Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Bio 202 > Photosynthesis > Flashcards

Photosynthesis Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

Photosynthesis

A

Conceptually, photosynthesis is the reverse of cellular respiration.

  • Solar energy is converted into chemical energy in the form of chemical bonds in organic molecules
  • Photosynthesis occurs in the plant cell chloroplasts
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Chloroplasts

A

Thylakoid membrane contains chlorophyll that absorbs light energy for photosynthesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Photosynthesis reaction

A

In the presence of sunlight, green plants produce oxygen and food from carbon dioxide and water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Photosynthesis vs. Respiration

A
  • Photosynthesis occurs in the chloroplasts (endergonic)

- Occurs in the mitochondria (exergonic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Movement of Oxygen

A
  • CO2 oxygen goes to glucose oxygen (carbon fixation). Solar energy is used to reduce CO2 into sugar by transferring electrons together with H+ from H2O to CO2 (thuse photosynthesis is a redox reaction)
  • H2O oxygen goes to O2 (splitting of water). Therefore, the oxygen comes from the splitting of H2O, and H+ is then used to produce food
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Light Reactions

A

Convert solar energy into NADPH and ATP and release molecular oxygen (splitting of water)

  • Require light
  • ATP is made by photophosphorylation
  • NADPH made by transferring an electron (and H+) from H2O to NADP+. Also releases molecular oxygen as by-product.
  • No sugar is produced during light reactions
  • ATP and NADPH are then used in the Calvin cycle to make sugar
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Calvin Cycle (general)

A

Converts CO2, ATP and NADPH into sugar (carbon fixation)

- Does not require light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Why are chloroplasts green?

A

Plants absorb Blue and Red light and transmit Green light (therefore they are green).
- Chloroplasts have 3 major types of pigments: chlorophyll a, chlorophyll b, and carotenoids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Structure of chlorophyll

A
  • Porphyrin ring with MG atom (light absorbing region)

- Hydrophobic tail anchors it to the thylakoid membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Photoexcitation of chlorophyll

A

Chlorophyll a

  1. Ground state = electron in the normal orbital
  2. With light => excited state = electron goes to a higher orbital
  3. Electron is transferred to the primary acceptor => ATP and NADPH synthesis
    - In an isolated system, the “fall” of the electron from the excited to ground state releases energy (heat + fluorescence)
    - In nature, the energy is not lost; electrons are transferred to other molecules
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Photosystem

A 
Step 1. Light
Step 2. Pigments
- Antenna: 
-> Many pigment molecules (chl a, chl b, carotenoids)
-> Farther from the primary acceptor
-> Gather light and transfer electrons to reaction center
- Reaction Center:
-> 2 molecules of chlorophyll a
-> Close to the primary acceptor
-> Transfers e- to the primary acceptor
Step 3: Primary electron acceptor
- Receives e- from reaction center and transfers them to reactions of ATP/NADPH synthesis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Two Photosystems

A
  1. Photosystem 1 (P700)
    - Reaction center has chlorophyll a that absorbs light at 700nm
  2. Photosystem 2 (P680)
    - Reaction center has chlorophyll a that absorbs light at 680 nm
    - Differences between P700 and P680 chlorophylls a: they are associated with different proteins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do photosystems work?

A

They transfer electrons by:

  1. Cyclic electron flow:
    - Only in photosystem 1
    - Only ATP is made
  2. Non-cyclic electron flow:
    - Both in photosystem 1 and 2
    - ATP and NADPH are made
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Cyclic electron flow

A
  • No NADPH or O2 is synthesized

- H+ gradient is made by chemiosmosis and it drives the ATP synthase to make ATP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Major Steps in non-cyclic electron flow

A

Step 1:
- Photosystem 2 absorbs light (photons)
- Electrons in chlorophyll are excited
- Excited electrons are transferred to the primary acceptor of photosystem 2
- Because chlorophyll of photosystem 2 lost an electron, it needs to be reduced back
Step 2:
- An enzyme splits water into H+ and 1/2 O2
- Electrons are then transferred back to chlorophyll of photosystem 2, reducing it
- 1/2 O2 combines with another oxygen atom to make O2 which is then released
Step 3:
- Electrons pass from the primary acceptor of photosystem 2 through ETC and release energy used to make ATP by photophosphorylation (this ATP is used to drive the biosynthetic Calvin cycle)
Step 4:
- After ETC, electrons originating from photosystem 2 go to photosystem 1 (which has already been excited by light and lost an electron) to reduce it.
Step 5:
- Photosystem 1 has already been excited by absorbing light and losing electrons to its primary acceptor
- Electrons from the primary acceptor of photosystem 1 go through the second ETC to ferredoxin and NADP+ reductase to make NADPH (this NADPH is used in the Calvin cycle)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Cyclic vs. Non-cyclic electron flow

