Biology Notes

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1) Classification and Evolution: Core Idea

Classification groups organisms based on shared characteristics such as appearance and behavior.
Examples of characteristics:

• Number of limbs

• Skin covering/color

• Food habits

• How food is obtained

Key Concept:

• The more characteristics organisms share, the more closely related they are.

• Example:

  • Dog & Wolf → very closely related

  • Dog & Chimpanzee → less related

  • Human & Chimpanzee → more related than Human & Dog

2) Evolutionary Link

• Organisms that are closely related share a recent common ancestor.

• Distantly related organisms share a common ancestor further back in time.

Examples:

• Dogs & Wolves → common ancestor a few thousand years ago

• Humans & Chimpanzees → common ancestor millions of years ago

• Humans & Dogs → even further back

• Humans & Plants → billions of years ago, from single-celled ancestors

Key Insight:

3) Big Picture: LUCA and Abiogenesis

• All living organisms trace back to a single common ancestor, called LUCA (Last Universal Common Ancestor).

• Where LUCA came from is unknown and studied under a different field: abiogenesis (origin of life from non-living matter).

4) Carl Linnaeus & Modern Taxonomy

Who?

• Carl Linnaeus (1707, Sweden) = Father of Modern Taxonomy

What He Did:

• Introduced a hierarchical system of classification:

  • Species → Genus → Family → Order → Class → Phylum → Kingdom

• Created binomial nomenclature: two-part scientific names (e.g., Homo sapiens)

  • Genus is capitalized, species is lowercase

Later Developments in Taxonomy:

• Darwin's theory of evolution

• Fossil records

• Genetics (especially DNA similarity)

Note:

• Taxonomy is both science and art.

• Higher ranks (e.g., kingdom, phylum) are partly arbitrary and can change with new data.

5) Human Classification Example

6) Defining Species

• A species is a group of organisms that can interbreed and produce fertile offspring.

• Visual similarity is not enough — reproductive compatibility is the key.

Examples:

• Lions + Tigers = ligers (usually sterile) → different species

• Donkeys + Horses = mules (sterile) → different species

• All Dog Breeds = same species (can interbreed and produce fertile offspring)

7) Taxonomic Ranks (General Meaning)

8) Phylogenetic Tree (Tree of Life)

• Diagram showing evolutionary relationships between organisms

• Shows common ancestry and divergence

• Estimated species: ~2 million known; total may be 5–100 million

• Nature is complex: classification constantly evolves as new data is found

9) Domains – Above Kingdom Level

10) The 4 Kingdoms of Eukarya

a) Protista

• Mostly single-celled

• Some are autotrophs, some heterotrophs

• Very diverse ("junk drawer" kingdom)

b) Fungi

• Heterotrophic

• External digestion

• Cell walls made of chitin

c) Plantae

• Autotrophic (photosynthesis)

• Cell walls of cellulose, contain chloroplasts

d) Animalia

• Multicellular heterotrophs

• Motile at some life stage

• Develop germ layers during embryonic development

11) Homologous vs. Analogous Traits

12) Prokaryotic vs Eukaryotic, Autotroph vs Heterotroph

Prokaryotic

• No nucleus

• No membrane-bound organelles

• Small, simple

• Examples: bacteria, archaea

Eukaryotic

• Nucleus present

• Has organelles

• Large, complex

• Examples: animals, plants, fungi, protists

Autotrophic

• Makes own food from sunlight or chemicals

• Examples: plants, algae, some bacteria

Heterotrophic

• Consumes other organisms

• Examples: animals, fungi, most bacteria

Final Summary

• Taxonomy helps organize life and understand evolutionary relationships.

• It’s a tool that’s still evolving with technology (especially genetics).

• All life is related through common ancestry.

• Classification is based on shared traits, but the best definition of species is reproductive compatibility.

• The entire system helps biologists communicate, predict traits, and understand biodiversity.

Need a diagram of a phylogenetic tree or a classification chart?

We can use a pretty straightforward method to find the most recent common ancestor of any pair or group of species. In this method, we start at the branch ends carrying the two species of interest and “walk backwards” in the tree until we find the point where the species’ lines converge.

When we are building phylogenetic trees, traits that arise during the evolution of a group and differ from the traits of the ancestor of the group are called derived traits. In our example, a fuzzy tail, big ears, and whiskers are derived traits, while a skinny tail, small ears, and lack of whiskers are ancestral traits.

In general, though, when we compare the sequences of a gene or protein between species:

• A larger number of differences corresponds to less related species

• A smaller number of differences corresponds to more related species

Key Info – Trophic Pyramid

1. Definition & Structure

• A trophic pyramid shows food relationships: who eats whom and how energy flows in an ecosystem.

• Base = Primary producers (autotrophs): use sunlight and nutrients to create biomass (stored energy).

• Levels above = Consumers: each level eats the one below.

2. Energy Transfer

• Only ~10% of energy is transferred from one level to the next.

• The rest is lost as:

  • Heat

  • Movement/metabolism

  • Undigested waste (poop)

  • Dead biomass (used by decomposers)

3. Energy Values Example

• Primary producers: 20,000 kcal/m²/year

• Primary consumers: 2,000 kcal/m²/year

• Secondary consumers: 200 kcal/m²/year

• Tertiary consumers: 20 kcal/m²/year

• Apex predators: 2 kcal/m²/year

4. Decomposers

• Feed on waste and dead organisms, recycling nutrients back to producers.

5. Impact of Ecosystem Changes

• Volcano blocks sunlight → energy production drops:

  • Primary producers: from 20,000 → 2,000 kcal/m²/year

  • Cascading drop across all levels.

• Pesticides killing primary consumers → reduces biomass at higher levels.

6. Core Concept

• Ecosystems are energy transfer systems driven by the sun.

• Each level depends on the energy availability from the level below.

• Disruption at one level affects the entire pyramid.