Caso 1 - Background Information

Initiating discussion and examining parts of plants can begin with you showing the parts of a plant using plants growing in the classroom, plants students bring from home, or plants that can be found growing on the school grounds. Don't be afraid to remove some of the plants from their pots to show roots.

There are various ways to categorize plants. Two of the most common are structure and life cycle.

Plant structure. Plants can be either herbaceous or woody. Herbaceous plants generally have stems that are soft, green, and contain little woody tissue. These plants are ones that usually die to the ground each year. Most annual and perennial flowers fall into this category along with vegetables and houseplants.

Life cycle. A designation which usually describes how long a plant lives or how long it takes to complete its life cycle (grow, flower, set seed). Plants are classified as either an annual, perennial, or biennial.

Annual. A plant that completes its life cycle in one growing season. It will grow, flower, set seed, and die. Examples: marigolds, tomatoes, and petunias.

Perennial. A plant that lives through several growing seasons. It can grow, flower, and set seed for many years. Underground portions live for many years and regrow new stems (herbaceous perennial), or the stems can also live for many years (woody perennial). Examples: daisies, chrysanthemums, and roses.

Biennial. A plant that requires two growing seasons to complete its lifecycle. It grows vegetatively (produces leaves) one season, does not die over the winter, and then grows flowers, sets seed, and dies the second season. Examples: parsley, carrots, and foxglove.

Plant Parts

Basic parts of most all plants are roots, stems, leaves, flowers, fruits, and seeds.

The roots help provide support by anchoring the plant and absorbing water and nutrients needed for growth. They can also serve as storage organs for sugars and carbohydrates the plant uses to carry out other functions. Plants can have either a primary tap root system (such as carrots) or a fibrous root system (such as turfgrass). In both cases, the roots are the links between the water and nutrients needed for plant growth.

Stems house the plumbing works of the plant so water and nutrients absorbed by the roots can travel to the leaves, and then the food produced by the leaves is able to move to other parts of the plant. The cells that do this work and are housed in the stems are called the xylem cells (move water) and phloem cells (move food). Stems also provide support for the plant allowing the leaves to reach the sunlight they need to produce food.

Leaves are the food producing factories of green plants. Leaves come in many different shapes and sizes. Leaves can be simple, consisting of a single leaf blade attached by a petiole to the stem (oak, maple), or compound, in which the leaf blade is divided into separate leaflets attached by a petiole to the stem (ash, locust).

Leaves are designed to intercept light. Leaves have openings that allow gas exchange and water exchange. The outer surface of the leaf has a waxy coating called a cuticle which protects the leaf. A network of veins carry water and nutrients within the leaf.

Leaves are the site of the food production process called photosynthesis. In this process, carbon dioxide and water in the presence of chlorophyll (the green pigment) and light energy are converted into glucose. This energy rich sugar is the source of food used by most plants. Photosynthesis is a very extensive chemical reaction unique to green plants. In the process, photosynthesis supplies food for the plant while supplying oxygen for other organisms needing it to survive.

Flowers may look cosmetic but, in fact, are important in the production of seeds. Flowers have some basic parts. The female organ is the pistil. The pistil usually is located in the center of the flower and is composed of three parts: the stigma, style, and ovary. The stigma is the sticky knob at the top of the pistil. It is attached to the long, tubelike structure called the style. The style leads to the ovary which contains the female egg cells called ovules. The male organs are called stamens and usually surround the pistil. The stamen is composed of two parts: the anther and filament. The anther produced pollen (male sperm cells) and the filament holds it up.

During the process of fertilization, pollen lands on the stigma, a tube grows down the style and enters the ovary. Male sperm cells travel down the tube and join with the ovule, fertilizing it. The fertilized ovule becomes the seed, and the ovary becomes the fruit.

Petals are also important parts of the flower because they help attract pollinators. You can also see tiny green leaf-like structures called sepals at the base of the flower. These help to protect the developing bud. Flowers may have evolved over time to accommodate certain types of pollinators thus assuring successful pollination.

The fruit is the ripened ovary of a plant containing the seeds. After fertilization, the ovary swells and becomes either fleshy or hard and dry to protect the developing seeds. Not only do fruit help protect the seeds, many fruit are designed to help in getting the seeds dispersed (maple seeds). Many things we call vegetables are technically fruit (tomato, cucumber, beans). Every seed is a tiny plant (embryo) complete with leaves, stems, and root parts waiting for the right conditions to germinate and grow. Seeds are protected by a coat. This coat can be very thin, giving the embryo little protection and allowing for quick germination, or very think and hard, providing long-term protection and germination after long periods under specific conditions. The seed also contains endosperm in the form of cotyledons. This endosperm is a short term food supply for the newly emerged seedling. Plants may either be monocots (one cotyledon) such as corn, or dicots (two cotyledon) such as oak trees. Seeds are able to tolerate extremes in the environment and can be transported to other growing areas.

