Cambridge IGCSE IGCSE & A-Level Sheet preview

Chemistry of Life

AP Biology · Topic 1

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Handout Vocabulary
1.1

Structure of Water and Hydrogen Bonding
Syllabus
Big IdeaLearning ObjectiveEssential Knowledge

Big Idea 4 — Systems Interactions
Biological systems interact, and these systems and their interactions exhibit complex properties.

1.1.A
Explain how the properties of water that result from its polarity and hydrogen bonding affect its biological function.

  • 1.1.A.1 Living systems depend on the properties of water to sustain life.
    • 1.1.A.1.i Water has polarity, because of the formation of polar covalent bonds between hydrogen and oxygen within water molecules. This polarity contributes to hydrogen bonding between and within biological molecules.
    • 1.1.A.1.ii Water has a high specific heat capacity, which allows for the maintenance of homeostatic body temperature within living organisms.
    • 1.1.A.1.iii Water has a high heat of vaporization, which allows for the evaporative cooling of the surrounding environment. In living organisms, this property allows for body temperature to be maintained.
  • 1.1.A.2 The hydrogen bonds between adjacent polar water molecules result in cohesion, adhesion, and surface tension.

Source: College Board AP Course and Exam Description

Water is polar 极性: its oxygen pulls electrons more strongly than its hydrogens, giving a slightly negative O and slightly positive H. This lets water molecules form hydrogen bonds 氢键 with each other, which explains water's life-supporting properties:

  • Cohesion 内聚力 and adhesion 附着力 (surface tension, capillary action, water rising in plants),
  • high specific heat 比热容 (resists temperature change, stabilizing organisms),
  • high heat of vaporization (evaporative cooling),
  • ice floating (less dense solid), and being a great solvent for polar and ionic substances.

A hydrogen bond between two polar water molecules A hydrogen bond between two polar water molecules

Explore

Explore how a covalent bond shares electrons

Step through two atoms overlapping to share a pair of electrons so each reaches a full shell. In $\text{H}_2$ the two atoms pull equally, so the bond is non-polar — the contrast that makes water's unequal sharing (and its $\delta^+/\delta^-$ dipole) so important.

Vocabulary Train
English Chinese Pinyin
polar 极性 jí xìng
hydrogen bonds 氢键 qīng jiàn
Cohesion 内聚力 nèi jù lì
adhesion 附着力 fù zhuó lì
specific heat 比热容 bǐ rè róng
Exercise sheet
1.2

Elements of Life
Syllabus
Big IdeaLearning ObjectiveEssential Knowledge

Big Idea 2 — Energetics
Biological systems use energy and molecular building blocks to grow, reproduce, and maintain dynamic homeostasis.

1.2.A
Describe the composition of macromolecules required by living organisms.

  • 1.2.A.1 Atoms and molecules from the environment are necessary to build new molecules. Carbon, hydrogen, and oxygen are the most prevalent elements used to build biological molecules such as carbohydrates, proteins, lipids, and nucleic acids. Additionally:
    • 1.2.A.1.i Sulfur is used in the building of proteins.
    • 1.2.A.1.ii Phosphorus is used in the building of phospholipids (a type of lipid) and nucleic acids.
    • 1.2.A.1.iii Nitrogen is used in the building of nucleic acids.

Source: College Board AP Course and Exam Description

Living matter is built mostly from a few elements – carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Carbon 碳 is central because it forms four stable covalent bonds, building long chains, branches, and rings – the skeletons of all biological molecules.

Carbohydrates and fats contain carbon, hydrogen, and oxygen; proteins also contain nitrogen Carbohydrates and fats contain carbon, hydrogen, and oxygen; proteins also contain nitrogen

Vocabulary Train
English Chinese Pinyin
Carbon 碳 tàn
Exercise sheet
1.3

Introduction to Macromolecules
Syllabus
Big IdeaLearning ObjectiveEssential Knowledge

Big Idea 4 — Systems Interactions
Biological systems interact, and these systems and their interactions exhibit complex properties.

