Chapter 10- Photosynthesis

Question 1

What is the difference between an autotroph and a heterotroph?

Answer 1

Autotrophs: Sustain themselves via photosynthesis or other means (producers- do not consume other organisms)

Heterotrophs: Obtain their organic material from OTHER organisms. (consumers)
Ex: Humans

Question 2

What cell has a lot of chloroplasts and is the location where a lot of photosynthesis occurs?

Answer 2

Mesophyll cells

Question 3

Which part of the plant does photosynthesis occur? (not the part of the cell, the part of the plant)

Answer 3

Leaves

Question 4

What are the “openings” of the leaf that CO2 enters through?

Answer 4

Stomata

Question 5

In which organel does photosynthesis occur in? Cellular respiration?

Answer 5

Chloroplasts, Mitochondria

Question 6

Parts of a chloroplast (name 3 “membranal spaces”, 3 things inside of it)

Answer 6

Outer membrane
Intermembranal space
Inner membrane
Thylakoids- the “pancake”-like disks
Granum- many thylakoids stacked on top of each other
Stroma- the fluid within the chloroplast

Question 7

What makes plants green? Where is it located?

Answer 7

Chlorophyll is located in Chloroplasts.

Question 8

What colors do leaves absorb? Which colors do leaves not absorb, and REFLECT?

Answer 8

All except green, green

Question 9

What is the photosynthesis equation? What is the cellular respiration equation?
How are they related?

Answer 9

Photosynthesis:
6CO2 + 6H20 + Light Energy = C6H12O6 + 6O2

Cellular Respiration:
C6H12O6 + 6O2 = ATP + 6CO2 + 6H20

They are OPPOSITES of each other. (with the exception of light energy/ATP)

Question 10

What are the two stages of photosynthesis? What do each do?

Answer 10

1: Light reactions- create NADPH and ATP to be used in the calvin cycle
2: Calvin Cycle- takes carbon and turns it into glucose (which is to be used in cellular respiration)

Question 11

What are NAD+, NADH, NADP+, and NADPH?

Answer 11

NADH: The electron carrier in CATABOLIC reactions. Created by reducing (adding on one hydrogen ion and 2 ELECTRONS) to NAD+.
(Cellular respiration)

NADPH: The electron carrier in ANABOLIC reactions. Created by reducing an NADP+.
(Photosynthesis)
Think “P- Photosynthesis”

Somewhat relevant but not crucial to know: NADP+ is converted from NAD+ via phosphorylation, when a phosphate group is attached to NAD+

Question 12

What are pigments? What is an absorption spectrum?

Answer 12

Pigments- Substances that absorb visible light

Absorption spectrum: plots a pigment’s light absorption

Question 13

What are the three photosynthetic pigments? Which one is the “main one”?
What colors do each one absorb?

Answer 13

Chlorophyll a (main)- Absorbs violet/blue/red light
Chlorophyll b- broadens absorption spectrum. Absorbs blue and red-orange light. (more on the orange side)
Carotenoids/Carotenes
Absorbs purple and blue. REFLECTS green, yellow, orange, and red. THIS IS WHY FALL LEAVES ARE COLORFUL!

All of them REFLECT green light.

Question 14

How is chlorophyll excited by light?

Answer 14

When a photon of light hits a chlorophyll molecule, the electron “jumps” into a higher energy state, then quickly “falls” back down, releasing more photons and heat, which is to be transferred to the next molecule…and the next…and the next…and the-…you get the point :)

Question 15

What are the two “main” parts of a photosystem?

Answer 15

1: Light harvesting complexes. On the both sides of the “rectangle”. Include pigments that absorb photons.

2: Reaction center complex. Located in the middle, in between the two light harvesting complexes. Includes a special pair of CHLOROPHYLL A molecules- the location where photolysis occurs (see slide 18 ), and the electron is jumped up into the PRIMARY ELECTRON ACCEPTOR.

Question 16

Where are the photosystems located?

