Notes, summaries, assignments, exams, and problems for Biology

Tissues: Types, Structure and Function

Tissue: a group of cells that assemble and function together. Between cells is the intercellular substance (extracellular matrix). Cells can be closely packed together or separated by this intercellular material.

Epithelial Tissue

Epithelial (covering) tissues form protective layers such as skin (the outer layer). They also form mucous membranes that line internal cavities and surfaces, and they include secretory tissues (glands). Epithelial tissues are made of crowded cells with little intercellular substance and may be arranged in one or several layers.

Nervous Tissue

Nervous tissue consists of neurons and supporting cells. It transmits nerve impulses and is responsible for coordination, sensation, and the... Continue reading "Tissues, Cells, Organs & Biomolecules: Structure and Function" »

Understanding Ecosystems and Their Dynamics

What is an Ecosystem?

An ecosystem is a natural system consisting of all living beings inhabiting a place (the biocenosis) and the physical and chemical characteristics of that site (the biotope). A multitude of relationships are established between the biotope and biocenosis.

Trophic Relationships

Trophic relationships are those established in an ecosystem through feeding, illustrating how energy and nutrients flow.

Key Components of an Ecosystem

Producers

Producers are autotrophic living beings. They produce their own food from inorganic material and an energy source (like sunlight), forming the fundamental base of all ecosystems.

Consumers

Consumers are heterotrophic organisms that obtain energy by feeding... Continue reading "Ecosystems Explained: Components, Interactions, and Cycles" »

Airway

Includes a conduction pipeline connecting it with the exterior lungs, which are:

• The nasal cavities: Two open cavities covered by nasal mucous. They communicate with the exterior through the nostrils and with the pharynx through the choanae (posterior openings).
• The pharynx: It is a common respiratory tract through the digestive tube and the epiglottis. The epiglottis is located above the larynx and prevents food from entering during swallowing, thus avoiding choking.
• Larynx: Communicates with the trachea and contains some folds (vocal cords) that vibrate and emit sounds.
• The bronchial tree: It consists of two bronchi that penetrate the lungs and branch into increasingly smaller bronchioles. The cells of the walls secrete mucus and have cilia,

Fixism (Cuvier) or fijista theory is a belief that holds that existing species have remained essentially unchanged since they were created, therefore, immutable. The fossil remains of animals would be killed in the biblical flood or by the vagaries of nature (as theories such as vis plastica).
Now become (Lamarck 1809): Progression from simple organisms to complex plants and animals, ultimately reaching humans. "Existence impulse towards perfection" - Cap. of the organisms for adaptability to environmental changes - Principle of use and disuse of organs - Inheritance of acquired characteristics.
Compression Fossils and Printing: This occurs when an organism is caught or parts of it are covered by sediments without decomposing, resulting in... Continue reading "Understanding Fixism and Evolutionary Concepts" »

Tracheophytes: The Vascular Plants

Key Features of Tracheophytes

• Also known as vascular plants due to their specialized conducting vessels (xylem and phloem).
• Possess true roots, stems, and leaves.
• Exhibit autotrophic nutrition, producing their own food through photosynthesis.
• Develop three primary tissue systems: vascular, ground, and dermal tissues.
• Many species reproduce via seeds, though some reproduce by spores.

Classification of Tracheophytes

• Lycopsida
• Sphenopsida
• Psilopsida

Ferns: Non-Seed Vascular Plants

Characteristics of Ferns

• Comprise approximately 10,000 known species.
• Typically herbaceous and rhizomatous (possessing underground stems).
• Often thrive in warm, humid environments, particularly in tropical forests.
• Possess true roots, stems, and leaves

Chromatin

Chromatin consists of strands of DNA at different degrees of condensation associated with proteins and scattered throughout the nucleoplasm. When the cell is going to divide, the chromatin filaments are organized and condensed to form thicker structures called chromosomes.

Genes

A gene is a unit of hereditary material. It is a fragment of nucleic acid that carries genetic information for a character, a protein, or a polypeptide chain. It corresponds to what Mendel called a hereditary factor.

Centriole

In animal cells, centrosomes present two small cylinders and consist of protein tubules.

Mitotic Spindle

The mitotic spindle forms when the nuclear membrane and nucleolus disappear.

Karyotype

A karyotype is a set of chromosomes from one species.... Continue reading "Cell Biology: Chromatin, Genes, Karyotype, and Cell Types" »

VIRUS H5N1

1a) Genetic Changes and Protein Expression

Changes are mutations of genetic material. Proteins are bound to gene expression. Genetic mutations must occur, or changes in proteins result from the translation process.

b) Immunity to H5N1

No person has been documented as having been infected with H5N1 antigens and subsequently acquired immunological memory that protects them.

2. Vaccine Efficacy and Viral Mutation

A vaccine produces a primary immune response (antigen-antibody) and a vaccinated person acquires immunological memory to respond effectively to the infection. Therefore, injecting a non-replicating virus (which possesses the same antigen) is difficult. In the case of the H5N1 virus, if it mutates easily, the vaccine might no longer... Continue reading "Understanding Viral Mutations and Immune Responses" »

Changes achieved through the development, acquisition, or loss of organs are maintained and transmitted to offspring, which preserves and increases these traits through successive generations. This concept is known as the inheritance of acquired characteristics. However, analysis of these proposals has not demonstrated any inherent tendency or impulse towards complexity in living things. In light of developments in genetics, the inheritance of acquired characteristics is not supported.

Natural Selection: Darwin and Wallace

Darwinian theory posits that in a changing world, organisms also change over time. Some features disappear, and new ones emerge. This process of change is gradual and continuous. Organisms with similarities are related and... Continue reading "Evolutionary Theories: Darwinism, Neo-Darwinism, and Hominid Origins" »

DNA and Chromosomes

DNA is the biomolecule that contains genetic information to make proteins in the cell.

The chromosomes are composed of chromatin (DNA + protein).

Before cell division the DNA is duplicated. Each chromosome is formed by two chromatids joined together.

Karyotype and Genome

Karyotype: chromosome set ordered by pairs. Humans have 23 pairs.

Genome: the complete set of genes.

Genes and Genetic Information

A gene is a segment of DNA containing information to produce a given necessary protein. Genes together make up the genome.

Cell Cycle and Division

Cellular division is the process by which a cell is divided into two daughter cells.

Interphase

Interphase is the stage of growth: the cell increases in size, the cytoplasm grows, and routine... Continue reading "DNA, Chromosomes, Mitosis & Meiosis — Genetics Fundamentals" »