Question

Match each term with its description. (a) Calvin cycle (b) Rubisco (c) Carbamate (d) Starch (e) Sucrose (f) Amylose (g) Amylopectin (h) \(\mathrm{C}_{3}\) plants (i) \(\mathrm{C}_{4}\) plants (j) Stomata 1\. \(\mathrm{CO}_{2}\) fixation 2\. Storage form of carbohydrates 3\. \(\alpha-1,4\) linkages only 4\. 3-Phosphoglycerate is formed after carbon fixation 5\. The dark reactions 6\. Includes \(\alpha-1,6\) linkages 7\. Required for rubisco activity 8\. Carbon fixation results in oxaloacetate formation 9\. Allow exchange of gases 10\. Transport form of carbohydrates

Short answer

(a) - 5, (b) - 1, (c) - 7, (d) - 2, (e) - 10, (f) - 3, (g) - 6, (h) - 4, (i) - 8, (j) - 9.

Step-by-step solution

Calvin cycle

The Calvin cycle is part of the photosynthesis process that occurs in chloroplasts, commonly referred to as the 'dark reactions' because they don't require light. Therefore, it matches with description 5: The dark reactions.

Rubisco

Rubisco is an enzyme involved in the first major step of carbon fixation. However, it requires a specific modification (formation of a carbamate) for activation. Therefore, it matches with description 1: CO2 fixation.

Carbamate

A carbamate is a compound that Rubisco needs to become active in the carbon fixation process. The activity of Rubisco necessitates the formation of a carbamate. Therefore, it matches with description 7: Required for rubisco activity.

Starch

Starch is a carbohydrate that serves as a storage form of energy in plants. Consequently, it matches with description 2: Storage form of carbohydrates.

Sucrose

Sucrose is used by plants to transport energy throughout the organism. Thus, it matches with description 10: Transport form of carbohydrates.

Amylose

Amylose is a form of starch characterized by its long chains of glucose units connected entirely by α-1,4 linkages. Therefore, it matches with description 3: α-1,4 linkages only.

Amylopectin

Amylopectin is a highly branched form of starch that contains α-1,6 linkages in addition to α-1,4 linkages. Thus, it matches with description 6: Includes α-1,6 linkages.

C3 plants

C3 plants are those where the carbon fixation process results in the formation of 3-phosphoglycerate, a 3-carbon compound. Hence, it matches with description 4: 3-Phosphoglycerate is formed after carbon fixation.

C4 plants

C4 plants carry out carbon fixation in a way that produces a 4-carbon compound, oxaloacetate. Thus, it matches with description 8: Carbon fixation results in oxaloacetate formation.

Stomata

Stomata are small openings on the surface of leaves that allow for the exchange of gases (such as CO2 and O2) between the plant and the atmosphere. Therefore, it matches with description 9: Allow exchange of gases.

Key concepts

Calvin Cycle

The Calvin Cycle is a fundamental component of photosynthesis, occurring in the chloroplasts of plant cells. It is often referred to as the 'dark reactions' because it does not require light to proceed. Instead, it uses ATP and NADPH, produced in the light-dependent reactions, to fix carbon dioxide into organic molecules. This cycle consists of three main stages:

• Carbon Fixation: CO₂ is attached to a five-carbon sugar ribulose bisphosphate (RuBP), facilitated by the enzyme Rubisco, forming a six-carbon compound that splits into two molecules of 3-phosphoglycerate (3-PGA).
• Reduction: ATP and NADPH are used to convert 3-PGA into glyceraldehyde 3-phosphate (G3P). Some of these G3P molecules go on to form glucose and other carbohydrates, while others are recycled.
• Regeneration: The remaining G3P molecules are used to regenerate RuBP, enabling the cycle to continue. This stage consumes additional ATP.

Rubisco

Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is considered one of the most important enzymes on Earth due to its central role in photosynthesis and carbon fixation. It catalyzes the first step in the Calvin Cycle by facilitating the attachment of CO₂ to RuBP. Despite its importance, Rubisco is inefficient and works slowly, leading plants to produce it in large quantities. Moreover, it has the tendency to bind oxygen instead of carbon dioxide, a process called photorespiration, which can hamper photosynthetic efficiency, especially under warm and dry conditions. Scientists and researchers are continually exploring ways to enhance Rubisco's efficiency to improve plant photosynthesis and agricultural productivity.

Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose. It can be broadly divided into two stages:

• Light-dependent Reactions: These occur in the thylakoid membranes, where sunlight is absorbed by chlorophyll. This energy is used to split water molecules, releasing oxygen and generating ATP and NADPH.
• Calvin Cycle (Light-independent Reactions): This occurs in the stroma, using ATP and NADPH from the light-dependent reactions to convert CO₂ into glucose.

Photosynthesis not only provides energy for plants but also supplies oxygen for other living organisms, making it vital to life on Earth.

Carbohydrates

Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen, primarily serving as energy sources and structural materials in living organisms. In plants, carbohydrates are synthesized during photosynthesis:

• Glucose, the simplest form of carbohydrate, is a building block for complex carbohydrates like starch and cellulose.
• Starch: A storage form of energy in plants, consisting of amylose (unbranched) and amylopectin (branched).
  • Amylose comprises glucose units joined by α-1,4 glycosidic linkages
  • Amylopectin features additional α-1,6 linkages, providing a branched structure
• Sucrose: A transport form of carbohydrate in plants, moving energy to various parts of the plant.

Carbohydrates play a critical role in plant metabolism, growth, and development.

Carbon Fixation

Carbon fixation is a key biochemical process where atmospheric CO₂ is converted into organic carbon compounds in the form of glucose, through photosynthesis. This process primarily occurs in the Calvin Cycle. During carbon fixation, Rubisco catalyzes the addition of CO₂ to RuBP, forming 3-phosphoglycerate in C3 plants, or oxaloacetate in C4 plants. This conversion is crucial because it transforms inorganic carbon, which most plants cannot use, into a form that is usable for growth and energy storage. Carbon fixation not only impacts plant life but also influences the global carbon cycle, impacting climate and atmospheric CO₂ levels.