AP Biology Exam Review - KEY

Science Practices

• Science practices assess knowledge on the AP Biology exam.

• Skills include concept explanation, visual representation, questions and methods, representing and describing data, statistical tests and data analysis, and argumentation.

Unit 1: Chemistry of Life

• Topics include the structure of water, elements of life, introduction to biological macromolecules, properties of biological macromolecules, and nucleic acids.

Topic 1.1: Structure of Water

• Water's polarity and hydrogen bonding affect its biological function.

• Hydrogen bonds are weak bonds between a proton and an electronegative atom.

• In water, hydrogen bonds form between H in one molecule and O in another molecule.

• In DNA, they're between nitrogenous bases (2 between A & T, 3 between C & G).

• Amino acid R groups can be polar (hydrophilic, folds out), nonpolar (hydrophobic, folds in), or charged (hydrophilic, folds out).

• Water properties: polar, excellent solvent, high heat capacity/vaporization, cohesion, adhesion, less dense as a solid.

• Cohesion and adhesion help water move up capillary tubes.

• Surface tension allows water striders to walk on water.

Topic 1.2: Elements of Life

• Four macromolecules: proteins, lipids, carbohydrates, nucleic acids.

• Carbohydrates: C, H, O; provide quick energy, structure, energy storage.

• Proteins: C, H, O, N; functional groups are amino, carboxyl, and R groups; functions include metabolism, support, transport.

• Nucleic Acids: C, H, O, N, P; parts are phosphate, sugar, base; function as DNA, RNA, ATP.

• Lipids: C, H, O; functions include steroids, insulation, waxes.

• Nitrogen is in proteins and nucleic acids.

• Phosphorus is in nucleic acids.

• R groups determine protein folding: hydrophobic (nonpolar) or hydrophilic (polar).

• Dehydration removes water to join subunits; hydrolysis adds water to break them apart.

Topic 1.3: Introduction to Biological Macromolecules

• Hydrolysis $H<em>2O$ addition breaks a polymer; inputs $H</em>2O$ and disaccharide, outputs 2 monosaccharides.

• Dehydration with water molecule removal joins monomers; inputs 2 monosaccharides, outputs water and disaccharide.

• Carbohydrates have Glycosidic bonds.

• Proteins have Peptide bonds.

• Nucleic acids have Phosphodiester bonds.

Topic 1.4: Properties of Biological Macromolecules

• Carbohydrate monomer: monosaccharide.

• Protein monomer: amino acid (central C, amino group, carboxyl group, R group).

• Nucleic acid monomer: nucleotide (phosphate, sugar, base).

• Phospholipids: hydrophilic head, hydrophobic tail.

• Starch: Glycosidic bonds.

• Cellulose: Hydrogen bonds. Animals can break Glycosidic Bonds.

• DNA vs. RNA: sugars (deoxyribose vs. ribose), bases (T vs. U), strandedness (double helix vs. single).

• Saturated fatty acids: single bonds, solid at room temperature.

• Unsaturated fatty acids: double bonds, liquid at room temperature.

Topic 1.5: Structure and Function of Biological Macromolecules

• Nonpolar to polar R group substitution changes protein structure/function based on hydrophobicity/hydrophilicity.

• Cytosine to thymine substitution in DNA changes binding and requires a change to it's pair.

• Deoxyribose to ribose changes DNA to RNA.

• Ends of nucleic acid polymer: 5' (phosphate group) and 3' (sugar).

• Nucleic acids elongate 5' to 3'.

• Base pairings: A-T (2 hydrogen bonds), G-C (3 hydrogen bonds).

• Protein folding levels: primary (amino acid sequence, covalent bonds), secondary (alpha helix/beta sheets, hydrogen bonds), tertiary (3D shape, R group interactions), quaternary (multiple chains).

• Carbohydrates have a 1C:1O:2H ratio; monomers are glucose, galactose, fructose.

• Fat molecules have glycerol and fatty acids; can be saturated or unsaturated.

• Phospholipids have a phosphate head and fatty acid tail.

• Steroids have 17 carbon atoms in 4 rings with different side chains for unique molecules.

Topic 1.6: Nucleic Acid

• DNA vs. RNA: sugar (deoxyribose vs. ribose), base (T vs. U), structure (double vs single stranded).

Unit 2: Cell Structure and Function

• Topics include cell structure, size, plasma membranes, membrane permeability/transport, facilitated diffusion, tonicity/osmoregulation, mechanisms of transport, and cell compartmentalization.

Topic 2.1: Cell Structure: Subcellular Components

• Ribosomes: rRNA and proteins; synthesize proteins. Can be bound to ER or floating.

• Endoplasmic Reticulum:

  • Rough ER: has ribosomes and is used in protein making.

  • Smooth ER: lipids, oils, fats, steroids/hormones are created.

  • The smooth ER uses enzymes made by the rough ER to facilitate the synthesis of these biomolecules and assist in detoxification processes within the cell.

• Golgi sorts protein and send it out.

• Mitochondria bean shape organelle that has two membranes. It converts energy stored in food to usable chemical energy called ATP.

• Lysosome digests macromolecules and worn out organelles and cell parts.

• Lysosomes aids in apoptosis because it has lipid mediators that trigger the apoptosis pathways. Proteases released by lysosomes into the cytosol contribute to the cascade of apoptosis.

• Vacuoles have Food vacuole, central vacuole and contractile vacuole.

• Chloroplasts converts light energy to chemical energy.

