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

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

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

The Miller-Urey Experiment: Origin of Life

The Miller-Urey experiment represents the first demonstration that organic molecules can form spontaneously from simple inorganic substances under simulated early Earth conditions. This groundbreaking experiment provided crucial insights into the chemical origins of life.

In the experiment, a gaseous mixture (simulating Earth's early atmosphere) was introduced into a sealed flask, where water was kept boiling to mimic the primordial ocean. The resulting vapor then underwent condensation. Substances were circulated continuously through the experimental setup, while two electrodes consistently produced electric shocks, simulating lightning.

Crucially, samples were extracted from the apparatus for analysis.... Continue reading "Evolutionary Biology: Miller-Urey, Lamarck, and Natural Selection" »

The Nervous System

The nervous system is a biological system that enables very complex beings to interact with what surrounds us. We can say that it is a huge network responsible for the collection of internal and external stimuli. It processes these stimuli to generate the response that the decision center (brain) considers optimal.

There are two main divisions:

• Central Nervous System: Consists of the brain and spinal cord.
• Peripheral Nervous System: Includes all the nerves of the body that connect internal and external stimuli to the central nervous system.

Peripheral Nervous System

The peripheral nervous system includes different types of nerves:

• Sensory Nerves: Transmit information from sensory receptors (like those for touch, pain, temperature)

The Origin of the Moon

• Sister. The Moon formed while the Earth did, but the Moon is 100 million years younger, and their densities are different.
• Adopted. Both formed, but the Moon formed in an area farthest from the Sun and would have been attracted to the Earth. This does not explain the difference in age.
• Daughter. A planet similar to Mars collided with the Earth. Part of the star that crashed formed a debris cloud that orbited around the Earth. The union of these materials created the Moon.

Prebiotic Synthesis

Hypotheses in which life would have originated on Earth as a result of a process:

• Formation of simple organic molecules. Radiation caused molecules to react, forming simple organic molecules.
• Formation of complex organic molecules.

HIV and AIDS: An Introduction

AIDS (Acquired Immunodeficiency Syndrome) is caused by infection with the retrovirus HIV. This virus attacks and destroys T4 lymphocytes and macrophages. Affected individuals have a depressed immune system, which can lead to certain types of cancers.

Development of the Disease

HIV is found in the blood and other bodily fluids of infected persons. Transmission to a healthy person can occur through various routes. These include contaminated blood transfusions and sexual intercourse between an infected and healthy individual.

Once HIV enters the blood of a new host, it joins T cells and penetrates inside. There, a large number of viruses are created, ultimately destroying the infected cell.

AIDS: Treatment and Prevention

There... Continue reading "HIV and AIDS: Understanding the Disease and Prevention" »

Food Chains and Trophic Levels

Living beings require material and energy, obtained from nutrients in food, to perform vital functions such as nutrition, relationships, and reproduction. Living things are classified into three groups or trophic levels:

• Producers: These are autotrophic organisms that produce organic matter from inorganic substances. Most are photosynthetic, using sunlight to convert water, mineral salts from the soil, and carbon dioxide from the atmosphere into organic material. This level is formed by plants, algae, and certain bacteria.
• Consumers: These are heterotrophic organisms that feed on organic matter from other living beings. Consumers are categorized into types:
  • Primary Consumers: They feed on producers. Herbivores are

The First Cells: Cell Evolution

All organisms that currently inhabit the Earth are related because they come from ancestral cells that emerged more than 3,800 million years ago as a result of a slow evolutionary process of organic molecules accumulated in the primeval oceans. It is believed that the decisive moment in the origin of cells was the appearance of a biological membrane.

• The membrane separated the external environment from the internal environment, which favored the existence of a rudimentary metabolism that enabled the ancestral cells to get energy (via nutrition) and use it to reproduce and respond to environmental changes.

Because they originated in a sea of organic molecules, the first cells were probably anaerobic fermentative