STUDY GUIDE FOR PHOTOSYNTHESIS



Honors BIO Photosynthesis Study Guide

1. History

a. Jan van Helmont – plants make new tissue from water (5-year plant)

b. Joseph Priestley – Plants interact with the air; make oxygen

i. “plants repair air damaged by animals and burning”

ii. (mouse in bell jar)

c. Ingenhousz – plants make oxygen only in sunlight

d. Senebier – plants remove carbon dioxide from air in sunlight

e. Englemann – plants absorb blue and red light best (prism on algae)

2. Basics

a. In chloroplast; two sets of reactions

b. Light-dependent: uses H2O, sunlight energy; makes O2, energy molecules

c. Light-independent: uses CO2, energy molecules; makes glucose

3. Light and absorption

a. Visible light – colors, high and low energy – depends on wavelength

b. Absorption spectrum – colors absorbed best by pigments

c. Absorbed and reflected light – why we see colors

d. Light travels in a wave, behaves like a particle

i. Photon - has specific amount of energy, absorb all or none

4. Photosynthetic pigments

a. Absorb specific wavelengths (colors) and reflect others

b. Chlorophyll a – primary pigment – begins reaction pathway

c. Chlorophyll b – accessory, transfers absorbed energy to chlorophyll a

d. Other accessory pigments: xanthophylls – yellow; carotenes – orange

5. Chloroplast

a. Thylakoid – photosynthetic membrane, contain pigment molecules, site for light reactions

b. Grana - stack of thylakoid sacs

c. Photosystem – cluster of pigment molecules, in thylakoid membranes

d. Stroma - fluid surrounding thylakoids, site for Calvin cycle

e. Also contain: DNA, ribosomes, starch grains (stored carbs)

6. Leaf – name and function of each part; stoma – role and function

7. Light-Dependent Reactions (in thylakoids)

a. Reactant: water (source of O2), sunlight energy

b. Products: O2, ATP and NADPH (energy molecules for next reactions)

c. Light absorbed by chlorophyll, electrons excited to higher energy level

d. Excited electrons enter Electron Transport Chain

i. Series of redox reactions – transfer electrons along chain of acceptor molecules

e. Chemiosmosis – synthesizes ATP

i. Electron energy in transport chain pumps H+ ions into thylakoid space

ii. Proton (H+) gradient

iii. protons diffuse back across membrane through ATP synthase enzyme

iv. ADP + P ( ATP

f. Water is split by light – makes oxygen gas

i. Hydrogen ions go to coenzyme NADP( NADPH

ii. Electrons replace the electrons lost from chlorophyll

8. Light-Independent Reactions (Calvin Cycle) – in stroma

a. Reactants: CO2 and energy molecules made in the light reactions

b. Product: glucose

c. Carbon Fixing: CO2 combines with RuBP ( Makes 3-carbon PGA

d. Rubisco - enzyme for carbon fixing

e. Uses ATP and NADPH; changes PGA into 3-carbon PGAL (or G3P)

f. 2 PGAL(or G3P) make one glucose

g. Remaining PGAL change back to RuBP for reuse

9. Factors affecting rate of photosynthesis

a. Temperature – warm speeds reactions, but HOT causes stomata to close

b. Water – low water slows reactions as stomata close to minimize evaporation

i. Transpiration - water evaporates from surface of leaves

c. Light intensity – brighter light speeds reactions

d. Concentration of CO2 – low concentration slows reactions

10. Hot weather adaptations: C4 and CAM plants

e. C3 pathway: normal Calvin cycle

i. Hot weather – stomata close to save water, slows CO2 entry

f. C4 plants – concentrate CO2 while stomata open, “fix” into 4-C compound

i. Use stored carbon when stomata close during hot part of day

ii. Corn, sugar cane, crabgrass

g. CAM – concentrate CO2 during the night, when air is cool and stomata open

i. Use stored carbon during day when stomata closed

ii. Cacti, succulents, pineapple

11. Heterotrophic plants – supplement photosynthesis

a. Carnivorous plants – eat insects for nitrogen, live where nitrogen low in soil

i. Venus fly trap, pitcher plant, sundew

b. Parasitic plants – suck plant sap from host

i. Mistletoe, dodder, Indian pipe

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