Aim: Study of Whole Mount of Amoeba
Amoeba is a genus of single-celled protozoa known for its
amorphous, constantly changing shape due to the formation of pseudopods.
Classification:
Kingdom: Protista
Phylum: Protozoa
Class: Sarcodina
Genus: Amoeba
External Features and Locomotion:
- Shape: Irregular
and asymmetrical, constantly changing as it moves.
- Pseudopodia: Temporary
cytoplasmic extensions ("false feet") used for locomotion
(amoeboid movement) and feeding (phagocytosis). These can be lobopodia
(broad, blunt).
- Ectoplasm: The
clear, non-granular, outer layer of cytoplasm.
- Endoplasm: The
granular, inner mass of cytoplasm containing organelles.
Internal Structures
(Cytoplasmic Organelles):
·
Nucleus: A single, discoid, biconcave nucleus,
usually visible as a clear, refractile body. It controls cell activities.
·
Contractile Vacuole: A clear, spherical vesicle that collects
excess water from the cytoplasm and expels it from the cell, thus maintaining
osmotic balance (osmoregulation). It periodically swells and then suddenly
contracts.
·
Food Vacuoles: Vary in size and number, containing
ingested food particles (algae, bacteria, other protozoa) undergoing digestion.
They are formed during phagocytosis.
·
Mitochondria: For cellular respiration.
·
Lysosomes: Contain digestive enzymes.
Aim: Study of Whole Mount
of Euglena
Euglena is a genus of flagellate protozoa, unique for possessing
both animal-like (motility, absence of cell wall) and plant-like (chloroplasts,
photosynthesis) characteristics.
Classification:
Kingdom: Protista
Phylum: Protozoa
Class: Mastigophora
Genus: Euglena
External Features and Locomotion:
- Shape: Spindle-shaped
or elongated, typically blunt anteriorly and pointed posteriorly. Its
shape can change due to the flexibility of its pellicle (euglenoid
movement).
- Pellicle: A
flexible, proteinaceous outer covering that maintains shape but allows for
movement.
- Flagellum: A
single, long, whip-like appendage emerging from a reservoir at the
anterior end, used for swimming. A shorter, non-emergent flagellum is also
present.
- Stigma (Eyespot): A
reddish pigment spot located near the reservoir, sensitive to light and
helps in phototaxis (movement towards light).
Internal Structures
(Cytoplasmic Organelles):
·
Nucleus: A single, large, centrally located nucleus.
·
Chloroplasts: Numerous oval or disc-shaped, green
organelles containing chlorophyll, responsible for photosynthesis.
·
Paramylon Granules: Clear, colorless starch-like storage
bodies (polysaccharide unique to Euglena).
·
Contractile Vacuole: Located near the reservoir, collects and
expels excess water.
·
Reservoir (Gullet): A flask-shaped invagination at the
anterior end, from which the flagellum originates.
Aim: Study of Whole Mount of Paramecium
Paramecium is a genus of ciliate protozoa, well-known for its
distinctive slipper-like shape and rapid, coordinated movement using cilia.
Classification:
Kingdom: Protista
Phylum: Protozoa
Class: Ciliata
Genus: Paramecium
External Features and Locomotion:
- Shape: Slipper-shaped
or elongated oval, with a rounded anterior and a somewhat pointed
posterior end. Its shape is maintained by a firm pellicle.
- Pellicle: A
strong, elastic outer membrane with hexagonal depressions containing
cilia.
- Cilia: Thousands
of short, hair-like appendages covering the entire body surface, used for
locomotion (coordinated beating) and creating feeding currents.
- Oral Groove: A
prominent indentation on one side of the body, leading to the mouth
(cytostome) and gullet (cytopharynx). Cilia within the oral groove sweep
food particles into the gullet.
- Cytostome (Mouth): The
actual cell mouth at the end of the oral groove.
- Cytoproct (Anus): A
temporary posterior opening for the expulsion of undigested food.
Internal Structures (Cytoplasmic Organelles):
- Nuclei: Paramecium is heterokaryotic,
possessing two nuclei:
- Macronucleus: Large,
kidney-bean shaped, polyploid, controls vegetative functions.
