Honors Biology Review
Unit 5: Photosynthesis
Biotic vs. Abiotic Factors:
Biotic factors are living components of an ecosystem.
Abiotic factors are non-living components of an ecosystem.
Keystone Species:
A keystone species plays a critical role in maintaining the structure of an ecological community and affects many other organisms in an ecosystem.
Example: Sea otters control sea urchin populations, preventing them from destroying kelp forests.
Competition vs. Predation:
Competition: Organisms vie for the same resources (e.g., food, space).
Predation: One organism (predator) hunts and kills another (prey) for food.
Symbiosis:
Mutualism: Both organisms benefit.
Commensalism: One organism benefits, and the other is neither harmed nor helped.
Parasitism: One organism (parasite) benefits at the expense of the other (host).
Food Chains and Food Webs:
Food chains are linear sequences of organisms through which nutrients and energy pass as one organism eats another.
Food webs are interconnected food chains that represent the complex feeding relationships in an ecosystem.
They illustrate the flow of matter and energy within an ecosystem.
Food Web Components:
Producer: An autotroph that makes its own food (e.g., plants, phytoplankton).
Carnivore: An animal that eats other animals.
Omnivore: An animal that eats both plants and animals.
Scavenger: An animal that feeds on dead organisms.
Herbivore: An animal that eats plants.
Primary Consumer: An organism that eats producers (herbivore).
Secondary Consumer: An organism that eats primary consumers (carnivore or omnivore).
Tertiary Consumer: An organism that eats secondary consumers (carnivore).
Energy Transfer in Food Webs:
Only about 10% of the energy available at one trophic level is transferred to the next level; the rest is lost as heat.
Example: If phytoplankton have 5,926 Joules of energy, the kittiwake (a tertiary consumer) would have significantly less energy available due to energy loss at each trophic level.
Carbohydrates:
Elements: Carbon, Hydrogen, and Oxygen.
Monomers: Monosaccharides (e.g., glucose, fructose).
Functions: Energy storage and structural support.
Monosaccharides are simple sugars; Disaccharides are two monosaccharides joined together; Polysaccharides are many monosaccharides joined together.
Polysaccharides:
Starch: Energy storage in plants.
Glycogen: Energy storage in animals.
Cellulose: Structural component of plant cell walls.
Polysaccharides are formed through dehydration reactions and broken down through hydrolysis.
ATP (Adenosine Triphosphate):
ATP is the primary energy currency of the cell.
It stores and releases energy for cellular activities.
Photosynthesis Equation:
Carbon dioxide + Water + Light Energy -> Glucose + Oxygen
Chloroplast Structure:
Grana/Granum: Stacks of thylakoids.
Stroma: Fluid-filled space surrounding the grana.
Thylakoid: Membrane-bound compartment inside the chloroplast.
Light Reaction vs. Calvin Cycle (Dark Reaction):
Light Reaction:
Purpose: Convert light energy into chemical energy (ATP and NADPH).
Inputs: Water, light, NADP+, ADP.
Outputs: Oxygen, ATP, NADPH.
Location: Thylakoid membranes.
Calvin Cycle:
Purpose: Use chemical energy (ATP and NADPH) to fix carbon dioxide and produce glucose.
Inputs: Carbon dioxide, ATP, NADPH.
Outputs: Glucose, ADP, NADP+.
Location: Stroma.
Isotopes in Photosynthesis:
Isotopes have been used to trace the pathway of carbon dioxide and water molecules during photosynthesis.
Chlorophyll:
A pigment that absorbs light energy to initiate the light reaction.
NADP+ and NADPH:
NADP+ is an electron carrier that accepts electrons during the light reaction, forming NADPH.
Energized Electrons:
Energized electrons from chlorophyll are passed along an electron transport chain, which generates ATP and NADPH.
Role of Water:
Water is split during the light reaction to provide electrons, protons, and oxygen.
ATP Production in Light Reaction:
ATP is produced through chemiosmosis, where protons flow down a concentration gradient across the thylakoid membrane, driving ATP synthase.
Final Product of Calvin Cycle:
G3P (glyceraldehyde-3-phosphate), a three-carbon sugar that can be used to produce glucose and other organic molecules.
