Comprehensive Study Notes on Cellular Respiration, Photosynthesis, and Cell Division

Vocabulary practice flashcards covering cell division (mitosis and meiosis), cellular respiration, and photosynthesis based on BIOS 1450 lecture notes and figures.

Binary Fission

The asexual reproductive process in prokaryotes where a single circular chromosome replicates and the origins attach to the plasma membrane as the cell pulls apart into two daughter cells.

Diploid ($2n$)

A cell condition containing two complete sets of chromosomes, one inherited from each parent (e.g., $46$ chromosomes in human somatic cells).

Haploid ($n$)

A cell condition containing only a single copy of each chromosome (e.g., gametes like egg and sperm).

Mitosis

Nuclear division in eukaryotic cells that produces two genetically identical daughter nuclei, each maintaining the original chromosome number.

Meiosis

A two-stage cellular division in sexually reproducing organisms that reduces the chromosome number from diploid ($2n$) to haploid ($n$), yielding four unique daughter cells.

Mitotic ($M$) Phase

The phase of the eukaryotic cell cycle, accounting for $<5\%$ of the total cycle duration, during which mitosis (nuclear division) and cytokinesis (cytoplasmic division) take place.

$G_1$ Phase (Gap 1)

The first growth phase of interphase, occupying $15\text{--}25\%$ of the cell cycle, during which the cell increases in size, accumulates protein, and prepares for DNA synthesis.

$S$ Phase (Synthesis)

The interphase stage comprising $40\text{--}50\%$ of the cell cycle, during which DNA is synthesized and duplicated into pairs of identical sister chromatids.

Sister Chromatids

Two identical copies of a duplicated chromosome produced during $S$ phase that remain joined together at the centromere.

Centromere

The constricted DNA region of a duplicated chromosome where two sister chromatids are held together and where kinetochores assemble.

Kinetochore

A specialized protein complex assembled at the centromere of each sister chromatid that binds to spindle microtubules and facilitates chromosome movement toward spindle poles.

$G_2$ Phase (Gap 2)

The second growth phase of interphase, taking up $20\text{--}25\%$ of the cell cycle, where protein content and cell size further increase to prepare for mitosis and cytokinesis.

$G_0$ Phase

A non-dividing, quiescent state exited from the cell cycle by cells that are not actively undergoing division.

DNA Damage Checkpoint

A regulatory checkpoint occurring before entry into $S$ phase (at the end of $G_1$) that monitors genomic integrity to prevent replication of damaged DNA.

DNA Replication Checkpoint

A regulatory control mechanism located at the end of $G_2$ that verifies whether the entire genome has successfully and completely replicated prior to mitosis.

Spindle Assembly Checkpoint

A mitotic checkpoint operating before anaphase that ensures every chromosome is properly attached to the mitotic spindle via its kinetochores.

Prophase (Mitosis)

The opening stage of mitosis characterized by chromosome condensation, nucleoli disappearance, and the outward migration of centrosomes as they radiate spindle microtubules.

Prometaphase

The transition stage of mitosis in which the nuclear envelope breaks down and spindle microtubules attach directly to chromosome kinetochores.

Metaphase (Mitosis)

The stage of mitosis where chromosomes are pulled into alignment along the center of the cell (the metaphase plate) by kinetochore microtubules.

Anaphase (Mitosis)

The mitotic stage during which centromeres split, sister chromatids separate into individual chromosomes, and motor proteins shorten microtubules at the kinetochore to pull them toward opposite poles.

Telophase (Mitosis)

The final stage of mitosis during which daughter nuclear envelopes re-form around decondensing chromosomes and nucleoli reappear.

Cleavage Furrow

A shallow contractile groove formed by microfilaments that pinches an animal cell cytoplasm into two daughter cells during cytokinesis.

Cell Plate

A partition formed during plant cell cytokinesis along the middle of the dividing cell by the aggregation and fusion of Golgi-derived vesicles.

Synapsis

The precise gene-for-gene physical pairing of homologous chromosomes that occurs during prophase I of meiosis.

Bivalent

A paired structure consisting of two homologous chromosomes (four chromatids) aligned together following synapsis in prophase I of meiosis.

Chiasma

An X-shaped physical crossing point between non-sister chromatids of homologous chromosomes where genetic exchange (crossing-over) occurs during prophase I of meiosis.

Crossing-Over

The reciprocal exchange of segments of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis.

