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

Type I Hypersensitivity Reactions: Immediate Allergic Responses

These are the most common type of allergic reactions. They are mediated by Immunoglobulin E (IgE) antibodies, which are primarily located on mast cells found in various tissues throughout the body. The reaction between an antibody (Ab) and an antigen (Ag), also known as an allergen in this context, triggers a cascade of responses that can sometimes lead to tissue damage.

Phases of Type I Hypersensitivity

Type I hypersensitivity reactions occur in two distinct phases:

• Immediate Phase: Mediated primarily by histamine, leading to rapid symptoms.
• Late-Phase Reaction: Mediated by other compounds such as Leukotriene C₄ (LTC₄) and Prostaglandin D₂ (PGD₂), which have similar inflammatory effects

Animal Tissues

Epithelial Tissue

Epithelial tissue consists of sheets of densely packed and connected cells that cover internal and external body surfaces.

Simple Epithelia

Simple epithelia are formed by a single layer of cells that can be:

• Flattened, like the endothelial walls of capillaries and the lining of blood vessels, which protect yet allow the exchange of substances.
• Polyhedral (cubic and cylindrical), such as the epithelial lining inside the intestine. Their cells possess microvilli or fingerings on the surface that faces the lumen of the tube.

Stratified Epithelia

Stratified epithelia consist of several layers of cells. Cells in the deepest layer are constantly dividing, and new cells push the older ones upward. The most superficial cells,... Continue reading "Animal Tissues: Epithelial, Muscle, and Nervous Tissues Explained" »

Biotope: The Foundation of Ecosystems

The biotope refers to the main components that determine the presence of living organisms: the medium and environmental (physical and chemical) factors.

The Medium

The medium is the place where living organisms reside and interact within an ecosystem, maintaining constant exchanges of matter and energy. Broadly speaking, we can distinguish two primary types of media:

• Terrestrial Medium: Located on the surface of continents, characterized by direct contact with the atmosphere.
• Aquatic Medium: Consists of water and is characteristic of aquatic ecosystems.

Abiotic Environmental Factors

Abiotic environmental factors encompass all physical and chemical conditions of the biotope. This set of external conditions significantly... Continue reading "Ecosystem Components: Biotope & Biocoenosis Explained" »

Vision Development in Infants

The visual system is designed to capture light effects. The apparatus of global vision allows us to perceive images based on the amount of light reflected. Light enters through the cornea, passes through the pupil to the lens, and is then sent to the retina.

Developmental Milestones

• Newborn: Distinguishes between light and dark (chiaroscuro).
• 1 Month: Can stare at a large object.
• 2 Months: Can accommodate and converge their vision.
• 3 Months: Can follow a moving object by turning their head.
• 4 Months: Has a vertical and horizontal visual field of 180 degrees.
• 6 Months: Acquires eye-hand coordination.
• 8 Months: Examines objects with more detail.
• 12 Months: Acquires adult-like visual acuity.

Vision Disorders

Refractive Errors

• Myopia

1.2. Carbohydrates and Lipids: Concept, Classification, and Functions

Carbohydrates

Carbohydrates are biomolecules formed fundamentally by C, H, and O in the proportion C_nH_2nO_n. Hence, H and O are in the same proportion as in water (H₂O), also called hydrates of carbon. Carbohydrate molecules are chains formed by carbon atoms attached to radical groups and hydroxyl (OH) groups. There may be an alcoholic or a carbonyl group; this group may be an aldehyde (gluc aldose) or a ketone (gluc ketonic). For this reason, they are defined as polyhydroxyaldehydes or polyhydroxyketones.

Classification:

Carbohydrates are classified in two forms:

1. According to the functional group they possess:
   • Ketoses: if they have ketone groups.
   • Aldoses: if they have aldehyde groups.

Mitosis and Cytokinesis

Mitosis

Mitosis (discovered by botanist Eduard Strasburger) is a process of nuclear division exclusive to eukaryotes, ensuring the segregation and equal distribution of sister chromatids between the daughter cells during cell division.

Mitosis is an equational division that ensures the conservation of the genetic and chromosomal makeup of the species. Thus, mitosis of a parent cell yields two daughter cells with the same number of chromosomes and genetic information as the parent cell.

Mitosis can be structured into five phases: prophase, prometaphase, metaphase, anaphase, and telophase.

Prophase

During prophase, the following key changes occur:

• Chromatin Condensation: Chromatin condenses into visible chromosomes, each composed

Plant Parts & Functions

• Roots: Anchorage & Absorption

  Roots provide anchorage for the plant and are responsible for the absorption of water and nutrients from the soil.

• Stems: Support & Transport

  Stems hold the leaves, flowers, and fruits, providing structural support. They also transport fluids (water, nutrients, and sugars) throughout the plant.

• Leaves: Gas Exchange & Vital Processes

  Leaves are the primary sites for gas exchange, which is essential for processes like photosynthesis, transpiration, and respiration.

• Flowers: Reproduction

  Flowers are modified leaves specialized for reproduction. They contain the reproductive organs of the plant.

• Fruits: Seed Protection & Dispersal

  Fruits protect the seeds and facilitate their dissemination

Nutrient Transport and the Circulatory System

Once nutrients have been absorbed, the circulatory system is responsible for transporting them to the rest of the body's cells. In animals, the circulatory system varies from poorly developed to highly complex. In more developed animals, the system is composed of transport liquids, vessels, and a heart.

Transport Liquids (Connective Tissue)

The transport liquid is a connective tissue that circulates through the circulatory system. It is formed by water, minerals, proteins, cells, and various pigments, primarily responsible for transporting gases and nutrients. Types include:

• Hydrolymph (Echinoderms)

  Its composition is very similar to that of seawater. It transports nutrients and waste substances.

• Hemolymph

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

Levels of Organization: These correspond to degrees of complexity in organized matter. The levels are: subatomic, atomic, molecular, cellular, tissue, system, organelle, and body.

Cell Structure: Eukaryotic cells possess several key elements:

• Plasma Membrane: A thin layer surrounding the cell, composed of proteins and lipids.
• Cytoplasm: An aqueous solution containing organelles.
• Nucleus: A spherical structure containing genetic material, formed by the nuclear membrane, nucleoplasm, chromatin, and the nucleolus.

The major organelles of eukaryotic cells include: mitochondria, endoplasmic reticulum, ribosomes, Golgi complex, vacuoles, lysosomes, and the centrosome.

Tissues: A tissue is a collection of similar cells with a very similar structure that... Continue reading "Biological Organization and Nutrition Fundamentals" »