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I have just discovered that my kitchen sink pipe has been leaking for quite some time (possibly months) which has resulted in water and food deposits collecting in my cupboard.
I smeared some of the residue onto a slide and looked at it under my microscope. I could see a large number of translucent organisms (visible at 40x magnification, they are roughly 100 µm in length). They all appeared to be of the same species although they varied in size and developmental stage. The 'adults' are quite long and look similar to maggots; they scrunch their bodies into balls and then stretch out in order to propel themselves.
Unfortunately I lack the equipment to take a photo of it but here's a rough sketch of what it looks like moving to the right:
Don't take the features too literally.
Can anyone hazard a guess as to what it might be?
It seems like Euglena but I need more parameters than what you have provided.
you can narrow it down by this:
You can find them in commonly found microorganism in kitchen:
What Does Niche Mean in Ecological Biology?
The term niche, when used in the science of ecological biology, is used to define an organism's role in an ecosystem. Not only does its niche include the environment that a given organism lives in, but it also includes the organism's "job" in that environment. A niche may also encompass what the organism eats, how it interacts with other living (biotic) elements, and also how it interacts with the nonliving (abiotic) aspects of the environment, as well.
Types of Organisms
Scientists classify organisms into 3 domains and 6 kingdoms, although this has changed throughout history. There are 3 recognized domains, or broadest classification of organism. These are Bacteria, Archaea, and Eukarya.
In the simplest case, an organism can be a bacteria, a DNA molecule containing genetic information wrapped in a protective plasma membrane. Organisms tend to separate their information molecules from the outside environment, where pH changes and unknown chemicals could do damage to the molecule. Bacteria contain their DNA in a simple ring, and replicate it through a process known as binary fission. The DNA is replicated so that two rings exists, and the cell divides its contents in half, each getting one ring of DNA.
Although bacteria are some of the smallest organisms on Earth, the can produce a huge effect. It is believed that soil bacteria can speed the effects of climate change, and that the bacteria in cow’s guts may be responsible for a large portion of the greenhouse gasses in the atmosphere. Other bacteria help us digest food, and some can make us sick.
The domain Archaea contains bacteria-like organisms that are unrelated to bacteria, and can perform a wide variety of functions. For instance, many archaea live in the most extreme environments on the planet, from hydrothermal vents to lakes so salty that no other life can become established. However, the archaea also exist in most “normal” habitats. It is thought that organisms in the Archaea, Bacteria, and Eukarya branched off from each other in the early history of life on Earth. The Archaea show a high level of antibiotic resistance, and it is thought that they may have evolved in response to a simple antibiotic produced by organisms at the time of divergence.
In a eukaryote, or an organism that has a membrane bound nucleus and organelles, the DNA is contained in the nucleus, and the highly specialized organelles complete the various functions of the cell. Some eukaryotes become highly complex, multi-celled organisms. The individual cells then group into tissues, which form organs. These organs allow large animals like ourselves to move, eat and reproduce. Most organisms that you can think of are eukaryotes.
All eukaryotic life starts as a single cell. The cell divides through the process of mitosis, and becomes many cells. As the cells begin to specialize, they are sent different signals either chemically or electrically, and grow or change as needed. In this way, large organisms can manage the processes of their bodies through the release of chemicals or through the nervous system.
Organisms in the Eukarya include 5 kingdoms: Animalia, Plantae, Fungi, Protozoa and Chromista. The protozoans and chromistans are single-celled organisms that have membrane-bound organelles and nuclei. Fungi includes mushrooms, molds, and yeasts. Plantae is a large and diverse group that contains everything from single-celled algae to the largest organisms on the planet: trees. The Animalia contains most of the typical multi-celled organism that we would see in a zoo.
Some scientists even consider viruses to be organisms, as they are self-replicating information molecules usually protected by a protein shell. The virus then uses the mechanisms of a cell it infects to replicate itself. Proponents of classifying the virus as an organism point this out, while other scientist note that unlike a living organism, the virus does not create or store energy or the mechanisms to do so. While the debate rages on, it is important to note that the definition of life is not static. New evidence is found, methods of observation are created, and breakthroughs are made every day. It may not be long before life is found on another planet that operates in a completely different way than life on Earth.
