Chapter No 13 Chemistry Class 10 Notes

Q.1:  Define biochemistry.

Ans: Biochemistry:

“The branch of chemistry which deals with the study of the synthesis, decomposition of substances and their reactions in living organisms such as plants and animals are called biochemistry”. OR

“The branch of chemistry that deals with the chemical compounds and processes occurring in the organism.”

Q.2:  What are biological molecules?

Ans: Biological molecules:

“The organic compounds present in living organisms are called biological molecules.”

Biological molecules include carbohydrates, proteins, lipids or fats, enzymes, vitamins and nucleic acids.

Q.3:  What are carbohydrates? Explain the classification of carbohydrates along with the uses of carbohydrates.

Ans: Carbohydrates:

Origin of name:

Since most of the carbohydrates have the general formula C_n(H₂O)_n. (n can have a value of 3 or more than 3) therefore, they are called carbohydrates meaning hydrates of carbon.

However, now a days many carbohydrates have been discovered which do not have the general formula of Cn(H₂O)_n and cannot be called hydrates of carbon however the name carbohydrate is still retained. e.g. Fructose(C₆H₁₂O₅).

Definition:

“Polyhydroxy ketones or polyhydroxy aldehydes are called carbohydrates.” OR

“Polyhydroxy derivatives of aldehydes and ketones are called carbohydrates.

Polyhydroxy means having many hydroxyl groups.

common name:

Carbohydrates are commonly-known as sugars. They are also referred to as saccharides (Latin word Saccharum meaning sugar) 

Composition:

Carbohydrates are poly functional (alcohol + aldehydes or ketones) organic compounds which mainly consist of carbon, hydrogen, and oxygen some time along with nitrogen (chitin) or Sulphur (keratin sulfate). Classification of carbohydrates:

Carbohydrates are classified into the following three groups:

1. Monosaccharides 2. Oligosaccharides 3. Polysaccharides Their detail is given below:

1. Monosaccharides:

Definition:

“The simplest carbohydrates which cannot be further hydrolyzed into smaller units are called monosaccharides.”

General formula:

They have the general formula of C_n(H₂O)_n, where n=3,4,5, and so on. 

Composition:

Monosaccharides are either aldoses having aldehydic functional group (for example glucose) or ketoses having a ketonic functional group for example fructose.

These may be trioses (C3H603), tetroses (C₄H₆O₄), pentoses (C₅H₁₀O₅) and hexoses (C6H₁₂O₆).

General properties of monosaccharides:

Some general properties of monosaccharides are:

i.Solubility:

They are soluble in water.

ii.  Physical state:

They are crystalline solids.

iii.Taste:

They have a sweet taste.

iv.Colour:

They are colorless.

v. Hydrolysis:

They cannot be hydrolyzed further.