Cellular Processes: Nutrition, Mitosis, and Meiosis Fundamentals

Nutritional Requirements and Metabolism

Nutrition Defined

Nutrition: Food intake in relation to the dietary needs of the organism.

Autotrophic Nutrition

Autotrophic: The body's ability to synthesize essential substances for metabolism from inorganic substances. Autotrophs have no need for nourishment from other living beings.

Heterotrophic Processes and Transport

Heterotrophic: Done through movements of molecules and ions via the diffusion process. The cell controls its internal chemical composition to regulate the traffic of substances across the membrane. This occurs through two mechanisms:

• Active Transport: Moves against concentration gradients.
• Passive Transport: Moves toward concentration gradients.

Cell Reproduction and Division Cycles

Cell Reproduction Overview

A cell can give rise to daughter cells. Key phases include:

• Interphase: Growth and synthesis.
• Cytokinesis: Division of the cytoplasm.
• Mitosis: Nuclear division (Prophase, Metaphase, Anaphase, Telophase).

Mitosis: Nuclear Division Phases

Mitosis is the process of cell division.

Prophase

• Chromatin condenses.
• Chromosomes become visible.
• Nucleus and cell membrane disappear.

Metaphase

• Chromosomes are longitudinally divided into chromatids.

Anaphase

• Chromatids definitively divide.
• Half the chromosomes migrate to each cell pole.

Telophase

• Nuclear membrane appears around each chromosome.
• Spindle disappears.
• Nucleoli appear.
• Chromosomes elongate.
• Cytoplasmic division begins.

Cytokinesis: Cytoplasm Division

Cytokinesis is the division of the cytoplasm.

• Fission (Escisión): Simple division.
• Sporulation (Esporulación): Division via spores.
• Budding (Gemación): Division via buds (yemas).

Gametogenesis and Meiotic Division

Spermatogenesis and Ova Production

Spermatogenesis Stages: Gonias, Citosyte I, Citosyte II, Spermatids, Spermatozoids.

Duration: 24–48 hours. Production: 200–300 million sperm.

Ova (Ovulation): Approximately 400–500 ova released up to age 35.

Meiosis I Phases

Prophase I

Key event: Crossing-over.

Metaphase I

• Cell membrane disappears.
• Spindle and chromosomes form on the equatorial plane.

Anaphase I

• Homologous chromosomes separate and migrate to respective poles.
• Chromatids remain attached.

Telophase I

• Nuclear membrane reconstructs.
• Nucleoli reappear.
• Each chromosome has two chromatids.

Meiosis II Phases

Prophase II

• Chromosomes maintain condensation; they do not replicate.
• Achromatic spindle forms.

Metaphase II

• Chromosomes attach to spindle fibers and migrate to the equatorial plane.
• Sister chromatids separate from each chromosome.

Anaphase II

• Chromosomes (now consisting of a single chromatid) migrate to opposite poles.

Telophase II

• Nuclei reconstruct.
• Cytoplasm divides (Cytokinesis follows).
• Nuclear membrane is restored.