16.2 Digestive System
All living organisms need nutrients to survive. While plants can obtain nutrients from their roots and the energy molecules required for cellular function through the process of photosynthesis, animals obtain their nutrients by the consumption of other organisms. At the cellular level, the biological molecules necessary for animal function are amino acids, lipid molecules, nucleotides, and simple sugars. However, the food consumed consists of protein, fat, and complex carbohydrates. Animals must convert these macromolecules into the simple molecules required for maintaining cellular function. The conversion of the food consumed to the nutrients required is a multistep process involving digestion and absorption. During digestion, food particles are broken down to smaller components, which are later absorbed by the body. This happens by both physical means, such as chewing, and by chemical means.
One of the challenges in human nutrition is maintaining a balance between food intake, storage, and energy expenditure. Taking in more food energy than is used in activity leads to storage of the excess in the form of fat deposits. The rise in obesity and the resulting diseases like type 2 diabetes makes understanding the role of diet and nutrition in maintaining good health all the more important.
The Human Digestive System
The process of digestion begins in the mouth with the intake of food (Figure 16.4). The teeth play an important role in masticating (chewing) or physically breaking food into smaller particles. The enzymes present in saliva also begin to chemically break down food. The food is then swallowed and enters the esophagus —a long tube that connects the mouth to the stomach. Using peristalsis , or wave-like smooth-muscle contractions, the muscles of the esophagus push the food toward the stomach. The stomach contents are extremely acidic, with a pH between 1.5 and 2.5. This acidity kills microorganisms, breaks down food tissues, and activates digestive enzymes. Further breakdown of food takes place in the small intestine where bile produced by the liver, and enzymes produced by the small intestine and the pancreas, continue the process of digestion. The smaller molecules are absorbed into the blood stream through the epithelial cells lining the walls of the small intestine. The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces it is stored until it is excreted through the anus.
Both physical and chemical digestion begin in the mouth or oral cavity , which is the point of entry of food into the digestive system. The food is broken into smaller particles by mastication, the chewing action of the teeth. All mammals have teeth and can chew their food to begin the process of physically breaking it down into smaller particles.
The chemical process of digestion begins during chewing as food mixes with saliva, produced by the salivary glands (Figure 16.5). Saliva contains mucus that moistens food and buffers the pH of the food. Saliva also contains lysozyme, which has antibacterial action. It also contains an enzyme called salivary amylase that begins the process of converting starches in the food into a disaccharide called maltose. Another enzyme called lipase is produced by cells in the tongue to break down fats. The chewing and wetting action provided by the teeth and saliva prepare the food into a mass called the bolus for swallowing. The tongue helps in swallowing—moving the bolus from the mouth into the pharynx. The pharynx opens to two passageways: the esophagus and the trachea. The esophagus leads to the stomach and the trachea leads to the lungs. The epiglottis is a flap of tissue that covers the tracheal opening during swallowing to prevent food from entering the lungs.
The esophagus is a tubular organ that connects the mouth to the stomach. The chewed and softened food passes through the esophagus after being swallowed. The smooth muscles of the esophagus undergo peristalsis that pushes the food toward the stomach. The peristaltic wave is unidirectional—it moves food from the mouth the stomach, and reverse movement is not possible, except in the case of the vomit reflex. The peristaltic movement of the esophagus is an involuntary reflex it takes place in response to the act of swallowing.
Ring-like muscles called sphincters form valves in the digestive system. The gastro-esophageal sphincter (or cardiac sphincter) is located at the stomach end of the esophagus. In response to swallowing and the pressure exerted by the bolus of food, this sphincter opens, and the bolus enters the stomach. When there is no swallowing action, this sphincter is shut and prevents the contents of the stomach from traveling up the esophagus. Acid reflux or “heartburn” occurs when the acidic digestive juices escape into the esophagus.
A large part of protein digestion occurs in the stomach (Figure 16.7). The stomach is a saclike organ that secretes gastric digestive juices.
Protein digestion is carried out by an enzyme called pepsin in the stomach chamber. The highly acidic environment kills many microorganisms in the food and, combined with the action of the enzyme pepsin, results in the catabolism of protein in the food. Chemical digestion is facilitated by the churning action of the stomach caused by contraction and relaxation of smooth muscles. The partially digested food and gastric juice mixture is called chyme . Gastric emptying occurs within two to six hours after a meal. Only a small amount of chyme is released into the small intestine at a time. The movement of chyme from the stomach into the small intestine is regulated by hormones, stomach distension and muscular reflexes that influence the pyloric sphincter.
