1. Energetics of Marine Ecosystems
Photosynthesis and chemosynthesis as means of energy capture
Productivity and energy flow along food chains

2. Explain that photosynthesis captures the energy of sunlight and makes the energy available to the food chain
Green plants, including phytoplankton in aquatic food chains, capture light energy and use this to synthesize organic substances, including carbohydrates, in the process of photosynthesis.
In this way, energy is made available to higher trophic levels in food chains and food webs.
Energy, in the form of organic substances, passes to the primary consumers, such as herbivorous zooplankton.

3. How do plants make energy & food?
Plants use the energy from the sun
to make ATP energy
to make sugars
glucose, sucrose, cellulose, starch, & more
Photosynthesis Song
sun
ATP
sugar

4. Building plants from sunlight & air
Photosynthesis
2 separate processes
ENERGY building reactions
collect sun energy
use it to make ATP
SUGAR building reactions
take the ATP energy
collect CO2 from air & H2O from ground
use all to build sugars
ATP
H2O +
CO2
sugars
carbon dioxide
CO2
water
H2O
sugars
C6H12O6 +

5. Using light & air to grow plants
Photosynthesis
using sun’s energy to make ATP
using CO2 & water to make sugar
in chloroplasts
allows plants to grow
makes a waste product
oxygen (O2)
(ATP) = used to build the sugar
 glucose + oxygen
carbon
dioxide
sun
energy
+ water +
6CO2
6H2O
C6H12O6
6O2
sun
energy  +

6. What do plants need to grow?
The “factory” for making energy & sugars
chloroplast
Fuels
sunlight
carbon dioxide
water
The Helpers
enzymes
sun
CO2
ATP
enzymes
sugars
H2O

7. Photosynthesis ATP ADP ENERGY building reactions
sun
Photosynthesis
ENERGY building reactions
ADP
ATP
SUGAR building reactions
used immediately to synthesize sugars
H2O
sugar
CO2

8. How are they connected? Respiration  Photosynthesis
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6
6O2
6CO2
6H2O
ATP  +
Photosynthesis
So, in effect, photosynthesis is respiration run backwards powered by light.
Cellular Respiration
oxidize C6H12O6  CO2 & produce H2O
fall of electrons downhill to O2
exergonic
Photosynthesis
reduce CO2  C6H12O6 & produce O2
boost electrons uphill by splitting H2O
endergonic
6CO2
6H2O
C6H12O6
6O2
light
energy  +
 glucose + oxygen
carbon
dioxide
sun
+ water +

10. Energy cycle ATP Photosynthesis Cellular Respiration sun CO2 O2 H2O
plants
H2O
CO2
glucose sugars O2
animals, plants
Cellular Respiration
ATP

11. Another view… ATP Photosynthesis Cellular Respiration sun CO2 O2 H2O
capture light energy
Photosynthesis
synthesis
producers, autotrophs
H2O
CO2
organic molecules food O2
waste
waste
waste
consumers, heterotrophs
digestion
Cellular Respiration
ATP
release chemical energy

12. In other words…
Take it from me!
All of the solid material of every plant was built out of thin air
All of the solid material of every animal was built from plant material
air
sun
Then all the cats, dogs, mice, people & elephants… are really strands of air woven together by sunlight!

13. Photosynthesis Overview
Energy for all life on Earth ultimately comes from photosynthesis.
6CO2 + 12H2O C6H12O6 + 6H2O + 6O2
Oxygenic photosynthesis is carried out by:
cyanobacteria, 7 groups of algae, all land plants

14. Electromagnetic Spectrum

15. Pigments Pigments: molecules that absorb visible light
Each pigment has a characteristic absorption spectrum, the range and efficiency of photons it is capable of absorbing.

