Light Quantity and the Rate

Light Quantity and the Rate of Photosynthesis

People have been interested in plants for hundreds of years, and a lot of people study them and grow them as hobbies. There are many different things that affect how a plant grows. Some of these are soil, temperature, oxygen, water, and nutrients (the soil, 2004). Light is also important for a growing plant because it must have light for photosynthesis to take place. In the simplest of terms, soil and light are the most important things for most experiments discussed and created with plants. The soil has a certain amount of water in it, and how much depends on what kind of soil it is. Different soils have different structures, and this determines how much water drains through and how much stays in the soil for the plant to use (the soil, 2004).

Soil also has gases in it that use up space where these is no water. These gases usually come from the organisms that live in the soil, and they produce a lot of carbon dioxide (the soil, 2004). It is important that there is a good mixture of water and gases in the soil so that plants can grow properly. The temperature of the soil also makes a difference in how well plants will grow in it. Soils that are dark will get hot faster and hold heat longer than soils that are light-colored. The organisms that live in the soil react differently to temperature and water evaporates faster from soil that is hot (the soil, 2004). This can affect how well a plant grows.

Even though soil is important, plants need light. Without light, plants cannot make enough energy to grow (Understanding, 1997). Plants can germinate without light, though, because they are starting out underneath the soil (Plants, 2003). Because of this, the food that the plant needs to start out is already there. Once the plant gets above ground, the light is much more important for it. Many people like to grow plants, but they have to understand how to care for them and give them what they need to grow. If the plants do not get enough light, if they get too much or not enough water, or if they are planted in the wrong kind of soil, they will die. For this experiment it is important to look at whether the wattage of the light bulb affects photosynthesis rates, or whether there is some other quality to the light that has more to do with it. The hypothesis here is that it is the quality of the light, not the quantity of the light that makes a difference, and having a lot more light will not necessarily make photosynthesis occur any faster.

Discussion

With an experiment like this there is always room for error. Measurements taken incorrectly is the biggest problem, because there are multiple steps to be taken each time the light source is moved, and it is very important to ensure that this is being addressed correctly. The quality of the plant and its health could also affect whether it produced photosynthesis rates that are appropriate and generalized for its species, as well. These are variables that can only be controlled to a certain degree and, as such, have to be accounted for.

Materials and Methods

In this experiment, the goal is to measure the rate of photosynthesis that Elodea shoots have when they are exposed to specific light sources and distances. The materials needed are:

Heat filter

Meterstick

Pipette, 1 ml

Plastic tubing, 7 cm lengths

Ring stand

Ring stand test-tube clamps

Scalpel or razor blade

Spot lamp, 300 watt, or fluorescent lamp

Syringe and needle, 5 ml

Test tube

Test-tube rack

Tubing clamp, screw-type

Sodium bicarbonate solution, 2%

Elodea shoots

In order to conduct this particular experiment, there are specific steps that must be carefully followed. The rate of photosynthesis will be studied for each bulb and distance and the number of oxygen bubbles that the Elodea shoot produces will be recorded so that the differences between bulbs can be addressed. This will show whether there is a clear difference in photosynthesis based on quantity of light, quality of light, or both.