Polar Body

A tiny, non-functional haploid cell produced during female meiosis (oogenesis) that receives virtually no cytoplasm relative to the developing oocyte.

Cellular Respiration

A catabolic pathway oxidizing organic fuels in the presence of oxygen to release energy: $C_6H_{12}O_6 + 6\,O_2 \rightarrow 6\,CO_2 + 6\,H_2O + \text{Energy (ATP + heat)}$.

Substrate-Level Phosphorylation

The direct synthesis of ATP by an enzyme transferring a phosphate group from a phosphorylated organic substrate directly to ADP.

Oxidative Phosphorylation

ATP synthesis driven by the transfer of electrons through an electron transport chain, creating an electrochemical proton gradient that powers ATP synthase.

Oxidation

The loss of electrons or removal of hydrogen atoms from a chemical substance during a redox reaction.

Reduction

The gain of electrons or addition of hydrogen atoms to a chemical substance during a redox reaction.

Reducing Agent

The electron donor in a redox reaction that reduces another compound and becomes oxidized itself.

Oxidizing Agent

The electron acceptor in a redox reaction that oxidizes another compound and becomes reduced itself (e.g., highly electronegative oxygen).

Glycolysis

The cytosolic breakdown of one glucose molecule ($6\text{-carbon}$) into two molecules of pyruvate ($C_3H_4O_3$), yielding a net product of $2\text{ ATP}$ and $2\text{ NADH}$.

Preparatory Phase of Glycolysis

The energy-investment stage of glycolysis where two ATP molecules are consumed to add two phosphate groups to glucose, yielding fructose 1,6-bisphosphate.

Cleavage Phase of Glycolysis

The stage of glycolysis where the destabilized six-carbon intermediate fructose 1,6-bisphosphate is cleaved into two three-carbon sugars: glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.

Payoff Phase of Glycolysis

The stage of glycolysis that generates $4\text{ ATP}$ (via substrate-level phosphorylation), $2\text{ NADH}$, and $2$ pyruvate molecules, producing a net gain of $2\text{ ATP}$.

Pyruvate Oxidation

The mitochondrial stage wherein pyruvate is actively transported into the matrix, oxidized to release $CO_2$ and $NADH$, and combined with Coenzyme A to form acetyl-CoA.

Acetyl-CoA

A high-energy two-carbon acetyl unit coupled to Coenzyme A (derived from vitamin B) that delivers fuel into the citric acid cycle.

Citric Acid Cycle

A cyclic metabolic pathway in the mitochondrial matrix that fully oxidizes acetyl-CoA, producing per turn $2\,CO_2$, $3\text{ NADH}$, $1\text{ FADH}_2$, and $1\text{ ATP}$ via substrate-level phosphorylation ($2$ turns per glucose).

Mitochondrial Matrix

The fluid-filled internal compartment bounded by the inner mitochondrial membrane where pyruvate oxidation and the citric acid cycle occur.

Intermembrane Space

The space located between the inner and outer membranes of a mitochondrion into which protons ($H^+$) are pumped to build an electrochemical gradient.

ATP Synthase

A rotary enzyme composed of a membrane-spanning channel ($F_o$ subunit) that turns as protons pass through, and a catalytic head ($F_1$ subunit) that uses rotational energy to phosphorylate ADP into ATP.

Anaerobic Respiration

A catabolic pathway that uses an electron transport chain with an inorganic terminal electron acceptor other than oxygen, such as sulfate ion ($SO_4^{2-}$).

Fermentation

An anaerobic cellular process that generates ATP solely via glycolysis by using an endogenous organic molecule to oxidize NADH back into $NAD^+$.

Alcohol Fermentation

A pathway in bacteria and yeast where pyruvate is converted to acetaldehyde and subsequently reduced to ethanol and $CO_2$ to regenerate $NAD^+$.

Lactic Acid Fermentation

A pathway in animals, fungi, and bacteria in which pyruvate is reduced directly by NADH to form lactic acid and regenerate $NAD^+$.

Phosphofructokinase-1 (PFK-1)

An allosteric regulatory enzyme catalyzing the irreversible third step of glycolysis (fructose 6-phosphate to fructose 1,6-bisphosphate), inhibited by high levels of ATP or citrate and activated by ADP or AMP.

Photosynthesis

The solar-powered anabolic process that reduces carbon dioxide and oxidizes water to synthesize carbohydrates and oxygen: $\text{Solar energy} + 6\,CO_2 + 6\,H_2O \rightarrow C_6H_{12}O_6 + 6\,O_2$.

