Model Matter and Energy Cycling - Biology

$CO_2$. Plants absorb this gas from air to build glucose molecules.

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$. Breaks down glucose with oxygen to produce carbon dioxide, water, and ATP.

Aerobic cellular respiration. These are the characteristic inputs and outputs of cellular respiration.

Aerobic cellular respiration. This equation shows glucose being oxidized to release energy as ATP.

Photosynthesis. This equation shows light energy converting $CO_2$ and water into glucose.

$6$. Balance requires 6 oxygen molecules to produce 6 $CO_2$ molecules.

$6$. Balance requires 6 carbon atoms on each side of the equation.

Chloroplast: makes sugars; mitochondrion: makes ATP from sugars. Each organelle has a distinct role in energy conversion processes.

Photosynthesis. This process uses energy to assemble glucose from carbon dioxide.

Cellular respiration. This process breaks chemical bonds to release stored energy.

Exergonic (releases energy). This process releases energy by breaking down glucose molecules.

Endergonic (requires energy input). This process requires energy input to build glucose from smaller molecules.

Sugar (ultimately glucose, $C_6H_{12}O_6$). The Calvin cycle produces this organic molecule from $CO_2$ fixation.

ATP and NADPH. These energy carriers power the Calvin cycle reactions.

Respiration produces $CO_2$; photosynthesis consumes $CO_2$. These processes cycle carbon dioxide in opposite directions.

Photosynthesis produces $O_2$; respiration consumes $O_2$. These processes cycle oxygen in opposite directions between organisms and atmosphere.

Energy enters as light and leaves as heat; it does not cycle. Energy flows one-way through ecosystems and is ultimately lost as heat.

Atoms in $CO_2$, $H_2O$, glucose, and $O_2$ are rearranged and reused. Matter is conserved and recycled between these complementary processes.

Cellular respiration. This process releases carbon from organic molecules back to the atmosphere.

Photosynthesis (carbon fixation in the Calvin cycle). This process incorporates atmospheric carbon into organic compounds.

$H_2O$. Water molecules are split to provide electrons, releasing oxygen gas.

$H_2O$. Oxygen combines with electrons and protons to form this molecule.

$O_2$. This molecule receives electrons at the end of the transport chain.

Inner mitochondrial membrane. This membrane contains the protein complexes that transport electrons.

Oxidative phosphorylation (electron transport chain + chemiosmosis). This process uses electron flow to pump protons and synthesize ATP.

Mitochondrial matrix. This inner compartment houses the enzymes for the citric acid cycle.

Krebs cycle (citric acid cycle). This cyclical pathway completely oxidizes acetyl groups to $CO_2$.

Cytoplasm (cytosol). This cellular compartment is where glucose is initially broken down.

Glycolysis. This pathway breaks glucose into two pyruvate molecules.