Why chemistry first
The molecular foundation of everything
Last week you learned that algae cells are tiny factories with specialised departments. This week you learn what those factories are actually made of — and what they make. Chemistry is the language life speaks. You don't need to become a chemist. You need to understand enough to know why some molecules are worth thousands of dollars per kilogram while others are virtually worthless.
By the end of these two weeks, you'll understand what atoms and molecules are, why water is strange and essential, why carbon is the backbone of all life, and what the four families of biological molecules are — and which ones microalgae produce commercially.
Part 1 of 4
Atoms — the LEGO bricks of everything
An atom is the smallest unit of a chemical element that still behaves like that element. Everything physical — your chair, the air, a drop of pond water, a microalgae cell — is made of atoms.
Atoms are unimaginably small. A single human hair is about one million carbon atoms wide. Yet despite their size, atoms have structure: a dense central nucleus containing protons (positive charge) and neutrons (no charge), surrounded by a cloud of electrons (negative charge) orbiting at a distance.
A carbon atom — the skeleton of all biological molecules
Carbon has 4 outer electrons available for bonding — the reason it can form the complex molecular chains that life depends on.
The key idea is the outer shell of electrons. Atoms are most stable when their outer shell is full. To fill it, they share electrons with neighbouring atoms — forming bonds. These bonds are what hold molecules together.
The only chemistry rule you need to remember
Atoms bond together by sharing electrons. The bonds between atoms are what create molecules. Break those bonds and you release energy — this is what happens when you burn wood, digest food, or run a cell's metabolism. Form those bonds and you store energy — this is what happens in photosynthesis, when algae build sugar from CO₂ and sunlight.
The six elements of life
All living things are built from just a handful of elements. Six dominate, and they're worth memorising with the mnemonic CHNOPS.
C
Carbon
Atomic no. 6
The backbone. Forms chains and rings. Every organic molecule is carbon-based. Makes up ~18% of your body.
H
Hydrogen
Atomic no. 1
The most abundant. Bonds to carbon everywhere. Central to water (H₂O). Key to energy transfer in cells.
N
Nitrogen
Atomic no. 7
Essential for proteins and DNA. ~79% of air is N₂ but most organisms can't use it directly — making nitrogen availability the #1 growth-limiting factor for algae.
O
Oxygen
Atomic no. 8
In water, CO₂, and all major biomolecules. Also released as a byproduct of photosynthesis — algae produce ~50% of Earth's atmospheric oxygen.
P
Phosphorus
Atomic no. 15
In DNA, RNA, and ATP (energy currency). Also in cell membranes. Often the limiting nutrient in water bodies — why phosphate runoff causes algae blooms.
S
Sulphur
Atomic no. 16
In some amino acids, which determine how proteins fold. Algae also produce DMS (dimethyl sulphide) — the compound responsible for the "sea smell."
Part 2 of 4
Water — the strangest molecule in the universe
Water is so ordinary that we take it entirely for granted. But water is genuinely weird — it behaves unlike almost any other substance. And those weird properties are precisely what allow life to exist. Without water's strangeness, there would be no algae, no cells, no life at all.
The water molecule (H₂O) — bent geometry creates a "polar" molecule
Water molecules attract each other
Because water is "polar" (one end slightly negative, other slightly positive), water molecules are attracted to each other like tiny magnets. These attractions are called hydrogen bonds.
This is why water is liquid at room temperature (most molecules its size are gases). Algae need liquid water to survive — and liquid water only exists because of this stickiness.
Water resists temperature change
Water absorbs a huge amount of heat before its temperature rises. It takes far more energy to heat water than almost any other liquid — this property is called high specific heat capacity.
Oceans and ponds act as thermal buffers. Algae cultures don't overheat rapidly even in hot sun. This stability is essential for consistent photosynthesis.
Water is a universal solvent
More substances dissolve in water than in any other liquid. Because of its polarity, water pulls ions and charged molecules apart, surrounding them and keeping them dissolved.
All the nutrients algae need — nitrogen, phosphorus, iron, CO₂ — must be dissolved in water before the cell can absorb them. Growing algae is fundamentally about managing what is dissolved in water.
Ice floats on liquid water
Almost every substance is denser as a solid than as a liquid — but water is the opposite. Ice is less dense than liquid water and floats. This is because hydrogen bonds in ice arrange molecules in an open lattice.
This means lakes and ponds freeze from the top down, not bottom up — leaving liquid water underneath where algae (and fish) can survive winter.
