Multi-celled organisms begin as one cell that develops into a fetus which becomes a whole individual, under the control of genes that are switched on and off.
Animals grow and develop from a single cell, under the control of genes that are switched on and off under the influence of interactions between the cells.
Plants grow and develop from seeds which contain a small food store that provides the material for the initial growth, to the point where leaves form.
Most animals develop further after birth, having been born with some parts of them less developed than others. The undeveloped parts vary between species.
The development of a whole organism from a single cell is controlled by the genes found in every cell, but which are not necessarily active unless switched on.
Most multi-celled plants and animals have tissues, and all advanced organisms are made up of different tissues, in which different genes are active.
Plants use a variety of hormones as signals from one part of the plant to another. Gibberellin is an example of an important plant growth hormone.
Tissues form organs, and they are most easily studied in thin sections. How tissues form is a fascinating aspect of biology, still not fully understood
Specific genes are switched on in cells of a certain kind: in most cells, most of the genes do not operate at any given time. Many of them do not ever operate.
Aging is a natural process. The telomeres on the chromosomes shorten as an organism gets older, and this seems to mark the age of cells in some readable way.
The Eutheria, the placental mammals, go through a period of gestation after conception, when they are nurtured internally as their tissues develop.
An insect larva becomes a pupa which becomes an imago, showing development and redevelopment over several stages, with tissues being resorbed and reconstructed.
Gigantism and dwarfism occur when hormonal balances are uncontrolled in the developing body, so that the cells of the body receive confusing signals.
Apoptosis helps to shape developing organisms This is a form of controlled cell suicide which serves to shape the individual, removing excess material.
Development often involves recapitulation of some of the stages that were present in their distant ancestors. This leaves the way open for neoteny.
Stem cells are unspecialized cells that can give rise to other types of cell. Some stem cells are more versatile than others, as the cells are less committed.
The most versatile stem cells are embryonic stem cells, which are better referred to as totipotent stem cells, a less emotive and more accurate name.