Exam Review (SBI-3UI) PDF

Unit 1: Diversity What is a Species? -​ Species: A group of organisms that can interbreed and produce fertile offspring under natural conditions. -​ Example: A lion (Panthera leo) and a tiger (Panthera tigris) are different species because they can interbreed (producing ligers),...

Unit 1: Diversity What is a Species? -​ Species: A group of organisms that can interbreed and produce fertile offspring under natural conditions. -​ Example: A lion (Panthera leo) and a tiger (Panthera tigris) are different species because they can interbreed (producing ligers), but the offspring are typically sterile. Different Types of Diversity in an Ecosystem 1.​ Species Diversity: -​ Refers to the variety and abundance of different species in an ecosystem. -​ Example: In a tropical rainforest, species diversity is high because it hosts a wide variety of organisms (plants, animals, fungi, etc.), each occupying different ecological niches. -​ Importance: Higher species diversity typically means more stable ecosystems that are better able to withstand environmental changes. 2.​ Genetic Diversity: -​ Refers to the variation of genes within a species. -​ Example: Different populations of wolves may have slight genetic differences that allow them to adapt to different environmental conditions. -​ Importance: Genetic diversity ensures that a species has a better chance of surviving diseases, changing environments, and other threats. 3.​ Ecosystems Diversity: -​ Organisms interact in various ways (e.g., predation, competition, mutualism), and these interactions help maintain ecosystem balance and stability. -​ Example: Bees (pollinators) and flowers have a mutualistic relationship where both benefit from the interaction. Factors Threatening Biodiversity 1.​ Habitat Destruction: Urbanization, deforestation, and agriculture disrupt ecosystems. 2.​ Pollution: Air, water, and soil pollution negatively affect many species. 3.​ Climate Change: Alters habitats and migration patterns, leading to the loss of species. 4.​ Invasive Species: Non-native species can outcompete native species for resources. 5.​ Overexploitation: Overfishing, hunting, and deforestation threaten species. How to Use and Construct a Dichotomous Key A Dichotomous Key is a tool used to identify organisms based on a series of paired statements. -​ Steps: -​ Start with a question that divides the organisms into two groups based on a characteristic (e.g., "Does the organism have wings?"). -​ Continue asking yes/no questions until you narrow down the organism to its species. ​ Example: 1.​ Does it have leaves? ​ Yes → Go to question 2 ​ No → It is a moss. 2.​ Are the leaves needle-like or broad? ​ Needle-like → Pine tree ​ Broad → Oak tree Classification Taxa and Binomial Nomenclature 1.​ Classification Taxa: -​ The system used to organize and categorize organisms. It follows a hierarchical structure: 1.​ Domain 2.​ Kingdom 3.​ Phylum 4.​ Class 5.​ Order 6.​ Family 7.​ Genus 8.​ Species 2.​ Binomial Nomenclature: -​ The scientific naming system of organisms developed by Carl Linnaeus. Each species is given a two-part name: genus (capitalized) and species (lowercase). -​ Example: Homo sapiens (Humans). Key Characteristics in 6 Kingdoms 1.​ Cell Types and Organization: -​ Prokaryotic Cells (no nucleus): Found in Bacteria and Archaea. -​ Eukaryotic Cells (with f): Found in Protista, Fungi, Plantae, and Animalia. 2.​ Cell Features: -​ Bacteria: Simple, single-celled organisms with no membrane-bound organelles. -​ Fungi, Plants, Animals: Multicellular organisms with specialized structures. 3.​ Habitats: -​ Bacteria: Found in extreme environments (e.g., hot springs, deep-sea vents) or common places (e.g., soil). -​ Protists: Mostly aquatic (e.g., ponds, oceans). -​ Plants: Terrestrial and aquatic environments. -​ Animals: Terrestrial and aquatic environments. 4.​ Method of Reproduction: -​ Bacteria: Asexual reproduction (binary fission). -​ Fungi: Both asexual (spores) and sexual reproduction. -​ Plants: Sexual reproduction (pollination, fertilization), some also reproduce asexually. -​ Animals: Sexual reproduction (internal or external fertilization). 5.​ Energy Source: -​ Autotrophic (produce their own food): Plants (photosynthesis), some bacteria (chemosynthesis). -​ Heterotrophic (consume other organisms for energy): Animals, fungi. Key Characteristics of the 6 Kingdoms 1.​ Archaea: -​ Prokaryotic, single-celled, live in extreme environments (e.g., hot springs, salt lakes), asexual reproduction. 2.​ Bacteria: -​ Prokaryotic, single-celled, can be found in diverse environments, asexual reproduction. 3.​ Protista: -​ Eukaryotic, mostly single-celled (e.g., algae, amoeba), some are autotrophic, others are heterotrophic. 4.​ Fungi: -​ Eukaryotic, mostly multicellular, heterotrophic (absorb nutrients from organic matter), asexual and sexual reproduction (e.g., mushrooms, molds).  5.​ Plantae: -​ Eukaryotic, multicellular, autotrophic (photosynthesis), sexual reproduction (flowers, seeds). 6.​ Animalia: -​ Eukaryotic, multicellular, heterotrophic, sexual reproduction (internal or external fertilization). Key Terms to Understand: ​ Binomial nomenclature: Two-part scientific naming system (genus + species). ​ Taxonomy: Science of classifying organisms. ​ Species: A group of organisms that can interbreed and produce fertile offspring. ​ Biodiversity: Variety of life in an ecosystem. ​ Prokaryotic/Eukaryotic: Prokaryotes lack a nucleus (e.g., bacteria), while eukaryotes have a nucleus (e.g., animals, plants). Short Answer Focus: 1.​ Prokaryotic vs. Eukaryotic: ○​ Prokaryotic: Simple, no nucleus (e.g., bacteria). ○​ Eukaryotic: Complex, with a nucleus (e.g., animals, plants). ○​ Theory of Eukaryotic Evolution: Endosymbiotic theory (mitochondria and chloroplasts evolved from prokaryotic cells that were engulfed by ancestors of eukaryotic cells). 2.​ Viruses and Living Things: Viruses are not considered living because they cannot reproduce on their own and require a host cell. 3.​ Domains and Kingdoms: ○​ 3 Domains: Bacteria, Archaea, Eukarya. ○​ 6 Kingdoms: Animalia, Plantae, Fungi, Protista, Archaea, Bacteria. 4.​ Taxonomy System: ○​ 8 taxonomic divisions: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. ○​ Binomial Nomenclature: Genus + species (e.g., Homo sapiens)  Unit 2: Animal Systems ​ Overview of Key Terms: 1.​ Digestion: The process by which food is broken down into smaller molecules so it can be absorbed and used by the body. This includes both mechanical and chemical processes. 2.