Biology 2
BIO 2 STUDY GUIDE ANSWERS (2026)
1. Describe the formation of tissue layers in embryos.
During early embryonic development, cells reorganize in a process called gastrulation, forming three primary tissue layers called germ layers. The ectoderm forms the outer layer, the endoderm forms the inner layer, and the mesoderm forms in between. These layers later differentiate into all tissues and organs in the body.
2. Compare and contrast acoelomate, pseudocoelomate, and coelomate body plans. Identify phyla that are examples of each plan.
Acoelomates have no body cavity (ex: flatworms/Platyhelminthes).
Pseudocoelomates have a partially lined cavity (ex: nematodes).
Coelomates have a fully lined body cavity (true coelom) (ex: annelids, mollusks, arthropods, chordates).
The coelom allows for better organ development and movement.
3. Identify some examples of body parts/organ systems that arise from endoderm, ectoderm, and mesoderm.
Endoderm → digestive tract, lungs
Ectoderm → skin, nervous system
Mesoderm → muscles, bones, circulatory system
4. Explain the adaptive significance & function of different symmetry patterns.
Radial symmetry allows organisms to interact with the environment from all sides (good for stationary animals).
Bilateral symmetry allows directional movement and better coordination (good for active animals).
5. Explain the significance of cephalization.
Cephalization is the concentration of sensory organs and brain at the front of the body. It allows organisms to better detect and respond to their environment, especially when moving forward.
6. Describe how segmentation can be important in evolution.
Segmentation allows body parts to specialize and evolve independently, improving movement and function (ex: arthropods, annelids).
7. Identify the functions of skeletons and give examples.
Skeletons provide support, protection, and movement.
Examples:
Exoskeleton (arthropods)
Endoskeleton (vertebrates)
Hydrostatic skeleton (annelids)
Chapter 33 Basal Invertebrates
8. List the characteristics (synapomorphies) of animals.
Multicellular, heterotrophic, no cell walls, have specialized tissues, and undergo embryonic development.
9. Draw a phylogenetic tree…
(For your doc, describe instead of draw)
Animals branch into major groups like sponges, cnidarians, protostomes, and deuterostomes. Key traits include tissues, symmetry, and body cavities.
10. Identify the phylum most ancestral besides sponges.
Ctenophora (comb jellies) are now considered possibly the most ancestral.
Protostomes
11. Contrast protostomes and deuterostomes.
Protostomes: blastopore becomes mouth, spiral cleavage, determinate development.
Deuterostomes: blastopore becomes anus, radial cleavage, indeterminate development.
12. Identify which phyla are protostomes vs deuterostomes.
Protostomes: mollusks, annelids, arthropods
Deuterostomes: echinoderms, chordates
13. Characteristics of mollusks.
Soft body, mantle, often a shell, muscular foot.
14. Characteristics of annelids.
Segmented body, true coelom, closed circulatory system.
15. Characteristics of arthropods.
Exoskeleton, jointed appendages, segmented body.
16. Characteristics of insects.
Three body parts, six legs, often wings.
17. Compare venom vs poison.
Venom is injected (bite/sting).
Poison is absorbed or ingested.
18. Advantages and limitations of an exoskeleton.
Advantages: protection, support, prevents water loss
Limitations: must molt, limits size
Deuterostomes
19. Characteristics of Echinodermata.
Radial symmetry (adult), water vascular system, tube feet.
20. Symmetry transition in echinoderms.
Larvae are bilateral (good for movement), adults are radial (good for stationary life).
21. How echinoderms achieve skeleton function.
They use an internal skeleton made of calcium plates.
Chordates
22. Characteristics of chordates.
Notochord, dorsal nerve cord, pharyngeal slits, post-anal tail.
23. Function of lateral line system.
Detects vibrations and movement in water.
24. Evolution of jaws.
Jaws evolved from modified gill arches, improving feeding.
25. Why shark scales are denticulate.
They resemble teeth (tooth-like structure).
26. Advantage of cartilage skeleton.
Lighter and more flexible than bone, improves movement.
27. Determine sex of shark/ray.
Males have claspers; females do not.
28. Ampullae of Lorenzini.
Electroreceptors that detect electrical signals in prey.
29. Cartilaginous vs ray-finned fishes.
Cartilaginous: skeleton made of cartilage
Ray-finned: bony skeleton, more diverse
30. Importance of Tiktaalik.
It shows transition from fish to land animals (tetrapods).
