Plant Cell and Animal Cell

Plant cells and animal cells are both eukaryotic, and so they share the fundamental architecture common to all eukaryotic cells: a true, membrane-bound nucleus, and a common set of membrane-bound organelles carrying out compartmentalised functions within the cytoplasm. Despite this shared underlying plan, the two cell types differ in several structural respects that reflect the very different ways plants and animals live -- a plant, rooted in place and manufacturing its own food by photosynthesis, has very different structural needs from an animal, which typically moves about and obtains its food by ingesting other organisms.

The most conspicuous difference is the presence of a rigid cell wall surrounding the plasma membrane of a plant cell, built mainly from cellulose along with hemicellulose, pectin and structural protein -- a feature entirely absent in animal cells, which are bounded only by the plasma membrane and are consequently far more variable and often more rounded or irregular in outline than the comparatively fixed, box-like shape typical of a mature plant cell. This wall, examined in more detail in the next section, gives the plant cell mechanical support and protection that the animal cell must obtain by other means, such as an internal or external skeleton at the level of the whole organism.

Plant cells uniquely contain plastids -- chloroplasts, chromoplasts and leucoplasts -- discussed in detail later in the chapter, which are entirely absent from animal cells. Chloroplasts, containing the green pigment chlorophyll, are what allow a plant cell to carry out photosynthesis and manufacture its own organic food, a capacity no animal cell possesses.

A mature plant cell also typically contains one very large, prominent central vacuole, often occupying as much as 90 per cent of the total cell volume, which pushes the cytoplasm and its organelles into a thin peripheral layer close to the cell wall. Animal cells, by contrast, generally contain only small vacuoles, or none at all, though some single-celled protists possess specialised vacuoles of their own, such as the contractile vacuole used by Amoeba to expel excess water, or temporary food vacuoles formed around ingested particles.

Centrioles -- paired, cylindrical organelles involved in organising the spindle apparatus during cell division -- are a regular and prominent feature of most animal cells but are generally absent from the cells of higher plants, though they do occur in some lower plant groups such as certain algae and bryophytes. Lysosomes, similarly, tend to be more numerous and functionally prominent in animal cells, where they carry out much of the cell's intracellular digestion; in plant cells, this digestive and storage role is largely taken over by the large central vacuole instead, so distinct lysosomes are comparatively few or, in some accounts, considered functionally replaced by the vacuole. …