Where Photosynthesis Occurs

-
Photosynthesis
Plant photosynthesis occurs in leaves and green stems within specialized cell structures called chloroplasts. One plant leaf is composed of tens of thousands of cells, and each cell contains 40 to 50 chloroplasts. The chloroplast, an oval-shaped structure, is divided by membranes into numerous disk-shaped compartments. These disklike compartments, called thylakoids, are arranged vertically in the chloroplast like a stack of plates or pancakes. A stack of thylakoids is called a granum (plural, grana); the grana lie suspended in a fluid known as stroma.

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. The pigments and enzymes are arranged in two types of units, Photosystem I and Photosystem II. Because a chloroplast may have dozens of thylakoids, and each thylakoid may contain thousands of photosystems, each chloroplast will contain millions of pigment molecules.

related articles:
photosynthesis
how photosynthesis works
photosynthesis variations

Comments

Post a Comment

Popular posts from this blog

Plant: Cell Structure And Function

-
Image
Plant Cell Plant cells contain a variety of membrane-bound structures called organelles. These include a nucleus that carries genetic material; mitochondria that generate energy; ribosomes and rough endoplasmic reticulum that manufacture proteins; smooth endoplasmic reticulum that manufactures lipids used for making membranes and storing energy; and a thin lipid membrane that surrounds the cell. Plant cells also contain chloroplasts that capture energy from sunlight and a single fluid-filled vacuole that stores compounds and helps in plant growth. Plant cells are surrounded by a rigid cell wall that protects the cell and maintains its shape. The tremendous variety of plant species is, in part, a reflection of the many distinct cell types that make up individual plants. Fundamental similarities exist among all these cell types, however, and these similarities indicate the common origin and the interrelationships of the different plant species. Each individual plant cell is at
Read more

Monocot and Dicot Seeds

-
Image
Monocotyledons (monocots) and dicotyledons (dicots) make up the two large groups of flowering plants, differentiated by their seed structures. Monocot seeds contain one cotyledon, or embryonic leaf. When these seeds germinate, the cotyledon remains below ground, absorbing nutrients from the endosperm, the starchy food supply in the seed. The coytledon transports these nutrients to the developing seedling. Dicot seeds contain two coytledons, which absorb and store the nutrients from the endosperm before the seed germinates. The cotyledons, thick with stored nutrients, emerge above ground during germination, and then transport the stored nutrients to the developing seedling. For a brief time, the cotyledons also serve as the first photosynthesizing leaves, but they wither and die when the true leaves emerge. related articles: flower flower variations in structure flower sexual reproduction flower pollination and fertilization flowering and the life cycle evolution of flowers angios
Read more

Parts of a flower

-
Image
All flowers share several basic features. Sepals, protective coverings that are closed over the bud before it blooms, are the outermost flower parts. One step inward lie the petals, which serve to attract pollinators using both coloration and scent-producing glands. Inside the petals are the flower's sexual organs, the stamens and pistil. Each stamen, the pollen producing part of the flower, includes an anther and a filament. At the center of the flower is the pistil, composed of a stigma, a style, and an ovary. Within the ovary is a small cavity that contains the ovule, an egg-shaped structure that, when fertilized, eventually becomes a seed. Flowers typically are composed of four parts, or whorls, arranged in concentric rings attached to the tip of the stem. From innermost to outermost, these whorls are the (1) pistil, (2) stamens, (3) petals, and (4) sepals. Pistil The innermost whorl, located in the center of the flower, is the female reproductive structure, or pistil. Often va
Read more