Biology Exam 2: Chapters 9-12

• Study notes for Biology Exam 2 covers topics from Chapters 9, 10, 11 and 12.

Chapter 9: Sponges and Cnidarians

Sponge Symmetry and Organization

• Sponges exhibit asymmetrical or superficially radial symmetry.
• The general organization includes an outer epithelial layer, a canal system lined by cells that move and filter water, and epithelial-lined spaces forming exit pathways.

Sponge Body Wall Layers

• Pinacoderm (pinacocytes): The outer body wall consisting of thin, flat, tightly connected cells.
• Mesohyl: A collagenous layer beneath the pinacoderm.
• Ostia: Openings that function as inlets for water into the sponge body.
• Choanoderm (choanocytes): The inner epithelial layer with flagellated cells that have collar-like rings of microvilli surrounding a flagellum.
• Oscula: External openings where water circulated by choanocytes is expelled.

Sponge Skeleton and Body Forms

• The sponge skeleton primarily consists of spicules and spongin.
• General body forms: ascon (least complex), sycon, and leucon (most complex).
• Ascon: vase-like body form.
• Sycon: body wall appears folded.
• Leucon: extensively branching canal system.

Sponge Feeding, Waste Removal, and Reproduction

• Choanocytes filter small, suspended food particles; food is trapped on the collar, moved along microvilli to the base, and enclosed in a food vacuole.
• The primary waste product is nitrogenous waste, mainly ammonia.
• Sexual reproduction: Sponges are monoecious, with sperm and egg production occurring at different times; choanocytes form sperm and eggs via meiosis, fertilization occurs in the ocean, and planktonic larvae develop before settling.
• Asexual reproduction includes gemmule formation (containing amoeboid archeocytes) and regeneration from cut or broken pieces.

Cnidarian Symmetry, Layers, and Cells

• Cnidarians have radial or modified biradial symmetry.
• They are diploblastic, meaning cells derive from two embryological layers.
• The ectoderm gives rise to the epidermis, and the endoderm forms the gastrodermis.
• Cnidocytes: Epidermal and/or gastrodermal cells with cnidae used for attachment, defense, and feeding.
• Nematocysts: A type of cnida used in food gathering and defense, discharging a tube armed with spines that penetrate prey and deliver toxins.

Cnidarian Body Forms, Nervous System, and Reproduction

• Cnidarians exhibit alternation of generations, possessing two body forms: medusa and polyp.
• They have a nerve net nervous system.
• Large surface-area-to-volume ratios facilitate oxygen, carbon dioxide, and nitrogenous waste exchange via diffusion.
• Reproduction involves sperm and eggs released into the gastrovascular cavity or outside the body; a blastula forms, surface cells migrate inward to form the gastrodermis, and the embryo elongates into a ciliated, free-swimming larva (planula). The planula attaches and develops into a polyp, while medusae form by budding from the polyp body wall.

Box Jellyfish Venom

• Box jellyfish venom causes potassium ion leakage from cells, potentially leading to heart failure.

Chapter 10: Platyhelminthes (Flatworms)

Unique Features and Body Wall

• Platyhelminthes are the first phylum to have organ level organization.
• The body wall has an outer layer of circular and an inner layer of longitudinal muscle.

Glandular Cells

• Rhabdites: Rod-like cells that swell and form a protective mucous sheath around the body.
• Adhesive glands: Produce chemicals for attachment to the substrate.
• Releaser glands: Secrete chemicals that dissolve attachments.

Digestion, Respiration, and Excretion

• Platyhelminthes exhibit incomplete digestion with only one opening serving as both mouth and anus.
• Respiratory gases and metabolic wastes are exchanged via diffusion.
• Protonephridia function by using cilia in flame cells to drive fluid, creating negative pressure, sucking fluids from tissues, and emptying them outside via nephridiopores.

Nervous System and Reproduction

• Turbellarians have sensory, motor, and association nervous tissue types.
• Asexual reproduction occurs through transverse fission.
• Turbellarians are hermaphroditic, possessing both male and female reproductive organs.
• Cross-fertilization occurs to maintain genetic diversity.

Class Trematoda (Flukes)

• Consists of flatworms which are mostly parasites of vertebrates.
• The outer layer of the body wall is called the tegument/epidermis.

Tegument Organization

• Syncytium: Continuous layer of fused cells.
• Has an organic layer of proteins and carbohydrates (glycocalyx) as its outer zone.

Subclass Digenea

• Organisms in this subclass tend to parasitize bloodstreams, digestive tracts, and ducts of digestive organs.
• The larva is called miracidium which swims until it finds the first host which is a snail.
• It develops into a sporocyst.
• Finds a second intermediate or final host.