Water has high surface tension
The hydrogen bonds between surface water molecules create a "skin" — strong enough for some insects to walk on. This is the highest surface tension of any common liquid.
Surface tension helps maintain the thin water films that keep microalgae suspended in upper sunlit layers of water bodies, where photosynthesis is most efficient.
Water participates in reactions
Water isn't just a medium — it actively participates in biological chemistry. Photosynthesis splits water molecules to extract electrons and produce oxygen. Digestion breaks molecules apart using water (hydrolysis).
The oxygen that algae release — half of Earth's atmospheric O₂ — comes directly from splitting water molecules during photosynthesis. Water is the raw material.
Part 3 of 4
Why carbon is special
Of the 118 known elements, one stands apart as the foundation of all life: carbon. It's not the most abundant element, not the most reactive, not the heaviest. But it has a unique combination of properties that makes it the perfect scaffold for building living molecules.
① Carbon makes 4 bonds
Carbon has exactly 4 outer electrons available for bonding. Most atoms make 1, 2, or 3 bonds. Carbon's 4 bonds let it connect to four other atoms simultaneously — the maximum connectivity of any common element. This is like a LEGO brick that can attach to four other bricks in all directions.
② Carbon bonds to other carbons
Carbon forms exceptionally strong bonds with other carbon atoms. This means carbons can chain together into long strings, rings, and branching networks. No other element does this as readily. These carbon chains and rings are the backbone of virtually every biological molecule — sugars, fats, proteins, DNA.
③ Carbon bonds are stable but breakable
Carbon bonds are strong enough to be stable at body temperature (molecules don't fall apart spontaneously) but weak enough to be broken by enzymes when the cell needs energy. This controllable stability is what makes carbon-based molecules ideal for storing and releasing energy on demand.
④ Carbon enables enormous diversity
Because carbon can chain, ring, branch, and bond with H, N, O, S, and P in almost unlimited combinations, it can form millions of structurally distinct molecules — each with different shapes and functions. Life's complexity is built on this molecular diversity. Astaxanthin, DHA, and DNA are all carbon-based but structurally completely different.
Carbon chains, rings, and branches — how complexity is built
Why this matters for microalgae value
The longer and more complex a carbon-based molecule, the more energy and molecular precision went into making it — and typically, the more valuable it is commercially. Bulk algae biomass is mostly simple carbohydrates (short carbon chains). Astaxanthin is a large, precisely-structured ring molecule. DHA is a 22-carbon chain with specific double bonds at specific positions. Pharmaceutical compounds are even more structurally elaborate. Molecular complexity = commercial value.
Part 4 of 4
The four families of biological molecules
Life uses millions of different molecules, but almost all of them belong to four families — sometimes called the four macromolecules of life. Microalgae make all four. Understanding each one tells you directly why certain algae products are valuable, how they're made, and what they do in the body.
Carbohydrates — the fuel and structure
Sugars, starches, cellulose — the most abundant molecules in living things
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What they are
Molecules made of carbon, hydrogen, and oxygen — always in roughly the ratio CH₂O, which is why they're called carbo-hydrates ("watered carbon"). Simple sugars like glucose are single units. Starches and cellulose are thousands of glucose units chained together.
What they do
Energy storage and release (glucose is the cell's primary fuel). Structural support (cellulose makes plant cell walls rigid). Cell signalling and identity (polysaccharides on cell surfaces act as identity tags).
What algae produce
Algae accumulate starch and other polysaccharides inside cells as energy reserves. They also produce unique polysaccharides on their surfaces — some with anti-inflammatory or immunostimulant properties.
Commercial relevance
Bulk algae biomass is ~30–50% carbohydrate by dry weight. Used as animal feed, biofuel feedstock (fermentable sugars), and specialty food ingredients. Also the raw material for bioplastics research.
Market price: ~$3–8/kg dry biomass
Proteins — the workers and builders
Enzymes, structural fibres, receptors — the molecules that do most of the actual work in cells
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What they are
Long chains of amino acids — small molecules that each contain a carbon, a nitrogen, an acid group, and a variable "side group." There are 20 different amino acids. A protein is a specific sequence of hundreds to thousands of them, folded into a precise 3D shape. The shape determines the function.
What they do
Enzymes (proteins that speed up chemical reactions — they run all of metabolism). Structural proteins (muscle, skin collagen, cell walls). Transport proteins (haemoglobin carries oxygen). Receptors (sense the environment). Antibodies (immune defence).
What algae produce
Spirulina is ~60–70% protein by dry weight — the highest of any natural food source. Chlorella is ~45–55%. Both contain all 9 essential amino acids, making them "complete" proteins equivalent to meat or eggs.
