Insect Metabolic Systems PDF

LESSON 3: METABOLIC SYSTEMS OF INSECTS Photo courtesy: Piotr Jaworski/Creative Commons. Taken from: +-----------------------------------+-----------------------------------+ | Module No. and Title | Module 1: Basic of insect | | | physiology a...

LESSON 3: METABOLIC SYSTEMS OF INSECTS Photo courtesy: Piotr Jaworski/Creative Commons. Taken from: +-----------------------------------+-----------------------------------+ | Module No. and Title | Module 1: Basic of insect | | | physiology and anatomy | +===================================+===================================+ | Lesson No. and Title | Lesson 3: Metabolic systems of | | | Insects | +-----------------------------------+-----------------------------------+ | Learning Outcomes | After learning the lesson, you | | | will be able to: | | | | | | 1. Discuss the structures and | | | functions associated with the | | | insect digestion and | | | excretory system | | | | | | 2. Explain the structures and | | | functions related to the | | | insect circulatory and | | | tracheal systems | +-----------------------------------+-----------------------------------+ | Time Frame | Week 5 and 6 | +-----------------------------------+-----------------------------------+ | Introduction | Welcome to Lesson 3 of Module 1. | | | Four metabolic systems will be | | | discussed in this lesson. They | | | are grouped in the sense that | | | they are connected from the | | | production of essential nutrients | | | and conversion into energy and | | | the production of toxic material | | | in the body of insects. These | | | absorbed materials need to be | | | distributed to each cell to | | | maintain healthy functioning. | | | However, after the process, lots | | | of toxic substances need to be | | | removed out of the body. | | | | | | Moreover, another relevant | | | product of metabolism is carbon | | | dioxide, and this has to be | | | removed through the tracheal | | | system. In this lesson, you will | | | learn the structures and | | | functions of digestive, | | | excretory, circulatory, and | | | tracheal systems. I hope that you | | | are in a good mood for ease of | | | accessing the information on | | | these topics. | +-----------------------------------+-----------------------------------+ | Activity | In your activity notebook, do the | | | following: | | | | | | 1\. Draw and differentiate the | | | alimentary canal of solid | | | feeding from liquid feeding | | | insects. | | | | | | 2\. Draw and differentiate the | | | open circulatory system of | | | insects from closed circulatory | | | in humans. | | | | | | 3\. Draw and differentiate | | | between an open and closed | | | tracheal system in insects. | | | Provide examples of each | | | system. | | | | | | 4\. Draw the major organs | | | involved in the excretory of | | | waste materials and maintain | | | ionic balance in the insect | | | body. | +-----------------------------------+-----------------------------------+ | Analysis | 1\. What more significant | | | advantage in terms of food | | | intake and food competition, | | | those insects that eat solid | | | food or those that feed on | | | liquid? | | | | | | 2\. What are symbionts? How they | | | improve digestion and nutrition | | | among insects? | | | | | | 3\. What important functions the | | | excretory system performs in | | | insect body? Why are these | | | important? | | | | | | 4\. How does the circulatory | | | system of humans differ from | | | that of insects? Which do you | | | think is more advantageous? | | | | | | 5\. What is the importance of | | | air sacs? How does it help | | | insects to travel long | | | distances, particularly | | | important to migratory insects? | +-----------------------------------+-----------------------------------+ | Abstraction | **Functions of the digestive | | | system** | | | | | | 1\. To obtain food materials. | | | | | | 2\. To breakdown mechanically | | | the food into smaller particles | | | so that the enzymes may act on | | | them. | | | | | | 3\. Converting food into | | | absorbable forms by the enzyme | | | actions in the midgut. | | | | | | 4\. To produce messengers (e.g., | | | Endocrines), that coordinate | | | feeding and other important | | | digestive tract activities. | | | | | | **ALIMENTARY CANAL** -- the basic | | | unit of the digestive system. It | | | is a simple tube that opens into | | | the mouth anteriorly and on the | | | anus posteriorly. The alimentary | | | canal is composed