1. Introduction

    Plants respond to the Earth’s gravitational attraction and light. Stems grow towards the source of light. Roots grow downward and away from light. These particular responses are called tropisms. Plants’ growth in response to gravity is known as gravitropism but the growth response to light is phototropism. Both tropisms are controlled by plant growth hormones. (Johnson,1999)

    Gravity sensing cells at the end of the roots called statocytes allow the plant to detect the direction of gravity. The process is known as gravitropism. Gravitropism occurs because of the plant hormone also called auxin that plays a crucial part in it. When the plant is laid on its side, the auxin concentration increases along the lower sides of the roots and stems of the plant. The auxin stimulates cell elongation on the stem which makes the stem bend up toward the sky. In the case of negative gravitropism, the auxin prohibits cell elongation in the roots which causes the roots to bend down into the soil. Gravitropism allows the plant to respond to gravity no matter what position the plant is in.(Kiss, n.d.) Roots show a positive response to gravity as they grow downward, whereas the stems show the opposite response. Tropism is a growth response between a plant and an external stimulus. The stimulus could be weather, touch, time, gravity or light. A positive response is indicated by growth toward a stimulus and a negative response is indicated by growth away from the stimulus.

Gravitropism is a plant's growth response to gravity. Typically roots grow down into the ground, and stems and leaves grow up above the ground. If one were to place a plant on its side, it would begin to bend in an upright position. This occurs because of the plant hormone also called auxin that plays a part in gravitropism. When the plant is laid on its side, the auxin concentration increases along the lower sides of the roots and stems of the plant. The auxin stimulates cell elongation on the stem which makes the stem bend up toward the sky. The auxin prohibits cell elongation in the roots which causes the roots to bend down into the soil. Gravitropism allows the plant to respond to gravity no matter what position the plant is in. (Thinkquest, 2008)

A seed grows by absorbing water from its roots. The inside of a root has four different parts. The epidermis is the outside part. It is like our skin. It protects the inside parts of the root. Plants take in water from the soil through their roots. The water passes through the vascular rays until it reaches the center of the root, the stele. This is where the veins are located. The veins are called xylem. They carry the water and food through the plant. Between the epidermis and the stele is the fleshy cortex. A seed needs water to germinate. Water assists the seed in breaking the seed coat, which in some cases can be very tough. For example, Morning Glory seeds have a very tough seed coat and need to be soaked in water before they are planted. The seed begins to grow as the cells within the seed begin to multiply. Eventually, usually within a few days, the seedling bursts from its seed coat and will continue to grow both downward and upward. The cotyledons, or first leaves, will be the first things you will see once the seedling has come out of the seed coat. Cotyledons are usually thicker leaves than the ones that will follow.

The shoot of the plant may also be visible as the leaves start growing upward. As the shoot and cotyledons are pushing upwards, the taproot and smaller root hairs will also begin to grow. The proper soil, or water with the right nutrients, is necessary in order for the plant to continue growing. A plant can grow in most environments as long as it receives the proper nutrients required for growth. The plant will continue to grow upward and outward as its cells multiply. New leaves will appear, as will flowers in many plants. As the plant grows, it will continue to need the proper nutrients from the soil and water as well as sunlight or the right artificial light. (Charlotte Gerber, n.d.)

Research Question

An investigation of whether gravity will affect the growth of plants.

Hypothesis

The hypothesis is the roots of the plant will grow in relation to the direction of gravity.

Independent variable(s)

The independent variable is the change of the direction of gravity.

Dependent variable

The direction of root growth.

Constants

1. Type of CD cases
2. Type of plant
3. Type of water
4. Volume of water for each plant
5. Size of CD cases