Biology Crash Course

🧬 Course Review: Life Science Biology Regent Exam

This review covers key life science biology concepts, particularly relevant for the New York Regent exam. While tailored for New York, the content is generally applicable, though you should always cross-reference with your specific state's standards.

⚖ Feedback and Homeostasis

Feedback loops are crucial for maintaining homeostasis, which is the balance of internal conditions necessary for an organism's survival.

• Examples of conditions regulated by homeostasis:

  • Water levels

  • Temperature

  • Heart rate

• Failure to maintain homeostasis can lead to disease or death.

Blood Pressure Regulation

Blood pressure regulation is an example of a feedback loop:

1. Normal blood pressure is the initial state.

2. A stressor causes blood pressure to rise.

3. Receptors detect the change and trigger a response.

4. The body decreases heart rate and increases blood vessel diameter.

5. Blood pressure returns to normal.

Stomata in Plants

Stomata, openings in plant leaves, regulate gas exchange and water loss.

• Guard cells surrounding the stomata open or close the stomata based on:

  • Water availability

  • Plant hormones

  • Environmental stressors

• Closing stomata prevents water loss.

• Opening stomata allows carbon dioxide intake for photosynthesis.

🚌 Cell Transport

Cells regulate their internal environment by controlling the movement of substances in and out. Three main types of cell transport:

• Diffusion: Movement of molecules from an area of high concentration to an area of low concentration. No energy is required.

  • Analogy: A child going down a slide.

• Facilitated Diffusion: Movement of molecules from high to low concentration with the help of a transport protein.

  • Analogy: A child going down a slide with a little push.

• Active Transport: Movement of molecules from low to high concentration, requiring energy (ATP).

  • Analogy: A child climbing up a slide.

🧬 DNA and Protein Synthesis

All living things contain DNA.

• In eukaryotic organisms, DNA is found in the nucleus.

• In prokaryotic organisms, DNA is found in the nucleoid.

• Monomers of DNA are nucleotides, which contain:

  • Phosphate

  • Sugar (deoxyribose)

  • Nitrogenous Base

The central dogma of biology, or protein synthesis, explains how the DNA code translates into physical characteristics.

1. Transcription: DNA is transcribed into mRNA in the nucleus.

   • DNA separates with the help of enzymes.

   • RNA bases are added to form an mRNA strand, complementary to the DNA.

   • mRNA leaves the nucleus.

2. Translation: mRNA is translated into a protein at the ribosome.

   • Each set of three mRNA bases (codon) pairs with a tRNA molecule.

   • tRNA brings a specific amino acid.

   • Amino acids are linked together to form a protein.

The order of amino acids determines how the protein folds and its function.

☀ Photosynthesis

Photosynthesis transforms light energy into chemical energy in plants, algae, and some bacteria.

• Occurs in the chloroplast.

• Chloroplasts contain chlorophyll, which absorbs light energy.

• Most of the energy for life on Earth originates from the sun and is captured through photosynthesis.

• General equation: Sunlight + Carbon Dioxide + Water→ Glucose + Oxygen Sunlight+CO2+H2O→C6H12O6+O2Sunlight+CO2​+H2​O→C6​H12​O6​+O2​

⚡️ Cellular Respiration

Cellular respiration uses oxygen and glucose to generate ATP (energy) for the cell, along with water and carbon dioxide as byproducts.

• Occurs in the mitochondria of eukaryotic organisms.

• All eukaryotic organisms perform cellular respiration.

• We inhale oxygen for this process and exhale carbon dioxide as a result.

• General equation: Glucose + Oxygen → Energy + Water + CarbonDioxide C6H12O6+O2→ATP+H2O+CO2C6​H12​O6​+O2​→ATP+H2​O+CO2​

Anaerobic Respiration

Anaerobic respiration occurs without oxygen.

• Less efficient than aerobic respiration.

• Generates less ATP.

• Some organisms primarily use anaerobic respiration; others, like humans, use it temporarily (e.g., in muscle cells during intense exercise).

• Inputs: Glucose (without oxygen)
  Outputs: Less ATP (energy), and byproducts like lactic acid

♻ Carbon Cycle

Carbon and other elements cycle through the environment via various processes. Key processes linking carbon to the environment:

• Photosynthesis: Plants take in carbon dioxide to generate glucose.

