Plants get most of the energy they need to survive via a two-stage process called photosynthesis. In the first stage, called the light-dependent reaction, sunlight is converted into two molecules.
In the second stage, called the light-independent reaction, these molecules work together to form and synthesize glucose. Glucose is a sugar that plants use for energy.
The cells of plants and animals differ slightly, in structure. For example, certain plant cells contain organelles called plastids, which help the cells store energy. Chloroplasts are plastids that contain the green pigment chlorophyll. This pigment is responsible for absorbing sunlight during the process of photosynthesis. Photosynthesis is a two-stage process. The first stage of photosynthesis is called the light-dependent reaction because sunlight must be present in order for the reaction to occur.
Before learning the details of how photoautotrophs convert light energy into chemical energy, it is important to become familiar with the structures involved. Chemical equation for photosynthesis : The basic equation for photosynthesis is deceptively simple.
In reality, the process includes many steps involving intermediate reactants and products. Glucose, the primary energy source in cells, is made from two three-carbon GA3P molecules. In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells.
The process of photosynthesis occurs in a middle layer called the mesophyll. The stomata are typically located on the underside of the leaf, which minimizes water loss. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes. Structure of a leaf cross-section : Photosynthesis takes place in the mesophyll. The palisade layer contains most of the chloroplast and principal region in which photosynthesis is carried out.
The airy spongy layer is the region of storage and gas exchange. The stomata regulate carbon dioxide and water balance. In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. For plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double membrane envelope composed of an outer membrane and an inner membrane.
Within the double membrane are stacked, disc-shaped structures called thylakoids. Embedded in the thylakoid membrane is chlorophyll, a pigment that absorbs certain portions of the visible spectrum and captures energy from sunlight. Chlorophyll gives plants their green color and is responsible for the initial interaction between light and plant material, as well as numerous proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen.
Structure of the Chloroplast : Photosynthesis takes place in chloroplasts, which have an outer membrane and an inner membrane. Stacks of thylakoids called grana form a third membrane layer. Light-dependent and light-independent reactions are two successive reactions that occur during photosynthesis. Just as the name implies, light-dependent reactions require sunlight. 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. B The transformations of organic to inorganic carbon through decomposition and photosynthesis continue in rivers; here, CO2 will re-exchange with the atmosphere degassing or be converted to dissolved carbonates.
These carbonates do not exchange with the atmosphere and are mainly exported to the coastal ocean. Pigments are molecules that bestow color on plants , algae and bacteria, but they are also responsible for effectively trapping sunlight. Pigments of different colors absorb different wavelengths of light. Below are the three main groups.
Photosynthetic eukaryotic organisms contain organelles called plastids in their cytoplasm. The double-membraned plastids in plants and algae are referred to as primary plastids, while the multiple-membraned variety found in plankton are called secondary plastids, according to an articlein the journal Nature Education by Cheong Xin Chan and Debashish Bhattacharya, researchers at Rutgers University in New Jersey.
Plastids generally contain pigments or can store nutrients. Colorless and nonpigmented leucoplasts store fats and starch, while chromoplasts contain carotenoids and chloroplasts contain chlorophyll, as explained in Geoffrey Cooper's book, " The Cell: A Molecular Approach " Sinauer Associates, Photosynthesis occurs in the chloroplasts; specifically, in the grana and stroma regions. The grana is the innermost portion of the organelle; a collection of disc-shaped membranes, stacked into columns like plates.
The individual discs are called thylakoids. It is here that the transfer of electrons takes place. The empty spaces between columns of grana constitute the stroma. Chloroplasts are similar to mitochondria , the energy centers of cells, in that they have their own genome, or collection of genes, contained within circular DNA.
These genes encode proteins essential to the organelle and to photosynthesis. Like mitochondria, chloroplasts are also thought to have originated from primitive bacterial cells through the process of endosymbiosis.
0コメント