New York State Regents Examinations Living Environment (Biology Regents Examination) Syllabus

What is homeostasis?

The maintenance of a stable internal environment within an organism despite changes in external conditions.

What is a negative feedback mechanism and give a biological example?

A control system in which a change triggers a response that reverses the change to restore balance; e.g., insulin lowering blood glucose when it rises (and glucagon raising it when it falls).

How does the body regulate blood glucose levels?

When glucose is high, the pancreas releases insulin (cells take up glucose, liver stores it); when glucose is low, the pancreas releases glucagon (liver releases glucose), keeping levels stable.

What is the role of receptor molecules in maintaining homeostasis and cell communication?

Receptors detect specific signal molecules (like hormones); their specific shape allows them to bind matching molecules, triggering a cellular response.

What is the function of the human digestive system?

To break down food (mechanically and chemically via enzymes) into nutrients small enough to be absorbed into the blood and used by cells.

What is the function of the human circulatory system?

To transport oxygen, nutrients, hormones, and wastes throughout the body via blood, the heart, and blood vessels.

What is the function of the human respiratory system?

To exchange gases — bringing oxygen into the blood and removing carbon dioxide — primarily at the alveoli of the lungs.

What is the function of the human immune system?

To defend the body against pathogens and foreign substances using white blood cells, antibodies, and the recognition of antigens.

How does a vaccine produce immunity?

It introduces weakened or dead pathogens (or antigens) that stimulate the immune system to produce antibodies and memory cells, providing protection against future infection.

What are the four major classes of organic compounds (biomolecules) in living things?

Carbohydrates, lipids (fats), proteins, and nucleic acids.

What are enzymes and what is their general function?

Enzymes are protein catalysts that speed up biochemical reactions by lowering activation energy, without being used up.

How does the 'lock-and-key' model explain enzyme specificity?

An enzyme's active site has a specific shape that fits only a particular substrate, like a key fitting one lock, so each enzyme catalyzes a specific reaction.

How do temperature and pH affect enzyme activity?

Each enzyme has an optimal temperature and pH; extreme values change the enzyme's shape (denaturation), reducing or stopping its activity.

What is the relationship between photosynthesis and cellular respiration?

Photosynthesis uses CO2 and water with light energy to make glucose and oxygen; respiration uses glucose and oxygen to release energy (ATP), producing CO2 and water — they are essentially reverse processes.

What are the four nitrogenous bases of DNA and how do they pair?

Adenine, Thymine, Cytosine, and Guanine; A pairs with T, and C pairs with G (complementary base pairing).

What is a gene?

A segment of DNA that codes for a specific protein (or trait); it is a unit of heredity.

What are the two main steps of protein synthesis?

Transcription (DNA is copied into messenger RNA in the nucleus) and translation (mRNA is read by ribosomes to assemble amino acids into a protein).

How does the sequence of DNA bases determine a protein?

The order of bases determines the order of codons in mRNA, which specifies the sequence of amino acids, which determines the protein's shape and function.

What is a mutation and what are its possible effects?

A change in the DNA base sequence; effects can be harmful, beneficial, or neutral, and only mutations in sex cells (gametes) can be passed to offspring.

What is mitosis and what is its result?

Cell division that produces two genetically identical daughter cells, each with the same chromosome number as the parent; used for growth and repair.

What is meiosis and what is its result?

Cell division that produces four sex cells (gametes) with half the chromosome number of the parent cell, introducing genetic variation.

How do asexual and sexual reproduction differ in terms of offspring genetics?

Asexual reproduction produces genetically identical offspring (clones) from one parent; sexual reproduction combines genes from two parents, producing genetically varied offspring.

What is the role of fertilization in sexual reproduction?

It joins a sperm and an egg (each with half the chromosomes) to form a zygote with the full chromosome number, combining genetic material from both parents.

What are the three main sources of genetic variation in sexually reproducing organisms?

Mutation, recombination/crossing-over during meiosis, and random fertilization (the combining of gametes from two parents).

What is the difference between a dominant and a recessive allele?

A dominant allele is expressed when at least one copy is present and masks the recessive allele; a recessive allele is expressed only when two copies are present (no dominant allele).

What is the difference between genotype and phenotype?

