Bio Unit 2

Cytoskeleton

A network of protein fibers inside a cell that provides structure, maintains shape, and helps with movement and transport.

Microtubules

Hollow tubes made of protein that help maintain cell shape, move chromosomes during cell division, and transport materials inside cells.

Microfilaments

Thin fibers made of actin that help cells move, change shape, and contract.

Connective Tissue

Tissue that supports, connects, protects, or binds other tissues and organs. Examples include bone, blood, cartilage, and fat.

Epithelial Tissue

Tissue that covers body surfaces, lines organs and cavities, and forms glands. It provides protection and can absorb or secrete substances.

Muscle Tissue

Tissue made of cells that contract to produce movement. The three types are skeletal, cardiac, and smooth muscle.

Nervous Tissue

Tissue made of neurons and supporting cells that receives and transmits signals throughout the body.

Gap Junction

A connection between animal cells that allows ions and small molecules to pass directly between neighboring cells.

Desmosome

A strong connection that holds neighboring cells together and helps tissues resist stretching and mechanical stress.

Tight Junction

A connection between neighboring cells that seals the space between them, preventing substances from easily passing between cells.

Reactants/Substrates

The starting materials in a chemical reaction. A substrate is the specific reactant an enzyme acts on.

Products

The substances formed as a result of a chemical reaction.

Transition State

A temporary, unstable state in which reactants are being converted into products.

Activation Energy

The minimum energy needed to start a chemical reaction.

Enzymes

Biological catalysts, usually proteins, that speed up chemical reactions by lowering activation energy without being used up.

Active Site

The specific region of an enzyme where the substrate binds and the chemical reaction occurs.

Metabolism

The sum of all chemical reactions that occur within an organism or cell.

Anabolic

Describes reactions that build larger molecules from smaller molecules and require energy. Example: building proteins from amino acids.

Catabolic

Describes reactions that break down larger molecules into smaller molecules and often release energy. Example: breaking down glucose during cellular respiration.

Competitive Modulator

A molecule that competes with a substrate for an enzyme's active site, reducing the substrate's ability to bind. Often called a competitive inhibitor when it reduces enzyme activity.

Allosteric Modulator

A molecule that binds to a site other than an enzyme's active site, changing the enzyme's shape and increasing or decreasing its activity.

Negative Feedback

A process in which the result of a system reduces or reverses the original change, helping maintain stability. Example: regulating body temperature.

Positive Feedback

A process in which the result of a system strengthens or increases the original change. Example: contractions becoming stronger during childbirth.

ATP

A molecule that stores and transfers usable energy in cells. Energy can be released when its terminal phosphate group is removed.

ATP Hydrolysis

A reaction in which water breaks ATP into ADP and inorganic phosphate, releasing usable energy under cellular conditions.

Phosphorylation

The addition of a phosphate group to a molecule, often changing its activity or storing/transferring energy.

Autotroph

An organism that makes its own organic food from inorganic substances using light energy or chemical energy. Example: plants.

Heterotroph

An organism that obtains energy and organic nutrients by consuming other organisms or organic matter. Example: animals.

Photosynthesis

The process by which plants, algae, and some bacteria use light energy to make sugars from carbon dioxide and water, releasing oxygen in oxygen-producing photosynthesis.

Cellular Respiration

The process by which cells break down organic molecules, such as glucose, to produce ATP. In aerobic respiration, oxygen is used and carbon dioxide and water are produced.

Endosymbiosis

The theory that mitochondria and chloroplasts evolved from free-living bacteria that were engulfed by an ancestral cell and formed a mutually beneficial relationship.

Chloroplasts

Organelles in plants and algae where photosynthesis occurs. They contain chlorophyll, which absorbs light energy.

Light Reactions

The first stage of photosynthesis, occurring in the thylakoid membranes. Light energy splits water, releases oxygen, and produces ATP and NADPH.

Calvin Cycle/Dark Reactions

The stage of photosynthesis that uses carbon dioxide, ATP, and NADPH to produce G3P, a molecule used to build sugars. It occurs in the stroma of chloroplasts and does not directly require light.

Pigments

Molecules that absorb certain wavelengths of light and reflect or transmit others. In photosynthesis, pigments such as chlorophyll capture light energy.

Flow of Electrons During Light Reactions

Light excites electrons in photosystem II. The electrons move through an electron transport chain, helping create a proton gradient for ATP production, and then reach photosystem I, where light re-energizes them. They ultimately help form NADPH. Water replaces the electrons lost by photosystem II, releasing oxygen.

ATP Synthase

A protein complex that uses the energy of hydrogen ions (protons) flowing down their gradient to produce ATP from ADP and phosphate.

Cyclic Electron Flow

A photosynthetic pathway in which electrons from photosystem I cycle back through an electron transport chain. It produces extra ATP but does not produce NADPH or release oxygen.

Transpiration

The loss of water vapor from a plant, mainly through openings in its leaves called stomata.

CAM Pathway

A photosynthesis adaptation in which plants open their stomata at night to take in CO₂, helping conserve water in hot, dry environments.

C4 Pathway

A photosynthesis adaptation that initially captures CO₂ into a four-carbon molecule, helping plants reduce photorespiration in hot, sunny environments.

Thylakoid

A flattened membrane sac inside chloroplasts where the light-dependent reactions of photosynthesis occur.

Stroma

The fluid-filled space inside a chloroplast surrounding the thylakoids, where the Calvin cycle occurs.

Glycolysis

The first step of cellular respiration, where one glucose molecule is broken into two pyruvate molecules, producing a net of 2 ATP and 2 NADH.

Pyruvic Acid/Pyruvate

A three-carbon molecule produced when glucose is broken down during glycolysis.

Citric Acid Cycle (Krebs Cycle)

A series of reactions that breaks down acetyl-CoA, releasing CO₂ and producing NADH, FADH₂, and ATP (or GTP).

Substrate-level Phosphorylation

The production of ATP by directly transferring a phosphate group from another molecule to ADP.

Acetyl-CoA

A two-carbon molecule attached to coenzyme A that carries carbon into the citric acid cycle

Anaerobic Respiration

The production of ATP without oxygen. Strictly speaking, anaerobic respiration uses an electron transport chain with a final electron acceptor other than oxygen.

Lactic Acid Fermentation

A process that converts pyruvate into lactate, regenerating NAD⁺ so glycolysis can continue producing ATP without oxygen.

Alcoholic Fermentation

A process in which pyruvate is converted into ethanol and CO₂, regenerating NAD⁺ so glycolysis can continue. It occurs in organisms such as yeast.