The stomach lining is unaffected by pepsin and the acidity because pepsin is released in an inactive form and the stomach has a thick mucus lining that protects the underlying tissue.
Chyme moves from the stomach to the small intestine. The small intestine is the organ where the digestion of protein, fats, and carbohydrates is completed. The small intestine is a long tube-like organ with a highly folded surface containing finger-like projections called the villi. The top surface of each villus has many microscopic projections called microvilli. The epithelial cells of these structures absorb nutrients from the digested food and release them to the bloodstream on the other side. The villi and microvilli, with their many folds, increase the surface area of the small intestine and increase absorption efficiency of the nutrients.
The human small intestine is over 6 m (19.6 ft) long and is divided into three parts: the duodenum, the jejunum and the ileum. The duodenum is separated from the stomach by the pyloric sphincter. The chyme is mixed with pancreatic juices, an alkaline solution rich in bicarbonate that neutralizes the acidity of chyme from the stomach. Pancreatic juices contain several digestive enzymes that break down starches, disaccharides, proteins, and fats. Bile is produced in the liver and stored and concentrated in the gallbladder it enters the duodenum through the bile duct. Bile contains bile salts, which make lipids accessible to the water-soluble enzymes. The monosaccharides, amino acids, bile salts, vitamins, and other nutrients are absorbed by the cells of the intestinal lining.
The undigested food is sent to the colon from the ileum via peristaltic movements. The ileum ends and the large intestine begins at the ileocecal valve. The vermiform, “worm-like,” appendix is located at the ileocecal valve. The appendix of humans has a minor role in immunity.
The large intestine reabsorbs the water from indigestible food material and processes the waste material (Figure 16.6). The human large intestine is much smaller in length compared to the small intestine but larger in diameter. It has three parts: the cecum, the colon, and the rectum. The cecum joins the ileum to the colon and is the receiving pouch for the waste matter. The colon is home to many bacteria or “intestinal flora” that aid in the digestive processes. The colon has four regions, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. The main functions of the colon are to extract the water and mineral salts from undigested food, and to store waste material.
The rectum (Figure 16.6) stores feces until defecation. The feces are propelled using peristaltic movements during elimination. The anus is an opening at the far-end of the digestive tract and is the exit point for the waste material. Two sphincters regulate the exit of feces, the inner sphincter is involuntary and the outer sphincter is voluntary.
The organs discussed above are the organs of the digestive tract through which food passes. Accessory organs add secretions and enzymes that break down food into nutrients. Accessory organs include the salivary glands, the liver, the pancreas, and the gall bladder. The secretions of the liver, pancreas, and gallbladder are regulated by hormones in response to food consumption.
The liver is the largest internal organ in humans and it plays an important role in digestion of fats and detoxifying blood. The liver produces bile, a digestive juice that is required for the breakdown of fats in the duodenum. The liver also processes the absorbed vitamins and fatty acids and synthesizes many plasma proteins. The gallbladder is a small organ that aids the liver by storing bile and concentrating bile salts.
The pancreas secretes bicarbonate that neutralizes the acidic chyme and a variety of enzymes for the digestion of protein and carbohydrates.
Which of the following statements about the digestive system is false?
- Chyme is a mixture of food and digestive juices that is produced in the stomach.
- Food enters the large intestine before the small intestine.
- In the small intestine, chyme mixes with bile, which emulsifies fats.
- The stomach is separated from the small intestine by the pyloric sphincter.
The human diet should be well balanced to provide nutrients required for bodily function and the minerals and vitamins required for maintaining structure and regulation necessary for good health and reproductive capability (Figure 16.8).
Concepts in Action
Explore this interactive United States Department of Agriculture website to learn more about each food group and the recommended daily amounts.
The organic molecules required for building cellular material and tissues must come from food. During digestion, digestible carbohydrates are ultimately broken down into glucose and used to provide energy within the cells of the body. Complex carbohydrates, including polysaccharides, can be broken down into glucose through biochemical modification however, humans do not produce the enzyme necessary to digest cellulose (fiber). The intestinal flora in the human gut are able to extract some nutrition from these plant fibers. These plant fibers are known as dietary fiber and are an important component of the diet. The excess sugars in the body are converted into glycogen and stored for later use in the liver and muscle tissue. Glycogen stores are used to fuel prolonged exertions, such as long-distance running, and to provide energy during food shortage. Fats are stored under the skin of mammals for insulation and energy reserves.
