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By the end of this section, you will be able to:
  • Explain how plants absorb energy from sunlight
  • Describe short and long wavelengths of light
  • Describe how and where photosynthesis takes place within a plant

How can light be used to make food? When a person turns on a lamp, electrical energy becomes light energy. Like all other forms of kinetic energy, light can travel, change form, and be harnessed to do work. In the case of photosynthesis, light energy is converted into chemical energy, which photoautotrophs use to build carbohydrate molecules ( [link] ). However, autotrophs only use a few specific components of sunlight.

A photo shows the silhouette of a grassy plant against the sun at sunset.
Photoautotrophs can capture light energy from the sun, converting it into the chemical energy used to build food molecules. (credit: Gerry Atwell)

What is light energy?

The sun emits an enormous amount of electromagnetic radiation (solar energy). Humans can see only a fraction of this energy, which portion is therefore referred to as “visible light.” The manner in which solar energy travels is described as waves. Scientists can determine the amount of energy of a wave by measuring its wavelength    , the distance between consecutive points of a wave. A single wave is measured from two consecutive points, such as from crest to crest or from trough to trough ( [link] ).

The illustration shows two waves. The distance between the crests (or troughs) is the wavelength.
The wavelength of a single wave is the distance between two consecutive points of similar position (two crests or two troughs) along the wave.

Visible light constitutes only one of many types of electromagnetic radiation emitted from the sun and other stars. Scientists differentiate the various types of radiant energy from the sun within the electromagnetic spectrum. The electromagnetic spectrum    is the range of all possible frequencies of radiation ( [link] ). The difference between wavelengths relates to the amount of energy carried by them.

The illustration lists the types of electromagnetic radiation in order of increasing wavelength. These include gamma rays, X-rays, ultraviolet, visible, infrared, and radio. Gamma rays have a very short wavelength, on the order of one thousandth of a nanometer. Radio waves have a very long wavelength, on the order of one kilometer. Visible light ranges from 380 nanometers at the violet end of the spectrum, to 750 nanometers at the red end of the spectrum.
The sun emits energy in the form of electromagnetic radiation. This radiation exists at different wavelengths, each of which has its own characteristic energy. All electromagnetic radiation, including visible light, is characterized by its wavelength.

Each type of electromagnetic radiation travels at a particular wavelength. The longer the wavelength (or the more stretched out it appears in the diagram), the less energy is carried. Short, tight waves carry the most energy. This may seem illogical, but think of it in terms of a piece of moving a heavy rope. It takes little effort by a person to move a rope in long, wide waves. To make a rope move in short, tight waves, a person would need to apply significantly more energy.

The electromagnetic spectrum ( [link] ) shows several types of electromagnetic radiation originating from the sun, including X-rays and ultraviolet (UV) rays. The higher-energy waves can penetrate tissues and damage cells and DNA, explaining why both X-rays and UV rays can be harmful to living organisms.

Absorption of light

Light energy initiates the process of photosynthesis when pigments absorb the light. Organic pigments, whether in the human retina or the chloroplast thylakoid, have a narrow range of energy levels that they can absorb. Energy levels lower than those represented by red light are insufficient to raise an orbital electron to a populatable, excited (quantum) state. Energy levels higher than those in blue light will physically tear the molecules apart, called bleaching. So retinal pigments can only “see” (absorb) 700 nm to 400 nm light, which is therefore called visible light. For the same reasons, plants pigment molecules absorb only light in the wavelength range of 700 nm to 400 nm; plant physiologists refer to this range for plants as photosynthetically active radiation.

Questions & Answers

what is hominids
Dauba Reply
what is genetics
Musa Reply
what is meiosis?
Musa
list three vertebrate animal and three invertebrate animal
Katie Reply
lizard, goat, frog ,earthworm, housefly, tapeworm
idoko
what is meant by radial symmetry?
Boadi
what is meaning of polysaccharide
mark Reply
water as a function in cell for inorganic substances
chisom Reply
hi john....wat about for mineral salts, its function in a cell and structure
chisom
hi chisom which topic is this
Ezeh
what is sepsis
Dauba
this biology is for which grade?
Janet Reply
A1
Boadi
state any one specialized animal cell and it's function
Pascal Reply
sperm cell: Fertilization
Tshering
Can DNA and RNA be praticalized
Oyewale Reply
you can make models of them and show how they replicate
Oswald
what is dentition
Tisa Reply
Study of teeths and their functions
Stanisla
what are the function
Tisa
it's not teeths. teeth is plural as well as singular noun. the function of the teeth is to cut and grind food for easier swallowing and for increasing the surface area if the fish as the substrate in which digestive enzymes work
Oswald
dentition is not the study of teeth but the arrangement of teeth in the mouth of species or individuals
Oswald
what are the two types of teeth
Tisa
upper lower jaw and upper jaw teeth
Dauba
Function of probosis
Adeola Reply
why do we study biology?
SYDNEY Reply
where biology began
Alhaji
What are chromesome
Talkmore Reply
condensed DNA wrapped with histone
Elias
chromosomes are gins that we take from our parents.when mom get pregnant the baby inside is made up of 23 chromosomes from his dad and 23 chromosomes from his mom.so a baby is made up of totally 46 chromosomes
ezera
chromosome are rod or thread shape body located in the nucleus of a cell.
Alhaji
what are chromosomes
Persiviour
what is chromosome?
Royd Reply
How can a person who has been in the vascular disease repairs his or her DNA
Rabson Reply
i need its explanation sir..pls provid na...🙁
Shaf Reply
Of wat
John
explanation for wat
Christian
Of war na so dat I can provide
John
Is d process which food is converted into substance dat can be utilize by d body
John

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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