Lab 3 Cnidaria Notes PDF

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Summary

Lab notes for Bio 102/Zoology 102 taught by Steffenie Widows...

Description

Part 1: Phylogeny -

General Aspects of Cnidarians and how they relate to Phylogeny - Cnidarians have tissue level of organization. - During development sheets of cells called embryonic germ layers form. - They develop from two primary germ layers - Each layer will eventually give rise to specific tissues. - Called ectoderm and endoderm - Animals that develop from two germ layers are called diploblastic. - Phylogenetically, animals that have tissues belong to the clade Eumatazoa - Nested within the greater clade, Metazoa (all animals) which also includes sponges - Cnidarians exist in two body forms - The polyp is a cylinder-like body with the mouth pointing up and the tentacles waving above - A sea anemone = a polyp - The medusa is a bell-shaped body with the mouth pointing down and the tentacles hanging - This body plan is familiar to jellyfish - Polyps are sessile which means they are stationary - Medusae are free-swimming or free-floating in the open sea - Cnidaria belong to Eumetazoa - Diploblasty - Radial symmetry - Nematocyst - Coral, Anemone and Jellyfish are all types of Cnidarians.

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Part 2: Body Plan & Staying Alive -

Aiptasia -- our model cnidarian polyp - Aiptasia are a type of anemone found on the southern US Atlantic and Gulf coasts from NC to TX and in the coastal Caribbean. - They are poets in home saltwater aquaria

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They reproduce quickly by sexual and asexual means and cen be stressful to other animals, like coral, in aquariums Body Plan -- Symmetry - Cnidarians have radial symmetry - Body is arranged around a central axis so that each part extends from the center. The animal can be cut along the central axis in more than one plane to produce equal halves. Body Plan of Cnidarians vs Body Plan of Sponges - Sponges - Sponges only have cell level of development - Body is made up of two cell layers (each 1 cell thick) - Middle layer is nonliving material - Cnidarians -- Highest Level of Organization = Tissues - Cnidarians have tissue level of organization. During development sheets of cell called embryonic germ layers form - Cnidarians develop from two primary germ layers - Each will eventually give rise to specific tissues - The two germ layers are called ectoderm and endoderm - Animals that develop from two germ layers are called diploblastic Body Plan - Highest Level of Organization = Tissues (Continued) - Cnidarians have true tissues (so do all animals except sponges) - Cnidarians are diploblastic - Embryonic Development: Tells us about animal evolutionary relationships because: - Genes control development, genes of development are highly conserved - What are Tissues? - A group of similar specialized cells that originated together in development and perform a specific function - Early in the life of an embryo, cells move to form layers. A groups of cells in the same layer interact with one another. - Each specific layer of cells develops into specific parts of the completed animal - These layers of cells are called germ layers - All structures of the animal develop from one of these layers - Diploblastic means the animal develops from 2 germ layers of cells - Triploblastic means the animal develops from 3 germ layers. - Embryonic Development and the Formation of Germ Layers

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Germ Layers → Tissue Layers - During development germ layers will eventually develop into tissue layers that make up an animal - Endotherm germ layer develops into the inner tissue layer of animals, this layer is called the Gastrodermis - Ectoderm germ layer develops into the outer

tissue layer of animals, this layer is called the Epidermis Cnidarians have a middle layer called the Mesoglea. This layer is very similar to the middle layer of Sponges Comparison of Body Wall of Porifera and Cnidaria -- Similarities and differences -

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Cnidarian - Outer tissue layer (epidermis) 1 cell layer thick - Inner tissue layer (gastrodermis) 1 cell layer thick - Specialized cells in each layer: epidermis (nematocyst); gastrodermis (ciliated cells and cells that produce enzymes, zooxanthellae if present) - Mesoglea sandwiched between these two layers - NON-LIVING Body Plan -- Organization of Nerve Tissue - Organization of nerve tissue (composed of nerve cells called neurons) - Cephalization - Concentration of neurons in one area in the animal, especially those neurons involved in sensing environment and coordination responses - Often refer to this area as the “head” - If animals are determined to be cephalized, it is often described as a “spectrum” of cephalization - Some animals will be more cephalized than other (i.e. humans are more cephalized than worms) - No Cephalization -- Cnidarians Have - No centralized concentration of neurons - Neurons are widely dispersed throughout the body, referred to as a Nerve Net - In Cnidarians, sensory cells are able to perceive chemical, light and touch stimuli Body Plan -- Shape, Support and Movement - Aiptasia move parts of their body, but generally do not move their whole bodies around much - Cnidarians have more complexity within their body than sponges - Part of this complexity is that they have muscles - There are two things muscles can do and one they can’t

