Chapter 46.3: Food Webs and Trophic Pyramids

Systems

 Set of interacting or interdependent components 

Open System

Resources including chemical substances and energy can enter or exit 

• Ecosystems: open systems as they depend on resources from other organism in their abiotic surroundings 

  • All the organism in an environment and their abiotic environment

  • Like dead matter going down a river

Closed System

Energy can enter or exit but chemical resources cannot be removed 

• Produces of sealed caves: Archaebacteria

  • Gain energy from chemical reaction that use methane, sulfides or other inorganic compounds as substrates

  • Chemosynthesis: The energy is then used to synthesis carbon compounds in this process

Sunlight

the initial source of energy in most ecosystems

• Harvested by producers through photosynthesis

  • Amount harvested/ available is variable due to the way sunlight works around earth 

    • Eg higher in the sahara desert but they have a lack of produces very low in colder countries but more producers 

• Water as a barrier for sunlight: Photosynthesis uses 400 to 700nm → the intensity that can reach lower is a lot higher and not a lot can actually reach 

  • High intensity like the blue colour is why the ocean is blue!!

Trophic Pyramid

 Shows energy and biomass at each level  

• Wide bas: Lots of producers - most energy that is available

  • The amount of energy needed to support each level increases but each level has less energy  

• Narrow Apex: Very few apex predators - least amount of energy 

Aquatic Ecosystems:

•  Trophic periods that are seemingly inverted - smaller producer biomass

• Produces have very fast reproduction but low biomass

• Consumers are much larger and have longer life spans 

• ENERGY FLOW STILL GOES FROM PRODUCERS TO HIGHER CONSUMERS

• Microorganism: In aquatics they fix N2 and decompose organic matter)

Parasites

• Can feed at multiple trophic levels (both producers or consumers)

Decomposers

•  Essential to recycle nutrients and carbon back to the environment 

Microorganisms

•  Fungi, bacteria and archaea → help break down matter and complete the carbon cycle 

Food Chain

Sequences of organism which feed on the previous one  - simple and linear

Producers

• Absorb sunlight and convert to chemical energy forming carbohydrates

  • Terrestrial Ecosystems: Vascular plants

  • Marine Ecosystems: Algae and cyanobacteria

    • Rely on chemoautotrophic bacteria and archaea

Autotrophs

• Use external energy sources (light or chemical) to synthesize their carbon compounds from inorganic substances - self feeding

  • Products: amino acids, sugar, fatty acids, etc…

  • Produce ATP through cellular respiration

  • Inorganic Substances: CO₂ HCO₃^-, nitrate phosphate etc…

  • Sources of energy: Needed due to the first reduction in the calvin cycle is endothermic

Sources of energy:

1. Photoautotrophs: Light absorbed by photosynthetic pigments

2. Chemoautotrophs: Exothermic inorganic chemical reactions

• Substrates in reduced states (S, HS, Fe, H, or NH₃) is oxidized and release energy that is used

• Iron-Oxidizing Bacteria - Acidithiobacillus Ferrooxidans: Remove electrons from Fe²⁺ after FeS₂ reacts with air → forming Fe³⁺  

  • The electron is used to carry energy through the membrane and reduces NAD

  • Or the electron is sued to form water 

Consumers

• Obtain energy by consuming other organism that have them 

  • Primary consumers eat producers, secondary consumers eat primary consumers

Heterotrophs

• Gain nutrients through other organism 

Assimilation

• Process of absorbing carbon compounds and making them part of the body

  • Molecules must be small and soluble 

• Produce ATP by cell respiration 

Apex Predator

•  On the top of the food chain - nothing eats it

Decomposer

• Dead organisms are digested by decomposers like saprotrophs 

  • Saprotrophs put their enzymes in the dead organism and digest it externally first before taking in its nutrients

  • Their hyphae secretes the enzymes out

Making food chains

complex and in actuality it's more web like - often eat many different trophic levels 

• Levels of the web show trophic levels but the arrows can go anywhere

• Energy pyramid: Shows the amount of energy gained by each trophic level per year 

  • Measured in unit area per year → 

Food Webs

 shows the many interconnected feeding relationships - more realistic 

• Food webs describe both energy transfer and carbon cycling through communities

Viral Loop

• Seen in ocean energy and carbon transfers 

  • Viruses alter the food web by infecting and lysing cells at EVERY level 

    • These viruses can kill 30% of primary producers → IN turn they mainly feed bacteria instead of primary consumers 

    • This then helps support different consumers and cause a different food web 

Energy Flow

 Does not cycle, only goes one way 

• 90% of energy is lost between trophic levels - only 10% passes on

Loss of energy between stages caused by….

1. Incomplete Consumption: Not fully consumed by organism in the next level like the bones or hair are left behind

2. Incomplete Digestion: Not all parts ingested are absorbed like hard fibers 

• It is egested in faeces and feces are given to decomposers

3. Cell Respiration: Substrates are oxidized in cell resperation carbon dioxide and water which are wastes that aren’t passed on to the next level 

• Going up the levels biomass decreases hence energy each trophic level contains lowers even though their energy per gram is a lot higher

Heat loss

Energy enters ecosystems as light until the energy is transformed into heat from organism back to the abiotic environment 

• Second law of thermodynamics: Energy transformations are never 100% efficient → a lot of it is transformed to heat 

  • Energy cannot be recycled in ecosystems unlike chemical elements - it will eventually radiate away 

• Because of the constant loss of energy - food chains are limited, can’t support another level 

Biomagnification

 Greater concentration of certain chemicals as it goes along the food chain 

• Sometimes the toxin can be taken up directly from the abiotic environment 

Bioaccumulation

Increase in the concentration of  toxin in body tissues during an animal's life

•  mainly the fat soluble toxins

• Micro and macro plastic pollution in the ocean can bioaccumulate or biomagnify in the organisms 

  • Macroplastic:  large visible debris like nuts ropes drink bottles

  •  micro plastic: normally smaller than 5 mm in diameter can be any shape