When does photosynthesis begin

Embedded in the membranes of the thylakoids are hundreds of molecules of chlorophyll, a light-trapping pigment required for photosynthesis. Additional light-trapping pigments, enzymes organic substances that speed up chemical reactions , and other molecules needed for photosynthesis are also located within the thylakoid membranes. Because a chloroplast may have dozens of thylakoids, and each thylakoid may contain thousands of photosystems, each chloroplast will contain millions of pigment molecules.

In the first stage, the light-dependent reaction, the chloroplast traps light energy and converts it into chemical energy contained in nicotinamide adenine dinucleotide phosphate NADPH and adenosine triphosphate ATP , two molecules used in the second stage of photosynthesis.

In the second stage, called the light-independent reaction formerly called the dark reaction , NADPH provides the hydrogen atoms that help form glucose, and ATP provides the energy for this and other reactions used to synthesize glucose. These two stages reflect the literal meaning of the term photosynthesis, to build with light. AThe Light-Dependent Reaction Photosynthesis relies on flows of energy and electrons initiated by light energy.

Electrons are minute particles that travel in a specific orbit around the nuclei of atoms and carry a small electrical charge. Light energy causes the electrons in chlorophyll and other light-trapping pigments to boost up and out of their orbit; the electrons instantly fall back into place, releasing resonance energy, or vibrating energy, as they go, all in millionths of a second.

Chlorophyll and the other pigments are clustered next to one another in the photosystems, and the vibrating energy passes rapidly from one chlorophyll or pigment molecule to the next, like the transfer of energy in billiard balls. Light contains many colors, each with a defined range of wavelengths measured in nanometers, or billionths of a meter.

Certain red and blue wavelengths of light are the most effective in photosynthesis because they have exactly the right amount of energy to energize, or excite, chlorophyll electrons and boost them out of their orbits to a higher energy level.

Other pigments, called accessory pigments, enhance the light-absorption capacity of the leaf by capturing a broader spectrum of blue and red wavelengths, along with yellow and orange wavelengths. None of the photosynthetic pigments absorb green light; as a result, green wavelengths are reflected, which is why plants appear green. Photosynthesis begins when light strikes Photosystem I pigments and excites their electrons.

The energy passes rapidly from molecule to molecule until it reaches a special chlorophyll molecule called P, so named because it absorbs light in the red region of the spectrum at wavelengths of nanometers. Until this point, only energy has moved from molecule to molecule; now electrons themselves transfer between molecules.

P uses the energy of the excited electrons to boost its own electrons to an energy level that enables an adjoining electron acceptor molecule to capture them. The electrons are then passed down a chain of carrier molecules, called an electron transport chain.

The electrons are passed from one carrier molecule to another in a downhill direction, like individuals in a bucket brigade passing water from the top of a hill to the bottom. Each electron carrier is at a lower energy level than the one before it, and the result is that electrons release energy as they move down the chain.

When P transfers its electrons to the electron acceptor, it becomes deficient in electrons. Before it can function again, it must be replenished with new electrons.

Photosystem II accomplishes this task. These pigments transfer the energy of their excited electrons to a special Photosystem II chlorophyll molecule, P, that absorbs light best in the red region at nanometers. Just as in Photosystem I, energy is transferred among pigment molecules and is then directed to the P chlorophyll, where the energy is used to transfer electrons from P to its adjoining electron acceptor molecule.

From the Photosystem II electron acceptor, the electrons are passed through a different electron transport chain. As they pass along the cascade of electron carrier molecules, the electrons give up some of their energy to fuel the production of ATP, formed by the addition of one phosphorous atom to adenosine diphosphate ADP.

D Anthoceros hornwort gametophyte showing unbranched sporophytes; magnification x 2. E Mnium moss gametophyte showing unbranched sporophytes with terminal sporangia capsule ; magnification x 4. F Huperzia clubmoss sporophyte with leaves showing sessile yellow sporangia; magnification x 0. G Dicranopteris fern sporophyte showing leaves with circinate vernation; magnification x 0.

H Psilotum whisk fern sporophyte with reduced leaves and spherical synangia three fused sporangia ; magnification x 0. I Equisetum horsetail sporophyte with whorled branches, reduced leaves, and a terminal cone; magnification x 0.

