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Section 8-1
Section 8-2
Section 8-3
Plants and some other types of organisms are able to use light energy from the sun to produce food. -Organisms such as plants, which make their own food, are called autotrophs -heterotrophs obtain energy from the foods they consume.
One of the principal chemical compounds that cells use to store and release energy is ATP. The characteristics of ATP make it exceptionally useful as the basic energy source of all cells. When the bond between the second and third phospahate group is broken, energy is released. ADP is similiar to ATP except it only has two phosphate groups. When a third is added, it becomes ATP.
One way cells use the energy provided by ATP is to carry out active transport. Energy from ATP powers other important events in the cell, including the synthesis of proteins and nucleic acids and responses to chemical signals at the cell surface. But cells only have a little bit of ATP because it can be regenerated at any time, so the effiecent thing is to only keep a small amount.
In the process of photosynthesis, plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates—sugars and starches—and oxygen, a waste product. The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists who finally discovered that in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen.
Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.
In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts. Plants gather the sun's energy with light-absorbing molecules called pigments. The plants' principal pigment is chlorophyll. When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. These high-energy electrons make photosynthesis work.
Inside a Chloroplast, contain saclike photosynthetic membranes called thylakoids Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters known as photosystems. These photosystems are the light-collecting units of the chloroplast.
Scientists describe the reactions of photosystems in two parts: the light-dependent reactions and the light-independent reactions, or Calvin cycle. The light-dependent reactions take place within the thylakoid membranes. The Calvin cycle takes place in the stroma, the region outside the thylakoid membranes. When sunlight excites electrons in chlorophyll, the electron gains a great deal of energy. These electrons gain a great deal of energy and need a carrier molecule to transport it. A carrier molecule is a compound that can accept a pair of high-energy electrons and transfer them along with most of their energy to another molecule. This process is called electron transport,
Factors that affect Photosynthesis : Temperature is a factor. Photosynthesis depends on enzymes that function best between 0C and 35C. Temperatures above or below this range may damage the enzymes, slowing down the rate of photosynthesis. The intensity of light also affects the rate at which photosynthesis occurs. As you might expect, increasing light intensity increases the rate of photosynthesis. Because water is one of the raw materials of photosynthesis, a shortage of water can slow or even stop photosynthesis.
The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.
The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars.
Images from google image search and online textbook
