Ecology: Energy Flow, Primary Productivity, and Photosynthesis

Vocabulary flashcards covering ecological energy capture, trophic transfer efficiency, chemosynthesis, photosynthesis, photorespiration, and plant adaptations.

Chemosynthesis

A biological process by which autotrophs capture energy from chemical compounds (such as $H_2S$ or ammonia) rather than sunlight to synthesize carbohydrates without light energy.

Hemiparasite

A partially parasitic plant (such as mistletoe) that is green and capable of photosynthesizing, but possesses specialized roots to extract sugars and nutrients from a host plant.

Holoparasite

A fully parasitic plant that lacks green coloration, cannot perform photosynthesis, and derives all of its nutrients and sugars entirely from a host plant.

Obligate Parasite

A parasite that relies entirely on a host organism to survive and meet its nutritional requirements, analogous to a holoparasitic plant.

Facultative Parasite

A parasite that can obtain nutrients parasitically but is also capable of feeding or surviving through alternative non-parasitic means.

Net Primary Productivity

The total amount of organic matter produced by autotrophs in an ecosystem, which serves as the primary driver determining ecosystem diversity and food web length.

Ecosystem Solar Radiation Capture

The proportion of incident solar energy captured directly by photoautotrophs, generally averaging about $1\%$ (typically ranging from $0.5\%$ to $2\%$).

Trophic Transfer Efficiency

The rule of thumb that only about $10\%$ of the energy consumed at one trophic level is typically incorporated into the next consumer level, with the remainder lost to metabolism/respiration, excretion, or non-digestible tissue.

Inverted Biomass Pyramid

An atypical biomass distribution occurring in marine open oceans where primary producer biomass (phytoplankton) at a single snapshot in time is smaller than consumer biomass (zooplankton) due to extremely rapid turnover and reproduction.

Nitrifying Bacteria

The most abundant chemosynthesizers on Earth, which oxidize toxic ammonia ($NH_4$ or $NH_3$ from animal excretion and protein breakdown) into nitrite, and subsequently into nitrate ($NO_3$) for plant use.

Nitrogen Fixation

The bacterial conversion of atmospheric nitrogen ($N_2$) into a biologically usable form, such as nitrate.

Denitrification

The bacterial process that converts biologically usable nitrogen compounds (such as nitrate) back into atmospheric nitrogen gas ($N_2$).

Light Compensation Point

The specific light level at which a plant's rate of photosynthesis exactly equals its rate of cellular respiration, resulting in net zero $CO_2$ exchange.

Light Saturation

The point beyond which increasing light intensity does not increase the photosynthetic rate because the plant's enzymatic and photosynthetic machinery is operating at maximum capacity.

Chlorophyll f

A specialized pigment found in certain cyanobacteria that absorbs light toward the red end of the spectrum, providing an adaptation for survival under shaded plant canopies.

Ecotype

Populations of the same species that have developed distinct physiological adaptations suited to their specific local environments (e.g., desert populations versus coastal populations).

Rubisco

The critical enzyme responsible for fixing carbon dioxide ($CO_2$) in the Calvin cycle to build sugars, which can also non-selectively bind oxygen ($O_2$).

Photorespiration

A wasteful biochemical pathway occurring when Rubisco binds to $O_2$ instead of $CO_2$, causing the plant to consume energy and release $CO_2$ without producing sugars; this is exacerbated by high light and high heat.

Stomata

Microscopic pores on leaf surfaces regulated by guard cells that allow $CO_2$ uptake and $O_2$ release, which close under hot, dry conditions to conserve water, leading to internal $O_2$ buildup.

Malate

A four-carbon intermediate molecule produced in $C_4$ and CAM plants that temporarily stores captured $CO_2$, allowing plants to decouple carbon capture from photorespiration.

Photosynthesis

primary route for solar energy to enter biological food webs via conversion of light energy into chemical energy through the production of glucose and oxygen from carbon dioxide and water

Autotroph

organism that capture and convert solar or chemical energy into organic compounds for use as food.

photoautotroph

organism that captures solar energy

chemoautotroph

organism that captures energy from chemical bonds of inorganic compounds

heterotroph

organism that obtains energy by consuming organic compounds from other organisms

trophic hierarchy

Primary Producers (Autotrophs) $\rightarrow$ Primary Consumers (Herbivores) $\rightarrow$ Secondary Consumers (Primary Carnivores) $\rightarrow$ Tertiary Consumers (Secondary Carnivores)

high net primary production

supports complex, multi-tiered food webs; tropical rainforests, wetlands

low net primary production

maintain shorter food chains and simpler ecosystems; open ocean, deserts, tundra

light-dependent reactions of photosynthesis

occur in thylakoid membranes, split water molecules to release oxygen and produce ATP and NADPH

calvin cycle

light independent, uses ATP and NADPH to convert carbon dioxide into glucose and sucrose

C3 plants

standard fixation pathway; highly susceptible to photorespiration under hot, dry temperatures

C4 plants

plants that use an alternative pathway for carbon fixation that produces malate to isolate oxygen minimize photorespiration, adapting to high temperatures and light intensities

CAM plants

plants that fix carbon dioxide at night, converting it to malic acid for use during the day, adapting to arid conditions.