Module 5- Photosynthesis and the Chloroplast

What is the origin of chloroplasts?

Chloroplasts are believed to have originated from O2-producing cyanobacteria that was engulfed by a non-photosynthetic eukaryotic cells. endosymbiosis.

What is the structure of a chloroplast?

Chloroplasts have a double membrane structure, containing an inner and outer membrane, and are filled with a fluid called stroma. Inside the stroma are thylakoids, which are organized into stacks called grana.

What are the roles of light-dependent reactions in photosynthesis?

Light-dependent reactions convert solar energy into chemical energy in the form of ATP and NADPH, releasing oxygen as a byproduct.

What are the roles of light-independent reactions in photosynthesis?

Light-independent reactions, also known as the Calvin cycle, use ATP and NADPH produced in light-dependent reactions to convert carbon dioxide into glucose.

What are chlorophylls?

Chlorophylls are green pigments found in chloroplasts that absorb light energy, primarily in the blue and red wavelengths, to drive photosynthesis.

What are carotenoids?

Carotenoids are pigments that provide yellow, orange, and red colors in plants and assist in photosynthesis by capturing light energy and protecting chlorophyll from photodamage.

What are chromoplasts?

Chromoplasts are a type of plastid that contain pigments other than chlorophyll, contributing to the coloration of fruits and flowers.

What is the difference between photosystem II and photosystem I?

Photosystem II absorbs light at 680 nm (P680) and is involved in the initial steps of photosynthesis, while Photosystem I absorbs light at 700 nm (P700) and is involved in the final steps of electron transport.

What is the Calvin cycle in C3 plants?

In C3 plants, the Calvin cycle involves the fixation of carbon dioxide into a 3-carbon compound (3-phosphoglycerate) using the enzyme RuBisCO.

What is the Calvin cycle in C4 plants?

In C4 plants, carbon dioxide is initially fixed into a 4-carbon compound in mesophyll cells before being transported to bundle-sheath cells for the Calvin cycle.

What is the Calvin cycle in CAM plants?

In CAM plants, carbon dioxide is fixed at night into organic acids, which are then used during the day for the Calvin cycle, allowing them to conserve water.

What is the absorption spectrum?

The absorption spectrum is a graph showing the wavelengths of light absorbed by chlorophyll and other pigments, indicating which wavelengths are most effective for photosynthesis.

What is the Z scheme in photosynthesis?

The Z scheme describes the flow of electrons during the light-dependent reactions of photosynthesis, illustrating how energy from light is used to drive the transfer of electrons through photosystems II and I.

Heterotrophs

Organisms that obtain their food by consuming other living things, such as plants and animals.

Autotrophs

Organisms that produce their own food from inorganic substances, typically through photosynthesis or chemosynthesis.

Chemoautotrophs

Organisms that obtain energy by oxidizing inorganic substances and use this energy to synthesize organic compounds from carbon dioxide.

Photoautotrophs

Organisms that use light energy to convert carbon dioxide and water into glucose and oxygen through photosynthesis.

Protons

Subatomic particles with a positive charge found in the nucleus of an atom; they determine the atomic number and identity of an element.

Ground state

The lowest energy state of an atom or molecule, where electrons occupy the closest possible orbitals to the nucleus.

Excited state

A state of an atom or molecule in which one or more electrons have absorbed energy and moved to a higher energy level.

CO2 fixation and carbohydrate synthesis

The process by which carbon dioxide is converted into organic compounds, such as glucose, during photosynthesis, primarily through the Calvin cycle.

Global warming and carbon sequestration

Global warming refers to the increase in Earth's average surface temperature due to rising levels of greenhouse gases. Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide to mitigate climate change.

Absorption spectrum

A spectrum showing the wavelengths of light absorbed by a substance; it typically appears as a series of dark lines or bands on a continuous spectrum. Wavelengths are measured in nanometers (nm).

Which statement regarding P680 is incorrect?

It is located in the reaction center of photosystem I.

What contributes to the proton gradient created through photosynthetic light reactions? (3 things)

Protons generated through splitting water molecule, reduction of plastoquinone (PQ), and reduction of NADP+

In photosynthesis, oxygen is derived from which reactant?

Water

Which plant organelle has the primary function of being colorful?

Chromoplast

In photosystem II, what happens to P680?

P680 is oxidized to P680+ and pheophytin is reduced to Pheo-.

What prevents Pheo- from reducing P680+ back to P680?

The opposite charges are moved to different sides of the thylakoid membrane.

Where is the higher concentration of protons found in chloroplasts?

Thylakoid lumen

Where is the lower concentration of protons found in chloroplasts?

Stroma

Which of the two photosystems generates the strongest reducing agent?

PSI

What is the strongest oxidizing agent in the photosynthesis process?

O2

What part of the chlorophyll molecule absorbs light?

Porphyrin ring

In what cells are chloroplasts located in plant leaves?

Mesophyll cells

what is the functional organization of a leaf?

highly organized, flat, and thin plant organ designed to maximize photosynthesis, gas exchange, and water transport. A photosynthetic mesophyll layer, vascular veins and stomata O2 regulation

structure of chlorophyll a

porphyrin ring (Mg surrounded by bonds) attached to a hydrocarbon tail

The absorption spectrum in higher plants

chlorophylls and , along with carotenoids, primarily absorb light in the blue (400-500 nm) and red (600-700 nm) regions to drive photosynthesis. Green light is poorly absorbed, resulting in its reflection, which gives plants their green appearance.

Describe the process from light hitting the LHCI to producing NADPH at PSI

Light hits LHCII at inner antenna, P680 gets excited, transfers e- to Pheo making it negative, separation through membrane due to charges. Pheo- passes e- to PQ, reducing to PQH2. electrons from PQH2 are bound to cytochrome b6f, from here they go to PC (plastocyanin) and from here they enter PSI. Electrons here excite P700, they move through carrier until they reach ferredoxin, here reduce NADP to NADPH

Difference between PSII and PSI (which one is oxidizing/reducing agent), what doe each produce

PSII:

Strong oxidizing agent

Splits water

Produces O₂

Contributes to proton gradient

PSI:

Strong reducing agent

Produces NADPH

Which is absent from the chloroplast stroma?

Galactose-contaning glycolipids

3 multiple choice options

Difference between C3, C4 and CAM plants? which one(s) uses pep carboxylase?

C3 plants regular plants: use rubisco to make carbs, close stromata to prevent water loss, main goal to increase CO2.

C4 plants (corn): use PEP for CO2 fixation to C4 in mesophyll, but calvin cycle in bundle sheath cells (diff location)

CAM (cactus): use PEP for night time CO2 fixation to C4 (diff timing), but calvin during the day.

ATP synthase in chloroplasts consists of:

CF1 and CF0

3 multiple choice options

how does Thioredoxin activates Calvin cycle enzymes in the light?

Light → PSI → ferredoxin → thioredoxin reduced → Calvin enzymes activated.

Compare structures, absorption and functions of chlorophylls and carotenoids

Chlorophyll a and b: porphyrin ring + hydrophobic phytol tail. Chlorophyll a= primary reaction center pigment

Chlorophyll b = accessory pigment broadening absorption

Carotenoids = absorbs blue green light and protects from photodamage

What are the results of photorespiration

Rubisco binds O₂ instead of CO₂

Produces 2-phosphoglycolate

Carbon loss