APES Unit 1 FRQ

Trophic Levels

Primary producers, primary consumers, secondary consumers, tertiary consumers

Primary Consumer

An organism that makes its own food through photosynthesis or chemosynthesis

Primary Consumer

An herbivore that eats producers (e.g., rabbit, zooplankton).

Secondary consumer

A carnivore or omnivore that eats primary consumers (e.g., snake, small fish).

Tertiary Consumers

Apex predators- animals at the top of a food chain that eat secondary consumers and primary consumers

Arrows in food web

The arrows always point in the direction of energy flow (from the eaten → to the eater). For example, grass → rabbit means energy moves from the grass to the rabbit.

Ecosystem

A community of living organisms in conjunction with the non-living components of their environment, interacting as a system (result of biotic and abiotic interactions)

Biogeochemical cycles

Self regulating, naturally occurring movements of chemical molecules through various sources and sinks.

These help to stabilize and regulate the flow of matter through ecosystems

Carbon Cycle

A movement of atoms and molecules containing the element carbon between sources and sinks

Processes that remove carbon from the atmosphere

• Photosynthesis (plants, algae, phytoplankton take in CO₂ and use it to make glucose).

• Dissolution into oceans (CO₂ dissolves directly from air into seawater).

Process that returns carbon as gas to atmosphere

• Cellular respiration (organisms release CO₂ when breaking down glucose).

• Also, decomposition and combustion release CO₂ via microbial respiration and return in breakdown of glucose molecules, but respiration is the main biological one.

How atmospheric carbon gets into the ocean

Diffusion / dissolution: CO₂ gas diffuses across the air-sea interface and dissolves into surface water.

Biological pump: Marine organisms (like phytoplankton) use dissolved CO₂ in photosynthesis, and when they die, their carbon-rich shells and bodies sink, storing carbon in deep ocean sediments.

Terrestrial carbon sink

Forests, which store carbon in their biomass through photosynthesis and long-term accumulation of organic matter.

Human Activities Increasing CO₂

One human activity that increases carbon dioxide in the atmosphere is the burning of fossil fuels such as coal, oil, and natural gas, which releases large amounts of stored carbon.

Another activity is deforestation, which decreases the number of trees that can absorb carbon dioxide through photosynthesis and often releases additional carbon when the cleared vegetation is burned or decomposes.

Nitrogen Cycle

Movement of atoms and molecules containing nitrogen between sources and sinks

Fixation

N2 fixed by lighting or microbes in soil/root molecules

Ammonifixation

NH3 is converted into NH4+ by soil bacteria; NH3 can also be added by the decay of organic matter

Nitrifixation

Soil bacteria convert ammonia (NH₃/NH₄⁺) into nitrites (NO₂⁻) and then into nitrates (NO₃⁻), which plants can absorb

Assimilation

NO₃⁻ up taken by plants through roots (then to animals)

Dentrification

NO₃⁻ can be converted back to N2 by soil bacteria, which returns to the atmosphere

Primary productivity

The rate at which energy from the sun is captured by autotrophs (like plants, algae, and phytoplankton) and converted into chemical energy (glucose) through photosynthesis

GPP

Conversion of light energy to chemical energy

NPP

Energy accumulated in plant biomass