31. Label forelimb bones.
Humerus (upper), radius and ulna (lower), digits (fingers).
32. Amphibians on land vs water.
Land: lungs, limbs
Water: eggs require water, skin needs moisture
33. Amniotic egg diagram (describe).
Shell protects, amnion cushions, chorion gas exchange, allantois waste storage, yolk nutrients.
34. Significance of amniotic egg.
Allows reproduction away from water.
35. Mammal characteristics.
Hair, mammary glands, warm-blooded.
36. Lower jaw bones comparison.
Reptiles: multiple bones
Mammals: one bone
37. Evolution of middle ear bones.
Jaw bones evolved into ear bones.
38. Turtle synapomorphies.
Shell and fused ribs.
39. Dinosaur pelvis types.
Saurischian (lizard-hipped) → birds evolved from this group
Ornithischian (bird-hipped)
40. Problem with nitrogen consumption.
Produces toxic ammonia waste.
41. Nitrogen waste trade-offs.
Ammonia: toxic, needs water
Urea: less toxic
Uric acid: least toxic, saves water
42. Animals with four-chambered hearts.
Birds, mammals, crocodilians.
43. Advantage of four-chambered heart.
Efficient oxygen separation.
Reproduction
44. Advantage of sexual reproduction.
Increases genetic variation.
45. Advantage of asexual reproduction.
Fast, no mate needed.
46. Define male vs female.
Male: small gametes (sperm)
Female: large gametes (eggs)
47. Male vs female strategies.
Males compete, females choose (due to higher investment).
48. Human reproductive cycle.
Males produce sperm continuously; females produce eggs before birth.
49. Hermaphrodite definitions.
Hermaphrodite: both sexes
Simultaneous: both at once
Sequential: change sex over time
Population Biology
50. Population size vs density.
Size = total number
Density = number per area
51. Exponential vs logistic growth.
Exponential = unlimited growth
Logistic = limited by carrying capacity (K)
52. All populations are regulated.
Resources and environmental factors limit growth.
53. Big four forces.
Births, deaths, immigration, emigration
54. Density-dependent vs independent.
Dependent: affected by population size
Independent: not affected (weather)
55. Human population growth.
Rapid exponential growth, approaching carrying capacity.
Climate & Biosphere
56. Define biome.
Large ecological region (ex: desert, rainforest). Determined by climate.
57. Climate vs weather.
Climate = long-term patterns
Weather = short-term conditions
58. Why poles are colder.
Sunlight hits at a lower angle.
59. Causes of seasons.
Earth’s tilt.
60. Long-term climate variation.
Changes in orbit, volcanic activity.
61. Water cycle.
Evaporation → condensation → precipitation
62. Lake effect.
Water warms air, increases precipitation.
63. Energy source for winds/currents.
Sun.
64. Why winds curve.
Coriolis effect.
65. Greenhouse effect.
Heat trapped by gases in atmosphere.
66. Greenhouse gases.
CO₂, methane, water vapor.
67. Moist air up mountains.
Cools → condenses → rain.
68. Rain shadow.
Dry area on leeward side.
69. Atmosphere change.
Increase in CO₂ due to human activity.
70. CO₂ levels now vs past.
Much higher now.
71. Climate history tools.
Tree rings, pollen, coral.
72. Ice caps form.
Snow compacts into ice over time.
73. Isotope definition.
Atoms with different neutrons.
74. Oxygen isotopes.
Lighter evaporate easier.
75. Temperature effects on water.
Warmer = more evaporation.
76. Ice isotope ratios.
Show past temperatures.
77. Ice core patterns.
CO₂ and temperature rise together.
78. Why scientists are alarmed.
Rapid recent changes.
79. Effects of climate change.
Sea level rise, extreme weather.
Comprehensive
80. Natural selection explanation.
Variation + competition + survival = evolution.
81. Types of selection.
Directional, stabilizing, disruptive, sexual selection.
82. Evolution terms.
Convergent = similar traits evolve
Homology = shared ancestry
Analogy = similar function, different origin
83. Endosymbiosis.
Cells engulfed others → organelles.
84. Speciation.
Geographic isolation or within same area.
85. Phylogenetic trees.
Show evolutionary relationships.
86. Evolution of animal bodies.
Changes in symmetry, segmentation, etc.
87. How traits work.
Traits improve survival (ex: symmetry, defenses).