16. Pigments chlorophyll a – primary pigment in plants and cyanobacteria
-absorbs violet-blue and red light
chlorophyll b – secondary pigment absorbing light wavelengths that chlorophyll a does not absorb

17. Pigments
A graph of percent of light absorbed at each wavelength is a compound’s absorption spectrum.
Action spectrum
Oxygen production and therefore photosynthetic activity is measured for plants under each specific wavelength; when plotted on a graph, this gives an action spectrum for a compound.
The action spectrum for chlorophyll resembles its absorption spectrum, thus indicating that chlorophyll contributes to photosynthesis.

18. Pigments
accessory pigments: secondary pigments absorbing light wavelengths other than those absorbed by chlorophyll a
increase the range of light wavelengths that can be used in photosynthesis
include: chlorophyll b, carotenoids, phycobiloproteins
carotenoids also act as antioxidants

19. How to Measure
Secchi Disk

20. Autotrophs photoautotrophs
Autotrophs (=self-nourishing) are called primary producers.
Photoautotrophs fix energy from the sun and store it in complex organic compounds
(= green plants, algae, some bacteria)
light
simple
inorganic
compounds
complex
organic
compounds
photoautotrophs

21. Chemoautotrophs (chemosynthesizers) are bacteria
oxidize reduced inorganic substances
(typically sulfur and ammonia compounds) and produce complex organic compounds
oxygen
reduced
inorganic
compounds
complex
organic
compounds
chemoautotrophs

22. Chemosynthesis near hydrothermal vents

23. Heterotrophs heterotrophs
Heterotrophs (=other-nourishing) cannot produce their own food directly from sunlight+ inorganic compounds. They require energy previously stored in complex molecules.
heat
complex
organic
compounds
simple
inorganic
compounds
heterotrophs
(this may include several steps, with
several different types of organisms)

24. The Laws of Thermodynamics
Energy flow is a one-directional process.
Sun  heat (longer wavelengths)
FIRST LAW of THERMODYNAMICS:
Energy can be converted from one form to another, but cannot be created or destroyed.

25. SECOND LAW of THERMODYNAMICS
Transformations of energy always result in some loss or dissipation of energy or
In energy exchanges in a closed system, the potential energy of the final state will be less than that of the initial state
Entropy tends to increase (entropy = amount of unavailable energy in a system)
Systems will tend to go from ordered states to disordered states (to maintain order, energy must be added to the system, to compensate for the loss of energy)

26. Examples
Internal combustion engines in cars are 25% efficient in converting chemical energy to kinetic energy; the rest is not used or is lost as heat.

27. Energy flow heat Simplistically: Producers Consumers
This pattern of energy flow among different organisms is the TROPHIC STRUCTURE of an ecosystem.
Producers
Consumers
Decomposers
heat

28. Food chains

29. Problems
Too simplistic
No detritivores
Chains too long

30. Rarely are things as simple as grass, rabbit, hawk, or indeed any simple linear sequence of organisms.
More typically, there are multiple interactions, so that we end up with a FOOD WEB.

31. Energy transfers among trophic levels
How much energy is passed from one trophic level to the next?
How efficient are such transfers?

32. Biomass-the dry mass of organic material in the organism(s).
(the mass of water is not usually included, since water content is variable and contains no usable energy)
Standing crop-the amount of biomass present at any point in time.

33. Primary productivity
Primary productivity is the rate of energy capture by producers.
= the amount of new biomass of producers, per unit time and space

34. Gross primary production (GPP)
= total amount of energy captured
Net primary production (NPP)
= GPP - respiration
Net primary production is thus the amount of energy stored by the producers and potentially available to consumers and decomposers.

35. Secondary productivity is the rate of production of new biomass by consumers, i.e., the rate at which consumers convert organic material into new biomass of consumers.
Note that secondary production simply involves the repackaging of energy previously captured by producers-no additional energy is introduced into the food chain.
And, since there are multiple levels of consumers and no new energy is being captured and introduced into the system, the modifiers gross and net are not very appropriate and are not usually used.

