BIOLOGY A LEVEL REVISION
UNIT 1: BIOLOGICAL
MOLECULES
COMMON CHEMISTRY OF LIFE
All life on Earth shares a similar chemical basis. This means that the types of
molecules and reactions found in cells are extremely similar in all organisms.
This similarity supports the theory of evolution because it suggests that all
life evolved from a common ancestor.
Key molecules in cells and their functions:
Carbohydrates
-Provide energy for respiration.
-Form structural components, e.g., cellulose in plant cell walls, which gives
strength and support.
-Found in plasma membranes as glycoproteins.
Lipids
-Make up cell membranes (phospholipid bilayer).
-Serve as energy storage (triglycerides store more energy per gram than
carbohydrates).
-Form some hormones, such as steroid hormones.
Proteins
-Build cell structures (cytoskeleton, connective tissue).
-Act as enzymes to catalyse chemical reactions.
-Serve as chemical messengers (hormones) and transport molecules (e.g.,
haemoglobin in blood).
-Nucleic Acids (DNA and RNA)
-Carry genetic information that directs protein synthesis.
-The genetic code is universal, supporting evolutionary relationships.
Water
,-Major component of cells (70–90% of cell content).
-Solvent for biochemical reactions.
-Helps maintain temperature due to high heat capacity.
-Cohesion between water molecules allows transport in plants and surface
tension at the water-air interface.
Practical link: Searching for life in space, focuses on liquid water because it is
essential for all known life.
, MONOMERS AND POLYMERS
Monomers are the small building blocks of biological molecules, while
Polymers are long chains of monomers.
Examples:
Monosaccharides → Polysaccharides
Amino acids → Proteins
Nucleotides → DNA/RNA
Key Reactions:
Condensation Reaction
-Joins two monomers to form a bond.
-Produces water as a by-product.
Example: Two glucose molecules forming maltose (a disaccharide).
Hydrolysis Reaction
-Breaks a bond between two monomers.
-Water is used to split the bond.
Example: Breaking maltose into two glucose molecules.
Explanation: Condensation and hydrolysis are necessary in metabolism
because they allow cells to build complex molecules for energy storage,
structure, and enzymes, and then they break them down for energy release.
UNIT 1: BIOLOGICAL
MOLECULES
COMMON CHEMISTRY OF LIFE
All life on Earth shares a similar chemical basis. This means that the types of
molecules and reactions found in cells are extremely similar in all organisms.
This similarity supports the theory of evolution because it suggests that all
life evolved from a common ancestor.
Key molecules in cells and their functions:
Carbohydrates
-Provide energy for respiration.
-Form structural components, e.g., cellulose in plant cell walls, which gives
strength and support.
-Found in plasma membranes as glycoproteins.
Lipids
-Make up cell membranes (phospholipid bilayer).
-Serve as energy storage (triglycerides store more energy per gram than
carbohydrates).
-Form some hormones, such as steroid hormones.
Proteins
-Build cell structures (cytoskeleton, connective tissue).
-Act as enzymes to catalyse chemical reactions.
-Serve as chemical messengers (hormones) and transport molecules (e.g.,
haemoglobin in blood).
-Nucleic Acids (DNA and RNA)
-Carry genetic information that directs protein synthesis.
-The genetic code is universal, supporting evolutionary relationships.
Water
,-Major component of cells (70–90% of cell content).
-Solvent for biochemical reactions.
-Helps maintain temperature due to high heat capacity.
-Cohesion between water molecules allows transport in plants and surface
tension at the water-air interface.
Practical link: Searching for life in space, focuses on liquid water because it is
essential for all known life.
, MONOMERS AND POLYMERS
Monomers are the small building blocks of biological molecules, while
Polymers are long chains of monomers.
Examples:
Monosaccharides → Polysaccharides
Amino acids → Proteins
Nucleotides → DNA/RNA
Key Reactions:
Condensation Reaction
-Joins two monomers to form a bond.
-Produces water as a by-product.
Example: Two glucose molecules forming maltose (a disaccharide).
Hydrolysis Reaction
-Breaks a bond between two monomers.
-Water is used to split the bond.
Example: Breaking maltose into two glucose molecules.
Explanation: Condensation and hydrolysis are necessary in metabolism
because they allow cells to build complex molecules for energy storage,
structure, and enzymes, and then they break them down for energy release.
