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

Stages of Human Embryonic Development

1. If a sperm finds an egg in a fallopian tube, it tries to get through its membrane. The egg then produces a hard coating that prevents the penetration of a second spermatozoon. Fertilization ends when the nuclei of the sperm and egg fuse. From this moment, embryonic development begins.
2. The zygote, formed by a single cell, continues to move down the tube on its way to the uterus and begins to divide.
3. The cells continue to divide until they form an embryo of 32 cells, called a morula.
4. A cavity forms inside the morula, which takes the form of a hollow ball, and is called an early blastocyst.
5. A condensed group of cells inside the blastocyst forms a compact mass at one end, ready to become the late blastocyst. The

... Continue reading "Human Embryonic Development & Stem Cell Classification" »

Comparing Oxygen Transport Capacity: Rest and Exercise

Oxygen transport by blood is essential for proper cellular metabolism in all tissues of the organism. O₂ is transported in two forms:

• A small percentage circulates dissolved in the plasma; its solubility is very low (0.3 ml of O₂ in 100 ml of blood).
• The remaining 97% is carried by hemoglobin through reversible binding.

Under normal conditions, O₂ is transported to tissues almost entirely by hemoglobin. The resting oxygen consumption of a normal individual is about 250 ml/min, and intense exercise can increase this more than 10 times. Atmospheric oxygen is the source of oxygen consumed at the mitochondrial level and reaches the alveoli through ventilation. From there, it diffuses into the pulmonary... Continue reading "Oxygen Transport Capacity: Rest vs. Exercise" »

Valve Components

Valves are essential mechanical devices used to control the flow of fluids. Their various components work in concert to achieve precise regulation. The upper structure of the valve often serves as a guide for the stem's movement and houses the packing and gland.

Actuator

Responsible for performing the movement of the valve, which can be either manual or automatic.

Body

The main part through which the fluid flow takes place and within which the shutter (or plug) moves.

Rod (Stem)

The element responsible for transmitting the movement from the actuator to the shutter.

Plugger (Plug/Disc)

The moving part within the fluid stream that determines a section of the flow path according to a given characteristic (e.g., fast, linear, isopercent)... Continue reading "Valve Components and Cavitation Phenomena" »

Euchromatin and Heterochromatin

Heterochromatin is abnormally condensed chromatin. It appears similar to fungal chromatin but is transcriptionally inactive. During mitosis, chromatin is divided into 46 chromosomes. For cell division, DNA must be doubled during the S phase of interphase. Heterochromatin, being highly condensed, replicates last. There are two types of heterochromatin: constitutive and facultative.

Constitutive Heterochromatin

Constitutive heterochromatin is discernible from mitotic chromatin. It is located around the centromere of chromosomes and forms alternating bands in mammalian chromosome arms.

Facultative Heterochromatin

Facultative heterochromatin is condensed only at certain physiological times in the cell, and its amount... Continue reading "Heterochromatin vs Euchromatin: Structure and Function" »

Cell Nucleus: Structure and Function

The nucleus, a defining structure of eukaryotic cells, controls cellular activities and transmits hereditary information across generations.

Morphology

The nucleus can mirror the cell's shape or be irregular.

Size

Nuclear size correlates with cytoplasmic volume and the cell's proliferative capacity; it tends to be larger in actively dividing cells.

Structure

The nucleus exhibits two distinct periods: interphase and mitosis. During interphase, the following are present:

• Nuclear Membrane: A double-layered structure enclosing the nucleus, separating it from the cytoplasm. It regulates the passage of ions and small molecules.
• Nucleoplasm: This consists of nuclear sap, the nucleolus, and chromatin.

Chromosomes

Chromosomes... Continue reading "Cell Nucleus and Chromosome Structure" »

Human Reproductive System

Male Reproductive Anatomy

In the absence of staff, an erection is achieved by blood entering the corpora cavernosa of the penile tissue above the urethra. This is surrounded by the spongy body, which widens to form the glans, covered by the foreskin.

The corpora cavernosa are spongy, erectile tissue (tissue capable of becoming erect when filled with blood). This tissue has abundant cavernous spaces formed by a network of trabeculae, composed of collagen, elastic, and muscle fibers. At the base of the penis are the Cowper glands, which secrete lubricating fluid to facilitate intercourse.

Female Reproductive Anatomy

Gonads: Ovaries

Almond-sized, housed in the abdominal cavity. Within the cortex (outer layer) of each ovary... Continue reading "Human Reproductive System: Anatomy & Physiology" »

The Human Circulatory System

The circulatory system transports and distributes nutrients and other substances dissolved in the blood throughout the body, collecting waste products to be expelled.

Blood Vessels

Blood vessels are the conduits where blood flows. They include:

• Arteries: Vessels that carry blood *away* from the heart. They have thick, slightly elastic walls to withstand high pressure.
• Veins: Vessels that carry blood *toward* the heart. They possess thin walls and one-way valves to prevent the backflow of blood.
• Capillaries: Tiny blood vessels with very thin walls, facilitating the exchange of substances between blood and cells.

The Heart

The heart is the organ responsible for pumping blood rhythmically to every cell in the body. It's made... Continue reading "Human Circulatory System: Heart, Vessels, and Blood" »

The Five Kingdoms of Life

Kingdom Monera

The Kingdom Monera is comprised of prokaryotic organisms, primarily bacteria. It is divided into two main groups, differentiated by their cell wall composition and specific characteristics of RNA and protein synthesis:

• Archaebacteria: Includes bacteria that thrive in extreme environments.
• Eubacteria: Represents typical bacteria, commonly found in diverse habitats.

Kingdom Protista

Often considered a "wastebasket taxon," the Kingdom Protista includes a diverse set of eukaryotic groups that are difficult to classify into other kingdoms. This kingdom encompasses both protozoa and algae, among other groups, with the sole condition that they cannot be included in another established kingdom.

Protozoa

Protozoa are... Continue reading "Biological Kingdoms: Classification and Key Features of Life" »

Understanding the Digestive System

The human digestive system is a complex network of organs and glands working together to process food and absorb vital nutrients. Let's explore its key components and functions.

Key Digestive Organs

The Esophagus

The esophagus is a muscular tube that passes behind the trachea. Its primary role is to transport the bolus (chewed food) from the pharynx down to the stomach. The walls of the esophagus produce mucus, which facilitates the smooth transit of food.

The Stomach

The stomach is a muscular, J-shaped sac that expands significantly when filled with food. Its inner walls are lined with numerous glands that produce gastric juice, essential for digestion. The stomach communicates with the esophagus through the cardiac

... Continue reading "Human Digestive System: Organs, Glands & Digestion" »

Heterotrophic Invertebrates

Heterotrophic organisms cannot produce their own food. They ingest their food. There are different types of symmetry.

Symmetry in Organisms

Symmetry is when one shape becomes exactly like another at any position. Symmetry can be divided into three groups:

• Asymmetrical: Organisms that lack symmetry and therefore are sessile, having no definite shape.
• Radially Symmetrical: Organisms that can be divided into similar halves by passing a plane at any angle along a central axis.
• Bilaterally Symmetrical: A body plan in which the left and right sides of the organism can be divided into approximate mirror images of each other.

Invertebrates

Invertebrates are organisms that do not have a backbone. 98% of animals are invertebrates.... Continue reading "Heterotrophic Invertebrates: Symmetry, Phylum Porifera, and Cnidarians" »