Carbon Fixation:
The energy of ATP and NADPH is used to convert carbon dioxide into G3P.
Rubisco:
An enzyme that catalyzes the first step of the Calvin cycle (carbon fixation).
Photosynthesis as an Overall Process:
The light and dark reactions work together to convert light energy, water, and carbon dioxide into glucose and oxygen.
Importance of Photosynthesis:
It is the foundation of most food chains, provides oxygen for the atmosphere, and removes carbon dioxide.
Cellular Respiration vs. Photosynthesis:
Photosynthesis uses carbon dioxide and water to produce glucose and oxygen.
Cellular respiration uses glucose and oxygen to produce carbon dioxide, water, and energy (ATP).
They are complementary processes.
Photosynthesis and Climate Change:
Photosynthesis helps to moderate climate change by removing carbon dioxide from the atmosphere.
Unit 6: Cellular Reproduction
Cell Specialization:
Cells differentiate to perform specific functions within an organism.
Important for development because it allows for the formation of complex tissues and organs.
Asexual Reproduction, Sexual Reproduction, and Growth/Regeneration:
Asexual Reproduction: A single parent produces offspring that are genetically identical to itself.
Sexual Reproduction: Two parents contribute genetic material to produce offspring that are genetically different from either parent.
Growth/Regeneration: Mitosis allows for growth, development, and repair of tissues.
Mitosis:
Important for growth, development, and repair because it produces new cells that are genetically identical to the parent cell.
Stages of Cell Division:
Interphase is the longest phase of the cell cycle, while prophase is the longest stage of mitosis.
Interphase:
G1 Phase: Cell growth and normal metabolic functions.
S Phase: DNA replication.
G2 Phase: Preparation for mitosis.
G0 Phase: A non-dividing state; cells exit the cell cycle and do not replicate.
Cell Cycle Checkpoints:
G1 Checkpoint: Checks for cell size, nutrients, growth factors, and DNA damage.
G2 Checkpoint: Checks for DNA replication completeness and DNA damage.
M Checkpoint: Checks for chromosome alignment during metaphase.
These checkpoints are important for ensuring that the cell cycle progresses correctly and that damaged cells do not divide.
Mitosis and Cancer:
Cancer is characterized by uncontrolled cell division, often due to mutations that bypass cell cycle checkpoints.
Eukaryotic Chromosome:
Chromosome: Structure containing DNA.
Centromere: Region where sister chromatids are joined.
Sister Chromatid: Identical copies of a chromosome.
Chromatin vs. Chromosome:
Chromatin: Uncondensed DNA found during interphase.
Chromosome: Condensed DNA found during cell division.
Homologous Chromosomes:
Pairs of chromosomes that have the same genes but may have different alleles.
Important in meiosis because they pair up and exchange genetic material during crossing over.
Haploid vs. Diploid Cells:
Haploid Cell: Contains one set of chromosomes (n).
Diploid Cell: Contains two sets of chromosomes (2n).
Crossing Over:
The exchange of genetic material between homologous chromosomes during meiosis.
Increases genetic variation.
Meiosis:
Meiosis needs to occur in sexually reproducing organisms to produce haploid gametes (sperm and egg cells).
Maintains the correct chromosome number in offspring after fertilization.
Mitosis vs. Meiosis:
Mitosis:
Purpose: Growth, repair, and asexual reproduction.
Daughter Cells: 2.
Ploidy: Diploid.
Genetic Relationship: Genetically identical to the parent cell.
Meiosis:
Purpose: Sexual reproduction.
Daughter Cells: 4.
Ploidy: Haploid.
Genetic Relationship: Genetically different from the parent cell and each other.
Unit 7: Patterns of Heredity (Genetics)
Gregor Mendel:
Considered the father of modern genetics.
Developed the basic principles of heredity through experiments with pea plants.
Principles of Inheritance:
Principle of Dominance: Some alleles are dominant and will mask the expression of recessive alleles.
Law of Segregation: Allele pairs separate during gamete formation.
Law of Independent Assortment: Alleles for different traits assort independently of one another during gamete formation.
Punnett Square Example:
Erect ears (E) is dominant over droopy ears (e).
If two heterozygous dogs (Ee) have puppies, the possible genotypes are EE, Ee, and ee.
