Unit 2 AP Biology Review

Mrs. Jones welcomes students to the Unit 2 AP Biology review, focusing on cells. She introduces herself and emphasizes the importance of various resources available on her website (apbiopenguins.weebly.com), including daily reviews, a 505-page review guide, FRQ Fridays with past free-response questions, and 120 Wayound games. Unit 2 constitutes 10-13% of the AP Biology exam, covering cell structure, function, size, membrane transport, and osmosis.

The review delves into the functions of essential organelles. Ribosomes (04:22) are crucial for protein synthesis, composed of large and small subunits, and found in all life forms. The endomembrane system (06:01) includes the ER (rough and smooth), Golgi apparatus, lysosomes, vacuoles, transport vesicles, nuclear membrane, and plasma membrane, all working together to package, transport, and modify cellular materials. The rough ER (07:20) synthesizes proteins for membranes or secretion, while the smooth ER (08:31) handles detoxification and lipid synthesis. The Golgi complex (09:00) further packages and modifies materials. Mitochondria (10:03) are the sites of the Krebs cycle and oxidative phosphorylation, providing ATP, and show evidence of endosymbiotic theory. Lysosomes (12:47) are responsible for intracellular digestion, using hydrolytic enzymes. Vacuoles (15:05) vary in function, with central vacuoles in plants maintaining turgor pressure, contractile vacuoles in freshwater organisms pumping out excess water, and food vacuoles aiding digestion. Chloroplasts (16:49) in plants and algae perform photosynthesis, also supporting the endosymbiotic theory. Compartmentalization by organelles (18:49) allows cells to be larger and more efficient.

Cell size is critical for efficiency, with a large surface area to small volume ratio being optimal for nutrient uptake and waste elimination. Smaller cells generally have a higher metabolic rate per body mass (24:18) due to greater heat loss, requiring more metabolism to maintain warmth. The video briefly mentions calculations for surface area and volume of various shapes, emphasizing that these formulas are provided on the exam's formula sheet.

The plasma membrane, or phospholipid bilayer, consists of hydrophilic heads and hydrophobic tails, cholesterol for fluidity, and glycoproteins/glycolipids for cell communication. Cell walls (32:29), found in bacteria, fungi, and plants, provide structural support and prevent osmotic lysis. Membrane transport (32:29) includes simple diffusion (32:37) for small, non-polar molecules directly across the membrane, facilitated diffusion (32:46) for polar or charged molecules aided by transport proteins (e.g., aquaporins for water), and active transport (34:35) which requires ATP to move substances against their concentration gradient (e.g., sodium-potassium pump). Bulk transport includes exocytosis (37:59) for expelling large molecules and endocytosis (39:00) for taking them in (phagocytosis, pinocytosis, receptor-mediated endocytosis).

Tenicity and osmoregulation are explained using hypotonic, hypertonic, and isotonic solutions (41:30). Water moves from areas of high water potential to low water potential. The video details the water potential formula (Ψ = Ψs + Ψp) and the solute potential formula (Ψs = -iCRT), providing an example calculation (45:30) for potato cores. The effects of different solutions on animal and plant cells are illustrated: animal cells can crenate in hypertonic solutions or lyse in hypotonic solutions, while plant cells undergo plasmolysis in hypertonic solutions and become turgid in hypotonic solutions due to their cell walls.

Several practice questions are reviewed: describing ribosome function (51:50), the polarity of membrane-embedded receptors (53:02), identifying the most efficient cell size for waste removal (54:06), differentiating passive and active transport (56:29), and explaining why chloride ion movement leads to water loss (01:01:31). Exam format details are provided (01:03:03), including the hybrid nature with digital multiple-choice and written FRQs. Students are advised to bring a calculator and use a pen for FRQs (except for graphs, where pencil is acceptable).

Mrs. Jones encourages students to utilize AP Classroom videos and progress checks, The Absolute Recap podcast, and the Barron's AP Bio review book. She reiterates the importance of practice exams and highlights her Instagram for daily instant reviews and Way Games. The video concludes with a reminder about the exam date (May 4th at 8 a.m.), study plans available on her website, and an offer to answer further questions.