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BIO 1210 > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

Define photosynthesis and provide the general chemical formula

A

The anabolic, endergonic process of converting energy from the sun and CO2 from the environment into chemical energy stored in glucose (sugar) and other organic molecules

6CO2 + 12H2O + light energy –> C6H12O6 + 6O2 + 6H2O

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2
Q

How does photosynthesis occur?

A

Plant (and other photosynthetic organism) cell chloroplasts capture light energy from the sun and convert it to chemical energy that is stored in sugar and other organic molecules

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3
Q

What is the importance of photosynthesis to plants and to life on Earth?

A

Photosynthesis provides energy either directly or indirectly for nearly all living organisms

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4
Q

Describe the process of photosynthesis in terms of reactants and products

A

The mesophyll chloroplasts of a plant convert carbon dioxide from the environment and sunlight into 3-C sugar (used to synthesize glucose), Oxygen gas and water

Reactants: 6 carbon dioxide, 12 water

Products: 3-C sugar (used to make 1 glucose), 6 oxygen gas and 6 water

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5
Q

Describe the process of photosynthesis in terms of redox reactions of the overall process

A

Water is split and electrons are removed (oxidized) and transferred along with hydrogen ions from the water to carbon dioxide, reducing it to sugar

reactant water is oxidized into O2
carbon dioxide is reduced into sugar (glucose)

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6
Q

Describe the process of photosynthesis in terms of light dependent and light independent reactions

A

light dependent:

  • electron flow pushes electrons from water (low state of energy)
  • transferred to NADPH (high potential energy)
  • also generates ATP
  • equipment of the thylakoid membrane converts light energy to chemical energy stored in ATP and NADPH (and O2 is a byproduct)

Light independent:
- uses the products of the light reactions to synthesize sugar from CO2

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7
Q

Define chloroplast and describe the structure

A

Chloroplasts are a eukaryotic double-membrane bound organelle found only in plant cells and other photosynthesizing eukaryotes.

Double membrane surrounds a dense fluid, the STROMA, in which a third membrane system made up of sacs, THYLAKOIDS, is suspended.
In some places, the thylakoids are stacked in columns called GRANA

Chlorophyll is located in the thylakoid membranes

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8
Q

Define and outline light reactions

A

the steps of photosynthesis that convert solar energy to chemical energy

water is split, providing a source of electrons and protons and produce O2 as a byproduct

light absorbed by chlorophyll drives a transfer of electrons and hydrogen ions from water to an acceptor (NADP+) where they are temporarily stored

NADP+ is reduced to NADPH by adding 2 electrons along with an H+. This is powered by sunlight

also generates ATP using chemiosmosis to power the addition of a phosphate group to ADP in a process called photophosphorylation

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9
Q

Define and outline the Calvin Cycle

A

incorporates atmospheric CO2 into organic molecules already present in the chloroplast (carbon fixation)

fixed carbon is reduced into carbohydrate by adding electrons. This occurs by NADPH as a reducing agent

In order to reduce fixed carbon, the CC requires ATP generated from the light reactions

The CC makes sugar but only with the help of NADPH and ATP produced by the light reactions

SUMMARY: the chloroplast uses light energy to make sugar by coordinating the two stages of photosynthesis

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10
Q

Describe the process of chemiosmosis that couples electron transport to photophosphorylation

A

Chemiosmosis powers the production of ATP in the light reactions by using solar energy to add a phosphate group to ADP

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11
Q

Where do the main stages of photosynthesis occur?

A

the light reactions occur in the thylakoids of chloroplast

the Calvin Cycle occurs in the stroma of chloroplasts

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12
Q

Describe visible light as a component of the electromagnetic spectrum

A

Light is a form of energy known as electromagnetic energy aka electromagnetic radiation.

Visible light is a small segment of electromagnetic radiation that has wavelengths seen as various colours by the human eye.

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13
Q

What is the role of visible light in photosynthesis in relation to properties of light and the visible light spectrum?

A

Visible light is the segment of electromagnetic radiation that has wavelengths conducive to photosynthesis

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14
Q

What is the role of visible light in photosynthesis in relation to the colour of leaves?

A

Substances can reflect visible light rather than absorb it

The chlorophyll, green pigments in chloroplasts, absorb violet-blue and red light waves and reflect green light waves which is why leaves (and other chlorophyll containing parts of plants) appear green

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15
Q

What is the role of visible light in photosynthesis in relation to the absorption of light by plant pigments?

A

Pigments are substances that ABSORB visible light

Different pigments absorb different wavelengths of visible light and reflects other wavelengths to give off a colour we see

Chlorophyll (the green pigment in chloroplasts) absorbs violet-blue and red light wavelengths which power photosynthesis

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16
Q

Define chlorophyll

A

Chlorophyll is the green pigment found in the chloroplasts of plant cells that is responsible for absorbing the wavelengths of visible light (violet-blue and red) required for powering photosynthesis while reflecting the green light

two kinds of chlorophyll:

Chlorophyll a: the key light capturing pigment that participates directly in the light reactions

Chlorophyll b: the accessory pigment works in conjunction with chlorophyll a

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17
Q

What is chlorophyll role in photosynthesis?

