Biology Chapter: The Chemical Basis of Life

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Questions and Answers

Which four elements make up 96% of living matter?

Sodium, Magnesium, Calcium, Oxygen

Hydrogen, Iron, Nitrogen, Carbon

Calcium, Sulfur, Potassium, Phosphorus

Carbon, Hydrogen, Oxygen, Nitrogen (correct)

What determines the chemical behavior of an atom?

The number of protons in the nucleus

The number of electrons in the outermost shell (correct)

The total number of neutrons

The atomic mass of the element

What type of bond involves the sharing of a pair of electrons between two atoms?

Ionic bond

Covalent bond (correct)

Hydrogen bond

Van der Waals bond

How many electrons can the first three shells hold?

2, 8, 8 Signup and view all the answers

What property of water allows it to have a high specific heat?

Molecular cohesion Signup and view all the answers

Which of the following best describes a polar molecule?

Unequal sharing of electrons Signup and view all the answers

What happens to water when it freezes?

It expands, causing it to float Signup and view all the answers

Which interaction occurs between a positive hydrogen atom in one water molecule and a negative oxygen atom in another?

Hydrogen bond Signup and view all the answers

What property of water contributes to its ability to maintain stable temperatures?

High heat of vaporization Signup and view all the answers

Which term describes the attraction of water molecules to other substances?

Adhesion Signup and view all the answers

What is the pH level of a solution if the concentration of hydronium ions ($H_3O^+$) is $1.0 imes 10^{-3}$?

3 Signup and view all the answers

What characteristic do hydrophilic substances possess?

They have an attraction to water Signup and view all the answers

Which of the following correctly describes a buffer?

A solution that can resist changes in pH Signup and view all the answers

What primary function do carbohydrates serve in biological systems?

Provide energy and structural support Signup and view all the answers

In what way do acids affect water molecules?

They donate hydrogen ions Signup and view all the answers

What defines a non-polar substance in relation to water?

It does not have an attraction to water Signup and view all the answers

What role do functional groups play in hydrocarbons?

They increase the solubility and reactivity of hydrocarbons. Signup and view all the answers

Which type of bond forms between carboxylic acids and alcohols?

Ester bonds Signup and view all the answers

What is the primary characteristic of macromolecules?

They are large, complex molecules made from smaller units. Signup and view all the answers

Which of the following is NOT a type of carbohydrate?

Polypeptides Signup and view all the answers

What distinguishes oligosaccharides from other carbohydrates?

They are composed of 3 to 10 monosaccharide units. Signup and view all the answers

Which of the following best describes metabolic intermediates?

They are cellular molecules synthesized through metabolic pathways. Signup and view all the answers

Which carbohydrate consists of two linked monosaccharide units?

Disaccharide Signup and view all the answers

Which biomolecule is primarily produced during photosynthesis?

Carbohydrates Signup and view all the answers

Which of the following is a structural component of plant cell walls?

Cellulose Signup and view all the answers

What type of lipid is characterized by its structure of four fused carbon rings?

Steroids Signup and view all the answers

Which of the following statements about triglycerides is correct?

They consist of three fatty acids attached to a glycerol molecule. Signup and view all the answers

Which nucleic acid serves as the genetic blueprint for all living organisms?

Deoxyribonucleic Acid (DNA) Signup and view all the answers

Which lipid type is primarily involved in forming the cell membrane?

Phospholipids Signup and view all the answers

Which of the following bases is found in RNA but not in DNA?

Uracil Signup and view all the answers

What is the primary role of proteins in living organisms?

Catalyzing chemical processes Signup and view all the answers

What kind of fatty acid has no double bonds in its hydrocarbon chain?

Saturated Fatty Acid Signup and view all the answers

Study Notes

The Chemical Basis of Life

Approximately 25 chemical elements are essential for life.
Four elements make up about 96% of living matter: carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).
Four additional elements make up most of the remaining 4%: phosphorus (P), calcium (Ca), sulfur (S), and potassium (K).
Everything is composed of matter, and matter is made up of atoms.

Bonding Properties

Atoms will fill their outermost shell (valence shell) with electrons to become stable.
The chemical behavior of an atom is determined by the number of electrons in its valence shell.
Electrons determine the chemical behavior of atoms.
Each electron shell fills from the inside out:
- 1st shell: 2 electrons
- 2nd shell: 8 electrons
- 3rd shell: 8 electrons

Elements and Their Valence Shells

Elements in the same row (period) of the periodic table have the same number of electron shells.
Elements in the same column (group) of the periodic table have the same number of valence electrons and similar chemical properties.

Chemical Reactivity

Atoms tend to:
- Complete a partially filled valence shell.
- Empty a partially filled valence shell.

Bonds in Biology

Strong bonds:
- Covalent bonds: Two atoms share a pair of electrons.
Weak bonds:
- Hydrogen bonds: Occur between a hydrogen atom covalently linked to a highly electronegative atom (like oxygen) and an electronegative atom on a different molecule.
- Hydrophobic and hydrophilic interactions: These interactions involve the attraction or repulsion of water molecules. Hydrophilic molecules are attracted to water, while hydrophobic molecules are repelled by water.
- Ionic bonds: Occur when one atom donates an electron to another atom, resulting in the formation of ions (charged atoms).

Covalent Bonds

Two atoms share a pair of electrons.
Both atoms hold onto the electrons.
Forms molecules.