Commercial relevance
The alternative protein market. Spirulina protein for human nutrition and sport supplements. Chlorella as animal feed. The phycocyanin in Spirulina is a protein-pigment complex worth $500–1,500/kg as a natural blue food colourant.
Spirulina powder: $10–30/kg · Phycocyanin: $500–1,500/kg
Lipids (fats and oils) — the storehouse and membranes
Fatty acids, oils, waxes, sterols, pigments — the most energy-dense biomolecule family
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What they are
Molecules built on long carbon chains, mostly non-polar (they repel water — "hydrophobic"). This water-repelling property is fundamental: it's why cell membranes can form (oily molecules spontaneously arrange into a sheet in water), and why fats store more energy per gram than carbohydrates or proteins.
What they do
Energy storage (fat contains twice the energy of carbohydrate per gram). Cell membrane structure (phospholipids). Signalling hormones (many are lipid-based). Insulation and protection. Pigments like carotenoids (including astaxanthin) are also classified as lipids.
What algae produce
Under stress (nitrogen starvation, high light), algae divert energy from growth into producing lipids — sometimes 50–70% of dry weight. Key products: DHA and EPA (omega-3 fatty acids), astaxanthin, beta-carotene, lutein, zeaxanthin. These are all in the lipid family.
Commercial relevance
The highest-value products from algae are almost all lipids. DHA for infant formula, omega-3 supplements. Astaxanthin for aquaculture feed (salmon colour), cosmetics, supplements. The global omega-3 market alone exceeds $3 billion/year.
DHA oil: $50–200/kg · Astaxanthin: $2,000–5,000/kg
Nucleic acids (DNA and RNA) — the information
The molecules that store, copy, and execute the instructions for building all the other molecules
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What they are
Long chains of nucleotides — each nucleotide is a sugar + phosphate + one of four "bases" (in DNA: Adenine, Thymine, Guanine, Cytosine, abbreviated A, T, G, C). DNA is double-stranded (the famous double helix). The sequence of A, T, G, C letters encodes genetic information. RNA is single-stranded and acts as a messenger, carrying instructions from DNA to the ribosomes.
What they do
DNA stores the master instructions for making every protein in the cell. RNA copies specific instructions and carries them out of the nucleus to ribosomes, where proteins are built. DNA replication copies the instructions before a cell divides. This is the fundamental information flow of all life on Earth.
What algae produce
The algae genome (its complete DNA) encodes the instructions for every enzyme that builds every product — astaxanthin, DHA, phycocyanin, and the rest. Understanding which genes control which products is the foundation of algae genetic engineering.
Commercial relevance
DNA is the target of CRISPR and other genetic engineering tools — editing it changes what the organism produces. Sequencing algae genomes is now cheap and fast. Companies use genomics to find "super-producer" strains or to design algae that make novel molecules.
Key tool: whole genome sequencing now costs ~$200–$1,000/strain
Why molecular complexity drives price
Here is the direct connection between what you've just learned and the commercial landscape of microalgae. More structurally complex molecules require more enzymatic steps to build, more precise cellular conditions, and more sophisticated extraction — which is directly reflected in price.
Approximate market price per kg of dry or purified product
Bulk biomass
~$5/kg
Spirulina powder
~$20/kg
Chlorella extract
~$45/kg
DHA algae oil
~$150/kg
Phycocyanin (blue)
~$1,000/kg
Astaxanthin
~$3,500/kg
Pharma compounds
varies
Preview — what you'll fully understand in weeks 5–7
Now that you know what atoms, molecules, carbon, and the four biomolecules are — the equation that runs the microalgae industry makes intuitive sense. Photosynthesis is simply: carbon (from CO₂) + hydrogen (from H₂O) + energy (from sunlight) → carbon-chain molecules (sugars, fats, pigments) + oxygen.
