Biology Chapter 10: Photosynthesis Flashcards

Questions and Answers

What is the definition of autotroph?

Decomposer that breaks down organic material

Self-feeder that synthesizes its own glucose (correct)

Organism that cannot produce its own food

Consumer that lives on compounds produced by other organisms

What is the definition of a heterotroph?

Consumer that lives on compounds produced by other organisms (correct)

Organism that only decomposes matter

Self-feeder

Producer that synthesizes its own glucose

What is a granum?

A stack of thylakoids

What is the definition of stroma?

A thick fluid enclosed by the membrane of a chloroplast Signup and view all the answers

Using 18O as a basis, explain how oxygen released in photosynthesis comes from water.

18O is a heavy isotope that was traced through the process, and it only showed up in the released O2 if it began in water. Signup and view all the answers

What occurs in the light reactions stage of photosynthesis?

Light is converted to chemical energy; water is split, releasing electrons, hydrogen ions, and oxygen. Signup and view all the answers

Explain the Calvin cycle.

ATP and NADPH power carbon fixation, turning 3CO2 into 1 net G3P molecule. Signup and view all the answers

What are the inputs and outputs into the thylakoid?

Light and water in, oxygen out. Signup and view all the answers

What are the inputs and outputs into the stroma?

CO2 in, sugar out. Signup and view all the answers

What are absorption spectra?

The range of light wavelengths that a pigment absorbs. Signup and view all the answers

What is the action spectrum?

The rate of photosynthesis versus wavelength, showing the effectiveness of certain wavelengths. Signup and view all the answers

How did Engelmann form an action spectrum before the invention of a spectrophotometer?

He exposed different parts of a filamentous alga to different wavelengths, observing where aerobic bacteria concentrated. Signup and view all the answers

A photosystem is composed of a protein complex called a surrounded by several _.

reaction-center complex, light-harvesting complexes Signup and view all the answers

What is the reaction center complex?

A protein complex containing 2 chlorophyll a molecules that release one excited electron at a time. Signup and view all the answers

What are the advantages of the light harvesting complex?

It consists of various pigment molecules that allow the photosystem to harvest light over a larger surface and spectrum. Signup and view all the answers

What is the primary electron acceptor?

A molecule capable of accepting electrons from the special pair and becoming reduced. Signup and view all the answers

What is photosystem I also known as?

P700, the wavelength at which its reaction center best absorbs light. Signup and view all the answers

What is photosystem II also known as?

P680. Signup and view all the answers

What happens as electrons fall between PSII and PSI?

The cytochrome complex changes shape and uses energy to pump hydrogen ions. Signup and view all the answers

What is the order of electron flow from PSII primary electron acceptor to PSI?

Primary electron acceptor, electron carrier Pq, cytochrome complex, protein Pc, special pair of P700, primary a. Signup and view all the answers

What is the order of electron flow from PSI primary electron acceptor to NADPH?

Primary a., protein Fd, NADP+ reductase, NADPH. Signup and view all the answers

What is chemiosmosis?

The movement of ions across a selectively permeable membrane, down their electrochemical gradient. Signup and view all the answers

What is the purpose of the excited electrons leaving PSII?

They are used by NADP+ reductase to form NADPH. Signup and view all the answers

Why is cyclic electron flow considered evolutionarily significant?

It is thought to be one of the first forms of photosynthesis to evolve. Signup and view all the answers

How does cyclic electron flow benefit organisms?

It protects plants from light-induced damage by allowing them to survive in intense light conditions. Signup and view all the answers

What are the similarities between chemiosmosis in photosynthesis and cellular respiration?

Both use electron transport chains to create proton gradients that synthesize ATP. Signup and view all the answers

What are two differences of chemiosmosis between photosynthesis and cellular respiration?

ATP synthase is located in the thylakoid membrane in photosynthesis; H+ comes from water in photosynthesis. Signup and view all the answers

What is the first step of linear electron flow in light reactions?

A photon hits a pigment molecule in PSII, boosting its electron to a higher energy level. Signup and view all the answers

What is the second step of linear electron flow in the light reactions?

The charge excites an electron in the special pair, transferred to the primary electron acceptor. Signup and view all the answers

What happens in the third step of linear electron flow during light reactions?

PSII has higher electron affinity, causes water to split, replacing lost electrons. Signup and view all the answers

What occurs in the fourth step of linear electron flow during light reactions?

Electrons travel by the ETC to PSI, losing energy and pumping H+ ions across the membrane. Signup and view all the answers

What is the fifth step of linear electron flow in light reactions?

Photons hit PSI, leading to electron transfer to NADP+ reductase for NADPH synthesis. Signup and view all the answers

How many turns of the Calvin cycle fix CO2 molecules for one net G3P?

3 Signup and view all the answers

Explain the important events in the carbon fixation stage of the Calvin cycle.

CO2 is attached to RuBP, catalyzed by RuBisCo, forming two 3-phosphoglycerates. Signup and view all the answers

What is Rubisco?

The enzyme responsible for carbon fixation in the Calvin cycle. Signup and view all the answers

What happens during the reduction stage of the Calvin cycle?

NADPH donates electrons to form the 3-carbon sugar G3P. Signup and view all the answers

What is formed after fixing 3 CO2 using rubisco?

6 G3Ps with a total of 18 carbons, net gain of 3 or one net G3P molecule. Signup and view all the answers

Why does it take 3 turns of the Calvin cycle to produce only one net G3P?

5 of the 6 G3Ps produced are rearranged to become 3 RuBPs needed in the next steps. Signup and view all the answers

How is RuBP regenerated in the Calvin cycle?

5 G3Ps are converted into 3 RuBP using the energy of ATP. Signup and view all the answers

What is the first product of C3 plants?