• Cellular Respiration: Organisms consume glucose, releasing carbon dioxide.

♻ Nutrient Cycles

Carbon Cycle

Carbon in glucose, produced by other organisms, is eventually released through respiration. It can also be released through:

• Decomposition: Decomposers break down dead organisms and organic matter, releasing carbon back into the environment as carbon dioxide (CO2CO2​).

• Combustion: Burning organic materials (like fossil fuels or wood) also releases carbon into the atmosphere as carbon dioxide (CO2CO2​).

The carbon dioxide then goes back into photosynthesis or is absorbed by the ocean.

Nitrogen Cycle

Nitrogen is abundant in the environment and is needed in the molecules in our cells. Plants and animals rely on the nitrogen cycle to change nitrogen into a form they can use.

• Bacteria plays a large role by converting nitrogen into different nitrogen products like ammonium and then nitrate, which can be taken up by plant roots and consumed by animals.

• When organisms decompose, nitrogen is converted back into ammonium and nitrate.

• Nitrogen fixation converts nitrogen into usable forms like ammonium and nitrate, which plants can absorb.

• Nitrogen, like carbon, constantly moves throughout the environment.

⚡️ Energy Flow in Ecosystems

As one organism consumes another, it consumes its molecules containing energy. As we go up in trophic levels, energy is lost.

• Most energy is at the bottom of a trophic pyramid.

• ~90% of energy is lost as heat.

• Most organisms and biomass are at the bottom levels of the pyramid.

As we go up trophic levels, more energy is lost to the environment.

⚖ Ecosystem Dynamics

Ecosystems are complex with interactions between organisms and factors like food, water, competition, and diseases affecting population sizes.

• Carrying Capacity:

  The maximum population size that an environment can sustain.

Population growth often levels off at the carrying capacity.

Ecosystems can undergo changes from:

• Forest fires

• Eutrophication:

  Excess nutrients introduced to a system, causing overgrowth of one type of organism and altering the balance.

Other dramatic events like fire, flooding, and earthquakes can also cause changes.

🌳 Earth's Resources and Human Impact

Humans rely on Earth's resources, including:

• Renewable Resources:

  Resources that can be replaced by natural processes relatively quickly (e.g., forests, sunlight).

• Non-Renewable Resources:

  Resources that cannot be replaced within human lifetimes (e.g., fossil fuels).

Human population and consumption impact resource availability.

• Global Warming:

  An increase in the average temperature of the biosphere, mainly due to humans burning fossil fuels.

Continued global warming can lead to rising sea levels and coastal flooding. Conserving resources and cutting back on greenhouse gas emissions can help.

Disruptions to Environments

• Introduction of non-native species

• Introduction of diseases

• Human-caused habitat changes (urbanization, pollution, deforestation, logging)

🧬 DNA and Chromosomes

DNA is condensed into chromosomes for cell division.

• Inside the cell, uncondensed DNA is in the form of chromatin.

• A duplicated chromosome has an "X" or butterfly figure.

• The identical strands of DNA are called sister chromatids.

⚙ Cell Cycle

Before cell division, DNA condenses into chromosomes, part of the cell cycle.

• The cell cycle has checkpoints.

• Interphase: Includes G1, S, and G2 phases.

• M Phase: Cell division occurs.

DNA replication happens during the S phase to ensure each daughter cell gets an exact copy of DNA. Cytokinesis is when the cell physically splits into two new daughter cells.

DNA replication is semiconservative: each new DNA strand has one old strand and one new strand.

➗ Mitosis

Mitosis Stages: PMAT (Prophase, Metaphase, Anaphase, Telophase), followed by Cytokinesis.

👶 Meiosis

• Mitosis is for regular growth and cell division, producing identical daughter cells. It's used for asexual reproduction.

• Meiosis is for creating new organisms through sexual reproduction, producing genetically unique haploid gametes (sperm and egg cells).
  

🧬 Cell Differentiation

Cells can differentiate by activating different parts of their DNA.

• Every organism has the same DNA in all cells, but different parts are expressed.

• Different parts of DNA are activated in muscle cells versus neurons.

🚧 Cell Cycle Checkpoints

The cell cycle has checkpoints regulated by proteins. If these checkpoints are messed up, then...

