Biology: Organismal Responses, Plant Hormones, and the Nervous System

Comprehensive vocabulary flashcards covering organismal responses, plant hormones, tropisms and nastic movements, sensory receptor classes, neuron anatomy, action potential phases, and synaptic transmission mechanisms.

Stimulus (Uyaran)

Any living or non-living external factor that induces a response in an organism, such as light, sound, temperature, water, food availability, chemical substances, pressure, or touch.

Response (Tepki)

The behavior or physiological defense and adaptation mechanism an organism exhibits to counter external factors that disrupt internal balance, serving to maintain homeostasis and survival.

Sensory Reception (Uyaranın Alınması)

The initial step of response formation in which internal or external environmental changes are detected by biological sensors or receptors specific to the organism.

Signal Processing (Uyarı İletimi ve Yorumlama)

The second stage of response formation where received stimuli are evaluated and transmitted through intracellular or intercellular chemical communication, or via neural pathways.

Auxin (Oksin)

A plant growth hormone synthesized in shoot tips, young leaves, developing fruits, seeds, and roots that promotes cell division, apical stem elongation, lateral root formation, and phototropism.

Apical Dominance

A phenomenon mediated by auxin wherein elongation at the shoot tip suppresses the outgrowth of lateral buds, allowing the plant to maximize light capture through vertical growth.

Cytokinin (Sitokinin)

A plant hormone produced in roots, seed embryos, and actively growing leaves and fruits; transported via xylem to promote cytokinesis, lateral branching, chloroplast formation, chlorophyll synthesis, and delay senescence.

Gibberellin (Giberellin)

A plant hormone produced in seeds, buds, young leaves, and roots that breaks seed dormancy to stimulate germination, promotes stem elongation, flowering, and accelerates starch hydrolysis into glucose for ATP production.

Abscisic Acid (ABA)

A stress hormone synthesized in plastid-containing plant cells that counteracts growth hormones, enforces bud and seed dormancy, and triggers stomatal closure during drought to prevent water loss.

Ethylene (Etilen)

A gaseous plant hormone produced across all organs—especially in aging tissues and ripening fruits—that diffuses to accelerate fruit ripening, fruit softening via cell wall breakdown, starch sweetening, and leaf abscission.

Tropism (Tropizma)

A directional growth movement of a plant whose orientation depends on the direction of the stimulus, driven by asymmetric hormonal (auxin) distribution.

Phototropism (Fototropizma)

A plant growth response to light where shoot tips show positive tropism by bending toward the light source as auxin accumulates on the shaded side and accelerates cell elongation there.

Geotropism (Gravitropism)

A plant growth response to gravity in which roots show positive geotropism by growing downward toward water and minerals, while shoots show negative geotropism by growing upward toward light.

Hydrotropism (Hidrotropizma)

A directional plant growth movement in response to water, characterized by roots growing toward regions of higher moisture (positive hydrotropism), having a stronger effect than gravity.

Chemotropism (Kemotropizma)

A plant growth response toward or away from chemical substances, such as roots exhibiting positive chemotropism toward fertilizers and minerals, and negative chemotropism away from lime or excess salt.

Thigmotropism / Haptotropism (Haptotropizma)

A plant growth movement triggered by mechanical contact or touch, enabling climbing plants like ivy to wrap around or cling to physical supports.

Nastic Movement (Nasti)

A reversible, non-directional plant movement triggered by changes in turgor pressure rather than the direction of the stimulus; it occurs significantly faster than tropisms.

Photonasty (Fotonasti)

A non-directional nastic movement occurring in response to changes in light intensity, such as the closing of four o'clock flower (Mirabilis jalapa) petals or leaves in high light conditions.

Seismonasty (Sismonasti)

A nastic movement provoked by mechanical shock, vibration, or direct physical contact, such as the rapid leaf-folding exhibited by Mimosa pudica when touched.

Thermonasty (Termonasti)

A nastic movement occurring in response to temperature fluctuations, causing flowers or leaves to open or close at specific temperature thresholds.

Sensory Receptor (Duyu Reseptörü)

A specialized biological sensor (epithelial cell or modified neuron) in sensory organs that detects specific environmental stimuli and converts them into electrical or chemical impulses.

