National School of Agriculture - Guatemala

Welcome to the Natural Sciences guide! This text was created by the National School of Agriculture (ENCA) in Guatemala to help prepare students for entrance exams. The school offers three specialized agriculture-related careers: Agricultural Technician, Forestry Technician, and Agro-industrial Technician.

This guide will cover essential topics in natural sciences including biology as a science, origins of the universe and life, biochemistry, cells, tissues, biodiversity, and ecology. These foundations are critical whether you want to study agricultural systems, forest management, or food production.

Did you know? The National School of Agriculture in Guatemala was founded in 1921 and has been training agricultural specialists for over a century!

Table of Contents

This guide is organized into seven main sections that build your understanding from basic biology to complex ecological systems:

1. Biology as a Science: Explores what biology is, its branches, scientific method, and characteristics of living things
2. Origin of the Universe and Life: Examines different theories about how everything began
3. Biochemical Characteristics of Life: Covers the essential molecules that make up living organisms
4. The Cell: Examines cell types, structures, and how they function
5. Tissues: Explores how cells organize into specialized groups in plants and animals
6. Diversity of Life: Shows how scientists classify the incredible variety of living things
7. Ecology as a Science: Examines how organisms interact with each other and their environment

Each section concludes with an evaluation to test your understanding. This structured approach helps you build a solid foundation in biological sciences, starting with basic concepts and moving to more complex systems.

The topics covered here will be tested in the pre-selection exam and represent fundamental knowledge you'll need as you pursue studies in agriculture, forestry, or agro-industrial fields.

Introduction to the Guide

This guide has been created specifically to help you prepare for the Natural Sciences portion of the ENCA entrance exam. The agricultural, forestry, and agro-industrial careers offered at ENCA are deeply rooted in natural sciences, making this knowledge essential for your success.

The material focuses on seven key topics: biology as a science, origin of the universe and life, biochemical characteristics, cellular biology, tissues, biodiversity, and ecology. These subjects form the foundation you'll need both for the entrance exam and for your future studies at ENCA.

Each section includes clear explanations followed by practice questions to test your understanding. While this guide provides a solid introduction to these topics, you're encouraged to explore additional resources to deepen your knowledge. The more you understand about how living systems work, the better prepared you'll be for a career in agriculture or related fields.

Pro Tip: Don't just memorize facts! Try to understand the connections between different concepts, as this deeper understanding will help you apply your knowledge to new situations on the exam and in your future career.

Biology as a Science

Biology is the scientific study of living things. It began as a formal science in the 19th century, though its roots trace back to ancient Greece. What started as simple classification of living organisms has evolved into a complex field that examines functions, structures, development, inheritance, evolution, and how organisms interact with their environment and each other.

The definition of biology as the "science of life" only makes sense if we understand what "life" means. While no simple definition exists, living things share several key characteristics: specific organization, metabolism, homeostasis, growth, movement, irritability, reproduction, and adaptation/evolution. According to Villee (1988), "biology studies the multiple forms that living beings can adopt, as well as their structure, function, evolution, growth, and relationships with the environment."

Biology has grown into such a broad science that it has divided into numerous disciplines. However, all these fields share core principles and theories including cell theory, evolution theory, and gene theory, which give unity to biological thinking.

Branches of Biology

Biology has many specialized branches focusing on different aspects of life:

• Botany and Zoology study plants and animals respectively
• Anatomy, Physiology, and Embryology examine structure, function, and development
• Parasitology studies organisms that live on or in others
• Cytology focuses on cells, while Histology examines tissues
• Genetics studies how traits pass from one generation to the next
• Ecology examines relationships between organisms and their environment

Each field provides unique insights into how living systems work, with many overlapping to give us a comprehensive understanding of life.

Amazing Fact: Biology spans from studying the smallest bacterial cell (about 1 micrometer) to entire global ecosystems, covering an incredible range of size scales!

The Scientific Method

The goal of science is to explain observed phenomena and establish general principles that help predict relationships between phenomena. These explanations come through an organized form of common sense called the scientific method, though it's difficult to reduce this to a simple set of rules that apply to all sciences.

