Notes on Sugars, Respiration, Biomass, Carbon Cycle, Upwelling, and Orographic Effects
Sugars and their digestion
Sucrose and glucose are types of sugars; they are large organic molecules with carbon rings linked to one another.
Cellulose is described as a type of sugar; in biology, cellulose is a polysaccharide formed from glucose units. Humans (and many organisms) do not decompose cellulose as effectively as other carbohydrates via aerobic cellular respiration.
As oxygen breathers, many organisms use oxygen as an external electron acceptor in cellular respiration (aerobic respiration).
Anaerobic respiration uses a different terminal electron acceptor instead of oxygen; when oxygen is not used, the same reaction to break apart sugar for energy can proceed via alternative pathways.
Fermentation (e.g., by yeast) is a form of anaerobic respiration; it can produce byproducts such as CO₂ and ethanol (and other gases depending on the organism and substrate).
Organisms in environments with little to no oxygen (e.g., deep sediments, marshes) may rely on anaerobic processes; these environments can produce gases such as methane, CO₂, or other reduced gases.
Summary: organisms can obtain energy from sugars with or without oxygen, using aerobic respiration, anaerobic respiration, or fermentation depending on oxygen availability.
Biomass and trophic levels
Biomass is the total dry weight of all organisms in an area or ecosystem; it includes both primary producers and all consumers.
If you dehydrated and weighed all organisms (from primary producers to top predators like elephants or lions), you would obtain the total biomass of the system.
Primary producers contribute a large portion of biomass at the base, but higher trophic levels (herbivores, carnivores) also contribute to overall biomass.
Biomass typically decreases from the base (primary producers) to higher trophic levels due to energy losses at each transfer (not explicitly quantified here, but a general rule in ecology).
When you accumulate all biomass at a given trophic level and compare to the level below, you’re observing the transfer of energy and material through the food web.
If you dehydrate and weigh the entire set of organisms at each trophic level, you can illustrate how much biomass resides at the base vs. higher levels.
Digestion and macromolecules
A typical protein/plasma energy example: if you start with about 100 calories in a food item (e.g., peanuts), the digestion process breaks down macromolecules (carbohydrates, proteins, fats) into smaller units for absorption.
The first outputs are the smaller macromolecules (e.g., monosaccharides, amino acids, glycerol/fatty acids).
There is weight loss at each step from digestion and absorption, due to metabolic use, excretion, and inefficiencies in energy capture.
This illustrates that not all ingested mass becomes body mass; some is respired, excreted, or lost as heat during metabolism.
Carbon cycle: carbon fixation and primary productivity
CO₂ is a gas and is inorganic; organic molecules (containing carbon) are produced via carbon fixation.
Carbon fixation is the process of converting inorganic CO₂ into organic molecules within living organisms (e.g., via photosynthesis in plants and phytoplankton).
The rate of primary productivity is the rate at which CO₂ is converted into organic carbon at a given location and time; it measures how much CO₂ is fixed into biomass per unit area per unit time.
Equations (conceptual):
Primary productivity rate: where C is the carbon in organic matter, with units typically (or similar).
Related concept: growth rate vs. rate. Growth rate is how much an organism grows over time at a location; a rate is inherently time-dependent and can vary.
Primary productivity is a foundational process that fuels secondary production (see below).
Primary vs. secondary production
Primary production refers to the rate of carbon fixation by autotrophs (e.g., photosynthetic organisms). It is about converting CO₂ into organic matter.
Secondary production is the rate of growth of heterotrophs (consumers) driven by consuming the organic matter produced by primary producers; it is not directly about atmospheric CO₂ fixation.
Growth rate concept: growth is the amount an organism increases in size/biomass over time; rates change over time depending on resources and conditions.
Secondary production is linked to how fast consumers convert ingested organic material into new biomass; it is a key measure of energy transfer up the food web.
Process link: growth of consumers (secondary production) is fueled by the glucose and other organic molecules produced by primary producers and later returned to CO₂ via cellular respiration.
