Answer:
Independent Variable: Amount of Light Energy
Dependent Variable: Photosynthesis
What is photosynthesis, and how does it work?
Photosynthesis is a biochemical process in which plants use energy from the sun to convert carbon dioxide into a usable form of carbon (sugar). The process of photosynthesis is divided into two types of enzyme mediated reactions: light-dependent reactions and light-independent reactions (Calvin/dark cycle). The light-dependent reactions take place in the thylakoid membrane of the plant leaf and during this process energy from the sunlight (which contains all wavelengths of light) is converted into chemical energy (ATP). The light-independent processes take place in the stroma of the plant and occurs both in the presence and absence of light. The overall equation for photosynthesis is written 6CO2 + 6H2O ------> C6H12O6 + 6O2. The equation shows that plants require, water, carbon dioxide, light & chlorophyll for photosynthesis to occur. Simple experiments can be conducted to show this using a bicarbonate solution, a sufficient light source and plant leaves. Leaves, which are considered photosynthetic organs, have a clear waxy upper epidermis which allows a significant amount of light through to the plant and reduces water loss. The stomata (a minute epidermal pore in a leaf) on the lower epidermis of the plant allow it to absorb carbon dioxide and expel oxygen. The chloroplasts absorb light and use this in addition to carbon dioxide and water to produce food for the plant. Although chlorophyll is critical to photosynthesis there are other important pigments in addition to chlorophyll that are useful to plants. The presence of these pigments can be observed when completing a simple chromatography experiment using plant leaves and alcohol. It is important to note that the different pigments only absorb certain wavelengths of light. For example, chlorophyll A and B only absorb light in the range red/blue violet and carotenoids absorb blue-green light. The wavelengths that are most absorbed are also the wavelengths that result in the most efficient photosynthesis.
What is the specific function of light energy in photosynthesis?
Light serves a few roles in photosynthesis. It is energizes the chlorophylls, which then transfer that energy to the reaction centers of the photosystems to initiate the transfer of an electron. Light is also used to signal the activation of the Calvin-Benson cycle (which is inhibited in the dark to conserve energy in the chloroplast) and to regulate many other developmental processes that affect photosynthesis. The synthesis of chlorophyll itself involves a light catalyzed reaction. In motile plants (such as swimming green algae), light is also used for navigation. Then of course there are all of the negative processes caused by light during photosynthesis. Light energy absorbed by a chlorophyll can transfer to molecular oxygen to form reactive oxygen species (aka free radicals), especially on a bright sunny day when the supply of light energy exceeds the rate of CO2 diffusion into the chloroplast. UV light can directly damage the photosystems and also causes damage to the chloroplast DNA (and nuclear and mitochondrial DNA too).
Independent and Dependent Variable:
I’ll answer with an example:
Let’s say there is homework, an exam, or instructional course material being taught. The amount of effort or personal engagement you attempt to have with said material (e.g., statistics or research methods), measured by some value, can be an independent variable.
This effort/engagement variable may affect the value of another variable, let’s say understanding of course material, or degree of good habits as a learner or student. This too is measured by some hypothetical value. We manipulate the first value, engagement or effort, to see if there are changes in the degree or amount of understanding or good learning habits. This second value is a dependent variable.
So in an experiment, we test this proposed relationship and see whether changes in the independent variable of effort impacts the dependent variable of understanding. A high value in the effort variable could represent your reading the material carefully, trying to understand the implications of the concepts being taught. A low value in this variable could be, for example, asking homework questions on Quora. I leave it as an exercise to the reader to decide what form the relationship between effort and understanding might take in this context.
Thanks,
Eddie