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

Gram Staining: Positive and Negative Bacteria

In bacteria, the cell wall is a determinant of cell shape and has also served as a classification criterion. In 1884, French bacteriologist Christian Gram developed a method to observe bacteria under light microscopy using specific staining. However, not all bacteria are stained with this method, which led to their classification into two groups: Gram-positive bacteria, which retain the stain, and Gram-negative bacteria, which do not retain the stain.

This distinction reflects structural differences in the bacterial cell wall. In Gram-positive bacteria, the wall is mainly composed of peptidoglycan and teichoic acid. In contrast, Gram-negative bacteria have, in addition to peptidoglycan, an outer membrane... Continue reading "Bacterial Basics: Gram Staining, Morphology, and Reproduction" »

Understanding Diet and Nutrition

What is Diet?

Diet: The amount and type of food we consume.

Types of Diets

Balanced Diet: A healthy diet provides the body with the right amount of energy and different types of nutrients.

Mediterranean Diet: This is a balanced diet that combines all foods properly.

Genetically Modified Organisms

GMO Foods: These are produced from organisms that have had genetic material from another living being introduced.

Food Preservation and Additives

Food Preservation Methods

Food can be preserved using chemical and physical methods:

• Heating foods to high temperatures for a few seconds can eliminate a number of bacteria.
• Preservation by cold (refrigeration/freezing).
• Freeze-drying eliminates water from food.
• Chemical preservation uses

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" »

A gene is the carrier of an inherited feature that is passed from generation to generation.

Alleles are possible alternatives for a character. Alleles stand at the same site on two chromosomes in an individual, one from each parent. Alleles are equal when it is said that the individual is homozygous or pure-bred for the character. If different, they are heterozygous or hybrid.

A dominant allele is the character that is always represented (capital letters).

A recessive character emerges only in homozygous individuals (lowercase).

Genotype is the joint of the genes, half from one progenitor and the other half from the other.

Phenotype is the set of characters that manifests externally. This is particular, but the genotype influences the environment.... Continue reading "Understanding Genes, Alleles, and Inheritance" »

Cellular Foundations and Body Tissues

Understanding Cell Components

• Cell Membrane: The thin layer that wraps the cell and separates it from the external environment.
• Cytoplasm: The contents of the cell, excluding the nucleus.
• Nucleus: A structure bounded by a double membrane, traversed by pores that allow substance exchange between the nucleus and the cytoplasm. Contains DNA.

Metabolic Processes

• Catabolism: A set of reactions that break down complex molecules to provide energy for cellular activities.
• Anabolism: A set of reactions that build complex molecules from simpler ones, requiring energy.
• Diffusion: Small molecules like oxygen and carbon dioxide freely pass through the plasma membrane.

Cell Specialization and Organization

• Cell Specialization:

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:

Digestive System Processes

Ingestion

Seizure of food by the digestive system through the mouth.

Chewing

Spraying of food through chewing movements and mixing with saliva.

Swallowing

Movement of food from the mouth to the stomach.

Digestion

Mechanical and chemical breakdown of food into absorbable molecules.

Absorption

Passage of monomers of food molecules through the mucous membranes of the intestine into the bloodstream.

Peristalsis

Waves of rhythmic contractions that propel food along the digestive tract.

Elimination (Clarification)

Discarding of indigestible waste, called feces, which contains water, dead cells, dead bacteria, mucus, and gas.

Digestive System Phases

• Propulsion: Movement of food along the digestive tract.
• Secretion: Release of digestive juices.

What are Tissues?

A tissue consists of a group of specialized cells. Often, in addition to the cells themselves, tissues also contain substances created by the cells. These are called extracellular substances or the extracellular matrix. A set of cells that work together to perform the same function is called a tissue. In most cases, tissues are made up of cells of the same type.

Types of Tissue

There are four main types of tissue in the human body:

Epithelial Tissue

Epithelial tissue covers the external surface of the body and lines the internal and external surfaces of organs. There are two main types:

• Covering or Lining Epithelium: This type may be made up of one or several layers of cells. Its primary function is protection.
• Glandular Epithelium:

Meiosis: Cell Division for Reproduction

Meiosis is a type of cell division involved in sexual reproduction. Its purpose is to produce reproductive cells called gametes, which have half the number of chromosomes as normal somatic cells (they are haploid). Meiosis consists of two consecutive divisions. Starting with a single diploid cell, four haploid daughter cells are obtained. These daughter cells are genetically different due to the exchange of information between homologous chromosomes. Meiosis occurs in the reproductive organs or gonads: ovaries and testes in animals, and ovaries and anthers in plants.

Meiosis I

Prophase I

Meiosis begins with steps similar to mitosis. The main difference is that homologous chromosomes pair up and become fully... Continue reading "Meiosis Cell Division: Stages and Purpose" »