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

Animal Sensory Organs

The Lateral Line System

The lateral line is a specialized sensory organ found in fish and amphibian larvae. It can be identified as longitudinal lines on each side of the animal's body. These lines are formed by a succession of small pores that cross the scales and connect with a long, fluid-filled tube running beneath the skin along the animal's flanks. The inner tube is lined with hair cells, capable of capturing even the smallest water vibrations.

Facial Pits

The facial pit is a thermosensitive organ found in some snakes, such as rattlesnakes. It consists of two structures located between the eyes and mouth. These pits contain receptors capable of capturing infrared radiation, i.e., the heat emitted by other bodies. This... Continue reading "Animal Adaptations: Sensory Organs and Protective Structures" »

Heart Muscle Contraction: How Does the Pacemaker Work?

The heart muscle consists of sarcomeres containing alternating thick and thin filaments. The cells tend to contract rhythmically and spontaneously, but these contractions are synchronized by electrical signals produced by specialized muscle fibers of the sinoatrial node. Cardiac muscle fibers are electrically interconnected by links between cells located interspersed. This allows for coordinated contraction. Specialized fibers act as a pacemaker. Action potentials that originate in the pacemaker spread quickly through the heart using specialized areas in which interspersed links connect adjacent muscle cell membranes. These allow the potential to synchronize their contractions as they travel... Continue reading "Heart Muscle Contraction, Lymphatic & Circulatory Systems in Animals" »

Trachea

Trachea are elongated cells, with thick walls and lose their cytoplasm at maturity, so they are dead cells. The terminal walls dissolve and form continuous tubes called vessels.

Sieve Tube

These cells are at the end to end and form long sieve tubes. Polyhedral cells of epithelium lining the trachea have cilia that beat synchronously to move substances.

DNSO

The fibers are arranged in different directions and at different levels, allowing them to endure stretching in all directions.

Internal Environment

Unicellular organisms trade directly with the extracellular environment they live in, while multicellular organisms rely on an internal environment as an intermediary between the external and intracellular environments.

Benefits

• Cells provide

The Origins of Life and Biological Evolution

About 15 billion years ago, the universe was smaller than an atom and devoid of matter. Life arose soon after Earth formed, about 3.5 billion years ago. Since that time, life began to evolve.

Defining Biological Evolution

Biological evolution is the process of anatomical and physiological changes experienced by populations of living things, which results in the formation of new species.

Human Evolution: A Unique Process

Human evolution is part of the general evolutionary process, but humanity is a unique species within the process of natural evolution.

Foundational Theories of Evolutionary Change

Various theories of evolution attempt to explain this mysterious unfolding of life.

Lamarckism: Acquired Characteristics

Jean-... Continue reading "The History and Mechanisms of Biological Evolution" »

Mendel's Pea Plant Inheritance Studies

What is a Pure Race for a Character?

Pea flowers can be white or purple. When crossing two plants with purple flowers, some offspring plants had white flowers, and others had purple flowers. After repeating this process for several generations (remembering there is only one crop of peas per year), offspring were obtained solely from plants with purple flowers. This outcome persisted in subsequent generations. These purple-flowered plants represent a pure race for that specific character.

Character Study: Crossing Pure Breeds

Mendel studied several characters by crossing pure breeds (varieties):

• Seed Color

  • Dominant Alternative: Yellow
  • Recessive Alternative: Green

• Seed Aspect

  • Dominant Alternative: Smooth
  • Recessive

The Digestive System

Functions of the Digestive System

The digestive system performs the following vital functions:

• Breaks down food into molecules the body can use.
• Absorbs molecules into the blood and carries them throughout the body.
• Eliminates wastes from the body.

Types of Digestion

There are two main types of digestion:

• Mechanical Digestion: Foods are physically broken down into smaller pieces.
• Chemical Digestion: Chemicals produced by the body break foods into their smaller chemical building blocks. Most chemical digestion occurs in the stomach.

Key Components and Processes

Saliva

Saliva is the fluid released when your mouth waters. It is produced by salivary glands and plays an important role in chemical digestive processes.

Teeth

• Incisors: Central

The Immune System and Disease Prevention

The immune system is a set of organs, cells, and molecules whose primary function is to defend the body against infectious agents and abnormal cells within the organism.

It is responsible for defense once infectious agents have crossed the skin or mucous membranes, and it acts through:

Nonspecific Defenses

Nonspecific defenses, such as inflammation, are not dependent on the nature of the pathogen.

Specific Defenses

Specific defenses are based on the specific recognition of foreign substances, known as antigens, against which an immune response is triggered. This response has the following characteristics:

• Specificity: Lymphocytes, which are cells of the immune system, distinguish specific antigens from others

Vegetative Reproduction in Plants

Vegetative reproduction is a form of asexual reproduction in plants. A part of a single individual, a cell (e.g., spores), or a group of cells (fragmentation) develops into a duplicate of the progenitor. The offspring are identical to each other and identical to their preserved vegetative progenitor. Plants always have embryonic tissues, the meristems, which consist of totipotent cells. Therefore, they have a great capacity for regeneration, and asexual reproduction is common.

Structures Involved in Asexual Reproduction

• Stolons: Stems that run parallel to the ground, which occasionally produce roots and new stems and leaves. Example: Strawberries.
• Rhizomes: Underground stems that occasionally produce roots and

Immunology

By removing serum from pustules of the udder of a cow and injecting it into human skin, an individual suffered from a mild illness but never acquired smallpox. It was the first experiment of active immunization.

1. The Body's Defenses

All organisms have developed mechanisms of defense against the invasion of pathogens. These mechanisms may be nonspecific, preventing entry into the body or destroying them quickly, or very specific, which is known as the immune response.

1.1 Nonspecific Defense Mechanisms

These act against any organism or foreign substance. They are of three types:

a) Natural Barriers: Skin and secretions from the mucosal surfaces.

• Skin is a mechanical barrier because its outermost stratum corneum is fully keratinized.
• It