Biology.

Placebo A placebo prevents the test subjects from knowing whether they are being given the real therapeutic drug or not. This helps the examiner understand the true effects of the drug. Experimentation involves a set of procedures used to test a particular hypothesis. Double-blind keeps the identity of subjects hidden from the researcher to avoid any researcher-patient bias in the experiments. Evaluation involves analyzing the results of experiments and drawing valid, scientific conclusions from them.

Kingdom is a higher or more inclusive level of the hierarchical system of classification than the phylum level. Living organisms are classified from most inclusive to least inclusive: Domain Kingdom Phylum Class Order Family Genus Species

The amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius. This refers to specific heat. The unit of specific heat is joules per gram per degree (J/g°C). The amount of heat needed to reduce the temperature of one kilogram of a substance by one degree Celsius refers to heat capacity (but the focus here is on raising the temperature, not lowering it). The amount of heat needed to raise the temperature of one kilogram of a substance by one degree Celsius is not the correct definition of specific heat, which is typically defined for one gram of a substance, not one kilogram. The amount of heat needed to reduce the temperature of one gram of a substance by one degree Celsius is about lowering the temperature, not raising it, and also specifies the wrong unit of mass (gram instead of kilogram).

Solvent Polarity allows water to be a good solvent and other polar substances can be dissolved in water easily. Water is not a solute or a solution. Polarity does not make water a good molecule, there is no such thing as a “good” molecule.

Carbohydrates are turned into glucose and absorbed into the blood via the walls of the small intestine. Digestion Process: Carbohydrates are broken down into simpler sugars during digestion. Complex carbohydrates (like starch) are broken down into disaccharides (like maltose) and eventually into monosaccharides (like glucose). This breakdown primarily occurs in the mouth (salivary amylase) and the small intestine (pancreatic amylase and other enzymes). Absorption:Monosaccharides, particularly glucose, are absorbed through the walls of the small intestine.The cells lining the small intestine have specialized transport proteins that actively transport glucose into the bloodstream. Transport in the Blood: Once absorbed, glucose enters the bloodstream and is transported to cells throughout the body, where it is used for energy or stored as glycogen. Disaccharides and the stomach: Carbohydrates are not absorbed as disaccharides. The stomach’s acidic environment does not significantly digest carbohydrates, as its role is primarily protein digestion. Absorption happens in the small intestine, not the stomach. Carbohydrates turning into oxygen: Carbohydrates are not turned into oxygen, and the lungs do not play a role in carbohydrate digestion or absorption. Carbohydrates turning into fatty acids and the large intestine: Carbohydrates are not converted into fatty acids during digestion. Fatty acids come from lipid digestion. The large intestine absorbs water and electrolytes, not carbohydrates.

Protein Animals and humans obtain the nitrogen they require by consuming protein. Proteins are made of carbon, hydrogen, oxygen, and nitrogen, which are arranged as chains (polymers) of amino acids Lipids are organic compounds like fats, oils, and waxes. They are made primarily of carbon, hydrogen, and oxygen, but they do not contain nitrogen in significant amounts.They serve as energy storage molecules, structural components of cell membranes (like phospholipids), and signaling molecules (like steroids). Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. Examples include glucose, starch, and cellulose. They are the primary source of energy for many organisms but do not contain nitrogen Glucose is a simple sugar (monosaccharide) and an important carbohydrate. Its chemical formula is C₆H₁₂O₆. It serves as a primary energy source for cells but, like other carbohydrates, does not contain nitrogen.

Proteins are polymers of amino acids. They consist of carbon, hydrogen, oxygen, and nitrogen arranged in chains of amino acids linked by peptide bonds. Lipids are not true polymers. They are esters of glycerol and fatty acids (triglycerides), or other structures like phospholipids and steroids. They contain a long nonpolar hydrocarbon chain with a small polar region. Nucleic acids are composed of nucleotide monomers (a 5-carbon sugar, phosphate group, and nitrogenous base). DNA and RNA are nucleic acids. Steroids are a type of lipid. They serve as membrane components and signaling molecules (hormones).

Enzymes Enzymes are a type of protein that catalyze (cause or accelerate) different reactions and processes. Almost all cellular function is catalyzed by some type of enzyme. Amino acids are what make up proteins. Proteins are polymers of 20 amino acids. Phospholipids are a type of lipid. They consist of two fatty acids bonded to a phosphate group. The phosphate group is polar and soluble in water whereas the hydrocarbon tail of the fatty acids is nonpolar and non-soluble in water. This quality is important in the function of cellular membranes, including the plasma membrane, as the molecules organize themselves in a way that creates a barrier to protect the cell. Steroids are a type of lipid. They are a component of membranes and an essential part of many hormones and drugs.

