Meditaliano IMAT Preparation

Sessions 16: Evolution, Diversity, and Ecology

Evolution & Ecosystems: The Big Picture

This comprehensive module unites two critical areas of biology: Evolution, which explains the unity and diversity of life through time, and Ecology, which explains interactions between organisms and their environment. Mastering these concepts is essential for understanding the interconnectedness of biological systems required for the IMAT.

Learning Objectives:

Understand mechanisms of evolution: Natural Selection, Genetic Drift, Gene Flow, and Speciation.
Distinguish between homologous and analogous structures (Divergent vs. Convergent evolution).
Classify organisms using the 3-Domain system and identify key characteristics of major Animal Phyla.
Analyze energy flow in ecosystems (Trophic levels, 10% rule) and biogeochemical cycles.
Calculate population growth (Exponential vs. Logistic) and interpret survivorship curves.
Understand human evolution and conservation biology concepts.

Part 1: The Mechanisms of Evolution

1.1 Natural Selection

Proposed by Charles Darwin, this is the only mechanism that consistently leads to adaptive evolution. Individuals with traits better suited to the environment survive and reproduce more successfully.

Modes of Natural Selection

1.2 Genetic Drift & Gene Flow

Evolution is defined as a change in allele frequencies in a population over time. Besides selection, two other major forces drive this:

Image 1: Population Genetics & Hardy-Weinberg Equilibrium

Visual Analysis: Allele Math

This visual translates population dynamics into algebraic equations (LO 13.5/16.1).

Equation 1 ($p+q=1$): Tracks the frequency of individual alleles (Dominant vs. Recessive).
Equation 2 ($p^2 + 2pq + q^2 = 1$): Tracks the distribution of genotypes (Homozygous vs. Heterozygous carriers).
Assumptions: Recaps the conditions for equilibrium: Large population, random mating, no mutation, no migration, and no selection.

Genetic Drift (Random)

Change in allele frequencies due to chance events. Significant in small populations.

Bottleneck Effect: Disaster drastically reduces population size (e.g., cheetahs).
Founder Effect: Few individuals colonize a new area (e.g., Darwin's finches).

Gene Flow (Migration)

Transfer of alleles into or out of a population due to the movement of fertile individuals.

Reduces genetic differences between populations.
Can introduce new alleles.

1.3 Evidence for Evolution

Evidence Type	Description	Example
Homologous Structures	Same origin, different function. Evidence of Divergent Evolution.	Human arm vs. Bat wing vs. Whale flipper (pentadactyl limb).
Analogous Structures	Different origin, same function. Evidence of Convergent Evolution.	Bird wing vs. Insect wing.
Vestigial Structures	Remnants of structures that served a function in ancestors.	Human appendix, Whale pelvic bone.
Molecular	Universal genetic code (DNA/RNA) and protein sequences.	Cytochrome c similarity between humans and chimps.

1.4 Speciation & Reproductive Isolation

Speciation is the process by which one species splits into two. It requires Reproductive Isolation.

Modes of Speciation

Allopatric: Geographic barrier separates population (e.g., mountain range, river).
Sympatric: Speciation without geographic separation (e.g., polyploidy in plants).

Reproductive Barriers

Pre-zygotic: Prevent fertilization (Temporal, Habitat, Behavioral, Mechanical, Gametic isolation).
Post-zygotic: Hybrid inviability, Hybrid sterility (Mule), Hybrid breakdown.

1.5 Human Evolution

Humans are primates. Our evolution is characterized by bipedalism (walking upright) first, followed by increased brain size.

Australopithecus: Bipedal, small brain (e.g., Lucy).
Homo habilis: "Handy man", first stone tools.
Homo erectus: First to migrate out of Africa, used fire.
Homo sapiens: Evolved in Africa ~200,000 years ago. Large complex brains.

Part 2: The Diversity of Life

2.1 Phylogenetic Classification

Taxonomy organizes life into hierarchical groups. The order from broadest to most specific is:

Domain $\rightarrow$ Kingdom $\rightarrow$ Phylum $\rightarrow$ Class $\rightarrow$ Order $\rightarrow$ Family $\rightarrow$ Genus $\rightarrow$ Species

Mnemonic: Dear King Phillip Came Over For Good Soup.

2.2 The Three Domains

1. Bacteria

Prokaryotic (no nucleus).
Cell wall with Peptidoglycan.
Unicellular.
Ex: E. coli, Cyanobacteria.

2. Archaea

Prokaryotic.
No Peptidoglycan.
Extremophiles (heat/salt lovers).
More closely related to Eukarya than Bacteria.

3. Eukarya

Eukaryotic (nucleus + organelles).
Includes 4 Kingdoms: Protista, Fungi, Plantae, Animalia.

2.3 Kingdoms of Eukarya

Kingdom	Cell Wall	Nutrition	Multicellular?
Fungi	Chitin	Heterotroph (Absorption)	Mostly Yes (Yeast is uni)
Plantae	Cellulose	Autotroph (Photosynthesis)	Yes
Animalia	None	Heterotroph (Ingestion)	Yes
Protista	Various	Various	Mostly No (Algae is multi)

2.4 Key Animal Phyla (IMAT Must-Know)

Phylum	Key Characteristics	Examples
Porifera	No tissues, asymmetry, filter feeders.	Sponges
Cnidaria	Radial symmetry, cnidocytes (stinging cells).	Jellyfish, Corals
Platyhelminthes	Flatworms, bilateral symmetry, acoelomate.	Tapeworms, Planaria
Annelida	Segmented worms, closed circulatory system.	Earthworms, Leeches
Mollusca	Soft body, mantle, foot, radula.	Snails, Octopuses
Arthropoda	Exoskeleton (chitin), jointed appendages. Largest phylum.	Insects, Crustaceans
Chordata	Notochord, dorsal nerve cord, pharyngeal slits, post-anal tail.	Vertebrates (Mammals, Fish)

Part 3: Ecosystem Ecology

3.1 Trophic Levels & Energy Flow

Energy flows one way: Sun $\rightarrow$ Producers $\rightarrow$ Consumers. Matter cycles.