1.3.A
Describe the chemical reactions that build and break biological macromolecules.

  • 1.3.A.1 Hydrolysis is a chemical reaction involving the cleaving of covalent bonds. This type of reaction breaks down molecules into smaller molecules. When water is added to the bond between monomers in a polymer, the bond is broken. The hydrogen ion from a water molecule is added to one monomer and the hydroxyl group of the water molecule is added to the other monomer, completing the reaction.
  • 1.3.A.2 Dehydration synthesis occurs when two smaller molecules are joined together through covalent bonding. A hydrogen ion is removed from one monomer and a hydroxyl group is removed from the other. This causes the loss of the equivalent of a water molecule from the reactants and the connection of the two remaining monomers. The connection of many monomers is known as polymerization.

Source: College Board AP Course and Exam Description

Large biological molecules – macromolecules 大分子 – are polymers 聚合物 built from repeating monomers 单体. Cells join monomers by dehydration synthesis 脱水缩合 (removing water to form a bond) and break polymers by hydrolysis 水解 (adding water). Four classes: carbohydrates, lipids, nucleic acids, and proteins.

Dehydration synthesis builds polymers and releases water; hydrolysis reverses it Dehydration synthesis builds polymers and releases water; hydrolysis reverses it

Explore

Explore the four classes of macromolecule by their monomer

Sort each clue into the right macromolecule class by matching the monomer that builds it — sugars, nucleotides or amino acids — and notice that lipids are the odd one out that are not true polymers.

Vocabulary Train
English Chinese Pinyin
macromolecules 大分子 dà fēn zi
polymers 聚合物 jù hé wù
monomers 单体 dān tǐ
dehydration synthesis 脱水缩合 tuō shuǐ suō hé
hydrolysis 水解 shuǐ jiě
Exercise sheet
1.4

Carbohydrates
Syllabus
Big IdeaLearning ObjectiveEssential Knowledge

Big Idea 4 — Systems Interactions
Biological systems interact, and these systems and their interactions exhibit complex properties.

1.4.A
Describe the structure and function of carbohydrates.

  • 1.4.A.1 Monosaccharides (simple sugars) are the monomers for polysaccharides (complex carbohydrates). These monomers are connected by covalent bonds to form polymers such as complex carbohydrates, which may be linear or branched.
    • Illustrative examples for 1.4.A.1:
      • Cellulose
      • Starch
      • Glycogen
    • Exclusion statement: The molecular structure of specific carbohydrate polymers is beyond the scope of the AP Exam.

Source: College Board AP Course and Exam Description

Carbohydrates 碳水化合物 are made of sugar monomers (monosaccharides 单糖 like glucose). They store energy (starch, glycogen) and provide structure (cellulose 纤维素 in plant walls). Their many hydroxyl groups make them polar and water-soluble.

The shapes of storage polysaccharides (starch, glycogen) and structural cellulose The shapes of storage polysaccharides (starch, glycogen) and structural cellulose

Vocabulary Train
English Chinese Pinyin
Carbohydrates 碳水化合物 tàn shuǐ huà hé wù
monosaccharides 单糖 dān táng
cellulose 纤维素 xiān wéi sù
Exercise sheet
1.5

Lipids
Syllabus
Big IdeaLearning ObjectiveEssential Knowledge

Big Idea 4 — Systems Interactions
Biological systems interact, and these systems and their interactions exhibit complex properties.

1.5.A
Describe the structure and function of lipids.