Topic 2.2: Cell Structure and Function

*the Smooth ER helps transport materials to other parts of the cell.
*the Rough ER is where the ribosomes make proteins.
*Vacuoles assists in storage of macromolecules

Topic 2.3: Cell Size

• Surface Area: Sphere: $4πr^2$, Cube: $6s^2$, Rectangular solid: $2(lw + lh + wh)$, Cylinder: $2πrh + 2πr^2$

• Volume: Sphere: $(4/3)πr^3$, Cube: $s^3$, Rectangular solid: $lwh$, Cylinder: $πr^2h$
  *Surface area effects heat exchange
  *Cells Increase surface area by using projections.

Topic 2.4: Plasma Membranes

*The phospholipid bilayer maintain the internal environment of a cell
*It helps allow water and other solutes to pass in and out of the cell when needed
*Peripheral membrane found on one side of the membrane
*Glycoproteins help with cell signaling and stability of cell structure.
*Glycolipids help with cell stability and are involved in cell interactions

Topic 2.5: Membrane Permeability

*The cell membrane is selectively permeable using membrane structure
*Small nonpolar, uncharged molecules pass easily through the membrane
*Polar and charged molecules, and large compounds require a protein to pass through the membrane
*Molecules like proteins and polysaccharides need to be transported through vesicles.

Topic 2.7: Facilitated Diffusion

*charged ions pass with protein tunnels
*Water goes though simple diffusion
*The concentration gradients
*Potassium ions move down the concentration gradient to the outside of the cell and sodium ions move down the concentration gradient to the inside and the separation of charges causes a membrane potential.

Topic 2.8: Tonicity and Osmoregulation

*Solution is hypotonic when its concentration is lower than inside the cell
*Solution is hypertonic when its concentration is higher than inside the cell
*Iso tonic happens when solutions have equal concentration

Topic 3.5: Photosynthesis

• First evolved by cyanobacteria
  *the thylakoid membrane embedded in the chloroplast absorb light energy and convert it to high energy molecules in the ETC.

siRNA, or small interfering RNA, is a class of double-stranded RNA molecules, typically 20-25 base pairs in length, that play a crucial role in the RNA interference (RNAi) pathway. siRNA molecules are involved in the regulation of gene expression by promoting the degradation of specific mRNA molecules, thus preventing translation. This mechanism is essential for various biological processes, including the defense against viral infections and the regulation of gene expression in various cellular processes.

Krebs cycle

The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a series of chemical reactions used by all aerobic organisms to generate energy. It takes place in the mitochondria and is a key component of cellular respiration. The cycle begins with the condensation of acetyl-CoA (derived from carbohydrates, fats, or proteins) with oxaloacetate to form citric acid.

Key Steps in the Krebs Cycle:

1. Formation of Citric Acid: Acetyl-CoA combines with oxaloacetate to form citric acid (citrate).

2. Conversion to Isocitrate: Citrate is rearranged to form isocitrate.

3. Oxidative Decarboxylation: Isocitrate is oxidized and decarboxylated to form α-ketoglutarate, producing NADH and releasing CO₂.

4. Further Decarboxylation: α-Ketoglutarate is further oxidized to succinyl-CoA, generating another NADH and releasing CO₂.

5. Conversion to Succinate: Succinyl-CoA is converted to succinate, producing ATP (or GTP) in the process.

6. Oxidation of Succinate: Succinate is oxidized to fumarate, generating FADH₂.

7. Hydration: Fumarate undergoes hydration to form malate.

8. Regeneration of Oxaloacetate: Malate is oxidized back to oxaloacetate, producing another NADH.

Overall Outputs of the Cycle:

• 3 NADH

• 1 FADH₂

• 1 ATP (or GTP)

• 2 CO₂

These electron carriers (NADH and FADH₂) are then used in the electron transport chain to produce more ATP, making the Krebs cycle vital for energy production in cells.

I give 3(NADH) and 1 FADH₂, which ultimately contribute to the generation of approximately 30-32 ATP molecules during cellular respiration.

Carbon-14

Carbon-14 (6C) is a radioactive isotope of carbon that is naturally occurring and has a half-life of about 5,730 years. It is formed in the atmosphere when cosmic rays interact with nitrogen, converting it into carbon-14. This isotope is used extensively in radiocarbon dating to determine the age of organic materials, such as wood or bone, by measuring the amount of carbon-14 remaining in a sample. When living organisms are alive, they constantly take in carbon, including carbon-14, from their environment. Upon death, the uptake of carbon ceases, and the carbon-14 begins to decay, allowing scientists to estimate when the organism died based on the remaining quantity of carbon-14.

Chi-Square test

The chi-square test is a statistical method used to determine if there is a significant association between categorical variables. It compares the observed frequencies of events in different categories to the frequencies expected if there were no association between the variables. Here are the key components of the chi-square test:

1. Types of Chi-Square Tests:

   • Chi-Square Test of Independence: Used to determine if two categorical variables are independent.

   • Chi-Square Goodness of Fit Test: Used to determine if a sample distribution matches a theoretical distribution.

2. Calculating the Chi-Square Statistic:

   • The formula for the chi-square statistic is:
     $\chi^2 = \sum \frac{(O - E)^2}{E}$
     where O is the observed frequency and E is the expected frequency.

3. Degrees of Freedom:

   • The degrees of freedom for the chi-square test is calculated as:
     $df = (r - 1)(c - 1)$
     where r is the number of rows and c is the number of columns in the contingency table for the chi-square test of independence.

4. Interpreting Results:

   • After calculating the chi-square statistic, compare it to a critical value from the chi-square distribution table based on the desired significance level (e.g., 0.05) and the calculated degrees of freedom. If the chi-square statistic exceeds the critical value, the null hypothesis of independence is rejected, indicating a significant association between the variables.

5. Assumptions:

   • The chi-square test assumes that sample observations are independent, the data should be in frequency counts, and expected frequencies should be sufficiently large (typically at least 5 in each category).

Overall, the chi-square test is a useful tool for analyzing categorical data and assessing relationships between variables.