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

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

Site of

Infectious Disease Prevention and Treatment

Infections can be treated with antiseptics, which kill microorganisms but can only be applied to the skin's surface. Antibiotics are substances that selectively attack bacteria and can be ingested or injected. Penicillin was the first known antibiotic. The English physician Jenner invented vaccines, which involve injecting small amounts of dead or fragmented pathogens.

Healthy Habits

• Eat in moderation at least three times a day, always including breakfast.
• Eat a balanced diet with the appropriate proportion of nutrients.
• Sleep eight hours a day.
• Exercise moderately to maintain muscle tone.
• Maintain a proper weight for your age, sex, and build.
• Practice proper hygiene.
• Avoid snuff, alcohol, and other drugs.

Evolutionism

According to biology, fixism maintained that the existing living species were independent and immutable and that they had always existed with the same basic characteristics.

From the works of Lamarck and Darwin, evolutionism emerged. It holds that the universe and life in all its manifestations, and therefore all species, are the result of change and adaptation. This theory is called evolution and argues that species living today come from others who have disappeared, and these in turn from another, until reaching the first living organisms. For evolution, all living creatures belong to a single large family that has developed over Earth's history.

Early Evolutionary Theories

Scientists disagree on:

• The mechanisms causing species diversification.

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" »

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