ULTRASTRUCTURE OF ALGAE

ULTRASTRUCTURE OF ALGAE

Cell wall

·       The Algal cell is bounded by a thin, cellulose cell wall.

·     Cellulose is the major component of the Algal cell wall but in some cases some other components like Glycoprotein or Agar or Calcium carbonate or Alginic acid also present in Algal cell wall along with Cellulose.

·       Cellulose layer is finely striated with parallel Cellulose fibrils.

·     In many species of Algae, there is a Pectose layer external to it which dissolves in water and forms a mucilaginous Pectin layer.

·       Cell wall is absent in the Algae belonging to the Phylum Euglenophyta.

Plasmalemma

·   Plasmalemma is present just below the Cell wall and consists of two opaque layers which remain separated by less opaque zone.

Protoplast

·       Protoplast is bounded by Plasmalemma.

·  Protoplast is differentiated into Cytoplasm, Nucleus, Chloroplast with one or more Pyrenoids, Mitochondria, Golgi bodies, two Contractile vacuoles, a red Eye spot and two Flagella.

Nucleus

·       The Nucleus contains the genetic material DNA of the cell.

· In most Algae, the DNA molecules exist as linear strands that are condensed into obvious Chromosomes only at the time of Nuclear division (Mitosis).

·       In all Algae, the two membranes that surround the Nucleus are referred to as the Nuclear Envelope.

      The Nuclear envelope typically has specialized nuclear pores that regulate the movement of molecules into and out of the nucleus.

Ribosomes

·       Ribosome is the site of Protein synthesis (Translation) and 80 S type of Ribosomes are present in Algae.

Mitochondria

·      Mitochondria (Power house of cell) are the sites where food molecules are broken down and carbon-di-oxide, water, and chemical bond energy (ATP) are released, a process called Cellular respiration

Endoplasmic Reticulum

·       The Endoplasmic reticulum is a complex membranous system that forms Intracellular compartments.

·       It also acts as a Transport system within the cell.

·       It serves as a site for synthesizing Fats, Oils and Proteins.

Golgi apparatus

·    Golgi apparatus, a series of flattened, membranous sacs that are arranged in a stack, performs four distinct functions:

a)     It sorts many molecules synthesized elsewhere in the cell.

b)    It produces carbohydrates, such as cellulose or sugars, and sometimes attaches the sugars to other molecules.

c)     It packages molecules in small vesicles.

d)     It marks the vesicles so that they are routed to the proper destination.

Chloroplast

·    Plastids are Cytoplasmic organelles of Photosynthetic protists and Plants that often possess pigments such as Chlorophylls and Carotenoids, and are the sites of synthesis and storage of food reserves. The most important type of plastid is the Chloroplast.

·   Chloroplast is the site of Photosynthesis and it contains Photosynthetic pigment Chlorophyll, Carotenoids and Phycobiliproteins.

·   Chloroplasts are Oval or Biconvex in shape. Chloroplasts are Double-membrane organelle with the presence of Outer membrane and Inner membrane.

·    The pigments of Chloroplasts gather Light energy to produce ATP and form Sugar from Carbon-di-oxide.

·       Algal chloroplast has Thylakoid membrane, Pyrenoid and Stigma or Eyespot.    

i) Thylakoid membrane

·       The third membrane in Chloroplast is folded into small, disclike sacs called Thylakoids.

·       The Chlorophyll pigments are found in the Thylakoid membranes.

·       Thylakoid is the sight for the process of Light-dependent reactions of the Photosynthesis process.

ii) Pyrenoids

·      The Chloroplasts of many Algae contain a Pyrenoid, a dense region of Protein surrounded by Starch or another Polysaccharide.

·       Pyrenoids participate in Polysaccharide synthesis.

iii) Stigma or Eyespot

·      The anterior side (front side) of the Chloroplast contains a tiny spot of Orange or Reddish colour called Stigma or Eyespot.

·     The Eyespot is made of curved pigmented plate. The plate contains 2 - 3 parallel rows of droplets or granules containing Carotenoids.

·       Eyespot is Photoreceptive organ concerned with the direction of the movement of Flagella.

Contractile Vacuole

·     Contractile vacuoles function as Osmoregulatory organelles (active regulation of Osmotic pressure) to regulate the Water content in Algae that live in Hypotonic environments, such as freshwater lakes.  

Vacuoles

·      Vacuoles are membranous sacs that store many different substances, depending on the organism and its metabolic state.

Lysosomes

·    Lysosomes is a specialized vacuole that contains Digestive enzymes that break down old organelles, cells or cellular components.

Flagella

·       The anterior part of Algal thallus bears two flagella.

·       Both the flagella are Whiplash or Acronematic type, equal in size.

·     Each flagellum originates from a Basal granule or Blepharoplast and comes out through a fine canal in Cell wall.

·       Algal flagella confer motility to the Algal cell.