Physiological Processes in Crop Production

Physiological Processes Affecting Crop Production

• Crop growth and development depend on the interaction of various physiological processes
• Key processes include photosynthesis, respiration, transpiration, and translocation
• These processes are fundamental to crop yield

Photosynthesis - A Chemical Reaction

• Photosynthesis is an autotrophic process, meaning plants and plant-like organisms (algae) use sunlight to create energy (glucose)
• The produced glucose is stored as carbohydrate within these organisms
• Photosynthesis is considered the most important biological process because it provides organic molecules from inorganic materials like carbon dioxide and water
• It supports all food chains and webs, and produces oxygen

Photosynthesis Requirements

• Plants require water, carbon dioxide, light, and chlorophyll for photosynthesis

Photo-synthesis Definition

• Photosynthesis is the process of "putting together with light"
• It converts water and carbon dioxide into glucose (a sugar) using sunlight
• Plants use glucose for energy and as a building block for growth
• Autotrophs produce glucose; heterotrophs consume it.

Two Types of Photosynthesis

• Anoxygenic photosynthesis is used by obligate anaerobes, capturing light energy to make ATP without oxygen production. Water is not used as an electron source.
• Oxygenic photosynthesis is the common form in plants, algae, and cyanobacteria. Water is the initial electron donor, resulting in molecular oxygen as a byproduct.

Photosynthesis Equation

• 6CO2 + 6H2O + energy → C6H12O6 + 6O2 (carbon dioxide + water + energy → glucose + oxygen)

Significance of Photosynthesis

• Green plants contain chlorophyll, capturing, converting, transferring, and storing energy for all life on Earth.
• Photosynthesis is the process of converting light energy into chemical energy.
• Other organisms rely on green plants for food production and survival.

The Photosynthetic Organ - Leaf

• The leaf is the primary site of photosynthesis.
• Leaf structure includes upper and lower epidermis (with stomates), mesophyll cells (containing chlorophyll), and vascular bundles (for transport)
• Mesophyll is further divided into palisade parenchyma (upper layer with regular cells) and spongy parenchyma (lower layer with irregular cells)

Stomata

• Stomata are openings on the leaf's underside that allow gas exchange.

Chloroplasts

• Chloroplasts are tiny green structures within leaf cells where photosynthesis happens
• These structures are clearly visible under a high magnification microscope.

Chloroplasts and Sugars/Oxygen

• Chloroplasts produce sugars (glucose).
• Chloroplasts also produce oxygen.

Photosynthesis Stage 2

• Captured light energy from Stage 1 is used to produce sugars and oxygen from water
• Sugars produced are used by the plant cells for energy
• Oxygen is released through the stomata on the leaf's underside
• Glucose provides energy for producing other plant materials, such as wax and proteins

Leaves and Chlorophyll

• Leaves are green due to the pigment chlorophyll, which absorbs light.
• Leaves have a large surface area for maximum light absorption.

Photosynthetic Pigments

• The photosynthetic pigments include carotenoids, which absorb light in regions of the spectrum not absorbed by chlorophyll, and chlorophyll, the principal pigment in photosynthesis
• Chlorophyll absorbs light maximally in the violet-blue and red parts of the spectrum; it reflects green light (hence the green color of leaves)

Visible Light and Electromagnetic Spectrum

• Visible light is a small part of the electromagnetic spectrum, which encompasses all forms of light

Chlorophyll Details

• Chlorophyll is located at the partition between adjacent thylakoids
• Its basic unit is a porphyrin ring system composed of four pyrrole nuclei linked by carbon linkages
• The porphyrin center contains a single magnesium atom.

Kinds of Chlorophyll

• Chlorophyll a (bluish green) is found in most autotrophic organisms besides photosynthetic bacteria.
• Chlorophyll b (yellowish green)

Light Absorption

• Leaves generally absorb around 83% of light, reflecting 12% and transmitting 5%
• Only about 4% of absorbed light is used in photosynthesis; the rest is lost as heat.

Photochemical and Biosynthetic Phase

• Photosynthesis takes place in chloroplasts.
• Photosynthesis involves light reactions and dark reactions.
• Light reactions take place in the grana of the chloroplasts (where chlorophyll is located). Dark reactions take place in the stroma of the chloroplasts (where chlorophyll is not found).

Light Reaction Details

• The light reaction of light-dependent reactions happen in the chloroplast's mesophyll cells of the leaves.
• The primary purpose of the light reaction is to create ATP and NADPH compounds for subsequent dark reactions.

Light Reaction Steps

• Chlorophyll absorbs red and blue light most efficiently for photosynthesis.
• Light absorption excites electrons in chlorophyll.
• This process happens within photosystems (PSI and PSII).
• Chlorophyll releases energized electrons, which are replaced by water splitting. This releases hydrogen ions and oxygen.
• Electrons reach a reaction center where they combine with NADP+ to form NADPH.
• The built-up hydrogen ions create energy enabling ATP formation.

Light Reaction Steps - Continued

• Oxygen is released as a byproduct.
• Electrons move along a transport chain losing energy
• Electron transport chain energy used to produce ATP

Light Reaction End Products

• ATP and NADPH are the end products of light reactions, used to fix CO2 in the dark reaction

Synthesis of ATP

• Light-induced phosphorylation (adding a phosphate group to ADP) produces ATP. This is called photophosphorylation (with non-cyclic and cyclic options).

Dark Reaction Details

• Dark reactions occur in the stroma of the chloroplasts.
• Dark reactions are how inorganic carbon gets converted to carbon.
• Carbon dioxide reduction and the formation of carbohydrates are part of the dark reaction.
• Carbon fixation occurs via three pathways:

Dark Reaction Pathways

1. Calvin Benson Cycle - fixation/reduction of carbon dioxide (requires 3 ATP and 2 NADPH); takes place in the chloroplast's mesophyll cell; utilizes RUBP (CO2 acceptor) and RUBP Carboxylase enzyme; 3-PGA is the first stable product.

2. C4 or Hatch Slack Pathway - the first product is 4-carbon oxaloacetic acid (utilizing PEPC enzyme for CO2 fixation and decarboxylation in bundle sheath cells); occurs with Kranz anatomy.

3. CAM or Crassulacean Acid Metabolism Pathway - stomata close during the day and open during the night to reduce water loss and collect CO2; CO2 is stored as malate, then reacts with RuBisco to produce sugar

Factors Affecting Photosynthesis

• Internal factors include chlorophyll amount, leaf age/anatomy, and demand for photosynthetic products
• External factors include temperature, light, carbon dioxide, water, and mineral elements. Environmental factors affect photosynthesis indirectly by impacting internal processes.

Explore the essential physiological processes that influence crop growth and yield, focusing on key factors such as photosynthesis, respiration, and transpiration. This quiz delves into how these processes interact to determine overall plant health and productivity.