Energy Flow and Photosynthesis in Ecosystems - Class XII

Chlorophyll is the pigment responsible for photosynthesis. The light active in photosynthesis is a small part in the visible spectrum (400- 700 nm). The chlorophyll pigments mainly absorb blue and red light. Maximum absorption is in blue light but maximum photosynthesis occurs in red light.

Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis. Sunlight comprises all effective lights PAR (photosynthetically active radiations) as required for photosynthesis. Thus, option A is correct.

• Around 50% of the total radiation from sunlight falls under photosynthetically active radiation and supports the process of photosynthesis. It constitutes the light of 400-700 nm wavelength which is absorbed by chlorophyll pigment. Out of which only 2 - 10% are captured by plants. Thus, the correct answer is option B.

Source of energy in an ecosystem is solar energy. 50 per cent of the solar energy incident over Earth is present in PAR (photosynthetically active radiation). Almost 1 to 5 percent of incident solar energy or 2 to 10 percent of PAR is captured by photosynthetic organisms in synthesis of organic matter. 

Sunlight is like a rain of photons of different frequencies. Visible light consists of radiations having a wavelength of 390-760 nm. Part of spectrum used in photosynthesis has a wavelength of 400-700 nm. It is called photosynthetically active radiation (PAR). The proportion of PAR of the total solar radiation is less than 50%. Only 2-10% of PAR is captured by the plants.

• Ultraviolet rays: UV rays have a wavelength of 0.01 - 10 nm. These rays can have adverse effects like sunburn, skin cancer if exposure occurs for a long period of time.
• Visible light: Visible spectrum lies in the range of wavelength 400 - 700 nm. These rays are perceived by human eyes. A part of the visible spectrum is used by plants for photosynthesis.
• Infrared rays: These rays have a wavelength beyond the visible spectrum. Most of the radiation emitted from the sun is in the form of infrared radiation.

Photosynthesis is the process by which light energy is converted to chemical energy. In plants, light is absorbed by pigments such as chlorophyll. Light hits these molecules and raises them to a higher energy. Light, however, occurs in a spectrum of wavelengths ranging from ultraviolet to visible light to infrared. The energy accompanying the absorption of light is dependent on the wavelength of the light. The amount of energy absorbed during the processes of photosynthesis depends on the wavelength of light absorbed. For processes requiring more energy, pigment molecules must be able to absorb the necessary wavelengths. 680 nm wavelength is absorbed maximum for photosynthesis because, 680 nm will be utilized by both the pigment systems.

Carotenoids are organic pigments that are found in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms, including some bacteria and some fungi. Carotenoids absorb light in the blue-green and violet region and reflect the longer yellow, red, and orange wavelengths. These pigments also dispose excess energy out of the cell. Thus, option A is correct and other options are incorrect.

Plants and other oxygenic photosynthetic organisms harvest light energy from the sun to fix carbon dioxide into the food and fiber required to sustain the biosphere. Since plants cannot move, they must cope with regular day-night cycles, seasonal cycles and neighbouring vegetation, all of which influence the intensity, direction and spectral quality of light impinging on their leaves. 

Of the total incident solar radiation the proportion of PAR (photosynthetically active radiation) accounts to less than 50%. Photosynthetically active radiation designates the spectral range of solar radiation from 400 to 700 nanometers, that photosynthetic organisms are able to use in the process of photosynthesis.

The pyramid of energy is always upright because energy is lost as heat at each transfer, and producers have the highest energy availability, which decreases as you move up the trophic levels.

Higher plants utilize 1 to 2 % of sunlight for photosynthesis. Most crop plants store nearly 0.25% to 0.5% of the sunlight in the product. Examples are corn kernels, potato starch, etc. Photosynthesis increases linearly with light intensity at low intensity, but at higher intensity this is no longer the case.

Emerson defined red drop as decline in the quantum yield of photosynthesis  at wavelength beyond 680 nm. 

According to the ten percent law of energy transfer in ecosystems, energy decreases at each successive trophic level. Therefore, producers at the first trophic level possess the maximum amount of energy.