  • 1.5.A.1 Lipids are typically nonpolar, hydrophobic molecules whose structure and function are derived from the way their subcomponents are assembled. Fatty acids can be described as either saturated or unsaturated.
    • 1.5.A.1.i Saturated fatty acids contain only single bonds between carbon atoms.
    • 1.5.A.1.ii Unsaturated fatty acids contain at least one double bond between carbon atoms, which causes the carbon chain to kink.
    • 1.5.A.1.iii The more double bonds in a fatty acid tail, the more unsaturated the lipid becomes.
    • 1.5.A.1.iv The more unsaturated a lipid is, the more liquid it is at room temperature.
  • 1.5.A.2 Lipids provide a variety of functions for living organisms. Some examples of lipids are fats, steroids including cholesterol, and phospholipids.
    • 1.5.A.2.i Fats provide energy storage and support cell function. In some cases, they can also provide insulation to help keep mammals warm.
    • 1.5.A.2.ii Steroids are hormones that support physiological functions including growth and development, energy metabolism, and homeostasis.
    • 1.5.A.2.iii Cholesterol provides essential structural stability to animal cell membranes.
    • 1.5.A.2.iv Phospholipids group together to form the lipid bilayers found in plasma and cell membranes.
    • Exclusion statement: The molecular structure of specific lipids is beyond the scope of the AP Exam.

Source: College Board AP Course and Exam Description

Lipids 脂质 are nonpolar and do not mix with water (hydrophobic 疏水). They include fats (long-term energy storage), phospholipids 磷脂 (which build membranes), and steroids. A phospholipid has a polar "head" and nonpolar "tails," the key to the cell membrane.

A phospholipid has a polar head and two nonpolar tails, so phospholipids form a bilayer A phospholipid has a polar head and two nonpolar tails, so phospholipids form a bilayer

A triglyceride: glycerol joined to three fatty acids A triglyceride: glycerol joined to three fatty acids

Vocabulary Train
English Chinese Pinyin
Lipids 脂质 zhī zhì
hydrophobic 疏水 shū shuǐ
phospholipids 磷脂 lín zhī
Exercise sheet
1.6

Nucleic Acids
Syllabus
Big IdeaLearning ObjectiveEssential Knowledge

Big Idea 3 — Information Storage and Transmission
Living systems store, retrieve, transmit, and respond to information essential to life processes.

1.6.A
Describe the structure and function of DNA and RNA.

  • 1.6.A.1 In nucleic acids (DNA and RNA), biological information is encoded in sequences of nucleotide monomers. Each nucleotide has the following structural components: a five-carbon sugar (deoxyribose or ribose), a phosphate, and a nitrogenous base (adenine, thymine, guanine, cytosine, or uracil).
  • 1.6.A.2 Nucleic acids have a linear sequence of nucleotides that have ends, defined by the 3' (three prime) hydroxyl and 5' (five prime) phosphates of the sugar in the nucleotide. During nucleic acid synthesis, nucleotides are added to the 3' end of the growing strand, resulting in the formation of covalent bonds between nucleotides.
    • Exclusion statement: The molecular structure of specific nucleotides is beyond the scope of the AP Exam.
  • 1.6.A.3 DNA is structured as an antiparallel double helix, with two strands of nucleotides running in opposite 5' to 3' orientation. In DNA, adenine nucleotides pair with thymine nucleotides via hydrogen bonds (A-T), and cytosine nucleotides pair with guanine nucleotides via hydrogen bonds (C-G). In RNA, adenine pairs with uracil (A-U).
  • 1.6.A.4 Structural differences between DNA and RNA include:
    • 1.6.A.4.i DNA contains the sugar deoxyribose, and RNA contains the sugar ribose.
    • 1.6.A.4.ii DNA contains the nitrogenous base thymine, and RNA contains the nitrogenous base uracil.
    • 1.6.A.4.iii DNA is typically double stranded, while RNA is typically single stranded.

Source: College Board AP Course and Exam Description

Nucleic acids 核酸 (DNA and RNA) store and carry genetic information. Their monomers are nucleotides 核苷酸, each a sugar, a phosphate, and a nitrogen base. The base sequence encodes instructions; DNA is double-stranded, RNA single-stranded.

