Pleiotropy

“One faulty gene in sickle-cell affects blood, pain and immunity together.”

A single gene influences several unrelated traits.

Memory trick: One gene, many effects.

Polygenic inheritance

“Human height comes from hundreds of genes adding up.”

Traits like skin colour and height are controlled by many genes together.

Memory trick: Many genes, continuous range.

Mutualism

“Bees get nectar and flowers get pollinated — everyone wins.”

A relationship where both species benefit.

Memory trick: Both benefit.

Parasitism

“A tapeworm feasts while its host goes hungry.”

One organism benefits at the host's expense.

Memory trick: One gains, one loses.

Commensalism

“Barnacles hitch a free ride on a whale that barely notices.”

One species benefits while the other is unaffected.

Memory trick: One benefits, other neutral.

Primary productivity

“NPP is the energy actually available to feed everything else.”

The rate at which producers capture energy; gross (GPP) minus respiration is net (NPP).

Memory trick: NPP = GPP − respiration.

Gel electrophoresis

“It's the fingerprint reader behind DNA forensics.”

Separates DNA fragments by size using an electric field through a gel.

Memory trick: Sorts DNA by size.

Bioreactor

“Giant steel tanks brew insulin and vaccines by the litre.”

A vessel that grows cells or microbes at scale to make useful products.

Memory trick: Scales up biological production.

Vaccination

“A vaccine is a wanted poster shown before the criminal arrives.”

Introducing a harmless form of a pathogen to train immunity in advance.

Memory trick: Trains immunity ahead of time.

Allergy

“Your immune system overreacts to an innocent speck of dust.”

An exaggerated immune response to a harmless substance like pollen.

Memory trick: Immune overreaction.

Cell theory — common mistake

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

A frequent error is forgetting Virchow's addition that cells come only from other cells. In reality, all living organisms are made of cells, and every cell arises from a pre-existing cell.

Memory trick: Schleiden + Schwann said 'all life is cells'; Virchow added 'cells from cells'.

Prokaryotic cell

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

A cell without a membrane-bound nucleus or organelles — like bacteria.

Memory trick: they do have DNA — it just floats in a nucleoid, with no nuclear membrane.

Prokaryotic cell — common mistake

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

A frequent error is thinking prokaryotes have no DNA at all. In reality, a cell without a membrane-bound nucleus or organelles — like bacteria.

Memory trick: they do have DNA — it just floats in a nucleoid, with no nuclear membrane.

Mitochondria — common mistake

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

A frequent error is assuming all cellular energy is made in mitochondria (glycolysis is in the cytoplasm). In reality, the powerhouse of the cell, where aerobic respiration makes most of the ATP; it has its own DNA.

Memory trick: mitochondria run the ATP-rich aerobic stage of respiration.

Ribosomes

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

Tiny non-membrane-bound structures that build proteins.

Memory trick: ribosomes have no membrane — they're just RNA + protein factories.

Ribosomes — common mistake

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

A frequent error is listing ribosomes as membrane-bound organelles. In reality, tiny non-membrane-bound structures that build proteins.

Memory trick: ribosomes have no membrane — they're just RNA + protein factories.

Cell membrane — common mistake

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

A frequent error is thinking the membrane lets everything pass freely. In reality, a selectively permeable boundary described by the fluid-mosaic model.

Memory trick: 'selectively permeable' — it chooses what enters and leaves.

prokaryotic cell vs eukaryotic cell

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

Prokaryotic cells (bacteria) have no nucleus or membrane-bound organelles; eukaryotic cells (plants, animals) have a true nucleus and organelles.

plant cell vs animal cell

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

A plant cell has a cell wall, chloroplasts and a large vacuole; an animal cell has none of these but has centrioles.

rough ER vs smooth ER

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

Rough ER is studded with ribosomes and makes proteins; smooth ER lacks ribosomes and makes lipids.

Myth: Prokaryotes lack DNA

“You are a city of ~37 trillion cells, each one a tiny factory that never clocks out.”

Prokaryotes do have DNA, held in a nucleoid region — they just lack a nuclear membrane.

Enzymes — common mistake

“Enzymes are molecular matchmakers — they let reactions happen in seconds that would otherwise take years.”

A frequent error is thinking enzymes are used up in the reaction. In reality, biological catalysts (mostly proteins) that speed reactions by lowering activation energy.

Memory trick: enzymes are reusable — they come out unchanged and act again.

Enzyme specificity — common mistake

“Enzymes are molecular matchmakers — they let reactions happen in seconds that would otherwise take years.”

A frequent error is assuming one enzyme can catalyse many unrelated reactions. In reality, each enzyme acts on a specific substrate, like a lock fitting only its key.

Memory trick: the active site's shape makes enzymes highly specific.

Proteins

“Enzymes are molecular matchmakers — they let reactions happen in seconds that would otherwise take years.”

Polymers of amino acids that build tissues, act as enzymes, and transport molecules.

Memory trick: all enzymes are proteins (mostly), but not all proteins are enzymes.