​ Enzyme: A protein that speeds up (catalyzes) chemical reactions in the body, such as those involved in digestion (e.g., amylase, lipase, pepsin). 3.​ Gas Exchange: The process of exchanging gases (oxygen and carbon dioxide) between the air and the bloodstream in the lungs and at the tissues. 4.​ Veins: Blood vessels that carry blood toward the heart. Veins generally carry deoxygenated blood, except for pulmonary veins, which carry oxygenated blood. 5.​ Oral Cavity: The mouth, where food enters the body and is mechanically broken down by chewing and chemically digested by enzymes in saliva. 6.​ Proteins/Pepsin: Proteins are large molecules essential for growth and repair, while pepsin is an enzyme found in the stomach that breaks down proteins into smaller peptides. 7.​ Bronchioles: Small branches of the bronchi that carry air to the alveoli in the lungs. 8.​ Capillaries: Tiny blood vessels where gas exchange, nutrient delivery, and waste removal occur between blood and tissues. 9.​ Pharynx: The throat, a passageway for both air and food that leads to the larynx and esophagus. 10.​Peristalsis: A series of wave-like muscle contractions that move food along the digestive tract, such as in the esophagus and intestines. 11.​Alveoli: Tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged between the air and the blood. 12.​Plasma: The liquid portion of blood, consisting mostly of water, proteins, and dissolved nutrients, hormones, and waste products. 13.​Epiglottis: A flap of tissue that covers the trachea during swallowing to prevent food from entering the windpipe. 14.​Inhalation: The process of breathing in air, during which the diaphragm contracts and the chest cavity expands, reducing air pressure inside the lungs and drawing air in. 15.​Villi: Finger-like projections in the small intestine that increase surface area for absorption of nutrients. 16.​Leukocytes (WBC): White blood cells, which are part of the immune system and help protect the body from infection and disease. 17.​Esophagus: The muscular tube that connects the pharynx to the stomach, moving food via peristalsis. 18.​Exhalation: The process of breathing out, during which the diaphragm relaxes and the chest cavity contracts, increasing air pressure inside the lungs and expelling air. 19.​Microvilli: Smaller projections on the surface of epithelial cells, especially in the intestines, that increase the surface area for absorption. 20.​Erythrocytes (RBC): Red blood cells, which carry oxygen from the lungs to the body’s tissues and return carbon dioxide to be exhaled. 21.​Gastric Juice: The acidic digestive fluid produced by the stomach lining that contains hydrochloric acid, enzymes (like pepsin), and mucus. 22.​Open/Closed Circulatory System: In an open circulatory system, blood flows freely within body cavities. In a closed circulatory system (humans), blood circulates within vessels. 23.​Mucus: A sticky substance that helps protect and lubricate internal linings, such as in the digestive and respiratory systems. 24.​Stomach: An organ where food is mixed with gastric juices to begin the process of digestion, especially protein digestion. 25.​Nasal Cavity: The air passage in the nose, where air is filtered, warmed, and humidified before entering the lungs. 26.​Vital Capacity: The maximum amount of air a person can exhale after taking a deep breath. 27.​Platelets: Blood cells involved in clotting, helping to stop bleeding by forming a clot at injury sites. 28.​Intestines: The digestive organs (small and large) where nutrient absorption occurs, and waste is formed. 29.​Larynx: The voice box, located at the top of the trachea, containing the vocal cords and responsible for producing sound. 30.​Atrium: The upper chamber of the heart that receives blood from the body (right atrium) or lungs (left atrium). 31.​Heart Rate: The number of times the heart beats per minute, indicating cardiovascular health. 32.​Pancreas: An organ that produces digestive enzymes and hormones, including insulin, which regulates blood sugar. 33.​Lungs: Organs that facilitate gas exchange (oxygen and carbon dioxide) between the blood and the air. 34.​Ventricles: The lower chambers of the heart that pump blood to the lungs (right ventricle) and the rest of the body (left ventricle). 35.​Blood Pressure: The force of blood against the walls of the arteries as the heart pumps blood throughout the body. 36.​Gallbladder: An organ that stores bile produced by the liver, which helps digest fats. 37.​Trachea: The windpipe, which carries air to the bronchi and into the lungs. 38.​Aorta: The large artery that carries oxygenated blood from the left ventricle to the rest of the body.  39.​Lymphocytes: A type of white blood cell involved in immune responses, particularly in fighting viral infections and producing antibodies. 40.​Arteries: Blood vessels that carry oxygenated blood away from the heart, except for the pulmonary artery, which carries deoxygenated blood to the lungs. 41.​Clotting: The process by which blood forms a clot to stop bleeding, involving platelets and proteins like fibrin. Short Answer Questions: 1. Cardiovascular System: Blood Flow through the Heart – Oxygenated vs. Deoxygenated Blood: -​ Deoxygenated blood enters the right atrium of the heart from the body through the superior and inferior vena cava. -​ The right atrium contracts and sends blood through the tricuspid valve into the right ventricle. -​ The right ventricle pumps the blood through the pulmonary valve into the pulmonary artery, which carries the blood to the lungs for gas exchange (oxygenation). -​ Oxygenated blood from the lungs returns to the heart via the pulmonary veins into the left atrium. -​ The left atrium contracts, sending blood through the bicuspid valve into the left ventricle. -​ The left ventricle pumps the oxygenated blood through the aortic valve into the aorta, distributing oxygen-rich blood to the body. 2. Respiratory System: Gas Exchange Process – Breathing, External and Internal Respiration: -​ Breathing involves the inhalation of oxygen and exhalation of carbon dioxide. The diaphragm and rib muscles contract and relax to expand and compress the chest cavity. -​ External Respiration occurs in the lungs where oxygen diffuses from the alveoli (air sacs) into the capillaries and binds to hemoglobin in erythrocytes (red blood cells). Simultaneously, carbon dioxide from the blood diffuses into the alveoli to be exhaled. -​ Internal Respiration takes place in the tissues where oxygen is released from erythrocytes to cells and carbon dioxide from cells diffuses into the capillaries to be transported back to the lungs. 