What are the basic requirements for growing plants indoors?

1. Room to grow. All plants like to have room to grow and develop. The above ground portions of the plant need space so leaves can expand and develop properly in order to carry out the job of making food. Roots also need room to grow. Plants growing in small confined spaces will have their roots constricted resulting in reduced growth.

2. Temperature. Most plants are comfortable at temperatures that most humans like. Some may prefer warmer temperatures while other may prefer cooler temperatures for best growth. It is always good to know the natural habitat of the plant to provide conditions that are most "like home." Most plants like to have cooler temperatures at night and don't like to be in a drafty spot.

3. Light. Plants grown indoors like very bright light. Windows facing the south or west provide the best light. Try to place the plants as close to the windows as possible to take advantage of all the light. The further away from the window, the darker it becomes. Plants respond to low light by stretching toward the light source. This results in stems being thin and spindly. If natural light is provided, try to supply at least eight to 12 hours of bright light each day. Light can also be provided artificially. Due to poor window location or no window at all, this type of light source can result in excellent plant growth. You may also consider supplementing natural light with artificial. Cool white fluorescent tubes are a good source of light. Remember to position the light so it is about six to eight inches above the tops of the plants and leave the lights on for 14 to 16 hours a day.

4. Light terminology
   
   Light quantity refers to the intensity. This can vary during the year. Winter will provide very low intensities while summers provide very high light intensity. Light quality refers to the color of the light or wavelength reaching the leaf surface. Sunlight can be broken up by a prism into a variety of colors. Red and blue have the greatest effect on plant growth. Light duration refers to the amount of time that a plant is exposed to a light source. The flowering sequence of some plants is controlled by how many hours of light or darkness a plant receives.

5. Water. Water is the prime component in the plant¹s ability to manufacture and move nutrients within the plant. Without water and with too much water a plant dies. For this reason, watering is an important part of plant care. Most plants like to be watered when the soil is slightly dry to the touch. When watering, moisten the whole soil ball by using enough water so that is starts to come out of the drainage hole in the bottom. (This is why it is important to use containers with adequate drainage holes.) Watering intervals will be determined by the season of the year (less water is needed when light levels are low or the plant is in a reduced rate of growth), environmental conditions around the plant (dry rooms result in more water use by the plant), rate of growth of the plant, size of the container, amount of roots in the pot, and the type of plant (succulent plants need less than thin-leaved plants like lettuce).

6. Air. Plants utilize carbon dioxide in the air and return oxygen. Smoke, gases, and other air pollutants can result in damage to plants.

7. Nutrients. Most of the nutrients that a plant needs are dissolved in water and then absorbed by the plant through its roots. Applying fertilizers will help to keep the soil supplied with nutrients a plant needs. You should be cautious about applying too much too often. Apply fertilizers when plants are actively growing and only in amounts and frequencies stated on the fertilizer package label. Fertilizers should not be look upon as the correcting factor for poor light, poor drainage, poor soil, or just plain poor care. Liquid fertilizers are generally the easiest and safest to use. The three most important nutrients are nitrogen, phosphorous, and potassium. Nitrogen is used for above ground growth and results in a dark green color to the leaves. Too much nitrogen results in soft, tender growth. Some crops such as lettuce benefit from this. Phosphorous encourages plant cell division. It aids in flower and seed production and in the development of a strong root system. Potassium helps to increase the plant's resistance to disease. It acts as a regulator in the synthesis of carbohydrates and proteins.

8. Time. It takes time to grow and care for plants. Some plants require more time to reach maturity than others. Scheduling crops to come into flower at a certain time or to mature at a certain time can be both challenging and intriguing. Plants that normally grow outdoors have a certain number of days to flower or fruit. By using these estimates, you can time certain plants to come into flower or fruit on a certain date. This is a good lesson in both horticulture and math.

Tips on Growing Lettuce Indoors

You need plastic lock-type bags (one quart size works well), leaf lettuce seeds (green and red varieties), water, and soil mix (such as pro-mix, redi-earth, jiffy mix, or sunshine mix).

• Cut off the corners of the bag to allow for drainage.

• Fill the bag 3/4 of the way with moistened soil mix.

• Sprinkle seed on the surface. Don't use too much as plants will start to crowd.

• Lightly cover with soil. Only 1/8 inch is sufficient.

• Water lightly so the soil is uniformly moist and you get good seed-to-soil contact.

• Zip the bag closed leaving about one inch open to provide ventilation.

• Place the bag in a sunny window or under a grow light.

• When germination starts, open the bag. Continue to provide a sunny location. and water as needed to keep uniformly moist.

• Lettuce will grow fast in warm temperatures but quality may be better under cooler conditions (65-70 degrees F).

• As plants start to get large and grow together, start cutting and using it in a salad for the class.