Photosynthesis: Key Concepts and Terminology

These flashcards cover key concepts, terminology, and processes involved in photosynthesis, focusing on light-dependent and light-independent reactions.

What are the two types of reactions in photosynthesis?

Light-dependent and light-independent (dark) reactions.

What is the primary function of light-dependent reactions?

To convert photons into high-energy molecules ATP and NADPH.

Where do the light-dependent reactions occur?

In the thylakoid membranes of chloroplasts.

What is the main product of light-independent reactions (the Calvin Cycle)?

2G3P, which can then be converted into glucose outside of the cycle

What role does chlorophyll play in photosynthesis?

Chlorophyll (a pigment) absorbs photons and excites electrons within the photosystem for use in light reactions.

What is photophosphorylation?

The process of generating ATP from ADP using light energy.

How does the Calvin Cycle produce G3P?

By adding carbon dioxide to RuBP by using the enzyme rubisco, which produces an unstable 6 carbon compound that splits into two 3 carbon 3-phosphoglycerate (PGA) molecules which are individually converted into G3P through 3 reactions in which 12 ATP and 12 NADPH is used per glucose.

What is the equation for photosynthesis?

6CO2 + 6H2O + light energy → C6H12O6 + 6O2.

What do NADPH and ATP produced in light-dependent reactions provide energy?

They provide energy and reducing power for the Calvin Cycle (light independent reactions) to make G3P

What is the role of the thylakoid membrane?

It houses the two photosystems and is the site for light energy absorption as well as all light dependent reactions

What is the term for a cluster of pigments and proteins found in the thylakoid membrane?

A photosystem.

What are C3 plants?

Plants that

• live in moderate temperatures (20-25 degrees C) with lots of water

• use the Calvin cycle for photosynthesis, but due to the abundance of oxygen in the air (thriving conditions) also very often uses photorespiration

• They cannot avoid photorespiration (didn’t need to evolve to do so), wasting a lot of energy—but they still survive because their living conditions are perfect with an abundance of energy to be used.

Define photorespiration

• The use of oxygen instead of CO2 to produce glucose.

• Inefficient and wasteful of energy due to one of the products (2 carbon phosphoglycolate) from oxygen binding with RuBP being unusable within the cycle, and needing to undergo further reactions that require energy to be partly salvaged

  • It also doesn’t produce enough (2) PGA for use in one reaction, which means more energy is required to make another PGA before the Calvin Cycle can start

What are the two types of chlorophyll found in plants?

Chlorophyll a and chlorophyll b.

What role does the electron transport chain play in photosynthesis?

It transfers excited electrons to generate a proton gradient for ATP synthesis.

What are stomata?

Small openings in leaves that allow carbon dioxide to enter and oxygen to exit.

Why do plants expel Oxygen ?

because it is a waste product, as it is released as a by-product when water is split to replenish the electron stock of photosystem 2.

What is chemiosmosis?

The process of ATP synthesis driven by the movement of hydrogen ions across a membrane.

What is the action spectrum?

A graph showing the effectiveness of different wavelengths of light for photosynthesis.

What is the significance of accessory pigments like beta-carotene?

They expand the range of light wavelengths that can be used for photosynthesis, increasing ATP output.

How does the Krantz Anatomy of C4 plants help photosynthesize instead of photorespirate?

It separates carbon dioxide absorption and Calvin cycle reactions in different cells: Mesophyll and Bundle Sheath Cell. respectively.

The malate that is transferred into the bundle sheath cell loses is carbon dioxide through decarboxylation while producing pyruvate, which allows for a higher concentration of CO2 in the bundle sheath cell, allowing the Calvin cycle that is isolated there to use CO2 instead of O2 to react with RuBP.

What is the advantage of cyclic photophosphorylation?

It allows the production of additional ATP without reducing NADP+ when the cell is running low on NADP+ by recycling electrons from the last electron carrier back into the b6-f complex, allowing it to enter photosystem 1 again

What happens to the electron in photosystem I after it is excited in non-cyclic photophosphorylation?

It is passed to a high-energy electron acceptor to an electron carrier, which takes it to NADP reductase, which catalyzes the reduction reaction

NADP → NADPH

The NADPH then moves to the ATP synthase to make ATP

What is the role of ribulose bisphosphate (RuBP) in the Calvin cycle?

To combine with CO2 to form an unstable 6 carbon molecule that is unstable, breaking down into 2 PGA molecules per RuBP. Each PGA is then converted to G3P, a key component in producing glucose or other macromolecules.

Why do plants appear green?

because the primary pigment in plants, chlorophyll, reflects green light—which it cannot use—and absorbs red and blue light.

Name one key adaptation of C4 plants to hot, dry climates.

Their Krantz Anatomy

What process occurs when stomata are closed to conserve water?

Photorespiration

• elevated oxygen concertation from photosynthesis and reduced carbon dioxide concentration that can no longer be obtained from the outside environment causes O2 to bind with RuBP instead of CO2

What are the three stages of the Calvin cycle?