Cellular respiration (in all organisms) returns glucose and other organic molecules to CO₂ and water, releasing energy used for maintenance and growth.
In respiration: organic molecules are oxidized to CO₂ and H₂O, generating energy for cellular processes.
Growth, respiration, and energy flow in ecosystems
Growth rate vs. respiration: growth requires energy, which is produced by respiration; respiration returns carbon in the form of CO₂.
The overall flow of carbon through the system includes fixation, production, consumption, respiration, and release back to the atmosphere as CO₂.
As nutrients enter marine systems (e.g., via upwelling), growth can proceed explosively if resources are abundant; this is a hallmark of exponential growth when resources are not limiting.
Upwelling, nutrient inputs, and exponential growth
Upwelling: nutrient-rich, cold water rises from deep in the ocean to the surface, supplying a pulse of nutrients to surface waters.
Result: rapid, exponential growth in phytoplankton (primary producers) due to an influx of nutrients.
Follow-on effect: exponential growth of zooplankton (herbivores that feed on phytoplankton) as primary producers explode in biomass.
Biomass increases can be synchronized, particularly during spring upwelling events.
Carrying capacity concept: at some point, nutrient inputs from upwelling may diminish (upwelling may subside), leading to a crash in phytoplankton biomass because resources (nutrients) drop back to baseline.
When phytoplankton crash, higher trophic levels that relied on phytoplankton (e.g., forage fish) may also follow with reduced growth or declines.
Higher-level predators (e.g., tuna) rely on the earlier biomass, but their growth rates may not show the same rapid peaks as phytoplankton; they feed on multiple prey items and have longer lifespans.
Economic note: large fish like tuna can be extremely valuable; some individuals are worth significant amounts (described as “millions” in popular context).
Phytoplankton–zooplankton dynamics and biomass peaks
Spring upwelling can lead to a large, temporary increase in phytoplankton biomass, followed by a corresponding rise in zooplankton biomass.
If upwelling ceases, nutrient supply declines, and phytoplankton populations may crash, affecting the entire food chain above them.
The response of higher trophic levels depends on their feeding strategies and the time lag between primary production and consumer growth.
Higher trophic levels and ecosystem dynamics
As biomass shifts with upwelling events, higher trophic levels (e.g., large fish like tuna) experience indirect effects through changes in prey availability and growth opportunities.
The overall biomass supporting these higher predators is a fraction of the base biomass, leading to lower absolute biomass at higher trophic levels compared to primary producers.
The energy and material transfer through trophic levels is not perfectly efficient; a lot is lost as heat or through other metabolic processes.
Orographic effects and atmospheric movement (mountain ranges)
When air approaches a mountain range, it is typically warm and dry at the windward edge before it is forced to rise due to the terrain.
As air rises (orographic lift), it cools and condenses moisture, often causing precipitation on the windward side of the range.
The rising air leads to cloud formation and rainfall, shaping local climate and ecosystems on both windward and leeward sides.
Connections to foundational concepts and real-world relevance
Energy flow and ecological efficiency: energy enters ecosystems via primary production and is transferred to higher trophic levels with losses at each step.
Population dynamics: growth rates, carrying capacity (K), and resource limitation shape biomass distribution and species interactions (
Example: upwelling-driven pulses followed by crashes illustrate how resource pulses drive population dynamics and community structure).
Biogeochemical cycles: carbon fixation anchors the link between atmospheric CO₂ and organic carbon pools in ecosystems; respiration and decomposition return CO₂ to the atmosphere, completing the cycle.
Human relevance: understanding biomass distribution and upwelling dynamics informs fisheries management, ecosystem services, and responses to environmental change (e.g., nutrient loading, climate-driven shifts in productivity).
Key terms to remember
Sucrose, glucose, cellulose
Aerobic respiration vs. anaerobic respiration
Fermentation
Biomass
Primary producers and primary productivity
Secondary production
Carbon fixation
Organic vs inorganic carbon
Upwelling
Phytoplankton and zooplankton dynamics
Carrying capacity (K)
Exponential growth
Orographic lift and rain shadow
Respiration and energy transfer through trophic levels