Answer 16

The thylakoid membrane

Question 17

What are the two photosystems in photosynthesis? Which occurs first? What are the names for their respective reaction-center chlorophylls?

Answer 17

Photosystem II (PS2) comes first. The reaction-center chlorophyll is P680.

Photosystem I (PS1) comes SECOND. The reaction center chlorophyll is P700.

Question 18

What is photolysis? Where does it occur?

Answer 18

Photolysis- the splitting of a water molecule into 2 H+ (protons), 2 electrons, and 1/2 O2.
This occurs in PS2, near the special chlorophyll a molecules. Photolysis donates electrons to the chlorophyll a molecules (P680), which will be “jumped up” into the primary electron acceptor.

Question 19

Describe the full process of the light reactions

Answer 19

1: A photon of light hiits the PS2 chloroplast molecules.
2: The photon of light transfers it’s energy through a chain reaction, all the way to the special pair of chlorophyll a molecules (P680).
3: Photolysis occurs, where one water molecule (H2O) is split into 2 protons, 2 electrons, and 1/2 O2. It donates electrons to the chlorophyll a molecules.
4: Right when the energy is transferred to the chlorophyll a molecules, the electrons are donated via photolysis, and the electron “jumps up”.
5: Before the electron falls back down, the primary electron acceptor (pheophytin) “grabs” the electron.
6: The electron is shuttled down the ETC (electron transport chain), and generates ATP, to be used in the calvin cycle.
7: The electron is sent into PS1, where it undergoes the “chain reaction” again.
8: The primary electron acceptor of PS1 catches the electron.
9: The electron is sent down the ETC, and oxidizes NADP+ reductase, which then reduces it to become NADPH.
The NADPH is then used in the Calvin cycle.

Question 20

Linear vs Cyclic flow. How does Cyclic flow work?

Answer 20

Linear electron flow uses both photosystems and generates NADPH and ATP.

Cyclic electron flow, however, only generates ATP. It only uses photosystem 1 (the second photosystem), and the electron simply moves in and out of photosystem one, only generating ATP.

1: The electron “bounces” through the molecules.
2: It’s caught by the primary electron acceptor.
3: Shuttled through the electron transport chain. (generating ATP)
4: Brought back into photosystem 1.

Question 21

Both photosynthesis AND cellular respiration generates ATP via chemiosmosis. How does it differ between the two?

Answer 21

Photosynthesis:
Occurs in the chloroplasts.
H+ diffuses from the thylakoid space into the stroma. (inside to out)

Cellular respiration:
Occurs in the mitochondrion.
H+ diffuses from the inner membrane space to the mitochondrial matrix. (outside to in)

Question 22

Fill in the blanks.
The Calvin Cycle builds _________________ (mini ______) via ________.

Answer 22

The carbon cycle builds G3P (mini glucose) via carbon fixation.

Question 23

How many times does the calvin cycle have to “turn” in order to produce 1 G3P? 1 Glucose?

Answer 23

3 times for 1 G3P
6 times for 1 glucose

Question 24

Describe all the steps of the Calvin Cycle. (Include the 3 phases- Carbon Fixation, Reduction, and Regeneration of the Co2 acceptor)

Try to keep this one marked purple so that it gets repeated often.

Try using paper and pencil to diagram.

Answer 24

Phase 1: Carbon Fixation

1: 3 molecules of CO2 enter at a time.
2: The 3 carbons from the CO2 molecules combine with ribulose biophosphate (RuBP) with help from the enzyme rubisco, and turns into a short-lived intermediate.
3: These 3 short-lived intermediate break down into 6 molecules of 3-phosphoglycerate.

Phase 2 (Reduction)
4: 6 ATPs donates a phosphate group to each of the 3-phosphoglycerate, turning them into 6 molecules of 1, 3-Biophosphoglycerate
5: 6 NADPH are oxidized, turning the 3-phosphoglycerates into 6 G3Ps. However, only 1 G3P is outputed. The rest of the other 5 G3Ps are CONVERTED BACK into RuBP.

