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

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.

DNA Structure and Genetic Information

Genes are the carriers of biological information, found inside every cell. Their precise location was not known until their discovery within chromosomes. The chromosome number in sex cells is half that which exists in other somatic cells. Genes are contained within chromosomes, and each gene is made up of the molecule known as DNA (Deoxyribonucleic Acid).

DNA Replication: Ensuring Genetic Continuity

Each time a cell divides into two, the two resulting cells must receive the same genetic material. For this to happen, it is essential that DNA copies itself, a process known as replication or duplication.

RNA: Types and Functions

RNA (Ribonucleic Acid) is typically single-stranded. In RNA, the sugar deoxyribose... Continue reading "Fundamentals of Genetics: DNA, Genes, and Human Biology" »

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" »

Aquatic Respiration: Understanding Gills

Gills are highly effective respiratory structures adapted for life in water. They are laminar expansions formed by the filiform body wall of an animal. If these expansions project outside the body, they are called external gills. If they are housed inside a cavity that communicates with the outside, they are called internal gills.

External Gills: Simpler Respiratory Structures

External gills are evolutionarily the oldest, formed by expansions of the body surface. They occur in some mollusks, insects, and aquatic larvae of amphibians and crustaceans. However, they present several disadvantages:

• They are vulnerable to predators.
• They are easily injured.
• They can make movement difficult.
• Animals possessing these

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

Advanced Medical Imaging Techniques

• Computed Tomography (CT) Scans

  Computed Tomography (CT) allows for the visualization of body parts in very fine, successive cross-sections, revealing even the smallest details. The apparatus uses an X-ray tube and detectors that analyze the fraction of X-rays absorbed by tissues. Soft tissues absorb less radiation than hard tissues, allowing for differentiation.

• Magnetic Resonance Imaging (MRI)

  Magnetic Resonance Imaging (MRI) uses a powerful magnet to generate a magnetic field, which is absorbed by hydrogen atoms in the body. By changing the magnetic field, these atoms return to their original state, emitting signals that are detected and computed by a computer to generate detailed images. MRI can produce images

Human Development: Puberty and Sexual Characteristics

Gametes and Reproductive Capability

Gametes are the reproductive cells: sperm (male) and eggs (female). Humans acquire this ability during the first stage of adolescence, known as puberty.

Sexual Characteristics

Primary Sex Characteristics

These include the gonads and internal structures that house the embryo (the uterus) until the individual is born.

Secondary Sexual Characteristics

Secondary sexual characteristics are external features unique to either sex, which appear at puberty.

Changes in Males

• Shoulders widen.
• Hair appears (axillary, pubic, facial).
• The voice deepens (becomes lower pitched).
• The penis and testes increase in size.

Changes in Females

• Hips widen and the waist narrows.
• Hair appears

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

Photosynthesis

Photosynthesis is the process by which some cells can capture light energy from the sun and transform it into chemical energy. This process is carried out by plants, green or red algae, and some bacteria. Its purpose is to synthesize organic matter from inorganic matter (CO₂, H₂O, mineral salts) using light energy and releasing molecular oxygen into the atmosphere during the process.

In eukaryotic cells, it occurs in chloroplasts in two phases:

• Light Phase

  This occurs in the thylakoid membrane of chloroplasts, driven by chlorophyll. It captures light energy from the sun and converts it into chemical energy in the form of energy-rich ATP and a molecule with great reducing power, NADPH. The photolysis of water liberates O₂.

• Dark Phase

Physical Assessment of a Patient with Cancer

Skin

• Inspection: Color, integrity, turgor, humidity, temperature.
• Check for: Injuries (type, size, and location), purpura, petechiae, edema, and appearance of nails.

Head and Neck

• Inspect: Face (asymmetry), eyes, mouth, trachea, maxillary sinuses.
• Palpation: Thyroid.

Thorax

• Inspection: Breathing movements and rate.
• Palpation, percussion, auscultation: Tone, intensity, and duration of breath sounds.

Breasts and Armpits

• Inspection and palpation.

Cardiovascular

• Inspection: Tremors and palpitations in the chest.
• Auscultation, palpation, blood pressure.

Musculoskeletal

• Inspection: Hair distribution, abnormal masses or lesions, asymmetries, nodules.
• Palpation: Painful masses, joint range of motion.

Neurologic

• Presence of