🐇Honors Biology Unit 15 – Animal Structure & Reproduction

Key Concepts

• Animals are multicellular eukaryotic organisms that are heterotrophic, meaning they obtain energy by consuming other organisms
• Animal cells lack cell walls, which allows for greater flexibility and movement compared to plant cells
• Animals exhibit a wide range of body plans, from simple sponges to complex vertebrates with specialized organ systems
• Tissues are groups of cells with similar structure and function that work together to perform specific roles in the body
• Organs are composed of multiple tissue types that collaborate to carry out complex functions
• Organ systems are groups of organs that work together to maintain homeostasis and support life processes
• Sexual reproduction involves the fusion of haploid gametes (sperm and egg) to produce a diploid zygote
• Asexual reproduction occurs when an organism produces genetically identical offspring without the fusion of gametes
• Embryonic development is the process by which a fertilized egg (zygote) develops into a multicellular organism with specialized tissues and organs

Animal Body Plans

• Asymmetry is the simplest body plan, lacking any plane of symmetry (sponges)
• Radial symmetry is a body plan with multiple planes of symmetry arranged around a central axis (jellyfish, sea anemones)
• Bilateral symmetry is a body plan with a single plane of symmetry, dividing the body into left and right halves (most animals)
• Cephalization is the concentration of sensory and nervous tissue at the anterior end of the body, forming a head region
• Segmentation is the division of the body into repeating units along the anterior-posterior axis (earthworms, insects, vertebrates)
• Coelom is a fluid-filled body cavity that separates the digestive tract from the body wall
  • Acoelomates lack a coelom (flatworms)
  • Pseudocoelomates have a body cavity that is not completely lined with mesoderm (roundworms)
  • Coelomates have a true coelom completely lined with mesoderm (mollusks, annelids, arthropods, echinoderms, chordates)

Tissue Types and Functions

• Epithelial tissue covers body surfaces, lines cavities, and forms glands
  • Simple epithelium consists of a single layer of cells (squamous, cuboidal, columnar)
  • Stratified epithelium consists of multiple layers of cells (keratinized, transitional)
• Connective tissue supports and connects other tissues, providing structural and functional support
  • Loose connective tissue includes adipose tissue (fat storage), areolar tissue (binding), and reticular tissue (framework)
  • Dense connective tissue includes regular (tendons) and irregular (dermis) types
  • Specialized connective tissues include cartilage, bone, and blood
• Muscle tissue is responsible for movement and consists of cells called muscle fibers
  • Skeletal muscle is voluntary and striated, attached to bones via tendons
  • Smooth muscle is involuntary and non-striated, found in walls of internal organs
  • Cardiac muscle is involuntary, striated, and found only in the heart
• Nervous tissue is specialized for receiving stimuli and conducting electrical impulses
  • Neurons are the functional units of the nervous system, consisting of a cell body, dendrites, and an axon
  • Glial cells support and protect neurons, providing insulation, nutrition, and maintenance

Organ Systems Overview

• Integumentary system consists of the skin, hair, nails, and exocrine glands, providing protection, temperature regulation, and sensory reception
• Skeletal system includes bones, cartilage, and ligaments, providing support, protection, and movement
• Muscular system consists of skeletal, smooth, and cardiac muscle, responsible for movement, posture, and circulation
• Nervous system includes the brain, spinal cord, and peripheral nerves, coordinating and controlling body functions
• Endocrine system consists of glands that secrete hormones, regulating growth, development, and homeostasis
• Cardiovascular system includes the heart, blood vessels, and blood, transporting oxygen, nutrients, and waste products throughout the body
• Lymphatic system consists of lymph nodes, vessels, and organs, maintaining fluid balance and defending against pathogens
• Respiratory system includes the lungs, trachea, and associated structures, facilitating gas exchange between the air and blood
• Digestive system consists of the mouth, esophagus, stomach, intestines, and associated glands, processing food and absorbing nutrients
• Urinary system includes the kidneys, ureters, bladder, and urethra, filtering blood and eliminating waste products
• Reproductive system consists of gonads and associated structures, producing gametes and supporting reproduction