3. Digestive System: Five Organs and Their Functions: 1.​ Mouth (Oral Cavity): Digestion begins here with mechanical breakdown (chewing) and chemical digestion through saliva, which contains enzymes like amylase.  2.​ Stomach: Secretes gastric juice containing pepsin for protein digestion and hydrochloric acid for breaking down food. 3.​ Small Intestine: Where most nutrient absorption occurs, aided by villi and microvilli that increase surface area. 4.​ Liver: Produces bile, which emulsifies fats, and processes nutrients absorbed from the small intestine. 5.​ Pancreas: Produces digestive enzymes and releases insulin to regulate blood sugar levels. 4. Difference Between Inhalation and Exhalation – Diaphragm and Air Pressure: -​ Inhalation: The diaphragm contracts (moves down), increasing the volume of the chest cavity, decreasing air pressure, and drawing air into the lungs. -​ Exhalation: The diaphragm relaxes (moves up), decreasing the volume of the chest cavity, increasing air pressure, and expelling air from the lungs. 5. Compare the Structure and Function of Veins, Arteries, and Capillaries: ​ Arteries: Thick-walled, muscular, and elastic to withstand high pressure from the heart’s pumping action. Carry oxygenated blood (except pulmonary artery) away from the heart. ​ Veins: Thinner-walled with less muscle, contain valves to prevent backflow of blood as it moves toward the heart. Carry deoxygenated blood (except pulmonary veins) toward the heart. ​ Capillaries: Tiny, thin-walled vessels that allow for the exchange of gases, nutrients, and waste products between the blood and tissues. Chemical Digestion Overview: Macromolecules (large molecules like starches, proteins, and lipids) are broken down by specific enzymes into their smaller building blocks. These building blocks (products) can then be absorbed by the body for use in metabolism. Key Digestive Enzymes and Their Functions: 1.​ Carbohydrates (Starches): ○​ Enzyme: Amylase ​ Substrate: Starch ​ Product: Maltose (a disaccharide) ​ Location: Salivary amylase (in the mouth), pancreatic amylase (in the small intestine) ○​ Enzyme: Maltase (also produced in the small intestine) ​ Substrate: Maltose ​ Product: Glucose (simple sugar) ○​ Enzyme: Sucrase ​ Substrate: Sucrose (table sugar) ​ Product: Glucose and Fructose ○​ Enzyme: Lactase ​ Substrate: Lactose (milk sugar) ​ Product: Glucose and Galactose 2.​ Proteins: ○​ Enzyme: Pepsin (in the stomach) ​ Substrate: Proteins ​ Product: Polypeptides (smaller protein chains) ​ Activation: Pepsinogen is activated to pepsin in the acidic environment of the stomach, aided by hydrochloric acid (HCl). ○​ Enzyme: Trypsin (in the small intestine) ​ Substrate: Polypeptides ​ Product: Amino Acids (basic building blocks of proteins) ○​ Enzyme: Erepsin (also in the small intestine) ​ Substrate: Polypeptides (final breakdown) ​ Product: Amino Acids ​ 3.​ Lipids (Fats): ○​ Enzyme: Lipase (in the small intestine) ​ Substrate: Triglycerides (fats) ​ Product: Fatty Acids and Glycerol ○​ Emulsifier: Bile (produced by the liver, stored in the gallbladder) ​ Function: Breaks down large fat globules into smaller droplets (emulsifies fat), making it easier for lipase to break down the fats into fatty acids and glycerol. Digestive Chemicals (Enzymes and Emulsifiers) 1.​ Trypsinogen: Inactive form of trypsin. It is activated by enterokinase (an enzyme in the small intestine). 2.​ Pepsinogen: Inactive form of pepsin, activated by hydrochloric acid (HCl) in the stomach. 3.​ Enterokinase: Activates trypsinogen to trypsin in the small intestine. Diagram Example: Breakdown of Macromolecules by Enzymes -​ Here’s how you can represent the chemical digestion of macromolecules 1. Carbohydrate Digestion (Starch → Maltose → Glucose) ​ Amylase (Salivary and Pancreatic) ○​ Substrate: Starch ○​ Product: Maltose (disaccharide) ○​ Reaction: Starch → Maltose ​ Maltase (Small Intestine) ○​ Substrate: Maltose ○​ Product: Glucose ○​ Reaction: Maltose → Glucose 2. Protein Digestion (Protein → Polypeptides → Amino Acids) ​ Pepsin (Stomach) ○​ Substrate: Protein ○​ Product: Polypeptides ○​ Reaction: Protein → Polypeptides ​ Trypsin (Small Intestine) ○​ Substrate: Polypeptides ○​ Product: Amino Acids ○​ Reaction: Polypeptides → Amino Acids ​ Erepsin (Small Intestine) ○​ Substrate: Polypeptides ○​ Product: Amino Acids ○​ Reaction: Polypeptides → Amino Acids 3. Lipid Digestion (Triglycerides → Fatty Acids + Glycerol) ​ Bile (Liver) ○​ Function: Emulsifies fats, turning large fat globules into smaller fat droplets. ○​ Reaction: Fat Globules → Fat Droplets ​ Lipase (Small Intestine) ○​ Substrate: Triglycerides ○​ Product: Fatty Acids + Glycerol ○​ Reaction: Triglycerides → Fatty Acids + Glycerol 4. Sugar Digestion (Sucrose → Glucose + Fructose) ​ Sucrase (Small Intestine) ○​ Substrate: Sucrose ○​ Product: Glucose + Fructose ○​ Reaction: Sucrose → Glucose + Fructose 5. Lactose Digestion (Lactose → Glucose + Galactose) ​ Lactase (Small Intestine) ○​ Substrate: Lactose ○​ Product: Glucose + Galactose ○​ Reaction: Lactose → Glucose + Galactose Summary of Enzyme Actions and Products: Enzyme Substrate Product Amylase Starch Maltose Maltase Maltose Glucose Sucrase Sucrose Glucose + Fructose Lactase Lactose Glucose + Galactose Pepsin Protein Polypeptides Trypsin Polypeptides Amino Acids Erepsin Polypeptides Amino Acids Lipase Triglycerides Fatty Acids + Glycerol Bile Fat globules Fat droplets Important Digestive Chemicals: -​ Hydrochloric Acid (HCl): Activates pepsinogen to pepsin and helps in the acidic environment for protein digestion. -​ Enterokinase: Activates trypsinogen to trypsin in the small intestine. -​ Bile: Produced by the liver and stored in the gallbladder, it emulsifies fats into smaller droplets to aid in fat digestion by lipase. Diagram Tips: To visualize how macromolecules are broken down: 1.​ Draw an arrow for each enzyme’s action, starting from the substrate (macromolecule) to the product (simple molecule). 2.​ Label enzymes, substrates, and products clearly for each step. 3.​ Include hydrochloric acid and enterokinase where applicable (in the stomach and small intestine, respectively).  Unit 3: Genetics DNA and Chromatin -​ DNA (Deoxyribonucleic Acid): ○​ The molecule that carries genetic information. ○​ Structure: Double helix, composed of nucleotides (sugar, phosphate, nitrogenous base: adenine [A], thymine [T], cytosine [C], guanine [G]). ○​ Function: Directs protein synthesis and governs cell function -​ Chromatin: ○​ A complex of DNA and proteins (histones) found in the nucleus of eukaryotic cells. ○​ It condenses to form chromosomes during cell division. -​ Chromosomes: ○​ Highly coiled structures made of DNA. Humans have 46 chromosomes (23 pairs), including 22 autosomes and 1 pair of sex chromosomes. 