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.