J Cycas seed plant sporophyte showing leaves and terminal cone with seeds; magnification x 0. Origin of land plants. New York: J. Wiley and Sons, All rights reserved. Part B: courtesy of M. Feist, University of Montpellier. Coleochaete orbicularis. Both the gametophyte and the background are bright green.

The gametophyte has an irregular circular shape and a scalloped edge. It is divided into many box-like segments cells , each with a visible, round nucleus inside. Panel b shows a Chara gametophyte. The organism has branching, tendril-like leaves reaching from a primary stalk. The green leaves are punctuated with small, round, yellow structures. A green liverwort gametophyte, In panel c, is protruding from the soil.

Its four primary stems each diverge into two halves and then branch again at their termini, so that each has a forked end. Panel d shows a hornwort gametophyte. Each green stem resembles a single blade of grass. Panel e shows moss gametophytes with sporophytes protruding from the ground. The gametophytes have small green leaves, and the sporophytes are thin, unbranched, brown stalks. Each sporophyte has a fluorescent orange, oviform capsule called a sporangia perched on top of its stalk.

Panel f shows six clubmoss sporophytes emanating from the ground. Some stand vertically out of the soil, and some curve or have fallen horizontally.

They have many stiff, protruding, spine-like, green leaves. The sporangia are small yellow balls at the base of the leaves. Panel g shows fern sporophytes with many stems covered with small, elongated, symmetrical green leaves. Panel h shows a whisk fern sporophyte with long, straight, green stems beaded with yellow, round synangia along their lengths. In panel i, a horsetail sporophyte is shown. It has a single long stem, which is surrounded by a skirt of green leaves at its base and an elongated, yellow cone at the top.

In Panel j, a large Cycas seed plant sporophyte is shown. Long fronds emanate upwards from the plant's trunk, and in the center of them there is a large mass called the cone. Panel a is a photomicrograph of a gametophyte of a microscopic green alga called Coleochaete orbicularis. Most living things depend on photosynthetic cells to manufacture the complex organic molecules they require as a source of energy.

Photosynthetic cells are quite diverse and include cells found in green plants, phytoplankton, and cyanobacteria. During the process of photosynthesis, cells use carbon dioxide and energy from the Sun to make sugar molecules and oxygen. These sugar molecules are the basis for more complex molecules made by the photosynthetic cell, such as glucose. Then, via respiration processes, cells use oxygen and glucose to synthesize energy-rich carrier molecules, such as ATP, and carbon dioxide is produced as a waste product.

Therefore, the synthesis of glucose and its breakdown by cells are opposing processes. Figure 2 2 in the sky represents the process of photosynthesis. Two arrows are directed outwards from the trees towards the atmosphere.

One represents the production of biomass in the trees, and the other represents the production of atmospheric carbon dioxide CO 2. Arrows emanating from a tree's roots point to two molecular structures: inorganic carbon and organic carbon, which may decompose into inorganic carbon. Inorganic carbon and organic carbon are stored in the soil. This CO2 can return to the atmosphere or enter rivers; alternatively, it can react with soil minerals to form inorganic dissolved carbonates that remain stored in soils or are exported to rivers.

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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Plants are autotrophs, which means they produce their own food. They use the process of photosynthesis to transform water, sunlight, and carbon dioxide into oxygen, and simple sugars that the plant uses as fuel.

These primary producers form the base of an ecosystem and fuel the next trophic levels. Without this process, life on Earth as we know it would not be possible. We depend on plants for oxygen production and food. Learn more about this vital process with these classroom resources. Chlorophyll is a pigment that gives plants their green color, and it helps plants create their own food through photosynthesis. What does a plant leaf have to do with the solar energy panels on the White House?

Producers convert water, carbon dioxide, minerals, and sunlight into the organic molecules that are the foundation of all life on Earth. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.

Skip to content. Image Green Tree Leaves The plant leaves are green because that color is the part of sunlight reflected by a pigment in the leaves called chlorophyll. Photograph courtesy of Shutterstock. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. The process During photosynthesis, plants take in carbon dioxide CO 2 and water H 2 O from the air and soil.