of 3 | | | regions/divisions: | | | | | | Figure 32. The insect alimentary | | | canal and its parts. Photo | | | courtesy: Springerlink. Date | | | Accessed: July 27, 2020. Taken | | | from: | | | | | | a\. **Foregut/Stomodaeum** -- | | | the first region of the | | | alimentary canal, composed of | | | the pharynx, esophagus, crop | | | (enlarge food storage sac), and | | | proventriculus (possess teeth | | | that mechanically breakdown | | | food into smaller materials). | | | This region is composed of | | | cuticle because | | | embryologically, they are | | | derived from ectoderm, which | | | will become cuticle; hence, | | | they will also shed their | | | cuticle during the molting | | | process. No digestion is taking | | | place in this region. The | | | primary functions of the | | | foregut are as follows: | | | | | | 1\. ingestion of food | | | | | | 2\. Mechanically breaking down | | | food into smaller sizes | | | | | | 3\. Storage of food | | | | | | b\. **Midgut/Mesenteron** -- the | | | middle region of the alimentary | | | canal with no divisions. The | | | main organ in this region is | | | the ventriculus, where proper | | | digestion takes place. A | | | structure increases the surface | | | area of the midgut, the gastric | | | caeca, which is a hand-like | | | structure. This region has no | | | cuticle because they develop | | | endodermal during embryonic | | | development. The primary | | | functions of this region are as | | | follows: | | | | | | 1\. The major site for digestion | | | and absorption | | | | | | 2\. It contains the peritrophic | | | membrane, which protects the | | | midgut cells from abrasion from | | | solid particles and harmful | | | microbes. | | | | | | 3\. Possesses various enzymes | | | that convert large molecules | | | into absorbable forms. | | | | | | c\. **Hindgut/Proctodaeum** -- | | | the third region of the | | | alimentary canal composed of | | | the tubular intestine (ileum | | | and colon) and a short, | | | expanded rectum connected to | | | the anus. This region is also | | | made up of cuticle, develop | | | ectodermal, which will molt | | | during the molting process. The | | | major functions are as follows: | | | | | | 1\. It is the primary waste | | | dumping area from the | | | mesenteron and Malpighian | | | tubules. | | | | | | 2\. Involved in getting rid of | | | excessive water for sap and | | | blood-feeding insects | | | | | | 4\. Houses the symbionts that | | | use these waste products to | | | produce substances the insect | | | needs. | | | | | | 3\. Involved in the reabsorption | | | of certain salts and amino | | | acids from the insect body. | | | | | | 4\. It helps in maintaining the | | | hemolymp\'s osmotic pressure. | | | | | | 5\. Produces aggregation | | | pheromone in male scolytid | | | beetles. | | | | | | 6\. Aid in the Respiration in | | | naiad of dragonflies | | | | | | **SYMBIONTS** -- these are | | | beneficial microbes in the | | | hindgut that produces necessary | | | enzymes or nutrients that the | | | insect cannot manufacture. An | | | excellent example of this is the | | | microbe from the hindgut of | | | termites. The primary molecule | | | that comprises wood materials is | | | cellulose. The insect alone | | | cannot breakdown the sugar | | | because it can\'t produce it. | | | Hence, they acquire symbiont to | | | help them manufacture cellulase. | | | This enzyme breaks cellulose and | | | enables the termite to consume | | | wood. It can also be found among | | | grubs of rhinoceros beetle. | | | However, during molting these | | | microbes as also lost since | | | hindgut has cuticle and undergo | | | the process of molting. For them | | | to reacquire the microbes, they | | | have to eat the feces of other | | | individuals in the colony, the | | | process called tophallaxis. | | | Consider you are termite; can you | | | eat the garbage of your brother | | | or sister? | | | | | | Team:ZJU-China/Project/Termite | | | Issue - 2015.igem.org | | | | | | Figure 33. Termite while eating | | | the feces of its companion to | | | reacquire the beneficial microbe, | | | notes that the insects behind it | | | are newly molted; hence, the | | | symbionts are lost during | | | molting. Photo courtesy:iGEM2015: | | | Date accessed: July 27, 2020, | | | Taken from | | | | | | | | | **Other vital organ associated | | | with the alimentary canal** | | | | | | A. **SALIVARY GLAND** | | | | | | **Functions of salivary glands** | | | | | | 1\. Moisten