Punnett square:
|| E | e |
|---|---|
E | EE | Ee |
e | Ee | ee |
Genes and Alleles:
Gene: A segment of DNA that codes for a trait.
Allele: Different forms of a gene.
Genetic Terminology:
Homozygous: Having two identical alleles for a trait (e.g., EE or ee).
Heterozygous: Having two different alleles for a trait (e.g., Ee).
Dominant: An allele that masks the expression of a recessive allele.
Recessive: An allele that is masked by a dominant allele.
Genotype: The genetic makeup of an organism (e.g., EE, Ee, ee).
Phenotype: The physical expression of a trait (e.g., erect ears or droopy ears).
Dihybrid cross example:
Female guinea pig: heterozygous for both fur color (Dd) and coat texture (Rr)
Male guinea pig: dark fur (D_) and heterozygous for coat texture (Rr)
Dark fur color is dominant (D) and light fur (d) is recessive. Rough coat texture (R) is dominant, while smooth coat (r) is recessive.
Incomplete Dominance and Codominance:
Incomplete Dominance: The heterozygous phenotype is a blend of the two homozygous phenotypes.
Codominance: Both alleles are expressed equally in the heterozygous phenotype.
Multiple Alleles and Polygenic Traits:
Multiple Alleles: More than two alleles exist for a particular gene (e.g., human blood types).
Polygenic Traits: Traits controlled by multiple genes (e.g., human height, skin color).
Codominance Example:
Straight hair (SS) and curly hair (CC) are codominant, resulting in wavy hair (SC).
If a curly-haired female (CC) marries a wavy-haired male (SC), the chances of having a curly-haired child are 50%.
Sex-Linked Genes:
Genes located on the sex chromosomes (X and Y).
Sex-Linked Traits:
Occur more often in males because they only have one X chromosome.
Carriers:
Females can be carriers for sex-linked recessive traits because they have two X chromosomes; males cannot be carriers because they have only one X chromosome.
Sex-Linked Recessive Disease Example:
Colorblindness is inherited as a sex-linked recessive disease.
If an affected male marries a heterozygous female, there is a 50% chance of having an affected child.
Pedigree:
A diagram that shows the inheritance of a trait within a family.
Pedigree Analysis:
Used to determine the probability of having a child with a genetic disorder.
Pedigree Symbols:
Squares represent males; circles represent females.
Shading indicates that the individual has the trait.
Hemophilia Pedigree:
Individuals can be identified as carriers based on their position in the pedigree and the genotypes of their parents and offspring.
Unit 8: Molecular Inheritance (DNA)
Scientists and DNA:
Chargaff: Discovered that the amount of adenine (A) is equal to thymine (T) and the amount of guanine (G) is equal to cytosine (C).
Franklin: Used X-ray diffraction to capture the first image of DNA, revealing its helical structure.
Pauling: Proposed a triple-helix model of DNA (which was incorrect).
Watson & Crick: Developed the correct double helix model of DNA.
Monomer of DNA:
Nucleotide, composed of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
Nitrogenous Bases:
Adenine (A) and Guanine (G) are purines (double-ring structures).
Cytosine (C) and Thymine (T) are pyrimidines (single-ring structures).
Base Pairing:
Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
DNA Molecule Sketch:
Double helix with sugar-phosphate backbone and nitrogenous bases paired in the middle.
Antiparallel DNA:
DNA strands run in opposite directions (5' to 3' and 3' to 5').
This arrangement is important for DNA replication.
DNA Replication:
The process of copying a DNA molecule.
Semiconservative Replication:
Each new DNA molecule consists of one original strand and one new strand.
Leading and Lagging Strands:
Leading Strand: Synthesized continuously in the 5' to 3' direction.
Lagging Strand: Synthesized discontinuously in short fragments (Okazaki fragments) in the 5' to 3' direction.
Okazaki Fragments:
Short DNA fragments synthesized on the lagging strand.
They are dealt with by DNA ligase, which joins them together.
Enzymes in DNA Replication:
DNA Helicase: Unwinds the DNA double helix.
DNA Polymerase: Adds nucleotides to the growing DNA strand.
DNA Ligase: Joins Okazaki fragments together.
DNA Primase: Synthesizes RNA primers to initiate DNA synthesis.
