bio exam2 p2

1. 
   

Discuss how the surface area to volume ratio and the nuclear distance dictates cell

division.

1. Surface area to volume (SA: V) and nuclear distance. As a cell grows, volume (cubed) increases faster than surface area (squared), so SA: V falls. The membrane can no longer supply nutrients or remove waste fast enough for cytoplasm. Diffusion is also slow over long distances, and one nucleus can only control a limited volume of cytoplasm (the nuclear-cytoplasmic ratio). Past a certain size, the cell divides, which restores SA: V and keeps the nucleus close to all its cytoplasm.

Explain why most cell growth is initially fast, then slows as a cell ages.

2. Fast growth, then slowing. A small cell has a high SA: V, so exchange is efficient and growth is fast. As it grows, SA: V drops, so supply per unit volume falls, and growth slows. The cell approaches a size limit and divides.

3. How large cells cope with SA:V ratio

• Flattened or elongated shapes (neurons, red blood cells)  • Folding the membrane (microvilli)  • Many nuclei (skeletal muscle)  • Internal membranes and organelles that compartmentalize work • Cytoplasmic streaming and transport systems • A large central vacuole that pushes the cytoplasm into a thin layer (plants)

4. Cell theory.

• All living things are made of one or more cells.  • The cell is the basic unit of structure and function. • All cells come from pre-existing cells.

6. Prokaryotes vs. eukaryotes.

• Prokaryotes (bacteria, archaea) have no nucleus (DNA is in a nucleoid), no membrane-bound organelles,usually a single circular chromosome, and a cell wall. Many have a capsule, flagella, and pili. They are typically 1-10 µm.

 • Eukaryotes (protists, fungi, plants, animals) have a membrane-bound nucleus, membrane-bound organelles, and multiple linear chromosomes. They are typically 10-100 µm and may be unicellular or multicellular.

7. Autotrophs vs. heterotrophs.

• Autotrophs make their own organic molecules from inorganic sources. Photoautotrophs use light (plants, algae, cyanobacteria). Chemoautotrophs use chemical energy (sulfur bacteria).

• Heterotrophs must consume organic molecules made by others (animals, fungi, most bacteria and protists).

8. Kingdoms. Check which scheme your lecture used. A common one:

• Bacteria and Archaea: prokaryotic, mostly unicellular (E. coli methanogens, extreme halophiles).  

• Protista: eukaryotic, mostly unicellular, diverse nutrition (Paramecium, Amoeba, algae).

• Fungi: eukaryotic, chitin walls, absorptive heterotrophs (mushrooms, yeast, molds).

• Plantae: multicellular, cellulose walls, photosynthetic autotrophs (ferns, conifers, flowering plants).

• Animalia: multicellular, no cell walls, ingestive heterotrophs, motile (insects, fish, mammals)

Movement across membranes (Q9-21)

9. Bulk flow.

Mass movement of a fluid or gas from high to low pressure, driven by a pressure gradient rather than individual concentration differences. Examples: blood moving through vessels, air moving into lungs, sap flowing through phloem, water through a pipe.

10. Diffusion.

Net movement of particles from high to low concentration. It occurs because molecules are in constant random motion (kinetic energy), so they collide and spread out until evenly distributed. Examples: perfume spreading in a room, O₂ and CO₂ exchange across alveoli, dye in water. It is passive and needs no energy.

11. Dynamic equilibrium and concentration gradient.

At dynamic equilibrium, particles keep moving, but there is no net movement because rates in both directions are equal. A concentration gradient is a difference in concentration between two regions. Diffusion proceeds “down” the gradient.

12. Factors affecting diffusion rate.

• Steeper gradient: faster • Higher temperature: faster (more kinetic energy)  • Smaller molecules: faster • Shorter distance/thinner barrier: faster • Larger surface area: faster  • Medium: faster in gases than liquids  • Membrane permeability: more permeable is faster

13. Osmosis.

Diffusion of water across a selectively permeable membrane from lower solute concentration (higher water potential) to higher solute concentration (lower water potential). It occurs because water moves down its own concentration gradient when solutes can’t cross.

14. Tonicity (compares solutions, usually the outside to the inside of the cell):

• Hypertonic: more solute outside. Water leaves the cell (e.g., a cell in salt water).  • Hypotonic: less solute outside. Water enters the cell (e.g., a cell in pure water).  • Isotonic: equal solute. No net movement

15. Osmotic potential, tonicity, and water potential.. Water moves from higher Ψ to lower Ψ.

A hypertonic solution has lower water potential than the cell, so water flows out.  A hypotonic solution has higher water potential, so water flows in. Pressure (turgor) raises Ψ until equilibrium. Pure water at atmospheric pressure has Ψ = 0.

17. Factors affecting permeability.

• Lipid solubility (nonpolar molecules cross easily)  • Size (small is better) • Charge (ions and polar molecules are blocked) • Membrane composition (cholesterol, fatty acid saturation) • Number of channel or carrier proteins  • Temperature

18. Carrier proteins.

Membrane proteins that bind specific molecules and change shape to move them across. They provide specificity, move molecules that can’t cross the lipid bilayer, can be saturated, and are used in both facilitated and active transport.