6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂
carbon dioxide + water + sunlight → glucose (sugar) + oxygen released
carbon dioxide + water + sunlight → glucose (sugar) + oxygen released
Quick-reference summary
| Concept | One-line definition | Algae / commercial connection |
|---|---|---|
| Atom | Smallest unit of an element | Life is built from CHNOPS — these 6 elements make every algae product |
| Bond | Shared electrons linking atoms into molecules | Breaking bonds releases energy (metabolism); forming them stores it (photosynthesis) |
| Water | Polar molecule — solvent, thermal buffer, reaction participant | Medium for all algae growth; raw material for photosynthesis; O₂ released from it |
| Carbon | 4-bonding element that forms chains, rings, branches | Scaffold of every algae product. Complexity of carbon structure = commercial value |
| Carbohydrates | Sugar-based molecules — fuel and structure | Bulk algae biomass; biofuel feedstock; specialty polysaccharides |
| Proteins | Amino acid chains — workers, enzymes, structure | Spirulina protein (complete); phycocyanin (blue pigment/protein); enzymes in all metabolism |
| Lipids | Fat-based molecules — membranes, energy, pigments | DHA, EPA (omega-3s); astaxanthin, beta-carotene; highest commercial value category |
| Nucleic acids | DNA / RNA — information storage and execution | The genome encodes all product-making enzymes; target for CRISPR engineering |
Self-check — end of week 4
Try each question from memory. Reveal the answer only after you've attempted it.
1. An algae company says their product is "carbon-neutral." Using what you know about carbon and photosynthesis, explain why algae-based products could genuinely make this claim — and what condition must be met for it to be true.
Algae fix CO₂ from the atmosphere (or from industrial emissions) into their carbon-chain molecules during photosynthesis. If the product is then used in a way that eventually returns that CO₂ to the atmosphere (burned for fuel, composted, digested), the cycle is theoretically carbon-neutral — the CO₂ released equals the CO₂ that was captured. The condition: the energy used to grow and process the algae must itself be low-carbon. If a diesel-powered facility grows algae to make "green" biodiesel, the net carbon balance may still be positive. Life-cycle analysis (Phase 4 of this curriculum) is how this claim is rigorously tested.
2. Why does nitrogen limitation cause algae to produce more lipids (oils and pigments) instead of proteins? Explain using your knowledge of CHNOPS.
Proteins require nitrogen — every amino acid contains an N atom. When nitrogen is scarce in the growth medium, the cell cannot build protein. But it can still run photosynthesis (which only requires C, H, and O from CO₂ and H₂O). The cell continues to capture energy from sunlight, but with no nitrogen to build protein, it diverts that energy into lipid synthesis instead — which requires only C, H, and O. This is why nitrogen starvation is the standard commercial technique for triggering high lipid or astaxanthin accumulation in species like Haematococcus and Nannochloropsis.
3. Astaxanthin is classified as a lipid. DHA is also a lipid. Yet they are worth different amounts and do completely different things in the body. How is that possible if they're in the same family?
The lipid family is defined by a shared property (water-repelling, carbon-chain based) not by identical structure or function. Just as "proteins" includes both hair keratin and digestive enzymes — vastly different in structure and function — lipids span an enormous range. Astaxanthin is a carotenoid: a ring-based molecule with a very specific arrangement that gives it antioxidant properties and the red-orange colour. DHA is a fatty acid: a 22-carbon chain with specific double bonds that make cell membranes fluid and support brain function. Same family, completely different architecture and biological role. Commercial value reflects the difficulty of producing and isolating each specific structure.
4. If you dissolved a teaspoon of table salt in water, what property of water is making that possible — and why does this same property make water essential for growing algae?
Water's polarity makes it the universal solvent. The slightly negative oxygen end of water molecules is attracted to positive sodium ions (Na⁺), and the slightly positive hydrogen ends are attracted to negative chloride ions (Cl⁻). Water surrounds and separates the ions, keeping them dissolved. The same mechanism applies to all the nutrients algae need: nitrogen (as nitrate NO₃⁻), phosphorus (as phosphate PO₄³⁻), iron, and trace minerals must all dissolve in the growth medium before the cell can absorb them through its membrane. Managing the dissolved chemistry of the growth water — pH, nutrient concentrations, salinity — is the fundamental practical skill in algae cultivation.
5. Silicon (Si) sits directly below carbon in the periodic table and also forms 4 bonds. Some scientists call it a theoretical alternative basis for life. Why do you think carbon-based life, not silicon-based life, actually evolved on Earth?
Several reasons. Carbon forms bonds with other carbons that are stable in water at moderate temperatures; silicon-silicon bonds are much weaker. Carbon dioxide (CO₂) is a gas at Earth temperatures and easily dissolves in water — making it a readily available building block. Silicon dioxide (SiO₂) is solid (sand/quartz) and nearly insoluble in water — nearly impossible to use as a raw material. Carbon forms single, double, and triple bonds with remarkable versatility; silicon is much more limited in bond diversity. And carbon-based molecules are stable at the temperature range of liquid water — the solvent that life depends on. That said — note that diatom algae do use silicon for their glass cell walls, making algae the one form of life on Earth that bridges both chemistries.