Mitochondria are known as the powerhouses of the cell because they generate ATP through cellular respiration. They convert nutrients into usable energy, which is essential for cell function.

The modern cell theory states that cells come only from pre-existing cells, not spontaneously from non-living material. This foundational concept was established through experiments that disproved spontaneous generation.

Nitrogenous bases in DNA encode genetic information through their specific sequences. The sugar-phosphate backbone provides structural support but does not contain coding information.

Chlorophyll is the main pigment involved in absorbing light energy during photosynthesis. It captures light in the blue and red wavelengths, which is essential for converting light energy into chemical energy.

Enzymes act as catalysts by lowering the activation energy required for biochemical reactions, thereby speeding up these reactions. They do not alter the equilibrium state of the reaction.

The Electron Transport Chain produces the majority of ATP by leveraging a proton gradient across the inner mitochondrial membrane. Glycolysis and the Citric Acid Cycle contribute far less ATP compared to this final stage.

The Calvin cycle fixes carbon dioxide and converts it into sugars using ATP and NADPH produced in the light-dependent reactions. It does not capture light energy directly nor perform water splitting.

The lac repressor binds to the operator region of the lac operon to inhibit transcription when lactose is absent. When lactose is available, it binds to the repressor, changing its shape and preventing it from blocking transcription.

Temperature is a key control variable because fluctuations in temperature can affect enzyme activity and overall photosynthetic rates independently of light intensity. Keeping temperature constant allows a clearer analysis of the impact of light alone.

Homeostasis is the maintenance of stable internal conditions despite external fluctuations. This balance is crucial for the optimal functioning of cellular processes and overall organism health.

Natural selection drives evolutionary change by favoring traits that improve survival and reproduction. While genetic drift, mutation, and gene flow also influence evolution, natural selection provides a consistent mechanism for adapting to environmental challenges.

Simple diffusion is a passive transport mechanism that does not require energy, as molecules move from an area of higher concentration to one of lower concentration. Active transport and vesicle-mediated processes, such as endocytosis and exocytosis, require energy input.

Membrane receptors are the first point of contact for many extracellular signals, triggering intracellular signaling cascades. Their activation leads to a series of molecular events that ultimately result in a specific cellular response.

Predation involves one organism (the predator) hunting and consuming another organism (the prey). This interaction is a key factor in regulating population sizes and shaping ecosystem dynamics.

Stem cells are unique due to their ability to both self-renew and differentiate into multiple cell types. This versatility makes them crucial for development, tissue repair, and regenerative medicine.

Crossing over occurs during prophase I of meiosis when homologous chromosomes exchange segments, increasing genetic diversity. This recombinatory process is essential for producing genetically unique gametes in sexually reproducing organisms.

Allosteric regulation occurs when a molecule binds to an enzyme at a location other than the active site, causing a change in its conformation and activity. This reversible process allows cells to fine-tune metabolic pathways based on current needs.

Upon activation by a ligand-bound GPCR, the G-protein changes its conformation and activates downstream effectors, such as adenylate cyclase, which then produces cyclic AMP. This secondary messenger propagates the signal leading to a cellular response.

Deep homology highlights that different species use conserved genetic mechanisms during development, leading to analogous structures. This concept bridges the gap between genetics and morphology, underscoring a common evolutionary origin.

Neurotransmitters are chemical messengers released into the synaptic cleft that bind to receptors on the postsynaptic membrane, initiating a response. This binding can result in the generation of an action potential or modulation of neuronal activity.