Ammonification?

Answer 16

organic

Question 17

What compounds is carbon found in as a macronutrient, and what is its biological role?

Answer 17

DOC, CO2, CO3^2-, HCO3- used in cell material, photosynthesis and controlling the pH of water.

Question 18

What compounds is Phosphorus found in as a macronutrient, and what is its biological role?

Answer 18

Ortho- (PO4-) and poly- phosphates. It is a component of nucleotides DNA, RNA and ATP

Question 19

What compounds is nitrogen found in as a macronutrient, and what is its biological role?

Answer 19

DON, N2, NO3-, NO2- and NH4+. It is used as a component of amino acids and proteins.

Question 20

Name the four growth factors for microbes.

Answer 20

Vitamins, amino acids, purines, pyrimidines.

Question 21

What differentiates a typical macronutrient from a microntrient?

Answer 21

Macronutrients = microbes need in excess, whereas micronutrients they only need a very small amount of, so tend not to be limiting.

Question 22

Prokaryotes include which two groups of microorganisms?

Answer 22

Bacteria and Archae

Question 23

What comes under Eukaryotes in the phylogentic tree?

Answer 23

Eukarya, includes animals, plants and funghi

Question 24

Which of the following processes are carried out by Archae, Bacteria and Eukaryotes respectively:

• Nitrification
• Denitrification
• Nitrogen fixation

Answer 24

Archae and Bacteria both nitrogen fix and denitrify which Eukaryotes dont. Bacteria are the only ones to nitrify.

Question 25

How is organic carbon produced and what as?

Answer 25

Via chemotrophy as Chemotrophs and via photosynthesis (phototrophy) as phototrophs.

Question 26

Describe the presence of carbon in aquatic ecosystems.

Answer 26

Most is in dissolved formed, with a significant amount of phytoplankton production exudated to dissolved organic carbon pools.

Question 27

Heterotrophic bacteria are very abundant in aquatic ecosystems but what do they largely consume?

Answer 27

DOC

Question 28

Put these in size order from biggest to smallest -

metazoo-, Bacterio-, Viro-, Protozoo-, Nano- plankton.

Answer 28

Metazoo > Protozoo > Nano > Bacterio > Viro

Question 29

Where does a lot of bacterial biomass end up?

Answer 29

Being consumed by small protists.

Question 30

In the aquatic food chain, what produces DOM and what consumes it?

Answer 30

Phytoplankton produce it, whilst bacteria consume it.

Question 31

What three things are included in the viral loop?

Answer 31

Virus —> DOM –> Bacteria

Question 32

Viruses can affect the efficiency of the biological pump, via lysis. What is this, and what is its effect?

Answer 32

Lysis breaks up cells into DOC and POC, which reduces the rate at which carbon is exported to the deep ocean, instead it is retained in the surface ocean to be photo-oxidised and respired, increasing the atmospheric CO2 concentration relative to scenarios under which it sinks.

Question 33

What four things do Aquatic Viruses affect?

Answer 33

Biogeochemical cycle, community structure, phytoplankton mortality, genetic transfer and evolution.

Question 34

What does viral abundance vary with and where geographically?

Answer 34

Prokaryotic abundance and productivity. It is highest in close to the shore and in surface waters. Production occurs on the spatial scale of individual cells in microbial hotspots.

Question 35

How does viral lysis affect nutrient concentrations in the environment?

Answer 35

Lysis of prokaryotes frees biologically available iron to support phytoplankton. It also increases respiration in the system and influences the volume of carbon exported to the deep ocean via the bio-pump through sinking of infected cells.

Question 36

What does the viral shunt do?

Answer 36

Moves material from living organisms to particulate / dissolved pools of organic matter (where it is mostly converted to CO2 by respiration and photodegradation)