Choices A, B, and C are incorrect. Filter feeders are the aquatic animals that consume plants, algae, and small animals in the water. They have modified structures that resemble a net in order to strain out the food particles.

D. filter feeders

The picture shows a lion, which is a carnivore. Meat eaters have sharp teeth that are able to slice or tear the meat into small chunks.

A. Tearing meat

Meat eaters/carnivores:
a. Canine (sharp and pointed) – to tear or cut the meat
b. Molars (sharp edges) – to grind the meat into smaller chunks

Leaf-eaters/herbivores:
a. Canine – non-existent or reduced
b. Molars (broad and flat) – to grind the plant into a pulp

Mechanical digestion involves the physical breakdown of food into smaller chunks or pieces. On the other hand, chemical digestion occurs when the food is broken down into simpler compounds using a chemical reaction/process that involves the help of digestive enzymes.

Vertebrate filter feeders have modified structures that resemble a net in order to strain out the food particles, such as algae and plankton, in the water. As they swim underwater, the water passes over their filtering structure. This is where the tiny food is caught.

The stomach of a ruminant contains a rumen, which is a pouch-like chamber where the food from the esophagus goes. In addition, this is where the food is partly digested through the help of some bacteria that is able to digest cellulose. Eventually, ruminants bring the food back up to their mouth to chew it again. This allows the food to be exposed more to mechanical and chemical digestion.

The lungs of the birds, work efficiently during gas exchange despite being small. When the fresh air is inhaled by the bird, the air sacs allow the oxygen to move in a unidirectional flow. This ensures that more oxygen is diffused in the blood and no old air is trapped inside the lungs. In addition, the high oxygen intake of the birds allows them to power up their flight muscles for an extended period of time.

C. birds

Choices B, C, and D are incorrect. To facilitate efficient gas exchange, all respiratory systems of animals exhibit the following characteristics:
1. Large surface area
2. Moist, selectively permeable membrane
3. Ability to keep the differences in the oxygen and carbon dioxide concentrations on either side of the membrane to allow diffusion

A. thin, moist, selectively permeable membrane

Whales and turtles are aquatic animals that use their lungs for breathing. In this case, they are actually holding their breath underwater. Once they run out of oxygen, they come out to the surface of the ocean to refill breathe.

In the absence of gills or lungs, other animals rely on other respiratory structures such as skin and body surface. Some aquatic invertebrates, such as cnidarians and flatworms, have a thin, moist skin that allows diffusion of gases across their body covering.

Lungs are the respiratory organs that are present in all terrestrial vertebrates. This structure allows them to exchange gases between the air and the blood.

First, the oxygen is inhaled and it is transported into the lungs. Then, the oxygen is carried through the bloodstream in order to transport the oxygen to the rest of the cells in the body. In turn, the cells exchange oxygen for carbon dioxide. Then, the carbon dioxide goes back into the lungs, where it is eliminated by exhaling or breathing out.

Instead of using lungs, all invertebrates that live on land use their skin, mantle cavities, book lungs, and tracheal tubes as the respiratory structures that help them breathe.

Choices A, C, and D are incorrect. A closed circulatory system has a heart that pumps blood into a system of blood vessels–arteries and veins that are located throughout the entire body. Nutrients and oxygen are also transported in the bloodstream.

B. blood travels through a system of blood vessels that extend throughout the body

The term diffusion is defined as the process of moving substances from a high concentration to a low concentration. This process must take place in order to facilitate gas exchange.

Respiration occurs when:
a. The concentration of oxygen in the air or water is greater than the concentration in the blood; hence, oxygen can get inside the body.

b. The concentration of carbon dioxide in the blood is greater than the concentration in the air or water; hence, carbon dioxide can get out of the body.

Therefore, the correct answer is C.

C. lower than the concentration of oxygen in the air or water

Here are the functions of the atrium and the ventricle:

The atrium, which is the upper heart chamber, is responsible for receiving blood that returns to the heart. It also pumps the blood into the ventricles.

The ventricle, which is the lower heart chamber, is responsible for returning the blood from the atrium. It forces the blood out of the heart into the rest of the body.

Arthropods and most mollusks have an open circulatory system wherein the heart pumps blood into the blood vessels that empty into an open cavity. Then, the blood from the cavity goes back into a large sinus that surrounds the heart.

On the other hand, all vertebrates and some large mollusks have a closed circulatory system, wherein the heart pumps blood into a system of blood vessels–arteries and veins that are located throughout the entire body.

Reptiles and amphibians both have a three-chambered heart. However, reptiles have evolved and developed a partition in their ventricle, which reduces the mixing of the oxygenated blood with the deoxygenated ones. This characteristic is similar to the four-chambered heart of the mammals.

Reptiles and amphibians have a three-chambered heart. However, only reptiles developed a partition in their ventricle. In this case, the dissected organism is an amphibian.

To maintain homeostasis, kidneys regulate the fluids in the body. When animals are living in a dry climate or a salty environment, their kidneys work extra hard in conserving the body fluids and regulating the body’s salt content in order to prevent dehydration.

A. some animals live in dry or salty environments

The process of excretion in insects takes place in a saclike organ called Malpighian tubules. This structure extracts the waste from the blood and converts it into uric acid, which eventually crystallizes and turns into a thick paste.

d. Malpighian tubules

The two ways in which animals eliminate ammonia are:
1. Animals immediately get rid of ammonia from their body by diffusion or excretion.
2. Animals convert it into other compounds, such as uric acid and urea, that are less toxic to the body.

Fishes that live in freshwater have a higher salt concentration inside their bodies than the water they live in; hence, osmosis causes the water to move inside their bodies. To maintain homeostasis, the kidneys of freshwater fishes prevents the accumulation of too much water inside their body, or else their cells would swell and burst. In this case, they excrete the excess water and produce a watery urine.

