Test 4

Embryonic Layers & Body Plans

• Diploblasts: 2 germ layers (ectoderm + endoderm) → Cnidarians, Ctenophores

• Triploblasts: 3 germ layers (ectoderm, mesoderm, endoderm) → all other animals

• Body Cavities:

  • Acoelomate – no body cavity (e.g. flatworms/Platyhelminthes)

  • Pseudocoelomate – cavity between mesoderm and endoderm (e.g. Nematodes)

  • Coelomate (Eucoelomate) – cavity fully within mesoderm (e.g. Annelids, Arthropods, Vertebrates)

🔄 Development: Protostomes vs Deuterostomes

• Protostome: Mouth develops first (e.g. Annelids, Arthropods, Mollusks)

• Deuterostome: Anus develops first (e.g. Echinoderms, Chordates)

• Germ Layers:

  • Ectoderm → skin, nervous system

  • Mesoderm → muscles, bones, circulatory

  • Endoderm → gut lining, organs

🌊 Echinoderms

• Radial symmetry (adults), bilateral (larvae)

• Water vascular system, tube feet, no head/brain

• Deuterostomes (like chordates)

• Endoskeleton of calcium carbonate

🪱 Worm Movements (3 Types)

• Annelids: segmented, use circular & longitudinal muscles

• Nematodes: thrash side-to-side (longitudinal muscles only)

• Flatworms: glide using cilia and muscle contractions

🧬 Hox Genes

• Master regulators of body plan

• Found in almost all animals

• Determine head-tail axis, segment identity

• Mutations → body part misplacement

🧠 Mammals vs Amphibians

• Shared: vertebrates, tetrapods, lungs, closed circulatory system

• Differences:

  • Mammals: hair, endothermic, mammary glands

  • Amphibians: moist skin, external fertilization, metamorphosis

🐸 Amphibians vs Reptiles (Respiration)

• Amphibians: cutaneous + lung breathing

• Reptiles: lungs only (more efficient, less skin respiration)

🦎 Mammals vs Reptiles (Hearing)

• Mammals: 3 middle ear bones (malleus, incus, stapes)

• Reptiles: 1 bone (stapes/columella)

🥚 Amniotic Egg Layers

1. Amnion – fluid cushion

2. Chorion – gas exchange

3. Allantois – waste storage

4. Yolk sac – nutrients

💧 Osmoregulation

• Freshwater salmon: urine is dilute to eliminate excess water

• Saltwater fish → conserve water, concentrated urine

🍽 Digestion

• Rumen: 1st chamber of a 4-chambered stomach (e.g. cow), microbial fermentation

• Pseudorumen: modified stomach in some animals (e.g. camelids) without true rumen structure

🦠 Energy Storage

• Fungi & Mammals both store glycogen as a short-term energy source

🔄 Feedback & Physiology

• Negative Feedback – Insulin:
  ↑ Blood glucose → insulin released → glucose taken up by cells → ↓ blood glucose

• Stationary for long periods → Skeletal muscle atrophy (muscle loss due to disuse)

👂 Vision & Hearing

• Rods: night vision, B/W, more numerous

• Cones: color, detail, need more light

• First jaws: evolved from gill arches in Placoderms (extinct jawed fish)

🦅 Avian Respiration

• Most efficient among vertebrates

• Unidirectional airflow via air sacs

• No mixing of fresh/stale air like mammals

🧫 Epithelial Tissue

• Transitional epithelium: stretchable, found in urinary bladder

• General traits: tightly packed cells, covers surfaces/lines organs, little ECM

⚖ Carrier Constant (Michaelis-Menten / Enzyme Concept)

• Refers to affinity of a transporter for its substrate

• Affects rate of diffusion across membrane

🧬 Ctenophora vs Cnidaria (Shared Features)

• Radial symmetry, diploblastic

• Cnidaria: stinging cells (cnidocytes), nerve nets

• Ctenophora: cilia for movement, no stingers

🪱 Worm Phyla Quick Comparison