AP Bio Review

AP Biology Review - UNIT I: CHEMISTRY OF LIFE

Elements

• All life forms are composed of matter.
• All matter is composed of elements.
• Elements are substances that cannot be broken down into smaller substances by chemical means.

Essential Elements of Life

• 96% of the mass of living things is composed of:
  • Oxygen (O)
  • Carbon (C)
  • Hydrogen (H)
  • Nitrogen (N)
• Other elements (4% of biomass):
  • Calcium (Ca)
  • Phosphorus (P)
  • Potassium (K)
  • Sulfur (S)
  • Sodium (Na)
  • Chlorine (Cl)
  • Magnesium (Mg)
• Trace elements:
  • Iron (Fe)
  • Iodine (I)
  • Copper (Cu)

Subatomic Particles

• Atom
  • The smallest unit of an element.
  • Building blocks of the physical world.
• Subatomic Particles
  • Protons
    • Packed with neutrons in the nucleus.
    • Positively charged.
    • Most atoms have the same number of protons and electrons, making them electrically neutral.
  • Neutrons
    • Packed with protons in the nucleus.
    • No charge.
    • Isotopes
      • Same element with different numbers of neutrons in the nucleus.
      • Vary in mass.
      • Radioactive isotopes decay spontaneously, giving off particles and energy.
  • Electrons
    • Negatively charged.
    • Spin around the nucleus.
    • Very small; effectively massless.
    • Electrons on an atom differ in their amounts of potential energy.
    • An electron's state of potential energy is called its energy level or electron shell.
    • Valence electrons are those in the outermost shell, or valence shell.
    • The chemical behavior of an atom is mostly determined by the distribution of electrons in electron shells.
      • The valence shell is the most important.
      • Elements with full valence shells are chemically inert.
      • Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms.
• Atoms of different elements differ in the number of subatomic particles.
  • Atomic number = #protons in the nucleus
  • Mass number = protons + neutrons
    • Average of all isotopes
  • Atomic mass = atom’s weighted average total mass

Compounds

• A compound occurs as a result of 2 or more individual elements combining in a fixed ratio.
  • Different properties from individual elements.
  • Formed by a chemical reaction.
• Bonds that hold compounds together:
  • Ionic bonds
    • Nonmetal + metal
    • One or more electrons are transferred from one atom to another.
    • One atom loses electrons (becomes positively charged), while the other gains electrons (becomes negatively charged).
    • Results from the attraction of two oppositely charged ions.
    • Cation: has a positive charge.
    • Anion: has a negative charge.
    • Cation and anion form to create an ionic bond.
  • Covalent bonds
    • Nonmetal + nonmetal
    • A molecule consists of 2 or more atoms held together by covalent bonds.
    • Formed when electrons are shared between atoms.
    • In a nonpolar covalent bond, electrons are shared equally.
    • In a polar covalent bond, electrons are shared unequally.
    • In a single covalent bond, one pair of electrons is shared.
      • Double covalent: when 2 pairs are shared, etc.
    • A structural formula is used to represent atoms and bonding (e.g., H-H).
    • A molecular formula abbreviates the structural formula (e.g., $H_2$).
    • Electronegativity is an atom’s attraction for the atoms in a covalent bond.
      • The more electronegative an atom, the more strongly it pulls shared electrons toward itself.
  • Hydrogen bonds
    • A hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom.
    • In living cells, hydrogen bonds usually involve oxygen or nitrogen atoms.
  • Van der Waals Interactions
    • Weakest bonds.
    • If electrons are distributed asymmetrically in molecules or atoms, they can result in “hot spots” of positive or negative charge.
    • Attractions between molecules that are close together as a result of these charges.
      • Example: how geckos climb.