One basic principle of the scientific method is rejecting authority—never accepting something just because someone claims it's true. Scientists are skeptical by nature and require independent confirmation of observations.

The scientific method involves asking questions and seeking answers. Both questions and answers must be "scientific"—arising from and verified by experiments and observations. Careful, precise observation is the foundation of scientific discovery, ideally conducted with controlled experiments and appropriate controls.

Based on observations, scientists form hypotheses—educated guesses about the nature of what they've observed. These hypotheses can then be tested through further experiments. When a hypothesis is supported by many different observations and experiments, it may become a theory—a generally accepted scientific principle that explains phenomena.

Characteristics of Living Things

Though the line between living and non-living can be blurry (viruses show some characteristics of life but not all), living organisms typically share these key traits:

1. Specific Organization: Living things have characteristic forms and structures with cells as their basic unit
2. Metabolism: The sum of chemical activities that allow cells to grow, maintain, and repair themselves
3. Homeostasis: The ability to maintain a stable internal environment despite external changes
4. Growth: Increase in cellular mass through cell enlargement or multiplication
5. Movement: From obvious animal locomotion to slower plant movements
6. Irritability: The ability to respond to stimuli like light, temperature, or chemical changes
7. Reproduction: Creating new individuals, either through simple division or complex sexual processes
8. Adaptation and Evolution: The ability to adjust to environmental changes, both immediately and across generations

These characteristics together define what it means to be alive, though not all living things display every characteristic in the same way.

Branches of Biology (Continued)

The field of biology connects with many other sciences and branches into numerous specialized areas. As shown in Figure 1, biology relates to fields like mathematics, chemistry, physics, and geology, while also dividing into specialized areas of study.

The major branches include:

• Zoology: Studies animals, with sub-branches like entomology (insects), herpetology (reptiles and amphibians), ornithology (birds), and ichthyology (fish)
• Botany: Studies plants, including ethnobotany, bryology (mosses), and pteridology (ferns)
• Microbiology: Examines microscopic organisms through bacteriology, protozoology, and virology
• General Branches: Include genetics, ecology, cytology, histology, anatomy, morphology, embryology, pathology, and ethology (animal behavior)

Each of these branches represents a specialized field of study with its own research methods and body of knowledge. However, they all connect to the fundamental principles that unite all of biology.

ACTIVITY: Create a glossary with definitions for each branch of biology shown in the figure. This will help you deepen your understanding of the scope of biological sciences.

Study Tip: Learning the branches of biology isn't just about memorizing terms—it's about understanding how scientists organize the vast study of life into manageable, specialized fields. This helps you see how different aspects of biology connect to form a complete picture.

The Scientific Method

The goal of science is to explain observed phenomena and establish principles that help predict relationships between various natural events. These explanations come through an organized approach called the scientific method, though it's not a rigid set of rules that apply to all sciences.

One fundamental principle of the scientific method is rejecting authority—never accepting something as true just because someone claims it is. Scientists remain skeptical and require independent confirmation of observations.

The scientific method involves asking questions and seeking answers based on experiments and observations. The foundation of this method is careful, precise observation, ideally conducted with controlled experiments that minimize variables.

Based on these observations, scientists develop hypotheses about what they've observed. These educated guesses can then be tested through additional experiments. When a hypothesis is supported by many different observations and experiments, it may develop into a theory—a generally accepted scientific principle that explains phenomena.

Characteristics of Living Things

Though the line between living and non-living can be blurry (viruses show some characteristics of life but not all), living organisms typically share these key traits:

1. Specific Organization: Living things have characteristic forms with cells as their basic structural unit. While non-living things may have any shape or size, organisms of each species have predictable forms. The cell itself is organized, with cells forming tissues, tissues forming organs, and organs forming systems.

2. Metabolism: All cells constantly change through acquiring and chemically modifying substances. Metabolic processes can be anabolic (building complex substances and storing energy) or catabolic (breaking down complex substances and releasing energy).

3. Homeostasis: Living things maintain a relatively constant internal environment despite external changes. This includes regulating the volume of blood and extracellular fluids, concentrations of solutes, and many other physiological functions.

