Life Processes &
the Chemistry of Life

The cellular process by which an organic substance (usually glucose) is chemically converted to release energy — captured as ATP — for life functions. Not the same as breathing, which is the gas exchange of getting oxygen into the body and CO₂ out.

Getting rid of chemical waste from cellular metabolism — CO₂, urea, ammonia, salt. Not the same as egestion, which is the expulsion of undigested food as faeces. Excretion gets rid of waste the body made; egestion gets rid of waste the body never absorbed.

Any change in the internal or external environment of an organism — light, temperature, touch, sound, smell, chemical balance. Organisms with sensitivity detect stimuli and react. A sea anemone closing when you touch it has detected a tactile stimulus.

Able to produce its own energy-rich food from inorganic compounds and an external energy source — plants and algae do this with photosynthesis (light energy); some deep-sea bacteria do it with chemosynthesis (chemical energy). Opposite: heterotrophic, organisms that must eat other organisms.

A compound containing carbon covalently bonded to hydrogen (and often oxygen, nitrogen, phosphorus too). Includes all carbohydrates, lipids, proteins and nucleic acids. Inorganic compounds — like water and salt — can contain carbon (e.g. CO₂) but never C and H together.

A chemical that speeds up a reaction without being used up by it. In biology, almost all catalysts are enzymes (a kind of protein). One enzyme can catalyse millions of reactions before wearing out.

What happens when a protein is exposed to high heat or extreme pH — it loses its precise 3D shape and stops working. The egg white going from clear to white as you cook it is denaturing in action. Why thermoregulation matters so much for living organisms.

The building block of nucleic acids. Each one is a sugar (deoxyribose in DNA, ribose in RNA) bonded to a nitrogen base and a phosphate group. Strung together by the millions, they form the DNA and RNA molecules that carry genetic information.

The monomers of proteins. There are 21 protein-forming amino acids; the number, combination and order of them decides which protein you get, and therefore its shape and its job. Each contains C, H, O and N — and it is that nitrogen that later has to leave as ammonia and urea.

Chemical processes enabling the production of larger, more complex compounds from smaller ones — building up. Joining amino acids into a protein is anabolic. It costs energy. Opposite of catabolic.

Very important proteins in animal immune systems which enable them to recognise, then target and destroy invasive pathogens. They work by shape-matching, which is why they are proteins and why heat destroys them.

Adenosine Triphosphate — the unstable energy-carrying molecule within most cells performing life processes. Made by respiration, spent by everything else. "Unstable" is the whole point: it gives its energy up easily, so it cannot be stockpiled.

Chemical processes in which complex compounds are broken into smaller ones — breaking down, e.g. digestion. It releases energy. Opposite of anabolic. Respiration is catabolic.

The process in which a cell develops from an unspecialised cell to a more specialised one — changing its structure so it can do a specific job. It is how one fertilised egg becomes an organism with eyes, gills and muscle.

The separation of an ionically bonded molecule into two or more ions in solution. Salt dissociating into Na⁺ and Cl⁻ in water is the example — and it only happens because water is a dipole. Once dissociated, the ions can react.

The process whereby an animal gets rid of undigested waste material in the form of faeces. Not excretion. Egestion removes what was never absorbed; excretion removes what the body's own metabolism made.

Proteins which act as catalysts in organic processes, facilitating both anabolic and catabolic reactions. Note the word both — an enzyme that only broke things down would be half a definition, and CAPS says "breaking down or synthesising".

Information passed from adults to offspring in the form of genetic material, which dictates their physical makeup and functioning. Carried by the nucleic acids — DNA and RNA.

Unable to produce its own food, and therefore relying on external sources of organic compounds from dead or living organisms. Every fish, whale, shark, squid and human. Opposite of autotrophic.

Organic compounds produced and released within an organism to trigger a response elsewhere within it — often proteins. They regulate growth, sexual maturation, metabolic rate and the response to danger. They find their target because membrane proteins recognise them.

An adverse reaction or condition due to taking in too much of a specific vitamin. It is mostly a risk with the fat-soluble vitamins (A, D, E, K), because those are the ones the body stores rather than excretes.

All elements and compounds which do not have a combination of Carbon and Hydrogen, or chains of Carbon, in them. Water and salts are inorganic. CO₂ contains carbon but no C–H bond, so it counts as inorganic too.

Chemical compounds needed in larger amounts. In this topic: Ca, Na, K, P, Mg and S. Do not confuse with micronutrients — one syllable apart, opposite meaning.

The sum total of all chemical reactions taking place within an organism — anabolic and catabolic together. Respiration, photosynthesis, digestion and muscle contraction are all metabolic processes, and all of them generate the waste that excretion has to remove.

Chemical compounds needed in smaller amounts, also called trace elements. In this topic: Cu, Zn and Fe. "Trace" describes the quantity, not the importance — no iron means no haemoglobin.

Biological sense (use this one): inorganic ions absorbed in relatively small amounts, taken up as compounds or dissolved ions, never as elements, and used as structural components or to enable chemical processes.

⚠️ Your booklet's glossary gives a geological definition instead — "inorganic crystalline material obtained by mining…mostly found in rocks". That is the right definition in Topic 10 and the wrong one here. See the flag in Section three.

The chemical building blocks of larger compounds. Monosaccharides are the monomers of carbohydrates, amino acids of proteins, nucleotides of nucleic acids. Learn the word and three examples together — it is a one-mark question.

Large, complex molecules made up of monomers (nucleotides) consisting of a sugar bonded to a nitrogen base and a phosphate group. They occur as DNA and RNA, and store and transfer hereditary information.

A combination of a large number of amino acids bonded together — normally more than 50, at which point it is called a protein. Two joined amino acids make a dipeptide; many make a polypeptide.

A fluid in which other molecules, known as solutes, can dissolve to form solutions. Water is the biological solvent, and it is good at the job because it is a dipole — which is the link straight back to Section three.

The ability to regulate and maintain a favourable body temperature. It matters because enzymes go inactive when too cold and are denatured when too hot — so an organism that cannot hold its temperature loses enzyme function across the board.