Phase 3 (Regeneration of the CO2 acceptor)

6: ATP convertes the remaining 5 G3Ps back into 3 molecules of RuBP, to be used once again in the cycle!

Question 25

Exercise: Fill in the blanks of the Calvin Cycle: USE PAPER AND PENCIL. *TIP: MARK THIS AS PURPLE (1) EVEN IF YOU GET IT CORRECT. This question is very important, and should be repeated often for maximum retention. Phase 1: ____________ 1: ___ molecules of CO2 enter. They each combine with ________ via the enzyme __________, to form 3 ___________ intermediates. 2: The short-lived intermediates automatically break down into ______ molecules of __________________________. Phase 2: _______________ 3: 6 ATPs donate a phosphate group to _______________, converting them into ___ molecules of __________________. 4: 6 NADPHs are_________ (oxidized/reduced), turning the 6 molecules of _______________ into 6 molecules of _____. Phase 3: __________________ 5: ___ molecule(s) of _____ is released as an output, and the other ___________ molecules are regenerated. 6: _______ helps convert the ___ molecules of _____ back into ___ molecules of __________.

Answer 25

Phase 1: Carbon fixation 1: 3 molecules of CO2 enter. They each combine with RuBP via the enzyme rubisco, to form 3 short-lived intermediates. 2: The short-lived intermediates automatically break down into 6 molecules of 3-phosphoglycerate. Phase 2: Reduction 3: 6 ATPs donate a phosphate group to 3-phosphoglycerate, converting them into 6 molecules of 1,3-biophosphoglycerate. 4: 6 NADPHs are oxidized, turning the 6 molecules of 1,3-biophosphoglycerate into 6 molecules of G3P. Phase 3: Regeneration of RuBP 5: 1 molecule of G3P is released as an output, and the other 5 molecules are regenerated. 6: ATP helps convert the 5 molecules of G3P back into 3 molecules of RuBP.

Question 26

What is rubisco?

Answer 26

It is the enzyme that assists in attaching carbon to RuBP. Also the most abundant protein on Earth!

Question 27

Why is closing stomata a problem? Why is opening stomata a problem? What does closing stomata lead to?

Answer 27

By opening stomata, CO2 intake increases and so does photosynthesis...but H2O is lost. By closing stomata, H20 is conserved, but CO2 intake ceases, and photosynthesis... Closing stomata in reducing CO2 intake can lead to photorespiration.

Question 28

What is photorespiration? What is it caused by? Why is it harmful?

Answer 28

Occurs in C3 plants. Occurs when the stomata closes too much, with too little CO2 . Rubisco, instead of attatching CO2 to RuBP, attatches oxygen to RuBP instead. What happens as a result is that glycolate is formed. Peroxisomes and mitochondrion then work very hard, consuming a lot of energy, to get rid of this glycolate, while also wasting CO2.

Question 29

What are C4 plants (examples, please). How do they minimize photorespiration?

Answer 29

C4 plants (grass, corn, rainforest canopies), minimze photorespiration by "pumping" CO2 into a DIFFERENT CELL for the Calvin Cycle. Seperates the CO2 and the location of the Calvin Cycle in DIFFERENT CELLS. Calvin Cycle occurs in bundle sheath cells now.

Question 30

What are the steps that C4 plants take regarding photosynthesis/Calvin Cycle?

Answer 30

1: The enzyme PEP carboxylaze adds Carbon Dioxide to PEP, creating Oxoalocate. 2: A 4 carbon compound such as malate is exported through plasmodesmata into bundle-sheath cells, releasing CO2. 3: The CO2 enters the Calvin Cycle in the bundle sheath cells. 4: The remaining Malate is turned into pyruvate, and through ATP, becomes PEP again.

Question 31

What are CAM plants? How do they lower the cost of photorespiration?

Answer 31

CAM plants: E.g. cacti, pineapple, use temporal seperation. During the night, they open stomata, intaking CO2. During the day, they use the CO2 for the Calvin Cycle.