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

Mitosis and Meiosis Comparison

Similarities Between Mitosis and Meiosis

• The sequence of changes in the nucleus and cytoplasm.
• The presence of the stages of prophase, metaphase, anaphase, and telophase.
• The spindle formation and the cycle of condensation of chromosomes.

Key Differences Between Mitosis and Meiosis

• Mitosis occurs in somatic cells, while meiosis is restricted to germ cells.
• In mitosis, each cycle of DNA replication is followed by one division. The resulting daughter cells are diploid (2n) and have the same amount of DNA as the parent cell.
• In meiosis, one DNA replication cycle is followed by two divisions, resulting in four haploid (n) daughter cells, which contain half the DNA of the parent cell.
• In mitosis, each chromosome behaves independently.

Evidence of Evolution

Paleontology

Fossils have been found with features intermediate between species and even different taxonomic groups.

Comparative Biochemistry

Comparative analysis of molecules that make up living things supports the evolutionary process:

• Essential chemical components of all organisms are the same.
• Metabolic processes are identical.
• The closer the relationship between two species, the more similar their protein chains and DNA composition.

Comparative Anatomy

This branch of biology examines the anatomy of animals and compares the organs of different species.

Domestication

The current features of wheat, cows, dogs, or pigs are the result of selection over centuries by humans.

Geographical Distribution

Analyzing the distribution of existing...

Mendel's Laws of Inheritance

Mendel's Laws are a set of ground rules for the inheritance of characteristics from parent organisms to their offspring. These basic rules of inheritance are the foundation of genetics. The laws are derived from the work of Gregor Mendel, published in 1865 and 1866, though they were largely ignored until their rediscovery in 1900.

The Model Organism: Pisum sativum

Mendel published his experiments with peas in 1865 and 1866. The main advantages of choosing Pisum sativum as a model organism include:

• Low cost
• Short generation time
• High rate of descent
• Diverse varieties within the same species (color, shape, size, etc.)
• Constant differentiating characters

Mendel's 1st Law: Law of Uniformity

This law states that if two pure breeds...

2. Genetic Engineering: Genetic engineering is defined as the set of technologies to manipulate the genetic material of a living being, i.e., modifying genes. This manipulation consists basically of: introducing new genes into a genome, removing existing genes from a genome, and modifying the information in a particular gene. The new genetic combinations are introduced into organisms capable of transmission to subsequent generations. It is also called recombinant DNA technology because most techniques rely on DNA fragments that recombine.

2.1. Genetic Engineering Tools To obtain new combinations of heritable material, you must use:

• 1. Restriction Enzymes: They are a type of protein that can recognize a specific DNA fragment and cut it. Using

Nutrient Transport

Ascent of Sap

Gross: The movement of water and minerals from the roots to the leaves via the stem's xylem. Water flows upward due to two factors:

• Transpiration Pull: Water loss during photosynthesis and transpiration creates negative pressure.
• Root Pressure: The lower osmotic concentration in the soil compared to the root interior drives water flow.

Gas Exchange

Plants have a lower respiratory rate than animals and require less oxygen. Gas exchange occurs through stomata, facilitated by the enzyme carbonic anhydrase:

H₂O + CO₂ ↔ H₂CO₃ ↔ H⁺ + HCO₃^-

Increased H⁺ concentration lowers pH, activating an enzyme that breaks down starch into glucose.

Photosynthesis

Photosynthesis occurs in chloroplasts, where chlorophyll and carotenoids...

Understanding Cellular Genetic Information

The Genetic Code and Protein Synthesis

The information contained in messenger RNA (mRNA) must be read and translated in the ribosomes. This information is interpreted using the genetic code, which is determined by the sequence of nitrogenous bases. A sequence of three nucleotide bases, known as a codon, carries specific information for a particular amino acid.

DNA Packaging: Chromatin and Chromosomes

Chromatin is the functional form of DNA within the nucleus. In this uncondensed state, DNA's information can be read to produce messenger RNA copies, which are then transported to the cell's cytoplasm for ribosomes to translate into corresponding proteins. DNA in chromatin is found associated with proteins...

Biological Life Cycles

A biological cycle traces an organism's life path, starting from its originating reproductive structures, through maturity, until it forms new reproductive structures similar to the first.

Nuclear Phases in Sexual Reproduction

In sexual reproduction, every organism possesses a life cycle that alternates between two stages. These stages are characterized by the level of ploidy (the chromosome number of the gametes) of the component cells and are known as nuclear phases:

• Haploid Phase (Haplophase): Corresponds to the number of chromosomes found in gametic cells (n).
• Diploid Phase (Diplophase): Corresponds to the number of chromosomes found in the zygote (2n).

The events defining a cycle are determined by the nuclear processes...

Diplotene

The synaptonemal complexes are disassembled, allowing homologous chromosomes to separate. This separation is not total, as they remain attached at points where crossover has occurred. These areas appear as X-shaped structures called chiasmata, which play an important role in the correct alignment of homologous pairs during metaphase I.

Diakinesis

Chromosomes reach their maximum degree of condensation. In each bivalent, the four chromatids (tetrads) are clearly observed, with each pair of sister chromatids joined at their centromeres, while non-sister (homologous) chromatids are held together at the crossover chiasmata.

Metaphase I

Homologous chromosome pairs (bivalents) are directed to the equatorial plane of the spindle, forming a metaphase...

Cell Membrane Differentiations: Junctions

Some areas of the cell membrane may have specific adaptations, such as invaginations (e.g., microvilli) to increase surface area, or structures that form unions between cells. These junctions are essential for stabilizing tissues and providing mechanical adhesion. They are particularly prevalent in tissues under heavy strain, like epithelial tissues or heart muscle, where their primary function is to provide mechanical strength to the union. These junctions are classified into:

Adherens Junctions (Bands of Adhesion)

• These junctions are formed by transmembrane proteins that bind cells together.
• On the intracellular side, these proteins are associated with actin filaments, which are part of the cytoskeleton.

Nucleic Acids: Fundamental Molecules of Life

Nucleic acids contain the instructions necessary for life processes and are responsible for all basic functions of living beings. They are heritable, possess the characteristic of self-duplication, are stable, contain the hereditary material of living things, allow for changes (mutation and recombination), and produce various molecules.

Nucleotide Structure

Nucleotides are the fundamental units that form nucleic acids. They are composed of a pentose sugar, a nitrogenous base, and one or more phosphate groups. Both the nitrogenous base and the phosphate groups are attached to the pentose, which is always an aldopentose.

Nitrogenous Bases

Nitrogenous bases can be of two types: purines, derived from the...