Water: The Versatile Molecule

• In water, electrons are not shared equally in the bonds between hydrogen and oxygen.
  • Hydrogen atoms have a partial positive charge, while oxygen atoms have a partial negative charge.
  • Water is polar.
• Hydrogen bonds
  • Weak attractions that result from water’s polarity.
    • The positive end of one polar molecule is attracted to the oxygen negative charge, and vice versa with the hydrogen end.
    • A hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom.
    • Weak individually, but strong on a larger scale.
  • Lend water many special properties:
    • Cohesion
      • The tendency for water to stick to water.
      • Important during transpiration.
        • Water evaporates, pulls other water molecules with it, pulling all the way down from leaves to roots.
    • Adhesion
      • The tendency of water to stick to other substances.
      • Cohesion + Adhesion = capillary action.
        • Allows water to flow up roots/trunks/branches of trees in thin vessels.
    • Surface tension
      • Results from the cohesion of water molecules.
      • Example: water striders can sit on top of water without sinking.
    • High heat capacity
      • Heat capacity = ability of a substance to resist temperature changes.
      • Keeps ocean temperatures stable.
      • Allows organisms to keep a constant body temperature since most life forms are mostly made up of water.
      • Heat is absorbed when hydrogen bonds break and released when hydrogen bonds form.
    • High heat of vaporization
      • Heat a liquid must absorb for 1g to be converted to gas.
      • Evaporative cooling
        • As a liquid evaporates, its remaining surface cools.
        • How sweat works to cool the body down.
    • Expansion on freezing
      • The lattice structure of ice causes water to expand on freezing.
      • Allows ice to float on top of lakes in winter.
        • Animal life can live beneath the ice.
    • Versatility as a solvent
      • A solution is a liquid that is a homogeneous mix of substances.
      • The solvent is the dissolving agent of a solution.
      • The solute is the substance that is dissolved.
      • An aqueous solution is one where water is the solvent.
      • The polarity of water allows it to be a versatile solvent.
        • Can form hydrogen bonds easily.
      • Hydrophobic substances do not dissolve in water, but hydrophilic ones will.

Acids and Bases

• A solution is acidic if it contains a lot of $H^+$.
• A solution is alkaline if it contains a lot of $OH^-$.
• Measured on the pH scale:
  • Logarithmic.
  • Numbered 1-14.
    • Acids: 1-7 pH.
    • Bases: 7-14 pH.
• Buffers maintain stable pH.

Organic Molecules

• An organic compound contains Carbon.
• An inorganic compound does not contain carbon.
• Carbon is often surrounded by hydrogen.
• Carbon is a versatile atom:
  • Can bind with many elements.
  • Many “slots” to bind with elements.
    • 4 valence electrons.
    • Can form 4 covalent bonds.
    • Makes large, complex molecules possible.
  • In molecules with multiple carbons, each carbon bonded to 4 other atoms has a tetrahedral shape.
  • When 2 carbons are formed by a double bond, the atoms joined to the carbons are on the same plane as the carbons.
  • Electron configuration gives it covalent compatibility with other elements.
• Hydrocarbons consist of only carbon and hydrogen.
  • Can undergo reactions that release a large amount of energy.
  • Isomers are compounds with the same molecular formula but different structures/properties.
    • Usually, only one isomer is biologically active.
  • Functional groups are the components of organic molecules that are most commonly involved in chemical reactions.
    • The number and arrangement of functional groups give each molecule its unique properties.

