Why is water so important to life?

Water is a polar molecule, so it forms hydrogen bonds. From that come cohesion and surface tension (water sticks to itself and moves up plants), adhesion (water sticks to surfaces), a high specific heat (water resists temperature change and buffers body and habitat temperatures), evaporative cooling (sweating), and being the universal solvent (the medium for the reactions and transport of life). Ice floats because water expands when it freezes, protecting aquatic life.

How does an enzyme speed up a reaction?

An enzyme is a biological catalyst, almost always a protein, that lowers the activation energy needed to start a reaction, so the reaction happens faster at the cell's temperature, without the enzyme being used up. Each enzyme's active site fits a specific substrate (lock and key). Rate rises with temperature up to an optimum, then falls because heat denatures the enzyme; each enzyme also has an optimum pH.

How are photosynthesis and cellular respiration related?

They are essentially opposite processes. Photosynthesis uses carbon dioxide and water plus light energy to build glucose and release oxygen, storing energy. Cellular respiration uses glucose and oxygen to release energy as ATP, producing carbon dioxide and water. The products of one are the reactants of the other, so together they cycle carbon, oxygen, and energy between organisms and the atmosphere. Plants do both.

Where does cellular respiration take place, and what is ATP?

Most aerobic cellular respiration takes place in the mitochondrion, whose folded inner membrane gives a large surface area, which is why energy-hungry cells have many mitochondria. The energy released from glucose is transferred to ATP (adenosine triphosphate), the cell's usable energy currency, which the cell spends on movement, active transport, and building molecules. Without oxygen, cells use fermentation, which yields much less ATP.

TennesseeBiology

Tennessee Biology I EOC LS1 (Biochemistry and Energy): a complete overview of water, macromolecules, enzymes, photosynthesis, and cellular respiration

Q: What does the biochemistry-and-energy part of LS1 on the Tennessee Biology I EOC cover?

It covers the properties of water (polarity, hydrogen bonding, cohesion, high specific heat, and being the universal solvent), the four macromolecules (carbohydrates, lipids, proteins, and nucleic acids) and their monomers and functions, how enzymes lower activation energy and how temperature and pH change their activity, photosynthesis (light energy stored as glucose), and cellular respiration (energy released from glucose as ATP). The recurring theme is energy and matter.

A deep-dive guide to the biochemistry-and-energy part of the LS1 core idea on the Tennessee Biology I EOC: the properties of water, the four macromolecules, how enzymes lower activation energy, photosynthesis, and cellular respiration, with the item types the EOC uses.

Generated by Claude Opus 4.815 min readBIO1.LS1Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What the biochemistry-and-energy part of LS1 demands
Water: the molecule of life
The four macromolecules
Enzymes
Photosynthesis
Cellular respiration
Check your knowledge

What the biochemistry-and-energy part of LS1 demands

The From Molecules to Organisms (LS1) core idea includes the chemistry that powers cells. This guide covers the biochemistry-and-energy half: the water that life depends on, the four macromolecules, the enzymes that run the reactions, and the two energy processes, photosynthesis and cellular respiration. (The cell-and-transport half of LS1 is in the cells and transport guide.) The recurring crosscutting concept is energy and matter: tracing how energy is captured, stored, released, and transformed, and how atoms are rearranged but never created or destroyed.

This guide ties together the matching topic pages, each with its own practice questions: the chemistry of life and water, the macromolecules of life, enzymes and activation energy, photosynthesis, and cellular respiration.

Water: the molecule of life

Water is polar (a slightly negative oxygen end, slightly positive hydrogen ends), so its molecules form hydrogen bonds. From this come cohesion and surface tension, adhesion, a high specific heat that buffers temperature, evaporative cooling (sweating), and being the universal solvent for the reactions and transport of life. Ice floats because water expands as it freezes, insulating the water below. Every special property of water traces back to its polarity.

The four macromolecules

Life's molecules are polymers built from monomers: carbohydrates (monosaccharides) for quick energy and structure; lipids (fatty acids and glycerol) for long-term storage and membranes; proteins (amino acids) for almost everything, including enzymes; and nucleic acids (nucleotides) for genetic information. The headline idea is structure and function: a protein's amino-acid order sets its folded shape, and its shape sets its job, so changing the sequence can change the function.

