🧬 Biology

Cells, taxonomy, genetics, and the history of biology.

Cell types and organelles

The key components of a typical animal and plant cell.

Nucleus
Holds the cell's DNA and directs its activities; surrounded by the nuclear membrane.
Mitochondrion
The cell's "power plant" – converts nutrients into energy (ATP) through cellular respiration.
Ribosome
Builds proteins from instructions carried by mRNA.
Cell membrane
The fatty membrane surrounding the cell that controls what enters and leaves.
Cytoplasm
The gel-like fluid inside the cell in which the organelles sit.
Chloroplast
Found only in plant cells – carries out photosynthesis, converting light into chemical energy.
Golgi apparatus
Packages and ships proteins to their destination inside or outside the cell.
Endoplasmic reticulum
A network of membranes that produces and transports proteins and lipids.

Taxonomy

The biological classification hierarchy, from broadest to most specific, illustrated with humans as an example.

RankHuman classification
DomainEukaryota
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderPrimates
FamilyHominidae
GenusHomo
SpeciesHomo sapiens

Genetics – key concepts

The building blocks of DNA and RNA, plus central concepts in heredity.

DNA bases
A
Adenine
Pairs with thymine (T)
T
Thymine
Pairs with adenine (A)
G
Guanine
Pairs with cytosine (C)
C
Cytosine
Pairs with guanine (G)
RNA bases
A
Adenine
U
Uracil
Replaces thymine in RNA
G
Guanine
C
Cytosine
Key concepts
Gene
Gene
A stretch of DNA that codes for a protein or trait
Chromosome
Chromosome
A tightly packaged strand of DNA
Allele
Allele
A variant of a gene
Genotype
Genotype
An organism's genetic makeup
Phenotype
Phenotype
The observable traits produced by the genotype
Mutation
Mutation
A change in the DNA sequence

History of biology

From Aristotle's classification to modern genetic engineering.

4th century BCE

Aristotle's classification

Aristotle groups living things by their characteristics – an early attempt at biological systematics.

1735

Linnaeus's systematics

Carl Linnaeus introduces the binomial naming system (genus + species), still used to name species today.

1859

Darwin's theory of evolution

Charles Darwin publishes "On the Origin of Species", describing natural selection as the driving force behind the diversity of species.

1866

Mendel's laws of inheritance

Gregor Mendel derives the basic rules of heredity from experiments with pea plants, founding the field of genetics.

1953

The structure of DNA

James Watson and Francis Crick describe DNA's double-helix structure, building on Rosalind Franklin's X-ray diffraction images.

2003

The Human Genome Project

Scientists map the entire human genome for the first time, opening new doors in medicine and genetics.

2012–today

CRISPR and modern genetic engineering

CRISPR-Cas9 technology enables precise DNA editing, revolutionising research, medicine and agriculture.

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