Biology Chapter: Properties of Water

Nutritional Biochemistry: Principles of Chemistry: Water

• Matter is composed of elements, and compounds are combinations of elements.
• Key elements for life include carbon, oxygen, hydrogen, and nitrogen (96% of living organisms).
• Atomic number represents the number of protons in an atom.
• Isotopes of an element have different numbers of neutrons.
• Electrons exist in energy levels within atoms.
• Strong bonds include covalent bonds (sharing electrons) and ionic bonds (donating electrons).
• Weak bonds include van der Waals interactions and hydrogen bonds.
• Biology is understood using chemical principles.

Last Time - Quiz

• Trace elements differ from other elements in their abundance and role in biological processes.
• Atomic number is the number of protons, while atomic mass is the total number of protons and neutrons in an atom.
• Major elements (carbon, hydrogen, oxygen, nitrogen) have atomic values; the atomic masses and numbers for each should be known.
• Isotopes of an element have similar numbers of protons but different numbers of neutrons, hence differing atomic masses. Values for the five isotopes of zinc are provided.
• Covalent bonds involve electron sharing, while ionic bonds involve electron transfer.
• Weak bonds (van der Waals interactions, hydrogen bonds), have significance in biological molecules.
• Macromolecular structures utilize the different types of bonds

Learning Outcomes

• Understand the relationship of polarity and hydrogen bonding to water's properties.
• Describe the properties of water, including its polarity, hydrogen bonding, and other chemical interactions that relate to biological function.
• Detail how acid-base conditions are regulated in blood and cells.
• Explain the importance of diffusion in water movement (osmosis).

The Molecule That Supports Life: Water

• Water on other planets is important for supporting life as we know it on Earth.
• All organisms primarily consist of water.
• Life on Earth originated and evolved in water before spreading to land.

The Molecule That Supports Life: Water (2)

• Humans can survive weeks without food, but only a short time without water.
• Water is essential to many biological reactions.
• Biological cells are primarily composed of water.

Clinical Relevance

• Water requirements vary among different demographics.
• Proper water intake is vital for general bodily functions, including neuroendocrine regulation and metabolism.
• Prolonged inadequate water intake can impact various bodily processes, leading to chronic health issues.

The Polarity of Water Molecules

• Water (H₂O) has a more electronegative oxygen atom, drawing electrons in the covalent bonds towards it.
• This unequal electron distribution creates polar covalent bonds within the water molecules.
• The resulting polarity causes the molecules to possess distinct negative and positive poles.

Water and Hydrogen Bonds

• Water molecules are attracted to each other due to hydrogen bonding between a slightly positive hydrogen atom of one molecule to a slightly negative oxygen atom of a nearby molecule.
• Hydrogen bonds are relatively weak compared to covalent bonds.
• The properties of water stem from the hydrogen bonding between its molecules.

Activity

• Students need to draw water molecules showing covalent bonding and hydrogen bonding with appropriate partial charge labels.
• Electronegativity affects intermolecular interactions in water.
• Water molecule arrangements are unlikely in a particular way that doesn't follow the rules of their attraction.
• Water properties depend on the unequal sharing of electrons between oxygen and hydrogen.

Answers

• Water molecules cannot form hydrogen bonds without sufficient electronegativity difference.

Properties of Water: Cohesion

• Water molecules are attracted to each other due to hydrogen bonding, creating cohesion.
• This cohesion provides water with structure, allowing it to travel against gravity.

Properties of Water: Moderation of Temperature

• Water absorbs and releases heat effectively, moderating temperature changes.
• The ability to absorb heat with minimal temperature changes makes water important to living organisms, particularly in regulating body temperature.

Properties of Water: Temperature Continued

• A calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1°C.
• A kilocalorie (kcal) is the amount of energy needed to raise the temperature of 1 kilogram of water by 1°C.
• Measurements on food packaging use these units to indicate the caloric content of food.

Properties of Water: Solvent

• Water's polarity allows it to dissolve many substances.
• Solutions are homogeneous mixtures of two or more substances, where water is the solvent in many biological reactions.
• Water's ability to dissolve substances is very important to living organisms.

Properties of Water: Solvent 2

• Water's polarity is crucial for dissolving ions and polar molecules.
• Water molecules surround and separate ions in a solution, which is termed hydration shell.

Properties of Water: Solvent 3

• Water surrounds and shields ions within a solution.
• This process is critical for dissolving various substances in aqueous solutions.

Properties of Water: Solvent 4

• Water's polarity can dissolve many types of compounds, including non-ionic polar molecules.
• This is crucial as it permits biological fluids that contain a range of compounds to function properly.

Properties of Water: Summary

• Water plays a critical role in maintaining the structure, regulating temperature, and delivering essential molecules within cells.

