Bio 94 Midterm 3 — Comprehensive Study Notes Summary & Study Notes

🧬 Overview and How to Use These Notes

Short guide: Read each heading, focus on the bolded key terms, and link the terms to example exam questions. Use the phylogeny-related sections to practice placing synapomorphies on branches.

🧪 Animals vs Fungi (Question 1)

Multicellularity is shared across animals, plants, and fungi, but animals differ from fungi in how they obtain food. Fungi absorb nutrients externally and often use chitin in cell walls; animals are heterotrophs that usually ingest food. Key distinction: animals ingest; fungi secrete enzymes and absorb.

🥚 Reproductive Modes (Question 2)

• Oviparous: lay eggs that hatch outside the mother.
• Viviparous: live birth with direct nourishment from mother (placental mammals).
• Ovoviviparous: eggs retained internally, embryo nourished by yolk, then live birth. Remember: yolk usage and site of embryonic development (inside vs outside) define these terms.

🧠 Evolutionary Genetics Example — Bajau Spleen (Question 3)

To support the hypothesis of ongoing adaptation (e.g., larger spleens): the trait must have a heritable genetic basis. If spleen-size variation is heritable and under selection, evolution can act. Non-heritable or identical traits across the population do not support recent adaptive evolution.

🩺 Yolk Sac vs Placenta (Question 4)

In mammals, the yolk sac is reduced because the placenta largely replaces yolk function by transporting nutrients from mother to embryo. Egg-laying amniotes retain larger yolk sacs to nourish embryos until hatching.

🍄 Fungi and Mycorrhizae (Question 5)

Mycorrhizal fungi help plants acquire minerals because fungal hyphae have a very high surface-area-to-volume ratio compared to root hairs. This greater surface area increases nutrient absorption efficiency. Note: fungi secrete enzymes to break down complex molecules (they do not ingest in the animal sense).

🐸 Chordate Traits — Tadpole vs Tunicate (Question 6)

Key chordate characters include pharyngeal gills, dorsal hollow nerve cord, post-anal tail, and—in vertebrates—vertebral column. A larval amphibian (tadpole) is a vertebrate and therefore has a vertebral column; tunicates lack a true vertebral column.

🐙 Cephalopod Color Change (Question 7)

Rapid color change in animals with tentacles, mantle, and a siphon points to cephalopods (e.g., octopus). These animals have specialized pigment cells (chromatophores) controlled by the nervous system for fast color shifts.

🔁 Convergent Traits: Segmentation (Question 8)

Annelids and arthropods were once grouped together because both show segmented bodies. This is a case where similar morphology can reflect convergent evolution or deep homology; exam questions test recognizing segmentation as the shared trait.

🧟‍♂️ Ophiocordyceps “Zombie” Fungus (Question 9)

Behavioral manipulation by the fungus involves hyphae invading host tissues (muscle; sometimes neural tissue) causing muscle dysfunction and driving ants to specific locations optimal for fungal reproduction. Hyphal invasion of muscle explains loss of muscle function.

🦈 Fossil Record of Sharks (Question 10)

Sharks (chondrichthyans) have cartilaginous skeletons, which do not fossilize as readily as bone; their teeth preserve well because they are mineralized. Hence sparse fossil record except for teeth.

🐶 Developmental Categories (Question 11)

Classify animals by germ layers, symmetry, and developmental mode: a dog is triploblastic (three germ layers), bilaterally symmetric, and a deuterostome (blastopore fate and developmental lineage). So: triploblastic bilateral deuterostome.

🕷️ Arthropod ID: Chelicerae (Question 12)

Among crustaceans (crab, shrimp) and sea spiders, chelicerae are found in chelicerates (spiders, scorpions). To distinguish groups, identify unique structures: chelicerae point to chelicerates; jointed legs and exoskeleton are general arthropod traits.

🌳 Synapomorphies on a Phylogeny (Questions 13–15, 19–21)

• Synapomorphy = shared derived trait that defines a clade. Examples in the exam: amniotic egg, four limbs, hinged jaws, endothermy, dorsal hollow nerve cord.
• Use the tree: place traits at the node where they first appear. Traits like multicellularity and diploblasty/triploblasty map deep; coelom is a major innovation that appears at a specific internal node.

🌍 Transitions to Land (Question 16)

Fossil and phylogenetic evidence indicates multiple independent transitions from water to land among animal lineages (e.g., arthropods, vertebrates, many plants/fungi separately), not just a single event.

🪳 Insect Metamorphosis (Question 17)

If juveniles resemble adults (nymphs) and treatments that kill adults also kill juveniles, the insect exhibits incomplete metamorphosis (hemimetabolous development). Complete metamorphosis would have distinct larval stages that differ strongly from adults.

☀️ Skin Pigmentation and UV-B (Question 18)

Dark skin in high UV-B regions is favored because it protects folate (folic acid) from UV-induced degradation. Folate is crucial for development and reproduction; too much UV can break it down.

🧩 Regeneration and Planarians (Questions 22–23)

Model systems for regeneration (planarians) help identify genes controlling regrowth. Experimental approaches include activating or inhibiting genes (e.g., wnt/beta-catenin pathways) to induce regeneration in non-regenerating species, rather than excluding variants.

🪱 Distinguishing Segmented, Coelomate Worms (Questions 24–25)

If a worm has segments and a coelom, it could be an annelid or an arthropod (arthropods are segmented + coelomate derivatives), but platyhelminths lack a coelom and nematodes lack true segmentation. Genes involved: Hox genes and other transcription factors related to body plan (e.g., segmentation regulators) differ between annelids and arthropods; a Hox-related factor would often be diagnostic.

✅ Study Tips Specific to This Midterm

• Memorize definitions: oviparous/viviparous/ovoviviparous, diploblasty/triploblasty, protostome/deuterostome.
• Practice mapping synapomorphies onto simple phylogenies.
• For physiology/evolution questions (Bajau, skin pigmentation), link phenotype → heritability → selection.
• For identification questions, focus on unique morphological structures (e.g., vertebral column, chelicerae, amniotic egg).

✨ Student Request Context

You asked: “help me better understand this.” Below are concise study strategies tailored to the midterm content.

📚 How to Approach These Questions (from your request)

Start by identifying the key concept each question tests (morphology, development, phylogeny, or physiology). Rephrase the question in one sentence: what trait or process is being compared? Then retrieve the single defining feature (e.g., ingestion vs absorption, presence vs absence of vertebral column).

🧭 Quick Study Workflow

1. Scan question and underline the biological category (e.g., reproduction, phylogeny).
2. Recall the defining keywords from these notes (oviparous, coelom, synapomorphy, heterotroph).
3. Eliminate answers that contradict definitions or basic principles.
4. For phylogeny problems, work from the root to the tip placing traits at the earliest node that could produce them.

🧩 Final Tip

If a question references a specific organism or trait, ask: “What unique structure or developmental process distinguishes this group?” That single insight usually yields the correct choice.