This lesson is easily nested into a storyline as an episode exploring the phenomenon of photosynthesis. In this episode, students investigate the question, "Why is light important for plants?" Keep in mind that phenomena-based lessons include storylines which emerge based upon student questions. Other lesson plans in the National Agricultural Literacy Curriculum Matrix may be used as episodes to investigate student questions needing science-based explanations. For more information about phenomena storylines, visit nextgenstorylines.org.
Plants require nutrients, water, air, and light to survive and grow. Nutrients are the vitamins and minerals plants need for healthy growth. They come from the decomposition of rocks, dead plants, and animals and are absorbed through the roots and transported to the rest of the plant through the stem. Water helps keep plants rigid and transport nutrients throughout the plant. Air enters the plant through tiny holes in the leaves called stomata. The roots absorb oxygen to convert food into energy, a process called respiration. Plants use energy from light to make food. In nature, plants typically get nutrients from soil, water from rain, carbon dioxide and oxygen from the air surrounding them and from air pockets in the soil, and light from the sun. It is important to understand that plants do not need soil and sun. They need nutrients and light, which can be provided from the soil and sun or other, sometimes artificial, sources.
Photosynthesis is the process by which green plants and certain other organisms transform light energy into chemical energy. Plants use the energy of light to convert carbon dioxide and water into sugar (glucose) and oxygen. Carbon dioxide is absorbed by the leaves through the stomata. Water enters the plant at its roots and travels through the stem to reach the leaves. The leaves are the primary site where the photosynthesis process takes place. Inside the leaf cells are structures called chloroplasts. Each chloroplast contains chlorophyll, a chemical that gives leaves their green color. When the leaves receive light, chlorophyll captures the light's energy and stores it to eventually be used to convert water into hydrogen and oxygen. The water's hydrogen and oxygen atoms are combined with the carbon dioxide's carbon and oxygen atoms to create glucose molecules which are used by the plant to produce its food. Oxygen, a byproduct of the photosynthesis process, is released into the atmosphere through the stomata. In plants, photosynthesis only occurs in the presence of light.
Light requirements vary by plant species. Green plants need light to perform photosynthesis, although the intensity, quality, and duration needs will differ by plant. Understanding the light preferences of a plant is important when choosing an appropriate planting location and/or light source.
A grow light is an artificial light source designed to stimulate plant growth by emitting a light appropriate for photosynthesis.1 The purpose of a grow light is to replicate the natural solar spectrum of sunlight or to provide a light spectrum tailored to the needs of a particular plant. There are three main types of grow lights—fluorescent, LED (light-emitting diodes), and HID (high-intensity discharge).2 Grow lights differ from traditional light bulbs that are used to light homes. Unlike a traditional light bulb, grow lights produce the full spectrum of light and appropriate intensity necessary for photosynthesis. Grow lights also produce less heat than a traditional bulb, which prevents the scorching of plants.
Plants differ in their light intensity requirements. For grow lights, light intensity is determined by a bulb's brightness and the proximity of the light source to the plant. Plants native to tropical jungles or shady forests typically require less light as compared to plants from dry, sunny climates.
All plants need a rest from light. Respiration, an important part of a plant's growth process, occurs when it's dark. Botanists usually divide plants into three categories relating to their preferred day length—short-day plants grow best with less than 12 hours of light per day, long-day plants require 14-18 hours of light per day, and day neutral plants depend on 8-12 hours per day all year long.
Indoor farming is a method of growing crops or plants, usually on a large scale, entirely indoors.3 This method of growing crops utilizes grow lights or a combination of artificial light and sunlight in a greenhouse setting. Aquaponics, hydroponics, and vertical farming are all examples of indoor farming approaches. Indoor farming is particularly popular in urban areas where less land is available for growing crops or soil is contaminated. The crops grown in indoor farms can be used to boost local food supplies, provide locally-grown fresh food throughout the year, and provide access to nutritious food. Indoor farming enables growers to have increased control over the environment when compared to traditional growing conditions.
around the battery so that the longer prong is touching the positive side of the battery. Once the light is lit, hold the prongs in place by wrapping the electrical tape around the prongs and battery.
