Practical 1: Non-chordates
Table of Contents
1. Study of Protozoa Whole Mounts
This exercise involves identifying and drawing prepared slides of common protozoans.
A. Amoeba
- Principle: To observe the key features of an amoeboid protozoan.
- Observation: Look for an irregular, shapeless mass of protoplasm.
- Identification Points (Draw and Label):
- Pseudopodia: Finger-like, blunt extensions of the cytoplasm (ectoplasm and endoplasm) used for locomotion and feeding.
- Plasma Membrane: The thin outer boundary.
- Nucleus: A single, large, disc-shaped nucleus, usually stained dark.
- Contractile Vacuole: A clear, spherical vacuole for osmoregulation.
- Food Vacuoles: Small, dark vesicles containing food particles.
[Image of Amoeba proteus labeled diagram]
B. Euglena
- Principle: To observe the features of a flagellated protozoan, which is a connecting link between plants and animals.
- Observation: Look for a small, green, spindle-shaped organism.
- Identification Points (Draw and Label):
- Pellicle: A flexible outer covering, maintaining its shape.
- Flagellum: A single, long, whip-like structure at the anterior end for locomotion.
- Stigma (Eyespot): A small, reddish pigment spot that is light-sensitive.
- Chloroplasts: Green, elongated structures for photosynthesis.
- Nucleus: A large, centrally located nucleus.
- Contractile Vacuole: A vacuole at the anterior end.
[Image of Euglena labeled diagram]
C. Paramecium
- Principle: To observe the features of a ciliated protozoan.
- Observation: Look for a slipper-shaped organism, often stained pink or purple.
- Identification Points (Draw and Label):
- Shape: "Slipper-shaped," with a blunt anterior and pointed posterior.
- Cilia: Numerous small, hair-like projections covering the entire body for locomotion.
- Oral Groove: A large depression on one side leading to the cytostome (mouth).
- Macronucleus: A large, kidney-bean-shaped nucleus controlling metabolic functions.
- Micronucleus: A small, spherical nucleus (often hard to see) involved in reproduction.
- Contractile Vacuoles: Two "star-shaped" vacuoles (one at each end) for osmoregulation.
[Image of Paramecium caudatum labeled diagram]
2. Reproduction in Paramecium (Slides)
A. Binary Fission (Asexual)
- Principle: To observe the transverse binary fission in *Paramecium*.
- Observation: Look for a single *Paramecium* that is elongated and "pinched" in the middle.
- Identification Points:
- The macronucleus elongates and divides amitotically.
- The micronucleus divides mitotically.
- A transverse furrow (constriction) appears in the middle of the cell.
- The cell divides into two smaller daughter cells (a proter and an opisthe).
[Image of Paramecium binary fission stages]
B. Conjugation (Sexual)
- Principle: To observe sexual reproduction in *Paramecium* for genetic recombination.
- Observation: Look for two *Paramecium* individuals fused together along their oral grooves.
- Identification Points:
- Two cells (conjugants) are attached.
- The macronucleus degenerates (disappears).
- The micronucleus undergoes meiosis to form haploid pronuclei.
- A migratory (male) pronucleus from each cell crosses over and fuses with the stationary (female) pronucleus of the other.
- This forms a diploid zygote nucleus (synkaryon).
- The cells then separate (exconjugants) and undergo further divisions to restore the normal nuclear setup.
3. Examination of Pond Water for Protista
- Principle: To observe the wide diversity of living protists and other microorganisms in a natural aquatic ecosystem.
- Requirements: Pond water sample (ideally with algae or decaying leaves), microscope, glass slide, coverslip, dropper.
- Procedure:
- Collect a pond water sample.
- Place one drop of the sample on a clean glass slide.
- Gently lower a coverslip over the drop, avoiding air bubbles.
- Observe under the microscope, starting with low power and then moving to high power.
- Reduce the diaphragm aperture (light) to increase contrast, making transparent organisms visible.
- Observation: Look for, identify, and draw various moving organisms. Common examples include:
- Ciliates: *Paramecium*, *Vorticella* (bell-shaped, on a stalk), *Stentor* (trumpet-shaped).
- Flagellates: *Euglena*, *Volvox* (large, green, spherical colonies).
- Amoeboids: *Amoeba*.
- Algae: Diatoms (geometric shapes), *Spirogyra* (spiral chloroplasts).
- Metazoans: Rotifers (wheel-like ciliary organs), *Daphnia* (water fleas), *Cyclops*.