Ribosomes Ribosomes are responsible for protein synthesis. Ribosomes read RNA produced in the nucleus and translate the genetic instructions provided to produce proteins. Cells with a high rate of protein synthesis typically contain a high number of ribosomes. Mitochondria are the powerhouse of most eukaryotic cells and is the site of cellular respiration. Lysosomes are the digestive system of the cell. Lysosomes contain hydrolytic enzymes which allow them to hydrolyze (break down) proteins, fats, sugars, and nucleic acids taken into the cell as well as break down other worn out organelles within the cell. Lysosomes contain an acidic environment with a pH of around 4.5. Vacuoles provide storage for the cell. Vacuoles are membrane-enclosed structures that have a variety of functions depending on cell type. Many cells uptake food through the cell membrane (this process is called phagocytosis), creating a food vacuole. Plant cells have a central vacuole that functions as storage, waste disposal, protection, and hydrolysis.

Active transport Active transport is one of the ways materials move across the plasma membrane. In active transport, a protein moves the material across the membrane from a region of lower concentration to a higher concentration. Because this movement is happening against the concentration gradient (going from low to high concentration rather than high to low) the cell must use energy to make the transportation happen. Passive transport involves moving substances from an area of high concentration to an area of low concentration. Osmosis and diffusion are examples of passive transport.

A bilayer of phospholipid molecules Phospholipids are molecules composed of two parts: a hydrophilic (attracts water) phosphate head and a hydrophobic (repels water) lipid tail. The cell membrane consists of a bilayer of phospholipids where the phospholipids line up tail-to-tail. This bilayer creates a hydrophobic region between two layers of lipids, making it selectively permeable. Selectively permeable means that the cell membrane allows specific molecules or ions to pass through it while keeping others out. A single layer of phospholipid molecules: A single layer would not provide the necessary barrier and structural integrity. The bilayer is essential for the selective permeability and function of the membrane. A rigid layer of cytoskeleton: The cytoskeleton provides structural support inside the cell but is not part of the cell membrane. A wall of cholesterol and phospholipids: While cholesterol is present in the membrane, it is not a wall. The membrane is a flexible bilayer. Detailed diagram of the cell membrane

Mitochondria. The citric acid cycle and oxidative phosphorylation occur in the mitochondria, producing the bulk of ATP during cellular respiration. Glycolysis, the first stage, occurs in the cytoplasm, not the mitochondria. Pyruvate then enters the mitochondria for further processing. Golgi apparatus packages and ships proteins from the ER. Smooth ER handles detoxification, lipid synthesis, and calcium storage. Rough ER (studded with ribosomes) is the site of protein synthesis and membrane production.

Cellular respiration Cellular respiration is a metabolic pathway that breaks down glucose and produces ATP. The stages of cellular respiration include glycolysis, pyruvate oxidation, citric acid or Krebs cycle, and oxidative phosphorylation. Photosynthesis is an anabolic process in which plants or autotrophic organisms consume carbon dioxide, water, and light energy to produce glucose and oxygen. Gluconeogenesis refers to the synthesis of new glucose from noncarbohydrate precursors, providing glucose when dietary intake is insufficient or absent. It is also essential in the regulation of acid-base balance, amino acid metabolism, and synthesis of carbohydrate-derived structural components. “Gluco” refers to glucose, “Neo” means new, and “Genesis” means formation. Lipolysis is the process of breaking down lipids (fats) into fatty acids and glycerol. “Lipo” means lipids and “Lysis” means breakdown.

Glycolysis Glycolysis is the first step in the process of breaking down glucose to extract energy for cellular metabolism. It occurs in the cytoplasm of the cell and does not require oxygen (anaerobic process). Glucose (a six-carbon molecule) is broken down into two molecules of pyruvate (a three-carbon molecule). This process generates a small amount of energy: 2 ATP (net gain) and 2 NADH molecules (used later in cellular respiration for more ATP production). The significance is that Glycolysis provides the substrates for further energy-extracting pathways: If oxygen is available, pyruvate enters the mitochondria for the Krebs cycle and oxidative phosphorylation. If oxygen is absent, pyruvate is converted into lactate (in animals) or ethanol and carbon dioxide (in yeast) through fermentation. Fermentation occurs after glycolysis if oxygen is unavailable. It regenerates NAD+ but does not directly break down glucose. Oxidative phosphorylation is the final stage of aerobic respiration, where most ATP is produced. It occurs in the mitochondria and requires electrons from NADH and FADH₂. Gluconeogenesis This is the process of synthesizing glucose from non-carbohydrate precursors (e.g., amino acids or lactate) and is essentially the reverse of glycolysis. It occurs in the liver and is not part of glucose breakdown.

