Cellular Metabolism, Photosynthesis, and Nervous System Flashcards

Comprehensive vocabulary flashcards covering photosynthesis, the nervous system, and cellular central metabolism.

Photoautotrophs

Organisms, such as plants, algae, and cyanobacteria, that capture light energy to synthesize their own organic molecules.

Chemoautotrophs

Organisms, including certain bacteria and archaea, that manufacture organic molecules using energy derived from inorganic chemicals rather than sunlight.

Stomata

Microscopic pores located on leaf undersides that open and close to admit $CO_2$ and release $H_2O$ and $O_2$; they contain no chloroplasts and do not photosynthesize.

Mesophyll Cells

Chloroplast-containing cells located in the leaf interior that serve as the primary tissue site of photosynthesis.

Thylakoid Membrane

The internal membrane system of chloroplasts where chlorophyll pigments are embedded, organized into stacked disk-like structures called grana.

Stroma

The fluid-filled space within the chloroplast enclosing the thylakoid membranes, serving as the site of the Calvin cycle.

Chlorophyll a

The primary photosynthetic pigment in plants that absorbs blue-violet and red wavelengths of visible light and reflects green light.

Carotenoids

Accessory pigments in chloroplasts that absorb broad bands of blue and violet light and reflect yellow, orange, or reddish light.

Antenna Complex

The light-harvesting outer region of a photosystem composed of proteins, chlorophyll a, chlorophyll b, and carotenoids that absorbs photons and directs excitation energy toward the reaction center.

Photosystem II (PSII)

A membrane-bound protein-pigment complex containing a P680 reaction center that absorbs light, splits $H_2O$, releases $O_2$, and transfers high-energy electrons down an electron transport chain.

Photosystem I (PSI)

A protein-pigment complex containing a P700 reaction center that re-excites electrons using absorbed light to reduce $NADP^+$ to NADPH, or participates in cyclic photophosphorylation.

Cyclic Electron Flow

A light-dependent photosynthetic pathway involving only Photosystem I and an electron transport chain to generate ATP via cyclic photophosphorylation without producing NADPH or releasing $O_2$.

Rubisco

Ribulose bisphosphate carboxylase; the most abundant enzyme and protein on Earth, responsible for fixing inorganic $CO_2$ to RuBP in the Calvin cycle.

3-Phosphoglycerate (3PGA)

The first stable 3-carbon intermediate generated immediately after carbon fixation during C3 photosynthesis.

Photorespiration

A wasteful process occurring on hot, dry days when stomata close; Rubisco binds $O_2$ instead of $CO_2$, yielding toxic 2-phosphoglycolate and consuming ATP while releasing $CO_2$.

PEP Carboxylase

An enzyme utilized in C4 and CAM plants that fixes $CO_2$ into a 4-carbon compound; it has a high affinity for $CO_2$ and does not bind $O_2$.

C4 Photosynthesis

A photosynthetic adaptation featuring spatial separation of steps: initial carbon fixation occurs via PEP carboxylase in mesophyll cells, and the Calvin cycle operates with Rubisco in bundle-sheath cells.

CAM (Crassulacean Acid Metabolism)

A photosynthetic pathway in succulent plants using temporal separation: stomata open at night to fix $CO_2$ into 4-carbon organic acids, which are broken down during the day to release $CO_2$ for the Calvin cycle while stomata remain closed.

Axon Hillock

The junction where the neuron cell body connects to the axon; it integrates incoming graded electrical signals from dendrites to determine whether an action potential is triggered.

Resting Potential

The electrical charge difference across a resting neuronal membrane, typically about $-70\,mV$, maintained primarily by $Na^+-K^+$ pumps and potassium leak channels.

Action Potential

An all-or-none electrical impulse lasting $1\text{--}2\,ms$, triggered when membrane depolarization reaches threshold, causing rapid $Na^+$ influx up to $+40\,mV$ followed by $K^+$ efflux and hyperpolarization.

Refractory Period

The phase during which voltage-gated $Na^+$ channels are inactivated following an action potential, preventing immediate restimulation and enforcing one-way propagation down the axon.

Myelin Sheath

An insulating lipid coating around axons formed by Schwann cells in the PNS and oligodendrocytes in the CNS that accelerates electrical impulse conduction.

Nodes of Ranvier

Unmyelinated gaps situated between adjacent glial cells along an axon where voltage-gated ion channels are concentrated.

Saltatory Conduction

The rapid jumping of action potentials from one Node of Ranvier to the next along a myelinated axon in vertebrates.

Electrical Synapse

A direct neuronal junction connected by gap junctions with a $2\,nm$ gap that allows ions to flow directly between cells, providing rapid transmission without variation in intensity.