36. Ecological pyramids
The standing crop, productivity, number of organisms, etc. of an ecosystem can be conveniently depicted using “pyramids”, where the size of each compartment represents the amount of the item in each trophic level of a food chain.
Note that the complexities of the interactions in a food web are not shown in a pyramid; but, pyramids are often useful conceptual devices--they give one a sense of the overall form of the trophic structure of an ecosystem.
producers
herbivores
carnivores

37. Pyramid of energy
A pyramid of energy depicts the energy flow, or productivity, of each trophic level.
Due to the Laws of Thermodynamics, each higher level must be smaller than lower levels, due to loss of some energy as heat (via respiration) within each level.
Energy flow in :
producers
herbivores
carnivores

38. Pyramid of numbers
A pyramid of numbers indicates the number of individuals in each trophic level.
Since the size of individuals may vary widely and may not indicate the productivity of that individual, pyramids of numbers say little or nothing about the amount of energy moving through the ecosystem.
# of carnivores
# of herbivores
# of producers

39. Pyramid of standing crop
A pyramid of standing crop indicates how much biomass is present in each trophic level at any one time.
As for pyramids of numbers, a pyramid of standing crop may not well reflect the flow of energy through the system, due to different sizes and growth rates of organisms.
biomass of carnivores
biomass of herbivores
biomass of producers
(at one point in time)

40. Pyramid of yearly biomass production
If the biomass produced by a trophic level is summed over a year (or the appropriate complete cycle period), then the pyramid of total biomass produced must resemble the pyramid of energy flow, since biomass can be equated to energy.
Yearly biomass production
(or energy flow) of:
producers
herbivores
carnivores

41. Note that pyramids of energy and yearly biomass production can never be inverted, since this would violate the laws of thermodynamics.
Pyramids of standing crop and numbers can be inverted, since the amount of organisms at any one time does not indicate the amount of energy flowing through the system.
E.g., consider the amount of food you eat in a year compared to the amount on hand in your pantry.

43. There is no light for photosynthesis in the deep ocean.
Explain that chemosynthesis captures the chemical energy of dissolved minerals and that chemosynthetic bacteria at hydrothermal vents make energy available to the food chain
There is no light for photosynthesis in the deep ocean.
Some species of bacteria are able to derive energy from the oxidation of inorganic substances, such as hydrogen sulphide, and use this energy to synthesize organic compounds.
This process is called chemosynthesis.

45. Explain that chemosynthesis captures the chemical energy of dissolved minerals and that chemosynthetic bacteria at hydrothermal vents make energy available to the food chain
Fluid emerging from hydrothermal vents is rich in hydrogen sulphide and other gases.
Chemosynthetic bacteria oxidize hydrogen sulphide and are able to fix carbon dioxide to form organic substances. These organic substances provide a food source for all other animals in the hydrothermal vent ecosystem.
note that these chemosynthetic bacteria form symbiotic relationships with tube worms and giant clams.

47. Vent Food Web

48. Explain the meaning of the term productivity and how productivity may influence the food chain.
Productivity: the rate of production of biomass.
In almost all ecosystems, green plants are the primary producers and we usually refer to primary production in relation to plants.
Productivity is often measured in terms of energy capture per unit area (or per unit volume in the case of aquatic ecosystems) per year.
Since consumers depend directly or indirectly on the energy captured by primary producers, the productivity of an ecosystem affects all trophic levels. When conditions are favorable for photosynthesis, the productivity of the ecosystem tends to be relatively high, such as in tropical rain forests, algal beds and reefs.

50. Calculate and explain the energy losses along food chains due to respiration and wastage
Of the total energy reaching the Earth from the Sun, only a very small percentage is captured and used for the synthesis of organic substances by primary producers.
Light energy is reflected by surfaces, or may pass straight through a producer without being absorbed. Energy loss also occurs thorough inefficiencies of photosynthesis.
Candidates may be asked, for example, to calculate the percentage of incident light energy which appears as energy of newly synthesized organic substances.