During low amounts of oxygen Fermentation is a widespread pathway, but it is not the only way to get energy from fuels anaerobically (in the absence of oxygen). Some living systems use an inorganic molecule other than O2, such as sulfate, as a final electron acceptor for an electron transport chain. This process, called anaerobic cellular respiration, is performed by some bacteria and archaea. These fermentation pathways consist of glycolysis with some extra reactions tacked on at the end. In yeast, the extra reactions make alcohol, while in your muscles, they make lactic acid. During low amount of nitrogen, nitrogen is essential for building proteins and nucleic acids, but its availability does not directly affect fermentation or aerobic respiration. During high amounts of oxygen, when oxygen is plentiful, cells perform aerobic respiration, which is much more efficient than fermentation. During high amounts of nitrogen, nitrogen levels do not influence the switch between fermentation and aerobic respiration. Oxygen availability is the key factor.

Glucose and oxygen Photosynthesis is represented by; 6CO2 + 6H2O → C6H12O6 + 6O2 During photosynthesis, energy from the sun is used to produce glucose and oxygen from carbon dioxide and water. Water and carbon dioxide are the reactants in photosynthesis, not the products.

Supply electrons in the light reactions The role of water in photosynthesis is to be split by light energy and supply the electrons used to produce ATP in the light reactions step. Water plays a critical role in the light-dependent reactions of photosynthesis, which occur in the thylakoid membranes of the chloroplast. Splitting of water (Photolysis), water molecules are split into oxygen, protons (H⁺), and electrons in a process called photolysis. The role of the electrons is the electrons from water replenish the electrons lost by chlorophyll molecules in Photosystem II when they are excited by light energy. These electrons move through the electron transport chain, leading to the production of ATP and NADPH, which are used in the Calvin cycle. With oxygen production, oxygen is released as a byproduct of water splitting and is expelled into the atmosphere. Convert solar energy to chemical energy is the role of the chlorophyll pigment and the electron transport chain, not water. Absorb light energy is absorbed by chlorophyll and other pigments, not water. Provide sugars to be used in the Calvin cycle, Water does not provide sugars. Sugars are synthesized in the Calvin cycle using ATP, NADPH, and carbon dioxide.

Mitosis results in two identical daughter cells to their parent cell. Mitosis is the nuclear cell division that occurs in eukaryotic cells when a single parent cell divides into two identical daughter cells. The image below shows the phases of the mitotic cell cycle. You can see that after telophase, the cell divides into two identical daughter cells. Mitotic cell division gives rise to four unique daughter cells describes meiosis, which produces four genetically unique haploid cells. Mitosis produces only two identical daughter cells. Mitotic daughter cells have half the number of chromosomes than their parent cell describes meiosis, not mitosis. Meiosis results in haploid cells (e.g., gametes), which have half the chromosome number. Mitotic daughter cells are formed as a result of crossing over of genetic materials occurs during meiosis (prophase I), not mitosis. Mitosis does not involve the exchange of genetic material between homologous chromosomes.

Prophase, Metaphase, Anaphase, Telophase Mitosis is a type of cell division in which one cell (the mother) divides to produce two new cells (the daughters) that are genetically identical to itself. The mitotic cell cycle is divided into certain phases. Before Mitosis: Interphase: Interphase is the longest part of the cell cycle. This is when the cell grows and copies its DNA before moving into mitosis. During Mitosis: Prophase: The cell starts to break down some structures and build others up, setting the stage for the division of the chromosomes. Chromosomes start to condense, spindle formation begins, nuclear membrane disappears, microtubules bind to chromosomes at the kinetochore, a patch of protein found on the centromere of each sister chromatid, and aster is formed. Metaphase: Meta means middle or center. In metaphase, all the chromosomes are lined up at the middle of the cell called the metaphase plate. Anaphase: Ana means up. In anaphase, sister chromatids separate from each other and are pulled towards opposite ends of the cell. Telophase: In telophase, the cell is nearly done dividing, and it starts to re-establish its normal structures as cytokinesis (a division of the cell contents) takes place. Two nuclei are formed, nuclear membrane reforms, and chromosomes decondense. Tip to remember: You can remember the order of the phases with the famous mnemonic: [Please] Pee on the MAT.