2. Genes and Alleles -​ Genes: ○​ Segments of DNA that code for specific proteins, determining traits (e.g., eye color). -​ Alleles: ○​ Different versions of a gene. Each individual has two alleles for each gene (one from each parent). ○​ Dominant Alleles: Expressed when present (e.g., "A" for brown eyes). ○​ Recessive Alleles: Only expressed when two copies are present (e.g., "a" for blue eyes). 3. Somatic vs. Reproductive Cells ​ Somatic Cells: ○​ Body cells (e.g., skin, muscle cells). ○​ Diploid: Contain two sets of chromosomes (46 total in humans). ​ Reproductive Cells (Gametes): ○​ Sex cells (sperm in males, eggs in females). ○​ Haploid: Contain one set of chromosomes (23 total in humans). 4. Autosomes vs. Sex Chromosomes ​ Autosomes: ○​ The 22 pairs of chromosomes in humans that are not involved in determining sex. ​ Sex Chromosomes: ○​ The pair of chromosomes that determine an individual’s sex. ○​ XX: Female ○​ XY: Male 5. Mitosis (Importance of Cell Division) Purpose of Mitosis: -​ Growth, repair, and asexual reproduction. Mitosis produces two genetically identical diploid daughter cells. Phases of Mitosis: 1.​ Interphase: Cell grows and DNA replicates. 2.​ Prophase: Chromosomes condense, nuclear membrane breaks down. 3.​ Metaphase: Chromosomes align at the cell equator. 4.​ Anaphase: Sister chromatids are pulled apart to opposite poles. 5.​ Telophase: Nuclear membranes re-form, chromosomes begin to de-condense. 6.​ Cytokinesis: Division of the cytoplasm, resulting in two daughter cells. 6. Meiosis (Importance of Meiosis and Unique Haploid Daughter Cells) Importance of Meiosis: 1.​ Reduction in chromosome number: Meiosis creates haploid cells (sperm and eggs) from diploid cells, ensuring that fertilization restores the diploid number of chromosomes. 2.​ Genetic diversity: Meiosis introduces variation through crossing over (exchange of genetic material between homologous chromosomes) and independent assortment of chromosomes. Phases of Meiosis:​ 3.​ Meiosis I: Reduces chromosome number by half, separating homologous chromosomes. -​ Prophase I: Crossing over occurs. -​ Metaphase I: Homologous chromosomes align. -​ Anaphase I: Homologous chromosomes separate. -​ Telophase I: Two haploid daughter cells form. 4.​ Meiosis II: Similar to mitosis, but it separates sister chromatids. -​ Prophase II: Chromosomes condense in both haploid cells. -​ Metaphase II: Chromosomes align at the center. -​ Anaphase II: Sister chromatids separate. -​ Telophase II: Four genetically unique haploid cells form. 7. Atypical Meiosis -​ Atypical meiosis may result from errors in chromosome separation, leading to conditions such as Down syndrome (extra chromosome 21), Turner syndrome (monosomy of X chromosome), or Klinefelter syndrome (extra X chromosome in males). 8. Genetic Technologies Restriction Enzymes: -​ Proteins that cut DNA at specific sequences, used in genetic engineering and biotechnology. Recombinant DNA: -​ DNA that is artificially created by combining DNA from different organisms. Used in gene cloning and production of GMOs (genetically modified organisms). Transgenic Organisms: -​ Organisms that have been genetically modified to carry genes from other species. Example: Bt corn (corn with a gene from a bacterium that produces a protein toxic to certain pests). Genetic Screening Technologies: -​ Techniques like PCR (Polymerase Chain Reaction) and gel electrophoresis used to analyze DNA for mutations, inherited disorders, or to identify individuals (e.g., in forensic science). 9. Mendelian Genetics Background Information on Mendel: -​ Gregor Mendel: The father of modern genetics. He discovered the principles of inheritance by studying pea plants, and his findings established the foundation for our understanding of dominant and recessive traits. Mendel’s Laws: 1.​ Law of Segregation: Each organism has two alleles for each gene, and these alleles segregate (separate) during the formation of gametes. 2.​ Law of Independent Assortment: Alleles for different traits segregate independently during gamete formation. 10. Types of Inheritance Patterns Monohybrid Cross: -​ Involves the inheritance of a single trait (e.g., flower color). -​ Example: Cross between a homozygous dominant (RR) and a homozygous recessive (rr) parent. Dihybrid Cross: -​ Involves the inheritance of two traits simultaneously (e.g., seed color and seed shape). -​ Example: Cross between two plants heterozygous for both traits (RrYy × RrYy). Incomplete Dominance: -​ Neither allele is fully dominant, resulting in an intermediate phenotype. -​ Example: Red (RR) × White (WW) flowers produce pink (RW) offspring. Codominance: -​ Both alleles are fully expressed in the phenotype. -​ Example: AB blood type (both A and B alleles are expressed). Multiple Alleles: -​ A gene may have more than two alleles. -​ Example: Human blood types (A, B, O alleles). Sex-Linked Inheritance: -​ Genes located on the sex chromosomes (X or Y). Most sex-linked traits are carried on the X chromosome. -​ Example: Color blindness, hemophilia (X-linked recessive traits). 11. Interpreting Inheritance Patterns from Pedigrees Pedigrees: Diagrams that track the inheritance of traits over several generations. -​ Circle: Female -​ Square: Male -​ Shaded: Affected individual -​ Unshaded: Unaffected individual You can use pedigrees to determine whether a trait is dominant or recessive and whether it is sex-linked or autosomal. Key processes: -​ Meiosis creates genetic diversity, mitosis maintains genetic stability, and Mendelian genetics explains inheritance patterns. -​ Genetic technologies like recombinant DNA and genetic screening are essential for modern medicine and biotechnology. -​ Inheritance patterns help us understand how traits are passed down and predict the likelihood of genetic disorders. Key Terms and Their Functions/Roles/Meanings: 1.​ DNA (Deoxyribonucleic Acid): ○​ The molecule that carries genetic information. It is composed of nucleotides (adenine, thymine, cytosine, guanine) and forms the basis of genetic inheritance. 2.​ Gene: ○​ A segment of DNA that codes for a specific protein or trait. 3.​ Trait: ○​ A characteristic or feature that is inherited, such as eye color or height. 4.