Notes, summaries, assignments, exams, and exercises for Biology for Baccalaureate

Prokaryotic Cells: Key Characteristics

• Nucleus: Absent.
• Plasma Membrane: Possesses a lipoprotein envelope similar to that of eukaryotes.
• Mesosomes: Infoldings of the plasma membrane containing numerous enzymes.
• Cell Wall: Present, but distinct from plant cells as it lacks cellulose; composed of nitrogenous substances.
• Capsule: In some cases, the wall is covered by a capsule composed of polysaccharides and proteins.

Cytoplasm and Genetic Material

The cytoplasm contains numerous 70S ribosomes and inclusions of reserve substances. The genetic material consists of a single-stranded, circular DNA molecule, weakly associated with proteins and localized in the nucleoid.

Plasmids and Appendages

Bacterial chromosomes often contain small rings of DNA called plasmids:...

Cell Cycle Checkpoints and Regulation

Several checkpoints coordinate and regulate the transition from one stage of the cell cycle to the next. These include:

The G1 to S Phase Transition

The checkpoint situated at the end of the G1 stage was first described in the yeast Saccharomyces cerevisiae and was designated as START or the restriction point. Once this point is passed, the S phase inevitably occurs, and the cell cycle continues, eventually ending with cell division. Overcoming this point depends on cell size and the presence of extracellular growth factors. Thus, in the presence of these factors, cells pass through and continue their cell cycle into the S phase. If growth factors are absent during the G1 phase, the cell enters a period of...

DNA Replication Process

DNA replicates just before cell division, ensuring daughter cells inherit the same genetic information as the stem cell. Genetic information is transmitted via genes. In general, each DNA strand serves as a template. Specific enzymes, known as DNA polymerases, join nucleotides one by one. A new chain is formed that is complementary to the template and identical to the chain that was previously attached to it. This process results in two double-stranded DNA molecules.

On occasion, errors occur during DNA replication that give rise to mutations. Some mutations can lead to certain types of diseases. The extraordinary importance of base complementarity allows DNA strands to be copied from a stem cell to a daughter cell, and...

Epithelial Tissue

Lining Epithelia

• Simple Epithelia: Flattened cells (endothelium) lining capillaries and blood vessels.
• Polyhedral Cells: Lining the inside of the intestine (villi).

Stratified Epithelia

Formed by several layers of cells. Lining the mouth, esophagus, and vagina.

Glandular Epithelia

• Endocrine Glands: Ductless; empty secretions into the blood.
• Exocrine Glands: Secretion to the exterior (e.g., sweat glands, shedding skin).

Muscle Tissue

Responsible for movements.

Striated Muscle Fiber

Contractile element involves myofibrils (actin and myosin).

• Skeletal Muscle: Voluntary reaction, responsible for skeletal movement.
• Heart Muscle: Involuntary reaction.

Smooth Muscle

Cells are uninucleate and fusiform (found in invertebrates).

Nervous Tissue

Responsible...

The endosymbiotic theory explains the process of moving from a prokaryotic cell, which lacks most organelles, through symbiogenetic additions.

The Three Stages of Endosymbiosis

1. A bacterium that uses sulfur as an energy source merges with a swimming bacterium to form a new entity. The result was the first eukaryotic cell. The nucleoplasm of animal cells, plants, and fungi would be the result of the union of these two bacteria. A baseline characteristic of both cells was added: a new, more complex morphology. DNA remained confined to an inner core separated from the rest of the cell by a membrane.
2. This new organization was still anaerobic, unable to metabolize oxygen, as this gas was poisonous to it. Therefore, they lived in environments where oxygen,

Bacteria are unicellular microorganisms that have a size of some micrometers long (between 0.5 and 5 ìm, usually) and different shapes including spheres, rods and hélices.Hook cell discovered in 1667. Jassen brothers discovered the microscope.
The HICAS .- is an enzyme that opens the DNA chain
Classes of RNA: transfer, messenger, ribosomal
4 nitrogenous bases: cytokine, guanine, thymine, adenine
4 forms of cells: nerve, streptococcus, amoeba, monococo
Mitosis: prophase, metaphase, anaphase, telophase, interphase
Centromere: The zone where the chromosome interacts with the spindle fibers from prophase to anaphase, both in mitosis and in meiosis Reproduction <http://es.Wikipedia.Org/wiki/Mitosis> cells: bipartition gemancion, sporulation...

Core Biological Processes

Gametogenesis: Formation of Gametes

Gametogenesis is the process involving the formation of two types of propagating phase gametes.

Oogenesis (Egg Formation)

The germ cells reach sexual maturity via mitosis, leading to the subsequent rise of oogonia (2n). The growth phase involves some oogonia increasing in size due to the accumulation of cytoplasm, transforming them into primary oocytes (2n).

Each maturing primary oocyte undergoes Meiosis I, resulting in:

• A secondary oocyte (n)
• The first polar corpuscle (n)

The secondary oocyte then undergoes Meiosis II, generating an ovotid (n) and the second polar corpuscle.

Spermatogenesis (Sperm Formation)

When the organism reaches sexual maturity, cells in the testes multiply via mitosis,...

The Miller-Urey Experiment: Origin of Life

The Miller-Urey experiment represents the first demonstration that organic molecules can form spontaneously from simple inorganic substances under simulated early Earth conditions. This groundbreaking experiment provided crucial insights into the chemical origins of life.

In the experiment, a gaseous mixture (simulating Earth's early atmosphere) was introduced into a sealed flask, where water was kept boiling to mimic the primordial ocean. The resulting vapor then underwent condensation. Substances were circulated continuously through the experimental setup, while two electrodes consistently produced electric shocks, simulating lightning.

Crucially, samples were extracted from the apparatus for analysis....

Cellular Respiration and Energy Pathways

Following glycolysis, cellular respiration proceeds through two primary stages:

The Krebs Cycle

Occurring within the mitochondria, a two-carbon compound is degraded into carbon dioxide, releasing energy stored as ATP.

The Respiratory Chain

Also located in the mitochondria, the energy released from glucose is utilized to synthesize ATP molecules, with oxygen ultimately forming water.

Cellular Organelles

Mitochondria

These membranous organelles are found in most eukaryotic cells. Often described as the "powerhouse of the cell," they produce the majority of the cell's supply of adenosine triphosphate (ATP), which serves as the primary source of chemical energy.

Chloroplasts

These are the cellular organelles in eukaryotic...

Objections to Darwin's Evolutionary Theory

Following Darwin's evolutionary theories, two major objections were filed. On one hand, there was a lack of proof of why variations occurred in these organisms, to which he had no response. On the other hand, there was a lack of intermediate fossil records between groups of organisms, often called missing links.

The Rise of Neo-Darwinism

At the beginning of the 20th century, with the rediscovery of Mendel's laws and the discovery of the phenomenon of genetic mutation, Darwinism regained strength. The increased fossil record and the introduction of statistics enabled the formulation in the 1940s and 1950s of the synthetic theory of evolution or Neo-Darwinism.

Sources of Genetic Variation

There are two sources...