Chapter 7 8 Photosynthesis Cellular Respiration Metabolism Matter

Chapter 7 & 8: Photosynthesis & Cellular Respiration

Metabolism: Matter, Energy, and Organization • Organisms have highly organized structures that must be maintained in their orderly state by a CONSTANT supply of ENERGY. • Metabolism is the sum of all chemical reactions in an organism.

(1) Photosynthesis (only possible way to capture solar energy) • Converts SOLAR energy into CHEMICAL energy using special pigments and chemicals. (2) Autotrophs (a. k. a. , producers) • Capable of using chemical processes to manufacture their own FOOD.

(3) Heterotrophs (a. k. a. , consumers) • Must CONSUME pre-made food to extract the energy necessary to carry out life processes.

(4) Cellular Respiration • Biochemical reactions (occuring in the mitochondria) in which cells make ATP by breaking down organic compounds (sugars).

ATP- the energy molecule • Adenosine is bonded to 3 phosphate groups. • Each bond stores energy. • The last bond is fairly unstable, so it tends to break easily, releasing its energy (so the cell can do work).

Capturing The Energy in Light I. Energy for Life Processes (1) A Biochemical Pathway (e. g. , photosynthesis) • Series of reactions where the product of one reaction is used in the next reaction.

PHOTOSYNTHESIS has (3 STAGES) (1) LIGHT RXNS: NRG is captured from sunlight; WATER is split into Hydrogen Ions (H+), Electrons (e-), and Oxygen (O 2). (2) E- transport chain: Light NRG is converted to Chemical NRG temporarily stored in ATP and NADPH. (3) CALVIN CYCLE: ATP and NADPH power the formation of organic compounds (carbohydrates) using CO 2. 1 2 3

II. STAGE 1: Light Absorption in Chloroplasts (i. e. , light rxns) • Photosynthesis begins inside thylakoid membranes, stacked to form grana within the chloroplast. • These membranes contain the pigment CHLOROPHYLL, which absorbs red & blue light, reflecting yellow and green.

Chloroplast Pigments (absorb orange-red and blue-violet light) • Compounds manufactured and stored in the chloroplast. (1) Chlorophylls (types “a” & “b”) • Pigments clumped into two photosystems, I and II.

(2) Carotenoids (yellow, orange, and brown pigments) • Assist chlorophylls by capturing wavelengths of sunlight NOT absorbed by chlorophyll (i. e. , blue and green light).

Light reactions BEGIN when pigments in the thylakoids absorb sunlight, acquiring some ENERGY. • The energy causes electrons to become “excited” , and this energy is trapped to power the 2 nd stage.

(A) Restoring the chlorophyll • Recall that electrons LEFT chlorophyll molecules when they got excited by the light energy. • If the e- were NOT replaced, the chemical reactions would stop, preventing photosynthesis. • Replacement e- are provided by splitting H 2 O molecules into H+, electrons, and O 2 (which gets released).

STAGE 2: Electron Transport Chain • Electrons are PASSED from one molecule to the next until a final e acceptor (NADP) is reached NADPH. • As the e- pass from molecule to molecule in the e- transport chain, they lose most of their energy, of which gets harnessed to move protons (H+) into the thylakoid.

• When these H+ return to their original position by facilitated diffusion, the energy is harnessed to build ATP from ADP. Interior of thylakoid stroma

• The two energy-storing compounds (NADPH and ATP) are now used to power the chemical reactions in Stage 3.

Stage 3: the Calvin Cycle (aka “dark reactions”) I. Carbon Fixation • A series of reactions that produces organic compounds (glucose), using CO 2 obtained from the atmosphere. • This does not require light to take place Light-independent reactions.

This is called a cycle because while some CO 2 is taken from atmosphere, some carbon molecules get recycled over and over. • The Calvin Cycle occurs within the fluid-filled STROMA of the chloroplast (outside thylakoids).

(A) Balance Sheet for Photosynthesis (3 ATP, 2 NADPH used each turn) 6 CO 2 + 6 H 2 O + solar energy C 6 H 12 O 6 + 6 O 2

III. Rate of Photosynthesis • Rates of photosynthesis will be INFLUENCED by… • SOLAR Intensity (Light Energy) [peak, then PLATEAU] • [CO 2] [peak, then PLATEAU] • Temperature [peak then DROP]

Critical Thinking A famous scientist once said that wherever in the universe life exists, some of those life-forms MUST be colored. Why would the scientist make such a statement?

EXTRA CREDIT: Alternative Pathways • Although Calvin cycle is the most common for carbon fixation, some plant species can use OTHER biochemical pathways including: C 3, C 4 and the CAM

EXTRA CREDIT: Alternative Pathways (1) C 3 Plants (open stomata during the day) • Fix carbon through the Calvin cycle; named after the 3 -C compound, PGA.

EXTRA CREDIT: Alternative Pathways (2) Stomata (stoma) • Are small pores for CO 2 , & H 2 O gases, to enter and leave a plant (commonly found on underside of leaves) • When stomata close, [CO 2] drops and [O 2] rises; both of these features INHIBIT carbon fixation—plants who AVOID opening of stomata have ADAPTED to deal with this problem.

EXTRA CREDIT: Alternative Pathways (A) The C 4 Pathway (open PARTIALLY during the day) • Cells use an enzyme that can fix CO 2 into a 4 -C compound even when the CO 2 level is LOW and the O 2 level is HIGH. • C 4 plants include corn and crabgrass, and LOSE only HALF the WATER as C 3 plants when producing the SAME amount of CARBOHYDRATE.

EXTRA CREDIT: Alternative Pathways (B) The CAM Pathway (similar to C 3 and C 4 pathways, BUT…) • At NIGHT, CAM plants open stomata to take in and store CO 2 ; during the day (closed stomata), CO 2 is released to enter the Calvin cycle. • Cacti, pineapples, and other species adapted to HOT, dry climates fix carbon through the CAM pathway.