Gymnosperms

by Alina Cheema //Cycads//
 * Gymnosperms **

Diagnostic characteristics of the group
Depending on the phyla of gymnosperm, the gymnosperms has various characteristics. Most gymnosperms bear cones, which are the main reproductive system of the gymnosperms. So, one can usually identify a gymnosperm by whether it bears a cone or not. Also, many of the gymnosperms consisit of pines instead of leaves, some other gymnosperms do have long and fanlike leaves as well. Gymnosperm means "naked seed" meaning that gymnosperms do not have seeds that enclosed within a fruit. (CW)(4) Before the gymnosperms, were the progymnoperms which were seedless plants. Seeds did evolve, ofcourse, over time and specifically by the end of the Devonian peroid. Following this, came the production of different phyla of the gymnoperms. 

Habitats
Gymnosperms are found all over the world, in many different habitats depending on the phyla of gymnsperm. Gnetophytes are found in the tropics and in the deserts. Conifers are predominantly found throughout the forests of the Northern Hemisphere. The ginkgo phylum of gymnosperms is native to China, but is planted worldwide. Cycads are predominantly distributed in tropical and subtropical habitats. The habitats of gnetophytes are seemingly more diverse because of the different subgroups. Ephedra is a group of gnetophytes that is composed of shrubs that are native to deserts and semi-arid areas. Gnetum is a group inclusive of climbing vines and one tree species that have a tropical rainforest habitat. Lastly the group that only contains the species Welwitchia mirabilis is native to the desert of Southwest Africa. Conifers have an extremely vast habitat. They grow in all climates and on all continents expect Antarctica. (CW)(5)

[[image:http://mytko.org/random/ginkgo3.jpg width="171" height="209" align="right"]]Major types
Gymnoperms are grouped into four different phyla including ginkgo, cycads gnetophytes and conifers. **Phylum Ginkgophyta** can be characterized as trees that have green fanlike leaves in the summer that turn gold in the fall; they are deciduous during this time.The Ginkgophyta also referred to as ginkgos, are conifer-like seed plants with fan-shaped leaves with dichotomous branching of the veins. . Their pollen has walls with [|1 suture] and no [|saccus]. The microgametophyte has 2 [|prothallial] cells, a [|stalk] cell, 2 multiflagellate sperm and a [|tube] cell. Their ovules, sometimes even having two of them on a long peduncle, have three tissue layers surrounding its nucleus. Their stems have monopidal growth and is composed of a lot if wood. (YA)(12)

//(14 NG)// **Phylum Cycadophyta's** appearance resemble the flowering plants that are known as palms. "Apogeotropic roots, or roots that bend away from the ground, are formed that enclose mutualistic cyanobacteria that fix nitrogen." [MS] [|4] Cycas species are tropical palm-like trees, and are larger than most species of gymnosperms. They have free-swimming sperm and they are sometimes pollinated by insects. However, they pose an ecological dilemma because they are both beneficial and detrimental to organisms in the environment. While they form symbiotic associations with nitrogen fixing bacteria, they also are highly toxic to livestock. (MT) (10) //A pretty picture of a cycad. Very pretty picture. (RL)(17)// **Phylum Gnetophyta** is divided and described as three genera: Welwitschia, Gnetum, and Ephedra.Welwitschia has giant straplike leaves. Gnetum plants are trees and vines that are predominantly found in the tropic regions. They have large leathery leaves. The shrubs that grow in the American deserts are the Ephedra. They have small, scale like leaves and jointed stems.(KL)([|13])  <span style="font-family: Arial,Helvetica,sans-serif;">The most commonly known types of gymnosperms are the conifers, **phylum Coniferaphyta**. These plants are characterized by the cones that they bear. This phyla is the largest of the gymnosperms. Examples of conifers are the spruce, pine, fir, cedar, cypress, redwood, yew, juniper and larch trees. Conifers are known as evergreens which means that these trees bear leaves throughout the entire year. <span style="font-family: Arial,Helvetica,sans-serif;">Conifer seeds are produced in tiny scale-like structures called seed cones or ovulate cones. Once these seed cones have become pollinated and the pollen grains' male sex germs have united with the female sex germ in the ovules, the seed cone begins to grow and ultimately becomes the kind of pine cone we're all familiar with.(CC) ([|8] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">)