Multiple Covalent Bonds

Pairs of electrons shared unequally by two atoms.
Example: Water (H₂O): Oxygen has a stronger attraction for electrons than hydrogen, resulting in a polar molecule with positive and negative poles.

Hydrogen Bonding

Polar water molecules form attractions between positive hydrogen atoms and negative oxygen atoms.
Can occur wherever an -OH group exists in a larger molecule.

Life Needs Water

Water is essential for all life, both inside and outside cells.

Special Properties of Water

Cohesion and adhesion:
- Cohesion: H-bonding between water molecules.
- Adhesion: H-bonding between water molecules and other substances.
Surface tension: Cohesion creates a strong surface tension.
Capillary action: Adhesion allows water to climb up narrow spaces.
Good solvent: Many polar molecules dissolve in water.
Hydrophilic vs. hydrophobic: Hydrophilic molecules are attracted to water, while hydrophobic molecules are repelled by water.
Lower density as a solid: Ice floats because water molecules form a crystalline structure when frozen, making it less dense than liquid water.
High specific heat: Water can absorb a large amount of heat energy before its temperature changes significantly.
High heat of vaporization: Water requires a significant amount of energy to vaporize because of the strong hydrogen bonds.

Cohesion & Adhesion

Cohesion: H-bonding between H₂O molecules.
Adhesion: H-bonding between H₂O and other substances.

Hydrophilic

Substances attracted to water.
Polar.

Hydrophobic

Substances not attracted to water.
Non-polar.

Ionization of Water & pH

Water ionizes, meaning it can split into a hydrogen ion (H+) and a hydroxide ion (OH-).
Neutral water has an equal concentration of H+ and OH-.
Acidic water has a higher concentration of H+.
Basic water has a higher concentration of OH-.

pH Scale

Measures the acidity or basicity of a solution.
pH 1-7: acidic
pH 7: neutral
pH 7-14: basic

Buffers & Cellular Regulation

Cells need a stable pH of 7.
pH affects the shape of molecules, which affects their function.
pH affects cellular function.

Acids, Bases, and Buffers

Acid: Donates a hydrogen ion (H+).
Base: Accepts a hydrogen ion (H+).
Buffer: A solution that resists changes in pH.

The Nature of Biological Molecules

Biological molecules (biomolecules): Essential for life.
Four main types:
- Carbohydrates: Provide energy and structural support.
- Proteins: Perform functions like enzyme activity, structure, and immune responses.
- Lipids: Store energy, form cell membranes, and act as signaling molecules.
- Nucleic Acids: Store and transmit genetic information (DNA and RNA).
Biomolecules are often polymers (large molecules built from smaller units called monomers) and interact with water.
Many reactions are catalyzed by enzymes.

Functional Groups

Hydrocarbons: Organic molecules primarily made up of carbon and hydrogen. Relatively inactive chemically.
Functional groups: Small groups of atoms within molecules that provide specific chemical properties, making hydrocarbons more soluble and reactive.

Common Types of Functional Groups

Often contain electronegative atoms (N, P, O, S), which make organic molecules more polar, water-soluble, and reactive.

Classification of Biological Molecules by Function

Macromolecules: Large, complex molecules essential for cell structure and function.
- Made up of dozens to millions of carbon atoms.
- Polymers are large molecules built from smaller units (monomers) through polymerization.
Building blocks of macromolecules: Include the precursors needed to build new macromolecules.
Metabolic intermediates (metabolites): Cellular molecules synthesized through metabolic pathways.
Molecules of miscellaneous function: Molecules with diverse, but less abundant functions, compared to macromolecules and their precursors.

The Four Types of Biological Molecules

Carbohydrates

Organic molecules composed of carbon, hydrogen, and oxygen.
Crucial energy sources and structural components.
Classified based on the number of sugar units:
- Monosaccharides: Single sugar unit (e.g., glucose, fructose, galactose)
- Disaccharides: Two monosaccharide units linked (e.g., sucrose, lactose, maltose)
- Oligosaccharides: 3-10 monosaccharide units.
- Polysaccharides: Many monosaccharide units (e.g., starch, glycogen, cellulose)

Lipids

Hydrophobic molecules with diverse functions, including energy storage, cell membrane formation, and signaling.
Classified into four main types:
- Fatty acids: Long hydrocarbon chain with a carboxyl group (e.g., palmitic acid, oleic acid)
- Triglycerides: Three fatty acids attached to a glycerol molecule (e.g., fats, oils)
- Phospholipids: Two fatty acids and a phosphate group attached to a glycerol backbone (e.g., phosphatidylcholine), key component of cell membranes.
- Steroids: Four fused carbon rings with various functions (e.g., cholesterol, testosterone, estrogen)

Nucleic Acids

Primary information carriers in cells, directing protein synthesis.
Long chains of nucleotides, each comprised of a sugar, phosphate group, and an organic base.
Two main types:
- DNA: The genetic blueprint, containing the bases adenine (A), cytosine (C), guanine (G), and thymine (T).
- RNA: Essential for protein synthesis, containing the bases adenine (A), cytosine (C), guanine (G), and uracil (U).

Proteins

Complex molecules essential for life, involved in a vast array of functions.
Hold immense nutritional value.
Essential for the chemical processes that sustain life.

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Description

This quiz covers the essential chemical elements necessary for life and their bonding properties. You will learn about atoms, electron configurations, and the periodic table's organization. Test your knowledge of how these elements contribute to life's chemical foundation.