52. The total energy captured by primary producers is referred to as the gross primary production (GPP). Some of the organic substances will be used by the producers as substrates for respiration. This represents a loss of energy. The remaining organic substances, referred to as the net primary production (NPP), represent an energy source which can be transferred to higher trophic levels. We can represent this in the form of an equation:

53. Calculate and explain the energy losses along food chains due to respiration and wastage
NPP = GPP – R
where NPP is the net primary production; GPP is the gross primary production and R represents energy losses through respiration.
Approximately 10% of the energy available at one trophic level is transferred to the next trophic level. Reasons for wastage include that facts that not all of one organism may be eaten by another; there are also losses in excretion and egestion. Substrates are used for respiration to provide energy for movement and consequently energy is lost in the form of heat.

56. Calculate and account for the efficiency of energy transfer between trophic levels
Suppose that the net productivity of plants in a food chain is kJ per m2 per year and that the net production of herbivores is kJ per m2 per year.

57. The efficiency of transfer of energy from the producers to the herbivores is therefore (1 700 ÷ ) × 100 = 4.72%.
Energy Flow

58. Energy losses from the energy consumed by the herbivore include heat from respiration, losses in urine and undigested plant material in feces. The energy of production of herbivores represents the total energy available to carnivores, the next trophic level.

59. Represent food chains as pyramids of energy, numbers and biomass
Ecological pyramids are a way of representing food chains graphically. An ecological pyramid has the producers at the base, then a series of horizontal bars representing the successive trophic levels. In each case, the width of the bar is proportional to the numbers, biomass, or energy.

60. Ecological pyramids
The standing crop, productivity, number of organisms, etc. of an ecosystem can be conveniently depicted using “pyramids”, where the size of each compartment represents the amount of the item in each trophic level of a food chain.
Note that the complexities of the interactions in a food web are not shown in a pyramid; but, pyramids are often useful conceptual devices--they give one a sense of the overall form of the trophic structure of an ecosystem.
producers
herbivores
carnivores

61. Pyramid of energy
A pyramid of energy depicts the energy flow, or productivity, of each trophic level.
Due to the Laws of Thermodynamics, each higher level must be smaller than lower levels, due to loss of some energy as heat (via respiration) within each level.
Energy flow in :
producers
herbivores
carnivores

62. Pyramid of numbers
A pyramid of numbers indicates the number of individuals in each trophic level.
Since the size of individuals may vary widely and may not indicate the productivity of that individual, pyramids of numbers say little or nothing about the amount of energy moving through the ecosystem.
# of carnivores
# of herbivores
# of producers

63. Pyramid of standing crop
A pyramid of standing crop indicates how much biomass is present in each trophic level at any one time.
As for pyramids of numbers, a pyramid of standing crop may not well reflect the flow of energy through the system, due to different sizes and growth rates of organisms.
biomass of carnivores
biomass of herbivores
biomass of producers
(at one point in time)

64. Pyramid of yearly biomass production
If the biomass produced by a trophic level is summed over a year (or the appropriate complete cycle period), then the pyramid of total biomass produced must resemble the pyramid of energy flow, since biomass can be equated to energy.
Yearly biomass production
(or energy flow) of:
producers
herbivores
carnivores

65. Note that pyramids of energy and yearly biomass production can never be inverted, since this would violate the laws of thermodynamics.
Pyramids of standing crop and numbers can be inverted, since the amount of organisms at any one time does not indicate the amount of energy flowing through the system.
E.g., consider the amount of food you eat in a year compared to the amount on hand in your pantry.

66. Represent food chains as pyramids of energy, numbers and biomass
It is possible to have inverted pyramids of numbers and biomass, but pyramids of energy are
always the ‘right way up’ because it is impossible to have more energy in a higher trophic level than
in a lower trophic level. Figure 3.3 shows a typical pyramid of energy.

67. Represent food chains as pyramids of energy, numbers and biomass

68. And that’s how it all works!