Proteins in food are broken down during digestion and the resulting amino acids are absorbed. All of the proteins in the body must be formed from these amino-acid constituents no proteins are obtained directly from food.
Fats add flavor to food and promote a sense of satiety or fullness. Fatty foods are also significant sources of energy, and fatty acids are required for the construction of lipid membranes. Fats are also required in the diet to aid the absorption of fat-soluble vitamins and the production of fat-soluble hormones.
While the animal body can synthesize many of the molecules required for function from precursors, there are some nutrients that must be obtained from food. These nutrients are termed essential nutrients , meaning they must be eaten, because the body cannot produce them.
The fatty acids omega-3 alpha-linolenic acid and omega-6 linoleic acid are essential fatty acids needed to make some membrane phospholipids. Vitamins are another class of essential organic molecules that are required in small quantities. Many of these assist enzymes in their function and, for this reason, are called coenzymes. Absence or low levels of vitamins can have a dramatic effect on health. Minerals are another set of inorganic essential nutrients that must be obtained from food. Minerals perform many functions, from muscle and nerve function, to acting as enzyme cofactors. Certain amino acids also must be procured from food and cannot be synthesized by the body. These amino acids are the “essential” amino acids. The human body can synthesize only 11 of the 20 required amino acids the rest must be obtained from food.
With obesity at high rates in the United States, there is a public health focus on reducing obesity and associated health risks, which include diabetes, colon and breast cancer, and cardiovascular disease. How does the food consumed contribute to obesity?
Fatty foods are calorie-dense, meaning that they have more calories per unit mass than carbohydrates or proteins. One gram of carbohydrates has four calories, one gram of protein has four calories, and one gram of fat has nine calories. Animals tend to seek lipid-rich food for their higher energy content. Greater amounts of food energy taken in than the body’s requirements will result in storage of the excess in fat deposits.
Excess carbohydrate is used by the liver to synthesize glycogen. When glycogen stores are full, additional glucose is converted into fatty acids. These fatty acids are stored in adipose tissue cells—the fat cells in the mammalian body whose primary role is to store fat for later use.
Marine Food Chains and Biodiversity
Students use marine organism cards and trophic level classifications to identify and describe food chains in several marine ecosystems.
Biology, Ecology, Earth Science, Oceanography, Geography, Physical Geography
1. Define the role of marine microbes.
Explain to students that, in a single drop of salt water, thousands of microbes (tiny organisms), including bacteria and phytoplankton (tiny floating plants), are interacting to form the base of the food web for the entire ocean. The oxygen and biomass they produce also sustains terrestrial life. Tell students that phytoplankton (algae) take in sunlight, nutrients, carbon dioxide, and water to produce oxygen and food for other organisms. Ask: What is this process called? (photosynthesis) Explain that other microbes, like many bacteria, play a role at the other end of the food chain by breaking down dead plant and animal material and changing it into a form that can be re-used as nutrients by phytoplankton and other organisms. Ask: What is this process called? (decomposition)
2. Watch the National Geographic video “Tiny New Sea Species Discovered.”
Show students the National Geographic video (2 minutes, 30 seconds) “Tiny New Sea Species Discovered.” Ask:
- What is the goal of the Census of Marine Life? (for scientists to try to uncover as much as possible about diversity, distribution, and abundance of life in the ocean within ten years)
- What have scientists learned about the importance of microbes in the ocean? (Microbes play a key role in the way nutrients move through the ocean.)
- What do all microbes in the global ocean collectively weigh? (the equivalent of 240 billion African elephants, or about 90 percent of all the ocean’s biomass)
Summarize that microbes, including phytoplankton and bacteria, are the beginning and end, respectively, of ocean food chains and are therefore essential components of marine ecosystems.