​ RNA (Ribonucleic Acid): ○​ A molecule that plays a central role in the synthesis of proteins. Unlike DNA, RNA uses ribose sugar and has uracil (U) instead of thymine (T). 5.​ Homologous Pairs: ○​ Chromosomes that are similar in shape, size, and genetic content, with one inherited from each parent. 6.​ Recessive: ○​ An allele that is only expressed in the phenotype if two copies are present (i.e., homozygous). 7.​ Dominant: ○​ An allele that is expressed in the phenotype even if only one copy is present (i.e., heterozygous). 8.​ Adenine (A) – Thymine (T): ○​ The nitrogenous bases that pair together in DNA. Adenine always pairs with thymine. 9.​ Cytosine (C) – Guanine (G): ○​ The nitrogenous bases that pair together in DNA. Cytosine always pairs with guanine. 10.​Gametes: ○​ Reproductive cells (sperm and egg) that carry half the genetic information (haploid). 11.​Autosomal: ○​ Refers to chromosomes that are not sex chromosomes (the first 22 pairs of chromosomes in humans). 12.​Sex-Linked: ○​ Refers to genes located on the sex chromosomes (X or Y). Most sex-linked traits are X-linked. 13.​Incomplete Dominance: ○​ A form of inheritance where neither allele is completely dominant over the other, resulting in an intermediate phenotype (e.g., red and white flowers producing pink offspring). ○​ 14.​Co-dominance: ○​ A situation where both alleles are fully expressed in the phenotype (e.g., AB blood type). 15.​Multiple Alleles: ○​ More than two alleles for a gene exist in the population, though each individual only has two alleles (e.g., human blood type). 16.​Chromosome: ○​ A structure that contains a long DNA molecule. Humans have 46 chromosomes (23 pairs). 17.​Chromatin: ○​ The uncondensed form of DNA in the nucleus when the cell is not dividing. 18.​Chromatid: ○​ One half of a duplicated chromosome, which is formed during DNA replication. 19.​Homozygous: ○​ An individual with two identical alleles for a gene (e.g., AA or aa). 20.​Heterozygous: ○​ An individual with two different alleles for a gene (e.g., Aa). 21.​Polygenic Traits: ○​ Traits controlled by two or more genes, often resulting in a range of phenotypes (e.g., height, skin color). 22.​DNA Replication: ○​ The process by which DNA is copied during cell division, ensuring that each daughter cell receives an exact copy of the DNA. 23.​Mitosis: ○​ The process of cell division that results in two genetically identical diploid daughter cells. 24.​Meiosis: ○​ The process of cell division that reduces the chromosome number by half, producing haploid gametes (sperm and egg). 25.​Genotype: ○​ The genetic makeup of an individual, represented by the alleles (e.g., Aa, BB). 26.​Phenotype: ○​ The observable characteristics or traits of an individual, determined by the genotype and environmental factors. 27.​Asexual Reproduction: ○​ Reproduction that involves a single parent and produces offspring genetically identical to the parent. 28.​Sexual Reproduction: ○​ Reproduction involving two parents, producing genetically diverse offspring through the fusion of gametes (sperm and egg).  29.​Zygote: ○​ The fertilized egg formed by the fusion of sperm and egg. 30.​Nucleic Acids: ○​ Biomolecules (DNA and RNA) that store and transmit genetic information. 31.​Carbohydrates: ○​ Organic compounds used as a primary energy source in organisms. 32.​Lipids: ○​ Fatty acids and glycerol, which are used for energy storage and structural components in cells. Short Answer Questions: 1. What does DNA stand for? What are the base pairings? What is the function of DNA? -​ DNA stands for Deoxyribonucleic Acid. -​ Base Pairings: ○​ Adenine (A) pairs with Thymine (T), ○​ Cytosine (C) pairs with Guanine (G). -​ Function of DNA: DNA stores genetic information, which directs the synthesis of proteins that control the functions of the body. What are Mendel’s laws? (Explain - Law of Independent Assortment, Law of Segregation) -​ Law of Segregation: During gamete formation, the two alleles for each gene separate, so each gamete receives only one allele from each pair. -​ Law of Independent Assortment: Genes for different traits are inherited independently of one another (only applies if genes are on different chromosomes). Draw “Summary Tables” to distinguish between Dominant Disorders and Recessive Disorders -​ Dominant Disorders: ○​ Only one copy of the allele is needed for the disorder to be expressed. ○​ Examples: Huntington's disease, Marfan syndrome. -​ Recessive Disorders: ○​ Two copies of the allele are needed for the disorder to be expressed. ○​ Examples: Cystic fibrosis, sickle cell anemia. Be able to label a Pedigree Flowchart with genotype alleles and be able to recognize the disorder as autosomal or sex-linked and dominant or recessive. -​ Pedigree Flowchart: A diagram that traces the inheritance of a trait through multiple generations. ○​ Autosomal: The trait is carried on one of the 22 autosomes. ○​ Sex-linked: The trait is carried on the X or Y chromosome. ○​ Dominant: The trait appears if at least one dominant allele is present. ○​ Recessive: The trait appears only if both alleles are recessive. Recognize pictures to identify and label the stages of Meiosis. What is the main purpose of Meiosis? -​ Main Purpose of Meiosis: To reduce the chromosome number by half, creating haploid gametes (sperm and egg) for sexual reproduction. Meiosis Stages: 1.​ Prophase I: Chromosomes condense and homologous chromosomes pair up. 2.​ Metaphase I: Homologous chromosome pairs align in the center. 3.​ Anaphase I: Homologous chromosomes are pulled to opposite poles. 4.​ Telophase I: Two haploid cells form. 5.​ Meiosis II: Separates the sister chromatids, resulting in four haploid cells. Crossing Over: Occurs in Prophase I; homologous chromosomes exchange segments, increasing genetic diversity. Independent Assortment: Occurs during Metaphase I; chromosomes line up randomly, leading to genetic variation.​ Be able to do both monohybrid and dihybrid crosses. -​ Monohybrid Cross: A cross between two individuals to examine the inheritance of a single trait. -​ Example: Cross between a homozygous dominant (AA) and homozygous recessive (aa) for a gene. ○​ Punnett Square: Predicts the genotypic and phenotypic ratios of offspring.  -​ Dihybrid Cross: A cross examining two traits at the same time. Example: Cross between two individuals heterozygous for both traits (AaBb × AaBb). ○​ Punnett Square: Predicts the genotypic and phenotypic ratios for two traits. What are the multiple alleles of human blood types? -​ The three alleles for human blood types are A, B, and O. ○​ A and B are dominant to O. ○​ AB blood type is an example of co-dominance (both A and B alleles are expressed). Be able to do both multiple alleles and sex-linked crosses. -​ Multiple Alleles Cross: Can involve blood type inheritance or traits controlled by multiple alleles (like coat color in animals). -​ Sex-Linked Cross: Typically involves X-linked traits like color blindness or hemophilia. Example: Cross between a female carrier (X^N X^n) and a male with the condition (X^n Y). Use a Punnett square to predict offspring outcomes. Review Tips: ​ Practice Punnett Squares for both monohybrid and dihybrid crosses. ​ Understand Pedigree Analysis: Be able to determine whether a disorder is autosomal or sex-linked, dominant or recessive. ​ Know Meiosis and Mitosis thoroughly, including stages and key concepts like crossing over and independent assortment.  Unit 4: Plants Plant Hormones and Human Applications 1.​ Auxin: ○​ Function: Causes cell elongation, promoting growth towards light. ○​ Human Application: Used in plant growth regulation, weed killers (over-extension). 2.​ Cytokinins: ○​ Function: Stimulates cell division, promotes growth in terminal and side buds, and delays aging in fruits and flowers. ○​ Human Application: Used to prolong shelf life of produce, create bushier plants by reducing auxin levels. 3.​ Gibberellins: ○​ Function: Stimulates cell elongation and division, promotes seed germination. ○​ Human Application: Increases fruit production, delays fruit ripening for better quality. 4.​ Abscisic Acid (ABA): ○​ Function: Inhibits growth, induces dormancy under stress conditions like drought or extreme temperatures. ○​ Human Application: Used to improve drought resistance, aid in food storage and transport. 5.​ Ethylene: ○​ Function: Promotes ripening and senescence (aging) of fruits and leaves. ○​ Human Application: Used to ripen fruits like bananas for consumption. Fast Plant Movements (Nastic Movements) ​ Definition: Movements that occur due to changes in turgor pressure (water movement) within plant cells, often involving osmosis. ​ Examples: ○​ Venus flytrap: Closes its leaves to trap prey when triggered by touch. ○​ Mimosa: Leaves fold up when touched, likely as a defense mechanism. ​ Purpose: These fast movements help the plant respond to stimuli, such as capturing prey or protecting itself from herbivores. Slow Plant Movements (Tropisms) ​ Definition: Directional growth responses to environmental stimuli. Types of Tropism: -​ Phototropism: Growth toward light (positive phototropism in shoots, negative in roots). -​ Gravitropism: Growth response to gravity (positive gravitropism in roots, negative in shoots). -​ Thigmotropism: Response to touch (e.g., vines coiling around supports). ​ Positive vs Negative Tropisms: ○​ Positive Tropism: Growth toward the stimulus (e.g., roots growing downward due to gravity). ○​ Negative Tropism: Growth away from the stimulus (e.g., roots growing away from light in negative phototropism). Plant Responses and Adaptations to Stress 1.​ Drought: ○​ Adaptations: Thick cuticles, smaller leaves, and stomata closing to conserve water. ○​ Response: Production of ABA to induce dormancy and reduce water loss. 2.​ Flooding: ○​ Adaptations: Ethylene production in submerged roots, creating air tubes for oxygen transport. ○​ Examples: Mangrove trees with roots partly above water for oxygen supply. 3.​ Salty Soil: ○​ Adaptations: Halophytes have salt glands to excrete excess salt (e.g., mangroves). ○​ Response: Plant dormancy through ABA release. 4.​ Low-Nutrient Soil: ○​ Adaptations: Symbiotic relationships with mycorrhizal fungi to enhance nutrient absorption. 5.​ Predation by Herbivores: ○​ Defensive Strategies: Release of chemicals like nicotine or solanine to deter herbivores. ○​ Physical Defenses: Thorns, spines, and tough outer bark. 6.​ Pathogens (Bacteria and Viruses): ○​ Response: Release of antimicrobial chemicals and strengthening of cell walls (e.g., lignin). Function of Soil Nutrients and Signs of Deficiency ​ Nutrients: ○​ Macronutrients: Nitrogen, phosphorus, potassium (NPK), which are critical for growth. ○​ Micronutrients: Iron, magnesium, and others important for various biochemical functions. ​ Signs of Deficiency: ○​ Nitrogen: Yellowing leaves (chlorosis) due to lack of chlorophyll.  ○​ Phosphorus: Poor growth, purple or dark leaves. ○​ Potassium: Browning or scorching of leaf edges. Plant Organs and Components 1.​ Leaf: ○​ Function: Photosynthesis, gas exchange, protection, and sometimes storage. ○​ Parts: Blade, petiole, stomata, cuticle, mesophyll layers, vascular tissue (xylem and phloem).- 2.​ Roots: ○​ Function: Water and nutrient absorption, anchoring, storage. ○​ Types: Taproots (e.g., carrots), fibrous roots (e.g., grass). 3.​ Stem: ○​ Function: Supports leaves and reproductive organs, transports water/nutrients, stores carbs. ○​ Types: Herbaceous (non-woody), woody (hard, with bark). 4.​ Flower: ○​ Function: Reproductive organ. ○​ Parts: Stamen (male, produces pollen), carpel (female, contains ovary and ovules). 5.​ Seeds: ○​ Function: Protect and nourish the embryo, facilitate dispersal. Function of Plant Tissues 1.​ Meristematic Tissue: Areas of active cell division (e.g., root and shoot tips). 2.​ Dermal Tissue: Protective outer layer (e.g., epidermis and periderm). 3.​ Ground Tissue: Functions in storage, photosynthesis, and structural support. 4.​ Vascular Tissue: Transports water (xylem) and nutrients (phloem). Xylem: transports water (unidirectional ↑ flow Phloem: transports sugars (bidirectional ↑↓ flow) Plant Reproductive Strategies 1.​ Asexual Reproduction (Vegetative Propagation): ○​ Benefits: Clonal growth, faster reproduction, genetically identical, strong plantlets. ○​ Costs: Lack of genetic diversity, vulnerability to disease. ○​ Examples: Rhizomes, tubers, and leaf cuttings.  2.​ Sexual Reproduction: ○​ Benefits: Genetic diversity, seed dispersal, increased adaptability. ○​ Costs: Requires two parents, more energy-intensive (production of flowers, seeds). ○​ Examples: Flowers, fruit production. Plant Classification 1.​ Mosses: Non-vascular, rely on water for reproduction. 2.​ Ferns: Vascular, reproduce with spores. 3.​ Gymnosperms: Seed-producing, non-flowering plants (e.g., conifers). 4.​ Angiosperms: ○​ Monocots: Parallel-veined leaves, scattered vascular bundles. ○​ Dicots: Net-veined leaves, vascular bundles in a circle. Primary vs Secondary Growth 1.​ Primary Growth: Involves lengthening of stems and roots at the apical meristems. 2.