22.2 Basic Needs, Classification, Plant Structures & Human Body Systems

Overview & Exam Relevance

Competency 011 (Structure and Function of Living Things) asks you to understand that organisms have basic needs, that structure complements function at every level (cells, tissues, organs, organ systems, and organisms), and the human body systems and their functions. It also covers the relationship between an organism's characteristics and structures and its taxonomic classification. This section covers basic needs, classification of living things, plant structures, and human body systems; cells and organelles are covered in the previous section.

---

Basic Needs of Organisms

• Animals need air (oxygen), water, food, and shelter or space.
• Plants need light, water, air (carbon dioxide), nutrients (minerals), and space.
• A common misconception is that plants need soil. Plants need the water and minerals soil provides, and they can grow hydroponically in mineral-rich water.
• Fungi need moisture and a food source to break down, since they cannot make their own food.

---

Classifying Living Things

Scientists group organisms by shared characteristics and evolutionary relationships. Carl Linnaeus (1700s) introduced binomial nomenclature, the two-part scientific name of genus plus species (Homo sapiens). The classification levels, from broadest to most specific, are domain, kingdom, phylum, class, order, family, genus, species.

• Three domains: Bacteria, Archaea (both prokaryotes), and Eukarya (organisms whose cells have a nucleus).
• Eukaryotic kingdoms commonly taught: animals, plants, fungi (mushrooms, yeasts, and molds absorb nutrients from their food and are not plants because they lack chlorophyll), and protists (mostly single-celled, such as amoebas and algae).

Vertebrates: Animals with Backbones

Invertebrates: Animals Without Backbones

The great majority of animal species are invertebrates. Arthropods have exoskeletons, jointed legs, and segmented bodies. They include insects (three body parts, six legs, usually antennae and wings) and arachnids (two body parts, eight legs, no antennae), so a spider is not an insect. Arthropods also include crustaceans and centipedes. Other groups include mollusks (snails, clams, octopuses), segmented worms (earthworms), cnidarians (jellyfish), echinoderms (sea stars), and sponges.

Plants

---

Plant Structures and Their Functions

• Roots anchor the plant, absorb water and minerals, and sometimes store food (carrots).
• Stems support the plant and transport materials: xylem carries water and minerals up from the roots, and phloem carries sugars made in the leaves to other parts.
• Leaves carry out photosynthesis. Tiny pores called stomata let carbon dioxide in and oxygen and water vapor out.
• Flowers are reproductive structures. The stamen (anther and filament) produces pollen, and the pistil (stigma, style, and ovary) receives pollen and contains the ovules.
• Fruits protect seeds and help disperse them, and seeds contain an embryo, stored food, and a protective seed coat.

---

Hierarchical Organization of Multicellular Life

Multicellular organisms are not amorphous agglomerations of identical cells; they display an intricately coordinated structural hierarchy. Each level of organization exhibits emergent properties—novel characteristics that arise from the collaborative interactions of its component parts that do not exist in the isolated components alone.

THE MULTICELLULAR HIERARCHY

  ┌────────────────────────────────────────────────────────┐
  │ 1. CELL (Basic structural and functional unit of life) │
  │    E.g., Cardiac muscle cell, leaf mesophyll cell      │
  └───────────────────────────┬────────────────────────────┘
                              ▼
  ┌────────────────────────────────────────────────────────┐
  │ 2. TISSUE (Group of similar cells performing a function│
  │    E.g., Cardiac muscle tissue, palisade mesophyll     │
  └───────────────────────────┬────────────────────────────┘
                              ▼
  ┌────────────────────────────────────────────────────────┐
  │ 3. ORGAN (Structure of multiple tissues working cooper-│
  │    atively; e.g., Heart, Plant leaf)                   │
  └───────────────────────────┬────────────────────────────┘
                              ▼
  ┌────────────────────────────────────────────────────────┐
  │ 4. ORGAN SYSTEM (Group of organs collaborating for an  │
  │    overarching physiological process; e.g., Circulatory│
  └───────────────────────────┬────────────────────────────┘
                              ▼
  ┌────────────────────────────────────────────────────────┐
  │ 5. ORGANISM (The integrated, living multicellular entity│
  │    E.g., Human being, Oak tree                         │
  └────────────────────────────────────────────────────────┘

• 1. Cell: The most basic structural and functional unit of living matter capable of independent biochemical life (e.g., motor neuron, erythrocyte, root hair cell).
• 2. Tissue: A coordinated group of specialized cells with common embryonic origin and morphology working collectively to execute a specific task. In animals, the four primary tissue types are epithelial (protective linings), connective (bone, blood, adipose, cartilage), muscle (skeletal, cardiac, smooth), and nervous (neurons, glial cells). In plants, the three primary tissue systems are dermal (protective epidermis), ground (parenchyma, collenchyma, sclerenchyma for storage and photosynthesis), and vascular (xylem for water/minerals, phloem for photosynthate sugars).
• 3. Organ: A distinct anatomical structure composed of two or more integrated tissue types that perform complex physiological tasks (e.g., the animal stomach, composed of epithelial mucosa, smooth muscle tissue, connective tissue, and autonomic nervous tissue; or the plant leaf, composed of dermal epidermis, photosynthetic mesophyll ground tissue, and vascular veins).
• 4. Organ System: An assemblage of organs that function cooperatively to execute overarching bodily functions (e.g., digestive system, cardiovascular system, respiratory system; or the plant root system and shoot system).
• 5. Organism: The complete, autonomous living entity exhibiting homeostatic self-regulation and reproduction.

