Orchid

Page 13 Orchid This picture shows the basic structure of a flowering plant specifically an orchid.


 * 1. Classification/Diagnostic Characteristics**

The Orchid family, also known as Orchidacaea, are one of the two largest groups of flowering plants along with Asteraceae. Orchids are a type of angiosperm plant.
 * **Angiosperm**- This is a category of flowering plants. They are characterized by stomata, persistently green sporophytes, tracheids which are vascular cells, true roots, megaphylls, heterospory and seeds, flowers and a triploid endosperm.

Orchids are very easily identifiable plants, as they have many distinctive properties including:
 * Bilateral symmetry (line symmetry)
 * Resupinate petals (petals opposite their normal direction)
 * Extremely small seeds
 * Fused stamens and carpels

This picture shows the Singapore National Orchid Garden.
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 * 2. Relationship to Humans**
 * Back in the 1860s many people were "enchanted" in raising orchids. Charles Darwin wanted to know why orchids had such strong diversification and saw pollinators as an important part of this process. He thought that these examples could demonstrate natural selection. Darwin found the orchid of the genus Catasetum shooting a packet of pollen at an insect that was landing on its flower. He also found the orchid Angraecum sesquipedale which had a nectar tube over a foot long. Through this they discovered different animals that were adapted to these characteristics of orchids.


 * 3. Habitat and Niche**
 * Vascular plants such as the Orchid exist on land, causing them to have a series of adaptations from the water plants to allow them to have structure and to be able to take in water. Adaptations allow orchids to exist in subterranean environments along with rocks (**lithophytes**) although most are **epiphytes**, meaning they grow on top of other plants and trees. They are able to survive in this way outside of soil by gaining nutrients from the water, air, and decomposing materials. Common epiphytes include phalaenopsis, cattleya, dendrobium, and oncidium. Some epiphytes develop a mutualistic symbiotic relationship with a type of fungi. The fungi helps the orchid absorb nutrients from the environment, and the orchid provides the fungi with nutrients from photosynthesis. Orchids can grow in almost any habitat on earth- excluding Antarctica- from rain forests to swamps and savannas, although the majority are found in humid environments, especially in Central America and South America.


 * 4. Predator Avoidance**
 * Orchids have pigments to avoid harm from ultra violet radiation, their spore walls also protect these plants from desiccation and decay. Other than these ways to avoid harm orchids have no real predator avoidance mechanisms because they are flowers that provide food and beauty.


 * 5. Nutrient Acquisition**
 * Orchids have a mutualistic relationship with fungi that promotes nutrient uptake from the soil. The fungi nourishes seedlings and transfers nutrients and minerals to fully-matured orchids. The colonization of this fungi is controlled by the orchid (1). The xylem is a tissue in orchids which conducts water and minerals from soil to the other parts of the plant. This xylem is spreading nutrients to the areas of the plant which need them. Orchids are also autotrophs who acquire their nutrients through photosynthesis. **Photosynthesis** is when a plant converts light energy into chemical energy. Carbohydrates and oxygen are synthesized from water and carbon dioxide.


 * 6. Reproduction and Life Cycle**
 * When a pollen grain, otherwise known as plant sperm, arrives at the landing point close to a female gametophyte the plant is pollinated. The species of the gametophytes must be the same for fertilization to occur. The developing pollen produces a pollen tube to make its way to the gametophyte and fertilize it. During embryonic development there is division of the zygote until a seed is made. The seed is in a resting stage, but it will germinate when conditions are favorable for growth. After the seed develops it contains a diploid zygote and a triploid endosperm.

This picture shows the flower structure of an orchid and specifically relates to orchid reproduction and pollination. One can see the petals used for attracting pollinators as well as the path to pollination. []
 * Orchids have developed a deceptive mechanism that aids in reproduction and pollination. In this pollination system, the plant produces flowers that use one of the two following methods of deception; food and sexual.The food deception is when the plant produces flowers that smell or look like food, attracting pollinating insects to thier buds where the pollen is. Sexual deception has the same effect, but attracts only male pollinators by smelling or looking similar to a female insect. Populations of Orchids that utilize sexual deception have been found to have a higher pollen transport efficiency aka sexual reproduction.
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 * 7. Growth and Development**
 * During growth and development, there is division of the zygote until a seed is made. The seed sits and waits in a resting stage until there are favorable growth conditions in which the seed will germinate. The seed continues to grow through meiosis and double fertilization to form an endosperm along with the zygote. These will eventually form a mature sporophyte with a flower. The flower has petals and sepals in order to communicate with animals for fertilization.


 * Orchids are either monopedal or sympodial. **Monopedal** orchids grow in a single, upright stem with one leaf following another. **Sympodial** orchids have an individual shoot with small leaves.