3. Introduce trophic level vocabulary.
Ask: What is a food chain? Ask students to list the organisms in a terrestrial or aquatic food chain that they are familiar with. Explain to students that the trophic level of an organism is the position it occupies on the food chain. An organism’s trophic level is measured by the number of steps it is away from a primary producer/autotroph (photosynthesizer). Write the trophic levels and definitions listed below on the board, leaving off the examples provided. Have students try to identify the trophic level for each of the organisms on their list. Invite volunteers to share their answers with the class. Discuss the correct answers. Next ask students to brainstorm ocean examples of each trophic level and write their correct responses on the board. Eventually, add all of the examples listed below.
- primary producer/autotrophs—organisms, like plants, that produce food. Examples: phytoplankton, algae
- primary consumer/heterotroph—an animal that eats primary producers. Examples: mussels, oysters, krill, copepods, shrimp
- secondary consumer/heterotroph—an animal that eats primary consumers. Examples: blue claw crab, lobster, seastar, humpback whale, silverside
- tertiary consumer/heterotroph—an animal that eats secondary consumers. Examples: shark, dolphin
- apex predator/heterotroph—an animal at the top of the food chain with no predators. Examples: shark, dolphin
- decomposer/detritivores—organisms that break down dead plant and animal material and wastes and release it again as energy and nutrients in the ecosystem. Examples: bacteria, fungi, worms, crabs
4. Have students watch the National Geographic video “Krill.”
Explain to students they are going to watch a video that highlights a marine food chain. Tell students that while they are watching the film, they are going to write examples of organisms from each trophic level. When the film is over, they will identify each organism’s trophic level using the information from the board. Show students the National Geographic video (2 minutes) “Krill.” After the video is over, allow students a couple of minutes to properly identify the trophic levels of each of the organisms shown in the film. Ask:
- What is the ultimate source of energy in this ecosystem? (the sun photosynthesis)
- What is the primary producer in the video? (phytoplankton and other algae)
- What is the primary consumer in the video? Is it an herbivore or carnivore? (krill herbivore)
- What secondary and tertiary consumers are shown in the video? Are they herbivores or carnivores? (anchovies, sardines, birds, salmon, tuna, humpback and blue whales carnivores)
5. Have students create food chains.
Remind students that food chains connect organisms through energy transfer among producers, consumers, and decomposers. These energy levels are called trophic levels. A significant amount of energy is lost between trophic levels. Divide students into five groups. Assign each group one of the following marine ecosystems:
Have groups identify the geographic locations of their marine ecosystems on their World Physical Tabletop Maps, included in the Physical World MapMaker Kit. Then give each group its assigned Marine Ecosystem Cards Handout, and each student a Feeding Frenzy worksheet. Have students cut out the ecosystem cards, discuss the activity as a group, and then individually complete the Feeding Frenzy worksheet.
6. Have a whole-class discussion about the marine ecosystems and food chains.
Invite small groups to share their completed Feeding Frenzy worksheets with the whole class. Review each of the five food chains, as well as the ecosystems in which each food chain is likely to be found. Ask:
- Looking across the different food chains, which of the organisms can make their own food through photosynthesis?
- Compare the food chains to terrestrial food chains you may know. How are the marine food chains the same? How are they different?
- How might humans be a part of the food chains?
Use the provided Feeding Frenzy Answer Key to assess students' comprehension.
Extending the Learning
Have students use their food chain cards to create food webs. Discuss the role each organism plays in the food web.
Filter-feeding is a common strategy in aquatic habitats, especially the ocean. It uses anatomical devices that act as strainers to remove small food items from the water. Sessile filter-feeders, such as barnacles, oysters, fanworms, brachiopods, and tunicates sit in one place, pumping sea water and straining plankton from it. Other filter-feeders are mobile. Herring swim with their mouths open, letting water flow through the gill rakers, which strain small particles of food from it. Flamingoes take in mouthfuls of water and mud, then force the water through the fringed edges of their bills, which serve as strainers that retain food such as brine shrimp, aquatic insects, and plankton in the mouth. Small and even microscopic food in the water may not seem very abundant, yet the largest animals on Earth — the basking sharks, whale sharks, manta rays, and baleen whales, including the largest species alive today, the great blue whale — nourish themselves entirely in this way. Filter-feeding is more common in the ocean than in fresh water, because plankton is less concentrated in fresh water.