Photosynthetically Active Radiation (PAR) is the amount of light available for photosynthesis, which is light in the 400 to 700 nanometer wavelength range. PAR changes seasonally and varies depending on the latitude and time of day.

Chemosynthesis is the process by which certain organisms (like bacteria) obtain energy by oxidizing inorganic chemical compounds rather than using sunlight.

Ecosystems generally depend on two main energy sources: solar energy (for photoautotrophs) and chemical energy (for chemoautotrophs).

Organisms in an estuary, particularly producers like phytoplankton and algae, convert solar energy into organic matter through photosynthesis. This organic matter forms the base of the estuarine food web.

Photosynthesis is the process by which plants convert light energy into chemical energy. This light energy is derived from solar radiation.

Photosynthetically active radiation or PAR is, the spectral range (wave band) of solar radiation from 400 to 700 nanometers. At this range, an autotroph synthesises the food by the process of photosynthesis. Hence option B is correct.

Photosynthesis occurs in small portion of spectrum, called as 'photosynthetically active radiation' or PAR (400-700 nm). Maximum absorption of light occurs in blue region (around 400 nm) followed by red light (around 700 nm). Maximum photosynthesis, however, occurs in red light. Least photosynthesis occurs in green light.

The photosynthesis process is essentially a light dependent synthetic process, which results in synthesis of sugars. A small part of the solar spectrum in the visible portion is used in the process of photosynthesis. This small portion of the solar spectrum is called photosynthetically active radiations or PAR. The wavelength of light active in PAR occur between 400 to 700 nm.

Blue light of the spectrum is absorbed more for the process of photosynthesis. Plants have two types of chlorophylls - a and b. Chloropphyll a is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light. A yellow-green chlorophyll pigment which occurs only in plants and green algae. It functions as a light harvesting pigment that pass on the light excitation to chlorophyll a. It absorbs well at wavelength of 450-500 nm and 600-650 nm.

Chlorophyll absorbs red and violet-blue light, while transmitting and reflecting green light. Chlorophyll 'a' absorbs blue light with wavelengths of 430 nm and red light of 662 nm. 453 nm and 642 nm wavelengths are absorbed by chlorophyll 'b'.

Theodor Wilhelm Engelmann was a German botanist, phsiologist, microbiologist, university professor and musician, whose 1882 experiment measured the effects of different colours of light on photosynthetic activity and showed that the conversion of light energy to chemical energy took place in the chloroplast. Both blue and red wavelength are effective because the amount of oxygen released was found to be maximum in blue and red absorption bands of the chlorophyll.

Small part of visible light in the range of 400 to 700 nm is active in photosynthesis. It is called as photosynthetically active region or PAR. The chlorophyll absorbs maximum in the blue region and red region. The blue region of PAR is near 400 nm after violet and indigo light, while the red region is near 700 nm. The blue region is centered around 460 nm, where chlorophyll a shows maximum absorption.

During photosynthesis 1 to 4% light is utilized. Photosynthesis is more in intense light and is also counted as a limiting factor. Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.

An ecological efficiency is the efficiency of energy transfer from one trophic level to the next trophic level. In other words, it is the energy in biomass production at a trophic level divided by energy in biomass production at previous trophic level. It is the ratio of energy flows at different trophic levels in a food-chain. It is expressed in percentage.

Wavelength of light absorbed during photosynthesis is 440 nm (violet to blue light). It is the main function of chlorophyll molecule, which is called as the photosynthetic pigment. the violet, blue light have shorter wave length and higher energy content. 

The second law of thermodynamics states that energy transfers are never 100% efficient, as some energy is always lost as heat during the conversion process.

In a solar ecosystem, plants use solar energy to synthesize organic matter from inorganic substances. This organic matter serves as the energy source for the rest of the ecosystem.

The conversion of energy, including solar energy into chemical energy, is governed by the laws of thermodynamics, specifically the first and second laws.

Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers, that photosynthetic organisms are able to use in the process of photosynthesis. This spectral region corresponds more or less with the range of light visible to the human eye.