Warmup 11/16/15 What do you think plants use minerals for? What do you think humans use them for? Objective Tonight’s Homework To learn how plants absorb and use minerals pp 322: 1, 2

Notes on Plants and Minerals / Hormones Minerals in the Soil What do minerals do for plants? As in humans, minerals serve many purposes for plants. Let’s discuss some of them:

Notes on Plants and Minerals / Hormones Minerals in the Soil What do minerals do for plants? As in humans, minerals serve many purposes for plants. Let’s discuss some of them: Nitrates- Builds amino acids and proteins Phosphates- Help create energy Potassium- Cell membranes and proteins Sulfur- Proteins and amino acids Calcium- Cell walls, mineral regulation Magnesium- Chlorophyll and some enzymes Iron- Chlorophyll and some enzymes

Notes on Plants and Minerals / Hormones As a plant grows, it depletes these minerals from the soil. If a farmer continues to grow the same crops, they will grow more and more poorly until the soil cannot grow that crop any more.

Notes on Plants and Minerals / Hormones As a plant grows, it depletes these minerals from the soil. If a farmer continues to grow the same crops, they will grow more and more poorly until the soil cannot grow that crop any more. There are a few methods to fix this: Bumper crops use few nutrients and can be grown for a few years to let the soil naturally replenish, if there’s enough rain. Crop Rotation is a practice where different crops are grown each year. Some of the crops pull nitrogen from the air and put it in the soil.

Notes on Plants and Minerals / Hormones Absorption by Roots Plant roots must use active transport to pull in minerals. This requires oxygen. If a plant doesn’t get enough oxygen (even though it breathes in CO 2 ), the roots won’t be able to absorb minerals and the plant will wilt.

Notes on Plants and Minerals / Hormones Absorption by Roots Plant roots must use active transport to pull in minerals. This requires oxygen. If a plant doesn’t get enough oxygen (even though it breathes in CO 2 ), the roots won’t be able to absorb minerals and the plant will wilt. If soil contains too many nutrients, water will be pulled from the roots through passive transport. This causes the cells to shrivel up and die.

Notes on Plants and Minerals / Hormones Plant Hormones Let’s change topic here and talk about plant hormones. In the 1920s, a few experiments were done with the main growing stem of a plant. This involved the apical meristem, and the coleoptile (the stem part right under the meristem).

Notes on Plants and Minerals / Hormones  With the apical meristem removed, the plant stopped growing.

Notes on Plants and Minerals / Hormones  With the apical meristem removed, the plant stopped growing. When the apical meristem was replaced, the plant began growing again.

Notes on Plants and Minerals / Hormones  With the apical meristem removed, the plant stopped growing. When the apical meristem was replaced, the plant began growing again. This led to two conclusions about the apical meristem. Either the weight of it makes the plant grow, or a hormone it contains, or both.

Notes on Plants and Minerals / Hormones  The weight was tested by taking a plant, removing the apical meristem, and placing a piece of agar (a gelatinous sugar). The thought was that if weight is all the coleoptile needs, anything will do. When this experiment was done, it was found that the plant did not grow.

Notes on Plants and Minerals / Hormones   Next, they wanted to test if there was some sort of hormone that was making the coleoptile get longer. They took the agar and placed it under the meristem, hoping hormones would leak from the meristem. They then placed the agar back on the plant. As time passed the plant grew. It seems a hormone is responsible for growth!

Notes on Plants and Minerals / Hormones   One last test was done. A small slice of hormone-soaked agar was placed on just one side of the coleoptile. It was found that that side grew faster than the side without the hormone, causing the plant to bend.

Notes on Plants and Minerals / Hormones This hormone for plant growth was named “auxin”. Auxins vary greatly from species to species and from plant part to plant part.

Notes on Plants and Minerals / Hormones This hormone for plant growth was named “auxin”. Auxins vary greatly from species to species and from plant part to plant part. Some common auxin functions are: - Keeping fruit from falling off a tree - Turning flowers into fruit - Can turn roots into stems

Notes on Plants and Minerals / Hormones There are other plant hormones as well. “gibberellins” have been found in over 20 kinds of plants. These stimulate elongation in both leaves and stems.

Notes on Plants and Minerals / Hormones There are other plant hormones as well. “gibberellins” have been found in over 20 kinds of plants. These stimulate elongation in both leaves and stems. Dwarf plants have lost the ability to respond to this hormone and thus remain stunted. In some plants, this hormone also helps seeds grow.

Notes on Plants and Minerals / Hormones Our last hormone is called “abscissic acid”. This hormone stimulates the falling of leaves and fruit. It controls the formation of bark layers and, if put on plant tips, can cause a plant to form buds.

Exit Question What hormone is responsible for a plant growing upward? a) coleoptile b) gibberellins c) abscissic d) tropism e) auxin f) None of the above