Genotype is the genetic makeup (allele combination, e.g., Bb); phenotype is the observable physical trait expressed (e.g., brown eyes).

What are the four main ideas of Darwin's theory of evolution by natural selection?

Organisms produce more offspring than can survive; there is variation among individuals; some variations give a survival/reproductive advantage; favorable traits are passed on, so populations change over time.

What is 'survival of the fittest' in evolutionary terms?

Individuals with traits best adapted to their environment are more likely to survive and reproduce, passing those favorable traits to the next generation.

What is speciation and how can geographic isolation cause it?

Speciation is the formation of new species; geographic isolation separates populations so they no longer interbreed, and over time genetic differences accumulate until they can no longer reproduce together.

How do structural similarities (homologous structures) provide evidence for evolution?

Similar bone/body structures in different species suggest a common ancestor, indicating evolutionary relationships.

How does comparing DNA or amino acid sequences indicate evolutionary relationships?

The more similar the DNA or protein sequences between two species, the more closely related they are and the more recently they shared a common ancestor.

Why does biodiversity (genetic variation) increase a species' chance of long-term survival?

Greater variation means a higher chance that some individuals have traits allowing them to survive environmental changes, reducing the risk of extinction.

In a food chain, what is the original source of energy and how does energy flow?

The Sun is the original energy source; energy flows from producers to consumers (herbivores, then carnivores) and to decomposers, in one direction.

In an energy pyramid, why does available energy decrease at each higher trophic level?

Only about 10% of energy is passed to the next level; the rest is lost as heat or used for the organism's life processes, so less energy is available higher up.

What is the role of decomposers in an ecosystem?

They break down dead organisms and wastes, recycling nutrients (like carbon and nitrogen) back into the environment for reuse by producers.

Describe the basic carbon cycle.

Producers remove CO2 from the air via photosynthesis; respiration, decomposition, and combustion of fuels return CO2 to the atmosphere, recycling carbon between organisms and the environment.

What is the difference between a producer and a consumer?

A producer (autotroph) makes its own food via photosynthesis; a consumer (heterotroph) obtains energy by eating other organisms.

What is carrying capacity?

The maximum population size of a species that an environment can support indefinitely given available resources (food, water, space).

List four limiting factors that can control the size of a population.

Food/resource availability, space, water, predation, disease, and competition (any factor that limits growth).

Define the symbiotic relationships mutualism, commensalism, and parasitism.

Mutualism: both species benefit; commensalism: one benefits and the other is unaffected; parasitism: one benefits (parasite) while the other (host) is harmed.

What is the difference between a predator and its prey, and how do their populations interact?

A predator hunts and eats prey; their populations cycle — as prey increase, predators increase, which then reduces prey, causing predators to decline (interdependent cycling).

What is ecological succession?

The gradual, predictable change in the species composition of a community over time, eventually leading toward a stable climax community.

What is the difference between primary and secondary succession?

Primary succession begins in a lifeless area with no soil (e.g., bare rock) starting with pioneer species; secondary succession occurs where a community was disturbed but soil remains (e.g., after a fire).

Why does greater biodiversity tend to make an ecosystem more stable?

More species and variety provide alternative food sources and functional redundancy, so the ecosystem can better withstand and recover from disturbances.

What is a pioneer species and what role does it play in succession?

A hardy first colonizer (such as lichens or moss) that begins growing in a barren area, breaking down rock and building soil so other species can later move in.

How does deforestation negatively impact the environment?

It destroys habitats (reducing biodiversity), decreases photosynthesis/oxygen production, increases atmospheric CO2, and causes soil erosion.

How do human activities contribute to global warming?

Burning fossil fuels and deforestation increase atmospheric carbon dioxide (a greenhouse gas), which traps heat and raises Earth's average temperature.

What is biological magnification (bioaccumulation)?

The increasing concentration of toxins (such as pesticides like DDT) in organisms at higher trophic levels as the toxins are passed up the food chain.

Give two ways humans can reduce their negative impact on the environment.

Examples: recycling and reducing waste, conserving energy/using renewable resources, reducing pollution, protecting habitats, and reforestation.

How can an introduced (invasive) species harm a native ecosystem?

Lacking natural predators, it can outcompete native species for resources, reduce biodiversity, and disrupt the balance of the ecosystem.