---

Human Organ Systems and Physiological Interdependence

Under Competency 011, prospective teachers must possess a thorough understanding of the major organ systems of the human body and their vital interdependence—the reality that no human organ system operates in isolation.

Primary Human Organ Systems

• Circulatory (Cardiovascular) System: Composed of the muscular four-chambered heart, blood vessels (high-pressure muscular arteries, thin-walled permeable capillaries, and low-pressure veins with one-way valves), and blood (plasma, erythrocytes, leukocytes, platelets). It transports oxygen, glucose, amino acids, hormones, and immune cells to somatic tissues, while removing carbon dioxide, urea, and metabolic heat.
• Respiratory System: Encompasses the nasal cavity, pharynx, larynx, trachea, primary and secondary bronchi, bronchioles, and microscopic alveoli within the lungs. Facilitates gas exchange: inhaled atmospheric oxygen diffuses across the thin, moist alveolar-capillary respiratory membrane into erythrocytes, while metabolic carbon dioxide diffuses from plasma into alveoli for exhalation.
• Digestive System: Comprises the gastrointestinal tract (oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum) and accessory digestive glands (salivary glands, liver, gallbladder, pancreas). Mechanically masticates and chemically cleaves macromolecular carbohydrates, proteins, and lipids into monomers (glucose, amino acids, fatty acids), absorbing them across intestinal microvilli into circulatory capillaries and lymphatic lacteals.
• Musculoskeletal System: Formed by the union of the skeletal system (206 bones, articular cartilage, ligaments, and joints) and the muscular system (skeletal muscles attached to bones via inelastic fibrous tendons, cardiac muscle of the heart, and involuntary smooth muscle within visceral organs). Together, they provide structural support, protect delicate vital organs (cranium protecting the brain, ribcage shielding thoracic organs), store calcium and phosphorus, house hematopoiesis in red bone marrow, and execute locomotion.
• Nervous System: Comprises the Central Nervous System (brain and spinal cord) and Peripheral Nervous System (cranial nerves, spinal nerves, sensory receptors, autonomic ganglia). Transmits rapid electrochemical impulses (action potentials) via neurons to perceive sensory stimuli, coordinate reflex arcs, formulate cognitive decisions, and regulate voluntary and involuntary motor actions.
• Excretory (Urinary) System: Composed of the bilateral kidneys, ureters, urinary bladder, and urethra. Functional microscopic nephrons in the kidneys filter blood under hydrostatic pressure, reabsorb water, glucose, and essential electrolytes, and concentrate toxic nitrogenous metabolic wastes (urea, uric acid, creatinine) into urine to maintain systemic osmotic and acid-base homeostasis.
• Endocrine System: A distributed network of ductless glands (pituitary, hypothalamus, thyroid, parathyroids, adrenals, pancreatic islets of Langerhans, ovaries, and testes) that synthesize biochemical messenger molecules (hormones) secreted directly into the bloodstream to regulate metabolism, somatic growth, electrolyte balance, stress responses, and sexual maturation over sustained timescales.
• Immune and Lymphatic System: Encompasses lymphatic vessels, lymph nodes, the spleen, thymus, bone marrow, and specialized white blood cells (phagocytic neutrophils and macrophages, antibody-producing B lymphocytes, and cytotoxic T lymphocytes). Identifies, neutralizes, and eliminates pathogenic viruses, bacteria, protozoa, and malignant neoplastic cells.

System Interdependence in Action: The Exercise Homeostatic Response

A classic scenario tested on the TExES 391 involves analyzing how multiple human body systems coordinate their actions in response to a physiological challenge, such as sustained athletic exercise:

1. Musculoskeletal Demand: Contracting skeletal muscle fibers consume cellular ATP at an accelerated rate, depleting intracellular glucose and oxygen reserves while releasing massive quantities of metabolic carbon dioxide ($CO_2$) and thermal heat.
2. Nervous System Detection: Chemoreceptors located in the carotid arteries, aortic arch, and medulla oblongata detect elevated arterial carbon dioxide concentrations and falling blood pH (carbonic acid formation).
3. Respiratory and Circulatory Interdependence: The respiratory control center in the brainstem stimulates the diaphragm and intercostal muscles to increase ventilation rate and respiratory depth, rapidly exhausting carbon dioxide and oxygenating blood. Concurrently, the autonomic nervous system stimulates the sinoatrial node of the heart to increase cardiac output (elevating stroke volume and heart rate), while causing systemic vasodilation in skeletal muscles and vasoconstriction in digestive organs, rapidly shuttling oxygenated blood and glucose to working muscles.
4. Endocrine and Integumentary Coordination: Adrenal glands secrete epinephrine to accelerate glycogenolysis (glucose release) in the liver, while the nervous system activates dermal sweat glands to dissipate metabolic heat via evaporative cooling, preventing hyperthermia.