Complementary base pairing holds the two antiparallel strands of DNA together Complementary base pairing holds the two antiparallel strands of DNA together

Explore

Explore complementary base pairing

Step along a DNA template and watch each base pair to its partner by complementary base pairing ($A$ with $T$, $G$ with $C$) — the rule that lets either strand act as a template to rebuild the other.

Vocabulary Train
English Chinese Pinyin
Nucleic acids 核酸 hé suān
nucleotides 核苷酸 hé gān suān
Exercise sheet
1.7

Proteins
Syllabus
Big IdeaLearning ObjectiveEssential Knowledge

Big Idea 3 — Information Storage and Transmission
Living systems store, retrieve, transmit, and respond to information essential to life processes.

1.7.A
Describe the structure and function of proteins.

  • 1.7.A.1 Proteins comprise linear chains of amino acids connected by the formation of covalent (peptide) bonds that form between a carboxyl group ($-\text{COOH}$) of one amino acid and an amine group ($-\text{NH}_2$) of the next amino acid, resulting in a growing peptide chain.
  • 1.7.A.2 Amino acids are composed of a central carbon atom with a hydrogen atom, a carboxyl group, an amine group, and a variable R group covalently bound to it. The R group of an amino acid can be categorized by three possible chemical properties: hydrophobic/nonpolar, hydrophilic/polar, or ionic. The interactions of these R groups determine the structure and function of that region of the protein.
  • 1.7.A.3 The specific sequence of amino acids in proteins determines the primary structure of a polypeptide as well as the overall shape of the protein.
    • Exclusion statement: The molecular structure of amino acids is beyond the scope of the AP Exam.
  • 1.7.A.4 Secondary structures of proteins are made through the local folding that forms from interactions between atoms of the polypeptide backbone of the amino acid chain. Hydrogen bonding forms shapes such as alpha-helices and beta-pleated sheets.
  • 1.7.A.5 The three-dimensional shape of the tertiary structure of a protein results from the formation of hydrogen bonds, hydrophobic interactions, ionic interactions, or disulfide bridges.
  • 1.7.A.6 The quaternary structure arises from interactions between multiple polypeptides. All four levels of a protein structure determine the function of a protein.

Source: College Board AP Course and Exam Description

Proteins 蛋白质 are polymers of amino acids 氨基酸 joined by peptide bonds 肽键. Their sequence folds into a specific 3-D shape at four levels (primary, secondary, tertiary, quaternary), and shape determines function – as enzymes, transporters, receptors, and structural parts. Changing the environment (heat, pH) can denature 变性 a protein, unfolding it and stopping its function.

An amino acid, and the peptide bond formed by condensation An amino acid, and the peptide bond formed by condensation

The four levels of protein structure The four levels of protein structure

Worked example. Building a polymer from 10 monomers by dehydration synthesis forms 9 bonds and releases 9 water molecules — one per bond, so $N$ monomers release $N-1$ waters. Hydrolysis reverses this exactly: adding those 9 waters breaks the polymer back into 10 monomers. This is why biosynthesis (dehydration) and digestion (hydrolysis) are chemical opposites.

Vocabulary Train
English Chinese Pinyin
Proteins 蛋白质 dàn bái zhì
amino acids 氨基酸 ān jī suān
peptide bonds 肽键 tài jiàn
denature 变性 biàn xìng
Exercise sheet
1.7

Exam tips
  • Trace every property of water back to its polarity and hydrogen bonding (cohesion, high specific heat, solvent power).
  • Know the four macromolecule classes and their monomers; polymers are built by dehydration synthesis and broken by hydrolysis.
  • For proteins, structure (shape) determines function — heat or a pH change denatures them and stops them working.
  • In DNA the bases pair A–T and C–G on antiparallel strands; RNA is single-stranded and uses U.
  • Link each molecule to its role (carbohydrates: energy/structure; lipids: membranes/storage; nucleic acids: information).

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