Biology Chapter: Water as Life's Medium

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Questions and Answers

What characteristic defines a hydrophilic substance?

It has an affinity for water. (correct)

It repels water.

It is always nonpolar.

It can only dissolve in organic solvents.

What is the definition of molarity?

The number of moles of solute per liter of solution. (correct)

The concentration of solute in grams per liter.

The mass of solute per liter of solution.

The volume of solute per volume of solution.

Which type of molecules can water dissolve according to their structure?

Only large proteins.

Only ionic compounds.

Nonionic polar molecules with ionic regions. (correct)

Nonpolar molecules like oil.

What is the significance of Avogadro’s number in chemistry?

It represents the number of molecules in a mole. Signup and view all the answers

Why are oil molecules considered hydrophobic?

They have relatively nonpolar bonds. Signup and view all the answers

What is the heat of vaporization for water?

540 cal/gram Signup and view all the answers

Why does ice float on liquid water?

Hydrogen bonds in ice are more ordered Signup and view all the answers

What is the process called when evaporation leads to cooling of the remaining liquid?

Evaporative cooling Signup and view all the answers

At what temperature does water reach its greatest density?

4°C Signup and view all the answers

What term describes a liquid that is a homogeneous mixture of substances?

Solution Signup and view all the answers

What surrounds each ion in a solution when an ionic compound is dissolved in water?

Hydration shell Signup and view all the answers

What characteristic of water makes it a versatile solvent?

Its polarity Signup and view all the answers

What would likely happen if ice did not float and sank in bodies of water?

All bodies of water would eventually freeze solid Signup and view all the answers

What property of water allows it to transport nutrients against gravity in plants?

Cohesion Signup and view all the answers

Which of the following is NOT an emergent property of water that supports life?

High vapor pressure Signup and view all the answers

What is the significance of water's polarity?

It facilitates hydrogen bonding between water molecules. Signup and view all the answers

How does the ability of water to moderate temperature benefit life on Earth?

It minimizes temperature fluctuations in the environment. Signup and view all the answers

What phenomenon measures how hard it is to break the surface of water?

Surface tension Signup and view all the answers

What role does adhesion play in plant water transport?

It helps water move through plant cell walls. Signup and view all the answers

Why is water considered a versatile solvent?

It can dissolve polar and ionic substances effectively. Signup and view all the answers

In terms of cellular composition, what is the approximate percentage of water found in most cells?

70-95% Signup and view all the answers

Which of the following substances is the most acidic?

Gastric juice Signup and view all the answers

What is the pH level of pure water?

7 Signup and view all the answers

Which of these solutions is classified as basic?

Household ammonia Signup and view all the answers

Buffers in biological systems primarily consist of what?

Acid-base pairs Signup and view all the answers

Which of the following has a pH level closest to that of human blood?

Seawater Signup and view all the answers

What characteristic does an acidic solution possess?

[H+] > [OH−] Signup and view all the answers

Which substance would most likely have a pH level of about 11?

Oven cleaner Signup and view all the answers

What role do buffers play in biological systems?

To prevent pH changes Signup and view all the answers

What happens to a water molecule when it loses a proton?

It becomes a hydroxide ion. Signup and view all the answers

What is the relationship between hydrogen ion concentration and pH?

pH is the negative logarithm of hydrogen ion concentration. Signup and view all the answers

Which of the following statements about acids is true?

Acids increase the H+ concentration of a solution. Signup and view all the answers

At 25°C, what is the product of H+ and OH– concentrations in a neutral solution?

$10^{-14}$ Signup and view all the answers

What is the pH of a solution with a hydrogen ion concentration of $10^{-6}$ M?

6 Signup and view all the answers

Which statement correctly defines a base?

A base reduces the concentration of H+ ions. Signup and view all the answers

What is the typical pH range for most biological fluids?

6 to 8 Signup and view all the answers

Which ion is often represented as H+ in aqueous solutions?

Proton Signup and view all the answers

Study Notes

Overview of Water's Importance

Water is essential for all living organisms, serving as the primary biological medium on Earth.
Cells consist of approximately 70-95% water, highlighting its critical role in biological functions.
The abundance of water makes Earth habitable, supporting various life forms.

Water's Molecular Structure

Water molecules are polar, possessing opposite charges at each end, facilitating hydrogen bonding.
Hydrogen bonds result from the polarity of water, allowing water molecules to interact cohesively.

Emergent Properties of Water

Key properties that make Earth suitable for life include:
- Cohesive behavior: Hydrogen bonds enable water molecules to stay together, aiding in water transport in plants.
- Temperature moderation: Water can absorb and release heat, helping to stabilize environmental temperatures.
- Expansion upon freezing: Ice is less dense than liquid water, allowing it to float and insulate bodies of water.
- Solvent versatility: Water is capable of dissolving a wide range of substances due to its polarity.

Cohesion and Adhesion

Cohesion facilitates the upward movement of water in plants against gravity.
Adhesion refers to the attraction between different substances, such as water and plant cell walls.

Surface Tension and Evaporation

Water has high surface tension due to cohesive hydrogen bonds, which makes it difficult to break the surface of the liquid.
Evaporation allows water to cool when the remaining liquid absorbs heat, a process known as evaporative cooling, vital for temperature regulation in organisms.

Ice's Unique Properties

Ice floats because hydrogen bonds arrange molecules in a structured way, making it less dense than liquid water.
Water is most dense at 4°C; if ice sank, aquatic ecosystems would freeze solid, threatening life.

Water as a Solvent

In solutions, water acts as a solvent (dissolving agent) while solutes are the substances being dissolved.
A hydration shell forms around ions when ionic compounds dissolve in water, facilitating ion distribution.

Hydrophilic and Hydrophobic Substances

Hydrophilic substances are attracted to water, while hydrophobic substances repel water.
Nonpolar molecules like oil are hydrophobic, indicating their lack of affinity for water.

Concentration and Chemical Reactions

Most biochemical reactions occur in water, which is essential for molecular collisions.
Molarity (M) measures dissolved substance concentration in solution, with one mole equaling 6.02 x 10²³ molecules.

Acids, Bases, and pH Scale

Water can dissociate into H+ (hydrogen ion) and OH− (hydroxide ion), essential for acid-base chemistry.
Acids increase H+ in a solution, while bases decrease H+ concentration.
The pH scale quantifies acidity and basicity, with pure water having a neutral pH of 7.

Buffers and Cellular pH

Cellular pH typically remains close to 7, critical for maintaining biochemical processes.
Buffers are substances that stabilize pH by preventing drastic changes in H+ and OH– concentrations, usually comprising an acid-base pair.

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Description

Explore the vital role of water as the biological medium that supports all life on Earth. This quiz delves into the molecular structure of water, its abundance, and its importance for living organisms. Understand how water influences habitats and cell structures.