PLANT+OREINTATION

Learning Objectives

 * Describe environmental factors that are important to pland and how plants respond to them
 * Describe tropisms, including gravitropism and phototropism and thier role in plant growth and development
 * Desribe nastic responses and their adaptive advantage.
 * Explain the role of phytohormones in regulating plant responses to environmental factors including light and gravity.
 * Discuss the source and effects of the following plant hormones on plant growth: auxins, abscisic acid cytokinins ethylene and gibberelins

We have spoken about the tropisms in class.

These are controlled by the hormones that are produced by the plant in response to an environmental factor. To full explain how these tropisms occur we need to consider the role of the hormones in creating the growth oreintation repsponse.

Below are some clips on tropsms and also the links to the vids we watched today from TAFE that give a clear and simple description of the types of hormones and experiments used to determine how these growth responses work.

[] Plant Hormones Part 1 of 3

[] Plant Hormones Part 2 of 3

[] Plant Hormones Part 3 of 3

[] More on Coleoptile experiements

[] This is more info than you need but a nice link to gene control in the Genetics standard

__**Tropism**__ //is the movement of plant parts in growth, in a direction which depends upon the direction of a stimulus.// Most plants show positive phototropism. The stimulus is detected by the tip of the coleoptile (hollow, spear-like structure that sheaths and protects that foliage leaves of grass seedlings during their upward movement through soil). Phototropism consists of three components:
 * **Phototropism** - response to light
 * 1) Detection of the stimulus by the tip
 * 2) Transmission of some form of message from the tip to the region behind
 * 3) The response itself.
 * **Gravitropism** - response to gravity
 * **Thigmotropism** - response to contact
 * **Chemotropism** - response to chemicals

Nastic movements are plant movements that occur in response to environmental stimuli but unlike tropic movements, the direction of the response is not dependent on the direction of the stimulus. Some of the most spectacular plant movements are nastic movements. These include the closing of the carnivorous Venus Flytrap leaf when it captures prey or the folding of the mimosa leaf when it is disturbed.
 * NASTIC RESPONSES.**

This is a site that shows a few examples on nastic movements in plants such as the Venus Flytrap, morning glory etc.

[]

at the side navigator, you will also see some other links that are related to this topic such as tropisms and circadian responses which we will be learning later on in this topic. this is a very helpful site!

These responses can be caused by localised turgor changes or the result of rapid cell growth in different parts of the plant. When the direction of the plant response is independent of the direction of the stimulus the response is said to be **nastic.** An example of this is the sensitive plant //Mimosa pudica.// It has long, compound leaves and when the leaf is touched, it would collapse and its leaflets would fold together. Strong disturbances causes the entire leaf to droop from its base. This type of nastic repsonse is called **haptonasty.** Another type is called **photonasty.** "sleep movements" (**nyctinasties**) is when a plant closes up their flowers or lower their leaves at night and open them during the day. Adaptive advantage for these nastic responses is for protection when they are being disturbed. Or they can benefit as it can increase chances of survival during temperature chance or rest from photosynthesis during the night.
 * __Nastic Respones__** or TURGOR RESPONSES - //are quite rapid, reversible movemnts made by plants.//
 * Thermonasty** is also another, this is the opening and closing of flowers to changes in air temperature, an example is the tulip flowers.

Tropism is the directional movement of a plant in response to the stimuli (external environmental factors) such as gravity, light etc. Tropism is of many types such as:
 * 1) **Chemotropism -** This involves plants responding to chemicals.
 * 2) **Geotropism or gravitropism -** this is a response to gravity. In plants, shoots of a plant are negatively geotropic (growing upward), while roots are positively geotropic (growing downward).
 * 3) **Hydrotropism -** a response to water or moisture, in which roots grow toward the water source.
 * 4) **Phototropism** //-// a response to light. A plant may be positively phototropic (bending toward the light source) or negatively phototropic (bending away from the light source).


 * Desribe nastic responses and their adaptive advantage.

__**Nastic Responses **__ <span style="font-family: 'Arial','sans-serif'; font-size: 15px;">Nastic responses are responses to stimuli which are not related to the direction of the stimulus. The suffix for naming of nastic responses is -nasty.

<span style="font-family: 'Arial','sans-serif'; font-size: 15px;">Examples of nastic responses include the opening or closing of leaves or petals in response to touch or light intensity.

<span style="font-family: 'Arial','sans-serif'; font-size: 15px;">e.g.
 * <span style="font-family: 'Arial','sans-serif'; font-size: 15px;">tulips close their petals at night in response to the temperature drop. this is an example of thermonasty.
 * <span style="font-family: 'Arial','sans-serif'; font-size: 15px;">mimosa trees close their leaves when they are touched


 * <span style="font-family: 'Arial','sans-serif'; font-size: 15px;">Explain the role of phytohormones in regulating plant responses to environmental factors including light and gravity.
 * <span style="font-family: 'Arial','sans-serif'; font-size: 15px;">Discuss the source and effects of the following plant hormones on plant growth: auxins, abscisic acid cytokinins ethylene and gibberelins

<span style="font-family: 'Arial','sans-serif'; font-size: 15px;">Tropisms