Honors Biology - Unit 6 ✅

10% rule

Only about 10% of the energy at one trophic level is transferred to the next level; the rest is lost as heat and life processes.

Abiotic factor

Nonliving parts of an ecosystem (temperature, water, sunlight, rocks, soil).

Autotroph

An organism that makes its own food using energy from sunlight or chemicals (producer).

Biotic factor

Living or once-living components of an ecosystem.

Calvin cycle

The light-independent reactions of photosynthesis that build sugars from CO₂ using ATP and NADPH.

Carbon fixation

The process of converting inorganic CO₂ into organic molecules (like G3P) during photosynthesis.

Chemical potential energy

Energy stored in chemical bonds of molecules.

Chlorophyll

The main green pigment in plants that absorbs light energy for photosynthesis.

Chloroplast

The organelle where photosynthesis occurs in plant and algal cells.

Commensalism

A symbiotic relationship where one organism benefits and the other is neither helped nor harmed.

Competition

Interaction where organisms fight for the same limited resources (food, space, mates, etc.).

Dark reaction

Another name for the Calvin cycle; does not require light directly.

Energy pyramid

A diagram showing the flow of energy through trophic levels in an ecosystem.

Food chain

A single pathway of energy flow

Food web

Interconnected food chains in an ecosystem

G3P (glyceraldehyde-3-phosphate)

A 3-carbon sugar produced in the Calvin cycle; can be used to build glucose and other molecules.

Glucose

A 6-carbon sugar (C₆H₁₂O₆) that stores chemical energy for cells.

Granum

A stack of thylakoids

Grana

Multiple stacks of thylakoids

Heterotroph

An organism that must consume other organisms for energy (consumer).

Keystone species

A species that has a disproportionately large effect on its ecosystem; its removal causes major changes.

Light reaction

First stage of photosynthesis; light energy is converted to chemical energy (ATP & NADPH) and oxygen is released.

Mutualism

A symbiotic relationship where both organisms benefit.

NADP⁺

an electron carrier molecule

NADPH

the reduced form of NADP⁺ that carries high-energy electrons to the Calvin cycle

Parasitism

A symbiotic relationship where one organism benefits and the other is harmed.

Photosynthesis

The process where plants, algae, and some bacteria convert light energy, CO₂, and H₂O into glucose and oxygen.

Photosystem

A cluster of chlorophyll and proteins in the thylakoid membrane that captures light energy.

Pigment

A molecule that absorbs specific wavelengths of light.

Predation

Interaction where one organism (predator) kills and eats another (prey).

Radiant energy

Energy that travels in electromagnetic waves, such as sunlight.

RuBP (ribulose bisphosphate)

A 5-carbon molecule that reacts with CO₂ in the Calvin cycle.

Rubisco

The enzyme that attaches CO₂ to RuBP during carbon fixation.

Stroma

The fluid-filled space inside a chloroplast surrounding the grana; site of the Calvin cycle.

Symbiosis

A close, long-term relationship between two different species.

Trophic cascade

A chain reaction in an ecosystem that occurs when changes at one trophic level affect many other levels.

Trophic levels

Feeding levels in an ecosystem (producers, primary consumers, etc.).

Thylakoid

Flattened membrane sacs inside chloroplasts where light reactions occur.