The feeding positions in a food chain or web are called trophic levels. The different trophic levels are defined in the Table below. Examples are also given in the table. All food chains and webs have at least two or three trophic levels. Generally, there are a maximum of four trophic levels.
|Trophic Level||Where It Gets Food||Example|
|1st Trophic Level: Producer||Makes its own food||Plants make food|
|2nd Trophic Level: Primary Consumer||Consumes producers||Mice eat plant seeds|
|3rd Trophic Level: Secondary Consumer||Consumes primary consumers||Snakes eat mice|
|4th Trophic Level: Tertiary Consumer||Consumes secondary consumers||Hawks eat snakes|
Many consumers feed at more than one trophic level. Humans, for example, are primary consumers when they eat plants such as vegetables. They are secondary consumers when they eat cows. They are tertiary consumers when they eat salmon.
Trophic Levels and Energy
Energy is passed up a food chain or web from lower to higher trophic levels. However, generally only about 10 percent of the energy at one level is available to the next level. This is represented by the ecological pyramid in Figure below. What happens to the other 90 percent of energy? It is used for metabolic processes or given off to the environment as heat. This loss of energy explains why there are rarely more than four trophic levels in a food chain or web. Sometimes there may be a fifth trophic level, but usually there&rsquos not enough energy left to support any additional levels.
Ecological Pyramid. This pyramid shows how energy and biomass decrease from lower to higher trophic levels. Assume that producers in this pyramid have 1,000,000 kilocalories of energy. How much energy is available to primary consumers?
Ecological pyramids can demonstrate the decrease in energy, biomass or numbers within an ecosystem.
Trophic Levels and Biomass
With less energy at higher trophic levels, there are usually fewer organisms as well. Organisms tend to be larger in size at higher trophic levels, but their smaller numbers result in less biomass. Biomass is the total mass of organisms at a trophic level. The decrease in biomass from lower to higher levels is also represented by Figure above.
Food Chain in Ecosystem (Explained with Diagrams)
For an ecosystem to work there has to be a flow of energy within it. The organisms of the ecosystem need energy in the form of food.
The ultimate source of this energy is the sun. Producers like green plants trap solar energy and convert it into the chemical energy of food. When a primary consumer eats the producer, a part of this energy is passed on to it.
The primary consumer is then eaten by a secondary consumer. And the secondary consumer may be eaten by a tertiary consumer, and so on. In this way energy gets transferred from one consumer to the next higher level of consumer. A series of organisms through which food energy flows in an ecosystem is called a food chain. It may also be defined as follows.
A food chain in an ecosystem is a series of organisms in which each organism feeds on the one below it in the series.
In a forest ecosystem, grass is eaten by a deer, which in turn is eaten by a tiger. The grass, deer and tiger form a food chain (Figure 8.2). In this food chain, energy flows from the grass (producer) to the deer (primary consumer) to the tiger (secondary consumer).
A food chain in a grassland ecosystem may consist of grasses and other plants, grasshoppers, frogs, snakes and hawks (Figure 8.3).
In a freshwater aquatic ecosystem like a pond, the organisms in the food chain include algae, small animals, insects and their larvae, small fish, big fish and a fish-eating bird or animal (Figure 8.4).
A food chain always begins with producers. Herbivores (plant-eaters) come next in the chain. They are consumed by carnivores (flesh-eaters). A few food chains can be long and may extend to the fourth, fifth or even sixth order of consumers.
How to Draw a Food Web
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Creating a food web is a really great way to learn more about how organisms and animals live in their natural habitats. While a food chain shows how ecosystems function in a linear way, a food web is a more visual approach with multiple animals connected to one another. To create a food web, write out the primary producers, herbivores, omnivores, and carnivores for the chosen habitat. Connect them with arrows showing both predator and prey. The final product may look like an actual web or map. It can be hard to do this so don't stress out! If this is for a class grade, make sure to do your best on this.
The Plant or Plantae kingdom encompasses all flowering plants, mosses and ferns. Plants are multi-celled, complex organisms and are considered Autotrophic. This means that plants create their own food through photosynthesis. The Plant kingdom is thought to be the second largest with over 25,000 known species.
The largest kingdom of organisms is the Animal or Animalia kingdom. This kingdom is made up of complex, multi-celled organisms ranging from sea sponge colonies to elephants. All organisms in the Animal kingdom are Heterotrophs meaning, unlike plants which produce their own food, animals feed upon other organisms. The Animal kingdom is the world's largest with over one million known species.