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

Fertilization

Fertilization is the fusion of male and female gametes, initiating the process of reproduction. It's important to note that fertilization of the egg is not immediate upon contact.

Human Fertilization

In humans, fertilization occurs when a sperm and egg unite in the fallopian tubes after sexual intercourse. Humans develop from the union of these two tiny cells. Mature eggs measure approximately 0.135 mm in diameter, while sperm are even smaller. Each ejaculation can contain between 120 and 600 million sperm. The union of these cells has the potential to create a new human being with extraordinary abilities.

Zygote

In biology, a zygote is the cell formed by the union of male and female gametes during sexual reproduction in organisms... Continue reading "Human Reproduction: From Fertilization to Embryonic Development" »

Infectious Diseases

Definition

Temporary or permanent loss of health caused by microorganisms.

Types of Microorganisms

• Bacteria: Unicellular prokaryotic organisms that multiply and can destroy cells and tissues.
• Viruses: Not considered living organisms. They reproduce by entering cells and using their resources, causing damage.
• Protozoa: Single-celled eukaryotes. Some cause disease.
• Fungi: Unicellular and multicellular eukaryotes. Some can cause disease in weakened individuals.
• Parasites: Multicellular organisms that live at the expense of a host, weakening but not killing it.
• Prions: Misfolded proteins that accumulate and cause neuron degeneration.

Non-Infectious Diseases

Nonspecific Defenses

Mechanisms that prevent the entry of microorganisms:

• Skin: Acts

Definition of Infectious Diseases

An infectious disease occurs when a parasite develops and multiplies within a host. The causal agent of transmissible diseases is usually a living organism that moves from one individual to another by contagion. The set of elements that define a communicable disease consists of:

• Reservoir: Where infectious agents are usually found.
• Source of Infection: Animate or inanimate object from which the causative agent originates.
• Mechanism of Transmission: The pathways that allow the causal agent of a transmissible disease to contact the host.
• Host: A person susceptible to contracting a communicable disease upon contact with the source of infection.

Samples arriving at the laboratory for the diagnosis of causative agents... Continue reading "Infectious Diseases: Definition, Transmission, and Diagnosis" »

Genetics and Heredity

Genetics is the science that studies how traits are inherited. Besides hereditary traits, external factors, including the environment, cause changes. Species variation is the manifestation of differences between individuals of the same species. The main causes are genetic variations.

Continuous and Discontinuous Variation

Continuous variation occurs when a trait has slightly different manifestations, like hair or skin color. Discontinuous variation occurs when a trait is clearly expressed as different and is genetically determined, not changing during an individual's life.

Phenotypic and Genotypic Variations

Phenotypic variations are observable traits (weight, height, color) resulting from the environment and genotype. Genotypic

Main Characteristics of Mammals

In general, mammals are characterized by the following:

• They are warm-blooded; their body temperature is constant.
• Mothers have mammary glands that produce milk for their young.
• The mouth is surrounded by lips, allowing young to suckle.
• They have abundant glands (sebaceous, sweat, and odoriferous) and are generally covered in fur, which they shed periodically.
• They have teeth to chew food.
• They have pulmonary respiration.
• Circulation is double (pulmonary and general).
• Most are viviparous: The embryo develops inside the mother and is nourished through the placenta.

Mammals are among the most highly evolved animals. They can live on land, fly, or live in the water.

Here, we will examine in more detail some common characteristics... Continue reading "Key Characteristics and Evolution of Mammals" »

Blood Tissue

Blood is a tissue fluid that flows through the veins and arteries of all vertebrates. Its characteristic red color is due to the presence of the pigment hemoglobin in red blood cells.

Blood has a solid phase and a liquid phase, represented by the plasma. Its main function is the logistics of distribution and systematic integration.

Blood consists of formed elements and blood plasma.

Platelets

Platelets are small cell fragments (2-3 um in diameter), oval and without nuclei. They are produced in the bone marrow from the fragmentation of the cytoplasm of megakaryocytes. Their normal quantitative value is between 150,000 and 450,000 platelets per mm3.

They serve to plug injuries that could affect blood vessels. Platelets contribute to clot... Continue reading "Understanding Blood, Cartilage, Muscle, and Nervous Tissue" »

Sensory Receptors

Sensory receptors are structures formed by nerve cells specialized to capture and transform stimuli into nerve impulses. The receptors are classified as:

• Chemoreceptors: Sensitive to chemicals.
• Mechanoreceptors: Sensitive to mechanical stimuli such as touch, pressure, sound, or gravity.
• Photoreceptors: Sensitive to light.
• Thermoreceptors: Sensitive to changes in temperature.
• Nociceptors: Sensitive to heavy pressure and responsible for pain.

Receptors can also be classified according to their location:

• Internal receptors: Located inside the body, particularly in the viscera. Responsible for collecting information from internal organs.
• External receptors: Located on the surface of the body. Responsible for collecting external stimuli

Milk and Dairy

Provides protein, vitamins, and calcium. Recommended serving: 250 mL of milk and 80g of dairy products.

Meat, Fish, and Eggs

Excellent sources of protein, vitamins, and iron. Recommended serving: 100g of meat and 150g of fish.

Legumes and Potatoes

Offer carbohydrates and protein. Recommended serving: 80g of pulses and 180g of potatoes.

Vegetables

Rich in vitamins, minerals, and fiber. Recommended serving: 125g.

Fruits

Packed with vitamins, fiber, minerals, and carbohydrates. Recommended serving: 125g.

Cereals and Grains

Provide carbohydrates. Recommended serving: 80g of pasta or rice, 50g of bread.

Fats, Oils, and Butter

Sources of lipids.

Carbohydrates

Nutrients that provide energy. Simple sugars, like glucose, are the primary source of cellular... Continue reading "Nutrition Essentials: Building a Balanced Diet" »

The Biosphere

The biosphere is the set of all living things on Earth.

Understanding Ecosystems

An ecosystem consists of interconnected components:

• Biotic Components: Living things that inhabit a particular place and interrelate.
• Abiotic Components: All the physical environmental conditions or non-living elements within the dwelling of living beings.

Relations Between Components: Living organisms in a specific location are adapted to certain conditions of their physical environment and, in turn, modify it.

Ecological Relationships

There are relationships between individuals of the same species and between different species, such as predation, parasitism, symbiosis, and commensalism.

Photosynthesis

Photosynthesis is the process of converting light energy... Continue reading "Understanding Earth's Living Systems" »