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

Geological Ages

Precambrian (4600-1000 million years ago)

• The most extensive
• Evolution at the cellular level
• Domain prokaryotes
• Emergence of Eukaryotes
• Cell organisms of greater size and complexity
• First multicellular organisms

Paleozoic (544 to 245 million years ago)

• Appearance of life forms that gave rise to the current lifestyles
• Mainly aquatic organisms
• Invasion of terrestrial environments, first plants (vascular)
• Emergence of arthropods

Mesozoic (245-65 million years ago)

• Pangea begins to split, affecting the climate
• Emergence and domain of dinosaurs (Jurassic); origin of mammals
• Arise flowering plants (angiosperms) and Conifers (Araucaria pines)
• At the end of the Age, massive extinction of marine and some terrestrial species (dinosaurs)

Cenozoic (65 million... Continue reading "Earth's Geological Ages and Evolution of Life" »

Features of Living Things

• Nutrition: Processes by which living things obtain matter and energy.
  • Autotrophs: Organisms that transform inorganic matter into organic matter, such as plants and bacteria. Two types of autotrophic nutrition exist:
    • Photosynthesis (using light)
    • Chemosynthesis (using chemicals)
  • Heterotrophs: Organisms that obtain matter from organic compounds, such as animals and fungi. Two types of heterotrophic nutrition exist, depending on the:
    • Presence of oxygen: Cellular respiration (aerobic)
    • Absence of oxygen: Fermentation (anaerobic)
• Interaction: The capacity of living beings to interact with their environment.
• Reproduction: The process by which living beings produce descendants, leading to the perpetuation of life.
  • Asexual: Descendants

1. Vomer Bone

Shape: Part of the postero-inferior nasal septum. Anatomical Features: Alae (wings), ridge, and furrow for choanal articulation with the vomer.

2. Sutures and Fontanelles

The bones of the cranial vault are joined by synfibrosis. We distinguish:

• Coronal suture
• Sagittal suture
• Squamous sutures
• Metopic suture
• Lambdoid suture

Schindylesis: Vomer and sphenoid crest articulation.

In newborns, skull bones are not yet firmly united at the sutures, leaving spaces called fontanelles. There are six:

• Bregmatic: Diamond-shaped, between the parietal and frontal bones.
• Lambdoid: Triangle-shaped, between the sagittal and lambdoid sutures.
• Pterygoid: Located at the junction of the frontal, parietal, temporal, and sphenoid bones.
• Asteroid: Star-shaped, between

GREAT PLANTS (Metaphytes) belong to this group of photosynthesizing multicellular eukaryotic organisms whose cells have cell walls of cellulose. Plants have a biological cycle in which dipohaplonte diploid and haploid phases are distinguished with different development. There are two divisions: Bryophytes and Tracheophytes.

Bryophytes: Simple Plants

Bryophytes are the less evolved plants. They present a thallus-type organization, with no tissues or organs. This group includes mosses and liverworts, where the haploid body is more developed. Bryophytes are considered an evolution of algae.

Tracheophytes: Developed Plants

Tracheophytes are more developed plants; they have tissues and organs. Conducting structures of food substances are known as vascular.... Continue reading "Plant Kingdom: Classification, Characteristics, and Evolution" »

HIV Replication Cycle in T Cells

When the Human Immunodeficiency Virus (HIV) enters the body, it reaches the bloodstream and is distributed throughout the organism. The mechanism of action within T lymphocytes occurs in the following steps:

1. Attachment: Viral GP120 proteins bind to the CD4 receptors on the surface of the T lymphocyte.
2. Fusion and Entry: The virus fuses with the cell membrane, allowing the viral nucleocapsid to enter the cell's cytoplasm.
3. Uncoating: The nucleocapsid breaks down, releasing the viral RNA genome and essential enzymes like reverse transcriptase and integrase.
4. Reverse Transcription: Reverse transcriptase synthesizes a single DNA strand using the viral RNA as a template.
5. DNA Synthesis: The original RNA strand is degraded,

