Background
	Diffusion is the movement of a substance in a certain direction along its concentration gradient. Substances can diffuse through two different pathways: active and passive transport. Active transport requires the energy released by the hydrolysis of adenosine triphosphate (ATP) to move a substance against its concentration. The sodium-potassium is an important application of active transport, using energy to push three Na+ out of the cell and bring two K+ into the cell, which can be used to manipulate the electrochemical gradient of the cell and facilitate nerve responses. It is generally used for transporting ions, which generally cannot permeate the covalent molecules of the plasma membrane. In contrast, passive transport does not require energy. Passive transport manifests as facilitated and simple diffusion. Facilitated diffusion utilizes specialized proteins to transport polar-covalent substances through the membrane and bypass the nonpolar fatty acid tails. Aquaporins are an example of proteins used to facilitate and expedite the diffusion of polar water molecules into the cell. Unlike facilitated diffusion and active transport, simple diffusion does not require any specialized mechanism. As entropy always increases within a system, the substance undergoing diffusion will be distributed evenly within the solution until it reaches equilibrium. Osmosis is defined as the simple diffusion of water along its concentration gradient. In other words, water moves from an area of high concentration to an area of low concentration. Osmosis has several important applications in biology. Osmotic pressure exerted by water contained within plant cells creates turgor pressure; this contributes to rigidity and growth while preventing wilting. While plant cells prefer hypotonicity, animal cells lack cell walls and thus must maintain an isotonic environment.
Recent studies demonstrate the important applications of osmosis. For example Casas et al. (2024) found that forward osmosis removed over 95% of organic pollutants from wastewater treatment plant effluent. In contrast, Sayed et al. (2021) found that techniques such as reverse osmosis were incapable of bringing pesticide residues below the European potable water limit in potatoes.
	This study aims to analyze the role of osmosis in the effect of sucrose concentration on the mass of a dialysis packet and the mass of potato. For both objects, it was hypothesized that sucrose concentration would be directly proportional to mass because both would be hypotonic to a sucrose solution.


Write a background on Plant Pigment and Photosynthesis pertaining to Spectrophotometers, as well as the process of Photosynthesis in particular using the information below in the style of the background above:

Light is a part of a continuum of radiation, or energy waves. Shorter wavelengths of
energy have greater amounts of energy. For example, high-energy ultraviolet rays,
with wavelengths of approximately 1 nanometer (nm) to 380 nm, can harm living
tissues due to the large amount of energy they carry. Wavelengths of light within the
visible part of the light spectrum power photosynthesis. The visible light spectrum is
from about 400 to 750 nm (1 billionth of a meter). Only visible light, with its
intermediate wavelengths, has enough energy to cause chemical change without
destroying biological molecules. The short, high frequency waves of gamma rays
(10-5
nm) have too much energy and break the hydrogen bonds found within biological
molecules such as proteins and nucleic acids like DNA. The longer waves of heat,
microwaves and radio waves (103
nm to 103 meters) do not possess enough energy and
are absorbed by the water molecules in a plant.
When light is absorbed by leaf pigments such as chlorophyll a or b, electrons within
each Photosystem are boosted to a higher energy level. This energy is used to produce
ATP, to reduce NADP to NADPH and then used to incorporate carbon dioxide (CO2) into
organic molecules in a process called carbon fixation. Leaf disks float, normally.
When the air spaces are infiltrated with a solution the overall density of the leaf disk
increases and the disk sinks. The infiltration solution includes a small amount of
sodium bicarbonate (NaHCO3) thus enabling the bicarbonate ion to serve as the carbon
source for photosynthesis. As photosynthesis proceeds, oxygen is released into the
interior of the leaf which changes its buoyancy causing the disks to rise. Since cellular
respiration is taking place at the same time within the leaf, consuming the oxygen
generated by photosynthesis, the rate that the disks rise is an indirect measurement
of the net rate of photosynthesis. In this lab, you will measure the net rate of
photosynthesis for several plants under various lighting conditions.

Chloroplasts and Photosynthesis

Plants, along with algae, cyanobacteria, and a few other organisms, perform photosynthesis, using light energy to power a chemical reaction that yields food. In plants, chloroplasts are the organelles of photosynthesis. Every green part of a plant contains some chloroplasts, but they are most concentrated in leaves. Chloroplasts contain the green pigment chlorophyll, which colors the leaves and absorbs sunlight.

Light Reactions of Photosynthesis

In the light reactions of photosynthesis, light energy is absorbed by chlorophyll and used to excite electrons. The excited electrons then enter one of two electron transport chains. One chain consists of enzymes that convert adenosine diphosphate (ADP) and another phosphate to adenosine triphosphate (ATP). The other chain consists of enzymes that convert nicotinamide adenine dinucleotide phosphate (NADP) and hydrogen (H) to NADPH. In this activity, students will use DPIP (2,6-dichlorophenol-indophenol, a blue dye) as an indicator of the light reaction. The DPIP, when added to a suspension of chloroplasts, will react like NADP as follows: DPIP + H → DPIPH. DPIPH is colorless, so as the light reactions take place, the blue color of the solution diminishes. The rate of color change indicates the rate of the light reaction.

Chromatography

It is often useful to determine whether a material is a pure substance or a mixture and, if a mixture, to separate its components. Several basic techniques, often referred to collectively as separation science, have been developed for this purpose. Paper chromatography is frequently used to separate mixtures of biological compounds. In this activity, you will use paper chromatography to determine if a green leaf contains only one pigment or a mixture of pigments. Each pigment consists of a particular molecule whose properties give it a characteristic color. If a leaf contains multiple pigments, you may expect that each will dissolve in the solvent and travel up the paper at a different rate. Also, some will tend to bond more or less strongly to the cellulose in the paper. These differences lead to the formation of different-colored bands on the paper, one band for each pigment in the mixture. If the leaf contains only one pigment, expect to obtain only one color band.

Four pigments are widely found in leaves: carotene, xanthophyll, chlorophyll a, and chlorophyll b. Carotene is highly soluble in the chromatography solvent that you will use, and its molecules do not form hydrogen bonds with cellulose. Carotene produces a faint band of yellow to yellow-orange. Xanthophyll is slightly less soluble than carotene in the solvent, and it does form some hydrogen bonds with cellulose. Xanthophyll produces a yellow band. Both chlorophyll a and chlorophyll b readily form hydrogen bonds with cellulose. Chlorophyll a produces a band of bright green to blue-green. Chlorophyll b produces a band of yellow-green to dark olive green.

Spectrophotometers and colorimeters

You will use either a spectrophotometer or colorimeter to measure the color change of DPIP. You will prepare a sample by adding a chloroplast suspension, DPIP, and a buffer to water in a vial called a cuvette. The cuvette is the appropriate size to fit the chamber of the instrument. The instrument works by shining a beam of light of known intensity through the clear cuvette. On the opposite side from the light source is a photoresistor that detects the intensity of light that has passed through the sample. DPIP will absorb some of the light that enters the cuvette. As the light reaction continues and the DPIP is replaced by the colorless DPIPH, less light is absorbed in the cuvette, so the photoresistor detects increasing intensity. Since DPIP absorbs light most strongly at orange-red wavelengths, you will set the spectrophotometer to read the amount of light transmitted in that part of the spectrum (605 nm). If you are using a colorimeter, a data-logger device will set the amount of light transmitted, or, if connected to a computer, the software will set the light transmission. The following procedure is written for use with a spectrophotometer. Your teacher may give you additional instructions specific to the particular instrument that you use.