4. Growth: True growth involves an increase in the amount of living substance in an organism, either through increasing cell size or number.

Characteristics of Living Things (Continued)

5. Movement: While animal movement is obvious (swimming, running, flying), plant movement is slower but definitely exists. Movement can result from muscle contraction, beating of cilia or flagella, or slow expansion of cellular material. In plant leaf cells, the flowing movement of living matter is called cyclosis.

6. Irritability: Living things respond to stimuli and physical or chemical changes in their immediate environment. Stimuli that can trigger responses include changes in light intensity or direction, temperature variations, pressure changes, sound, and chemical composition of soil or water.

7. Reproduction: This can be as simple as an organism dividing in two or as complex as the production of sperm (male) and eggs (female) that must unite to form a fertilized egg or zygote, which develops into a new organism.

8. Adaptation and Evolution: The ability of organisms to adapt to their environment allows them to withstand environmental changes. Adaptation can involve immediate changes based on cellular irritability or enzyme system responses, while evolution results from long-term selection and mutation processes that are passed to future generations.

No single organism can adapt to all possible environments, which is why species are limited in their distribution by factors like water, light, temperature, food availability, predators, competitors, and parasites.

Think About It: Which characteristic of life do you think is most fundamental? Is it possible to have life without the ability to reproduce or without metabolism? These questions continue to challenge biologists as they explore the boundaries of what we consider "alive."

Reproduction

Reproduction can be very simple, such as when an individual divides into two. In many animals, it requires the production of sperm (male) and eggs (female), and in some plants, the formation of pollen grains (male) and egg cells (female). These reproductive cells, called gametes, must unite to form a fertilized egg or zygote from which the new organism develops.

Adaptation and Evolution

The ability of plants and animals to adapt to their environment is what allows them to survive environmental changes. Adaptation can involve immediate changes that depend on the irritability of cells or enzyme system responses. Evolution, on the other hand, results from long-term selection and mutation processes that pass to subsequent generations.

No single organism can adapt to all possible environments, which is why species have limits to where they can survive. The list of factors that restrict a species' distribution is nearly endless: water availability, light, temperature, food sources, predators, competitors, parasites, and many more.

These eight characteristics—specific organization, metabolism, homeostasis, growth, movement, irritability, reproduction, and adaptation/evolution—collectively define what it means to be alive. While non-living objects may exhibit one or two of these traits (like crystals that appear to "grow"), only living organisms display all of these characteristics working together as an integrated whole.

Connecting Concepts: Notice how these characteristics of life are interconnected. For example, metabolism provides the energy needed for growth, movement, and reproduction, while specific organization makes metabolism possible in the first place!

Evaluation 1

This section tests your understanding of the branches of biology and characteristics of living things.

Part A asks you to match scientific works with the appropriate branch of biology, such as identifying "Flora of Mesoamerica" as a botanical work or "Forest pests in western Guatemala" as entomological research.

Part B presents scenarios that demonstrate various characteristics of living things:

1. Bat pups fleeing from light demonstrates irritability—the ability to respond to stimuli.

2. A pregnant woman feeling fetal movements illustrates movement in living organisms.

3. Cyclosis (rotation of chloroplasts) in aquatic plant cells represents movement at the cellular level.

4. An Acacia plant folding its leaves when touched by an insect shows irritability.

5. Sunflowers tracking the sun involves chemical changes that cause greater growth on the non-illuminated side, demonstrating both irritability and growth.

6. Cell division to heal a coyote's wound represents growth.

7. Fruit flies reproducing with genetic similarity demonstrates reproduction.

8. Siblings born on the same day but with different traits illustrates sexual reproduction.

9. The image shows a type of asexual reproduction.

10. Gas production after eating papaya is an example of metabolism.

Understanding these characteristics helps you recognize what makes something alive versus non-living matter. These fundamental traits apply to all living organisms, from single-celled bacteria to complex plants and animals.

Reminder: When studying the characteristics of life, try to identify examples from your own observations. Can you see evidence of homeostasis, reproduction, or irritability in organisms around you?