Python Notes for mca i year students osmania university.docx
02 Energy Flow through Ecosystems
1. Energy Flow Through Ecosystems
• Inside the cell, source of energy is
adenosine triphosphate (ATP)
• The source of energy for making ATP is
other organic molecules such as
carbohydrates, lipids and proteins
(respiration)
• Energy is stored in carbohydrates, lipids
and proteins through photosynthesis
ALBIO9700/2006JK
3. First Trophic Second Trophic Third Trophic Fourth Trophic
Level Level Level Level
Producers Primary Secondary Tertiary
(plants) consumers consumers consumers
(herbivores) (carnivores) (top carnivores)
Heat Heat Heat
Solar
energy
Heat Heat
Heat Heat
Detritivores Heat
(decomposers and detritus feeders)
ALBIO9700/2006JK
4. Heat
Tertiary Heat
consumers Decomposers
(human)
Heat
10
Secondary
consumers
(perch)
Heat
100
Primary
1,000 consumers
(zooplankton) Heat
10,000 Producers
Usable energy (phytoplankton)
Available at
Each tropic level
(in kilocalories)
ALBIO9700/2006JK
5. • Producers – autotrophic organisms; organisms
that obtain its food from inorganic sources by
photosynthesis or chemosynthesis
• Consumers – heterotrophic organisms;
organisms that obtain its food in organic form,
either directly or indirectly from that which has
been synthesised by producers
• Decomposers/Detritivores – feed on detritus
(dead organisms and waste material, such as
dead leaves, faeces and urine)
ALBIO9700/2006JK
6. Scavengers Decomposers
Termite
Bark beetle Carpenter and
engraving ant carpenter
Long-
horned galleries ant work Dry rot
fungus
beetle
holes Wood
reduced
to Mushroom
powder
Time Powder broken down by decomposers
progression into plant nutrients in soil
ALBIO9700/2006JK
8. Food chains and food webs
• Food chain – the way in which energy
flows from producer to consumers
• Food web – inter-relationships between
many food chains
• Trophic level – the level in a food chain
at which an organism feeds
ALBIO9700/2006JK
11. Blue whale Humans Sperm whale
Crabeater Elephant
seal seal
Killer whale
Leopard
seal
Adelie
penguins Emperor
penguin
Squid
Petrel Fish
Carnivorous plankton
Krill Herbivorous
plankton
Phytoplankton
ALBIO9700/2006JK
12. • Herbivores – are always primary
consumers
• Carnivores – feed at several
different trophic levels in different
food chains
• Omnivores – animals which
regularly feed as both primary and
higher-level consumers
ALBIO9700/2006JK
13. Energy loss along food chains
• Energy is lost as heat when energy is
transferred from one form, or from one system,
to another
• Only small percentage of sunlight is converted
into chemical energy because:
– Some sunlight misses leaves
– Some sunlight reflected from surfaces of leaves
– Some sunlight passes through leaves
– Chlorophyll only absorbs certain wavelengths of light
– Energy losses as energy absorbed by chlorophyll is
transferred to carbohydrates during photosynthesis
ALBIO9700/2006JK
14. • Almost half of the chemical potential
energy stored by plants is used by the
plants themselves (released through
respiration/used for active transport)
• Losses between plants and primary
consumer:
– Not all parts of plants available to be eaten
– Not all parts eaten are digestible
– Energy losses as heat within consumer’s
digestive system
• Similar losses occur at each trophic level
ALBIO9700/2006JK
15. Productivity
• The rate at which plants convert light into
chemical potential energy – productivity
or primary productivity
• Kilojoules of energy transferred per
square metre per year (kJ m-2 year-1)
• Gross primary productivity – total
quantity of energy converted by plants in
this way
• Net primary productivity – energy
which remains as chemical energy after
the plants have supplied their own needs
in respiration
ALBIO9700/2006JK
Notas del editor
Figure 3.17 Natural capital: a food chain. The arrows show how chemical energy in food flows through various trophic levels in energy transfers; most of the energy is degraded to heat, in accordance with the second law of thermodynamics.
Figure 3.19 Natural capital: generalized pyramid of energy flow showing the decrease in usable energy available at each succeeding trophic level in a food chain or web. In nature, ecological efficiency varies from 2% to 40%, with 10% efficiency being common. This model assumes a 10% ecological efficiency (90% loss in usable energy to the environment, in the form of low-quality heat) with each transfer from one trophic level to another. QUESTION: Why is it a scientific error to call this a pyramid of energy?
Figure 3.13 Natural capital: various scavengers (detritivores) and decomposers (mostly fungi and bacteria) can “ feed on ” or digest parts of a log and eventually convert its complex organic chemicals into simpler inorganic nutrients that can be taken up by producers.
Figure 3.18 Natural capital: a greatly simplified food web in the Antarctic. Many more participants in the web, including an array of decomposer organisms, are not depicted here.