A
  1. Cyclic electron flow:
    - Electrons originated from photosystem 1 go back to photosystem 1 to reduce it
    - Only ATP is made during cyclic electron flow
  2. Non-cyclic electron flow:
    - Electrons from photosystem 1 go to make NADPH. Another electron comes from photosystem 2 to reduce photosystem 1, and yet another electron comes form H2O to reduce photosystem 2 and make O2.
    - NADPH, ATP, O2 are made during non-cyclic electron flow.
17
Q

Why is there both cyclic and non-cyclic flow?

A

Non-cyclic makes similar amounts of ATP and NADPH, but Calvin cycle uses more ATP than NADPH, so additional ATP comes from the cyclic flow.

18
Q

ATP synthesis

A
  1. ATP synthesis in chloroplasts (= photophosphorylation) is driven by chemiosmosis (similar to oxidative phosphorylation in mitochondria)
    - Chemiosmosis = the process by which ATP is produced on the thylakoid membrane of a chloroplast. The ETC transfers H+ from the stroma into the thylatoid space; as the H+ flow back to the stroma through the ATP synthase, the energy of their movement is used to add Pi to ADP, making ATP
  2. Cytochrome complex = electron transport chain
    - Pumps H+ from the stroma into the thylakoid space
    - H+ diffuses back and drives ATP synthase which makes ATP in the stroma, where it is used in the Calvin cycle
19
Q

Reactions in the thylakoid

A
  • H+ come from water (and stroma), but not from NADH as in respiration
  • ATP and NADPH are made in the stroma and can go directly to the Calvin cycle
20
Q

Mitochondria vs Chloroplasts: ATP Production

A 
Mitochondria:
- Oxidative phosphorylation
- Energy of electrons comes from food
- Protons are pumped from the matrix to the intermembrane space
- ATP is made in the matrix
- ATP is made utilizing NADH
Chloroplasts:
- Photophosphorylatin
- Energy of electrons comes from sunlight
- Protons are pumped from stroma into the thylakoid space
- ATP is made in stroma
- ATP is made without utilizing NADPH
21
Q

Reactants in Calvin Cycle

A

ATP and NADPH are used to make sugar from CO2 in Calvin cycle

  • No requirement for light
  • Incorporates (fixes) CO2 into a simple sugar glyceraldehyde-3-phosphate, G3P (or GAP)
  • To make one molecule of G3P, requires: 3 CO2, 9 ATP, 6 NADPH.
22
Q

Calvin Cycle

A

Step 1: Carbon fixation
- CO2 from the air is attached to a CO2 receptor, RuBP sugar
- Catalyzed by RUBISCO the most abundant protein on Earth
Step 2: Reduction
- Reactions use NADPH as an H+ source. Also, phosphorylation reactions occur that use ATP. NADPH and ATP come from the light reactions
- 6 molecules of G3P are made. Only 1 exits the cycle (product) to be used in the biosynthesis of other products
Step 3: Regeneration of RuBP
- Other 5 molecules of G3P are used to recreate RuBP. More phosphorylation occurs using ATP from the light reactions. The Calvin cycle is then ready to start again.`

23
Q

Summary of Photosynthesis

A

Light Reaction:
- H2O enters photsystem 2, electron transport chain, and photosystem 1 to produce O2.
Intermediate products:
- NADP+ and ADP and Pi from Calvin cycle to light reactions
- ATP and NADPH from light reactions to Calvin cycle
Calvin Cycle:
- Carbon fixation
- Sucrose (export to other organs of the plant).

24
Q

C4 Plants

A
  • Corn, sugarcane
  • Adaptation to semi-dry conditions (stomata are open only partially during hot days). First they fix CO2 into organic acids in a specific type of cells (mesophyll), then they transport these organic acids to another type of cells (bundle sheath), where the organic acids enter the Calvin cycle as carbon source (instead of CO2 directly). Separation between CO2 fixation and Calvin cycle is spatial
25
Q

CAM plants

A
  • Cacti, pineappples
  • Adaptation to dry conditions (stomata are closed during hot days). To prevent evaporation of water through stomata during the day, they take up CO2 only at night and incorporate it into organic acids. Then, when there is light, and ATP and NADPH are made, the organic acids enter the Calvin Cycle as carbon source. All this happens in the same cells. Separation between CO2 fixation and Calvin cycle is temporal.

Bio 202 (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions