Notes, abstracts, papers, exams and problems of Biology

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" »

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" »

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" »

Glycolysis and the Krebs Cycle

The Krebs cycle (also known as the citric acid cycle or tricarboxylic acid cycle) is named after its discoverer, Hans Krebs, who proposed the key elements of O₂ consumption in an amount disproportionate to the amounts added. Based on experimental observations, Hans Krebs proposed a cyclic pathway and cell reactions. The sequence, being a functional unit of all organisms, has a very coordinated and specific operation of all its organelles. However, within all this perfect machine, it is paramount that it takes energy for all this machinery to work to perfection. Cells use energy in the form of ATP (adenosine triphosphate). This is a molecule consisting of one molecule of adenine, a ribose, and three phosphate groups.... Continue reading "Glycolysis and Krebs Cycle: Energy Production in Cells" »

Neurons: The Building Blocks of the Nervous System

Neurons are fundamental cells of the nervous system, representing the anatomical and functional unit of the human brain. They are specialized cells designed to receive, carry, and transmit electrochemical signals called nerve impulses.

Neurons are irreplaceable. Once they age, are injured, or die, they cannot be replaced. This is because these cells are primarily formed during the prenatal period of gestation. A child is born with the largest number of neurons, approximately 100 billion, which immediately begin to decrease in number.

Glial Cells: Supporting the Neurons

The name 'glial' comes from the Greek root 'glia,' meaning concrete. These cells lack axons and are not essential for directly... Continue reading "Understanding Neurons, Glial Cells, Axons, Dendrites, and Synapses" »

Anatomy Q&A

Respiratory System

Bronchioles

1. Lack of cartilage

Alveoli

2. Gas exchange (hematosis) occurs in the lung alveoli.

Pleura

3. Plural recesses provide more space for lung expansion during inspiration.

Bronchi

4. The right main bronchus has a larger diameter than the left.

Larynx

5. The glottic cleft is the space between the vocal cords.

Digestive System

Duodenum

6. The hepatopancreatic ampulla is located in the descending portion of the duodenum.

Esophagus

7. The muscular layer of the esophagus transports the food bolus via peristalsis.

Stomach

15. The lesser curvature of the stomach is supplied by the left and right gastric arteries.

Hepatic Portal System

16. The splenic vein opens into the portal vein.

17. The superior mesenteric vein and splenic... Continue reading "Anatomy Q&A: Respiratory, Digestive, Circulatory, and Nervous Systems" »

Genetic Material

Genetic information is stored in the DNA molecule and is composed of three elements:

• Silica
• A sugar phosphate group
• A nitrogenous base

Chromosome

Hereditary information for each individual is stored in the DNA. This is called the genome, and the protein formed by it is called chromatin.

Genes

A gene is the unit of living legacy and consists of a linear sequence of nucleotides in the DNA molecule.

Homologous Chromosome

In somatic cells, each chromosome has a companion, which constitutes a pair of homologous chromosomes.

Mutation

A mutation is an alteration or change of genetic information in a living being. Therefore, it will produce a change of features spontaneously and can be transmitted or inherited by the offspring.

Genetic Mutation

A... Continue reading "Understanding Genetic Material and Mutations" »