Plant Hormones

     Auxin is a hormone that controls plant cell growth. This allows for many things to happen, two being phototropism and root/stem growth. In the case of phototropism, there is sunlight on one side of the plant. This triggers auxin to excrete in the shaded side. Auxin causes cell walls to elongate, eventually leading to longer cells. When this happens, the plant will lean towards the sun. This is important because it will increase the amount of sunlight a plant is getting, which will lead to more photosynthesis, which will create glucose and oxygen. This glucose can then be broken down in cell respiration to provide the plant with ATP. This glucose will also go down the tissue called phloem to the roots of the cell to provide nutrition in the form of glucose and fructose, which can combine to create sucrose. This sucrose is the sap you see on most plants.

Auxin has created elongated cells on the shaded side causing the plant to lean towards the sun
http://bio1152.nicerweb.com/Locked/media/ch39/39_05PhototropismExper.jpg

A plant in which this phototropism has occurred
http://cdn.phys.org/newman/gfx/news/hires/2013/howdoplantsg.jpg

The other example was root and stem growth in plants. As we have observed thus far in our lab that Siri and I did, no matter which way the seed is originally facing, the roots will grow down and the stem will grow up. The force of gravity tells the plant which way the ground is, and this causes auxin to be released into the roots and stem. In the roots, it will inhibit elongation on one side to cause a downward bend. In the stem, it will cause growth on one side to cause an upward bend. This entire process is called gravitropism.

Seeds undergoing gravitropism after sprouting
http://botit.botany.wisc.edu/Resources/Botany/Root/+%20gravitropism%20MC%20.jpg

Plant undergoing gravitropism
http://www.visualphotos.com/photo/1x8469278/gravitropism_geotropism_BJ1486.jpg

     Abscisic Acid is a plant hormone that slows germination. This is very important to plants, especially those that live in conditions that are very harsh, for example the desert. An excess of abscisic acid would require a lot of water to be washed away, therefore many larger desert plants, such as cacti, have a lot of abscisic acid on the seed. This means that in order for it to begin germination, there must be a sufficient amount of water, therefore the plant's growth can be sustained. This usually will occur after the rainy season. A low amount would be present in smaller plants, like desert grasses. They don't live very long and require less water, so therefore a small amount of water would be enough to wash the acid away and begin germination.

A cacti, which is an example of a plant that requires a lot of water to germinate.
http://fvcgeography.files.wordpress.com/2011/10/cactus72.jpg

     Ethylene is a gas that is naturally produced by fruits that cause them to ripen. This means that if one fruit ripens, the others will ripen quickly. This was an evolutionary benefit, as it makes the plant get eaten more quickly by an animal which means its seeds can be spread more quickly.

A plant that has ripened due to Ethylene gas
http://www.rsc.org/chemistryworld/sites/default/files/upload/x0612CW_NIBS_pg004-300.jpg