Life Science: Biology Regents Review - June 2026

Survival Strategies in Colder Climates: Hibernation

• Definition and Function: Hibernation is an evolved adaptation in certain species to conserve energy during winter. It is a period of inactivity that slows down life processes.

• Energy Conservation: It is estimated that hibernation allows organisms to use nearly $70$ to $100$ times less energy when environmental resources are limited.

• Example Species: Some species of ground squirrels and bears utilize this strategy.

• Ground Squirrel Anatomy: Key body systems involved in the hibernation model include:

• Respiratory System: Lungs.

  • Nervous System: Brain.

  • Digestive/Excretory Systems: Mouth, stomach, liver, kidney, small intestine, large intestine.

  • Circulatory/Muscular/Skeletal Systems: Heart, muscle, bone, blood vessels.

Physiological Changes During Hibernation

• Blood Clot Prevention: Hibernators exhibit physiological changes to prevent blood clots. A primary change is the significant difference in platelet count during hibernation compared to periods of activity.

  • Platelets: These are blood components formed in the marrow of bones (e.g., leg bones) that assist in blood clotting.

  • Mechanism: The bone marrow of the skeletal system decreases platelet production, which are then released into the circulatory system at lower rates to prevent clots from disrupting blood flow during inactivity.

• Cellular Respiration Process: To convert matter and energy into usable forms (ATP), the ground squirrel cells undergo chemical processes with the following inputs and outputs:

  • Inputs: Sugar and Oxygen.

  • Outputs: Water, ATP, and Carbon Dioxide.

Immune System Responses and Evolutionary Adaptation

• White Blood Cell (WBC) Reduction: Studies show immune system function is affected during hibernation to conserve energy.

  • Scandinavian Brown Bear: Approximately $40\%$ reduction.

  • 13-Lined Ground Squirrel: Approximately $90\%$ reduction.

  • Northern Long-Eared Bat: Approximately $45\%$ reduction.

• Fungal Infection in Bats: A fungus has caused massive losses in bat populations. Bats that awaken periodically during hibernation can reactivate their immune systems, potentially leading to an evolutionary increase in this trait within the population due to survival and reproduction.

Impact of Nitrogen on Aquatic Ecosystems

• Algae Population Dynamics: Researchers tested the effect of nitrogen ($N$) and pH on algae growth (measured in cell density, $\text{cells/mL} \times 10^6$).

• Nitrogen Effects (over 13-14 days):

  • Higher nitrogen concentrations lead to higher peak cell densities.

  • Concentrations tested: $0\text{ mg/L}$, $36\text{ mg/L}$, $72\text{ mg/L}$, and $144\text{ mg/L}$.

  • At $144\text{ mg/L}$, the density reaches its peak after approximately $13$ days.

• pH Effects: Algae growth varies with acidity; a pH of $7$ shows steady growth after day $7$, while pH $8$ reaches high density early but declines.

• Trophic Levels and Food Web: In a freshwater food web (Algae $\rightarrow$ Zooplankton/Clams/Aquatic Plants $\rightarrow$ Small fish/Duck $\rightarrow$ Large fish/Eagle):

  • Addition of nitrogen increases producer populations (algae), which increases available energy and raising the carrying capacity for the rest of the web.

• Harmful Algae Blooms (HABs): Excess fertilizer runoff (nitrogen) causes HABs, which impact dissolved oxygen. Higher algae density leads to lower dissolved oxygen levels ($\text{mg/L}$), negatively impacting aquatic life.

• Proposed Solutions: Minimizing runoff through agricultural practices is considered more effective/safe than adding chemicals or non-native species.

Genetics and Selection in Chernobyl Wildlife

• Event: 1986 nuclear reactor disaster released radioactive material in Eastern Europe.

• Eastern Tree Frog ($Hyla orientalis$): Variation in skin color (green vs. black) is determined by melanin levels.

  • Before disaster: Mostly green (camouflage in trees) with a minority of black frogs.

  • After disaster: Population became significantly darker (more black frogs) near high radiation areas.

• Melanin and Luminance: Higher melanin levels result in lower dorsal skin luminance (perceived brightness). Frogs closest to the nuclear plant show the lowest luminance.

• Wildlife Persistence: Despite radiation, elk, roe deer, and wild boar populations have rebounded to levels similar to protected reserves. The roe deer population, initially near zero, increased through natural selection as survivors with favorable traits reproduced.

Reproductive Biology and PCOS

• Polycystic Ovary Syndrome (PCOS): Affects $8\%$ to $13\%$ of women. It involves a failure in feedback mechanisms.

• Hormonal Regulation: The 28-day cycle involves Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), Estrogen, and Progesterone.

  • In PCOS, patients may lack the sharp peak in FSH or experience elevated Estrogen and FSH without proper follicle maturation.

  • PCOS patients often have twice the number of follicles, but most remain underdeveloped.

• Fertilization Mechanisms: When a sperm binds to an egg, the Endoplasmic Reticulum (ER) releases signal molecules. This triggers reactions leading to the construction of an impenetrable membrane to prevent polyspermy.

• Treatment Trade-offs:

  • Plan 1 (Medication): May be more reliable but has safety/side-effect concerns.

  • Plan 2 (Exercise/Diet): Safer and lower cost, but requires significant behavioral consistency.