Mechanoreceptor (Mekanoreseptör)

A sensory receptor that detects physical deformations resulting from mechanical energy forms, including hearing, balance, touch, pressure, stretching, and movement; abundant in skin and ears.

Chemoreceptor (Kemoreseptör)

A receptor specialized in detecting dissolved chemical molecules responsible for taste and smell; includes hypothalamic osmoreceptors that monitor total solute concentration changes in the blood.

Electromagnetic Receptor (Elektromanyetik Reseptör)

A receptor that detects forms of electromagnetic energy such as visible light, electricity, and magnetic fields; includes photoreceptors in eyes and magnetic orientation receptors in migratory birds.

Thermoreceptor (Termoreseptör)

A sensory receptor located in the skin and tongue that senses temperature shifts; also activated by capsaicin (interpreted as heat) and menthol (interpreted as cold).

Nociceptor (Nosiseptör / Ağrı Reseptörü)

A sensory pain receptor found in nearly all tissues and organs that responds to potentially damaging stimuli, such as extreme pressure, excessive temperature, or noxious chemicals, with pain amplified by prostaglandins.

Neuron (Sinir Hücresi)

A specialized nerve cell responsible for generating and transmitting electrochemical impulses throughout the nervous system, structurally divided into a cell body (soma), dendrites, and an axon.

Neurofibril (Nörofibril)

Thin protein filaments extending along the cytoplasm of a neuron that provide structural shape, support, and facilitate intracellular transport of substances.

Dendrite (Dendrit)

Short, highly branched extensions projecting from the neuronal soma that function to receive incoming stimuli and impulses and carry them toward the cell body.

Axon (Akson)

A single, elongated cytoplasmic projection extending from the cell body that conducts electrical impulses away from the soma toward target cells or other neurons.

Myelin Sheath (Miyelin Kılıf)

An insulating, lipid-rich lipoprotein layer produced by Schwann cells surrounding certain axons; it prevents ion leakage across the membrane and substantially accelerates impulse transmission.

Node of Ranvier (Ranvier Boğumu)

Unmyelinated gaps located between adjacent myelin segments on an axon where voltage-gated ion exchange occurs, enabling fast saltatory conduction.

Resting Membrane Potential (Dinlenme Zar Potansiyeli)

The electrical charge difference across the neuronal plasma membrane when no impulse is being conducted, measured at approximately $-70\,\text{mV}$.

Polarization (Polarizasyon)

The resting, polarized state of an unexcited neuron where the cell interior is negatively charged relative to the positive exterior, actively maintained by the $Na^+-K^+$ pump using ATP.

Depolarization (Depolarizasyon)

The phase of an action potential triggered by a threshold stimulus where voltage-gated $Na^+$ channels open, allowing an influx of $Na^+$ ions by diffusion without ATP expenditure, shifting the membrane potential to approximately $+40\,\text{mV}$.

Repolarization (Repolarizasyon)

The phase following depolarization wherein voltage-gated $K^+$ channels open and $K^+$ ions exit the cell by diffusion without ATP expenditure, restoring the internal negative and external positive electrical charge.

Threshold Intensity (Eşik Şiddeti / Değeri)

The minimum stimulus strength required to depolarize a neuron's membrane to the level necessary to trigger an action potential.

All-or-None Law (Ya Hep Ya Hiç Yasası)

The physiological principle stating that a single neuron will either generate a full-sized action potential if the stimulus reaches or exceeds the threshold value, or generate no action potential at all if it falls below threshold.

Synapse (Sinaps)

The specialized functional junction through which an axon terminal of a presynaptic neuron communicates with a postsynaptic neuron, muscle fiber, or gland cell.

Neurotransmitter (Nörotransmitter)

Chemical messengers stored within presynaptic vesicles that are released via exocytosis into the synaptic cleft upon $Ca^{2+}$ influx to bind to specific postsynaptic receptors.

Excitatory Synapse (Uyarıcı Sinaps)

A synapse where neurotransmitter binding brings the postsynaptic membrane closer to threshold via depolarization, promoting the generation of an action potential.

Inhibitory Synapse (Engelleyici Sinaps)

A synapse where neurotransmitter binding induces hyperpolarization across the postsynaptic membrane, moving it further from threshold and decreasing the probability of impulse generation.