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Muscles can contract when stimulated by nerves, causing muscles to shorten - Muscles can relax and be lengthened if an opposing force stretches them - Muscles cannot be stimulated to lengthen. Once oncracted (shortened) muscles need to relax and another force needs to stretch them so they can return to their original shape. - This is why antagonistic muscles are needed In Cnidarians, the antagonists are circular muscles, which encircle the fluid filled cavity and longitudinal muscles, which run lengthwise along the fluid filled cavity.

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Circular muscles: encircle

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longitudinal muscles: run lengthwise

Animal body wall with both

Muscles apply various types of pressure on the body of animals. - How do you think circular and longitudinal muscles may change the shape of a water balloon? - Circular muscles would make them longer and thinner - Longitudinal muscles would return to normal size - Cnidarians use longitudinal and circular muscles to move. - Cnidarians have a fluid filled system - Skeletal structure known as Hydrostatic Skeleton - Hydrostatic Skeleton - Any change in the pressure applied to an enclosed, non compressible fluid is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel. - Requirements - Enclosed cavity with fluid that can not be compressed - Volume of the fluid must remain constant - Antagonistic muscles surrounding the cavity - Stimulation by the nervous system - Must have a flexible outer membrane - Sea anemones are just one of the animals that rely on a hydrostatic skeleton in which force of muscle contraction is transmitted by internal water pressure - In animals, a body part must act as their hydrostatic skeleton. - For Cnidarians, the fluid filled cavity that acts as the hydrostatic

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skeleton is a part known as the gastrovascular cavity (GVC) - The GVC is a sack within Cnidarians that makes up the majority of its internal body space - When the anemone’s mouth is closed, it becomes a closed cavity - GVC Meeting Requirements of a Hydrostatic Skeleton - Enclosed cavity with fluid that can not be compressed - GVC, water is noncompressible - Volume of the fluid must remain constant - Mouth can be closed, volume in GVC is constant - Antagonistic muscles surrounding the cavity - Cnidarians have Antagonistic Muscles: Circular and Longitudinal - Stimulation by the nervous system - Cnidarians have a Nerve Net - Must have a flexible outer membrane - Cnidarians do not have a hard outer skeleton or shell. They have a body wall that is flexible Tasks of Staying Alive: Getting Nutrients - Cnidarians are able to snag prey using a specialized structure called a nematocyst, which is a barbed, venomous coiled thread-like structure, within the cells of the body wall - They can be expelled in self-defense or to capture prey - Once captured by nematocysts, the food is brought into the mouth and then into the GVC. - The GVC not only acts as the hydrostatic skeleton, but it also aids in the process of getting and digesting nutrients - Nematocysts are what “sting” you when you come in contact with a jellyfish or anemones. - They are found in two parts of anemones: - Within the tentacles - Helps anemones catch prey, as the nematocysts immobilize their food so they can subsequently ingest it - In acontia - Acontia are white, threadlike substances that anemones shoot out when they are threatened or disturbed. This helps protect anemones from being eating - Acontia is full of nematocysts - Nematocysts are triggered by chemical and mechanical stimuli

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Fired Nematocysts - The barbed ends penetrate and attach to prey. The barns inject toxins - Aiptasia’s toxins do not affect humans, but there are some cnidarians that are deadly to humans, like the box jellyfish Prey contacts the tentacles and it is seized by discharged nematocysts - Chemicals coming from the wounded prey cause the anemone to open its mouth, bend tentacles to mouth and stuff the prey inside through the mouth and then into the Gastrovascular Cavity

