Cell Structure and Function: Microscopy, Organelles, and Cellular Processes

Posted on Jan 8, 2025 in Biology

Optical Microscope

The optical microscope has a resolving power of roughly 1000x. Resolving power is the minimum distance between two points that may be seen as different. The human eye has a resolving power of 0.2 mm.

Cell Theory

It was not until the mid-nineteenth century that the cell theory was developed. The cell theory states that:

  1. All living beings are composed of cells.
  2. The cell is the anatomical or structural unit of all living beings.
  3. The cell is the physiological unit of all living beings.
  4. Every cell comes from another cell.

Electron Microscopy

Electron microscopy uses a beam of electrons instead of light. It has a resolving power of 5nm, which is an increase of 106x compared to the optical microscope.

Levels of Organization of Living Matter

There are three levels of organization of living matter, with the following properties:

  1. Any level is formed by the lower levels.
  2. A level is more complex and has more energy than the lower levels.
  3. In any level, new properties called emergent properties may appear that do not appear at lower levels.

Cell Structure

  • Mitochondria: Energy production.
  • Endoplasmic reticulum: Rough membranes; transporting substances.
  • Ribosomes: Making substances.
  • Golgi apparatus: Secretion of substances.
  • Lysosomes: These are small vesicles that have the function of cellular digestion, transforming large molecules into smaller ones during digestion.
  • Vacuoles: These are cavities where reserve substances are stored. In plant cells, they are larger and more numerous than in animal cells.

Organelles Not Common to All Cells

  1. Animal Cell: Centrosome, directing cell movement.
  2. Plant Cell: Cell wall and chloroplasts.

Interphase Nucleus

The interphase nucleus is the part of the cell cycle that exists between two consecutive divisions. It has a double membrane that controls the passage of substances from the cytoplasm to the nucleus and vice versa.

  • Cell membrane: This membrane has some holes called nuclear pores.
  • Chromatin: A set of filaments that are easily stained red. This includes DNA and proteins.
  • Nucleolus: These are spherical organelles, and their function is directing the production of ribosomes.

Nucleus in Division

During cell division, the nucleolus disappears. The chromatin condenses, giving rise to chromosomes.

  • Chromosome: They comprise two arms, which may or may not be equal. The site where the arms join is called the centromere.
  • Composition: DNA + protein.
  • Feature: Contains the genetic material.

Reproductive Functions

These are the functions by which living things give rise to other organisms similar to themselves.

  • Asexual reproduction: Offspring are identical.
  • Sexual reproduction: Offspring are different.

Functions of Cellular Nutrition

These functions are related to the exchange of matter and energy.

  1. Autotrophic Nutrition: Autotrophic organisms are those capable of producing organic matter from inorganic matter. For example, using light to convert inorganic matter into organic matter.

  2. Heterotrophic Nutrition: Heterotrophic organisms are unable to produce organic matter from inorganic matter, so they must obtain it from other living beings. Examples include animals, fungi, and some bacteria. Heterotrophic organisms must digest organic matter to transform it into simpler nutrients.

  3. Production of Energy: All living things need to produce energy to make new molecules, for movement, and for other processes that require energy expenditure.

    • Respiration: A set of processes by which energy is obtained from organic nutrients.

      • Aerobic respiration: Requires oxygen, involves complete oxidation of organic compounds, and takes place in the mitochondria.

      • Fermentation: Involves incomplete oxidation of organic matter that occurs in the cytoplasm. Being incomplete, it produces less energy than aerobic respiration, and the end products are organic compounds such as lactic acid.

Prokaryotic Cells

Prokaryotic cells are those that do not have a nuclear membrane and therefore do not have a true nucleus. The only prokaryotic cells are bacteria. Characteristics:

  • They have a cell wall that is made of cellulose.
  • They are small but have ribosomes.
  • They do not have mitochondria, and respiration takes place in membrane structures called mesosomes.