Evolution and Diversity of Multicellular Organisms (#14)
Office Hours and Important Dates
- Office Hours: Keck 230, 4-4:50 PM
- Next Quiz: Scheduled for next Thursday.
- Exit Ticket: Due within 24 hours of class finishing.
Quiz 2 Feedback
- Scores: Posted on Canvas, with feedback available on GradeScope.
- Grading Rubric: All answers evaluated based on a standardized rubric.
- Regrade Policy: Submit regrade requests within 1 week if an error in scoring is believed.
- Study Assistance: Discuss strategies during office hours or attend SI sessions.
- Correlation: Strong link between class engagement and exam grades, accounting for almost half of the variance (p < 0.0001, $R^2 = 0.46$).
- Recommendation: Regular attendance and completion of engagement assignments result in higher exam scores.
Objectives for Plant Diversity (Chapters 8 & 9)
- Understand traits that unite land plants versus other organisms.
- Identify challenges plants face living on land, including key innovations for adaptation.
- Describe, compare, and contrast major morphological and developmental features of plant groups.
- Classify or identify major features when provided with descriptions or images.
Distinguishing Traits Between Plants and Animals
| Characteristic | Plants | Animals |
|---|
| Energy Production | Photosynthesis | Consume organic matter |
| Cell Structure | Rigid cell walls, chloroplasts | No cell walls or chloroplasts |
| Movement | Stationary | Most can move |
| Growth | Continuous throughout lifespan | Limited to defined mature size |
| Reproduction | Seeds, spores, vegetative methods | Primarily sexual reproduction |
| Response to Stimuli | Slow | Rapid |
Plant Characteristics
- Eukaryotic: Contains nucleus and organelles.
- Multicellular: Composed of multiple cells.
- Photosynthetic Autotrophs: Capable of producing their own food through photosynthesis.
- Cell Walls: Composed of cellulose, providing structure.
Role of Chloroplasts
- Function: Sites of photosynthesis within plant cells.
- Photosynthesis Equation:
Carbon Dioxide+Water+Light Energy→Glucose+Oxygen
Importance of Cell Walls
- Structural Support: Provide rigidity, maintain shape, grow upright against gravity.
- Environmental Protection: Act as a barrier against environmental stresses.
Osmotic Pressure and Cell Shape
- Function: Protects against changes in osmotic pressure, maintaining cell shape.
- Osmotic Pressure: The force generated by water diffusion through a membrane.
Evolution of Plants from Green Algae
- Specialized groups of green algae are ancestors to land plants, showing similarities like:
- Photosynthetic processes
- Presence of chlorophyll and cellulose cell walls
Challenges in Transitioning from Water to Land
- Desiccation Resistance: Essential for retaining water and preventing drying out.
- Structural Support: Need mechanisms to resist gravity without water buoyancy.
- Water Management: Adaptations necessary for freshwater/saltwater regulation and osmolarity management.
Advantages of Transitioning to Land
- Photosynthetic Efficiency: Ability to capture more sunlight than aquatic ancestors.
- Phototropism: Growth towards light leads to complex structures.
- Light Competition: Taller plants developed to avoid shading from competitors.
Derived Traits for Life on Land
- Waxy Cuticle: Water loss barrier to prevent dehydration in terrestrial environments.
- Stomatal Regulation: Developed stomata that can:
- Closed: Prevent water vapor loss in dry conditions.
- Open: Facilitate gas exchange during photosynthesis.
Conditions for Stomatal Closure
- Heat, drought, high winds, and intense sunlight lead to stomatal closure to reduce water loss.
Evolutionary History of Plants
- Origin: Approximately 470 million years ago (mya), with significant milestones:
- Nonvascular Plants: Liverworts, hornworts, mosses.
- Vascular Plants: Originated about 425 mya with Lycophytes and Monilophytes.
- Seed Plants: Emerged around 360 mya, including gymnosperms and angiosperms.
Taxonomic Classification
- Monophyletic: Includes a common ancestor and all descendants.
- Paraphyletic: Includes a common ancestor and some but not all descendants.
- Polyphyletic: Members derived from multiple ancestral sources.
Nonvascular and Seedless Vascular Plants
- Nonvascular Plants: Paraphyletic group including mosses, liverworts, and hornworts; lack true vascular tissue.
- Seedless Vascular Plants: Also paraphyletic; includes ferns and club mosses, reproducing via spores.
Monophyletic Seed Plants
- Definition: Includes gymnosperms and angiosperms, sharing the key innovation of seeds for reproduction.
Characteristics of Nonvascular Plants
- Small size due to lack of vascular tissue.
- Simple structure; growth is ground-level.
- Dependency on moist environments for reproduction and survival.
Comparison with Invertebrates
- Nonvascular plants share physiological similarities with flatworms, primarily using diffusion across surface for resource transportation primarily due to their maximized surface area.