Biology For Dummies
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Plants have a root system, a stem or trunk, branches, leaves, and reproductive structures (sometimes flowers, sometimes cones or spores, and so on). Most plants are vascular, which means they have a system of tubules inside them that carry nutrients around the plant.

Vascular plants are differentiated from plants such as algae, which do not have a vascular system. Most vascular plants are seed plants, and seed plants are most often the model used in biology and botany textbooks and the type of plant with which you're probably the most familiar.

The basic structures of a vascular plant.

The basic structures of a vascular plant.

Plant tissues

There are two main types of seed plants: gymnosperms (conifers, which produce pinecones) and angiosperms (flowering plants). Of the 500,000 different species of plants, more than 300,000 are flowering plants.

Flowering plants are divided by how many cotyledons they have. Cotyledons are the tissues that provide nourishment to a developing seedling. Flowering plants can be monocotyledons, which means they have one cotyledon, or dicotyledons, which means they have two cotyledons.

Three types of plant tissues exist:

  • Vascular tissue, which consists of xylem (pronounced “zi-lem”) and phloem (pronounced “flow-em”) — the main tubes through which nutrients are transported

  • Dermal tissue, which includes the outer cells (epidermis), guards cells surrounding a stoma, and special cells found on the outer surface of plants, such as hair cells or cells that cause a stinging sensation

  • Ground tissue, which consists of three types of cells:

    • Parenchyma cells are the most common ground cells. They are involved in many basic cell functions including storage, photosynthesis, and secretion.

    • Collenchyma cells have thick cell walls and are involved in mechanical support.

    • Sclerenchyma cells are similar to collenchyma cells, but their walls are even thicker.

Plant cells

Plant cells differ from animal cells in that they have a cell wall. Animal cells have a cell membrane as the outer membrane of a cell; plant cells also have a cell membrane, but they have the additional, more rigid cell wall surrounding it. Here is a list of what you’d find in a typical animal cell. Then, compare it to what you’d find in a typical plant cell.

Animal cells have these organelles and suborganellar structures:

  • Centrioles

  • Cell membrane

  • Nucleus and nucleolus

  • Mitochondria

  • Golgi apparatus

  • Small vacuoles

  • Lysosomes

  • Endoplasmic reticulum

  • Ribosomes

Plant cells have all the organelles an animal cell has, plus:
  • Cell wall (cellulose in cell wall provides structure and rigidity)

  • Large vacuole (for storage of large molecules of starch)

  • Chloroplasts, which contain chlorophyll (the green pigment in plants)

The reason that plant cells have the extra structures is that plants harness and store their energy in a different way than animals do. First of all, plants get their energy from the sun, whereas the start of the animal food chain is a plant. Animals cannot harness energy from the sun directly. The plants harness energy from the sun using chloroplasts, and they store the energy they convert into carbohydrate molecules in the cell wall and vacuoles.

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