Functional Groups

• Most macromolecules are chains of building blocks called polymers. The individual building blocks of a polymer are called monomers.
• Carbohydrates
  • Contain carbon, hydrogen, and oxygen in a 1:2:1 ratio.
  • Monosaccharides
    • Most common are glucose and fructose.
      • Glucose.
        • Most abundant.
        • Part of the food humans eat.
        • Made by plants during photosynthesis.
          • Broken down to release energy.
      • Fructose
        • Common sugar in fruits.
    • Can be depicted as either straight or rings.
    • 6 carbon-sugars.
    • Formula: $C<em>6H</em>{12}O_6$
  • Disaccharides
    • 1 monosaccharide + 1 monosaccharide = 1 Disaccharide
    • Formed by dehydration synthesis (aka condensation).
      • Hydrogen (-H) from one sugar combines with the hydroxyl group (-OH) of another sugar molecule to create water as a byproduct.
      • The bond is called a glycosidic linkage.
    • Broken apart by hydrolysis
      • Reverse of dehydration.
      • Water is used to break apart the glycosidic linkage.
  • Polysaccharides
    • Repeated units of monosaccharides.
    • Most common:
      • Starch
        • Stores sugar in plants.
        • Made up of alpha-glucose molecules.
      • Cellulose
        • Made up of beta-glucose molecules.
      • Chitin
        • Structural molecule in walls of fungi/arthropod exoskeletons.
        • Used as surgical thread since it breaks down in the body.
      • Glycogen
        • Stores sugar in animals.
• Proteins
  • Amino acids = monomers of proteins.
    • 20 kinds of naturally occurring amino acids.
    • Contain:
      • Carbon
      • Hydrogen
      • Oxygen
      • Nitrogen
    • 4 parts of an amino acid are centered around a central carbon:
      • Amino group (-NH2).
      • Carboxyl group (-COOH).
      • Hydrogen.
      • R group (aka side chain).
        • Interchangeable.
        • Vary in composition, polarity, charge, and shape depending on the specific side chain.
        • Polar R groups point outward; hydrophobic R groups point inward.
  • Polypeptides
    • Amino acid + amino acid = dipeptide
      • Formed by dehydration synthesis.
      • The bond is called a peptide bond.
    • Multiple amino acids = polypeptide.
    • Once a polypeptide chain twists and folds on itself, it forms a 3D structure called a protein.
  • Higher protein structure (4 levels total):
    • Primary structure
      • Linear sequence of amino acids.
      • Covalent (peptide) bonds.
    • Secondary structure
      • The protein begins to twist (2 options).
        • Forms a coil (alpha-helix).
        • Zigzagging pattern (known as beta-pleated sheets).
      • The shape depends on the R-group.
      • Formed by amino acids that interact with other amino acids nearby in the primary structure.
      • Hydrogen bonds between the carbonyl and amino groups.
      • Interactions between the amino and carboxyl groups of the protein backbone.
      • After secondary structure forms, formerly distant amino acids are now nearby; tertiary structure can form.
    • Tertiary structure
      • Can be both alpha and beta helix/sheets within the structure.
      • A covalent disulfide bridge often stabilizes structure.
      • Bonds between R groups:
        • Hydrogen bonds.
        • Ionic bonds.
        • Disulfide bridges.
        • Hydrophobic interactions.
    • Quaternary structure
      • Several different polypeptide chains sometimes interact with each other.
      • Same bonds as above, but between peptide chains rather than between R groups.
  • Mistakes in structure can denature a protein.
    • Change of shape = change of function.
      • Ex. pH or heat can denature a protein.
    • Protein folding can involve chaperone proteins (chaperonins).
      • Help protein fold properly.
      • Make the process more efficient.

Kinds of Proteins

• Lipids
  • Like carbs, consist of carbon, hydrogen, and oxygen, but not in a fixed ratio.
  • Do not form polymers.
  • Little-no affinity for water.
    • Hydrophobic due to nonpolar covalent bonds of hydrocarbons.
  • Common examples:
    • Triglycerides
      • A glycerol molecule + 3 fatty acid chains attached.
        • A fatty acid chain is mostly a long chain of carbons where each carbon is covered in hydrogen; one end of the chain has a carboxyl group (-COOH).
          • Vary in length and #/location(s) of double bonds.
        • Glycerol is a 3-carbon alcohol with a hydroxyl group attached to each carbon.
      • Fats separate from water because water forms hydrogen bonds with itself while excluding the fats.
      • To be made, each of the carboxyl groups of the 3 fatty acids must react with one of the 3 hydroxyl groups of the glycerol molecule via dehydration synthesis.
        • The bond = ester linkage.
      • Saturated fatty acid
        • No double bond.
        • The carbon chain is completely filled (“saturated”) with hydrogen.
        • Usually solid at room temp.
      • Unsaturated fatty acid
        • A double bond along the carbon chain, causing a bend.
          • The bend allows the triglyceride to become LESS dense, making it liquid at room temperature.
        • A polyunsaturated fatty acid has multiple double bonds within the fatty acid, causing many bends.
    • Phospholipids
      • 2 fatty acid “tails” + 1 negatively charged phosphate “head.”
        • Tails are hydrophobic, while the head is hydrophilic (the negative charge on the head attracts polar water).
        • Amphipathic molecule (a molecule that is both polar and nonpolar).
      • In water, phospholipids self-assemble into a “bilayer arrangement.”
        • Hydrophobic tails face towards the interior.
        • Found in cell membranes.
    • Steroids
      • Cholesterol
        • 4-ringed molecule dispersed throughout the membrane.
        • Maintains membrane stability.
        • Increases membrane fluidity at lower temperatures by disrupting close packing.
        • Decreases fluidity at high temperatures through its constant movement.
• Nucleic Acids
  • Contain carbon, hydrogen, oxygen, nitrogen, and phosphorus.
  • Structure
    • Nitrogenous base.
    • Pentose sugar.
    • Phosphate group.
    • The portion of the nucleotide without the phosphate group is called nucleoside.
  • Store, transmit, and help express hereditary information.
  • Monomer = nucleotides.
  • The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene.
    • Made up of DNA.
  • Deoxyribonucleic acid (DNA)
    • Sugar = deoxyribose.
    • Contains genetic/hereditary information.
    • Provides directions for its own replication.
    • Directs synthesis of messenger RNA (mRNA), and through mRNA, controls protein synthesis.
      • Occurs on ribosomes.
  • Ribonucleic acid (RNA)
    • Sugar = ribose.
    • Essential for protein synthesis.
    • 2 families of nitrogenous bases:
      • Pyrimidines
        • A single 6-membered ring.
        • Examples:
          • Cytosine.
          • Thymine (only in DNA).
          • Uracil (only in RNA).
      • Purines
        • A 6-membered ring fused to a 5-membered ring.
        • Examples:
          • Adenine
          • Guanine
  • Nucleotide Polymers
    • Nucleotide polymers are linked together to build a polynucleotide.
    • Adjacent nucleotides are joined by covalent bonds that form between the -OH group on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon on the next.
      • Links create a backbone of sugar-phosphate units with nitrogenous bases as appendages.
    • RNA molecules usually exist as single polypeptide chains.
    • DNA molecules have 2 polynucleotides spiraling around an imaginary axis, forming a double helix.
      • Two backbones run in opposite 5’→3’ directions from each other (antiparallel).
      • One DNA molecule contains many genes.
      • Nitrogenous bases pair up and form hydrogen bonds:
        • Adenine - Thymine.
        • Guanine - Cytosine.
        • Complementary base pairing.
      • In RNA, thymine is replaced by uracil, so A and U pair.

