Food Webs, Biodiversity, and Genetics

Definition of Matter
- Matter = atoms that constitute every biotic (living) and abiotic (non-living) component of an ecosystem.
- $\text{Matter cycles}$ continuously between living organisms and their physical environment (e.g., carbon, nitrogen, water cycles).
Definition of Energy
- Energy changes form while moving through an ecosystem (chemical → kinetic → thermal, etc.).
- All energy that enters an ecosystem will eventually exit as heat due to the 2nd Law of Thermodynamics (entropy increase).
Producers (Autotrophs)
- Organisms that manufacture their own food internally—most via photosynthesis.
- By converting solar energy into chemical energy, producers are the entry point for energy in food webs.
Consumers (Heterotrophs)
- Obtain matter & energy by eating other organisms.
- Transfer of biomass → transfer of stored chemical energy.
- Classification by diet level:
- Primary consumers eat producers.
- Secondary consumers eat primary consumers (tertiary and quaternary levels implied though not explicitly stated).
Decomposers
- Consume dead plant & animal matter (detritus).
- Release inorganic nutrients back to the environment, closing matter cycles.
Food Webs
- Graphical models displaying pathways of matter & energy among producers, consumers, and decomposers.
- Emphasize complexity over simple food chains; many interconnected routes.

Biodiversity
- Defined as the variety of species within an ecosystem.
- Expressed through species richness, evenness, genetic variability, and functional diversity (only the first explicitly named in transcript).
Extinction & Decline
- Biodiversity decreases when species go extinct (die out).
- Extinction drivers include organisms’ inability to survive altered environmental conditions.
Human Impacts
- Habitat loss & climate change (both driven by human actions) are actively lowering Earth’s biodiversity.
Ecosystem Functioning
- Reduced biodiversity → diminished ecosystem functionality (e.g., nutrient cycling, productivity, resilience).
- Scientists evaluate an ecosystem’s "health" by assessing how complete its biodiversity is.

Inheritance of Traits
- All organisms inherit traits (observable physical features, behaviors, disease susceptibility) from parents.
Genes
- Pieces of hereditary material passed parent → offspring.
- Located on chromosomes.
Chromosomes
- Cellular structures in the nucleus (for multicellular eukaryotes) composed of one long DNA molecule plus proteins.
- Each chromosome carries many genes.
DNA (Deoxyribonucleic Acid)
- Double-stranded molecule built from smaller units called nucleotides.
- Four nucleotide types with standard abbreviations:
- $A$ = adenine
- $C$ = cytosine
- $T$ = thymine
- $G$ = guanine
- A gene is a specific sequence ("stretch") of nucleotides along a chromosome.

Protein Basics
- Proteins perform structural, catalytic, transport, and regulatory functions inside cells.
- Made of amino acids linked in a precise order → determines 3-D shape → determines function.
Gene → Protein Flow (Central Dogma simplified)
- Order of nucleotides in a gene encodes the order of amino acids in one or more proteins.
- Multiple genes → multiple proteins → wide array of traits.
Significance
- Mutations (changes in nucleotide order) can alter amino-acid sequence, potentially changing protein function and, therefore, traits.

Species-Specific Chromosome Number
- Each species possesses a characteristic chromosome count; e.g., typical human somatic (body) cell holds $46$ chromosomes.
Homologous Chromosomes
- Chromosomes occur in matching pairs in many species.
- Human set: $23$ homologous pairs → totaling $46$ chromosomes.
- Homologous chromosomes are identical in size & shape and carry the same genes, though not necessarily the same alleles (gene versions).
Karyotype
- Laboratory image or diagram of an organism’s complete set of chromosomes.
- Homologous pairs arranged side-by-side → facilitates detection of structural differences or aneuploidies (e.g., trisomy, monosomy) that may cause genetic conditions.

Food-web knowledge underpins conservation strategies: knowing producer/consumer/decomposer roles guides restoration or management plans.
Declining biodiversity (human-driven) directly influences food-web stability and, by extension, ecosystem services (pollination, water purification).
Understanding chromosomes & genes is foundational for medical genetics, biotechnology, and ethical debates (e.g., gene editing, conservation of endangered species’ genomes).