Cellular Energetics

Seven topics on how cells manage energy. Enzyme structure and why each active site fits only its substrate, enzyme catalysis and how enzymes lower activation energy without being consumed, the environmental impacts of temperature and pH that push enzymes past their optimum into denaturation, cellular energy and how ATP releases energy by hydrolysis, photosynthesis capturing light to build sugars, cellular respiration releasing that energy to make ATP, and how efficient metabolism ties directly to an organism's fitness.

Topics

3.1

Enzyme Structure

Enzyme Catalysis

Environmental Impacts on Enzyme Function

Cellular Energy

Photosynthesis

Cellular Respiration

Fitness

Lesson

Diag

locked

Key relationships Not a formula-heavy unit — the two core relationships to know

Photosynthesis

$$6\,CO_2 + 6\,H_2O + \text{light} \rightarrow C_6H_{12}O_6 + 6\,O_2$$

Cellular respiration

the reverse: $$C_6H_{12}O_6 + 6\,O_2 \rightarrow 6\,CO_2 + 6\,H_2O + \text{energy (ATP)}$$

Photosynthesis inputs

light energy is captured and stored in the bonds of glucose; the released O₂ comes from splitting water, not CO₂

Respiration output

glucose is oxidized to release that stored energy, which is transferred to ATP — cells do not create energy

Gibbs free energy

$$\Delta G = \Delta H - T\Delta S$$

Terms

ΔH = change in enthalpy, T = absolute temperature, ΔS = change in entropy

Spontaneity

ΔG < 0 = exergonic (spontaneous, releases energy); ΔG > 0 = endergonic (requires energy input)

What enzymes do

enzymes lower the activation energy of a reaction — they do not change ΔG or shift the equilibrium

Unit 3 tools

Challenge bank

1 / 60

60 open-ended problems.

Read the question, work it out, then flip the card to compare your reasoning to the worked solution. Mark each card so you can return to the ones that still bite.

Question

Tap card to reveal explanation

Worked solution

Tap card to return to question

Cumulative assessment

Test the unit.

Twenty mixed items pulled from across all 7 topics. Identifies which misconceptions still bite when you cannot see which topic the question came from.