*Tertiary(0.1%) Energy Loss (Heat)

10% Rule: Only ~10% of energy is transferred to the next level. The rest is lost as heat (cellular respiration) or unassimilated waste. This limits food chains to 4-5 levels.

3.2 Biogeochemical Cycles

Crucial for IMAT: Memorize the role of bacteria in the Nitrogen Cycle.

Nitrogen Cycle Steps

Fixation: $N_2 \rightarrow NH_3$ (Bacteria in root nodules).
Nitrification: $NH_3 \rightarrow NO_2^- \rightarrow NO_3^-$ (Nitrifying bacteria).
Assimilation: Plants absorb $NO_3^-$ to make proteins.
Ammonification: Decomposers turn dead matter back to $NH_3$.
Denitrification: $NO_3^- \rightarrow N_2$ (Anaerobic bacteria).

Other Cycles

Carbon: Balanced by Photosynthesis (removes $CO_2$) and Respiration/Combustion (adds $CO_2$).
Phosphorus: No atmospheric component. Slow cycle involving rocks and soil. Critical for ATP/DNA.

3.3 Ecological Succession

The sequence of community changes after a disturbance.

Primary Succession: Starts on lifeless ground (no soil), e.g., after volcanic eruption. Pioneer species: Lichens/Moss.
Secondary Succession: Soil remains, e.g., after a fire. Faster recovery.

3.4 Major Biomes

Biome	Climate	Key Vegetation
Tropical Rainforest	Hot, Wet	Canopy trees, highest biodiversity.
Taiga (Boreal Forest)	Cold winter, wet	Conifers (Pines).
Tundra	Very cold, dry	Mosses, lichens (Permafrost present).
Desert	Dry (hot or cold)	Succulents (Cacti).

Part 4: Population Dynamics

4.1 Growth Models

Exponential Growth (J-Curve)

Unlimited resources. Growth rate is constant.

$$ \frac{dN}{dt} = r_{\text{max}}N $$

Logistic Growth (S-Curve)

Limited resources. Slows near Carrying Capacity (K).

$$ \frac{dN}{dt} = r_{\text{max}}N \left( \frac{K-N}{K} \right) $$

4.2 Survivorship Curves

Type I (K-selected): Low death rate early/middle life. High parental care. (e.g., Humans, Elephants).
Type II: Constant death rate. (e.g., Squirrels).
Type III (r-selected): High death rate early life. Many offspring, little care. (e.g., Oysters, Insects).

4.3 Community Interactions

Interactions between species define the structure of the community. A Niche is the role a species plays. The Competitive Exclusion Principle states that two species cannot coexist if they occupy the exact same niche.

Interaction	Effect	Description
Competition	(-/-)	Both species harmed fighting for limited resources.
Predation	(+/-)	One kills and eats the other. Includes Keystone Species (e.g., Sea Otters) that maintain diversity.
Parasitism	(+/-)	One benefits, host is harmed (but usually not killed).
Mutualism	(+/+)	Both benefit (e.g., Bacteria in gut, Lichen).
Commensalism	(+/0)	One benefits, other unaffected (e.g., Barnacles on whale).

4.4 Conservation Biology

The greatest threats to biodiversity can be remembered by HIPPO:

Habitat Loss (Biggest threat)
Invasive Species
Pollution (Biomagnification)
Population Growth (Human)
Overharvesting

Chemistry Visual Resources (Visual Supplements)

These visually refined study resources are designed to help you prepare for the IMAT exam. Key terms are clearly identified. The Meditaliano logo is placed at the bottom right of each image.

1. Visualizing Solvation of NaCl (Hydration Process)

This diagram shows how water molecules surround Na+ and Cl- ions. The oxygen atoms ($\delta-$) orient towards the sodium cation, while the hydrogen atoms ($\delta+$) face the chloride anion.

2. Effect of Temperature on Particle Energy Distribution (Kinetics)

This graph illustrates the distribution of kinetic energy at low (blue) and high (red) temperatures. It highlights the activation energy (Ea) threshold and demonstrates how increasing the temperature significantly increases the fraction of molecules with energy $E \ge E_a$.

3. Dynamic Equilibrium and Le Chatelier's Adjustments (System Shifts)

This diagram visualizes the state of dynamic equilibrium where the rates of the forward and reverse reactions are equal. It also shows how the system shifts in response to external stresses (concentration, pressure, temperature) according to Le Chatelier's Principle.

4. Comparison of Acid-Base Definitions & The pH Scale

This visual guide compares the three major acid-base definitions (Arrhenius, Brønsted-Lowry, and Lewis) and displays the pH scale with a color gradient from acidic to basic.

5. Mechanism of a Galvanic Cell (Daniell Cell)

This detailed diagram of a Zn-Cu galvanic cell shows the arrangement of the anode (Zn), cathode (Cu), salt bridge, external circuit, and voltmeter. It indicates the direction of electron flow and the half-reactions occurring at each electrode.

Part 5: Comprehensive Practice Quiz

Test your knowledge of evolution and ecology.