Class Cestoidea (Tapeworms)

• Organisms in this class take in nutrients directly through the body wall.
• Repeating units are called proglottids which contain one or two complete sets of reproductive structures.
• Proglottids is a self-sufficient reproducing unit with all of the sexual organs necessary to reproduce.

Cestoidea Body Regions

• Three body regions: scolex, neck, and strobila.
• Scolex: A holdfast that contains circular or leaflike suckers or hooks.
• Neck: Region directly behind scolex that connects to body.
• Strobila: The body region of tapeworm, series of linearly arranged proglottids.

Chapter 11: Molluscs

Main Mollusc Regions

• Head-foot region contains the head, mouth and certain nervous and sensory structures, the foot is used for attachment and locomotion.
• Visceral mass contains the organs of digestion, circulation, reproduction, and excretion.

Mollusc Shell Layers

• Periostracum: The outer layer secreted by mantle cells containing protein.
• Prismatic layer: The thickest middle layer made of calcium carbonate and organic materials.
• Nacreous layer: The innermost layer made of calcium carbonate sheets alternating with organic matter.

Radula

• A rasping structure with curved teeth on a chitinous belt used for scraping or cutting food.

Class Gastropoda

• Consists of snails, limpets, slugs.

Torsion

• 180° counterclockwise twisting of the visceral mass, mantle, and mantle cavity.
• Significance: Head enters first for protection.

Gastropod Feeding and Circulatory System

• Utilize radula or muscles for feeding.
• Open circulatory system where blood leaves vessels and bathes cells.
• The heart consists of a single, muscular ventricle and two auricles.

Gas Exchange and Waste Removal

• Gas exchange involves the mantle cavity with one or two gills.
• Land snails do not have gills or have reduced gills.
• Nephridium modifies wastes by reabsorbing ions and molecules.
• Land gastropods convert ammonia to uric acid (less toxic and conserves water on excretion).

Bivalves

• Main feature is two convex halves of the shell (valves).
• The dorsal margin has a proteinaceous hinge and teeth modifications.
• Umbo is the oldest part of the shell.
• The valves open when muscles relax
• Adductor muscles close the shell.

Pearl Formation

• Sand grain or a parasite lodges between the shell and the mantle, → nacre secretion → a pearl.

Gill Function and Feeding in Bivalves

• Gills form a folded sheet.
• Water tubes allow blood and water to be close for gas exchange.
• Gills trap food particles brought into the mantle cavity.
• Cilia move trapped food particles to the mouth.

Bivalve Fertilization

• Most bivalves utilize external fertilization: gametes exit through suprabranchial chamber of mantle cavity and the exhalant opening.

Cephalopods Jet Propulsion

• The mantle contains radial and circular muscles.
• Circular muscles contract and decrease the volume of the mantle cavity, valves prevent water from leaving.
• Water is forced out a narrow siphon.

Cephalopod Venom

• Almost all studied cephalopods are venemous.
• Venom is ejected from salivary glands onto or into prey.

Cephalopod Circulatory System

• Closed circulatory system contains blood in a collection of blood vessels (different from other mollusks).

Cephalopod Hunting

• Cephalopods find prey using eyes.

Cephalopod Features

• Chromatophores: pigment cells in mantle and body wall (muscles contract and alter size of chromatophores → color change).
• Ink glands: Allows escape from predator due to predator confusion.

Cephalopod Reproduction

• Utilizes a hectocotylus: during reproduction tentacles intertwine and the modified arm is inserted into the mantle cavity near the oviduct to release a spermatophore.

Chapter 12: Annelids

Metamerism

• Segmental arrangement of body parts in an animal.

Advantages of Segmentation

• Creation of hydrostatic compartments → enhanced locomotor and supportive functions.
• Lessened impact of injury.
• Tagmatization allows for specialization of body regions.

Parapodia

• Lateral extensions on each segment used for locomotion and holding the worm in place.

Annelid Gas Exchange

• Respiratory gases diffuse across the body wall.
• Parapodia increase surface area for these exchanges.

Annelid Circulatory System

• Closed circulatory system.
• Oxygen is carried in combination with respiratory pigments in plasma.
• Dorsal aorta propels blood from rear to front.
• Ventral aorta moves blood from front to rear.

Annelid Senses

• Vary degrees of light sensitivity to varying degrees (react negatively - helps avoid predation).

Annelid Waste

• Earthworms secrete urea as opposed to ammonia (less toxic nitrogenous waste).