Photosynthesis and Tonicity

AP Biology Photosynthesis Test Review

Test Format will be 25-30 multiple-choice questions - Topics 2.8 Tonicity and Osmoregulation and 3.5 Photosynthesis

Graphing Review - Topic 2.8 Video #2

- independent variable - the variable being manipulated - goes on the x-axis

- dependent variable - the variable you are measuring - goes on the y-axis

- The following acronym can be used in constructing a graph - TAILS - Title, Axes labeled, Intervals are Equal, Labeled Lines/Bars, and Scale is Appropriate)

Study the notes that were handed out over Photosynthesis and AP Classroom Daily Videos 2.8 and 3.5

Topic 3.4 Cellular Energy
Oxidation - occurs when a molecule loses electrons (e.g. H₂O → 2H⁺ + 2e^- + 1/2O₂)
Reduction - occurs when a molecule gains electrons (e.g. NADP⁺ + 2e^- + 2H⁺ → NADPH)
A low pH (or high concentration of H⁺) = an acidic environment
A high pH (or low concentration of H⁺) = a basic environment
Endergonic (non-spontaneous) - the products of a reaction have more energy than the reactants - examples: photosynthesis and other types of synthesis reactions; also include reactions in which a phosphate group from ATP is used to drive a synthesis reaction

ATP - how does it provide energy for cellular work? When ATP breaks down into ADP + P_i (remember that ATP can do this readily because of the negative charges on phosphate groups- causes the phosphate groups to repel each other), the released P_i attaches to a protein and provides energy for the protein to do some type of work -- e.g. active transport, movement like myosin heads in muscle contractions

Topic 3.5 Photosynthesis

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

Thylakoid membrane- site of the light-dependent reactions

Stroma - site of the light-independent reactions

Chlorophyll a molecules (reaction center) - Magnesium atoms within chlorophyll - source of electrons that get excited by light energy

Primary Electron acceptor - this is the 1st protein to capture the energized electrons from chlorophyll

Photosystem II (680 wavelength-red light) - where water is broken down - provides replacement electrons for Photosystem II

Photosystem I (700 wavelength - far red light) - where NADP⁺ is reduced into NADPH

Photolysis (breakdown of water - provides the replacement electrons for Photosystem II - H₂O → 2H⁺ + 2e^- + 1/2O₂), the Z protein (produced by plants) is the molecule that catalyzes the breakdown of water into 2H⁺ + 2e^- + 1/2O₂

Electron transport chain - as electrons are transported by the proteins in the ETC, the electrons are losing potential energy (the proteins in the ETC become progressively more electronegative); the electrons lost energy is used by the same proteins in pumping hydrogen ions from the stroma to the thylakoid space

Proton pump - used to establish a proton gradient (H⁺); a proton gradient is a separation of hydrogen ions across a membrane - in other words, hydrogen ions (protons) become more concentrated on one side of a membrane; (this is where hydrogen ions are actively transported from the stroma to the thylakoid space by the same proteins that are transporting electrons)

Chemiosmosis - production of ATP by ATP Synthase (refers to the diffusion of hydrogen ions from thylakoid space to the stroma by way of ATP synthase; the diffusion of hydrogen ions are used to power ATP synthase into making ATP)

Calvin cycle (light independent reactions) occurs in the stroma - NADPH provides the electrons & hydrogen ions in reducing carbon dioxide to glucose; and ATP is used in Calvin cycle to make substrate molecules reactive (by adding a phosphate to them); NADPH & ATP were produced in the light-dependent reactions

Topic 2.8 Tonicity and Osmoregulation

Water Potential Calculations:

Water Potential = solute potential + pressure potential

Ѱ = Ѱ_s + Ѱ_p

Solute potential (Ѱ_s = -icRT)

Key points about water potential:

*Water potential measures the tendency of water to move from a high water potential area to a low water potential area (example: water always moves towards the lower or more negative water potential environment)

*An increase in solute concentration lowers the solute potential (in other words, the increase in solute concentration makes the solute potential more negative).

*All types of sugar molecules have an ionization constant of 1 since sugar is still 1 ion when it dissolves in water; NaCl has an ionization constant of 2 (since NaCl breaks up into 2 ions when it dissolves in water)

*At equilibrium, the cell and its outer environment have the same water potential value (the value can be negative or positive for both of them)

*An increase in solute concentration lowers the solute potential

Hypertonic - refers to an environment that has a greater amount of solute concentration relative to another environment; a plant cell placed in a hypertonic environment will plasmolyze (shrink)
Hypotonic - refers to an environment that has a lower amount of solute concentration relative to another environment; a plant cell placed in a hypotonic environment will become turgid (swell)
Isotonic - refers to an environment that has the same amount of solute concentration relative to another environment; a plant cell in an isotonic environment is flaccid
There will be questions on the test from the Osmosis in Plant Cells Lab - so make sure you review the lab. This is the lab where we placed potato cores in different concentrations of sucrose. We used the percent change in mass in determining the solute concentration and solute potential of the potato cores.
Calculate %change in mass = ( Final value - Initial value) x 100

Initial Value