Human Sensory Organs

The Eye: Structure and Function

The eyeball consists of the globe itself and attached structures. Key parts include:

• Enveloping Membranes:
  • Sclera: The outermost, opaque, white part.
  • Cornea: The transparent front part.
  • Choroid: A dark-colored layer carrying nutrients to the eye.
  • Iris: A colored disk that regulates the amount of light entering.
  • Pupil: The opening in the center of the iris that controls light entry.
  • Retina: Formed by photoreceptor cells. Contains two types:
    • Cones: Responsible for color vision.
    • Rods: Appreciate light intensities (more numerous in the periphery).
  • Blind Spot: The area where the optic nerve exits the eye.
• Internal Structures:
  • Lens: Focuses images onto the retina.
  • Aqueous Humor: Fluid maintaining the eye's shape

Facial Muscles

Occipitofrontalis muscle (frontal belly): Elevates the brow and wrinkles the forehead.

Procerus muscle: Depresses the medial angle of the eyebrow and wrinkles the root of the nose.

Corrugator supercilii: Draws the eyebrow medially and inferiorly, creating vertical wrinkles between the eyebrows.

Depressor supercilii: Depresses the eyebrow.

Orbicularis oculi: Has three parts: palpebral (gently closes the eyelid), orbital (forcefully closes the eye), and lacrimal (compresses the lacrimal gland, aiding tear production).

Levator labii superioris alaeque nasi: Elevates the upper lip and dilates the nostril.

Levator labii superioris: Elevates the upper lip.

Zygomaticus minor: Elevates the upper lip.

Zygomaticus major: Draws the corner of the... Continue reading "Facial Muscles, Spine Joints, and Ligaments: An Anatomical Study" »

Plant Tissues

Supporting Tissue

Supporting tissue is found in the interior of the plant body. These tissues form the plant skeleton, giving it rigidity and strength. Their cells have very thickened walls.

Types of Supporting Tissue

• Collenchyma: Found in younger parts, consisting of living parenchymal cells reinforced by cellulose in some areas.
• Sclerenchyma: Supporting tissue of the developed parts, consisting of dead cells with thickened walls and lignin. If they are elongated, they are called fibers, and if they are round, they are called stone cells.

Secretory Tissues

Secretory tissues are varied, modified epidermal cells, such as those that accumulate aromatic substances, resin canals, and lactiferous ducts.

Animal Tissues

Epithelial Tissue

Types

Plant Reproduction: From Ovary to Seed

Carpel Structure

Each carpel consists of:

• a) Ovary: Ovoid, spherical, cylindrical, or elongated, in the form of a modified leaf sheath. Ovules originate within the ovary.
• b) Style: A filamentous prolongation of the ovary.
• c) Stigma: Situated at the end of the style. It has a wide shape and secretes a liquid that absorbs and adheres to pollen grains.

The ovule is a small, spherical or ovoid corpuscle. It joins the ovary wall by a filament called the funiculus, a bundle of vascular tissue. The site where the ovule joins is called the raphe. It has two membranes: an outer one, the primine, and an inner one, the secundine. Both are traversed by a hole called the micropyle and surround a cluster of cells called the... Continue reading "Plant Reproduction and Structure: From Ovary to Seed" »

Male Reproductive System

• Glands: The seminal vesicles and prostate gland produce substances that are dumped into the vas deferens. These secretions, along with sperm, constitute semen.
• Genital Tracts:
  • Epididymis: A folded tube where spermatozoa are stored.
  • Vas deferens: Tubes leading sperm from the epididymis to the urethra.
  • Urethra: The evacuation duct of the bladder where the vas deferens also flows.
• Penis: A cylindrical cone with an enlarged tip called the glans, covered by a fold of skin called the foreskin.
• Testes: Two organs contained in a bag called the scrotum. They produce sperm and testosterone.

Stages of Labor

• Dilation Phase: Spontaneous contractions of the uterine wall begin. These contractions push the child toward the exit of the uterus,