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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 different between Latin name and common names
mary Reply
what structure help root hair cells to take up water.
Jackson Reply
which two part of a plant cell are affected when the is immersed in sucrose solution?
Jackson
which two part of a plant cell are affected when the is immersed in sucrose solution?
Jackson
the xylem cells absorbs water and mineral salt from the soil to all part of the plant.
Nana
And the phloem cell take up food prepared from the leaves to all part of the plant
Nana
what is genetic engineering
Mavis Reply
what are the three main type of ecosystem
Mavis
biosphere,
Bigenis
biosphere
Adeniyi
what is mitochondria
Might Reply
please what's genetics erngee
Abanke Reply
what is genetic engineering
Eveline Reply
what is the meaning of term mitosis
Lwitiko Reply
outline the significance of mitosis to organisms
Lwitiko
significant of meiosis are to increase in variation and leads to the formation of haploid gamete
Eveline
thanks
Abanke
name the resources to be conserved
Oreva Reply
define natural resources
Oreva
name the agencies responsible for the conservation of natural resources
Oreva
land,water,forests,
Kiiza
nema,uwa
Kiiza
wassup guyz
Peace
land ,water
Erika
Good Land and Water
garnhial
food, fish, livelihoods,forest, land and water
garnhial
explain the importance of carbon dioxide in the body
Kiiza Reply
how does that works
SAMUEL
diagram of Prokaryotic cells
Magreth Reply
where is it?
Yazi
ʜɪ
Malikie
ʜɪ
Malikie
where is the diagram?
Yazi
waiting.....
Yazi
what
Malikie
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Joelia
gd morning
Hannalyn
morning how are u doing
Paul
doing all fyn en u
Joelia
👍👍👍
Gruxz
morning everyone.. by is Grace we have be saved... Ephesians 2:8....
Cosmo
hi
Kisa
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Ellie
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Joelia
🍑🐕
Ken
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Sulaiman
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Peace
thanks
Ellie
..amitabatha..
Ken
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Peace
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Reine
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James
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Reine
how re u Reine Balla
James
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Peace
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James
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Peace
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James
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Tafadzwa
Define the term Biology element atom
James
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Rons
Do you really no the one you text with.
Israel
I'm fine James, just boredom want to finish me!!
Reine
what is a cell of a bacteria called
Sahfe Reply
what is genotype
James
genotype: this is the combination of alleles an organism has for a given characteristic..
Cosmo
what is maiotic
Gabriel Reply
what is sexual reproduction
Gabriel
is system which usually happens to sexual things
GABRIEL
what are the effects of concentration gradient in the uptake of water by plant's
Harleen Reply
ls it ok if you have sex during pregnancy
Kags Reply
no
Bernard
yes!!!
Yazi
Yes
Babie
hello
Cabdi
Babie Maseuse .. Hello .. how are you ?
kf
yes it make the baby's strength stay longer
REAL
Who are you?
Babie
why not it's nicer and more enjoyable more than ok for the woman
Lamin
danso from the Gambia and you why do you ask
Lamin
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Lamin
unless medically advised to stop or hault and those conditions are also applicable to certain problem in pregancies. Pls any further comment pls never hesitate to ask
Lamin
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Tony
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Lamin
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Nyakato
Hello
george
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Lamin
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george
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Cosmo
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Cosmo
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Joelia
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Lamin
InshaAllah
Joelia
Marsha Allah
Lamin
yes
James
What is the meaning of organ
Ronald Reply
tissue combined to form organ
zameer
join
Elishs
orga- these are tissues join together to perform a specific functions.
Elishs
then what are tissues
Kags
group of cells working together to perform a particular function
Harleen
tissue are group of cells put together to perform a certain goal
Bernard
Organs are group of tissues working together to perform a specific function
Peter

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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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