23 The number of chromosomes in a cell is halved during meiosis I and maintained during meiosis II. So, when a cell containing 46 chromosomes undergoes gametogenesis, the resulting daughter cells each contain 23 chromosomes after meiosis I and 23 chromosomes after meiosis II. The process results in four daughter cells that are haploid, which means they contain half the number of chromosomes of the diploid parent cell. Meiosis has both similarities to and differences from mitosis, which is a cell division process in which a parent cell produces two identical daughter cells. 92 would be double the diploid number and does not occur during meiosis or normal cell division. 138 is not biologically relevant for humans. 46 is the diploid number found in somatic (non-reproductive) cells, not the haploid gametes produced by meiosis.

Formation of sex cells or gametes Meiosis is responsible for the formation of sex cells or gametes that are responsible for sexual reproduction. It activates the genetic information for the development of sex cells. Growth is primarily achieved by mitosis, not meiosis. Repairing the cell involves mitosis, not meiosis. Replacement of worn-out cells occurs through mitosis, not meiotic division.

Homozygous Alleles are different versions of a gene that determine specific traits. For example, a gene for eye color might have alleles for blue or brown eyes. When an organism has two alleles of the same type for a specific gene (e.g., both alleles code for blue eyes or both code for brown eyes), it is called homozygous. Example: AA (homozygous dominant) or aa (homozygous recessive) Heterozygous refers to having two different alleles for a specific gene (e.g., one allele for blue eyes and one for brown eyes, such as Aa). Mutations are changes in the DNA sequence of a gene, not a term used to describe alleles of the same type. Dominant is one that masks the effect of a recessive allele when they are paired together in a heterozygous combination (e.g., A dominates over a in Aa).

The set of observable characteristics of an individual A genotype is the combination of alleles. It is the genetic makeup of an individual organism (e.g. bb, Bb, or BB) The phenotype is how the genetic makeup of an organism expresses itself (e.g. brown hair, blonde hair, red hair). The environmental factors which affect the characteristics of an individual: While environmental factors influence the phenotype, they are not the definition of the phenotype itself. The genetic makeup of a cell refers to the genotype, not the phenotype. The genotype consists of the specific alleles an organism inherits from its parents. In summary: Phenotype = Observable traits. Genotype = Genetic code. Environment + Genotype = Phenotype.

ACGU DNA is a long molecule that contains our unique genetic code. It holds the instructions for making all the proteins in our bodies. DNA is a double helical structure (like a twisted ladder) that contains the four nitrogenous bases: adenine, thymine, guanine, and cytosine. Each base forms hydrogen bonds with another base on the complementary strand. During transcription, DNA is used as a template to synthesize mRNA. The rules of base pairing apply, but with one key difference: In RNA, uracil (U) replaces thymine (T). The complementary base-pairing rules are: A (adenine) pairs with U (uracil) in RNA. T (thymine) pairs with A (adenine). G (guanine) pairs with C (cytosine). C (cytosine) pairs with G (guanine). TUGT: RNA does not use T (thymine). Instead, it uses U (uracil). TGCA: This is the original DNA sequence, not the complementary mRNA strand. ACGT: While this has the correct base pairing for DNA, it is incorrect for RNA because it uses T (thymine) instead of U (uracil). Remember: DNA: AT/GC RNA: AU/GC

From DNA to ribosomes Messenger RNA (mRNA) plays a critical role in the process of protein synthesis. Transcription occurs in the nucleus, mRNA is synthesized as a complementary copy of the DNA template. This step transfers the genetic information from DNA to mRNA. Translation is when the mRNA leaves the nucleus and travels to the ribosomes in the cytoplasm. Ribosomes read the sequence of mRNA bases in codons (groups of three nucleotides) to synthesize proteins with the help of transfer RNA (tRNA) and ribosomal RNA (rRNA). mRNA acts as the intermediary, carrying instructions encoded in the DNA to the ribosomes, where proteins are assembled. You may use the diagram below as a visual reference for the process of translation. From DNA to glucose: mRNA does not play a role in glucose metabolism. From RNA to DNA: This is reverse transcription process occurs in retroviruses, not in typical mRNA function in cells. From DNA to proteins: mRNA does not directly create proteins; it transfers the information to ribosomes, where proteins are synthesized.