​ Secondary Growth: Involves thickening of stems and roots, due to lateral meristems (e.g., vascular cambium). Water and Sap Transport ​ Water Transport: Occurs via capillary action and transpiration. Xylem conducts water unidirectionally. ​ Sap Transport: Phloem transports sugars and nutrients through active and passive processes. Human Uses of Plants 1.​ Food: Fruits, vegetables, grains, and legumes. 2.​ Pharmaceuticals: Medicinal plants like willow (aspirin) and aloe vera. 3.​ Biofuels: Ethanol from corn and other plant matter. 4.​ Building Materials: Wood, bamboo, flax, and hemp for construction and textiles. Short Answer Questions 1.​ Four Main Types of Plant Tissues:​ ○​ Meristematic tissue: Responsible for plant growth (found in tips of roots and shoots). ○​ Dermal tissue: Protects the plant and regulates water loss (outer layer of plant). ○​ Vascular tissue: Transports water, nutrients, and sugars (xylem and phloem). ○​ Ground tissue: Supports, stores, and conducts photosynthesis (includes parenchyma, collenchyma, and sclerenchyma cells). 2.​ Flower Diagram:​ ○​ Male reproductive organs: Anthers (produce pollen) and Filament (supports anther). ○​ Female reproductive organs: Stigma (receives pollen), Style (connects stigma to ovary), Ovary (contains ovules, where fertilization occurs). 3.​ Difference Between Gymnosperms and Angiosperms:​ ○​ Gymnosperms: Seed-producing plants without flowers; seeds are exposed (e.g., conifers). ○​ Angiosperms: Seed-producing plants with flowers; seeds are enclosed within a fruit. 4.​ Differences Between Monocots and Dicots:​ ○​ Monocots: One cotyledon, parallel-veined leaves, scattered vascular bundles, fibrous root system. ○​ Dicots: Two cotyledons, net-veined leaves, vascular bundles in a ring, taproot system. 5.​ Beneficial Roles of Plants:​ ○​ Produce oxygen through photosynthesis. ○​ Provide food and habitat for animals. ○​ Help regulate climate by absorbing carbon dioxide. ○​ Prevent soil erosion and improve soil health. ○​ Contribute to the water cycle. 6.​ If Plants Went Extinct:​ ○​ Loss of oxygen production would severely affect animal life, leading to respiratory adaptations (e.g., more efficient lungs or alternative oxygen sources). ○​ Herbivores would adapt to new food sources, possibly shifting to a carnivorous diet or evolving to process other forms of energy.  ○​ Reduced biodiversity could lead to significant shifts in ecosystems, with fewer plants possibly leading to a more animal-dominated environment. Unit 5: Evolution Terms Breakdown: 1.​ Evolution: The process by which different kinds of living organisms develop and diversify from earlier forms over generations. 2.​ Mutation: A change in the DNA sequence of an organism, which can lead to genetic variation. 3.​ Homologous Structure: Structures in different species that have similar underlying anatomy but may serve different functions, indicating common ancestry. 4.​ Darwin: Charles Darwin, the scientist who proposed the theory of natural selection, explaining how species evolve over time due to environmental pressures. 5.​ Fossil: Preserved remains or traces of organisms from the past, often used to understand evolutionary changes over time. 6.​ Analogous Structure: Structures in different species that serve similar functions but do not share common ancestry. 7.​ Natural Selection: A process by which organisms better adapted to their environment tend to survive and reproduce, passing on their advantageous traits. 8.​ Fossilization: The process through which organisms become preserved as fossils, typically through mineralization or other preservation methods. 9.​ Microevolution: Small-scale evolutionary changes within a population, such as shifts in allele frequencies. 10.​Artificial Selection: The process by which humans breed plants and animals for specific traits. 11.​Gradualism: The idea that evolution occurs slowly and steadily over long periods. 12.​Macroevolution: Large-scale evolutionary changes that result in the emergence of new species or groups over long timescales. 13.​Adaptation: Traits that increase an organism's chances of surviving and reproducing in a particular environment. 14.​Punctuated Equilibrium: The theory that evolution occurs in rapid bursts, followed by periods of little to no change. 15.​Vestigial Structure: A structure that has lost its original function through evolution, providing evidence of ancestral traits.  16.​Adaptation Types: The three types of adaptations are: ○​ Structural: Physical features of an organism (e.g., beaks of birds). ○​ Behavioral: Actions organisms take to survive (e.g., migration patterns). ○​ Physiological: Internal processes that improve survival (e.g., hibernation). 17.​Allopatric vs. Sympatric Speciation: ○​ Allopatric Speciation: The formation of new species due to geographic isolation. ○​ Sympatric Speciation: The formation of new species in the same geographic area due to other factors like behavioral differences. 18.​Speciation: The process through which new species are formed. 19.​Selective Advantage: Traits that improve an organism's chances of surviving and reproducing, leading to natural selection. 20.​Speciation Mechanisms: The processes through which new species arise, including geographic isolation, behavioral isolation, and reproductive isolation. 21.​Mimicry: A phenomenon where one species evolves to resemble another species for protection or other advantages. Short Answer Questions: 1.​ What is evolution, and why is it referred to as a theory? Evolution is the process by which species change over time through genetic variation and natural selection. It is referred to as a theory because it is a well-supported explanation based on a wide body of evidence but still subject to further research and refinement.​ 2.​ What is Darwin’s theory of Natural Selection? Darwin's theory of natural selection suggests that individuals within a species show variation, and those with traits that are better suited for their environment are more likely to survive and reproduce. Over time, these advantageous traits become more common in the population.​ 3.​ What is meant by the term vestigial structure? How do they provide evidence of evolution? A vestigial structure is a body part that no longer serves a significant function but is retained from an ancestor. Examples include the human appendix or whale pelvic bones. These structures provide evidence of evolution because they show how organisms evolve and lose functions over time.​ 4.​ Define the Theory of Gradualism – be able to identify and label a graph. Gradualism suggests that evolutionary changes occur slowly and steadily over long periods of time. On a graph, this would be represented as a smooth, continuous line with gradual upward or downward trends.