food | | | | | | 2\. Lubricate the mouthparts | | | | | | 3\. It contains digestive | | | enzymes (May include enzyme | | | amylase, which breaks down | | | complex sugars into simpler | | | sugars. These enzymes are used | | | to pre-digest prey food enzymes | | | that are used by both predatory | | | insects inject the saliva and | | | preoral digestion that occurs | | | in some insects). | | | | | | 4\. Non-digestive processes | | | | | | a\. It contains toxins of | | | predators that act on the | | | nervous system of prey food, | | | such as asilids and giant water | | | bugs. | | | | | | b\. In some plant feeders | | | contain substances that counter | | | the action of plant | | | allelochemicals (chemicals | | | associated with interspecific | | | interactions -- allomones and | | | kairomones) | | | | | | c\. Anticoagulants | | | | | | d\. Formation of | | | silk-Lepidopteran larvae | | | | | | e\. Contain bacteria in myiasis | | | producing flies | | | | | | **B. THE INSECT EXCRETORY | | | SYSTEM** | | | | | | Functions of the Excretory system | | | | | | 1\. Excretion - removal of waste | | | materials from the body. This | | | waste material in the form of | | | feces, either in liquid or | | | solid pellets/Frass, contains | | | both undigested food and | | | metabolic excretions. | | | | | | 2\. Osmoregulation - maintenance | | | of favorable osmotic pressure | | | and ionic concentration of body | | | fluid. | | | | | | **Major organs for excretion** | | | | | | 1**. Malpighian tubules** -- is | | | the major organ for excretion | | | among insects. It is a structure | | | that floats freely in the | | | hemocoel (body cavity, spaces | | | within the body) and extracting | | | waste materials from the | | | hemolymph (insect blood) in the | | | form of nitrogen waste (uric | | | acid), a product of metabolism | | | (Figure 34). | | | | | | It is located in the hindgut, a | | | long thin tube made up of a | | | single cell layer. | | | | | | Varies in number among species | | | with 200 among grasshoppers, 60 | | | among roaches, and meager amount | | | among most homopterans while | | | absent among aphids and | | | collembolan (springtail) | | | | | | 2\. **Rectum** -- a | | | short-expanded structure | | | directly connected to the anus | | | involved mainly in | | | osmoregulation that is the | | | maintenance of salt and ions in | | | the body to maintain | | | homeostasis. | | | | | | Figure 34. The alimentary canal | | | of a typical insect showing the | | | Malpighian tubules, the main | | | organ for excretion of waste | | | materials. Photo courtesy: | | | Denigma: Date accessed: July 27, | | | 2020. Taken from: | | | | | | | | | **Excretory Process** | | | | | | When the blood passes through the | | | Malpighian tubules, the waste | | | product of metabolism, such as | | | uric acid, will diffuse or be | | | actively transported to the | | | tubules. Other substances that | | | are picked up by the tubules are | | | amino acids, different ions, and | | | water. A potassium-ion gradient | | | causes the urine to flow, then | | | will be discharged to the | | | hindgut, particularly to the | | | rectum. Have you observed that | | | feces or frass of insects are | | | dry? Because the lining of the | | | rectum reabsorb 90% of the water | | | from the wastes and reabsorb the | | | inorganic ions and amino acids | | | from the urine to the hemolymph | | | to maintain ionic balance within | | | the body. | | | | | | Figure 11.1.3a/a -- Malpighian | | | tubules | | | | | | Figure 35. A portion of the | | | alimentary canal (hindgut region) | | | where the major organs of | | | excretion are located. Photo | | | courtesy: Philpot education. Date | | | accessed: July 27, 2020. Taken | | | from: | | | | | | FAT BODY -- other than the | | | alimentary canal as the main | | | organ for digestion, the fat body | | | also performs primary digestive | | | functions such as metabolism of | | | fats, proteins, and | | | carbohydrates. Other than the | | | digestive function, the fat body | | | also serves as an essential | | | storage organ for energy sources, | | | particularly during difficult | | | parts of its life cycle. These | | | strenuous activities happen | | | during reproduction, migration, | | | and diapause and molting, which | | | energy is badly needed to sustain | | | such operations. Figure 36 shows | | | the fat body in cockroaches. | | | | | |  | | | | | | Figure 36. The body of cockroach | | | as covered with white