PHOTOSYNTHESIS IN HIGHER PLANTS NEET

In this video, we explore a series of experiments conducted by various scientists who collaborated to uncover the facts about photosynthesis.

Early Experiments in Photosynthesis:

• Joseph Priestley’s Bell Jar Experiment (1770): Through a series of experiments, Priestley concluded that air is essential for photosynthesis and plant growth.

• Jan Ingenhousz: He demonstrated that sunlight is crucial for photosynthesis, during which carbon dioxide is absorbed and oxygen is released.

• Julius Von Sachs: He discovered that photosynthesis results in the production of glucose molecules.

• T.W. Engelmann: Engelmann identified the role of chlorophyll in the photosynthesis process.

• Cornelius van Niel: He introduced the chemical equation for photosynthesis and revealed that the oxygen released during the process comes from water, not carbon dioxide.

Van Niel observed that certain bacteria used hydrogen sulfide (H₂S) instead of water for photosynthesis and produced sulfur as a byproduct. This led him to propose that the oxygen released by plants during photosynthesis comes from the splitting of water molecules.

To test this hypothesis, Ruben and Kamen conducted an experiment using water labeled with radioactive oxygen-18 (¹⁸O). Their results showed that the oxygen released by plants contained the labeled isotope, confirming that water is the source of oxygen in photosynthesis. Van Niel’s work provided the theoretical basis for this discovery, which was later experimentally validated by Ruben and Kamen.

Red drop effect , discovered by Emerson, occurs due to the disruption of photochemical activity in PS II. Wavelengths beyond 700nm are ineffective for photosynthesis, leading to a significant drop in efficiency at 700nm.

Quantum yield refers to the number of oxygen molecules released per light quanta. Simply put, quantum yield declines beyond 680nm, which is observed in the red region of the spectrum. Since PS II operates at 680nm, its disruption leaves only PS I functional, which has an optimum wavelength of 700nm. As a result, the red drop effect occurs due to the impaired photochemical activity of PS II.

The Emerson effect - The increase in the rate of photosynthesis occurs when chloroplasts are exposed to light at wavelengths of 670 nm (red light) and 700 nm (far-red light). When both wavelengths are applied simultaneously, the photosynthetic rate significantly exceeds the combined rates observed under individual exposures.

• These effects provide evidence for the existence of two distinct Photosystems.

Chloroplasts are present in all higher plants and are typically oval or biconvex in shape, located within the mesophyll cells. Their size generally ranges from 4-6 µm in diameter and 1-3 µm in thickness. These organelles have a double membrane consisting of an outer membrane, an inner membrane, and an intermembrane space.

Inside the chloroplast, there are two main regions: the grana and the stroma. Grana are composed of stacks of disc-shaped structures called thylakoids or lamellae. These structures contain chlorophyll pigments and serve as the functional units of the chloroplast. The stroma is a gel-like matrix that surrounds the grana, similar to cytoplasm in cells, and contains enzymes, DNA, ribosomes, and other essential molecules. Additionally, stroma lamellae connect the thylakoid stacks, facilitating interaction between them.

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  Plastids are specialized organelles in plant cells and algae, categorized into three main types based on their function and pigmentation:

  1. Chromoplasts – These are colored plastids that contain pigments like carotenoids, giving flowers and fruits their distinctive hues. They play a key role in attracting pollinators and aiding seed dispersal.

  2. Chloroplasts – These green plastids contain chlorophyll, the pigment essential for photosynthesis. They help convert light energy into chemical energy, enabling plants to produce their own food.

  3. Leucoplasts – These are colorless plastids primarily involved in storing essential nutrients such as starch, lipids, and proteins within plant cells.

Chloroplasts are present in all higher plants and are typically oval or biconvex in shape, located within the mesophyll cells. Their size generally ranges from 4-6 µm in diameter and 1-3 µm in thickness. These organelles have a double membrane consisting of an outer membrane, an inner membrane, and an intermembrane space.

Inside the chloroplast, there are two main regions: the grana and the stroma. Grana are composed of stacks of disc-shaped structures called thylakoids or lamellae. These structures contain chlorophyll pigments and serve as the functional units of the chloroplast. The stroma is a gel-like matrix that surrounds the grana, similar to cytoplasm in cells, and contains enzymes, DNA, ribosomes, and other essential molecules. Additionally, stroma lamellae connect the thylakoid stacks, facilitating interaction between them.

• 
  

  Plastids are specialized organelles in plant cells and algae, categorized into three main types based on their function and pigmentation:

  1. Chromoplasts – These are colored plastids that contain pigments like carotenoids, giving flowers and fruits their distinctive hues. They play a key role in attracting pollinators and aiding seed dispersal.

  2. Chloroplasts – These green plastids contain chlorophyll, the pigment essential for photosynthesis. They help convert light energy into chemical energy, enabling plants to produce their own food.

  3. Leucoplasts – These are colorless plastids primarily involved in storing essential nutrients such as starch, lipids, and proteins within plant cells.