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Theory - To Test the Presence of Starch in Potato, Biology, Science, Class 9 | Science Class 9 PDF Download

Objective

Our objective is to test for the presence of starch in a given food sample.


The Theory

Starch is the most common carbohydrate in the human diet and is contained in many staple foods. The major sources of starch intake worldwide are cereals (rice, wheat, and maize) and root vegetables (potatoes and cassava). We can use iodine solution to test for the presence of starch. If starch is present is a food item, it turns blue-black colour when iodine solution is added to it.


What are Carbohydrates?

Carbohydrates are one of the main components of our daily diet. This category of foods include sugars, starches, and fibre. Carbohydrates are built up of sugar molecules that contain hydrogen, carbon and oxygen. Chemically, most of these carbon atoms have a hydrogen group and hydroxyl group attached to it. Thus, the word Carbohydrates Cn(H2O)n literally mean carbon (carbo) + water (hydrate). 


Classification of Carbohydrates

Carbohydrates are classified as simple or complex. This classification depends on the chemical structure of the food, and how quickly the sugar is digested and absorbed.


Simple Carbohydrates

Simple carbohydrates are simple sugars with a chemical structure that is composed of one or two sugars. There are two types of simple carbohydrates - monosaccharides and disaccharides.

  • Monosaccharides consist of only one sugar, and examples are glucose, fructose and galactose.

  • Disaccharides consist of two chemically-linked monosaccharides, and examples are sucrose, lactose and matose.


Complex Carbohydrates

Complex carbohydrates have three or more sugars and are classified as oligosaccharides and polysaccharides.

  • Oligosaccharides consist of a small number of monosaccharides, which does not exceed 10. They are important in the absorption of certain minerals and the formation of fatty acids. Examples are raffinose and stachyose.

  • Polysaccharides are often made up of a large number of monosaccharides and disaccharides. Examples are starch, glycogen and cellulose.

Theory - To Test the Presence of Starch in Potato, Biology, Science, Class 9 | Science Class 9

 

What is Starch?

Starch is the major carbohydrate reserved in plant tubers and seed endosperm. It is stored in plant cells. Starch molecules arrange themselves in the plant in semi-crystalline granules. A starch molecule contains a large number of glucose molecules. These glucose molecules are arranged either as occasionally branched chains (amylopectin) or as unbranched chains (amylose). Amylose is a much smaller molecule than amylopectin.

Theory - To Test the Presence of Starch in Potato, Biology, Science, Class 9 | Science Class 9  Theory - To Test the Presence of Starch in Potato, Biology, Science, Class 9 | Science Class 9

The colour of natural starch is milky white and the pure form of starch is insoluble in water and alcohol. Depending on the plant, starch generally contains 20-25% amylase and 75-80% amylopectin. Each plant species have a unique starch granular size.  Rice starch is relatively small (about 2μm), while potato starches have larger granules (up to 100μm). Starch becomes soluble in water when heated.

Theory - To Test the Presence of Starch in Potato, Biology, Science, Class 9 | Science Class 9
 

Learning Outcomes

  1. Students understand the terms carbohydrates, monosaccharides, disaccharides, oligosaccharides, polysaccharides and starch.

  2. Students understand the method to test for the presence of starch.

  3. Students acquire the skills to perform the experiment using different food samples having observed the animation and simulation.

The document Theory - To Test the Presence of Starch in Potato, Biology, Science, Class 9 | Science Class 9 is a part of the Class 9 Course Science Class 9.
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FAQs on Theory - To Test the Presence of Starch in Potato, Biology, Science, Class 9 - Science Class 9

1. What is the purpose of testing the presence of starch in potatoes?
Ans. The purpose of testing the presence of starch in potatoes is to determine the starch content, which can indicate the quality, freshness, and suitability of potatoes for consumption or various culinary purposes. Starch is an essential carbohydrate found in potatoes, and its presence affects the texture and taste of cooked potatoes.
2. How can the presence of starch in potatoes be tested?
Ans. The presence of starch in potatoes can be tested using iodine solution. Iodine reacts with starch to form a blue-black color, allowing us to visually determine whether or not starch is present in the potato. The potato is usually cut and a few drops of iodine solution are added to it. If the potato turns blue-black, it indicates the presence of starch.
3. Are potatoes the only food source that contains starch?
Ans. No, potatoes are not the only food source that contains starch. Starch is a common carbohydrate found in various plant-based foods such as rice, wheat, corn, and other grains. It is also present in starchy vegetables like sweet potatoes, yams, and cassava. Additionally, processed foods like bread, pasta, and cereals also contain starch.
4. What are the benefits of starch in potatoes?
Ans. Starch in potatoes provides several benefits. It is a major source of energy for the body due to its high carbohydrate content. Starch also helps in regulating blood sugar levels and promoting digestive health. Additionally, it contributes to the texture and thickness of various culinary preparations such as soups, stews, and sauces.
5. Can the presence of starch in potatoes affect their cooking properties?
Ans. Yes, the presence of starch in potatoes can significantly affect their cooking properties. Potatoes with a higher starch content, such as russet or Idaho potatoes, tend to be fluffier and absorbent when cooked. They are ideal for baking, mashing, or making fries. On the other hand, potatoes with lower starch content, like waxy potatoes, retain their shape better when cooked and are suitable for boiling or using in salads.
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