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

Living Organisms: An Introduction

What Defines a Living Being?

A living being, formed by one or more cells, carries out vital operations, including:

• Nutrition: The set of processes by which living things obtain or exchange matter and energy with the environment.
• Relationships: The ability of living beings to perceive changes in the environment and respond to them in the most suitable way for their survival.
• Reproduction: The ability to produce offspring that develop and maintain the characteristics of their parents over time.

Types of Organisms

Unicellular Beings

These organisms consist of a single cell that performs all vital functions. Their shape is highly variable and adapted to their lifestyle.

Colonies

Colonies are groupings of single-celled organisms... Continue reading "Understanding Living Organisms: Cells, Tissues, and Organs" »

Cellular Passive Transport Mechanisms

Osmosis: Water Movement Across Membranes

Osmosis refers to the passage of water through a semi-permeable membrane from a region of higher water concentration (purer) to one of lower water concentration (less pure).

Osmosis Effects in Animal Cells

• In an isotonic solution, there is a dynamic equilibrium; water enters and leaves the cell at the same rate.
• In a hypotonic solution, the cell absorbs water and swells, potentially bursting (a process called cytolysis).
• In a hypertonic solution, the cell loses water, shrivels, and becomes dehydrated (a process called crenation), which can lead to cell death.

Osmosis Effects in Plant Cells

• In an isotonic solution, there is a dynamic equilibrium.
• In a hypotonic solution, the

Bacteriophage Replication

The duplication of a bacteriophage is known as the lytic cycle and can be grouped into different stages:

1. Attachment
2. Entry
3. Replication
4. Assembly
5. Lysis and Release

The time required for viral multiplication is 30 to 35 minutes.

Retroviruses

Retroviruses are a type of virus present only in eukaryotic cells. Retroviruses have RNA as genetic material and within their capsid, they also bear a molecule of the reverse transcriptase enzyme that is able to catalyze the transformation of their messenger RNA molecules into DNA. In a later stage, the viral genome, DNA copied and called provirus, is integrated into the cell's DNA and can be transmitted to the descendants of the same when it divides. The next stage, which can occur after a... Continue reading "Bacteriophage and Eukaryotic Virus Replication: Stages and Structures" »

Biotic Factors in Ecosystems

Biotic factors are relationships that occur among living beings. They are classified as:

• Intraspecific: Between individuals of the same species.
• Interspecific: Between individuals of different species.

Intraspecific Relationships

Their purpose is the protection of the young, finding food, and defense.

• Family

  Made up of both parents and offspring, often to feed and protect the young.

• Gregarious

  Associations of organisms moving together, such as flocks of birds.

• Colonial

  Organisms that live intimately united, such as corals or sponges.

• Social

  Where a hierarchy and distribution of tasks are established, such as in colonies of bees and wasps.

Interspecific Relationships

• Competition

  Occurs when two organisms compete for the same resource,

Class 1 Malocclusion: Issues and Variations

Crossbite Complications

Crossbite (failure of dental arches to occlude correctly in the lateral dimension) can manifest in several ways within Class 1 malocclusion (normocclusion, often with a good relationship between the osseous bases):

• Unilateral Crossbite: Affects one side, from the canine to the last molar.
• Bilateral Crossbite: Affects both sides, from canine to molar. Often associated with maxillary micrognathia (narrow upper jaw) relative to the mandible. May be linked to habits like mouth breathing and finger sucking.
• Dental Crossbite: Normocclusion with a good skeletal base relationship, but involves incorrect inclination of a specific molar or canine due to lack of space, resulting in palatal

Organelles

An organelle is a small, specialized structure within a cell that performs a specific function. Examples include mitochondria and lysosomes.

Functions of the Cell or Plasma Membrane

1. This structure surrounds the cell, separating it from the external environment.
2. It forms a barrier that allows the cell to incorporate water and nutrients and remove metabolic waste.

Ribosomes

Ribosomes are organelles formed by the combination of different proteins and RNA (ribonucleic acid).

The Golgi apparatus is an organelle that receives immature proteins from the rough endoplasmic reticulum (RER) and releases vesicles containing mature proteins.

• RE: Endoplasmic reticulum
• PER: Ribosomes that have completed the synthesis of a protein

Location and Structure of

Chromosome Structure: A Detailed Explanation

A chromosome consists of two parallel, elongated, rod-shaped subunits called chromatids. The chromatids are not equally thick throughout their length because they contain chromomeres, which are condensed fragments of chromatin.

Chromomere size varies, but the thickness of the chromatid is roughly constant, between 0.25 and 2 micrometers.

Primary Constriction (Centromere)

A structure called the primary constriction, or centromere, divides the chromatid into two arms, which may be of equal or different lengths. This distinction allows for chromosome classification:

• Metacentric chromosome: Central centromere and arms of equal length.
• Submetacentric chromosome: Centromere shifted upward, resulting in upper

Defining Health and Disease

Health is typically defined as the state where the body's organs and systems are functioning correctly. When an alteration occurs in one or more of these systems, disrupting their function, a disorder known as disease arises. A disease manifests through a series of bodily changes or abnormalities called symptoms.

Classifying Disease Types

Diseases can be categorized based on their causes:

• Infectious Diseases: Caused by microorganisms such as viruses, some bacteria, fungi, and protozoa.
• Environmental Diseases: Resulting from components of the physical environment, such as extreme heat or cold, air pollution, radiation, etc.
• Toxic Diseases: Originating from breathing or ingesting certain toxic substances, like carbon monoxide

Fundamental Ecological Concepts

Key Ecological Definitions

• Biosphere: The set of all creatures that inhabit the Earth.
• Microorganisms: Bacteria or protozoa.
• Ecosystem: All living beings that inhabit a particular place, interacting with their environment.
• The Ecosphere: The set of all ecosystems on our planet.
• Ecosystems: Composed of biocoenosis and biotope.
• Biocoenosis: The living community within an ecosystem.
• Biotope: The inorganic part of an ecosystem.
• Habitat: The physical location within an ecosystem where individuals of a particular species live.
• Ecological Niche: The role of a species in the ecosystem. It is defined by behavior, the type of food consumed, where food is sought, etc.

Abiotic Factors in Ecosystems

These are the non-living components... Continue reading "Ecosystems: Concepts, Function, and Types" »