Biology SL/HL Study Notes

Course Information

• Course Code: Biology SL/HL Classroom code: zumus4p6

• Materials: Students will be provided with a book for notes and resources used in lessons.

  • Required information in book: Name, Mr. Visaggio, Biology.

• Learning Outcomes: Attach the learning outcomes for the first subunit, A1.1.

Course Content Overview

• Water (A1.1)

• Origins of water (AHL)

• Properties of water

• Importance of carbon (B1.1)

• Storing sugar

• Fats

• Fat droplets

• Nucleic acids (A1.2)

• DNA and RNA

• DNA structure and replication (AHL)

• Diversity of DNA

• Proteins (B1.2)

• Temperature and pH

• DNA is the key? (AHL)

• Protein structures (AHL)

• Polarity, form and function (AHL)

• Intro to enzymes (C1.1)

• Intro to enzymes (AHL)

• Out of the comfort zone (Enzymes)

• Rate of reaction (Enzymes)

• Inhibiting enzymes (AHL)

Lesson 1: Properties of Water (A1.1)

Introduction

• Central Question: Why is water the medium of life?

• Key Concept ($A1.1.2$): Hydrogen bonds form as a consequence of the polar covalent bonds within water molecules.

Learning Outcomes ($A1.1.1 - A1.1.4$)

• $A1.1.1$ Water as the medium for life.

• $A1.1.2$ Hydrogen bonds as a consequence of the polar covalent bonds within water molecules.

• $A1.1.3$ Cohesion of water molecules due to hydrogen bonding and consequences for organisms.

• $A1.1.4$ Adhesion of water to materials that are polar or charged and impacts for organisms.

Initial Properties

• Water is adhesive.

• Water is cohesive.

• (More properties will be introduced later)

Polarity and Hydrogen Bonding ($A1.1.2$)

• Water Molecule Structure: Consists of $2$ hydrogen atoms bonded to an oxygen atom.

• Charge Distribution (Polarity):

  • Hydrogen atoms have a slight positive ($+$) charge.

  • The oxygen atom has a slight negative ($−$) charge.

  • This makes water molecules dipoles, having $2$ poles: a positive hydrogen pole and a negative oxygen pole.

  • This characteristic is called polarity.

• Hydrogen Bond Formation:

  • A bond forms between the positive pole of one water molecule and the negative pole of another water molecule.

  • These are called hydrogen bonds.

  • In liquid water, many hydrogen bonds form, which gives water many of its fundamental properties.

Cohesion ($A1.1.3$)

• Definition: Water molecules are attracted to other water molecules.

• Mechanism: This attraction occurs because of the hydrogen bonds formed between them.

• Consequences for Organisms:

  • Plant Transport Systems: Strong pulling forces can be exerted to draw columns of water up to the tops of the tallest trees. These water columns rarely break due to cohesion.

  • Surface Tension:

    • At a surface, the cohesion of water molecules creates surface tension, making it difficult for small objects to break through.

    • Surface tension is a measure of the force required to stretch or break the surface of a liquid.

    • Example: Some animals, like mosquito larvae, use the water's surface as a habitat. Although denser than water, they remain on the surface and do not sink due to water's high surface tension caused by cohesion.

Adhesion ($A1.1.4$)

• Definition: Water can be attracted to other types of molecules.

• Condition: This occurs only if those other molecules can form hydrogen bonds with water (i.e., they are polar or charged).

• Consequences for Organisms:

  • Capillary Action: Water is adhesive to any substance with which it can form hydrogen bonds. This allows phenomena like water climbing up capillary tubes.

Practical Application: Demonstrating Hydrogen Bond Strength

• Activity: Observe capillary action by placing one end of a capillary tube inside a beaker of water.

• Safety: Be careful not to overload the apparatus.

Review & Homework

• Review Questions:

  • What are the two properties of water discussed today?

  • Where might you see this property occurring in real life (e.g., plants and water)?

  • What allows water to have these two properties?

• Homework: Complete