Solute Concentration in Aqueous Solutions

• Solutes dissolved in water are involved in numerous biological reactions.
• To understand these reactions, calculating the concentration is crucial.
• Molecular mass, the sum of atomic masses of constituent atoms, is needed for calculating solute concentration.

Glucose - Molecular Mass

• Calculate the molecular mass of glucose using its chemical formula (C₆H₁₂O₆).
• Daltons are units of mass, roughly corresponding to atomic masses, although measurements are in moles.

Calculating Glucose

• One mole (mol) of any substance contains Avogadro's number of molecules (6.02 × 10²³).
• Grams in one mole of substance equals the molecular mass

Why use Moles?

• The mole is a convenient unit to measure large quantities of substances, where quantities of atoms are equal irrespective of the substance.
• Molarity is used to denote the composition of solutions.
• Blood sodium concentration values are provided as an example.

Summary 1

• Water's polarity gives rise to several crucial properties.
• Properties of water, including cohesion, temperature moderation, and dissolving elements, are essential to maintaining life.

10 Minute Break

Acids and Bases

• Acid-base reactions are crucial for determining pH using titration methods.
• Acids (e.g., HCl) dissociate into H+ and correspondingly charged negatively-charged ions.
• Bases (e.g., NaOH) dissociate into Na+ and OH- correspondingly charged.

Clinical Relevance?

• Acid-base balance is critical to bodily functions.
• Lungs and kidneys are vital organs in regulating these conditions.

Acid and Base: Water

• Water molecules can exchange protons (H+) to form hydronium ions (H₃O⁺) and hydroxide ions (OH⁻).

Acid and Base: Equilibrium

• Acid and base reactions are reversible.
• An equilibrium state occurs when the rate of acid and base reactions are essentially the same.

Acid and Base: Reversible

• In pure water, the dissociation of water molecules to form H⁺ and OH⁻ is reversible.
• This equilibrium is critical for life's chemical processes.

Acid and Base Conditions

• Changes in H⁺ and OH⁻ concentrations significantly affect biological systems (e.g., proteins).
• Biologists utilize the pH scale to determine the acidity or basicity of a substance.

Acids

• Acids release H⁺ ions when dissolved in water.
• Hydrochloric acid (HCl) is an example of an acid found in the stomach.

Bases

• Bases accept H⁺ ions when dissolved in water.
• Ammonia (NH₃) and sodium hydroxide (NaOH) are examples of bases.

One Direction versus Dynamic

• HCl and NaOH reactions proceed to completion, whereas other acid-base reactions result in dynamic equilibrium.

Dynamic Equilibrium

• In dynamic equilibrium, forward and reverse reactions are balanced, with the rates being equal.
• The concentrations of products and reactants don't change with time in such a system.

Acid Dissociation Constant

• The acid dissociation constant (Ka) measures the strength of an acid.
• A higher Ka value indicates a stronger acid.

The pH Scale

• The pH scale measures the H⁺ concentration in a solution.
• Neutral solutions have an equal concentration of H⁺ and OH⁻.

pH in the Body

• The internal pH of most cells is close to 7.4 (slightly basic).
• Significant changes in pH can adversely affect biological processes and may lead to significant damage.

Buffers

• Buffers help to maintain the pH of solutions by minimizing changes in H⁺ and OH⁻ concentrations.

Carbonic Anhydrase

• Carbonic anhydrase catalyzes the conversion of carbon dioxide and water into carbonic acid (H₂CO₃).
• This reaction and its reverse are important in regulating pH.

Diffusion: Molecular Energy

• Diffusion is the process through which molecules move from a region of higher concentration to a region of lower concentration.
• Thermal energy of molecules drives this movement.

Diffusion: Semi Permeable Membrane

• Molecules can diffuse across the membrane when the concentration of the substance is higher on one side of the membrane.
• Semi permeable membrane allows diffusion of molecules into the side where concentration is lower

Diffusion Down a Gradient

• Diffusion occurs spontaneously.
• Substances move from higher to lower concentration.

Water Diffusion: Osmosis

• Water diffusion across a selectively permeable membrane is called osmosis.

Effects of Osmosis on water Balance

• The effect of osmosis relates to the differences in the concentrations of solutes.
• Osmosis is important for processes at the cellular level across cell membranes.

Summary 2

• Water molecules can transfer H+, resulting in the formation of hydronium and hydroxide ions.
• Buffers are critical for maintaining pH in biological systems.
• Diffusion and osmosis are fundamental to water movement and maintaining balance.

Questions

• What does polarity in water mean?
• What are the three important properties of water?
• Calculations of sucrose concentration are required.
• Water dissociation details and products are outlined.
• Reversible chemical reactions are defined and explained.
• Details about water molecule movement during osmosis.

Before Next Time

• It is essential to review the topic to be prepared for the next class.
• Further learning material for the next session is suggested.