20. Endocytosis vs. exocytosis.

• Endocytosis brings material in by vesicles. Exocytosis releases material by vesicle fusion with the membrane.  • Phagocytosis: “cell eating,” engulfs large particles or cells (white blood cells). • Pinocytosis: “cell drinking,” takes in fluid and dissolved solutes. • Receptor-mediated endocytosis: specific molecules bind receptors in coated pits, then are taken in (cholesterol/LDL uptake).

21. Cell junctions.

• Plasmodesmata: channels through plant cell walls connecting cytoplasm.  • Gap junctions: protein channels linking animal cells for ions and small molecules (heart muscle).  • Tight junctions: seal adjacent cells to prevent leakage (intestinal lining).  • Desmosomes: holds cells together , made through cytoskeleton

Energy and thermodynamics (Q22-28) 22.

Forms of energy.

Chemical (glucose, ATP),  light/radiant (sunlight),  heat/thermal,  electrical (nerve impulses, ion gradients),  mechanical (muscle contraction),  nuclear.

23. Laws of thermodynamics.

• First law: energy cannot be created or destroyed, only transformed. Organisms must take in energy (food or sunlight) and convert it.  • Second law: every energy transfer increases the entropy (disorder) of the universe, and some energy is lost as heat. Organisms need a constant energy input to maintain order.

24. Potential vs. kinetic.

Potential is stored energy (glucose bonds, a concentration gradient, water behind a dam). Kinetic is energy of motion (moving molecules, heat, a muscle contracting).

25. Entropy. A measure of disorder or randomness.

Living things stay highly ordered by taking in energy and releasing heat and waste (CO₂, H₂O). This increases the entropy of their surroundings more than it decreases their own, so the second law is not violated.

26. Exergonic vs. endergonic.

• Exergonic: releases energy (negative ΔG), spontaneous. Examples: cellular respiration, ATP hydrolysis. • Endergonic: requires energy input (positive ΔG), not spontaneous. Examples: photosynthesis, protein synthesis.

27. Activation energy.

The energy needed to start a reaction (reach the transition state). High activation energy makes organic molecules stable, so they don’t spontaneously break down. Reactions occur only when enzymes lower the barrier.

28. Catalyst.

A substance that speeds up a reaction by lowering activation energy without being consumed or changing ΔG. Enzymes (Q29-33)

29. Importance of enzyme.

Enzymes make the reactions of life fast enough at body temperature. They are specific, so they allow cells to control which reactions happen and when.

30. Mechanism of Enzyme reaction.

The substrate binds to the active site (induced fit), forming an enzyme/substrate complex. The enzyme strains bonds or orients substrates, lowering activation energy, then releases the product and is unchanged. Example: sucrase (enzyme) + sucrose (substrate) → glucose + fructose (products). Another: catalase + H₂O₂ → H₂O + O₂

31. Characteristics of enzymes

• Mostly proteins (some are RNA) • Specific to substrates • Reusable  • Lower activation energy • Don’t change equilibrium • Affected by temperature, pH, and substrate and enzyme concentration  • Can be regulated  • Active site binds substrate • Usually named with “-ase”

32. Simple vs. conjugated. enzyme

• Simple enzymes are only protein. *Conjugated enzymes need a non-protein part. • Apoenzyme: protein portion (inactive alone).  • Cofactor: non-protein helper, often a metal ion (Mg²⁺, Zn²⁺).  • Coenzyme: organic cofactor, often derived from vitamins (NAD⁺, FAD, CoA).  • Holoenzyme: apoenzyme + cofactor, the active complete enzyme.

33. Inhibition and regulation.

• Competitive: inhibitor resembles the substrate and binds the active site. It can be overcome by adding more substrate.

• Noncompetitive: inhibitor binds elsewhere Away from active site (an allosteric site), changing the enzyme’s shape.Not going to compete with the substrate in binding with the active site  

• Irreversible: inhibitor binds covalently and permanently, destroying function (nerve gases, penicillin, heavy metals).

• Feedback inhibition: the end product of a pathway inhibits an early enzyme, shutting down production when enough is made.

• Allosteric regulation: a molecule binds a site other than the active site and either activates or inhibits the enzyme by changing its shape.

Metabolism and redox (Q34-37)

34. Anabolism vs. catabolism.

• Anabolism builds complex molecules from simple ones (endergonic, uses energy (e.g., protein synthesis, photosynthesis)

• Catabolism breaks down complex molecules (exergonic, releases energy e.g., respiration).

• -Catabolism provides the ATP and building blocks that power anabolism..

35. How ATP is cycled and coupled reaction’s importance to anabolic activities.

• ATP hydrolysis (ATP → ADP + Pᵢ) releases energy

ADP is recharged to ATP using energy from catabolism (phosphorylation).

• In coupled reactions, the energy released by exergonic ATP breakdown drives endergonic anabolic reactions, so the overall reaction is spontaneous.

36. Oxidation and reduction.

Oxidation is loss of electrons (or hydrogens)

reduction is gain of electrons (or hydrogens). They always occur together (redox): one substance is oxidized as another is reduced. (Mnemonic: OIL RIG.)

37. Coenzymes in redox.

NAD⁺ and FAD act as electron/hydrogen carriers, shuttling energy from catabolism to the electron transport chain.