Plant Cell Types

There are many different plant cell types, but there are a few unique types that distinguish plants from animals. Meristem cells are found in the root apical, shoot apical, leaf bud, and vascular cambium meristems of plant, and are the regions of new plant cell synthesis. Undifferentiated cells in the meristems will turn into leaves, flowers, roots, xylem, phloem, and other plant organs depending on internal and external stimuli. Xylem and phloem are the vessels through which water and sugar flow, respectively. Xylem are dead cells, consisting of thin tracheids and large vessels, transporting water from root to shoot. Phloem are live cells, comporting two cell types joined together via branched plasmodesmata. The sieve element is largely devoid of organelles and even lacks a nucleus, leaving it mostly hollow, which allows for the transfer of nutrient laden liquid throughout the plant. The companion cell is linked to the sieve element and provides it with the cellular products it cannot make itself. Root hairs are epidermal cells found on roots that extend via tip growth in order to increase root surface area, allowing for more water and nutrient absorbance. Pollen is the plant equivalent of animal sperm and serves to fertilize female plant gametes. It is made up of two, sometimes three, nuclei of two types, vegetative and generative. The vegetative nuclei is responsible for the growth of the pollen tube, which extends into the stigma of the plant in order to allow for the male gametes produced by the generative nuclei to fertilize the egg and the endosperm. Stomata and trichomes are specialized structures found on any aerial plant surface. Stomata are openings that allow for gas exchange and are regulated by guard cells who open and close in response to blue light. Trichomes come in two forms, glandular and non-glandular, and more than one type of trichome can be found on a plant. The glandular form releases chemicals when burst that can deter predators or attract pollinators. The non-glandular form can be used as physical defence, trapping the predator on the plant, where it will die of thirst. Additionally, the non-glandular form provides an increased boundary layer that minimizes airflow around the aerial parts of the plant, thus decreasing water evaporation.