Sunlight is necessary for plants to grow, and to provide energy to warm the earth's atmosphere. Light intensity controls plant growth. Light duration affects plant flowering and animal/insect habits.
To begin photosynthesis, the chlorophyll molecule in photosystem II is excited by sunlight and the energy produced helps to break down a water molecule.
Easy Science for Kids Photosynthesis: How Plants Make Food and Energy
Bacteria with only a type I photosystem (PSI), such as green-sulfur bacteria, can be true photoautotrophs. Light energy oxidizes the reaction center chlorophyll, which reduces the the electron carrier NAD+ to make NADH. The oxidized reaction center chlorophyll must then be reduced by electrons from a chemical electron donor, such as hydrogen sulfide (H2S). The oxidized reaction center chlorophyll pulls electrons from H2S down the photosynthetic electron transport chain, which generates a proton gradient to make ATP. Thus green-sulfur bacteria use light energy to produce both ATP and reducing power; both are required for carbon fixation (reduction of CO2 to carbohydrate). However, they are limited by the availability of a suitable electron donor such as H2S.
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organisms (photoautotrophs) use light energy to make both ATP and reduced electron carriers (NADH or NADPH). The reduction of carbon dioxide (CO2) to carbohydrate (CH2O) requires both ATP and reducing power in the form of NADPH or NADH (NADP+ is NAD+ with a phosphate group added, and is used by chloroplasts instead of NAD+). The earliest phototrophs and photosynthetic organisms were prokaryotes with single photosystems that did not generate oxygen. Two different types of photosystems evolved, that were combined in cyanobacteria. One of the two photosystems in cyanobacteria evolved the power to oxidize water molecules as a source of electrons, releasing O2.
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We will present photosynthesis in two parts: this page will discuss the reactions that convert light energy to chemical energy in the form of ATP and reduced electron carriers (NADH or NADPH). Both are needed for carbon fixation reactions (the reduction of inorganic carbon to make organic carbon molecules) presented in the next page. An important by-product of the light reactions is the generation of oxygen gas. In the chemical equation above, the oxygen atoms in water are bolded in red to show that these are the source of the oxygen atoms in oxygen gas. Oxygenic photosynthesis evolved to take electrons from water to make oxygen gas, and ultimately give the electrons to carbon dioxide to form organic (reduced) carbon molecules (food) – the exact reverse of aerobic respiration, which takes electrons from organic carbon molecules and ultimately gives them to oxygen gas to make water.
What is chlorophyll and what is photosynthesis
The highly energetic NADPH molecule is then fed into the Calvin Cycle to conduct carbon fixation.
The Second Stage
The second stage of photosynthesis, which takes place in the stroma of the chloroplast, can occur without the presence of sunlight.
How does sunlight affect plant growth
Phytoplankton and kelp are both part of the family and have no roots, stems or leaves like land plants and can only grow in shallow water where they can get what they need from sunlight.