Feeding Strategy - Cnidarians have an active suspension feeding strategy like sponges - They wait for their food to come to them which also makes them suspension feeders. - Cnidarians are mostly sessile (immobile), so catching food is not always possible -- they must wait for the ocean current to bring food to them -making them passive - As a result, many Cnidarians established a symbiotic relation with a photosynthetic algae known as Zooxanthellae - Symbiosis is a relationship between two or more organisms that live closely together - In addition to ingesting prey, many cnidarians are symbiotically associated with populations of single-celled marine algae called zooxanthellae, which they house in their tissues - These algae transfer photosynthetically derived, energy-rich molecules to the host, in return for access to nitrogen, phosphorus and other nutrients derived from host metabolism -- as well as a place to live sequestered from the environment where there are other living things that would eat them - This is an example of a mutualistic symbiotic relationship -- both cnidarian and the zooxanthellae benefit - Zooxanthellae are single-celled, photosynthetic algae that belong to the group Symbiodinium - Aitapsia and the zooxanthellae have a symbiotic relationship in which both organisms benefit - Some of the products of the algae photosynthesis are used by the

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anemone for food - The anemone provides the algae with a protected environment and the inorganic nutrients they use for photosynthesis - Zooxanthellae have two very important roles for Cnidarians - They provide a 70-90% of anemone’s nutrition - They also give anemone its color Like all animals, Cnidaria are heterotrophs; they need to get nutrition (organic molecules) from other forms of life Steps of Getting Nutrients to Cells for Energy - 1. Obtaining Food - Two main ways in Aiptasia - 2. Digesting Food (breaking it down chemically) - The food the anemone ingests is composed of large organic molecules which must be broken down into smaller organic molecules. - Enzymes are required in order for these chemical reactions to occur efficiently - After entering the mouth, the food is moved to the Gastrovascular Cavity - The food is initially digested outside of the cells - The inner layer of tissue in the GVC secretes the enzymes that break down the large molecules into smaller ones - Individual cells then bring the nutrients inside where digestion is completed - 3. Distributing it to all parts of the body - In humans, the nutrients are distributed from our digestive tract to all parts of the body by our circulatory system composed of a heart, vessels and blood - Cnidarians don’t have these structures but they do have a structure that branches from the site of digestion to all parts of the body - The Gastrovascular Cavity - GVC is a system of canals that extends into tentacles. It is ciliated - Fluid containing partially digested food is distributed to all parts of body - Individual cells engulf and digest food - Also functions as hydrostatic skeleton - 4. Getting rid of indigestible material (feces) - Cnidarians have an incomplete digestive tract - One opening serves as mouth and anus - Food in and undigested material (feces) out the same

opening - GVC vs Complete Digestive Tract -

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Relationship Between: Symmetry, Mobility, Cephalization and Sophistication of Nervous System, and Feeding Strategy - The body plan of a group of animals is a combination of adaptation and constraints - The available architecture of a body plan is related to how a group of animals performs the tasks needed to stay alive and to the lifestyle of the animals Gas Exchange and Excretion of Waste (ammonia) - Cells need oxygen for metabolism that creates energy for cells, in the process they produce carbon dioxide - Food + Oxygen → ATP + Carbon Dioxide + Water - Cells digest protein and produce nitrogenous waste - Protein → amino acids → ammonia (toxic nitrogenous waste) -

Gas Exchange - Cells need oxygen, need to get rid of carbon dioxide Excretion of Nitrogenous Waste: - Get rid of ammonia Every cell is on a surface in direct contact with water either in the surrounding environment or in the GVC - Diffusion works efficiently across the body without the need of specialized gas exchange structures as long as diffusion distance to every cell is small - It is only effective over short distances - In cnidarians, every cell is in direct contact with water, either in the surrounding environment or in the GVC, it can occur without any specialized structures in cnidarians - Oxygen moves from water into cells - Carbon Dioxide and ammonia move from cells into the water

Part 3: Coral Bleaching -

Cnidaria Diversity: Coral - What is the relationship between Coral Colony, Coral Polyp and Coral Reef?

