Aquatic environments

Question 1

Oxygen and carbon cycle

Answer 1

Photosynthesis and respiration controls the oxygen and carbon cycles

Question 2

Phtoplankton

Answer 2

Oxygenic phototrophs suspended freely in water; include algae and cyanobacteria

Question 3

Benthic species

Answer 3

They are attached to the bottom or sides of a lake or stream

Question 4

Misbalance in productivity and consumption

Answer 4

If rate of productivity in a pond exceeds the rate of consumption of organic matter, it will stimulate heterotrophs to increase dramatically.
this results in O2 consumption being greater than production which will cause the pond to be anoxic

Question 5

heterotrophs and autotrophs

Answer 5

Activity of hetero is highly dependant on activity of primary producers; oxygenic phototrophs produce organic matter and oxygen

Question 6

Oxygen stratification

Answer 6

Oxygen has limited solubility in water, the deep layers of freshwater can become anoxic once oxygen is consumed
O2 concentrations are dependant on amount of organic matter present and physical mixing of the system

Question 7

Temporal variation

Answer 7

In day: Photoautotrophs photosynthesise and O2 is produced
At night: No photosynthesis occurs and O2 decreases

Question 8

Spatial variation

Answer 8

Lake is stratified according to the season.

Question 9

epilimnion

Answer 9

Warmer, less dense surface water of lake

Question 10

hypolimnion

Answer 10

it is the cooler, denser water at the bottom of lake or pond

Question 11

Thermocline

Answer 11

Seperates epilimnion and hypolimnion

Question 12

Aeration of epilimnion

Answer 12

-Production of O2 by phototrophs
-Diffusion of O2 by air into water

Question 13

chemicals in hypolimnion

Answer 13

There are chemorganotrophs in hypolimnion that break down organic matter produced by epilimnion anaerobically and produce H2S, Ammonia and Methane

Question 14

Summer stratification

Answer 14

Epilimnion is seperate from hypolimnion where Ep has O2 and organic nutrients and Hypo contains some organic matter but no O2

Question 15

Spring and Winter stratification

Answer 15

Water at top gets colder than water below
-Cooler water sinks which causes mixing of layers
-This causes the hypolimnion to become oxygenated, which affects microbe diversity and abundance in each layer.

Question 16

Strom effect on lake stratification

Answer 16

It causes mixing of layers which causes toxic substances found in bottom layers to mix with upper layers which causes many organisms to die

Question 17

River stratification

Answer 17

May be well mixed because of rapid water flow
-Can still suffer from oxygen deficiences because of high inputs of agricultural and industrial pollution

Question 18

Biochemical oxygen demand

Answer 18

-The microbial oxygen-consuming capacity of a body of water
-Increases with the influx of organic material and then decreases over time

Question 19

Effect pf input of organic rich waste waters into aquatic systems

Answer 19

-Sudden influx in sewage causes an increase in organic matter present
-This causes a sudden accumulation in heterotrophs
-This causes a decrease in autotrophs as oxygen and organic matter is used up
-When O2 is depleted, heterotrophs decrease which allows autotrophs and hence O2 to increase

Question 20

Autrophs outcompeted by heterotrophs

Answer 20

Heterotrophs can always respire and utilise the available energy while autotrophs only respire at night

Question 21

Phylogenetic sampling of lakes

Answer 21

Molecular studies such as 16S rRNA sequence is used as a culture-independant method.
-High microbial diversity reflects dynamic character of lake
-Seasonally variable inputs of endogenous and exogenous nutrients sustains a phylogenetically and metabolically complex community of Bacteria and a few groups of Archaea