Cellular Respiration & Photosynthesis: Processes & Cycles

Posted on Nov 10, 2024 in Biology

Cellular Respiration

Role in Cellular Respiration

  • Glucose: This organic molecule is oxidized (loses H+) in the presence of oxygen to CO2 and H2O.
  • Oxygen: The final electron acceptor and proton recipient, it reduces to H2O.
  • NAD+ and FAD: Coenzymes that capture the H+ lost during the oxidation of organic molecules like glucose. These are reduced to NADH + H+ and FADH2, respectively. Subsequently, these reduced coenzymes yield hydrogen to oxygen.
  • Electron Transport Proteins: Protein molecules located in the inner mitochondrial membrane, transporting electrons from reduced coenzymes to O2. Energy released in this process is stored in ATP (oxidative phosphorylation).
  • CO2: Inorganic molecule obtained from the oxidation of organic molecules like glucose.
  • H2O: Inorganic molecule obtained when oxygen captures electrons and protons transferred by the reduced coenzymes.
  • ATP: Molecule obtained from the phosphorylation of ADP, using energy released from oxidizing molecules like glucose. Two types of phosphorylation exist: substrate-level and oxidative.

Photosynthesis

Role in Photosynthesis

  • Glucose: Organic molecule obtained by reducing CO2.
  • Oxygen: Waste product from the photolysis of water.
  • NADP+: Coenzyme that captures hydrogens from water during the light phase, reducing to NADPH + H+. In the dark phase, NADPH + H+ yields hydrogen to reduce CO2.
  • Chlorophyll: Photosynthetic pigment capturing light energy, which is converted into chemical energy.
  • CO2: Inorganic molecule reduced in the dark phase to form organic compounds using ATP and NADPH + H+.
  • H2O: Splits during photolysis, providing H+ (reducing agent) which is transferred to NADP+.
  • ATP: Molecule formed in the light phase and used in the dark phase.

Cell Cycle and Division

Interphase

The period from cell formation until the start of division. DNA replication occurs during interphase, which has three phases:

  • G1 Phase: The newly formed cell grows and increases its number of organelles.
  • S Phase: DNA replication occurs, resulting in two copies of the genetic material.
  • G2 Phase: Structures necessary for cell division are synthesized.

Mitosis (Karyokinesis)

Division of the nucleus, producing two daughter nuclei with the same chromosome number as the mother nucleus.

  • Prophase: Chromatin condenses, chromosomes become visible. Each chromosome consists of two sister chromatids. The nucleolus disappears. Centrioles replicate and move to opposite cell ends, forming the mitotic spindle. The nuclear membrane fragments.
  • Metaphase: Chromosomes align at the spindle’s midplane (metaphase plate).
  • Anaphase: Centromeres split, sister chromatids separate and move to opposite poles.
  • Telophase: Nuclear membranes reform around each chromosome set. Chromosomes decondense. Cytokinesis usually begins.

Cytokinesis

Division of the cytoplasm:

  • Animal Cells: Occurs via constriction of the plasma membrane.
  • Plant Cells: A cell plate (phragmoplast) forms between daughter cells.

Life Cycles

Haplontic Cycle

Organism is haploid for most of its life cycle. Haploid adults produce haploid gametes by mitosis. Fusion of gametes forms a diploid zygote, which undergoes meiosis to produce haploid cells that develop into new haploid adults.

Diplontic Cycle

Organism is diploid for most of its life cycle. Diploid adults produce haploid gametes by meiosis. Fertilization produces a diploid zygote, which develops into a diploid adult through mitosis and cell differentiation.

Diplohaplontic Cycle

Alternation of diploid (sporophyte) and haploid (gametophyte) generations. Sporophyte produces haploid spores by meiosis. Spores develop into gametophytes, which produce gametes. Fusion of gametes forms a diploid zygote, which develops into a sporophyte.

Reproductive Differences: Coniferophytes vs. Angiosperms

  • Shorter pollen tube in coniferophytes.
  • More embryonic sac cells in angiosperms.
  • Open ovuliferous scales (naked ovules) in coniferophytes, enclosed carpel in angiosperms.
  • Simple fertilization in coniferophytes (one gamete involved).
  • Wind pollination (anemogamy) in coniferophytes.
  • Fertilization can take 1-2 years in coniferophytes.
  • No fruit in coniferophytes; seeds are exposed.