fatty | | | structures called the fat body. | | | Photo courtesy: Alchemy. Accessed | | | date: July 21, 2020. Taken from: | | | | | | | | | **Other Uses/Functions of | | | Malpighian tubuless:** | | | | | | 1\. Light-producing organ in | | | *Arachnocampa luminosa* (Figure | | | 37). | | | | | | Two Arachnocampa luminosa larvae | | | | | | Figure 37. Two A. luminosa | | | maggots on the roof of the cave. | | | Note the luminous structure | | | clinging on them, which was | | | produced by the Malphigian | | | tubules. Photo courtesy: | | | Mnolf/Wikimedia commons, Accessed | | | date: July 21, 2020. Taken from | | | | | | | | | 2\. Spittle production by the | | | spittle bug or frog hopper | | | (Figure 38) | | | | | |  | | | | | | Figure 38. A froghopper was | | | showing spittle production in a | | | tree twig. The functions are | | | protected from predators, as | | | insulators during extreme heat, | | | prevents dehydration. Photo | | | courtesy: Sandra | | | Standbridge/Getty Images Accessed | | | date: July 21, 2020. Taken From | | | | | | | | | **C. THE INSECT CIRCULATORY | | | SYSTEM** | | | | | | - Insects do have an open | | | circulatory system, that | | | unlike humans and other | | | vertebrates have an enclosed | | | circulatory system. The human | | | system is made up of a | | | centralized heart, and blood | | | is confined in specialized | | | vessels (arteries, veins, | | | capillaries). Insect blood or | | | hemolymph does not travel | | | along specialized vessels but | | | within the insect body cavity | | | or hemocoel. All insect cells | | | and tissues are surrounded by | | | basement membranes, which | | | separate integument from the | | | hemolymph. | | | | | | **DORSAL VESSEL** -- is the main | | | organ for blood circulation in | | | insects. The vessel is located | | | dorsally from the back of the | | | abdomen up to the head. The | | | dorsal vessel is composed of 2 | | | parts: | | | | | | 1\. Heart -- is the pumping | | | organ that draws hemolymph into | | | its opening called the Ostia. | | | The Ostia during the relax | | | stage will open and allow the | | | entry of hemolymph while during | | | contraction will close. This | | | action pushes the hemolymph to | | | the aorta. | | | | | | 2\. Aorta -- long thin tube | | | extending from the thorax to | | | the head regions where the | | | blood flows out to the | | | hemocoel. | | | | | | **Diaphragm or Septa** | | | | | | - To improve blood circulation, | | | the body cavity is separated | | | by the presence of dorsal | | | diaphragm that confined | | | organs located dorsally, and | | | the ventral diaphragm, which | | | its presence, separate organs | | | ventrally. Their presence | | | help guides the flow of | | | hemolymph. | | | | | | - The diaphragm is made up of a | | | muscular sheet, which may be | | | perforated, allowing blood to | | | pass through it and open | | | posteriorly in the abdomen | | | and extended up to the | | | thorax. Fan-shaped muscles | | | (alary muscle) of the dorsal | | | diaphragm are attached to the | | | heart. | | | | | | - The presence of diaphragm had | | | resulted in the | | | compartmentalization of the | | | circulation of blood in the | | | insect body. This compartment | | | had led to the formation of | | | spaces or sinuses. The sinus | | | that is created above the | | | dorsal diaphragm where the | | | dorsal vessel is suspended is | | | the pericardial sinus. The | | | sinus that forms below the | | | ventral diaphragm is called | | | the perineural sinus where | | | the ventral nerve cords are | | | located. On the other hand, | | | the space created medially | | | between the dorsal and | | | ventral diaphragms is called | | | the perivisceral sinus, where | | | the alimentary canal and | | | reproductive organs are | | | suspended (Figure 39). In the | | | thoracic region, the ventral | | | diaphragm is extended to the | | | leg/limb of insects to | | | provide blood to these | | | appendages (Figure 40). | | | https://cronodon.com/images/i | | | nsect\_circulation\_abdomen.jpg | | | | | | Figure 39. Cross-section of the | | | abdomen showing insect blood | | | directional flow in the various | | | sinuses and organs in the insect | | | body. Photo courtesy: | | | Cronodon.com | | | | | | Date accessed: July 22, 2020. | | | Taken from | | | | | | | | |  | | | | | | Figure 40. Cross-section of the | | | thorax showing insect blood | | | directional flow in the various | | | sinuses and organs in the