Question

What is implied about the energy requirements of photosystems I and II by the fact that there is a difference in the minimum wavelength of light needed for them to operate \((700 \text { nm for photosystem } I \text { and } 680 \text { nm for photosystem II }) ?\)

Short answer

Photosystem II requires more energy (due to its shorter wavelength requirement of 680 nm) compared to Photosystem I (which requires 700 nm).

Step-by-step solution

Understand Photosystems and Wavelengths

Photosystems are protein complexes involved in the light-dependent reactions of photosynthesis. Photosystem I operates with a minimum wavelength of 700 nm, while Photosystem II operates with a minimum wavelength of 680 nm. The wavelength of light is inversely related to the energy it carries.

Energy and Wavelength Relationship

Energy of light can be calculated using the formula: \[ E = \frac{hc}{\text{wavelength}} \] where \( E \) is the energy, \( h \) is Planck's constant, and \( c \) is the speed of light. From this relationship, shorter wavelengths correspond to higher energy.

Calculating Energy for Photosystem II

Using the formula, calculate the energy for a wavelength of 680 nm for Photosystem II. \[ E_{PSII} = \frac{6.626 \times 10^{-34} \text{ J} \text{ s} \times 3 \times 10^8 \text{ m/s}}{680 \times 10^{-9} \text{ m}} \ = 2.93 \times 10^{-19} \text{ J} \]

Calculating Energy for Photosystem I

Similarly, calculate the energy for a wavelength of 700 nm for Photosystem I. \[ E_{PSI} = \frac{6.626 \times 10^{-34} \text{ J} \text{ s} \times 3 \times 10^8 \text{ m/s}}{700 \times 10^{-9} \text{ m}} \ = 2.84 \times 10^{-19} \text{ J} \]

Comparing Energy Requirements

Compare the calculated energies: \[ E_{PSII} = 2.93 \times 10^{-19} \text{ J} \] is greater than \[ E_{PSI} = 2.84 \times 10^{-19} \text{ J} \]. This indicates that Photosystem II requires more energy to operate compared to Photosystem I.

Conclusion

The shorter minimum wavelength of Photosystem II (680 nm) corresponds to higher energy requirements compared to the longer minimum wavelength of Photosystem I (700 nm). Therefore, Photosystem II requires more energy to function than Photosystem I.

Key concepts

Photosystems

Photosystems are essential components in the process of photosynthesis. They are protein complexes located in the thylakoid membranes of chloroplasts.
These complexes play a crucial role in the light-dependent reactions of photosynthesis by capturing light energy and converting it into chemical energy.
There are two main types of photosystems: Photosystem I (PSI) and Photosystem II (PSII).
Each photosystem absorbs light at different wavelengths and thus operates at different energy levels.
PSI is most effective at a wavelength of 700 nm (P700), while PSII operates at 680 nm (P680).
The numbers indicate the absorption peak wavelengths in nanometers.
Both photosystems work together to drive the process of photosynthesis, but they have distinct roles and energy requirements.

Wavelength-Energy Relationship

The energy carried by light is inversely proportional to its wavelength.
This relationship is expressed through the formula: For example, when comparing the wavelengths utilized by PSI and PSII: In photosynthesis, this means that PSII requires more energy ( This inverse relationship is key in understanding why PSII, which absorbs at 680 nm, requires more energy than PSI, which absorbs at 700 nm.
These calculations highlight the distinct energy demands of the two photosystems.
Therefore, the shorter the wavelength, the higher the energy needed for the photosystem to function.

Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.
This process is vital for the production of oxygen and serves as the foundation of life on Earth.
Photosynthesis occurs in two main stages: light-dependent reactions and the Calvin Cycle. During the light-dependent reactions, which occur in the thylakoid membranes, photosystems I and II play a pivotal role.
Here, light energy is absorbed and used to drive the production of ATP and NADPH.
These molecules then act as energy carriers, fueling the second stage of photosynthesis.
In the Calvin Cycle, ATP and NADPH are used to convert carbon dioxide into glucose.
Thus, the light-dependent reactions, facilitated by photosystems, are essential for converting solar energy into a chemical form that plants can use for growth and metabolism.