North Carolina Biology EOC: Bioenergetics - a complete overview of the chemistry of life, photosynthesis, cellular respiration, and homeostasis

What the bioenergetics content demands

The bioenergetics content sits in the From Molecules to Organisms strand and is about energy and matter inside living things. This guide runs from the chemical foundations (water and ATP), through the two great energy processes (photosynthesis and cellular respiration) and how they connect, to homeostasis, which keeps the internal conditions that all this chemistry needs. The recurring crosscutting concepts are energy and matter and stability and change.

This guide ties together the matching topic pages, each with its own practice questions: the chemistry of life and water, photosynthesis, cellular respiration, comparing photosynthesis and respiration, and homeostasis and feedback.

The chemistry of life

Water is essential because it is polar: this makes it the universal solvent, gives it cohesion, and lets it resist temperature change, so the chemistry of life can happen in a stable, watery medium. ATP is the cell's energy currency: it stores energy in the bonds between its phosphate groups and releases it by becoming ADP, which respiration recharges back to ATP.

Photosynthesis

Photosynthesis stores light energy as chemical energy in glucose: $6CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2$. It happens in the chloroplast, where chlorophyll absorbs light. The light-dependent reactions capture light and split water (releasing oxygen); the Calvin cycle uses that energy to build glucose from carbon dioxide. The rate is limited by light, carbon dioxide, and temperature.

Cellular respiration

Respiration releases the energy in glucose as ATP: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$. Aerobic respiration uses oxygen and makes a lot of ATP in the mitochondrion; anaerobic respiration (fermentation) makes little ATP without oxygen, producing lactic acid in muscle or ethanol and carbon dioxide in yeast. All living cells respire.

How they connect: matter cycles, energy flows

The two processes are nearly opposite, so the products of one are the reactants of the other. This means matter cycles (carbon and oxygen atoms are reused), while energy flows one way: in as sunlight, stored in glucose, released as ATP, and lost as heat. Plants do both processes; only cells with chloroplasts photosynthesise, but all cells respire.

Homeostasis

Homeostasis keeps internal conditions stable, mainly through negative feedback: a change is detected and a response opposes it, returning the condition to its set point. Examples are temperature (sweating and shivering) and blood glucose (insulin lowers it, glucagon raises it). Positive feedback instead amplifies a change (childbirth, clotting). Homeostasis protects the narrow range in which enzymes work.

Check your knowledge

A mix of recall and reasoning questions covering the bioenergetics content. Attempt them under timed conditions, then check against the solutions.

1. State two properties of water that make it important to life. (2 marks)
2. Name the molecule that acts as the cell's energy currency. (1 mark)
3. Write the word equation for photosynthesis. (2 marks)
4. State where the oxygen released in photosynthesis comes from. (1 mark)
5. Write the word equation for aerobic cellular respiration. (2 marks)
6. State two differences between aerobic and anaerobic respiration. (2 marks)
7. Explain how the products of photosynthesis and respiration are related. (2 marks)
8. Explain the statement "matter cycles but energy flows." (2 marks)
9. After a meal blood glucose rises. Name the hormone that lowers it and the organ that releases it, and state the feedback type. (3 marks)