Sept. 6th; The Plant Cells and Tissue

In this lesson we learn about what makes up plant cells and tissue.

The plant cell is made up of a rigid cell walls and protoplast which contains cytoplasm, membrance bound organelles, a system of membrane, and non-membrane bound things.

The membrane bound organelles consist of things such as mitochondria and plastids. Plastids are only found in plants and algea. They are surrounded by two membranes; the internal system of membranes form flattened sacs called thylakoids, when theses are stacked up they are called grana.

The direct movement of organelles is known as Cytoplastic Streaming. It is a good idea for chloroplast to be able to move around in the cell to increase photosynthesis, when in low light, or to decrease photo damage, when in high light.

Chloroplasts are the only Plastids with Thylakoids and Grana, but there are other types of Plastids that include: Chromoplasts and Leucoplasts.

Chromoplasts
Contain no chlorophyll and retain carotenoid pigment. The chromoplasts are responsible for yellow, orange, and red colors of plants.

Leucoplasts
Are the least differentiated and contain no pigment. They synthesis/store starch, oils, or proteins.

Helpful Video on various Plastids

Plastid Conversions show that plastids can interconverse between these types of plastids. Here is where we see etioplast show up. They are chloroplasts that lack chlorophyll, so technically they are leucoplasts. Chloroplasts convert to etioplasts when under stress.

Vacuoles

Vacuoles are membrance bound organelles that make up 90%-95% of the volume of a cell. As adolesence there are multiple vacuoles that converge into one upon the cell reaching maturity. The membrane encapsolating the vacuole is called tonoplast. The vacuole contains “cell sap” that is a solution of water, saltst, sugars, amino acids, and inorganic ions. They breakdown and recylce macromolecules that are then repurposed in the sell. Also, it is the site for water-soluble pigment deposits and can act as the site where it sequesters toxic secondary metabolites such as; tannins, nicotine, and capsasin, which are used as defense for the plant.

An example of a water soluble pigment is Anthocyanin. This flavenoid, or class of plant pigment having a structure based on flavone, changes color based on the pH and can be seen as red, purple, or blue. The color can be so vivid that it maskes the chlorophyll in leaves. This phenomenon can be see in the ornimental red maple. This can also explain why we see a change of leaf color as seasons change. The down regulation of chlorophyll with the change in temperature and moisture allows the anthocyanin pigments to be visible in leaves.

Cell Wall

The cell wall determine the shape and size of a cell and gives it rigidity. Cell walls are mainly made up of cellulose. The secondary cell wall is deposited by protoplast after the primary wall has stopped growing to size. The secondary cell wall contains lignin, a polymer for structural material, is important for structure and water movement

Three Tissue Systems in Plants

Quick Video on Tissue Systems **Start at 2:32 and stop around 6:49**

  1. Dermal
    Has two sub categories, Epidermis and Protoderm. The  epidermis is covered in cuticle and possesses gaurd cells, trichomese and other specialized cells. The gaurd cells consist of pores and stoma, and the trichomese are little hairs that main purpose is to slow down small herbivores from consuming the plant. The protoderm is meristematic tissue that gives rise to dermal tissue
  2. Ground Tissue
    Has three sub categories, Parenchyma, Collenchyma, and Sclerenchyma. Parenchyma is found in generic plant cells, leaf mesophyll, fruit flesh, and in the cortex and pith, or center, of stems and roots. They are living cells and their functions  include wound healing, advantageous growth, storage, secreation, and are involved in photosynthesis.
    Collenchyma are found in distinct strands right under the epidermis in the stems and petioles. They are living cells with uneven primary walls and their main function is for structure.
    Sclerenchyma can be found anywhere depending on the plant. They are often dead at maturity and contain thick seconday walls. Their main function is for support and structure.
  3. Vascular Tissue
    Has two sub categories which were brought up in a previous lesson; xylem and phloem.
    Xylem, “Tracheary Elements”, and elongated cells with seconday walls. Their function is to bring water, marco-, and micro-nutrients into the cell. They are dead upon maturity and have spiral thickening lignin. There are two types of Xylem; Trachieds and Vessels. Trachieds are long tappered cells with pits found within  all plants including angiospersm and Vessels are grated cells found only in angiosperms.

    Tracheid and Vessel
    “Tracheids and Vessels”

    Phloem, “Sieve Elements”, are elongated cells with primary cell walls and are living at maturity, but they do not have a nucleus. They have companion cells that bracket to the seive tube. These companion cells control the metabolic function inside.

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