Reproductive Strategies

• Sexual reproduction involves the fusion of male and female gametes, resulting in genetic variation among offspring
  • Advantages include increased genetic diversity and the potential for rapid adaptation to changing environments
  • Disadvantages include the need to find a mate and the energy cost of producing gametes
• Asexual reproduction occurs when an organism produces genetically identical offspring without the fusion of gametes
  • Advantages include rapid population growth and the ability to reproduce in the absence of a mate
  • Disadvantages include reduced genetic diversity and increased vulnerability to environmental changes
• Parthenogenesis is a form of asexual reproduction in which an unfertilized egg develops into a new individual (some insects, reptiles)
• Budding is a form of asexual reproduction in which a new individual grows from the body of the parent organism (hydra, yeast)
• Fragmentation is a form of asexual reproduction in which an organism splits into multiple pieces, each capable of growing into a new individual (planaria, starfish)
• Hermaphroditism is a reproductive strategy in which an individual possesses both male and female reproductive organs (earthworms, snails)
  • Simultaneous hermaphrodites can produce both sperm and eggs at the same time
  • Sequential hermaphrodites change sex during their lifetime, starting as one sex and later transitioning to the other

Mating and Fertilization

• External fertilization occurs when gametes are released into the environment, and fertilization takes place outside the body (most aquatic animals)
  • Advantages include the potential for a large number of offspring and reduced parental investment
  • Disadvantages include increased exposure to predators and environmental hazards
• Internal fertilization occurs when sperm are deposited inside the female reproductive tract, and fertilization takes place within the body (most terrestrial animals)
  • Advantages include increased protection for developing embryos and the potential for parental care
  • Disadvantages include the need for specialized reproductive structures and behaviors
• Courtship behaviors are used by animals to attract and select mates, often involving visual, auditory, or chemical signals (bird songs, peacock displays)
• Copulation is the physical act of mating, involving the insertion of the male reproductive organ into the female reproductive tract
• Sperm competition occurs when sperm from multiple males compete to fertilize a female's eggs, leading to adaptations such as increased sperm production and sperm storage organs
• Cryptic female choice is a mechanism by which females can influence the success of sperm from different males, even after mating has occurred (selective sperm uptake, differential sperm storage)

Embryonic Development

• Cleavage is the rapid series of cell divisions that occur after fertilization, resulting in a solid ball of cells called a morula
• Blastulation is the formation of a hollow ball of cells called a blastula, with an inner cavity (blastocoel) and an outer layer of cells (blastoderm)
• Gastrulation is the process by which the blastula reorganizes into a three-layered structure called a gastrula, with an inner layer (endoderm), middle layer (mesoderm), and outer layer (ectoderm)
  • Endoderm gives rise to the lining of the digestive tract and associated organs (liver, pancreas, lungs)
  • Mesoderm gives rise to connective tissues, muscles, bones, blood, and reproductive organs
  • Ectoderm gives rise to the nervous system, sense organs, and outer layer of the skin
• Neurulation is the formation of the neural tube, which develops into the brain and spinal cord
• Organogenesis is the development of specific organs and tissues from the three germ layers
• Differentiation is the process by which cells become specialized for specific functions, expressing different sets of genes and proteins
• Morphogenesis is the shaping and organization of tissues and organs during development, involving cell migration, adhesion, and communication

Adaptations and Evolution

• Adaptations are traits that enhance an organism's survival and reproductive success in a particular environment
  • Structural adaptations involve changes in body form or function (bird beaks, mammalian fur)
  • Physiological adaptations involve changes in metabolic or biochemical processes (antifreeze proteins in fish, heat tolerance in desert animals)
  • Behavioral adaptations involve changes in an organism's actions or responses to stimuli (migration, courtship rituals)
• Natural selection is the process by which organisms with favorable traits survive and reproduce more successfully than those with less favorable traits
  • Variation within a population provides the raw material for natural selection to act upon
  • Differential survival and reproduction lead to changes in allele frequencies over time
  • Adaptations arise as a result of natural selection favoring traits that improve fitness in a given environment
• Convergent evolution occurs when similar adaptations evolve independently in different lineages facing similar environmental challenges (wings in birds and bats, fins in fish and dolphins)
• Coevolution occurs when two or more species reciprocally influence each other's evolution (flowers and pollinators, predators and prey)
• Sexual selection is a type of natural selection that favors traits that increase an individual's mating success, even if they do not directly improve survival (peacock tail, lion's mane)
  • Intrasexual selection involves competition among members of the same sex for access to mates (male-male combat, territorial defense)
  • Intersexual selection involves the preferential choice of mates by members of the opposite sex based on specific traits (female choice of colorful males)