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

The Digestive System

The digestive system is a set of organs and associated glands. It is responsible for converting food into simple, readily usable substances by the body. From the mouth to the anus, the digestive tract is about eleven meters in length.

Digestion Process

Digestion begins in the mouth. The teeth grind the food, and secretions from the salivary glands initiate and wet the chemical decomposition. Then, the bolus crosses the pharynx, goes into the esophagus, and then into the stomach. The stomach is a muscular bag, with a capacity of about two pints under normal conditions, which secretes potent gastric juice. In the stomach, food is agitated until it becomes chyme.

Small Intestine

At the outlet of the stomach, the digestive tract... Continue reading "Human Body Systems: Digestion, Excretion, Respiration" »

DNA technology refers to laboratory techniques that allow combining DNA from different origins, even from different species, into a single DNA molecule. Typically, only a few genes are transferred to other cells.

Applications of DNA Technology

In Agriculture

DNA technology has already been applied to many plants, producing new varieties with improved characteristics:

Protection against certain pests: These plants manufacture proteins or substances that protect them from attack by insects, diseases, or viruses. Herbicide resistance: Crops are not affected by herbicides, allowing for easier weed removal. Improved food characteristics: Producing foods with better characteristics or that are healthier. Increased tolerance to adverse conditions: Obtaining... Continue reading "Uses of DNA Technology in Key Sectors" »

The Absorption and Egestion

As a result of nutrient digestion, small molecules are obtained, allowing them to pass through the walls of the digestive tract and enter the blood. This process is called absorption.

Most substances are absorbed in the jejunum and ileum. In these sections, the inner walls of the small intestine are highly folded to form villi. Inside the villi, blood vessels collect and distribute digested substances to all body cells.

Egestion

Substances that have not been absorbed pass into the large intestine through peristaltic movements of its walls. In this part, almost all the water and mineral salts are absorbed, so the residues of digestion grow stronger until they become stool.

The large intestine also contains a large number... Continue reading "Digestive System: Absorption, Egestion, and Common Disorders" »

Digestive System

Initial Stage: Stomach

The first stage of digestion occurs in the stomach. Here, digestive substances break down food. The stomach cavity is wider than the intestinal walls and secretes gastric juices. This section also includes glands like the liver, which secrete substances that convert food molecules into smaller ones.

Second Stage: Small Intestine

In the second stage, nutrients are absorbed in the small intestine. This organ's extensive length and folded inner walls maximize absorption surface area.

Final Stage: Large Intestine

The last stage takes place in the large intestine (colon), where water is absorbed. This section is wider than the small intestine and lacks the folds of the previous section.

Transport of Nutrients

Blood

Negative and Positive Feedback in Hormonal Regulation

Negative feedback: This is the most widespread type and occurs when increased hormone levels, above a certain value, inhibit hormone secretion. Positive feedback: In this case, an increase in the values of a hormone causes an increase in its secretion. This type of regulation occurs in special situations, such as ovulation.

Immune System Barriers

The immune system can recognize and usually eliminate altered elements of itself.

In humans and higher vertebrates, three types of defensive barriers are distinguished: primary, secondary, and tertiary. Their function is to prevent the entry and development of pathogens.

Primary Barriers

• The skin: The first defensive barrier that prevents the entry of

There are eight fundamental characteristics of the structure of animals that distinguish this group from other groups of living things. These features are:

1. Animals are multicellular. This means that all individuals belonging to the animal kingdom consist of more than one cell, no matter what species they belong to.

   This feature clearly separates the animals from protozoa. Protozoa are a group of unicellular organisms (composed of a single cell) that were formerly classified in the animal kingdom but are now classified in a different group, the kingdom Protozoa, also known as Protista or Protoctista.

2. Animals are eukaryotic. All animals have true cells with nuclei and different organelles in the cytoplasm that perform specific functions. Deoxyribonucleic

Genetic Variations

All individuals within a population possess unique characteristics that distinguish them from one another. These individual differences are called variations and result from an individual's genetic makeup and environmental influences.

Types of Variations:

• Genotype: These are inherited differences passed from parents to offspring and are contained within an individual's genes.
• Phenotypic and Environmental: These variations result from the interaction of genes with the environment. In most cases, the phenotype does not fully express the genotype.

Gene Pool

Each individual in a population carries a unique combination of genes. The gene pool represents the sum of all genes within a population.

Populations evolve through changes in their... Continue reading "Understanding Genetic Variations, Gene Pools, and Stem Cells" »

Vital Functions of Living Beings

Vital functions refer to the specific actions that support life. There are three main functions:

1. Nutrition: Living beings obtain the matter and energy necessary to sustain life through this function.
2. Interaction: Living beings relate to their surrounding environment through this function.
3. Reproduction: Individual living beings are produced; this ensures the perpetuation of the species.

Biomolecules: The Building Blocks of Life

Biomolecules are the fundamental components of living organisms. They are mainly composed of carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus.

Organic Biomolecules

Organic molecules are exclusive to living beings. There are four main types:

1. Carbohydrates (Saccharides)

   These are the most

Health and Disease

Until recently, health was defined as "the absence of disease." However, the World Health Organization (WHO) has developed a more comprehensive definition. Health is a state of complete physical, mental, and social well-being.

Disease, on the other hand, is the state in which a person's health is altered, whether due to physical or social causes. We can distinguish three types of diseases:

• Physical diseases: Produced by injury, infection, or a degenerative process in the body. They are classified into:
  • Infectious diseases: Caused by a pathogen that reproduces within our body.
  • Non-infectious diseases: Due to other causes.
• Mental illness: Caused by a malfunction of the brain, resulting in a decline in mental capacity or some alteration