Double-membraned organelles found in most eukaryotic cells, responsible for generating the bulk of the cell's supply of adenosine triphosphate (ATP) through cellular respiration.
Often called the 'powerhouses' of the cell, they are unique for having their own circular DNA and ribosomes, suggesting an endosymbiotic origin.
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Rough Endoplasmic Reticulum
Answer
A network of interconnected membranes studded with ribosomes, primarily involved in the synthesis, folding, modification, and transport of proteins destined for secretion or insertion into membranes.
The 'rough' appearance is due to the attached ribosomes, differentiating it from the smooth ER which lacks ribosomes and focuses on lipid synthesis and detoxification.
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Lysosomes
Answer
Membrane-bound organelles containing hydrolytic enzymes that break down waste materials, cellular debris, and foreign invaders like bacteria and viruses.
These are the 'recycling centers' or 'digestive systems' of the cell, crucial for cellular waste management and defense, often confused with peroxisomes which handle different types of waste.
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Ribosomes
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Complex molecular machines composed of ribosomal RNA (rRNA) and proteins, responsible for protein synthesis (translation) by reading messenger RNA (mRNA) sequences.
Ribosomes are unique because they are not membrane-bound organelles and are found in both prokaryotic and eukaryotic cells, highlighting their fundamental role in all life.
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Diffusion
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The net movement of particles from an area of higher concentration to an area of lower concentration, driven by the random motion of molecules.
This is a fundamental passive transport mechanism for small, nonpolar molecules, distinct from facilitated diffusion which requires transport proteins.
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Facilitated Diffusion
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The passive movement of molecules across a cell membrane via specific transmembrane integral proteins (channels or carriers) down their concentration gradient.
While still passive, it 'facilitates' the movement of larger or charged molecules that cannot easily pass through the lipid bilayer directly.
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Sodium-Potassium Pump
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A transmembrane protein that actively transports three sodium ions out of the cell and two potassium ions into the cell for every ATP molecule hydrolyzed, establishing electrochemical gradients.
This pump is a crucial example of primary active transport, essential for nerve impulse transmission, muscle contraction, and maintaining cell volume.
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Endocytosis
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A process by which cells engulf substances from their external environment by invaginating a portion of the plasma membrane, forming a vesicle that encloses the substance and brings it into the cell.
This is a form of bulk transport for large molecules or particles, distinct from exocytosis which expels substances.
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Telophase
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The final stage of mitosis where chromosomes arrive at opposite poles, decondense, nuclear envelopes reform around the two new sets of chromosomes, and the mitotic spindle disappears.
Telophase essentially reverses the events of prophase, preparing the cell for cytoplasmic division.
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Cytokinesis
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The division of the cytoplasm to form two separate daughter cells, typically occurring concurrently with telophase and completing the process of cell division.
This process physically separates the two newly formed nuclei and their associated cytoplasm, concluding the M phase.
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Sister Chromatids
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Two identical copies of a chromosome joined together by a centromere, formed during DNA replication in S phase and separated during anaphase of mitosis.
They represent duplicated genetic material and are crucial for ensuring that daughter cells receive a complete and identical set of chromosomes.
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Krebs Cycle (Citric Acid Cycle)
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A series of enzyme-catalyzed reactions in the mitochondrial matrix that oxidizes acetyl-CoA, producing carbon dioxide, ATP, NADH, and FADH2.
This cycle completes the breakdown of glucose derivatives, generating electron carriers (NADH and FADH2) that will fuel the subsequent stage of ATP production.
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Electron Transport Chain (ETC)
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A series of protein complexes embedded in the inner mitochondrial membrane that accept electrons from NADH and FADH2, using the energy released to pump protons across the membrane.
The ETC establishes a proton gradient, which is then used by ATP synthase to produce the vast majority of ATP in aerobic respiration.
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ATP Synthase
Answer
A large enzyme complex located in the inner mitochondrial membrane (or thylakoid membrane in chloroplasts) that uses the energy from a proton (H+) gradient to synthesize ATP from ADP and inorganic phosphate.
This molecular motor is responsible for chemiosmosis, the direct synthesis of ATP by oxidative phosphorylation or photophosphorylation, making it central to energy production.
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Light-Dependent Reactions
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The first stage of photosynthesis, occurring in the thylakoid membranes of chloroplasts, where light energy is captured by chlorophyll and converted into chemical energy in the form of ATP and NADPH, with oxygen released as a byproduct.
These reactions are directly dependent on sunlight and produce the energy currency (ATP) and reducing power (NADPH) required for sugar synthesis in the Calvin Cycle.
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Calvin Cycle (Light-Independent Reactions)
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The second stage of photosynthesis, occurring in the stroma of chloroplasts, where ATP and NADPH from the light-dependent reactions are used to fix carbon dioxide into glucose.
Often called 'light-independent' because it does not directly require light, but it depends entirely on the ATP and NADPH produced by the light-dependent reactions.
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Chlorophyll
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The primary green pigment found in chloroplasts that absorbs light energy, particularly in the red and blue spectra, to initiate the light-dependent reactions of photosynthesis.
It is the molecule directly responsible for capturing the energy from sunlight, giving plants their characteristic green color because it reflects green light.