​ ​  Define the Theory of Punctuated Equilibrium – be able to identify and label a graph. Punctuated equilibrium proposes that evolution occurs in rapid bursts, followed by long periods of stability. On a graph, this would look like periods of little change with sudden spikes representing rapid evolutionary changes.​ 5.​ Name the 3 types of Adaptations and explain real-life examples for each.​ -​ Structural Adaptation: Physical features, such as the long neck of a giraffe, which helps it reach high foliage. -​ Behavioral Adaptation: Migration patterns in birds to escape harsh winters. -​ Physiological Adaptation: The ability of some animals, like camels, to conserve water in arid environments. 6.​ What defines a species as a species? What is the difference between homologous and analogous structures? A species is defined as a group of organisms that can interbreed and produce fertile offspring. -​ Homologous Structures: share common ancestry and may have different functions (e.g., human arm, bat wing, whale fin). ○​ Analogous Structures: serve similar functions but do not share common ancestry (e.g., wings of birds and insects). Darwin’s Theory of Natural Selection – Detailed Overview: 1. Darwin’s Observations That Led Him to Believe Species Possess Favored Traits: Darwin’s observations, particularly during his voyage on the HMS Beagle, led him to develop his theory of natural selection. Some key observations include: ​ Variation in Traits: Darwin noticed that individuals within a species showed variation in traits (e.g., beak sizes in finches) across different environments. This variation meant some individuals had traits better suited for survival in specific environments. ​ Struggle for Existence: Darwin observed that species tend to produce more offspring than can survive, leading to a "struggle for existence." This competition for resources means that only those individuals with advantageous traits are more likely to survive and reproduce. ​ Survival and Reproduction of the Fittest: He noted that those organisms with traits that give them a survival or reproductive advantage were more likely to pass those traits onto their offspring, increasing their prevalence in the population over generations. 2. How the Fossil Record Suggests that Species Share a Common Ancestor: The fossil record provides evidence of gradual change over time, showing a progression of species that are related through common ancestry. Fossils reveal: ​ Transitional Forms: Fossils show intermediate forms between different groups (e.g., the transitional fossil Archaeopteryx, which shows both dinosaur and bird characteristics). ​ Pattern of Similarity: Fossils of related species found in the same geological layers suggest a timeline of divergence from common ancestors. ​ Progression Over Time: The fossil record shows an ordered sequence of species evolving over long periods, with older layers containing simpler organisms and more recent layers containing more complex ones, reinforcing the idea of evolution from common ancestors. 3. Anatomical, Embryological, and Biochemical Similarities in Establishing Evolutionary Relationships: ​ Anatomical Similarities (Homologous Structures): The similar structures in different species (e.g., human arm, whale flipper, and bat wing) suggest a common ancestry, even though the structures may serve different functions. ​ Embryological Similarities: Embryos of different vertebrates often look strikingly similar early in development. For example, fish, birds, and humans all share pharyngeal pouches (gill slits) and tails in their embryonic stages, indicating a shared ancestry. ​ Biochemical Similarities: The genetic code (DNA) is almost universal across all living organisms. Similarities in the DNA sequences of different species provide strong evidence of common ancestry. For example, humans and chimpanzees share approximately 98% of their DNA. ​ Vestigial Structures: Structures that no longer serve a functional purpose, such as the human appendix or the pelvic bones in whales, suggest that these organisms share an ancestor in which these structures had a function. ​ Pseudogenes: These are genes that are no longer functional due to mutations but are similar to functional genes in related species. Their presence in different species suggests that they inherited the genes from a common ancestor, even if the genes are no longer used. 4. How Darwin Used Artificial Selection as Evidence for Natural Selection: Darwin used artificial selection (selective breeding by humans) as a powerful analogy for natural selection. In artificial selection, humans breed organisms with desirable traits (e.g., breeding dogs for specific traits like size or coat color). Darwin argued that if humans can artificially select traits over a relatively short time, natural selection could also cause changes in species over longer periods, with advantageous traits being passed down because they increase survival and reproduction. This helped strengthen his argument for the power of selection in driving evolutionary changes. 5. Contributions of Other Scientists to Darwin’s Theory: Several scientists contributed to Darwin’s theory by providing insights and evidence that helped him shape his ideas: ​ Charles Lyell: A geologist who proposed that the Earth’s features were shaped by gradual processes over long periods (uniformitarianism). This idea helped Darwin understand that the Earth had been around long enough for natural selection to occur. ​ Georges Cuvier: A paleontologist who proposed the idea of catastrophism, which suggested that the Earth had experienced sudden, violent events that wiped out species. While Darwin didn’t fully agree with Cuvier’s ideas, Cuvier’s fossil work highlighted the importance of the fossil record in understanding evolution. ​ Jean-Baptiste Lamarck: Lamarck proposed an early theory of evolution based on the idea that organisms could change during their lifetime and pass those changes on to offspring (e.g., giraffes stretching their necks to reach higher leaves). Though many of Lamarck’s ideas were later disproven, he was one of the first to propose that species evolve over time. ​ Thomas Malthus: An economist who argued that populations grow faster than the resources available, leading to competition and a “struggle for existence.” This concept of limited resources was key to Darwin’s understanding of how natural selection operates.