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

Larrel: The Root Structure

Larrel is a structure that has the dual mission to fix the plant in the soil and absorb water and mineral salts. In some cases, it serves as a reserve substance.

Parts of Larrel

They are morphologically and functionally different:

• Zone of Growth

  Formed by meristematic tissue, the apex is protected by the calyptra, composed of dead cells.

• Zone of Elongation

  Meristematic cells are transformed to become adult tissues. Elongation of cells is responsible for growth in length of the root.

• Piliferous Zone

  This is the closest to the stem. Here are found absorbent hairs.

Layers of Cells in Larrel

• The Cortical Cylinder

  • Epidermis: Its cells are absorptive hairs.
  • Cortical Parenchyma: Cells in which the plant stores food.
  • Endodermis: A monolayer

Activation Energy and the Activated Complex

Chemical reactions involve the breaking of some bonds in the reactants and the formation of new ones, resulting in specific products. For this to happen, a certain amount of energy, *q*, is required to activate the reactants. This energy is called activation energy and is necessary to initiate the reaction.

Molecules reach a higher-energy activated state or transition state where the bonds are partially broken. Because this reaction takes place, the products obtained are in a lower energy state. The higher the activation energy, the more difficult it will be to reach the activated state, and the reaction rate will be lower. One way to initiate the reaction is by heating the substance; the molecules... Continue reading "Activation Energy & Enzymes in Chemical Reactions" »

Basic Development Models

Protostomes

Protostomes: In protostomes, which translates to "mouth first", the mouth of the new individual develops separately from the blastopore, the first opening of the embryo.

Deuterostomes

Deuterostomes: In deuterostomes, which translates to "mouth second", the mouth opens later in a different place than the blastopore.

Extraembryonic Membranes

Extraembryonic membranes originate from the embryo but are not part of it. They form with input from all embryonic layers and play important roles in development:

• Yolk Sac: The first embryonic membrane that forms. It surrounds the mass of yolk, where one exists.
• Amnion: A membrane surrounding the embryo that secretes amniotic fluid, providing an aqueous environment.
• Chorion: Surrounds

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