insect | | | body. The ventral diaphragm is | | | extended up to the limb (leg) to | | | supply blood to it. Photo | | | courtesy: Cronodon.com. Date | | | accessed: July 22, 2020. Taken | | | from | | | | | | **MECHANISM OF BLOOD | | | CIRCULATION** | | | | | | - Hemolymph enters the dorsal | | | vessel through the | | | heart-opening called Ostia. | | | These one-way valves allow | | | hemolymph to enter the dorsal | | | vessel, where waves of muscle | | | contractions push the | | | hemolymph anteriorly via the | | | aorta moving out of the head | | | and goes through the | | | hemocoel. When already in the | | | hemocoel, blood flows into | | | the midgut/mesenteron to pick | | | up absorbed nutrients that | | | are ready for distribution | | | entirely to the body of an | | | insect. To ensure a | | | continuous flow of hemolymph | | | throughout the body, there | | | are pulsatile organs that are | | | located at the bases of | | | antennae, wings, and legs- | | | which act like heart, pumping | | | hemolymph through these | | | appendages. All of these | | | structures work to achieve a | | | regular flow of hemolymph | | | throughout the insect\'s body | | | (Figure 41). | | | | | | https://cdn.britannica.com/24/511 | | | 24-050-9916AF50/Circulatory-syste | | | m-insect.jpg | | | | | | Figure 41. The insect circulatory | | | system showing the various organs | | | for circulation and the pathways | | | of hemolymph throughout the | | | insect body. Photo courtesy: | | | Encyclopedia Britannica | | | Incorporated. Date accessed: July | | | 21, 2020. Taken from: | | | | | | | | | **INSECT BLOOD OR HEMOLYMPH** | | | | | | **Functions of Blood** | | | | | | 1. Transport medium for many | | | molecules, including wastes | | | | | | 2. Lubricant for tissues | | | | | | 3. Hydraulic medium | | | (caterpillars, molting) | | | | | | 4. Storage (amino acids and | | | glycerol) | | | | | | 5. Protection (reflex bleeding) | | | | | | 6. Non-cellular immune response | | | molecules and pathways | | | | | | **Composition of Insect Blood** | | | | | | 1. 90% Water | | | | | | 2. Inorganic ions, ex. Na, Ca, | | | K, | | | | | | 3. Nitrogenous wastes, uric acid | | | | | | 4. Carbohydrates-Alpha trehalose | | | (most important insect blood | | | sugar) | | | | | | glucose, glycerol (antifreeze | | | during winter season) | | | | | | 5. Lipids | | | | | | 6. Proteins and enzymes (Mixed | | | Function Oxidases, enzyme | | | that detoxify toxins/poisons | | | that enter to the body of | | | insect) | | | | | | 7. Antifreeze proteins | | | | | | 8. Pigments | | | | | | 9. Hormones | | | | | | **INSECT BLOOD CELLS OR | | | HEMOCYTE/HEMATOCYTE** | | | | | | **Functions of Hemocytes** | | | | | | 1\. Phagocytosis -- ingestion of | | | foreign pathological microbes. | | | | | | 2\. Encapsulation -- | | | encapsulating microbes and kill | | | them | | | | | | 3\. Coagulation -- to prevent | | | bleeding | | | | | | 4\. Wound Healing | | | | | | 5\. Nutrient distribution and | | | storage | | | | | | **D. THE INSECT TRACHEAL SYSTEM** | | | | | | - The tracheal system is | | | responsible for delivering | | | sufficient oxygen to all | | | cells of the body and to | | | remove carbon dioxide, the | | | waste product of metabolism. | | | The respiratory system of | | | insects is separate from the | | | circulatory system unlike the | | | human system where blood of | | | insect does not contain | | | hemoglobin. It is a complex | | | network of tubes that deliver | | | oxygen to every cell of the | | | body. | | | | | | **Structures of the Tracheal | | | System** | | | | | | **1. Spiracle** -- opening of the | | | tracheal system found in the | | | exoskeleton of insect. They are | | | located at the sides in the | | | abdomen (usually 8 pairs, a pair | | | per segment) and the thorax | | | (usually 2 pairs, a pair between | | | prothorax and mesothorax and the | | | other pair is between mesothorax | | | and metathorax). Spiracles maybe | | | surrounded with hairs to minimize | | | bulk air movement around the | | | opening, and thus minimize water | | | loss. | | | | | | **2**. **Trachea** -- also known | | | as respiratory tube that supplies | | | oxygen directly to tissues. The | | | trachea is composed of cuticle, | | | hence, will also molt during | | | molting process (Module 1 lesson | | | 1). Moreover, to provide | | | continuous supply of the | | | life-saving oxygen and to prevent | | | them from collapsing during | | | strenuous activities, spiracles | | | are