Enzymes

An enzyme is a protein catalyst that lowers activation energy so a reaction goes faster, without being used up. Its active site fits a specific substrate (lock and key). Rate rises with temperature to an optimum (more collisions), then falls because heat denatures the enzyme (the active site changes shape). Each enzyme has an optimum pH too. Increasing substrate concentration raises the rate until the active sites are saturated.

Photosynthesis

Photosynthesis captures light energy and stores it as glucose: $6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$ . It happens in the chloroplast, where chlorophyll absorbs light. Energy is transformed (light to chemical), not created. The oxygen is a by-product, and photosynthesis is the entry point of energy and carbon into ecosystems.

Cellular respiration

Respiration releases the energy in glucose as ATP: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$ . It is the reverse of photosynthesis, happening mostly in the mitochondrion. Without oxygen, cells use fermentation (lactic acid in muscle; alcohol and carbon dioxide in yeast), which yields far less ATP. Because the two processes interlock, they cycle carbon, oxygen, and energy, and plants do both.

The biochemistry-and-energy part of LS1 on the Tennessee Biology I EOC covers water (polar, hydrogen bonding gives cohesion, high specific heat, the universal solvent, and floating ice); the four macromolecules (carbohydrates from monosaccharides for quick energy, lipids from fatty acids and glycerol for storage and membranes, proteins from amino acids whose shape sets their function, and nucleic acids from nucleotides for genetic information); enzymes (protein catalysts that lower activation energy, fit a substrate lock-and-key, have an optimum temperature and pH, and denature when conditions change); photosynthesis (light energy stored as glucose, $6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$ , in the chloroplast); and cellular respiration (energy released from glucose as ATP, the reverse equation, in the mitochondrion, with fermentation when oxygen is absent). The recurring theme is energy and matter.

Check your knowledge

A mix of recall and reasoning questions covering the biochemistry-and-energy part of LS1. Attempt them under timed conditions, then check against the solutions.

State why water is described as polar. (1 mark)
Name one property of water that depends on hydrogen bonding and give an example of its importance to life. (2 marks)
Match each macromolecule to its monomer: carbohydrate, lipid, protein, nucleic acid. (4 marks)
Explain why a protein's function depends on its shape. (2 marks)
State what an enzyme does to the activation energy of a reaction. (1 mark)
Explain why enzyme activity falls sharply above its optimum temperature. (2 marks)
Write the word equation for photosynthesis. (2 marks)
State where most cellular respiration occurs and what energy molecule it produces. (2 marks)
Explain how photosynthesis and cellular respiration together cycle carbon. (2 marks)

Solutions

Q1: Oxygen attracts the shared electrons more than hydrogen, so water has a slightly negative oxygen end and slightly positive hydrogen ends (uneven charge).
Q2: Any one: cohesion or surface tension (water moves up plants; insects can stand on water); high specific heat (buffers body and habitat temperature); evaporative cooling (sweating cools the body); solvent (dissolves substances for reactions and transport).
Q3: Carbohydrate to monosaccharide; lipid to fatty acids and glycerol; protein to amino acid; nucleic acid to nucleotide.
Q4: The order of amino acids sets how the protein folds, and the folded three-dimensional shape determines what it can bind and do, so shape determines function.
Q5: It lowers the activation energy.
Q6: Above the optimum, heat breaks the bonds holding the enzyme's shape, so the active site changes shape (denatures) and can no longer bind the substrate, dropping the rate.
Q7: Carbon dioxide plus water, using light energy, produce glucose plus oxygen.
Q8: In the mitochondrion; it produces ATP.
Q9: Respiration releases carbon dioxide, which photosynthesis takes in to build glucose; the carbon moves between organisms and the air as the two processes run, so carbon is cycled rather than used up.

Sources & how we know this

Tennessee Academic Standards for Science — Tennessee Department of Education (2022)
Tennessee Comprehensive Assessment Program (TCAP) — Tennessee Department of Education (2024)