Metabolism in Cells: Rice Cultivation

Rice as a Staple Food

• Rice (Oryza sativa) feeds half the world's population, predominant in Asia, Africa, and Latin America.
• It is a cereal crop like wheat and corn, cultivated for its dry seeds (fruits).
• Grown submerged in 10-15 cm of water, rice roots thrive in low oxygen environments where most crops fail.
• Contains approximately 10% protein; requires supplementation with meat, fish, or protein-rich plants for balanced diets.
• White rice, produced through milling that removes bran and germ, is less nutritious than brown rice.

Metabolism Overview

• Metabolism encompasses all chemical processes in a cell, divided into anabolic and catabolic reactions.
• Anabolic reactions (anabolism) store energy by synthesizing complex molecules from simpler ones (e.g., photosynthesis produces glucose).
• Catabolic reactions (catabolism) release energy by breaking down larger molecules into simpler components (e.g., cellular respiration converts glucose to CO₂ and water).

Oxidation-Reduction Reactions

• Oxidation-reduction (redox) reactions are vital in metabolism, involving electron transfer between molecules.
• Oxidation denotes electron loss, while reduction indicates electron gain; these processes are interlinked.
• In cells, hydrogen removal signifies oxidation, and hydrogen gain signifies reduction.

Photosynthesis Process

• Photosynthesis transforms solar energy into chemical energy, yielding carbohydrates and oxygen from water and carbon dioxide.
• Acts as the foundational energy cycle for the biosphere, essential for life and oxygen supply to non-photosynthetic organisms.

Light and Its Properties

• Visible light is part of the electromagnetic spectrum (380-760 nm) and is crucial for photosynthesis.
• Light behaves as both a wave (with wavelength) and a particle (photons); its energy inversely correlates with wavelength.
• Short wavelengths (e.g., violet) carry more energy, while long wavelengths (e.g., radio waves) lack sufficient energy for photosynthesis.

Electron Excitation Mechanism

• Electrons can be energized by absorbing photons, transitioning from a ground state to a higher energy level.
• Energized electrons either return to ground state, releasing energy as heat/light, or transfer to another molecule, contributing to photosynthesis.

Chloroplast Structure and Function

• Photosynthesis occurs in chloroplasts, predominantly in mesophyll cells, containing multiple chloroplasts for optimal light absorption.
• Chloroplasts consist of two membranes with an internal stroma housing enzymes for carbohydrate synthesis and thylakoids for pigment storage.

Chlorophyll and Pigments

• Chlorophyll absorbs blue and red light, reflecting green, which leads to the characteristic color of plants.
• Chlorophyll a is the primary pigment initiating photosynthesis; chlorophyll b and carotenoids serve as accessory pigments that broaden light absorption.

Action and Absorption Spectrum

• The absorption spectrum illustrates pigment light absorption; chlorophyll a and b have distinct absorption profiles.
• The action spectrum indicates the effectiveness of light wavelengths for photosynthesis, correlating with but not matching the absorption spectrum.

Engelmann’s Experiment

• Engelmann (1883) demonstrated photosynthesis action spectrum using the alga Spirogyra, tracking bacteria movement towards oxygen production in blue and red light, confirming chlorophyll's role.

Photosynthesis Chemical Equation

• The general photosynthesis equation: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O.
• Carbon dioxide and water convert into glucose and oxygen using light energy; chlorophyll acts as a catalyst.

Energy Conversion and Stages of Photosynthesis

• Light energy absorbed by chlorophyll splits water into oxygen, electrons, and protons, aiding carbohydrate formation.
• Photosynthesis occurs in two stages: light-dependent reactions generate ATP and NADPH in thylakoid membranes, utilizing light energy.

Explore the unique metabolic processes of rice (Oryza sativa), a crucial staple food for millions. This quiz delves into its cultivation in water-logged conditions and the adaptations that allow it to thrive where other crops would struggle. Test your knowledge on the significance of rice in global agriculture.