Uncontrolled Cell Growth and Cell Structures 🧬

When cells divide uncontrollably, even when they shouldn't, it can lead to issues like cancer. This uncontrolled growth can result in tumors. These issues are often caused by mutations in the cell's DNA. DNA produces proteins called cyclins, and when these are disrupted or not produced in the correct amounts, it can lead to uncontrolled cell growth and cancer.

All cells are surrounded by a phospholipid bilayer membrane, contain genetic information in the form of DNA, and have cytoplasm.

Prokaryotic vs. Eukaryotic Cells 🦠

• Prokaryotic Cells: Simpler, with a membrane, ribosomes, and free-floating genetic information in a nucleoid. All bacteria are prokaryotic.

• Eukaryotic Cells: Larger and more complex, with membrane-bound organelles, allowing for compartmentalized and efficient reactions. Animals, plants, and fungi are eukaryotic.

A key difference is that eukaryotic organisms have a nucleus that surrounds the genetic information, while prokaryotic cells do not.

Major Organelles and Their Functions ⚙

Meiosis and Genetic Variation 🧬

Meiosis produces haploid cells (sperm or egg cells in humans) containing half the genetic information of the parent cell. During fertilization, two haploid cells combine to form a zygote with a complete set of chromosomes. The zygote then undergoes mitosis to grow and differentiate.

Human reproduction and development are influenced by hormones, the environment, and gene expression. In females, the menstrual cycle is regulated by hormone levels to prepare the uterus and ovaries for pregnancy.

Reproductive System Components 🫃

• Gonads: Sex organs (ovaries in females, testes in males).

• Gametes: Egg cells produced in the ovaries, which travel through the fallopian tubes. Sperm are produced in the testes.

• Uterus: Provides an environment for the development of the embryo and fetus after a fertilized egg implants.

• Placenta: Connected to the developing embryo via the umbilical cord, providing essential nutrients.

During embryonic growth, essential organs develop early. Environmental factors, such as alcohol or tobacco, can negatively affect the developing embryo.

Meiosis Details 🧐

Meiosis involves two rounds of division, resulting in cells with half the genetic information of the parent cell. Errors during meiosis, where chromosomes don't split correctly, can lead to chromosomal conditions like Trisomy 21 (Down syndrome), where there are three copies of the 21st chromosome instead of two.

Karyotypes: Organized displays of chromosomes used to identify chromosomal conditions. A typical biological female has two X chromosomes (XX), while a biological male has one X and one Y chromosome (XY).

Sources of Genetic Variation 🤹

Genetic variation among humans, even siblings, arises from how chromosomes align and combine during meiosis.

• Crossing Over: Homologous chromosomes exchange genetic material during prophase I of meiosis, creating new combinations of traits.

• Independent Assortment: Chromosomes line up in different orders, leading to different distributions of traits after meiosis.

• Mutations: Changes in the DNA sequence that can alter protein function and lead to different physical characteristics (phenotypes).

Mutation: A change in the DNA sequence can result in a change in the protein, which can lead to an altered protein function if it doesn't fold the way it normally does, which leads to a different phenotype or a different physical characteristic in the organism.

🧬 Mendelian Genetics

Gregor Mendel is considered the father of genetics. He determined that a single gene could have two different alleles, or versions (dominant and recessive). These combinations lead to the expression of different traits.

Genotypes and Phenotypes

• Genotype: Combination of alleles (heterozygous, homozygous dominant, homozygous recessive).

• Phenotype: Physical characteristic caused by the genotype.

For example:

• If yellow body color is dominant to blue, determine the phenotype of each fish.

• If gray is dominant to orange, determine the phenotype of each owl.

🧮 Punnett Squares

Punnett squares are used to determine the probability of offspring inheriting specific traits.

• Example: Albinism is recessive in axolotls. If two parents with pigment (at least one dominant allele) mate, what are the chances of the offspring being albino?

  • Cross: Two heterozygous parents (Big A little a x Big A little a).

  • Result: 25% chance of albino offspring, 75% chance of non-albino offspring.

🧬 Complex Genetic Traits

Most human traits are polygenic, meaning they are caused by many different genes. Some genetic conditions (cystic fibrosis, Huntington's) are caused by single alleles, but these are rare.

Co-dominance

*   Blood types are an example of co-dominance (AB blood type).