armed with cuticular spiral | | | to avoid kinking of the tube. | | | This structure is called | | | taenidia. | | | | | | **Types of trachea based on | | | location** | | | | | | a\. **Dorsal segmental trachea** | | | - When tracheae branch dorsally | | | and supplies oxygen directly to | | | the muscles and dorsal vessel. | | | | | | b\. **Visceral segmental | | | trachea** - When trachea branch | | | medially and directly supply | | | oxygen to the alimentary canal | | | and gonads. | | | | | | c\. **Ventral segmental | | | trachea** - when trachea branch | | | ventrally and supplies oxygen | | | to muscles and ventral nerve | | | cord. | | | | | | 3\. **Tracheoles -** These are | | | microscopic tracheae that | | | supplies oxygen directly to | | | cells or tissues of various | | | organs in the insect body. This | | | radiating tracheole network | | | resembles the capillary | | | networks in humans, and is | | | through these structures with | | | their extensive surface area | | | that most gaseous transfer | | | occurs. | | | | | | 4\. **Tracheal trunks** - are | | | longitudinal tubes that are | | | directly connected to the | | | spiracles which supplies oxygen | | | directly to the head of insect. | | | Tracheal trunks are large | | | tracheae on each side of insect | | | body that run the length of the | | | body and connect the grouped | | | tracheae of each segment. | | | | | | 5\. **Air sacs** -- are | | | enlargement of tracheal trunks | | | especially present among | | | fast-flying insects like house | | | fly. Their functions are: (a) | | | to serve as reservoirs of | | | oxygen; (b) to serve as bellows | | | in distributing air and cooling | | | the body; (c) to decrease | | | weight in fast-flying insects, | | | and; (d) to increase body | | | pressure during certain periods | | | such as molting. | | | | | |  | | | | | | Figure 42. The insect tracheal | | | system showing the various organs | | | involve in respiration by a | | | terrestrial insect. Photo | | | courtesy: Encyclopedia Britannica | | | Incorporated. Date accessed: July | | | 21, 2020. Taken from: | | | | | | | | | **RESPIRATORY PROCESS** | | | | | | - It is believed that | | | respiration occurs by the | | | diffusion of oxygen and | | | carbon dioxide through the | | | tracheal system, aided by | | | mechanical ventilation of | | | abdominal tracheae and air | | | sacs. The diffusion of oxygen | | | into the system is triggered | | | by a drop in oxygen pressure | | | at the tip of the tracheoles. | | | | | | - Similarly, carbon dioxide | | | diffuses out through the | | | tracheal system, and because | | | tissues are more permeable to | | | it, significant amounts of | | | carbon dioxide also escape | | | through the body wall. | | | | | | | | | | | | - They were occurring among | | | insects, where the spiracles | | | become non-functional or | | | absent. Examples are the | | | aquatic immatures (naiads) | | | are mayflies, stoneflies, | | | dragonflies, and damselflies. | | | Instead of spiracles, an | | | excellent network of | | | tracheoles runs under the | | | skin or into external gills. | | | | | | Figure 43. The naiad of mayfly in | | | aquatic environment where | | | spiracles ae non-functional, | | | hence, called closed tracheal | | | system. Photo courtesy: | | | Discoverlife.org. | +-----------------------------------+-----------------------------------+ | Application | **Make a dissection video** | | | | | | After learning the basic | | | metabolic processes and providing | | | you the parts and functions of | | | the various organs, let us | | | translate that topic into | | | reality. Make a video | | | presentation while dissecting a | | | cockroach to reveal the major | | | internal organs of the insect. | | | The focus of your dissection is | | | on the digestive system of | | | insects. Provided is the link | | | (https://cutt.ly/YaxraJz) from | | | youtube to guide you on your | | | study. Good luck. | +-----------------------------------+-----------------------------------+ | Closure | Congratulations! You\'ve finally | | | made it! You now have a full | | | understanding of the structures | | | and functions of the metabolic | | | systems comprising the digestive, | | | excretory, circulatory, and | | | tracheal systems. The activity | | | you have performed and completed | | | in this lesson prepared you for | | | the succeeding lessons. Keep | | | going! | +-----------------------------------+-----------------------------------+