Evolutionary Developmental Biology: Tails in Primates

• Primates Divergence: Hominoids (apes/humans) diverged from monkey-like primates $15$ to $20$ million years ago ($\text{Mya}$) and evolved without tails.

• TBXT Gene: Codes for a transcription factor protein that activates genes for tail production in early embryonic development.

• AluY Insertion: Taillessness is caused by the insertion of the $AluY$ base sequence into a noncoding region of the TBXT gene.

  • In the modified gene, coding region $6$ is spliced out and not expressed in the mRNA.

  • Missing region $6$ results in shortened or absent tails.

• Mouse Model (Hybrid Cross):

  • $TBXT^{-6} / TBXT^{-6}$: 0 surviving offspring.

  • $TBXT^{-6} / TBXT^{+}$: 63 offspring with no or short tails.

  • $TBXT^{+} / TBXT^{+}$: 35 offspring with long tails.

Earth Systems and Carbon Cycling

• Carboniferous Period ($359$ to $299\text{ Mya}$): High plant biomass led to fossil fuel formation. Carbon transferred from the biosphere (plants) to the geosphere (sediments) as coal, oil, and natural gas.

• Carbon Flux Data:

  • Combustion/Human use: $6.3 \times 10^9\text{ tons/year}$.

  • Sea-surface gas exchange: $92 \times 10^9\text{ tons/year}$ (atmosphere to ocean) vs. $90 \times 10^9\text{ tons/year}$ (ocean to atmosphere).

• Solutions to Overuse: Transitioning to electric passenger vehicles (EVs) to reduce atmospheric carbon and improve air quality, balancing criteria (cleaner air) vs. constraints (cost and style).

Honeybee Behavior and Ecosystem Services

• Pollination Service: Honeybees pollinate $80\%$ of all flowering plants, including over $130$ fruit and vegetable types.

• Social Roles:

  • Queen: Lays up to $2000$ eggs daily; controls social order.

  • Drones: Males that mate with the queen.

  • Workers: Gather nectar, defend the hive, produce honey, and release pheromones for communication.

• Threats: Introduction of parasitic mites and consolidation by breeders have decreased genetic diversity and population size.

• Transport Economics: Global honey market is expected to surpass $\$1\text{ billion}$ by 2028. However, transporting hives causes stress due to high heat, noise, and lack of water.

Tapirs: Rainforest Gardeners

• Ecological Role: Baird's tapir ($Baird's tapir$) in Costa Rica disperses seeds via feces.

• Seed Dispersal Data:

  • Undisturbed Area: $2950\text{ seeds per hectare}$.

  • Degraded Area: $9822\text{ seeds per hectare}$ (vital for regeneration).

• Trophic Levels: Tapirs (Primary Consumers) have more available energy ($10\%$) than jaguars (Tertiary Consumers, $0.1\%$), supporting a larger tapir population.

• Population Trends: Efforts include reintroductions (1929) and supplementary feeding to combat declines due to poaching and habitat loss.

Caffeine Consumption and ADORA2A Genetics

• Teenager Intake Limit: Pediatric doctors suggest consumers aged 12–18 limit intake to $100\text{ mg/day}$; many energy drinks contain $300\text{ mg}$.

• Physiological Effects: Caffeine binds to adenosine receptors in the nervous system, preventing adenosine (which regulates sleep/oxygen) from binding, lead to alertness.

• Genetic Variation in ADORA2A:

  • Ancestral Form (CC): Slow responder.

  • Hybrid (TC/CT): Slow responder.

  • Recent Variant (TT): Fast responder.

  • This is a single base substitution (mutation) in the DNA sequence.

• Enzymatic Digestion: The $CYP1A2$ enzyme is primarily responsible for digesting caffeine.

Australian Evolutionary History

• Geological Isolation: Australia separated from the supercontinent $130\text{ Mya}$. Marsupials (pouched mammals) dominated after placental mammals took over elsewhere following a mass extinction $65\text{ Mya}$.

• Koala Adaptation: Modern koalas ($4$–$15\text{ kg}$) survived in dry climates with eucalyptus, while the Giant koala ($15$–$20\text{ kg}$) from humid rainforests went extinct as conditions changed.

• Climate-Driven Morphological Changes: Since the late 1800s, rising global surface temperatures (correlation with $1.5\text{--}2.0^\text{o}\text{F}$ increase) have led to larger heat-regulating appendages in parrots (beaks), shrews (tails), and bats (wings).

Mercury Concentration in Onondaga Lake

• History: Mercury dumping occurred from 1880 to 1970.

• Biomagnification: Mercury concentration increases up the food chain (measured in $\text{ng/kg}$):

  • Water: $1$

  • Bacteria/Phytoplankton: $10$

  • Protozoa/Zooplankton: $100$

  • Insect Larvae: $1000$

  • Fish Frye (Young): $10,000$

  • Minnows: $100,000$

  • Medium Fish (Pumpkinseed): $1,000,000$

  • Predators (Walleye/Smallmouth): $10,000,000$

• Remediation Goal: Reduce tissue levels to less than $0.3\text{ ppm}$. Walleye and smallmouth bass mass reaches over $10,000\text{ g}$ and $2,900\text{ g}$ respectively, sequestering higher mercury levels than smaller fish like banded killifish ($1$–$5\text{ g}$).