PCR (Polymerase Chain Reaction):
A technique used to amplify a specific DNA sequence.
Connects to DNA replication because it uses DNA polymerase to copy DNA.
Gel Electrophoresis:
A technique used to separate DNA fragments based on size.
Connects to PCR because it can be used to analyze the products of PCR.
Shortest fragments travel farthest; longest fragments travel the least far.
DNA vs. RNA:
DNA: Double-stranded, deoxyribose sugar, thymine (T).
RNA: Single-stranded, ribose sugar, uracil (U).
Protein Synthesis:
Essential for all life because proteins perform a wide variety of functions in cells and organisms.
Transcription and Translation:
Transcription: DNA sequence is copied into mRNA; occurs in the nucleus.
Translation: mRNA sequence is used to synthesize a protein; occurs in the ribosome.
Codon vs. Anticodon:
Codon: A three-nucleotide sequence on mRNA that specifies an amino acid.
Anticodon: A three-nucleotide sequence on tRNA that is complementary to a codon on mRNA.
mRNA, tRNA, RNA Polymerase, and Ribosomes in Protein Synthesis:
mRNA: Carries the genetic code from DNA to the ribosome.
tRNA: Transfers amino acids to the ribosome.
RNA Polymerase: Synthesizes mRNA during transcription.
Ribosomes: Site of protein synthesis.
Example of Filling in the Blanks:
DNA: CGT
mRNA: GCA
Amino Acid: Alanine
tRNA anticodon: CGU
Mutation:
A change in the DNA sequence.
Mutations can impact the structure of proteins by changing the amino acid sequence.
Point Mutations vs. Chromosomal Mutations:
Point Mutations: Changes in a single nucleotide (e.g., substitution, insertion, deletion).
Chromosomal Mutations: Changes in the structure or number of chromosomes (e.g., deletion, duplication, inversion, translocation).
Frameshift Mutation:
Insertion or deletion of nucleotides that alters the reading frame of the mRNA.
Beneficial and Harmful Mutations:
Beneficial Mutations: Can lead to new traits that improve an organism's fitness.
Harmful Mutations: Can lead to genetic disorders or reduced fitness.
Unit 9: Biological Evolution
Charles Darwin:
Developed the theory of evolution by natural selection.
Evolution:
Change in the heritable characteristics of biological populations over successive generations.
Individuals Cannot Evolve:
Evolution occurs at the population level, not the individual level.
Species:
A group of organisms that can interbreed and produce fertile offspring.
Natural Selection:
The process by which organisms with traits that are better suited to their environment survive and reproduce more successfully.
Survival of the Fittest:
Refers to the ability of an organism to survive and reproduce in its environment.
Relative fitness is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.
Sexual Selection vs. Artificial Selection:
Sexual Selection: Individuals with certain traits are more likely to obtain mates (e.g., peacock feathers).
Artificial Selection: Humans selectively breed organisms for desired traits (e.g., dog breeds).
Selection is Non-Random:
Natural, sexual, and artificial selection are non-random processes because they favor certain traits over others.
Genetic Drift:
Random changes in allele frequencies due to chance events.
Founder Effect and Bottleneck Effect:
Founder Effect: A small group of individuals establishes a new population, leading to reduced genetic diversity.
Bottleneck Effect: A sudden reduction in population size due to a catastrophic event, leading to reduced genetic diversity.
Gene Flow:
The transfer of genetic material from one population to another.
Fossil Record:
Provides evidence for evolution by showing the history of life on Earth.
Molecular Evidence:
Similarities in DNA and protein sequences provide evidence for common ancestry.
Biogeography:
The study of the geographic distribution of species.
Distantly related species in different places may share similar traits due to convergent evolution.
Homologous Structures:
Structures that have a common ancestry but may have different functions.
Convergent Evolution:
The independent evolution of similar traits in different lineages.
Speciation:
The process by which new species arise.
Isolation and Speciation:
Geographic Isolation: Physical separation of populations.
Reproductive Isolation: Inability of populations to interbreed.
Cladogram:
A diagram that shows the evolutionary relationships among organisms.
Phylogenetic Tree:
Similar to a cladogram but also shows the amount of evolutionary time or change.
Cladogram Construction:
Construct a cladogram based on shared derived characters.