/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 2 Phases of Photosynthesis When a ... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 20: Problem 2

Phases of Photosynthesis When a suspension of green algae is illuminated in the absence of \(\mathrm{CO}_{2}\) and then incubated with \(^{14} \mathrm{CO}_{2}\) in the dark, \(^{14} \mathrm{CO}_{2}\) is converted to \(\left[^{14} \mathrm{C}\right]\) glucose for a brief time. What is the significance of this observation with regard to the \(\mathrm{CO}_{2}\) -assimilation process, and how is it related to the light reactions of photosynthesis? Why does the conversion of \(^{14} \mathrm{CO}_{2}\) to \(\left[^{14} \mathrm{C}\right]\) glucose stop after a brief time?

Short Answer

Expert verified
The experiment shows the Calvin cycle can proceed in the dark using ATP and NADPH from light reactions. Conversion stops when these energy carriers deplete.

Step by step solution

01

Understanding Photosynthesis Phases

Photosynthesis has two main phases: the light-dependent reactions and the Calvin cycle (light-independent reactions). In the light-dependent reactions, light energy is captured by chlorophyll and used to generate ATP and NADPH, which are then utilized in the Calvin cycle to fix carbon dioxide into glucose.
02

Observation Explained

The experiment details indicate that when green algae are illuminated in the absence of CO鈧�, they still perform light-dependent reactions, creating ATP and NADPH. When exposed to 14CO鈧� in the dark, these energy carriers are used in the Calvin cycle to convert 14CO鈧� into [14C] glucose.
03

Significance of the Observation

This observation shows that the Calvin cycle does not require light directly. It can proceed in the dark as long as ATP and NADPH from previous light reactions are available to drive the fixation of CO鈧� into carbohydrates.
04

Reason for Brief Conversion

The conversion of 14CO鈧� to [14C] glucose ceases after a short period because the ATP and NADPH generated during the previous light exposure get depleted, halting further carbon fixation until new supplies are generated by light reactions.
05

Connection to Light Reactions

The incident emphasizes the interdependence between the light reactions and the Calvin cycle. ATP and NADPH produced during light-dependent photosynthesis are essential for the Calvin cycle to assimilate CO鈧� into glucose.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Calvin cycle
The Calvin cycle, also known as the light-independent reactions or dark reactions, is a crucial part of the photosynthesis process that occurs in the chloroplasts of plant cells. Unlike the light-dependent reactions that require sunlight, the Calvin cycle operates independently of light.

Its primary function is to convert carbon dioxide ( CO_2) into glucose, a carbohydrate that plants utilize for energy and growth. This process takes place in a series of steps:
  • Carbon Fixation: CO_2 is attached to a 5-carbon sugar called ribulose bisphosphate (RuBP) by the enzyme RuBisCO, forming a 6-carbon compound that quickly splits into two 3-carbon molecules known as 3-phosphoglycerate (3-PGA).
  • Reduction Phase: ATP and NADPH, produced in the light-dependent reactions, provide energy and electrons to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), a sugar molecule.
  • Regeneration of RuBP: Some of the G3P molecules go towards making glucose, while others are used to regenerate RuBP, facilitating the cycle to continue.
This entire cycle is powered by ATP and NADPH, highlighting its dependency on the preceding light-dependent reactions to function effectively.
light-dependent reactions
The light-dependent reactions are the first phase in photosynthesis and occur within the thylakoid membranes of the chloroplasts. These reactions require sunlight and involve several key processes:
  • Photon Absorption: Chlorophyll and other pigments capture sunlight, energizing electrons.
  • Water Splitting: Water molecules ( H_2O) are split into oxygen ( O_2), protons, and electrons. The oxygen is released as a byproduct.
  • Electron Transport Chain: High-energy electrons from water move through a series of proteins, also known as the electron transport chain. As they move, they help pump protons into the thylakoid space, creating a gradient.
  • ATP and NADPH Formation: The proton gradient powers ATP synthase to generate ATP, while electrons reduce NADP^+ to form NADPH.
These products鈥擜TP and NADPH鈥攁re then utilized in the Calvin cycle to produce sugars like glucose, serving as a vital energy source for the plant.
CO2 assimilation
CO鈧� assimilation refers to the process by which plants take in carbon dioxide from the atmosphere and incorporate it into organic molecules. This process is primarily facilitated by the Calvin cycle, where CO鈧� is fixed into glucose.

During assimilation:
  • Carbon dioxide is captured by an enzyme called RuBisCO, which is one of the most abundant proteins on Earth.
  • The fixed carbon becomes part of a larger carbohydrate molecule, forming a stable energy source.
  • This energy is critical for plant growth and development, as well as for fuelling other life processes.
The efficiency of CO鈧� assimilation can be influenced by factors such as light intensity, temperature, and available water. It highlights the remarkable way plants use the energy from the sun to transform carbon dioxide into the building blocks of life.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Segregation of Metabolism in Organelles What are the advantages to the plant cell of having different organelles to carry out different reaction sequences that share intermediates?

Regulation of the Calvin Cycle Iodoacetate reacts irreversibly with the free \(-\) SH groups of Cys residues in proteins. Predict which Calvin cycle enzyme(s) would be inhibited by iodoacetate, and explain why.

Pathway of \(\mathrm{CO}_{2}\) Assimilation in Maize If a maize (corn) plant is illuminated in the presence of \(^{14} \mathrm{CO}_{2},\) after about 1 second, more than \(90 \%\) of all the radioactivity incorporated in the leaves is found at \(\mathrm{C}-4\) of malate, aspartate, and oxaloacetate. Only after 60 seconds does \(^{14} \mathrm{C}\) appear at \(\mathrm{C}-1\) of 3-phosphoglycerate. Explain.

Role of Sedoheptulose 1,7 -Bisphosphatase What effect on the cell and the organism might result from a defect in sedoheptulose 1,7 -bisphosphatase in (a) a human hepatocyte and (b) the leaf cell of a green plant?

Rubisco and the Composition of the Atmosphere N. E. Tolbert has argued that the dual specificity of rubisco for \(\mathrm{CO}_{2}\) and \(\mathrm{O}_{2}\) is not simply a leftover from evolution in a lowoxygen environment. He suggests that the relative activities of the carboxylase and oxygenase activities of rubisco actually have set, and now maintain, the ratio of \(\mathrm{CO}_{2}\) to \(\mathrm{O}_{2}\) in the earth's atmosphere. Discuss the pros and cons of this hypothesis, in molecular terms and in global terms. How does the existence of \(\mathrm{C}_{4}\) organisms bear on the hypothesis? Source: Tolbert, N.E. (1994) The role of photosynthesis and photorespiration in regulating atmospheric \(\mathrm{CO}_{2}\) and \(\mathrm{O}_{2}\). In Regulation of Atmospheric \(\mathrm{CO}_{2}\) and \(\mathrm{O}_{2}\) by Photosynthetic Carbon Metabolism (Tolbert, N.E., \& Preiss, J., eds), pp. 8-33, Oxford University Press, New York.
See all solutions

Recommended explanations on Chemistry Textbooks

The Earths Atmosphere

Read Explanation

Nuclear Chemistry

Read Explanation

Organic Chemistry

Read Explanation

Ionic and Molecular Compounds

Read Explanation

Chemistry Branches

Read Explanation

Inorganic Chemistry

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.