Macromolecule Relationships

Origins of the Earth

• Alexander Oparin and J. B. S. Haldane proposed that the primitive atmosphere contained the following gases:
  • Methane ($CH_4$).
  • Ammonia ($NH_3$).
  • Hydrogen ($H_2$).
  • Water ($H_2O$).
  • No free oxygen ($O_2$).
    • No oxidation/reduction.
    • Rocks do not release oxygen through weathering.
  • Gases collided, producing chemical reactions that eventually led to the organic molecules we know today.
    • Substantial support until 1953.
• 1953: Stanley Miller and Harold Urey simulated the conditions of primitive Earth in a lab.
  • Put theorized gases into a flask, struck them with electrical charges to simulate lightning, and organic compounds similar to amino acids appeared.
• The current theory of the origin of life suggests 4 main stages:
  • 1. Formation of amino acids.
  • 2. Monomers form polymers.
  • 3. Enclosure of small organic molecules into larger ones.
  • 4. Self-replicating molecules that can direct synthesis of other organic substances.
    • Energy sources for early organic synthesis:
      • Lightning.
      • Volcanic eruptions.
• RNA world hypothesis
  • Original life-forms were simple molecules of RNA.
    • RNA is not restricted to a double helix.
    • RNA is capable of replicating and passing genes.
  • Complex organic compounds must have formed via dehydration synthesis.
    • Organic compounds then used as food by cells.
    • Simple cells evolved into complex cells.
• Heterotrophs
  • Living organisms that rely on organic molecules for food.
  • Aka consumers.
• Autotrophs
  • Organisms that make their own food.
    • Most commonly via photosynthesis.
  • Aka producers.

UNIT II: Cells

Living Things

• All living things are composed of cells.
• According to cell theory, the cell is life’s basic unit of structure and function.
  • The cell is the smallest unit of living material that can carry out all the activities necessary for life.
• Why not be a GIANT CELL?
  • Specialization.
  • Must maintain a high surface area: volume ratio to allow cellular exchanges across the membrane!

Types of Cells and Organelles

• The invention of electron microscopes allowed scientists to figure out the exact functions of cells.
• Prokaryotic cells
  • Only in domains Bacteria and Archaea.
  • Smaller.
  • Simpler.
  • Circular DNA.
    • In the nucleoid region.
    • NO NUCLEUS.
  • Cell wall
    • Made up of peptidoglycans that surround a lipid layer called the plasma membrane.
  • Filled with semi-fluid cytosol.
  • Have ribosomes.
  • Can have flagella.
    • Long projections used for motility.
  • May have a thick capsule outside their cell wall to give them extra protection.
  • No membrane-bound organelles.
• Eukaryotic cells
  • More complex.
  • Organized into smaller structures called organelles.
  • DNA is in the nucleus bounded by a membranous nuclear envelope.
  • Cytoplasm is between the plasma membrane and the nucleus.

