Overview
This lecture covers animal body plans, factors limiting animal size and shape, how animals obtain and use energy, and the organization of animal body planes and cavities.
Body Plans and Symmetry
- Animals display three main symmetry types: asymmetrical (no symmetry), radial (body arranged around a central axis), and bilateral (right and left mirror images).
- Asymmetrical animals, like sponges, lack any organized pattern.
- Radial symmetry is typical in aquatic animals such as sea anemones.
- Bilateral symmetry, found in both land and aquatic animals, supports greater mobility.
- Key anatomical directions include anterior (front), posterior (rear), dorsal (back), and ventral (belly).
Limits on Animal Size and Shape
- Aquatic animals with bilateral symmetry usually have a fusiform (streamlined) shape to minimize water resistance.
- Land animals are more constrained by gravity than by air resistance.
- Exoskeletons (external skeletons) provide protection and support but limit size due to weight and the need for molting.
- Endoskeletons (internal skeletons) allow larger sizes as muscle and bone mass can increase to support more weight.
Limiting Effects of Diffusion
- Diffusion (movement of substances from high to low concentration) is efficient only over small distances, limiting cell and organism size.
- Surface-to-volume ratio decreases as size increases, reducing diffusion efficiency.
- Larger animals evolved multicellularity and specialized systems (circulatory, respiratory) to overcome diffusion limits.
Animal Bioenergetics
- Animals convert food into ATP for immediate use, and store excess energy as glycogen (short term) or triglycerides (long term).
- Metabolic rate is the total energy used over time and is higher in smaller animals due to greater surface area relative to mass.
- Endotherms (warm-blooded) generate heat internally; ectotherms (cold-blooded) rely on the environment for heat.
- Activity level and environmental factors (temperature, food) affect energy needs; torpor (reduced activity/metabolism) helps animals survive harsh conditions.
Body Planes and Cavities
- Animals can be divided by planes: sagittal (left/right), frontal (front/back), and transverse (upper/lower).
- Vertebrates have two main body cavities: dorsal (cranial, spinal) and ventral (thoracic, abdominopelvic).
Key Terms & Definitions
- Asymmetry — No body symmetry.
- Radial symmetry — Symmetry around a central axis.
- Bilateral symmetry — Body divided into left and right mirrored sides.
- Fusiform — Tapered, streamlined body shape.
- Exoskeleton — External skeleton providing structure and protection.
- Endoskeleton — Internal skeleton supporting the body.
- Diffusion — Passive movement of substances across cell membranes.
- Surface-to-volume ratio — Amount of surface area per unit volume, important for diffusion.
- ATP — Energy currency of the cell.
- Metabolic rate — Energy used per unit time.
- Endotherm — Animal that maintains body temperature using internal heat.
- Ectotherm — Animal relying on environmental heat.
- Torpor — State of reduced metabolic activity.
- Body planes — Imaginary lines dividing the body (sagittal, frontal, transverse).
- Body cavities — Spaces in the body housing organs (dorsal, ventral).
Action Items / Next Steps
- Review diagrams of body symmetry, planes, and anatomical cavities.
- Explore the recommended interactive site for virtual animal nanoscopy.
- Study the table of animal speeds for understanding adaptation limits.