Mesophyll

The internal ground tissue of a leaf packed with chloroplast-containing cells where the majority of photosynthesis occurs.

Stomata

Microscopic pores on leaf surfaces regulated to allow $CO_2$ intake and $O_2$ discharge for photosynthetic gas exchange.

Chloroplast

The photosynthetic organelle featuring an outer membrane, an inner membrane, an internal thylakoid membrane system, and the fluid stroma.

Stroma

The dense fluid matrix within the inner chloroplast membrane surrounding the thylakoid stacks, serving as the site of the Calvin cycle.

Thylakoid Membrane

The internal folded membrane network of chloroplasts that organizes photosynthetic pigments, light-harvesting photosystems, electron transport chains, and ATP synthase.

Grana

Stacks of disc-shaped thylakoid structures suspended in the stroma of chloroplasts.

Light-Dependent Reactions

Reactions localized on the thylakoid membrane that capture solar energy to generate ATP, split water to produce $O_2$, and reduce $NADP^+$ to NADPH.

Calvin Cycle

The light-independent metabolic cycle in the chloroplast stroma that reduces $CO_2$ into three-carbon carbohydrates using energy from ATP and electrons from NADPH.

Rubisco

The stromal enzyme (RuBP carboxylase-oxygenase) that catalyzes the carboxylation of ribulose-1,5-bisphosphate ($RuBP$) with $CO_2$ in phase 1 of the Calvin cycle.

Ribulose-1,5-bisphosphate (RuBP)

A five-carbon sugar that serves as the substrate accepting $CO_2$ during carbon fixation and is continuously regenerated from triose phosphates in the Calvin cycle.

3-Phosphoglycerate (3-PGA)

The initial three-carbon organic acid produced in the Calvin cycle when the unstable six-carbon product of rubisco carboxylation immediately splits.

Glyceraldehyde 3-Phosphate (G3P)

A three-carbon carbohydrate produced during the reduction phase of the Calvin cycle (using ATP and NADPH) that serves as the building block for glucose and other sugars.

Photon

A discrete, wave-traveling packet of electromagnetic radiation that carries a defined quantity of solar energy inversely proportional to its wavelength.

Chlorophyll a

The primary photosynthetic pigment in plants, which strongly absorbs blue ($405\,nm$) and red ($665\,nm$) wavelengths while reflecting green light.

Accessory Pigments

Molecules such as chlorophyll b and carotenoids that capture light at wavelengths not absorbed by chlorophyll a, broadening the spectrum of energy available for photosynthesis.

Porphyrin Ring

The light-absorbing planar head of a chlorophyll molecule that contains a coordinated central magnesium ($Mg$) atom.

Photosystem II (PSII)

A multi-protein complex in the thylakoid membrane containing a $P680$ reaction-center chlorophyll pair that absorbs light energy, extracts electrons by splitting water, and pumps protons via an electron transport chain.

Photosystem I (PSI)

A thylakoid protein complex containing a $P700$ reaction-center chlorophyll pair that absorbs light to boost electrons to ferredoxin, ultimately reducing $NADP^+$ to NADPH.

Linear Electron Flow

The non-cyclic light-driven flow of electrons from water through PSII, the cytochrome complex, and PSI to $NADP^+$ reductase, synthesizing both ATP and NADPH while releasing $O_2$.

Cyclic Electron Flow

An alternate light-driven pathway wherein electrons cycle from PSI primary acceptor to ferredoxin, back to the cytochrome complex, and return to $P700$, powering ATP synthesis without producing NADPH or oxygen.

Binary Fission

The method of asexual reproduction in prokaryotes where the single circular chromosome replicates and the replication origins attach to the plasma membrane as the dividing cell elongates and pulls apart.

Diploid ($2n$)

A condition or cell possessing two complete sets or copies of each chromosome, with one copy inherited from each parent (such as $46$ chromosomes in human somatic cells).

Haploid ($n$)

A cell containing only a single set or copy of each chromosome, such as gametes produced through meiosis.

Mitosis

A eukaryotic nuclear division process wherein a cell divides to yield two genetically identical daughter cells maintaining the exact chromosome number of the parent (diploid to diploid or haploid to haploid).

Meiosis

A specialized two-stage nuclear division that reduces chromosome sets from diploid ($2n$) to haploid ($n$), creating four genetically unique daughter cells for sexual reproduction.