Organelles

• Each organelle has its own special task.
• Plasma Membrane
  • Outer envelope.
  • Complex.
  • Phospholipid bilayer.
  • Encloses vacuole.
  • Regulates movement in/out of cell.
  • Flexible due to weak bonds holding it together.
    • Higher fluidity when more phospholipids have double bonds (causing a bend in the tail) since the molecules aren’t as packed.
  • Semipermeable
    • Only small hydrophobic molecules can pass through unaided.
    • Anything large/hydrophilic must pass through active/passive transport.
    • Water can’t move through easily due to its polarity.
  • Fluid-mosaic model
    • Peripheral proteins are loosely associated with the lipid bilayer.
      • Located on inner/outer surface of membrane.
    • Integral proteins are firmly bound into the plasma membrane.
      • Amphipathic to allow anchoring.
      • Some extend all the way through the membrane.
    • The membrane is peppered with different proteins/carb chains.
      • Adhesion proteins
        • Membrane proteins form junctions between adjacent cells.
      • Receptor proteins
        • Serve as docking sites for arrivals at the cell.
          • Ex. hormones.
      • Transport proteins
        • Form pumps that use ATP to actively transport solutes across the membrane.
        • Hydrophilic channel that certain molecules/ions can use as a tunnel.
          • Specific for the substance it moves.
        • Carrier proteins
          • Bind to molecules and change shape to shuttle them across the membrane.
        • Channel proteins
          • Selectively allow the passage of ions/molecules.
      • Cell surface marker
        • Exposed on the cellular surface.
        • Play a role in cell recognition/adhesion.
          • Ex. glycoproteins.
      • Carbohydrate side chains
        • Attached to the surface of some proteins.
        • Found only on the outer surface.
      • Cholesterol
        • Maintain fluidity (see pg. 11).
      • Unsaturated fats also lend membrane fluidity by increasing space between phospholipids due to bend.
• Nucleus
  • The largest organelle of the cell.
  • Directs what goes on in the cell.
  • Responsible for the cell’s ability to reproduce.
  • Home of hereditary information (DNA).
    • DNA is organized into large structures called chromosomes.
  • The most visible structure of the nucleus is the nucleolus, which is where rRNA is made and ribosomes are assembled.
• Ribosomes
  • Sites of protein synthesis.
  • Manufacture all proteins required/secreted by the cell.
  • Consist of RNA and other proteins.
  • Bind messenger RNA and transfer RNA to synthesize proteins.
  • Round structures consisting of 2 subunits: the large subunit and the small subunit.
  • Composed of RNA and proteins.
  • Can either be free-floating or attached to the endoplasmic reticulum (ER).
• Endoplasmic Reticulum (ER)
  • A continuous channel that extends into many regions of the cytoplasm.
  • Lipid proteins synthesis/transport.
  • Rough ER
    • Attached to the nucleus.
    • Studded with ribosomes.
    • Proteins generated here are trafficked to/across the plasma membrane or used to build Golgi bodies, lysosomes, or the ER.
  • Smooth ER
    • Lacks ribosomes.
    • Makes:
      • Lipids.
      • Hormones.
      • Steroids.
      • Breaks down toxic chemicals.
• Golgi Bodies
  • Process proteins.
  • Once the ribosomes on the rough ER have completed synthesizing proteins, the Golgi bodies modify, process, and sort the products.
  • Packaging/distribution centers for materials destined to be sent out of the cell.
  • Package final products into vesicles.
    • Carry protein products to the plasma membrane for export.
  • Involved in the production of lysosomes.
• Mitochondria
  • “PoWeRhOUsE oF ThE cElL”.
  • Responsible for converting the energy from organic molecules into useful energy for the cell.
  • The energy molecule in the cell is adenosine triphosphate (ATP).
  • Unique oblong shape and characteristic double membrane consisting of an inner portion and an outer portion.
  • The inner membrane forms folds called cristae.
    • Separates the innermost area (called the matrix) from the intermembrane space.
    • The outer membrane separates the intermembrane space from the cytoplasm.
    • Production of ATP is done on the cristae.
• Lysosomes
  • Tiny sacs that carry digestive enzymes.
  • Break down old/worn-out organelles/debris/large ingested particles.
  • Cells clean up crew.
  • Keep cytoplasm clear of unnecessary flotsam.
  • Sometimes contain hydrolytic enzymes that function only at an acidic pH, which is enclosed inside the lumen of the lysosome.
• Centrioles
  • Small paired cylindrical structures often found within microtubule organizing centers (MTOCs).
  • Most active during cellular division.
    • When a cell is ready to divide, centrioles produce microtubules, which pull the replicated chromosomes apart and move them to opposite ends of the cell.
  • Common in animal cells, but not in plants.
• Vacuoles
  • Latin for “empty cavity”.
  • Fluid-filled sacs that store water/food/wastes/salts/pigments for later use/removal.
  • Larger in plant cells.
• Peroxisomes
  • Breakdown of long fatty acids through beta-oxidation.
• Cytoskeleton
  • A network of fibers that maintain cell shape.
  • Most important:
    • Microtubules
      • Made up of protein tubulin.
      • Participate in cellular division/movement.
      • Integral part of centrioles/cilia/flagella.
    • Microfilaments
      • Important for movement.
      • Composed of protein actin.
      • Actin monomers joined together and broken apart as needed to allow microfilaments to grow and shrink.
      • Assist during cytokinesis/muscle contraction/formation of pseudopodia extension during cell movement.
• Cilia and Flagella
  • Allow motion in single-celled organisms.
  • In the respiratory tract, cilia sweep constantly back and forth to keep out pathogens/dust.
  • Every sperm cell has a flagellum, enabling it to swim through the female reproductive organs to fertilize the waiting ovum.
• Extracellular matrix
  • Molecules secreted by the cell.
    • Mostly glycoproteins or other carb/containing molecules, especially collagen.
  • Provides structure/biochemical support.
• Plant Cells vs. Animal Cells
  • Plants have plasmodesmata.
    • Connections between plant cells that allow communication amongst them.
  • Plant cells have a cell wall.
    • Rigid layer of cellulose.
    • Outside of the plasma membrane.
    • Provides support for the cell.
    • Prevents lysis.
  • Plant cells have chloroplasts.
    • Contain chlorophyll, making them green.
    • Involved in photosynthesis.
  • In plants, most of the cytoplasm is taken up by an enlarged vacuole that crowds out other organelles.
    • Contains cell sap in mature plants.
    • Full vacuole means plant is not dehydrated.
  • Plants do not contain centrioles.

