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Introduction to the lesson
In the previous lesson, we studied the carbohydrate monomers. In this lesson we will learn about how monosaccharides bond together to form disaccharides and polysaccharides and some properties of the resulting molecules.
Disaccharides and the glyosidic bond
Read the section "Disaccharides and the glycosidic bond" in your text book (p.31-32).
Learning Activity 1
Answer the following questions in your exercise book.
- What disaccharide is created by joining the following monosaccharides together:
- Glucose + glucose
- Glucose + fructose
- Glucose + galactose
- Name the process whereby two monosaccharides are joined?
- Name the process whereby a disaccharide is broken into two monosaccharides?
- Which process involves the addition of water?
- Which process involves the removal of water?
- Draw the process of joining two α-glucose molecules to form maltose. Indicate the reverse processes of condensation and hydrolysis.
- Draw the process of joining α-glucose with a β-fructose to form sucrose. Indicate the reverse process of condensation and hydrolysis.
- Which carbon atoms join to form a glycosidic bond?
- Define glycosidic bond.
Testing for reducing sugars
Read Box 2.1 “Testing for presence of sugars” on p.32 of your text book.
Learning Activity 2
Answer the following questions in your exercise book.
- Explain how you would test for reducing sugars
- Answer Question 2.2 (a and b)
- Explain how you would test for non-reducing sugars
- What are some common reducing sguars?
- What is the most common non-reducing sugar?
Polysaccharides
Read the section under the heading "polysaccharides" in your text book (p.33-34).
Learning Activity 3
Answer the following questions in your exercise book.
- List the three most important polysaccharides.
- Explain why the body cannot store glucose in the cell.
- What are the characteristics of a storage carbohydrate?
- How is glucose stored in the human body?
- In which organ(s) is glycogen stored in the human body? (recall from IG)
- How is glucose stored in plants?
- In which organ(s) is starch stored in plants? (recall from IG)
- Answer Question 2.3 (p.33).
- Answer Question 2.4 on (p.34).
Testing for the presence of starch
Read Box 2.2 “Testing for the presence of starch” on p.34 of your text book.
Learning Activity 4
In your exercise book, explain how to test for starch.
Cellulose
Read the section under the heading "Cellulose" in your text book (p.34-35).
Learning Activity 5
Answer the following questions in your exercise book.
- Describe a cellulose molecule (see Fig. 2.9). Draw the ring structure of a cellulose molecule. How is it different to that of polysaccharides made from alpha-glucose?
- Explain why the hydrogen bonds which are normally considered weak bonds are strong in a cellulose molecule.
- Answer Question 2.5 on p.35.
Dipoles and hydrogen bonds
Read the section under the heading "Dipoles and hydrogen bonds" in your text book (p.35-36).
Learning Activity 6
Answer the following questions in your exercise book.
- Describe a hydrogen bond.
- Explain the relationship between the terms:
- polar and hydrophilic
- Non-polar and hydrophobic
- What is meant when a molecule is said to be hydrophilic?
Definitions and review
Definitions
- Disaccharide
- Condensation
- Glycosidic bond
- Hydrolysis
- Reducing sugar
- Non-reducing sugar
- Reduction
- Oxidation
- Polysaccharide
- Amylose
- Amylopectin
- Starch
- Glycogen
- Cellulose
- Hydrogen bond
- Microfibrils
- Fibres
- Covalent bond
- Dipole
- Polar
- Non-polar
- Hydrophillic
- Hydrophobic
Mindmap
Add this section to your chapter two mindmap.