Notes, abstracts, papers, exams and problems of Biology

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

Kinds of Amino Acids

Amino acids can be classified into several categories:

• Nonpolar:
  • Aliphatic
  • Aromatic
• Polar Uncharged
• Charged:
  • Acidic (Anionic)
  • Basic (Cationic)

Proteins: Building Blocks of Life

Proteins are biopolymers formed by molecular chains of 20 different amino acids, each with its own characteristics.

Protein Structures

Primary Structure

The primary structure is characterized by the specific composition of amino acids and their sequential order within the polypeptide chain.

Secondary Structure

The secondary structure refers to the folding of the primary structure due to the formation of hydrogen bonds between the -C=O group of one peptide bond and the -NH group of another. This results in the side chains (R groups) adopting specific spatial arrangements... Continue reading "Amino Acids and Protein Structures: A Comprehensive Look" »

Ecosystems: Definition and Characteristics

An ecosystem is a system formed by the interaction between a community and a biocenosis, or physical environmental factors. An ecosystem model for the subject is closed but open to energy, being capable of regulating itself and remaining in dynamic equilibrium over time.

Population Dynamics

A population is comprised of a set of individuals of the same species living in a particular location. There are some factors that prevent a population from reaching its full biotic potential. These can be external or internal to the population:

• External Factors: These may be biotic (predators, parasites, or diseases caused by other agencies competing for a given resource) and abiotic (climate change, food shortages,

• In the pyramids of numbers, the lengths of the steps are proportional to the number of individuals of all species in each trophic level per unit area or volume.

  Biomass in the lengths of the steps are proportional to the dry weight of all individuals in each trophic level per unit area or volume.

  These pyramids best describe the trophic relationships of the ecosystem as they indicate the amount of organic matter that can be eaten at each trophic level, but do not express the amount transferred from one level to another.

  Energy in the lengths of the steps are proportional to the energy produced per unit time of all individuals in each trophic level per unit volume or surface.

  These pyramids provide a better overall picture of trophic relationships

Cholera

Pathogen: Vibrio cholerae

Methods of Transmission:

• Foodborne
• Waterborne

Note: 3/4 of infected people may be asymptomatic carriers and pass large numbers of bacteria in their feces.

Global Distribution: Asia, Africa

Incubation Period: 1-5 days

Site of Action: Wall of the small intestine; secretes a toxin called choleragen

Clinical Features:

• Severe diarrhea
• Loss of water and salts
• Weakness

Note: Can be fatal if not treated within 24 hours.

Method of Diagnosis: Microscopic analysis of feces

Annual Incidence Worldwide: 5.5 million

Annual Mortality Worldwide: 120,000

Treatment: Antibiotics

Tuberculosis

Pathogen: Mycobacterium tuberculosis

Transmission:

• Airborne droplets
• Infected meat

Global Distribution: Worldwide

Incubation Period: A few weeks or months

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