(//15)(SM)//

<span style="font-family: Arial,Helvetica,sans-serif;">Basic anatomy
<span style="font-family: Arial,Helvetica,sans-serif;">The gymnoperms are seed plants and are characterized by their large seeds, pines. The cones consist of packed scalelike **sporophylls**. These are the specialized seeds of the gymnoperms. After, fertilization, the embryo becomes a **pine seed**, then a **seedling** and devevlops into a **sporophtye** which are the gymnosperm plants that contain the sporophylls. <span style="font-family: Arial,Helvetica,sans-serif;">{These seed-bearing plants develop seeds on the surface of the reproductive structures such as the cones in pines. (DB) (2) <span style="font-family: Arial,Helvetica,sans-serif;">Gymnosperms are heterosporous which means that they produce different male and female spores.(KS) <span style="font-family: Arial,Helvetica,sans-serif;">Gymnosperms are vascular plants, meaning that they possess vascular tissue. Xylem transports water from the roots to the leaves, and phloem transports minerals and nutrients around the plant. (NI) <span style="font-family: Arial,Helvetica,sans-serif;"> <span style="font-family: Arial,Helvetica,sans-serif;">[The basic anatomy of a pine cone as shown besides, is similar to that of a flower. The reproductive mechanisms (anther, filament, stamen, ovary, ovule) are the same. What separates a flower and a pine cone is the receptacle and the pedicel. "The flower is a shoot bearing sporophylls (as is a Lycopodium strobilus or a pine cone). Spores are produced by the inner two whorls of sporophylls (stamens and pistils) whereas the outer sporophylls (calyx and corolla) have become sterile and serve for protection or attraction." (MP)[|9]]

<span style="font-family: Arial,Helvetica,sans-serif;">Transport of materials
<span style="font-family: Arial,Helvetica,sans-serif;">Simply said, gametes are transported through the **pollen**. Pollen has evolved to become airborne and transportation is dependent on air. That is why most gymosperms are tall so that the pollen can be uplifted from the plants by the wind and become airborne. <span style="font-family: Arial,Helvetica,sans-serif;">As all plants have roots for transportation of nutrients so do gymnospems. "Gymnosperms have a xylem/phloem system for transporting nutrients and water. The xlyem and phloem act like arteries, moving materials from the bottom of the roots to the tips of the leaves. Xylem, in its maturity, is dead tissue that transports water from the roots to the rest of plant. The Phloem is a living tissue that transports food and nutrients manufactured in the leaves to the rest of the plant. (JS) [|(7)]"

//(MLK) [|10]//

//<span style="font-family: Arial,Helvetica,sans-serif;">The Tracheid, Tracheae, Xylem parenchyma and Xylem fiber are the four elements that make up Xylem.(MLK) (10.) //

<span style="font-family: Arial,Helvetica,sans-serif;">The xylem in the wood of gymnosperms consists for the most part of tracheids rather than vessels. The tracheids are elongated cells that can transport water and salts (SD) (6).

<span style="font-family: Arial,Helvetica,sans-serif;">In the reproduction process, pollination occurs first and after more than a year fertilization then occurs. <span style="font-family: Arial,Helvetica,sans-serif;">Gymnosperms consist of **sporophylls** which are the specialized reproductive leaves of the plants. The gymnosperms are called **sporophytes**. Pollen cones and **ovulate cones** of the gymnosperms contain the sporophylls and these sporophylls contain hundreds of **microsporangia** in the pollen cones and megasporangia in the ovulate cones. Cells in the **microsporangia** give rise to **haploid microspores** after the microsporangia undergo meiosis. These haploid microspores then develop into **pollen grains** which are **immature male gametophytes**. The pollen is transported by the wind and lands on the ovulate cone. The pollen enters into the ovule and germinates there. Then a **pollen tube** forms from the pollen grain and reaches further into the cone all the way to the **megasporagium**. A megaspore mother cell produces four haploid cells through meiosis. One cell survives and becomes a **megaspore**. After dividing repeatedly, the megaspore becomes a female gametophyte (develops in the spore). The gametophyte contains eggs which are found in the **archegonia**. Fertilization occurs, when the eggs are ready and sperm cells have developed in the **male gametophyte.** By this time, the pollen tube has reached the female gametophyte, and the eggs is fertilized when the pollen tubes injects the sperm cell in the egg cell. <span style="font-family: Arial,Helvetica,sans-serif;">"The 'male' cones typically are found in clusters at the tips of lower, and side branches. The usually take several years to develop. In these cones, the modified leaves are called microsporophylls. Meanwhile, the 'female' cones typically form higher up in the tree, and also usually take several years to develop. Their modified leaves/scales are called megasporophylls. Each megasporophyll has two areas (megasporangia or ovules) where the megaspores can develop. Each ovule has a micropyle, a small hole in the end of the ovule wall so that the sperm can enter." (AK) (3)
 * <span style="font-family: Arial,Helvetica,sans-serif;">Reproduction **

media type="youtube" key="D9byVQxvMXs?fs=1" height="385" width="480" align="center"

