Bio Pd.docx

Experiment#: 8 Date: Topic: Ethylene/Planning and Designing

Problem Statement: Jack noticed that his parents would always place a ripe banana in a bunch of unripe bananas to increase their speed of ripening. Jack learned that some fruits (such as bananas) produce ethylene as they ripen. This gas stimulates fruit ripening. Plan and Design an experiment to show the effects of ethylene in fruit ripening. Hypothesis: The greater the number of ripe bananas placed alongside unripe bananas in a closed area, the greater the speed at which the unripe bananas ripen. Aim: To determine the effect of increased levels of ethylene on the speed of fruit ripening. Apparatus and Materials: unripe bananas, ripe banana, newspaper, iodine solution, Petri dish, stopwatch, knife, distilled water, tape. Procedure: 1. Cut an unripe banana in half and place one of the halves face down in 2 cm3 of iodine solution in a petri dish for 5 minutes. 2. Label each unripe banana sample A, B and C respectively. Place three ripe bananas along with sample C, wrap in newspapers and seal with tape. Repeat for sample B using one ripe banana, and sample A, using no ripe bananas. 3. Leave the bananas for 3 days at room temperature. . 4. On the final day, remove each samples from the newspapers. Cut one sample in half and place one of the halves face down in 2 cm3 of iodine solution in a Petri dish for 5 minutes. Repeat for the other samples. 5. After the 5 minutes, remove the bananas and lightly rinse the stained side. 6. Observe the degree to which each sample is stained and record observations according to either unstained, lightly stained and highly stained.

Controlled Variable: the length of time each sample was left in the iodine solutions, the type of bananas used Manipulated Variable: number of ripe bananas used alongside each sample Responding Variable: the speed at which the bananas ripen after the 3 days, the intensity of the stain on each fruit Expected Results: Banana Sample

Colour and

Intensity of

Texture After 3

Stain

Days A B C TABLE SHOWING LAYOUT OF EXPECTED RESULTS Over the three days, sample C will change colour from green to yellow most quickly followed by B then A. It will also produce the lightest stain in the iodine test. Of the three samples, A is expected to produce the darkest stain. The unripe banana that was initially tested will produce a higher intensity stain than the test subjects. Interpretation: Ethylene is a plant hormone which stimulates fruit ripening. It is secreted by various fruits (such as bananas) as they ripen. In the presence of this gas, the rate at which a fruit ripens is increased and thus, the fruit ripens faster than if it were not in the presence of the gas. The sealed newspapers are used to trap the ethylene produced by the bananas to help them ripen faster. As the bananas ripen, there is a change in colour (from green to yellow), texture (from hard to soft) and starch is converted to various sugars. Thus, sample C will show a greater change in colour (from green to yellow) and texture (from hard to soft) than sample A and B due to the presence of the two ripe bananas. Moreover, Sample B will show a greater colour and texture

change than Sample A due to the presence of a ripe banana. The iodine solution is used to test for the presence of starch. It binds to starch molecules producing a complex which gives a dark violet/blue colour depending on the concentration of starch present. The darker the stain, the more starch the substance contains. Therefore, the riper the fruit, the less starch it contains and the lighter the stain produced by the iodine complex. The extra unripe banana is used to serve as a reference point. It is expected to contain the most starch and thus, the darkest stain. Additionally, A is expected to produce a darker stain than B, as B is expected to be more ripe at the end of the experiment, and B will produce a darker stain than C, as C is expected to be the most ripe after the experiment.

Precautions: 

Choose unripe bananas of similar sizes and from the same bunch.

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Do not rinse the bananas too vigorously or too much to prevent removing any of the stains.

Assumptions: 

The three days are enough for there to be a noticeable difference in the level of ripeness of the bananas.

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Rinsing the stained side of the bananas had a negligible effect on the intensity of the stains.

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The extra unripe banana that was tested for starch can serve as a reference point as to the quantity of starch that each sample initially contained.

Limitations: 

The initial concentration of starch in each banana is unknown.

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The concentration of the iodine solution may not produce colour intensities which can be easily distinguished.