A

Chlorophyll absorbs the wavelengths of visible light that are required to power photosynthesis

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18
Q

Define accessory pigments and explain their role in photosynthesis

A

Pigments that are not the key light capturing pigments (ie, not chlorophyll a)

Chlorophyll b is an accessory pigment that works in conjunction with chlorophyll a

Carotenoids are a separate group of accessory pigments that are located in plant leaves

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19
Q

Define accessory pigments and explain their role in photosynthesis

A

Pigments that are not the key light capturing pigments (ie, not chlorophyll a)

Chlorophyll b is an accessory pigment that works in conjunction with chlorophyll a

Carotenoids are a separate group of accessory pigments that are located in plant leaves. They appear yellow and orange because they absorb violet, blue and green light.
- photoprotection: they absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with oxygen

These pigments broaden the spectrum of wavelengths that be absorbed and used for photosynthesis

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20
Q

Define action spectrum and explain what is meant by the action spectrum of photosynthesis

A

An action spectrum shows the relative effectiveness of different wavelengths of radiation in driving photosynthesis by plotting wavelength of different lights against a photosynthetic rate (such as CO2 consumption or O2 release)

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21
Q

Define photosystems

A

A photosystem is composed of a reaction-centre complex surrounded by several light harvesting complexes

Reaction-centre complex is an organized group of proteins that hold a special pair of chlorophyll a molecules

light harvesting complex consist of various pigment molecules (chlorophyll a or b, or carotenoids) bound to proteins

the number and variety of pigment molecules allow a photosystem to harvest light over a larger surface area and a larger portion of the spectrum than a single pigment molecule could alone

These are present in the thylakoid and there are two kinds

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22
Q

Describe the location, structure, and function of photosystem I (P700) and photosystem II (P680)

A

Located in the thylakoid membrane, both have a characteristic reaction-centre complex (a particular primary electron acceptor next to a specific pair of chlorophyll a molecules associated with specific proteins

Photosystem I (P700): 
- the chlorophyll a at the reaction-centre of this photosystem is called P700 because it best absorbs light at a wavelength of 700 nm (far red light)
Photosystem II (P680): 
- the reaction-centre chlorophyll a is known as P680 because it best absorbs light at a wavelength of 680nm (red light)

these two chlorophyll a molecules are almost the same, but their association with different proteins in the thylakoid membrane affects the electron distribution of the two pigments and explains their slight difference in absorption

23
Q

Define and describe linear electron flow (include the source of electrons and the purpose of this pathway)

A

The linear flow of electrons is the movement of electrons through the photosystems and other molecular components built into the thylakoid membrane. This occurs during the light reactions of photosynthesis

24
Q

Define and describe cyclic electron flow (include the source of electrons and the purpose of this pathway)

A

The cyclic electron flow uses photosystem I but not photosystem II

This short circuit does not produce NADPH or release oxygen

25
Q

What is the contribution of the light-dependent reactions to photosynthesis?

A

The light reactions use solar energy to generate ATP and NADPH which provide chemical energy and reducing power to the Calvin Cycle

26
Q

Define and describe cyclic electron flow (include the source of electrons and the purpose of this pathway)

A

The cyclic electron flow uses photosystem I but not photosystem II

This short circuit produces ATP but does not produce NADPH or release oxygen

27
Q

How does chemiosomosis occur in chloroplasts?

A
  • An ETC transports electrons while the redox energy is used to pump protons (H+) gradient across the membrane to form ATP

the high energy electrons that move down the ETC come from water molecules

do not need molecules from food to make ATP because their photosystems capture light energy to drive the electrons from water to top of transport chain

28
Q

How does chemiosmosis occur in mitochondria?

A

The high energy electrons that move down the ETC come from organic molecules

use chemiosmosis to transfer chemical energy from food molecules to ATP

29
Q

What similarities occur in chemiosmosis in chloroplasts and mitochondria?

A
  • an ETC assembled in a membrane pumps protons across the membrane as electrons are passed through a series of carriers that are progressively more EN
  • ETC converts redox energy to a proton-motive force (potential energy stored in H+ gradient across the membrane)
  • ATP Synthase complex in the same membrane couples the diffusion of H+ down their gradient to the phosphorylation of ADP to form ATP
  • both use similar cytochromes (iron-containing electron carriers)
  • the ATP synthase complex are both similar
30
Q

What differs between the chemiosmosis that occurs in the chloroplasts vs the mitochondria?

