Notes, abstracts, papers, exams and problems of Biology

Chemistry of Life

The universe is mainly composed of Hydrogen (H) and Helium (He). The Earth's crust is composed of Silicon (Si), Iron (Fe), Magnesium (Mg), and carbon (C). Living organisms form organic macromolecules. Oxygen and Hydrogen constitute 68-70% of living matter (Water = H₂O). Nitrogen (N) is part of proteins.

Properties of Living Beings

Living beings are complex materials that can interact with the world around them and reproduce.

Features

• Made mostly of Carbon and H₂O
• Their reactions inside cells are governed by the laws of physics and chemistry.
• They reproduce

Interaction with the Environment

Living beings evolve and react to external or internal stimuli, creating responses through the nervous and endocrine systems (hormones).

Nutrition

Living... Continue reading "Chemical Composition and Functions of Living Beings" »

Sun Energy and Life

The ecosphere is a hypothetical spherical zone located around any star, such as the Sun, where temperatures and appropriate conditions exist to allow living things to originate and evolve.

What is an Ecosystem?

An ecosystem is a particular area where environmental conditions allow some organisms to develop concretely.

• Biotope: The physical environment in which an ecosystem is stable.
• Biocenosis: All living beings inhabiting a biotope.

Factors of an Ecosystem

They fall into two types:

• Abiotic factors: All environmental factors in an ecosystem.
• Biotic factors: Establishing relationships between living things in an ecosystem.

What Effect do Abiotic Factors Have on Living Beings?

They can be:

• Climatic factors (temperature, rainfall, and

Asexual Reproduction in Animals

This is a reproductive process in which new individuals arise from the somatic cells of a single parent. It is common in less evolved animals.

Budding

This consists of the formation of a multicellular outgrowth (bud) on the parent animal's body. Later, these buds may separate to form an independent adult, or they may remain attached, giving rise to colonies, as seen in corals.

Fragmentation (Excision)

The parent body divides into two or more parts, each capable of regenerating into a new animal. Fragmentation can be:

• Longitudinal: Division occurs parallel to the main body axis.
• Transverse: Division occurs perpendicular to the main body axis.

Strobilation

This is a form of multiple transverse fragmentation found in some... Continue reading "Animal Reproduction: Asexual and Sexual Methods" »

Understanding the Nervous System

The nervous system is responsible for processing received information and generating appropriate responses. It connects with sensory receptors that receive stimuli and effector organs that execute the response.

Sensory Receptors

Receptors are specialized cells that capture stimuli and translate them into nerve impulses. Neurons are somewhat modified or non-nerve cells that connect chemically or electrically with other neurons.

Types of Receptors:

• Exteroceptors: Detect external stimuli.
• Interoceptors: Detect internal stimuli.
• Proprioceptors: Detect body position and movement.

Types of Neurons

Neurons can be classified in several ways:

By Number of Extensions:

• Monopolar: One extension.
• Bipolar: Two extensions.
• Multipolar:

Tissues represent an organizational level above the cellular level. They are a set of similar cells that specialize in a particular function and are classified into four basic groups: epithelial, connective, muscular, and nervous.

1. Epithelial Tissue

Formed by epithelia, epithelial tissue has two main types based on its features:

• Epithelial tissue lining: Lines the body's surface and internal body cavities. This is further divided into two types:
  • Simple: Just one layer of cells.
  • Stratified: Many layers of cells.
• Glandular epithelial tissue: Builds secreting cells that are exchanged or clustered epithelial cells to form glands.

Examples of Epithelial Tissue:

• Simple squamous epithelium: Flattened cells, wider than they are high. Lines the heart and

Digestive System

Function

The digestive system is responsible for processing food, absorbing molecules, and eliminating waste.

Types of Digestion

There are two main types of digestion: mechanical and chemical.

System Interactions

The digestive system interacts with the nervous, endocrine, and circulatory systems.

Functional Structure

1. Mouth: Digestion begins in the mouth.
2. Esophagus: Food travels down the esophagus.
3. Stomach: Gastric digestion occurs in the stomach.
4. Small Intestine: Intestinal digestion and absorption take place.
5. Large Intestine: Final absorption and waste processing.

Excretory System Structure

The excretory system plays a crucial role in waste removal.

• Cecum: Follows the ileocecal valve.
• Colon: Divided into ascending, transverse, and descending

Virus Characteristics

Viruses are unique pathogens, not classified as living organisms. A virus particle, a submicroscopic infectious agent, has a single nucleic acid type (DNA or RNA) within a protein coat called the viral capsid, forming the nucleocapsid.

Some viruses have a lipid-protein envelope. The capsid's protein organization determines the virus's shape, usually helical or polyhedral. Viruses are genetic elements in transit, switching between extracellular and intracellular states.

Extracellular Phase (Virion)

In the extracellular phase, the virion is metabolically inert. It carries viral genetic material from one cell to another.

Intracellular Phase

Inside a cell, the virus replicates, using the cell's machinery to synthesize new viral... Continue reading "Virus Structure, Classification, and Replication Cycles" »

1. Bacterial Antibodies

Which individual component of a bacterium should be injected into rabbits to generate effective antibodies against subsequent exposure to the same bacteria?
c. Bacterial chromosome DNA fragments

2. Lymphocytes

The lymphocyte, a type of leukocyte, is characterized by:
II. Providing long-term or short-term immunity to the body

3. Acquired Immunity

Acquired immunity, whether natural or artificial, is achieved by:
I. Suffering from an illness
II. Vaccination with an attenuated microbe
III. Administration of antibodies produced by another source

4. Natural Immunity

The term "natural immunity" refers to:
I. Immunity that develops during an individual's life as a result of the body's response to a pathogen
II. Immunity that is activated

**Functions of the Cell**

• Nutrition: Through nutrition, cells obtain the energy they need to create and maintain their structures and perform other vital functions. The molecules from which they obtain materials and energy are nutrients such as water, minerals, oxygen, and organic molecules.
• Relationship: By using this function, cells perceive physical and chemical changes that occur in the environment that surrounds them.
• Reproduction: Using this function, cells originate and divide into new cells.

**Types of Cells**

• Prokaryotes: They are characterized by a lower degree of complexity and a smaller number of organelles. These are single-celled organisms.
• Eukaryotes: They are characterized by a complex organization with many different compartments

Stages of Embryonic Development

A key feature that differentiates living things from non-living things is the ability to reproduce. Reproduction occurs through cell division. In more complex organisms, this includes sexual and asexual reproduction. The essential phenomenon is mitosis in plants and animals. Sexual reproduction involves meiosis, the process of gamete formation, or specialized cells for reproduction, with the participation of individuals of different sexes. Genetic and hormonal events, along with synchronization mechanisms, ensure the release of gametes for successful fertilization. This is followed by a series of events that characterize successive development and differentiation, transforming the egg or zygote into an adult individual.... Continue reading "Embryonic Development: Stages, Fertilization, and Processes" »