Cambridge IGCSE Biology - Biological Molecules, Food Tests, and DNA Structure

Vocabulary flashcards covering biological molecules, elemental composition, standard food tests, and DNA structure from IGCSE Biology notes.

Organic Molecules

Molecules present in living organisms that contain carbon, comprising categories such as carbohydrates, proteins, and lipids.

Carbohydrates

Biological molecules made of long chains of simple sugars, such as monosaccharides, which contain the chemical elements carbon (C), hydrogen (H), and oxygen (O).

Monosaccharide

A single simple sugar unit, such as glucose, that serves as a building block for larger carbohydrate chains.

Disaccharide

A double sugar molecule, such as maltose, formed when two simple sugar units (monosaccharides) join together.

Polysaccharide

A complex carbohydrate molecule formed when many glucose units join together, such as starch, glycogen, or cellulose.

Triglyceride

The basic structural unit of most lipids in the body, composed of one glycerol molecule chemically bonded to three fatty acid tails.

Fats and Oils

Subcategories of lipids defined by physical state: fats are solid at room temperature, whereas oils are liquid at room temperature.

Protein

A large organic molecule made up of long chains of amino acids joined together, always containing carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).

Amino Acids

The building blocks of proteins consisting of a common basic structure with a variable 'R' group, of which approximately 20 different kinds exist.

Benedict's Test

A food test for reducing sugars (glucose) where Benedict's solution is added to a sample and heated at $80\,^\circ\text{C}$ in a water bath for 5 minutes, changing from blue to orange or brick red if positive.

Iodine Test

A chemical test used to check for the presence or absence of starch in a food sample, changing colour from orange-brown to blue-black when positive.

Biuret Test

A food test used to detect proteins where Biuret solution is added to a sample, producing a colour change from blue to violet / purple for a positive result.

Ethanol Emulsion Test

A food test for lipids where a sample is mixed with $2\,\text{cm}^3$ of ethanol, shaken, and added to cold water, forming a cloudy emulsion for a positive result.

DCPIP Test

A food test for vitamin C where a liquid sample is added to $1\,\text{cm}^3$ of DCPIP solution, causing the blue dye to become colourless for a positive result.

Chromosome

A structure inside the nucleus consisting of a long strand of DNA wrapped around proteins.

DNA (Deoxyribonucleic Acid)

The double-stranded helical molecule containing instructions for the growth and development of all living organisms.

Nucleotide

The monomer unit of DNA consisting of a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases (A, T, C, or G).

Complementary Base Pairing

The specific matching rule in DNA where Adenine always pairs with Thymine (A-T) and Cytosine always pairs with Guanine (C-G) held together by hydrogen bonds.

Sugar-Phosphate Backbone

The outer structural framework of a DNA strand formed by repeating, alternating units of phosphate and deoxyribose sugar.