A

Photophosphorylation occurs in chloroplasts whereas

Oxidative phosphorylation occurs in mitochondria

basically, mitochondria transfer chemical energy derived from food molecules to ATP

whereas, chloroplasts transfer light energy into chemical energy in ATP

31
Q

Define the calvin cycle in terms of three stages, reactants, events/chemical reactions and products

A

The Calvin Cycle is an anabolic process that consumes energy to build carbohydrates from smaller molecules

carbon enters CC as atmospheric CO2 and leaves in the form of sugar
cycle spends ATP as an energy source and consumes NADPH as reducing power for adding high energy electrons to make the sugar

Phase 1:

Phase 2:

Phase 3:

32
Q

Define rubisco and explain its role

A

Rubisco (or RuBP carboxylase-oxygenase) is the enzyme that catalyzes the attachment of CO2 molecules to the RuBP sugar (the first step of carbon fixation) in the Calvin Cycle.

Rubisco is the most abundant protein in chloroplasts and possibly the most abundant protein on Earth

33
Q

Define the calvin cycle in terms of three stages, reactants, events/chemical reactions and products

A

The Calvin Cycle is an anabolic process that consumes energy to build carbohydrates from smaller molecules

carbon enters CC as atmospheric CO2 and leaves in the form of sugar
cycle spends ATP as an energy source and consumes NADPH as reducing power for adding high energy electrons to make the sugar

Phase 1: CARBON FIXATION

  • cycle incorporates each (3 per molecule of G3P) CO2 molecule one at a time by attaching it to ribulose biphosphate (RuBP; 5-C sugar)
  • Rubisco is the enzyme that catalyzes that step
  • produces an unstable intermediate and splits into two molecules of 3-phosphoglycerate (per one molecule of CO2)

Phase 2: REDUCTION

  • a phosphate group from ATP is added to each molecule of 3-phosphoglycerate = 1,3-biphosphoglycerate
  • NADPH donates a pair of electrons to reduce 1,3-biphosphoglycerate and a phosphate group is lost = glyceraldehyde 3-phosphate (G3P)

Phase 3: REGENERATION OF RuBP (CO2 acceptor)

  • reorganize the carbon skeleton of G3P into three molecules of RuBP by spending 3 molecules of ATP
  • RuBP will now receive CO2 again
34
Q

What is the contribution of the light-independent reactions to photosynthesis?

A

The light-independent reactions occur during the Calvin Cycle of photosynthesis which is when carbohydrates are synthesized

the cycle begins with 15 carbons, as carbohydrates in the form of 5-C sugar RuBP
the cycle ends with 18 carbons worth of carbohydrates in the 6 molecules of G3P and one exits the cycle to be used by the plant cell but the other 5 are recycled to regenerate 3 molecules of RuBP

35
Q

What does the Calvin Cycle consume in order to net produce ONE G3P molecule?

A

To produce one (net) G3P molecule, the CC consumes:

  • 9 molecules of ATP
  • ## 6 molecules of NADPH
36
Q

What are the four fates of the glucose produced by photosynthesis?

A
  1. immediately used to make ATP
  2. stored as starch for making ATP later
  3. Used to make cellulose
    4.
37
Q

What are 4 components of a photosystem?

A
  1. reaction-centre complex
  2. chlorophyll molecules
  3. light-harvesting complexes
  4. primary electron acceptor
38
Q

During which process is molecular oxygen produced in photosynthesis?

A

the light reactions by the linear electron flow

39
Q

During which process is molecular oxygen produced in photosynthesis?

A

the light reactions by the linear electron flow

40
Q

Where do the electrons entering photosystem II come from?

A

Water

41
Q

Where do the electrons entering photosystem II come from?

A

Water

42
Q

Metabolic pathways are typically redox processes. In photosynthesis, what molecule is oxidized and what molecule is reduced?

A

Water is oxidized

CO2 is reduced

43
Q

Metabolic pathways are typically redox processes. In photosynthesis, what molecule is oxidized and what molecule is reduced?

A

Water is oxidized (to become O2)

CO2 is reduced (to become glucose)

44
Q

Metabolic pathways are typically redox processes. In photosynthesis, what molecule is oxidized and what molecule is reduced?

A

Water is oxidized (to become O2)

CO2 is reduced (to become glucose)

45
Q

Where does the energy used to produce ATP in the light reactions of photosynthesis come from?

A

the movement of H+ through a membrane

46
Q

Where does the energy used to produce ATP in the light reactions of photosynthesis come from?

A

the movement of H+ through a membrane

47
Q

Which structure does the electrochemical gradient that drives chemiosmosis form across?

A

thylakoid membrane

48
Q

Which structure does the electrochemical gradient that drives chemiosmosis form across?

A

thylakoid membrane

49
Q

The light reactions of photosynthesis generate high energy electrons which end up in ____. The light reactions also produce ___ and ____.

A

NADPH; ATP; Oxygen

50
Q

The light reactions of photosynthesis generate high energy electrons which end up in ____. The light reactions also produce ___ and ____.

A

NADPH; ATP; Oxygen

51
Q

What happens to a chlorophyll pigment when it absorbs light?

A

its electrons become excited

52
Q

What happens to a chlorophyll pigment when it absorbs light?

A

its electrons become excited

53
Q

Glyceraldehyde 3-phosphate (G3P) is used in which processes?

A

Production of:

  • starch
  • sucrose
  • cellulose
  • glucose

BIO 1210 (16 decks)

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