- Micronucleus: Small,
typically spherical, diploid, involved in genetic recombination during
sexual reproduction (conjugation). Often nestled in a depression of the
macronucleus.
- Contractile
Vacuoles: Two star-shaped (with
radiating canals) contractile vacuoles, one at each end of the cell, for
osmoregulation. They rhythmically collect and expel water.
- Food
Vacuoles: Numerous, spherical
vacuoles that circulate within the cytoplasm along a specific path
(cyclosis) as digestion occurs.
- Trichocysts: Small, spindle-shaped organelles located just
beneath the pellicle. When stimulated, they discharge long, sharp
filaments, used for defense or anchorage.
Aim: Study of Sycon
Sycon (also known as Scypha) is a genus of
calcareous sponges belonging to the class Calcarea.
Classification:
Kingdom: Animalia
Phylum: Porifera
Class: Calcarea
Order: Leucosolenida
Genus: Sycon
External Morphology:
·
Shape and Size: Sycon typically has a vase-like or
cylindrical body, usually a few centimeters in height. It often grows in
clusters, appearing bushy.
·
Color: Varies, but commonly pale yellow, white,
or grayish.
·
Ostia: Numerous small pores on the outer surface
(dermal ostia) through which water enters the sponge. These are visible under
magnification.
·
Osculum: A single, larger opening at the top of the
cylinder, surrounded by a fringe of large monaxon spicules (oscular fringe).
This is where filtered water exits.
·
Attachment: The base of the sponge is attached to a
substratum (rocks, shells, algae) by a holdfast.
Internal
Morphology
·
Spongocoel (Paragastric Cavity): The central, spacious cavity within the
sponge body, opening to the outside via the osculum. It is lined by choanoderm
in asconoid sponges, but in Sycon (syconoid type), it is lined by pinacoderm.
·
Radial Canals
(Flagellated Canals): Numerous,
finger-like invaginations that extend outwards from the spongocoel towards the
dermal surface. These canals are lined by choanocytes (collar cells) and are
the sites of water filtration and feeding.
·
Incurrent Canals: Spaces between the radial canals, lined by
pinacocytes. Water enters these canals from the outside through dermal ostia.
·
Prosopyles: Small pores that connect the incurrent
canals to the radial canals.
·
Apopyle: Larger openings that connect the radial
canals to the spongocoel.
·
Dermal Pores
(Ostia): Openings on
the external surface that lead into the incurrent canals.
·
Dermal Membrane: The outer layer of the sponge (dermal
epithelium) covering the external surface.
·
Mesohyl (Mesoglea): A gelatinous, non-cellular matrix found
between the outer pinacoderm and the inner choanoderm layers. It contains
various amoeboid cells (amoebocytes) and spicules.
Microscopic
Structure:
·
Pinacoderm: The outermost protective layer, composed
of flattened cells called pinacocytes. It lines the exterior surface and the
incurrent canals, and the spongocoel.
·
Choanoderm: The inner layer lining the radial canals,
composed of flagellated collar cells called choanocytes. Each choanocyte has a
flagellum surrounded by a collar of microvilli. The beating of flagella creates
the water current, and the collar filters food particles.
·
Amoebocytes: Various types of amoeboid cells found in
the mesohyl, responsible for functions like:
o Scleroblasts: Secrete spicules (e.g., calcoblasts for
calcareous spicules).
o Archaeocytes: Totipotent cells involved in regeneration,
digestion, and reproduction.
o Trophocytes: Store food.
o Collencytes: Secrete collagen fibers.
·
Porocytes: Tubular cells that form the dermal ostia,
allowing water to enter the incurrent canals.
·
Spicules: Skeletal elements made of calcium
carbonate. In Sycon, spicules are characteristic and can be:
o Monaxons: Straight, rod-like (e.g., oxeas - pointed
at both ends, or styles - pointed at one end). These form the oscular fringe.
o Triaxons
(Triradiates): Three-pointed
spicules.
o
Tetraxons
(Quadriradiates): Four-pointed
spicules (less common in Sycon than triradiates).
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