Plant cells are also notorious for having huge vacuoles. Up to 90% of the volume of a mature cell may be taken up by a single large vacuole or several vacuoles. The vacuole is bound by a special membrane, called the tonoplast, and contains cell sap—which is composed of dissolved substances and may include pigments.
The cell cycle contains the process in which cells are either dividing or in between divisions. Cells that are not actively dividing are said to be in interphase, which has three distinct periods of intense activity that precedes the division of the nucleus, or mitosis. The division of the rest of the cell occurs as an end result of mitosis and this process occurs in regions of active cell division, called meristems. Meristems will be looked at in the plant tissue tutorial.
Mitosis is a process within the cell cycle that is divided into four phases which we will sum up here:
- Prophase—the chromosomes and their usual two-stranded nature becomes apparent, the nuclear envelope breaks down.
- Metaphase—the chromosomes become aligned at the equator of the cell. A spindle composed of spindle fibers is developed and some attach to the chromosomes at their centromere.
- Anaphase—the sister chromatids of each chromosome, that is now called the daughter chromosomes, separate lengthwise and each group of daughter chromosomes migrates to the opposite ends of the cell.
- Telophase—the groups of daughter chromosomes are grouped within a developing nuclear envelope which makes them separate nuclei. A wall forms between the two sets of daughter chromosomes thus creating two daughter cells.
In plants, as the cell wall is developing, droplets or vesicles of pectin merge forming a cell plate that eventually will become the middle lamella of the new cell wall.