$G_1$ Phase (Gap 1)

The first growth phase of interphase ($15\text{--}25\%$ of the cell cycle) characterized by an increase in cell size and protein content in preparation for DNA synthesis.

S Phase (Synthesis)

The interphase stage ($40\text{--}50\%$ of the cell cycle) during which DNA is replicated, resulting in chromosomes composed of two sister chromatids joined at the centromere.

$G_2$ Phase (Gap 2)

The second growth phase of interphase ($20\text{--}25\%$ of the cell cycle) where the cell continues to increase in size and protein content in preparation for mitosis and cytokinesis.

$G_0$ Phase

A non-dividing state of the cell cycle occupied by cells that have exited the active division cycle.

Cell Cycle Checkpoints

Regulatory stopping points within the cell cycle that prevent damaged cells from reproducing, including the DNA damage checkpoint (end of $G_1$), the DNA replication checkpoint (end of $G_2$), and the spindle assembly checkpoint (before anaphase in early mitosis).

Kinetochore

A protein structure situated at the centromere of each sister chromatid that serves as the attachment point for mitotic spindle microtubules.

Prophase (Mitosis)

The first stage of mitosis, marked by the condensation of chromatin into visible chromosomes, the disappearance of nucleoli, and the radiating of microtubules from separating centrosomes to form the mitotic spindle.

Prometaphase

The mitotic transition stage during which the nuclear envelope breaks down and spindle microtubules attach to the kinetochores of chromosomes.

Metaphase (Mitosis)

The mitotic stage where kinetochore microtubules align duplicated chromosomes along the center of the cell at the metaphase plate.

Anaphase (Mitosis)

The mitotic stage during which centromeres split and sister chromatids separate into individual chromosomes, moving toward opposite poles as kinetochore microtubules shorten.

Telophase (Mitosis)

The final stage of mitosis during which daughter nuclei form, nuclear envelopes re-form around the separated chromatin sets, and chromosomes decondense.

Cleavage Furrow

A groove formed during animal cell cytokinesis by a contracting ring of microfilaments that pinches the parent cell into two daughter cells.

Cell Plate

A membrane-bound partition formed across the center of a dividing plant cell during cytokinesis through the fusion of Golgi-derived vesicles.

Synapsis

The gene-for-gene pairing of homologous chromosomes during prophase I of meiosis to form bivalents (tetrads).

Chiasma

The visible X-shaped region between non-sister chromatids of homologous chromosomes where crossing over and reciprocal genetic exchange take place during meiotic prophase I.

Polar Bodies

Small, non-functional cells produced alongside the functional oocyte during female meiosis that receive very little cytoplasm due to unequal meiotic division.

Substrate-Level Phosphorylation

The direct enzymatic formation of ATP through the direct transfer of a phosphate group from an organic substrate to ADP.

Oxidative Phosphorylation

The generation of ATP using energy released as electrons pass through an electron transport chain to establish a proton gradient that drives ATP synthase.

Oxidation

The chemical process involving the loss of electrons or the removal of hydrogen atoms from an organic molecule.

Reduction

The chemical process involving the gain of electrons or the addition of hydrogen atoms to an organic molecule.

Glycolysis

The initial 10-step catabolic stage occurring in the cytosol that partially degrades one glucose molecule into two molecules of pyruvate ($\text{C}_3\text{H}_4\text{O}_3$), yielding a net of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Phosphofructokinase-1 (PFK-1)

An allosteric enzyme catalyzing the irreversible, ATP-consuming third step of glycolysis (fructose 6-phosphate to fructose 1,6-bisphosphate); it is inhibited by high ATP and citrate, and activated by ADP and AMP.

Pyruvate Oxidation

The second stage of cellular respiration wherein pyruvate is actively transported into the mitochondrial matrix, oxidized to release $\text{CO}_2$, coupled with Coenzyme A to yield acetyl-CoA, and produces $1\,\text{NADH}$ per pyruvate ($2\,\text{NADH}$ per glucose).

Citric Acid Cycle

The cyclic series of reactions in the mitochondrial matrix that completely oxidizes acetyl-CoA, producing $2\,\text{CO}_2$, $3\,\text{NADH}$, $1\,\text{FADH}_2$, and $1\,\text{ATP}$ per turn ($4\,\text{CO}_2$, $6\,\text{NADH}$, $2\,\text{FADH}_2$, and $2\,\text{ATP}$ per glucose).