Unit 3. Cellular Energetics (Photosynthesis)

heterotrophs vs. autotrophs

heterotrophs = eat other organisms for energy

autotrophs = make their own energy

what is photosynthesis and where does it occur

converts light energy to chemical energy that can be used to do work

• in the chloroplast

• mesophyll

• stomata

• chlorophyll

mesopghyll = where the chloroplasts mainly are

stomata = pores in the leaf where co2 enters and o2 exits

chlorophyll = the green pigment in thylakoids

photosynthesis equation

6co2 + 6h2o + light energy → c6h12o6 + 6o2

relationship between wavelength and energy

the shorter the wavelength, the higher the energy

the longer the wavelength, the lower the energy

how do pigments play a role in how much light is absorbed

green pigment of leaves = that bluish purple and red light is absorbed and green light is reflected

chlorophyll a

bluish green

• converts solar light to chemical energy

chlorophyll b

yellow green

• converts energy to chlorophyll a

carotenoids

yellow orange

• broadens the color spectrum

• used when the green chlorophyll a is used up

• seen with fall leaves

what does the porphyrin ring in the center of the chlorophyll determine?

gives the chlorophyll the capacity to absorb light in a unique way (different wavelengths)

absorption spectrum

determine effectiveness of different wavelengths for photosynthesis

• high transmittance (near 100) = low absorption

  • chlorophyll absorbs little green light

• low transmittance (near 0) = high absorption

  • chlorophyll absorbs most blue light

what was engelmann’s experiment

1. algae was placed under a light, allowing for it to do photosynthesis

2. aerobic bacteria would be introduced to the algae and would go where there was the most amount of oxygen

3. photosynthesis produces oxygen so wherever there was the greatest rate of photosynthesis would be where there would be the most oxygen

4. ALGAE WENT TO THE VIOLET BLUE AND RED LIGHTS

showed how photosynthesis worked the best with violet blue and red wavelengths

photosynthesis is split into two parts… and what can they also be called and where do they occurt?

light reactions/light-dependent reactions

• happens in the thylakoid membranes

calvin cycle/light-independent reactions

• happens in the stroma

how are electrons in chlorophyll molecules excited by light?

1. light is absorbed by chlorophyll

2. the electron at ground state becomes excited by the light energy and goes to its excited state

3. it will go back down to ground state as it gives off heat and fluorescence

photosystems

has reaction center and light harvesting complexes

light reactions/light-dependent reactions

IN THYLAKOID MEMBRANE

1. light is absorbed by the chlorophyll molecules in the light-harvesting complexes of photosystem II

2. the light is transferred between excited chlorophyll molecules

3. the energy ends up at a special pair of chlorophyll a molecules (in this case, P680) in the reaction center

4. the excited electron will be transferred to the primary electron acceptor

5. water is split into o2 and hydrogen (H+) by oxidation (release of electrons) to fill in the spot of the excited electron

6. the excited electron will move through the electron transport chain to photosystem I

7. in photosystem I, more light will excite the less excited electron to motivate it to move more

8. as the electron moves across, the energy will allow for H+ to be pumped into the thylakoid space/lumen

9. NADP+ picks up the electrons and is converted to NADPH

10. the H+ in the lumen will flow through ATP synthase into the stroma and generates ATP

reactants

• light energy

• water

• NADP+

• ADP + P

products

• o2

• ATP

• NADPH

photosystem II is known as…

photosystem I is known as…

photosystem II is known as PS 680

photosystem I is known as PS 700

calvin cycle/light-independent reactions

• what was the purpose of making ATP and NADPH in the light reactions

• where does the calvin cycle take place

• three steps

ATP and NADPH provide the energy to power the calvin cycle

3 co2, ENTER ONE AT A TIME

1. carbon fixation

   • RuBP (5C) and co2 (1C) present

   • RuBisCo (enzyme) will combine RuBP with co2

   • that 6C molecule will break into 2 3C molecules

2. reduction (counting the total amount now)

   • 6 ATP and 6 NADPH is used to produce 6 G3P (can be assembled quickly into sugars)

   • 1 of those G3P will be used to make sugars

   • the other 5 will be used to regenerate RuBP

3. regeneration of RuBP

   • 3 ATP is used to regenerate 3 RuBP

linear electron flow

most common, produces ATP, NADPH, and o2

• uses both PS II and I

cyclic electron flow

only uses PS I

• only produces ATP

• not o2 or NADPH

the charge of the thylakoid space/lumen

the charge of the stroma

lumen = positive (a lot of H+)

stroma = negative (less H+)

photorespiration, how did it come about

uses o2 + ATP and produces co2

• rubisco binds o2, not carbon

• happens on hot days when stomata close (save water)

because the early atmosphere had a lot of co2 and not much o2

c3 vs c4 vs CAM

c3

• photorespiration + no sugars made

• fixes co2 using rubisco into 3C

• water losssssss

• c fixation and calvin together

c4

• fixes co2 into 4C and then release co2 into calvin cycle in bundle sheath cells

• no photorespiration, makes sugar

• closed stomata during day, not much water loss (for hot and sunny)

• c fixation and calvin in different cells

• PEP carboxylase

CAM

• fix co2 at night since stomata open

• stomata closed during day, light reactions give ATP + NADPH

  • co2 released for calvin cycle

• for VERy dry places = little water loss

• c fixation and calvin at different times

• organic acid