Reduction of Starches in Banana Cells Lab, 2019
Why do ripe bananas soften and taste sweeter than unripen bananas? As a plant produces sugar by the process of photosynthesis, the sugar is stored in order to be used by the plant when necessary. In bananas, the excess sugar can be stored in its fruits as starch, a polysaccharide of joined glucose molecules (monosaccharides). Starches include the plant starches amylose and amylopectin and glycogen in animal cells. The starch molecules, besides aiding in providing nutrients to the plant, cause the tissue structure to be sturdy, thus making the banana firm. As the banana fruit ripens, the starches (which are found in organelles called amyloplasts) break down. The breaking down of the starch into simpler sugars will make the fruits taste a little sweeter and be softer. Using Lugol's solution, a starch indicator, will not detect simple sugars such as glucose or fructose; that's why unripe bananas are best for visualization of starch granules. That hypothesis is that a contrast in the amount of starch granules will be noticed between unripen and ripened bananas when Lugol’s solution is used as a starch indicator.
(1) Unripe Banana (green)
(1) Ripened Banana (brown)
(2) Slides and Cover Slips
(2) Toothpicks (flatted best)
Knife – cutting bananas in half
1. Using a toothpick, collect and smear a little (about the size of a “dime”) of an “unripen” green banana on a microscope slide. Smear well and distributed the sample thinly.
2. Place a drop of Lugol’s solution on top of the banana smear and place a coverslip on top of the sample.
3. Place the slide on the microscope, with 4x objective in position and find a field of view containing the cells. Then view at higher magnifications.
4. Note the number of purplish starch granules in the cells within the amyloplast organelles.
5. Using the other slide and cover slip, repeat steps 1-4 except this time for a “ripened” brown banana.
6. Answer the questions provided after observing both slides.
7. Return and clean all materials.