 * 8. Integument**
 * Only one of the meiotic products in a megasporangium, a structure producing more than one megaspore, survive. This haploid nucleus divides and divide to form a female gametophyte. This megasporangium is surrounded by sterile sporophytic structures, thus forming the integument to protect the megasporangium. The megasporangium and the integument or natural covering form the ovule which is the part of the plant that develops into a seed after the plant is fertilized.


 * 9. Movement**
 * Orchids themselves are planted into the ground and remain there, attached to roots. There is water movement through the xylem and phloem of the plant. The xylem transfers water and minerals from the soil to the rest of the plant and the phloem transports the products of photosynthesis to sites where they will be used and stored.


 * 10. Sensing the Environment**
 * During development Orchid seeds sense the changes in the environment to decide when they will begin to grow and become a flower. This could be sensing the rays of the sun or the amount of rainfall on a stormy day.


 * 11. Gas Exchange**
 * Plants use stomata as a way to regulate their gas exchange. **Stomata** are small openings in leaves that are able to open and close. This keeps water in the leaves when the plant needs it but keeps out CO2 after it is produced in photosynthesis. Guard cells control the opening and closing of stomata. When stomata are open, CO2 enters the leaf and water vapor diffuses out of the leaf. When stomatas are close water loss is prevented, but CO2 cannot enter the leaf.
 * [[image:stoma_diagram.gif]]
 * This picture shows a stoma and shows how CO2 enters the cell and water and oxygen leave the cell. This whole process changes based on when the stoma is open and closed.
 * http://evolution.berkeley.edu/evolibrary/images/interviews/stoma_diagram.gif
 * http://evolution.berkeley.edu/evolibrary/images/interviews/stoma_diagram.gif


 * 12. Waste Removal**
 * Orchids undergo **photosynthesis**, which is the process by which plants convert carbon dioxide and water into glucose and oxygen. Oxygen is released as a waste product through stomata, or small openings located on the epidermis of the leaf, which allow for transpiration and the removal of other gases.
 * [[image:photosynthesis.gif]]
 * This photo shows the process of photosynthesis in plants. It shows the products and reactants.
 * http://www.factmonster.com/images/photosynthesis.gif


 * 13. Environmental Physiology (Temperature, Water and Salt Regulation)**
 * Most orchids use their stomata for water regulation. At night, water is usually regulated because there is no photosynthesis so the plant does not need CO2 and can close its stomata to conserve water. The stoma close if water is being lost at too great a rate, even during the day. Salt regulation will occur through osmoregulation, which is the process of the diffusion of water molecules through a semi permeable membrane. Orchids best survive in warmer temperatures between 50 and 80 degrees Fahrenheit. However, many species have cold hardiness, which is the resistance to cold environments, therefore allowing some orchids to survive in cold and near freezing temperatures for a limited time.


 * 14. Internal Circulation**
 * Orchids use a system of xylem and phloem to transfer minerals throughout the plant. **Xylem** conduct water and minerals from soil to other parts of the plant while **phloem** takes the products of photosynthesis and take them to sites where they can be used or stored. Orchids also contain tracheids which are the water-conducting parts of the xylem.
 * [[image:Xylem-and-Phloem.jpg]]
 * This diagram explains the xylem and phloem in plants and how certain materials travel through the plant.
 * http://static.diffen.com/uploadz/6/6e/Xylem-and-Phloem.jpg


 * 15. Chemical Control (i.e. Endocrine System)**
 * Like other plants, orchids use hormones to control growth. Plant hormones, unlike animal hormones, often have overlap in their functions, making it difficult to determine exact actions. The two most important classes of hormones are gibberellins and auxins. **Auxins** trigger cell elongation, while **gibberellins** promote seed germination and stem growth.

1. Describe the classification of an orchid and relate it to two other species. 2. What is the extremely important process that orchids go through to obtain nutrients as well as release waste products to the environment? 3. What is the function of a stomata in an orchid and when is it open? 4. How are nutrients transferred through orchids? 5. How do Orchids make themselves more appealing to pollinators in the reproductive process?
 * Review Questions:**

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 * ** Sources: **
 * "Orchidaceae; Overview." //Encyclopedia of Life //. N.p., n.d. Web. 02 Dec. 2013. .
 * "Orchid Growth Patterns." //Orchid Growth Patterns//. N.p., n.d. Web. 02 Dec. 2013. .
 * "Cold Damage." //Cold Damage//. N.p., n.d. Web. 02 Dec. 2013. .
 * "Rainforest Alliance." //Orchid (Orchidaceae)//. N.p., n.d. Web. 02 Dec. 2013. .
 * "Tucson Botanical Gardens » Orchids." //Tucson Botanical Gardens RSS//. N.p., n.d. Web. 02 Dec. 2013. .
 * //Nature.com//. Nature Publishing Group, n.d. Web. 02 Dec. 2013. .