    *   Alleles: $I^A$, $I^B$, i (recessive)
    *   Possible phenotypes: A, B, O, AB

*   Example Cross: Homozygous type A ($I^AI^A$) x Homozygous type B ($I^BI^B$) = 100% chance of offspring being type AB.
*   Example Cross: Type B carrying recessive i ($I^B$i) x Type A carrying recessive i ($I^A$i) = 25% chance of offspring being type O.

Incomplete Dominance

*   Red and white combine to form pink.

📉 Polygenic Traits and Environmental Factors

• Many traits are polygenic, meaning they are controlled by multiple genes.

• Polygenic traits often show a bell curve distribution.

Environmental factors can alter traits:

• Sex determination in certain reptiles is influenced by environmental temperature.

• Hydrangea flower color changes based on soil pH.

🧪 Determining Evolutionary Relationships

DNA Similarity

DNA or protein samples can determine how related different species are. The greater the similarity in protein structure, the closer the relationship.

Gel Electrophoresis

• DNA samples are cut with restriction enzymes and run through a gel matrix with a current.

• Banding patterns indicate DNA similarity.

• Applications:

  • Determining relatedness

  • Forensic analysis: Matching DNA evidence from a crime scene to suspects

🧬 Biotechnology

• Applications:

  • Drugs

  • Medical treatments

  • Agriculture

• Ethical questions:

  • CRISPR gene editing

  • Genetic screening

  • Sterilizing mosquitoes

  • Lab-grown meat

⏳ Evolution

Natural Selection

• Evolutionary fitness: Measured by reproductive success (ability to survive, reproduce, and pass on genes).

• Environments change and act as a selective mechanism on populations.

• Antibiotic Resistance Example:

  • A bacterial population is exposed to antibiotics.

  • Bacteria with resistance survive and reproduce.

  • Over time, the population becomes primarily antibiotic-resistant.

🧬 Natural Selection and Adaptation

Natural selection occurs when certain traits are more favorable in a particular environment, allowing organisms with those traits to survive, reproduce, and pass on their genes more successfully. An example of this is antibiotic resistance, where bacteria that are resistant to antibiotics survive and reproduce after non-resistant bacteria are killed off.

Evidence for Evolution

Evidence for evolution comes from:

• The fossil record

• Geographic distribution of species

• DNA and amino acid sequences (biochemical evidence)

• Embryology, which reveals similarities in how organisms develop

Darwin's Model for Natural Selection

Darwin's ideas behind natural selection include:

• Species often produce more offspring than the environment can support, leading to a struggle for survival.

• Competition for limited resources occurs.

• Individuals with traits best suited to their environment have a competitive advantage.

Adaptations

However, if the environment changes, that adaptation may not be as favorable.

Similar Adaptations in Different Populations

Sometimes, similar adaptations can be seen in different populations. For instance, white fur is an adaptation in Arctic animals like polar bears and foxes, providing a survival advantage through camouflage.

Environmental Changes and Variation

Environments can change, such as experiencing droughts. In these cases, organisms best suited to survive are those that are drought resistant. Diversity within a population is beneficial because it increases the chances of survival in changing environmental conditions.

🌳 Three Domains of Life

The three domains of life are:

• Bacteria: Many species are beneficial and play essential roles in the environment and biotechnology.

• Archaea: These are prokaryotic, single-celled organisms known as extremophiles, living in harsh environments.

• Eukarya: Includes all eukaryotes like protists, fungi, plants, and animals.

🌲 Phylogeny and Evolutionary History

A phylogenetic tree or cladogram is a visualization of evolutionary relatedness between species.

Traits on Cladograms

Traits on cladograms show the evolution of characteristics:

• Each hash mark represents a trait.

• Everything after the hash mark includes that trait.

For example:

⏳ Timeline of Major Events in Earth's History

The Rise of Oxygen (Great Oxidation Event)

The release of oxygen by cyanobacteria transformed the Earth:

• Led to the extinction of many organisms.

• Enabled the rise of aerobic respiration and the evolution of multicellular organisms.

🌎 Positive Human Impact on the Environment

Ways humans can positively impact the environment:

• Reduce consumption of resources.

• Reuse and recycle resources.

• Compost to reduce methane gas buildup in landfills.

• Plant native species to support biodiversity.

• Support sustainable practices.

• Advocate for environmental policies.