Structural Characteristics of Cell Types

Transport Across the Plasma Membrane

• The ability to travel across the plasma membrane depends on (1) the semipermeability of the plasma membrane and (2) the size and charge of the molecules that want to get through.
• Lipid-soluble substances can cross the membrane easily due to the phospholipid tails of the membrane.
  • “Like dissolves like”.
• Facilitated transport
  • Substances must pass through a specific channel protein instead of directly through the membrane due to its hydrophilic/charge/etc.
  • Depends on a number of proteins that act as tunnels through the membrane.
  • Example: Aquaporins are water-specific channels.
• Simple transport: Simple and facilitated diffusion
  • Diffusion
    • A substance will move down its concentration gradient.
      • Simple Diffusion
        • If the diffusion molecule is hydrophobic, the nonpolar molecule can drift through the membrane unaided
      • Facilitated Diffusion
        • Diffusion of a substance requires the help of a channel protein
    • Called passive transport when that substance is moving down its concentration gradient
      • No energy required
      • At Dynamic equilibrium, as many molecules cross the membrane in one direction as the other
  • Osmosis
    • Process where water is diffused
    • Water always moves from areas where it is more concentrated to where it is less concentrate
      • Water moves to dilute solid particles
    • In both diffusion and osmosis, the final result is that the solute concentrations are the same on both sides of the membrane. The only difference is that in diffusion that membrane is usually permeable to the solute, and in osmosis it is not
  • Tonicity describes osmotic gradients
    • A Isotonic solution, the solute concentration is the same inside as outside
      • No net water movement
    • A hypertonic solution has more total dissolved solutes than the cell
      • Cell loses water
    • A hypotonic solution has less total dissolved solutes than the cell
      • Cell gains water
    • Cell walls help maintain water balance
      • A plant cell in a hypotonic solution swells until the wall opposes uptake, becoming turgid/firm; while an animal cell in a hypotonic solution will lyse/burst since their membrane are not as string
      • Plant cells experience lethal plasmolysis in a hypertonic environment
      • Plant cells become flaccid in an isotonic environment
  • Water potential (Ψ) is the measure of potential energy in water and describes the eagerness of water to flow from an area of high water potential to an area of low water potential
    • Affected by pressure potential Ψp and solute potential Ψs
    • Equations on AP sheet
  • ACtive Transport
    • Allows a substance to move against its