Chemical Synapse

A junction where an incoming action potential opens voltage-gated $Ca^{2+}$ channels, triggering exocytosis of neurotransmitters across a synaptic cleft ($< 50\,nm$) to bind postsynaptic ligand-gated receptors.

Glial Cells

Non-neuronal nervous system cells that provide structural support, regulate ion concentrations, control blood flow, protect against infection, and nourish neurons.

Brainstem

The region at the base of the brain comprising the pons and medulla oblongata that governs nonconscious homeostatic functions, including respiration, circulation, digestion, and sleep-wake cycles.

Cerebellum

The posterior brain structure responsible for nonconscious motor coordination, balance, hand-eye coordination, and muscle memory.

Thalamus

The diencephalon structure that acts as the primary sensory relay station (excluding olfaction) directing information to the cerebrum, while contributing to awareness.

Hypothalamus

A diencephalon brain structure that coordinates homeostatic functions such as body temperature, hunger, thirst, endocrine release, and circadian rhythms via the suprachiasmatic nucleus (SCN).

Pineal Gland

An endocrine component of the epithalamus that synthesizes and secretes melatonin in the evening following signals from the suprachiasmatic nucleus (SCN).

Cerebrum

The largest brain division, making up 80% of brain volume, responsible for higher cognition, decision-making, language, voluntary movement, sensory integration, and long-term memory.

Limbic System

A functional neural network spanning parts of the brainstem, diencephalon, and cerebrum that regulates emotion, motivation, memory processing of emotional experiences, aggression, sexuality, and olfaction.

Reticular Formation

A functional neuronal network situated mainly in the brainstem and epithalamus that mediates sleep, wakefulness, urination, defecation, and the filtering of repetitive sensory stimuli.

ATP (Adenosine Triphosphate)

The universal energy currency of cells, consisting of an adenine nitrogenous base, a ribose sugar, and three phosphate groups.

Oxidation

The loss of electrons from a chemical compound during a redox reaction, typically accompanied by the removal of protons.

Reduction

The gain of electrons by a chemical compound during a redox reaction, which decreases its overall oxidation state.

NADH

The reduced electron carrier derived from niacin (vitamin B3) that carries two high-energy electrons and one proton to Complex I of the mitochondrial electron transport chain.

FADH2

The reduced electron carrier derived from riboflavin (vitamin B2) that carries two high-energy electrons and two protons to Complex II of the mitochondrial electron transport chain.

Glycolysis

A ten-step metabolic pathway occurring in the cytosol that splits one molecule of glucose ($6C$) into two molecules of pyruvate ($3C$), generating a net of $2\,ATP$ and $2\,NADH$.

Phosphofructokinase (PFK)

The key regulatory and rate-limiting enzyme of glycolysis that converts fructose 6-phosphate to fructose 1,6-bisphosphate; allosterically inhibited by ATP and citrate, and stimulated by AMP.

Pyruvate Oxidation

The mitochondrial matrix reaction that converts 3-carbon pyruvate into 2-carbon acetyl CoA, releasing one $CO_2$ and producing one NADH per pyruvate molecule.

Citric Acid Cycle

A mitochondrial matrix cyclical pathway that oxidizes acetyl CoA to $CO_2$, producing $4\,CO_2$, $6\,NADH$, $2\,FADH_2$, and $2\,ATP$ per glucose molecule across two cycles.

Cytochromes

Iron-containing proteins with heme groups that serve as electron carriers in the multiprotein complexes of the mitochondrial inner membrane electron transport chain.

Chemiosmosis

The coupling of a proton ($H^+$) concentration gradient across the inner mitochondrial membrane to drive the catalytic synthesis of ATP from ADP and inorganic phosphate.

ATP Synthase

A multi-subunit membrane enzyme complex containing a rotor, stator, internal rod, and catalytic knob that uses proton diffusion from the intermembrane space into the matrix to generate ATP.

Lactic Acid Fermentation

An anaerobic metabolic process in active muscle and certain microorganisms where pyruvate is reduced to lactate to regenerate $NAD^+$ without producing $CO_2$, yielding $2\,ATP$ per glucose.

Alcohol Fermentation

An anaerobic metabolic pathway in yeast and bacteria that converts pyruvate into acetaldehyde and then ethanol, producing $CO_2$ and recycling $NAD^+$ to sustain glycolysis.

Auto-Brewery Syndrome

A medical disorder in which yeast or bacteria in the digestive tract ferment ingested carbohydrates into ethanol, causing intoxication in individuals who have consumed no alcohol.