Biology Key Points Digestive
The Digestive System
Molecules of Life
Carbohydrates consist of the elements carbon, hydrogen, and oxygen. Carbohydrates are the main
source of energy in humans and glucose is the main molecule in carbohydrates. Sucrose is 2 sugar units
and there are many other sugar units such as starch, cellulose, or glycogen. Glucose and sucrose are
simple sugars.
Proteins consist of carbon, hydrogen, oxygen and nitrogen and amino acids. As there are 20 different
types of amino acids, there are endless varieties of proteins. The bonds in proteins hold 3D shape.
, Lipids are fats which are made up of carbon, hydrogen, and oxygen. 3 fatty acids are needed to form 1
glycerol.
Carbohydrates are used in cellulose in the cell wall, starch and glycogen for storage and respiration.
Proteins are used for building cells and tissue, enzymes, and hair. Lipids are used as an energy store
which make up components of all membranes, hormones and keeps the body warm.
Required Practical
In GCSE, you must know how to identify starch, reducing sugars, proteins and lipids in different types of
food. The 5 different types of food are cheese, rice cake, bread, biscuit and cereal.
Testing for starch
The test for starch uses iodine solution to identify the presence of starch.
1) Place one spatula of broken down food on a dimple tile.
2) Place a few drops of iodine solution onto the food.
3) Record the name of the food and any change in colour.
Iodine is a yellow, brown colour and in the presence of starch, it changes colour to blue black.
The Digestive System
Molecules of Life
Carbohydrates consist of the elements carbon, hydrogen, and oxygen. Carbohydrates are the main
source of energy in humans and glucose is the main molecule in carbohydrates. Sucrose is 2 sugar units
and there are many other sugar units such as starch, cellulose, or glycogen. Glucose and sucrose are
simple sugars.
Proteins consist of carbon, hydrogen, oxygen and nitrogen and amino acids. As there are 20 different
types of amino acids, there are endless varieties of proteins. The bonds in proteins hold 3D shape.
, Lipids are fats which are made up of carbon, hydrogen, and oxygen. 3 fatty acids are needed to form 1
glycerol.
Carbohydrates are used in cellulose in the cell wall, starch and glycogen for storage and respiration.
Proteins are used for building cells and tissue, enzymes, and hair. Lipids are used as an energy store
which make up components of all membranes, hormones and keeps the body warm.
Required Practical
In GCSE, you must know how to identify starch, reducing sugars, proteins and lipids in different types of
food. The 5 different types of food are cheese, rice cake, bread, biscuit and cereal.
Testing for starch
The test for starch uses iodine solution to identify the presence of starch.
1) Place one spatula of broken down food on a dimple tile.
2) Place a few drops of iodine solution onto the food.
3) Record the name of the food and any change in colour.
Iodine is a yellow, brown colour and in the presence of starch, it changes colour to blue black.
