1. CHAPTER 10

2.  stomata – pores in lower epidermis of leaf  gas exchange  mesophyll – inner-leaf tissue  most chloroplasts located in these cells  veins (phloem & xylem)  phloem carries sugars away from leaves  xylem carries water to leaves

3.  stroma – inner fluid  thylakoids – interconnected membranous sacs  contains chlorophyll  grana – stacks of thylakoids

4.  involves redox reactions  2 stages:  light reactions – convert solar energy to chemical energy stored temporarily in ATP & NADPH  Calvin cycle – conversion of CO 2 into glucose using the energy stored in ATP & NADPH 6 CO 2 + 6 H 2 O + light energy  C 6 H 12 O 6 + 6 O 2

6.  a mixture of wavelengths 380-750 nm  when passed thru a prism, separates into the colors of the rainbow

7.  absorb visible light  some wavelengths (colors of light) are not absorbed but reflected or transmitted– this is the color we see  (ex) leaves look green because the pigment chlorophyll reflects and transmits green light

8.  a machine that determines the wavelengths of light absorbed by a pigment by measuring the percent transmittance of each color of light  allows us to create an absorption spectrum

9.  chlorophyll a absorbs blue-violet & red light best  chlorophyll b absorbs blue & orange light best

10.  pigments become excited when they absorb light because absorption of a photon of light boosts an electron to a higher energy level  if the energy is not captured, the electrons will quickly fall back to their ground state & the energy is released as heat  sometimes light is also emitted as the electrons fall back down to their ground state – the resulting after- glow is called fluorescence

11.  light-harvesting complexes in the thylakoid membranes consisting of pigment molecules bound to proteins  two types: photosystem II (P680) & photosystem I (P700)  create a greater surface area for absorbing light  increase the range of wavelengths that can be absorbed by the plant (due to presence of chlorophyll a, chlorophyll b, and carotenoids)  have two parts: reaction center (chlorophyll a + primary electron acceptor) surrounded by light- harvesting complexes

12.  light strikes pigment molecules in light- harvesting complexes  energy is passed from one pigment molecule to another until it reaches chlorophyll a in the reaction center  this excites an electron in chlorophyll a which is picked up by the primary electron acceptor

13.  non-cyclic electron flow  flow of electrons from PS II  PS I  NADP +  produces ATP and NADPH for the Calvin cycle  cyclic electron flow  cycling of electrons within PS I; does not involve PS II  produces additional ATP needed for Calvin cycle  NADPH concentration regulates which type occurs  high [NADPH] stimulates cyclic electron flow to balance out NADPH & ATP levels

16.  ATP is made during the light reactions using the same process (chemiosmosis) that makes ATP during oxidative phosphorylation of cellular respiration

17.  light strikes PS II causing electrons in chlorophyll a in the reaction center to become excited  the excited electrons are picked up by the primary electron acceptor & passed down an electron transport chain which drives the synthesis of ATP by chemiosmosis  meanwhile, light strikes PS I causing electrons in chlorophyll a in the reaction center to become excited  the excited electrons are picked up by the primary electron acceptor & passed down an electron transport chain to NADP + which is reduced to NADPH

18.  the electrons lost from the chlorophyll a molecules in each photosystem are restored as follows:  electrons are restored to PS II by the splitting of H 2 O which produces O 2 as a by-product  electrons are restored to PS I by the electron transport chain that follows PSII (PS I is the final electron acceptor for this ETC) cont.

20.  carbon fixation – CO 2 is attached to a molecule called RuBP by the enzyme rubisco forming an unstable six-carbon compound that immediately splits into two three-carbon compounds called 3- PGA  ATP & NADPH drive the conversion of 3-PGA to G3P  for every three CO 2 that enter the cycle, six G3P are made – one leaves the cycle and five are recycled to regenerate RuBP (requires ATP)  glucose is made from the G3P that leaves the Calvin cycle

22.  plants that perform the steps of photosynthesis previously discussed are called C 3 plants  C 3 plants use CO 2 directly from the air by opening their stomata  this can be a problem on hot, dry days when plants close their stomata to reduce water loss because when stomata are closed, no CO 2 can enter the leaf & no O 2 can get out  the O 2 build-up causes photorespiration, a process in which rubisco adds O 2 to RuBP in the Calvin cycle instead of CO 2  photorespiration does not produce glucose like photosynthesis or ATP like cellular respiration so it is basically a wasteful process

23.  C4 photosynthesis  PEP carboxylase (which has a higher affinity for CO 2 than rubisco & no affinity for O 2 ) combines CO 2 with PEP to make oxaloacetate which is converted to malate and stored in the bundle-sheath cells  CO 2 is released in the bundle-sheath cells and enters the Calvin cycle  this adaptation is used in hot regions with intense sunlight where stomata partially close during the day  examples of plants that use this adaptation are corn & sugarcane

25.  CAM photosynthesis  plants take in CO 2 at night and store it in organic acids  CO 2 is released during the day for use in the Calvin cycle when light is available for the light reactions  this adaptation is used by plants that live in extremely arid environments like deserts  examples of plants that use this adaptation are cacti, pineapples, & succulents (water-storing plants) cont.

26. C4 PHOTOSYNTHESISCAM PHOTOSYNTHESIS  spatial separation of steps  temporal separation of steps