Eukaryota

          A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Most living organisms, including all animals, plants, fungi, and protists, are eukaryotes. The defining membrane-bound structure that differentiates eukaryotic cells from prokaryotic cells is the nucleus. The presence of a nucleus gives these organisms their name, which comes from the Greek. Many eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts and Golgi bodies.

          Cell division in eukaryotes is different from organisms without a nucleus (prokaryotes). It involves separating the duplicated chromosomes, through movements directed by microtubules. There are two types of division processes. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (having two instances of each chromosome, one from each parent) undergoes recombination of each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes). Each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes.

          Eukaryotes appear to be monophyletic, and so make up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features.

Plant cell wall: Plant cells have a cell wall, a fairly rigid layer outside the cell membrane, providing the cell with structural support, protection, and a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell. The major carbohydrates making up the primary cell wall of land plants are cellulose, hemicellulose, and pectin. The cellulose microfibrils are linked via hemicellulosic tethers to form the cellulose-hemicellulose network, which is embedded in the pectin matrix. The most common hemicellulose in the primary cell wall is xyloglucan.

Plant cell: Plant cells are eukaryotic cells that differ in several key respects from the cells of other eukaryotic organisms. Their distinctive features include:

• A large central vacuole, a water-filled volume enclosed by a membrane known as the tonoplast maintains the cell's turgor, controls movement of molecules between the cytosol and sap, stores useful material and digests waste proteins and organelles.

• A cell wall composed of cellulose and hemicellulose, pectin and in many cases lignin, and secreted by the protoplast on the outside of the cell membrane. This contrasts with the cell walls of fungi (which are made of chitin), and of bacteria, which are made of peptidoglycan.

• Specialised cell-cell communication pathways known as plasmodesmata, pores in the primary cell wall through which the plasmalemma and endoplasmic reticulum of adjacent cells are continuous.

• Plastids, notably the chloroplasts which contain chlorophyll and the biochemical systems for light harvesting and photosynthesis, but also amyloplasts specialized for starch storage, elaioplasts specialized for fat storage and chromoplasts specialized for synthesis and storage of pigments. As in mitochondria, which have a genome encoding 37 genes plastids have their own genomes of about 100-120 unique genes and probably arose as prokaryotic endosymbionts living in the cells of an early eukaryotic ancestor of the land plants and algae.

• Cell division by construction of a phragmoplast as a template for building a cell plate late in cytokinesis is characteristic of land plants and a few groups of algae, notably the Charophytes and the Order Trentepohliales

• The sperm of Bryophytes have flagellae similar to those in animals, but higher plants, (including Gymnosperms and flowering plants) lack the flagellae and centrioles that are present in animal cells.