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A single coral polyp makes up a coral colony. Many coral colonies make up a coral reef

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Coral colonies are made up of genetically identical polyps. Polyps reproduce asexually, where a new offspring will bud off the parent. - In hard corals, colonies share a calcium carbonate skeleton Coral Reef: Many Colonies of Coral - Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by colonies of corals. Although the individual coral animals are small, reefs can be very large. They are built upon many generations of dead coral Coral Reef Locations - Reef-building corals are typically located in tropical and subtropical waters between 30 degrees North and 30 degrees South latitudes - Generally corals need shallow, sunlit and clear water to survive - They also need warm water. - Though different species of coral can withstand different amounts of temperature fluctuations, most corals survive in temperatures ranging from 64 degrees C to 85 degrees C Coral Reef Significance - Coral reefs represent some of the most magnificent living systems - They are diverse and valuable ecosystems - They support more species per unit area than any other marine environment - They support over 25% of all known marine species and are home to over 4,000 different species of fish, 800 species of coral and thousands of other plants and animals. - Scientists estimate that there may be another 1-8 million undiscovered species of organisms living in and around reefs - Coral reefs provide food, jobs, income and protection to billions of people worldwide - They serve as a buffer, protecting inshore areas from the pounding of ocean waves

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Without them, many beaches and buildings would become vulnerable to wave action and storm damage. - The beauty of reefs draws tourists - Although coral reefs are some of the most important global ecosystems, they are under incredible threats by Coral Bleaching. Value of Reefs: Biologically and Economically Valuable Ecosystems - Biodiversity: - One of the most diverse and valuable ecosystems on Earth - Less than 1% of Earth’s surface, at least 25% of marine life, foundations of food web - Coastal Protection: - Buffres coast from currents, waves and storms preventing loss of life, property and erosion - Fisheries: - At least 500 million people rely on coral reefs for food, coastal protection and livelihoods - Medical Advances - Important sources of new medicines being developed - Tourism and Recreation/Economic Development - At least 94 countries and territories benefit from reef tourism. - In 23 of these, reef tourism accounts for more than 15% of gross domestic product Natural Stresses on Reef -- Coral Reefs May Recover from Periodic Traumas Caused by Weather and other Natural Occurrences - Storms, Cyclones, Hurricanes - El Nino or other weather pattern that increases sea surface temperatures, decreases sea level, increases salinity - Predation: fish, marine worms, barnacles, crabs, snail sea stars - The fourth recorded outbreak of crown of thorns starfish is currently underway and is eating corals which survived recent bleaching events - Nutrient enrichment from agricultural land runoff may lead to these outbreaks because elevated nutrient levels cause phytoplankton blooms which provide a necessary food source for the starfish larvae Anthropogenic (Caused/Influenced by Humans) Stresses on Reef -- Coral Reefs may Recover from Periodic Traumas Caused by Weather and other Natural occurrences - Climate Change - Warmer ocean and increased acidity - Destructive fishing practices

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- Overfishing - Pollution - Sedimentation - Erosion caused by construction, mining, logging and farming increase sediment runoff that “smothers” corals - Careless tourism and recreational impacts - There have been three mass global bleaching events: 1998, 2010 and 2015-2017 Symbiotic Relationship Between Coral and Zooxanthellae - Corals that build reefs have the same relationship with the zooxanthellae as Aiptasia - Coral bleaching = when corals are stressed by changes in conditions such as temperature, light or nutrients, they expel the symbiotic algae living in their tissues. Great Barrier Reef as Example - Actually about 3,000 reefs covering 1,400 miles - 450 species of hard corals - 150 species of soft corals - 100 species of jellyfish - 30% of Australia’s sponge species - Over 1600 fish species - 3000 species of molluscs - 630 species of starfish - 14 breeding species of sea snakes - 6 of the worlds 7 species of marine turtles - 30 species of whales and dolphins - One of the world’s most important dugong populations - 1333 species of sharks and ray - And much more 2016 and 2017: Great Barrier Reef Bleaching - 2016 - Northern portion Severely Bleached - Northern Portion = 67% dead - 2016 mortality overall Great Barrier Reef 30% dead - 2017 - Central portion severely bleached - Overall death = 19% - For Total Back-to-Back Bleaching Event - ⅔ reef bleached, 50% of reef dead Telling the Story of Bleaching and Climate Change - The greenhouse effect is a natural process that warms the Earth’s surface. - When the sun’s energy reaches the Earth’s atmosphere, some of it is

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reflected back to space and the rest is absorbed and re-radiated by greenhouse gases - Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, ozone and some artificial chemicals such as chlorofluorocarbons (CFCs) - This absorbed energy increases the Carbon Dioxide Concentration on the earth - Greenhouse Gases - 29% Transportation - 28% Electricity - 22% Industry - 13% Commercial & Residential - 9% Agricultu...