1) Carbon fixation

2) Reduction

3) RuBP Regeneration Phase

In that order, then repeated.

How many ATP and NADPH are required to produce one glucose in the Calvin cycle?

18 ATP and 12 NADPH.

What is generated during noncyclic photophosphorylation?

ATP and NADPH

Define thylakoids.

• Individual disks that stack to form granum

• In stroma (cytoplast of the chloroplast)

• Light-dependent reactions occur on their membrane

How do chloroplasts help in the process of photosynthesis?

• Chloroplasts hold the entirety of photosynthesis

• The chlorophyll within absorbs photons and produces ATP

  • Inside the chlorophyll are thylakoids, their membranes hold photosystems that capture photons for light dependent reactions that produce ATP + NADPH for use in dark reactions that are required to make glucose.

  • The stroma (inside area of a chloroplast) hold the Calvin cycle, which is the dark reaction that uses the energy from thylakoids to make 2G3P after 6 cycles.

  • This G3P is used within the stroma to produce glucose or other macromolecules and complete photosynthesis

What is the function of ATP synthase in photosynthesis?

It synthesizes ATP by allowing hydrogen ions to flow back into the stroma from the thylakoid space.

Which type of plants are more adapted to photosynthesis in dry and hot conditions?

C4 (30+ degrees C hot) and CAM (extreme, desert hot & dry) plants.

What is G3P used for in plants?

To produce glucose

What determines the color of light that pigment absorbs"

The proteins they are associated with.

Which compound accumulates during photorespiration, reducing photosynthetic efficiency?

Phosphoglycolate

What happens when a photon is absorbed by chlorophyll?

Electrons within the photosystems become excited and are transferred to an electron transport chain.

How do noncyclic and cyclic photophosphorylation differ?

Noncyclic produces NADPH through the input of NADP+ and cannot repeat again without more NADP+, while cyclic can continually generate ATP without any outside input ( NADP+ ) and producing NADPH

What is the significance of ecological interactions in photosynthesis?

Photosynthetic organisms use CO2 produced by non-photosynthetic organisms and produce O2 as a byproduct which they need.

What is photolysis?

The process of splitting water into O2 and H+ through the use of light energy

What role does light intensity play in photosynthesis?

It influences the rate of photosynthesis, up to a saturation point.

How do external environmental factors affect photosynthesis efficiency?

• High temperatures causes the plant to close the stomata more often to avoid losing water as vapor. This closed stomata means there isn’t enough CO2 entering the plant for photosynthesis to continue, forcing photorespiration to take place instead, which is highly inefficient. Plants that have adapted to high temperature environments like C4 and CAM have mechanisms to avoid photorespiration

• A lack of water, caused by a dry environment means that the electrons of photosystem 2 are not being replenished as often as they should, reducing photosynthesis efficiency

• Lack of light means no photons to excite electrons, minimizing photosynthesis

What is the function of photolysis in photosynthesis?

To replenish the electron stock in photosystem 2 by splitting water molecules into oxygen and H+

What is a photosystem?

A protein based complex made from clusters of pigments that work together to absorb light energy from a variety of wavelengths

What is a photosynthetic pigment?

a compound that absorbs light energy and passes it onto other molecules (can only absorb specific wavelengths within the range of the human eye)

What are the two types of chlorophyll and their color?

• Chlorophyll a

• Chlorophyll b

• Green

What is the color of carotenoids, an accessory pigment type?

orange

What does “photo” and “synthesis” refer to in photosynthesis?

• “Photo” refers to the light dependent reactions using photons, the light energy, to make ATP and NADPH

• “Synthesis” refers to the dark reactions that use these ATP and NADPH molecules to make G3P in the Calvin Cycle to produce glucose

What are the different parts of a chloroplast & their function?

• Outer membrane: separates the chloroplast from the rest of the cell, allows compartmentalization. evidence for endosymbiotic theory

• Inner membrane: regulates the movement of materials

• Intermembrane space: the space between the outer and inner membranes of the chloroplast

• Stroma: the fluid within the inner membrane that holds the thylakoids in grana and lamella, the Calvin Cycle takes place here

• Lamella: the fibers between grana that hold them apart, allows for communication between grana

• Granum (Plural: grana): a stack of thylakoids

• Thylakoid: membrane-bound individual disks within granum

  • Thylakoid membrane: the light-dependent reactions of photosynthesis occur here, contains the photosystems + NADP reductase + ATP synthase

How do have CAM plants adapted to their environment, and how do they avoid photorespiration?

• Closed stomata during the day (avoids dehydration)

  • PEP is made into malate

• Open stomata at night (cooler temperatures prevents water loss)

  • Malate is turned into pyruvate, giving CO2 to the Calvin Cycle

    • Calvin Cycle only takes place at night when the stomata is open, and CO2 levels are high enough to avoid photorespiration