//<span style="font-family: Arial,Helvetica,sans-serif; font-size: 13px; line-height: 19px; margin: 0in 0in 10pt;">Seed production in gymnosperm video. (SI)(20) //



//<span style="font-family: Arial,Helvetica,sans-serif; font-size: 13px; line-height: 19px; margin: 0in 0in 10pt;">Gymnosperm Reproduction (ZS) (18) //

The **Life Cycle...** continues after the fertilization of the egg, as shown in the diagram above. The embryo, the egg and the sperm, become the new sporophyte or a **pine embryo**. This embryo has rudimentary roots and several embryonic leaves. The pine seed (embryo) grows into a seedling and then a **mature sporophtye**, a grown gymnosperm. The matured seed consists of three different "generations". The maternal sporophyte tissue, the mother gametophyte and "offspring" sporophyte (embryo) - After about two years the mature seeds are shed. (GR)[|19] Sporophytes define the life cycle of the gymnosperms.

media type="youtube" key="hS1hw0uAxmM?fs=1" height="385" width="480"//(MC)//

**Environmental Adaptations** The adaptations of gymnosperms revolved around successful reproduction. An environmental adaptation of the gymnosperms is the transportation for fertilization (or also called pollination). The pollen has evolved oer time and now can become airborne to be tranported to ovulate cones for pollination. One of these adaptations is that the sperm cells in some Gymnosperms retain the **flagellated condition.** The sperm has a flagella that allows movement for the sperm. The **sporophyte** allow simple reproductionf and growth for the gymnosperms and is becoming more increasingly dominant among the gymnosperms. Also, the seed is a vital part of the gymnosperms and has evolved to become resistant to harsh conditions and etc. The pine contains the seed, or is the seed and this mechanism strong agaisnt weather and animals compared other types of plant seeds. Because gymnosperms are often wind-pollinated, evolution tends to favor taller specimens. Seeds falling from higher trees are more likely to get picked up by the wind and thus travel longer distances. Because of competition for resources, the most environmentally fit individuals are not just those who survive to reproduce， but those whose offspring then grow to reach maturity. By landing far away, a seed is able to grow without competing for resources against its parent(although it may have to compete against other organisms). (ZXU)(1 - textbook)

1. How do the reproductive systems of gymnosperms lead to selection for taller specimen of plants? (LJ) 2. What about a pine cone reveals characteristics of gymnosperms anatomy or environment? (TM) 3. What are the benefits of the evoultionary development of seeds in gymnosperms? (LW) 4. In what ways have gymnosperms adapted to meet the changes in their environment? (MF) 5. What are the main differences between the phyla ginkgophyta, cycadophyta, gnetophyta, and coniferaphyta? (ORS) 6. What are the diagnostic characteristics of gymnosperms and how do they differ from angiosperms? (RG) 7. Describe the reproductive steps of gymnosperms. Do gymnosperms need water to reproduce? Why? (SR)
 * Review Questions**

Sources: all pictures and information came from.... Campbell, Neil A., and Jane B. Reece. Biology. Sixth Edition. Boston: Benjamin-Cummings Company, 2002

Edits: 3. [] 4. [] 5. [] 6. <span style="font-family: 'Times New Roman','serif'; font-size: 10pt; line-height: 115%;">[] <span style="font-family: 'Times New Roman','serif'; font-size: 10pt; line-height: 115%;">7. [] 8. http://www.backyardnature.net/conifers.htm 9. http://www.hcs.ohio-state.edu/hcs300/angio1.htm 10. [] 11. [] 12. http://comenius.susqu.edu/bi/202/ARCHAEPLASTIDA/VIRIDIPLANTAE/gymnosperms.htm 13. [] 14. [] (NG) 15. @http://universe-review.ca/I10-22a-pine.jpg 16. http://www.seedbiology.de/evolution.asp (CSR) 17. [] (RL) 18. http://biology.clc.uc.edu/graphics/bio106/pine%20cycle.jpg (ZS) 19.http://hcs.osu.edu/hcs300/gymno.htm (GR) 20. http://www.youtube.com/watch?v=D9byVQxvMXs