Gymnosperm

Gymnosperms were the first plants to evolve to use seeds to increase reproduction.Unlike angiosperm, gymnosperm do not have ovaries to hold their seeds are called "naked seed" plants (gymno meaning "naked", sperma meaning "seed") because the seeds develop on the surface of the plant's reproductive organs. The major types of gymnosperm are:

Phylum Cyadophyta, or Cyads

• There are around 100 existing species

• Reproduce via sacs bearing pollen

• Have coralloid roots that support nitrogen-fixing symbiotic cyanobacteria.

• Plants look like ferns or palm trees

Phylum Gnetophyta, or Gnetae

• About 70 existing species

• The only gymnosperm that undergoes double fertilization

• 3 genera:

• Welwitschia: contain large, strap like leaves

• Gnetum: tropical vines and trees

• Ephedra: a shrub found in American deserts

Phylum Coniferophyta, or Conifers

• The fossil record shows that conifers date back to the mesazoic era.

• Characterized by cones (such as pinecones), usually also have needles. However, it is the cones that define conifers rather than needles.

• Out of the four gymnosperm phyla, conifers are the largest

• There are about 550 existing species

The needles on conifers allow the plants to survive in drier climates, because the shape of the needles help the plant conserve water. Conifers also thrive in arid and mountian climates, and have an advantage over deciduous trees; they keep their leaves throughout the entirety of the year, and do not have to shut down photosynthesis like deciduous trees do.

Gymnosperms in general have adapted to their environment to posses Apical Meristems, which allow roots and shoots of the plant to use resources more efficiently while increasing growth and productivity. This adaptation is not only present in gymnosperms, but in other plants as well.

Gymnosperms are called Vascular Plants because they contain vascular tissue, in which a group of cells use capillary action to move water and nutrients throughout the body of the plant. This is done by using two types of vascular tissue, xylem and phloem. Water is transported from the roots of the plant to the shoots using xylem tissue. Xylem cells are specially designed for the transporation of water; they are long, tapered, and called tracheids. Phloem transports food, that food being sugar, to the rest of the plant, including the roots and the shoots, and is made of companion and sieve cell types.

In order for gymnosperms to develop a zygote, they, like other seed-bearing plants, must be pollinated by the transfer of pollen to the plant's ovules. When a grain of pollen lands next to an ovule, it will extend a tube that transfers the sperm of the pollen into the female gamete inside of the ovule. Pollen is most often carried through air and wind, causing the sperm cells in the pollen to not have an active transport mechanism through the tube. Some require a thin film of water to aid in the transportation of the sperm through the tube. Due to the varying environmental conditions caused by transportation of pollen by air, diversity of gymnosperm offspring is encouraged.

In order for a gymnosperm to reproduce, a sporophite, which produces spores, developes into a sporangium, which is an enclosure for the spores. After meiosis, the spores previously inside the sporangium develop outside the sporangium, and becomes into a gametohyte, which makes gametes. The male and female gametes eventually meet, and fertilize to form a zygote, which undergoes mitosis and form new sporophytes and gametohytes, which continue the process and reproduce.