4. Study of Museum Specimens (Non-chordate Phyla)
This is a "spotting" exercise. You must identify the specimen, classify it (Phylum and Class), and list 2-3 key reasons for your identification.
| Phylum | Specimen Example | Key Identification Points (Comments) |
|---|---|---|
| Porifera | Sycon (Scypha) | 1. Vase-shaped body. 2. Attached to a substratum. 3. Body surface is porous with spicules. 4. A large opening (osculum) at the top. |
| Cnidaria | Obelia (Colony) | 1. Plant-like, branching colony (polymorphic). 2. Shows polyps (hydranths for feeding) and blastostyles (for reproduction). |
| Cnidaria | Aurelia (Jellyfish) | 1. Bell-shaped or umbrella-shaped medusa. 2. Four oral arms and marginal tentacles. 3. Four horseshoe-shaped gonads are visible. |
| Platyhelminthes | Taenia solium (Tapeworm) | 1. Dorsoventrally flattened, ribbon-like body. 2. Body divided into scolex (head), neck, and proglottids (segments). 3. Scolex has suckers and hooks for attachment. |
| Platyhelminthes | Fasciola hepatica (Liver Fluke) | 1. Dorsoventrally flattened, leaf-like body. 2. Shows two suckers (oral and ventral) for attachment. 3. Incomplete digestive tract. |
| Nemathelminthes | Ascaris (Roundworm) | 1. Long, cylindrical, unsegmented body, pointed at both ends. 2. Sexual dimorphism: Female is longer and straight; Male is shorter with a curved posterior. |
| Annelida | Nereis (Clamworm) | 1. Metamerically segmented body. 2. Each segment (except head and tail) bears a pair of fleshy, paddle-like appendages called parapodia for swimming. |
| Annelida | Hirudinaria (Leech) | 1. Dorsoventrally flattened, segmented body. 2. Lacks setae and parapodia. 3. Has an anterior sucker (oral) and a posterior sucker for attachment and locomotion. |
| Arthropoda | Palaemon (Prawn) | 1. Body has a hard exoskeleton. 2. Body divided into an anterior cephalothorax (head and thorax fused) and a posterior abdomen. 3. Has jointed appendages. |
| Arthropoda | Limulus (King Crab) | 1. "Living fossil." 2. Body is boat-shaped, covered by a hard carapace. 3. Has a long, spike-like telson (tail). |
| Mollusca | Pila (Apple Snail) | 1. Asymmetrical, soft body. 2. Body is enclosed in a spirally coiled shell. 3. Possesses a muscular foot for creeping. |
| Mollusca | Octopus | 1. Soft, unsegmented body with a large head and a bag-like visceral mass. 2. Shell is absent. 3. Head bears 8 long, flexible arms (tentacles) with suckers. |
| Echinodermata | Asterias (Starfish) | 1. Pentamerous radial symmetry (star-shaped). 2. Body has a central disc and five arms. 3. Spiny-skinned (exoskeleton of calcareous plates). 4. A small, button-like madreporite is visible on the aboral (upper) surface. |
5. Study of Ctenophora Specimen
- Specimen Example: Pleurobrachia (Sea Gooseberry)
- Principle: To identify the features of the phylum Ctenophora (comb jellies).
- Identification Points:
- A transparent, gelatinous, pear-shaped body.
- Possesses eight ciliated comb rows (ctenes) on the body for locomotion, which may be visible.
- Has a pair of long, branched tentacles that are retractile into sheaths (unlike Cnidaria).
- Lacks stinging cells (nematocysts).
6. Mounts from Periplaneta (Cockroach)
This involves observing prepared permanent slides or fresh mounts of dissected cockroach parts.
A. Mouth Parts (Biting and Chewing Type)
- Observation: Look for the five major components arranged around the mouth.
- Identification Points (Draw and Label):
- Labrum: The flat, flap-like "upper lip."
- Mandibles: A pair of hard, toothed, pincer-like jaws for grinding food.
- Maxillae: A pair of accessory jaws, each with a 5-segmented palp (maxillary palp) for holding and sensing food.
- Labium: The "lower lip," formed by fused secondary maxillae, bearing a pair of 3-segmented palps (labial palps).
- Hypopharynx: A tongue-like structure within the mouth.
B. Digestive System
- Observation: A long tube divided into three distinct regions.
- Identification Points (Draw and Label):
- Foregut: Includes the pharynx, esophagus, a large crop (for storage), and a muscular gizzard (proventriculus) for grinding.
- Midgut (Mesenteron): A narrower tube. At its junction with the gizzard are 6-8 finger-like hepatic caeca (for digestive enzymes).
- Hindgut: At its junction with the midgut are numerous thin, thread-like Malpighian tubules (excretory organs). The hindgut consists of the ileum, colon, and rectum.
[Image of Periplaneta (cockroach) digestive system labeled]
C. Nervous System
- Observation: A "ladder-like" nervous system typical of arthropods.
- Identification Points (Draw and Label):
- Supra-oesophageal Ganglion (Brain): A large ganglion located above the esophagus.
- Circum-oesophageal Connectives: Nerves that loop around the esophagus, connecting the brain to the sub-oesophageal ganglion.
- Ventral Nerve Cord: A double nerve cord running along the ventral side of the body.
- Segmental Ganglia: Paired, fused ganglia in each thoracic and abdominal segment, giving it a ladder-like appearance.
[Image of Periplaneta (cockroach) nervous system labeled]