3-phosphoglycerate. Signup and view all the answers

What happens to a plant during photorespiration?

The calvin cycle is starved for CO2, leading Rubisco to bind O2 instead, producing a 2-carbon compound. Signup and view all the answers

What is the problem with photorespiration in agriculture?

It consumes energy rather than producing it, leading to decreased crop yields. Signup and view all the answers

What is the first product of C4 plants?

A 4-carbon compound. Signup and view all the answers

What is the role of PEP carboxylase in C4 plants?

It binds CO2 to oxaloacetate, avoiding photorespiration. Signup and view all the answers

Describe the structure of C4 plants.

They have mesophyll cells that convert CO2 into malate which then enters bundle-sheath cells. Signup and view all the answers

Why did C4 plants evolve?

To efficiently capture CO2 and reduce the effects of photorespiration in hot environments. Signup and view all the answers

What do CAM plants do?

They open stomata at night to conserve water during the day. Signup and view all the answers

What does CAM stand for?

Crassulacean acid metabolism. Signup and view all the answers

Explain why only the green cells of a plant are autotrophs.

Only green cells contain chlorophyll for photosynthesis; the rest depend on them. Signup and view all the answers

What are the three parts of Calvin cycle reactions?

They take place in the stroma, use ATP and NADPH, and convert CO2 to G3P. Signup and view all the answers

What are the three parts of light reactions?

They occur in the thylakoid membranes, converting light energy to ATP and NADPH and releasing oxygen. Signup and view all the answers

What is the most abundant organic molecule in the plant?

Cellulose. Signup and view all the answers

After arriving at non-photosynthetic cells, what does sucrose do?

Provides material for respiration and building blocks for proteins and lipids. Signup and view all the answers

What is the similarity between C4 and CAM plants?

Both convert CO2 to organic acid before it enters the Calvin cycle. Signup and view all the answers

What are the differences between C4 and CAM plants?

In C4 plants, conversion occurs in mesophyll cells, while in CAM plants, it occurs at night. Signup and view all the answers

Study Notes

Photosynthesis Overview

Autotrophs are self-feeders that synthesize their own glucose, whereas heterotrophs are consumers reliant on other organisms for organic compounds.
Granum consists of a stack of thylakoids, while stroma is a thick fluid within chloroplasts where sugars are synthesized during the Calvin cycle.

Oxygen Production

18O isotope tracing demonstrated that oxygen released during photosynthesis originates from water.

Light Reactions

Light energy is converted into chemical energy in the light reactions.
Water is split, releasing electrons (e-), hydrogen ions (H+), and O2; electrons reduce NADP+ to form NADPH, while H+ ions help synthesize ATP.

Calvin Cycle

ATP and NADPH fuel the Calvin cycle, converting three CO2 molecules into one net G3P molecule, a precursor to glucose.
Inputs of the thylakoid are light and water, while the stroma inputs CO2 and outputs sugar.

Light Absorption

Absorption spectra signify the range of light wavelengths a pigment captures; chlorophyll b absorbs from 410-510 nm in purple and blue ranges.
Action spectra measure the effectiveness of various wavelengths for photosynthesis, noting that green light is least effective since it is reflected.

Photosystems

Photosystems consist of a reaction-center complex surrounded by light-harvesting complexes, enabling energy absorption over broad wavelengths.
Photosystem I (P700) and II (P680) are designated by the preferred wavelengths they absorb.

Electron Transport Chain

Electrons travel from the primary electron acceptor of PSII through a sequence of carriers to PSI, where energy from their movement is used to pump H+ ions and create a gradient.
Key players in the electron flow include plastoquinone (Pq), cytochrome complex, and ferredoxin (Fd).

Chemiosmosis

Chemiosmosis refers to ion movement across membranes, generating ATP through a proton gradient facilitated by ATP synthase.
Both photosynthesis and cellular respiration utilize similar chemiosmotic processes but differ in their sources of protons and ATP synthase locations.

Carbon Fixation

RuBisCO catalyzes the initial step of carbon fixation in the Calvin cycle, converting CO2 and RuBP into 3-phosphoglycerate (3-PGA).
The cycle requires three turns to net one G3P, with five G3P molecules reconfigured to regenerate RuBP.

Photorespiration and Plant Types

C3 plants' initial product of carbon fixation is 3-phosphoglycerate.
Photorespiration occurs under stress from closed stomata, causing rubisco to bind O2 instead of CO2, leading to carbon loss and decreased yields.

C4 and CAM Photosynthesis

C4 plants initially produce a 4-carbon compound using PEP carboxylase to efficiently fix CO2 without engaging in photorespiration by separate spatial pathways.
CAM plants fix CO2 at night, converting it to organic acids, which are released during the day for the Calvin cycle, aiding water conservation in arid conditions.

Plant Structures and Functions

The most abundant organic molecule in plants is cellulose, which serves as a key structural component.
Sucrose acts as a transport molecule for photosynthate, providing energy for cellular respiration and building blocks for various organic compounds.

Summary of Processes

The Calvin cycle occurs in the stroma, using ATP and NADPH to convert CO2 into G3P while returning ADP and NADP+ to the light reactions.
Light reactions take place in the thylakoid membranes, generating ATP and NADPH while splitting water and releasing oxygen.

Comparisons and Differences

Both C4 and CAM plants convert CO2 to organic acids but do so through different timing and structural methods.
The adaptation of C4 plants allows them to thrive in high-temperature environments with minimized photorespiration effects.

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Test your knowledge on key terms related to photosynthesis with these flashcards. This quiz covers essential concepts such as autotrophs, heterotrophs, granum, and stroma. Perfect for studying and reinforcing your understanding of Chapter 10 in biology.