FBISE 1st Year Biology (Grade 11) — Study Lecture Notes
CHAPTER 2: BIOLOGICAL MOLECULES
(COMPLETE NOTES)
1. Introduction to Biochemistry
Biochemistry is the fundamental branch of biology that explores the chemical components,
molecular structures, and metabolic reactions taking place within living organisms. It forms the
foundation for understanding cellular physiology, genetics, and molecular biology.
DEFINITION: Biochemistry
The branch of science concerned with the chemical and physicochemical processes that occur
within living organisms.
Metabolism: Anabolism vs. Catabolism
All chemical biochemical pathways taking place simultaneously in a living cell are collectively
called metabolism. This is strictly divided into two synchronized pathways:
1. Anabolism: Processes where simple molecules combine to synthesize complex organic
structures. These are endergonic reactions requiring an input of free energy.
Example: Photosynthesis (6CO₂ + 6H₂O + Solar Energy → C₆H₁₂O₆ + 6O₂)
2. Catabolism: Processes where complex organic macromolecules are broken down into
simpler compounds, releasing chemical energy.
Example: Cellular Respiration (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy/ATP)
2. Water — The Universal Medium of Life
Water (H₂O) is the most abundant inorganic compound in living cells, spanning from 65% to
90% of total mass depending on tissue type. It serves as the absolute matrix for metabolic
reactions.
Key Physicochemical Properties of Water
A. Polarity & Solvent Action: Due to the extreme electronegativity of oxygen, water holds a
partial negative charge on oxygen and partial positive charges on hydrogen, establishing a polar
configuration.
Example: Ionic compounds (like NaCl) dissolve readily because water molecules surround
the ions (solvation spheres). Non-polar lipids are hydrophobic and form stable membrane
barriers.
, B. High Specific Heat Capacity: The quantity of heat needed to raise the temperature of 1g of
water by 1°C is exceptionally high due to the extensive network of hydrogen bonds.
Significance: It works as a temperature buffer, protecting organisms from sudden
environmental temperature shocks.
C. High Heat of Vaporization: Water requires massive heat energy to transition from a liquid
state into vapor (574 kcal/kg).
Example: Perspiration in humans and transpiration in plants release heat, providing an
essential evaporative cooling effect.
D. Cohesion and Adhesion: Cohesion is the attraction between water molecules themselves
(due to H-bonds). Adhesion is the attraction between water and polar surfaces (like cell walls).
Significance: Allows the continuous column of water to rise through xylem vessels in plants
(Ascent of Sap).
3. Carbohydrates
DEFINITION: Carbohydrates
Polyhydroxy aldehydes or ketones, or complex organic substances which yield such units upon
chemical hydrolysis. They are composed of Carbon, Hydrogen, and Oxygen in a general ratio of
1:2:1.
Classification of Carbohydrates
A. Monosaccharides (Simple Sugars)
They cannot be broken down any further into simpler sugars by hydrolysis. They are sweet,
soluble, and crystalline.
• Categories: Trioses (3-Carbon, e.g., Glyceraldehyde), Pentoses (5-Carbon, e.g., Ribose),
and Hexoses (6-Carbon, e.g., Glucose).
• Ring Structures: In water, sugars form stable ring structures: 5-membered rings are
Furanose (e.g., Ribofuranose) and 6-membered rings are Pyranose (e.g., Glucopyranose).
┌────────────────────────────────────────────────────────┐
│ DIAGRAM: GLUCOSE RING FORM (ALPHA-D-GLUCOPYRANOSE)
│
└────────────────────────────────────────────────────────┘
Figure: Structural schematic of Glucose Ring Form (Alpha-D-Glucopyranose). Please refer to textbook for
exam drawing.
B. Oligosaccharides
Yield 2 to 10 monosaccharide units upon hydrolysis. Linked covalently via a Glycosidic Bond
formed through condensation synthesis (removal of water).
CHAPTER 2: BIOLOGICAL MOLECULES
(COMPLETE NOTES)
1. Introduction to Biochemistry
Biochemistry is the fundamental branch of biology that explores the chemical components,
molecular structures, and metabolic reactions taking place within living organisms. It forms the
foundation for understanding cellular physiology, genetics, and molecular biology.
DEFINITION: Biochemistry
The branch of science concerned with the chemical and physicochemical processes that occur
within living organisms.
Metabolism: Anabolism vs. Catabolism
All chemical biochemical pathways taking place simultaneously in a living cell are collectively
called metabolism. This is strictly divided into two synchronized pathways:
1. Anabolism: Processes where simple molecules combine to synthesize complex organic
structures. These are endergonic reactions requiring an input of free energy.
Example: Photosynthesis (6CO₂ + 6H₂O + Solar Energy → C₆H₁₂O₆ + 6O₂)
2. Catabolism: Processes where complex organic macromolecules are broken down into
simpler compounds, releasing chemical energy.
Example: Cellular Respiration (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy/ATP)
2. Water — The Universal Medium of Life
Water (H₂O) is the most abundant inorganic compound in living cells, spanning from 65% to
90% of total mass depending on tissue type. It serves as the absolute matrix for metabolic
reactions.
Key Physicochemical Properties of Water
A. Polarity & Solvent Action: Due to the extreme electronegativity of oxygen, water holds a
partial negative charge on oxygen and partial positive charges on hydrogen, establishing a polar
configuration.
Example: Ionic compounds (like NaCl) dissolve readily because water molecules surround
the ions (solvation spheres). Non-polar lipids are hydrophobic and form stable membrane
barriers.
, B. High Specific Heat Capacity: The quantity of heat needed to raise the temperature of 1g of
water by 1°C is exceptionally high due to the extensive network of hydrogen bonds.
Significance: It works as a temperature buffer, protecting organisms from sudden
environmental temperature shocks.
C. High Heat of Vaporization: Water requires massive heat energy to transition from a liquid
state into vapor (574 kcal/kg).
Example: Perspiration in humans and transpiration in plants release heat, providing an
essential evaporative cooling effect.
D. Cohesion and Adhesion: Cohesion is the attraction between water molecules themselves
(due to H-bonds). Adhesion is the attraction between water and polar surfaces (like cell walls).
Significance: Allows the continuous column of water to rise through xylem vessels in plants
(Ascent of Sap).
3. Carbohydrates
DEFINITION: Carbohydrates
Polyhydroxy aldehydes or ketones, or complex organic substances which yield such units upon
chemical hydrolysis. They are composed of Carbon, Hydrogen, and Oxygen in a general ratio of
1:2:1.
Classification of Carbohydrates
A. Monosaccharides (Simple Sugars)
They cannot be broken down any further into simpler sugars by hydrolysis. They are sweet,
soluble, and crystalline.
• Categories: Trioses (3-Carbon, e.g., Glyceraldehyde), Pentoses (5-Carbon, e.g., Ribose),
and Hexoses (6-Carbon, e.g., Glucose).
• Ring Structures: In water, sugars form stable ring structures: 5-membered rings are
Furanose (e.g., Ribofuranose) and 6-membered rings are Pyranose (e.g., Glucopyranose).
┌────────────────────────────────────────────────────────┐
│ DIAGRAM: GLUCOSE RING FORM (ALPHA-D-GLUCOPYRANOSE)
│
└────────────────────────────────────────────────────────┘
Figure: Structural schematic of Glucose Ring Form (Alpha-D-Glucopyranose). Please refer to textbook for
exam drawing.
B. Oligosaccharides
Yield 2 to 10 monosaccharide units upon hydrolysis. Linked covalently via a Glycosidic Bond
formed through condensation synthesis (removal of water).