Fishes that live in saltwater have a less concentrated bodies than their environment. In this case, osmosis causes the water to leave their body. To prevent dehydration, their kidneys retain water by producing small amounts of urine.

Desert animals have limited access to water; hence, they have to conserve the water content in their bodies to prevent dehydration. In this case, their excretory system is designed to produce concentrated urine and dry feces.

Taking a lot of salt in the body can strain the kidneys and disrupt the homeostasis. For most animals, one effect is dehydration. This happens when too much water exits the body due to a high concentration of salt in the blood.

Unfortunately, some animals do not have the ability to eliminate concentrated salt in their body. Instead, they make their kidneys retain more fluid in the body to prevent dehydration. This can be very fatal because once the kidneys are too strained, it would stop performing its function in eliminating waste products. This will lead to the body being poisoned by the toxins.

Since no animals can produce enzymes that can digest the cellulose found in the leaves, fruits are more commonly used as foods. Unlike leaves, fruits are easier to digest.

One example of symbiosis is the mutualistic relationship occurs between humans and bacteria, such as Lactobacillus Acidophilus and other probiotics. Despite the notion that bacteria often cause diseases, there are some bacteria that play an essential role in our digestion. These probiotics assist in extracting the nutrients from the food, producing vitamins, processing of waste products, and improving the immune system’s response to pathogens. In turn, the human host provides the bacteria a place where they can live and feed.

Unlike a digestive tract with two openings, cnidarians have a digestive system that contains a digestive cavity with one opening. This only cavity serves as the mouth where the food is ingested and the anus where the waste is expelled.

In order to digest the food, the cells that line the cavity secretes enzymes that perform extracellular digestion. When the food particles are broken down by the enzymes, the nutrients are absorbed by the cells.

The questions that might help us discover more about the diet of bird species and their energy needs include the following:
a. What is the structure of the bird’s beak?
b. What is the bird’s feeding behavior?
c. Where does the bird live? What kind of environment does it have?
d. What is the bird’s ecological niche?

The jaws and teeth of the animal’s skeleton would be helpful in determining whether it is a meat-eater or a leaf-eater. Here are the characteristics of the mouthparts of a carnivore and a herbivore:

Meat eaters/carnivores:
a. Canine (sharp and pointed) – to tear or cut the meat
b. Molars (sharp edges) – to grind the meat into smaller chunks
c. Jaw bones – suited for up and down movement

Leaf-eaters/herbivores:
a. Canine – non-existent or reduced
b. Molars (broad and flat) – to grind the plant into a pulp
c. Jaw bones – suited for side to side movement

The jaws and teeth of the animal’s skeleton would be helpful in determining whether it is a meat-eater or a leaf-eater.

a. The circulatory system that shows a heart with little oxygen is diagram B. Since its heart does not have a partition, the deoxygenated and oxygenated blood mix together; hence, it contains carbon dioxide and oxygen, which is in a small amount.

b. The circulatory system that shows a four-chambered heart is diagram A. This shows a double-loop circulation, which is characterized by a two-pump system.

The respiratory system and the circulatory system works hand in hand in transporting blood and oxygen into the body of a fish. First, the gills take in the water and filter the oxygen. Then, the oxygen flows into the tiny blood vessels. When the blood becomes oxygenated, it goes into the rest of the body. Once the oxygen is absorbed by the cells, the deoxygenated blood (with carbon dioxide) goes back into the heart then into the gill capillaries. In turn, the carbon dioxide is diffused through the gills.

The statement is true. Waste products contain high levels of ammonia that are toxic to organisms. It can impair the organs and disrupt homeostasis. This is the reason why animals treat this as a problem that must be solved immediately. This can be done by either eliminating ammonia from the body or reducing it into other compounds that are less toxic to the body.

Since some animals on land do not have the adaptations that can excrete ammonia directly, they need to convert it first into uric acid, which is less toxic and less soluble in water. In this way, they can store the waste products until they can be eliminated from the body.

The rate of gas diffusion relies on the surface area of the respiratory system. In this case, if the surface area is large, more gases are diffused; hence, gas exchanges can happen more quickly.

Earthworms cannot grow like the size of an alligator. The largest size that they could get is 14 inches. They may emerge small but they are structurally designed to be fully formed in this size because of their feeding behavior and role in the ecosystem. Since the diet of earthworms consists of organic matter and microorganisms like bacteria and algae, their sizes are relatively small.

Animals that live in the dry environment have limited access to water; hence, they have to conserve the water content in their bodies to prevent dehydration. In this case, they are unable to excrete urine that is diluted. Their kidneys are designed to produce concentrated urine and dry feces.

The digestive tract of grass-eating herbivores (cattle and sheep) is designed to have long intestines with specialized parts that can digest the cellulose found in plant tissues. They have a rumen, which is a pouch-like chamber that is found in the esophagus. On the other hand, carnivores (lions and tigers) have a shorter digestive tract. They produce enzymes that can digest animal tissues easily.

The gills, which are mainly found in fishes and other aquatic organisms, are the feathery respiratory structures that allow the exchange of gases that occur underwater. This organ is made up of tiny capillaries that take the oxygen out of the water and release carbon dioxide back to the water.

On the other hand, the lungs are the respiratory structures of terrestrial organisms. This internal organ allows them to exchange gases between the air and the blood. First, the oxygen is inhaled and it is transported into the lungs. Then, the oxygen is carried through the bloodstream in order to transport the oxygen to the rest of the cells in the body. In turn, the cells exchange oxygen for carbon dioxide. Then, the carbon dioxide goes back into the lungs and gets rid of it by exhaling or breathing out.

According to the graph, when more drops of caffeine are added to the water that surrounds the Daphnia, its heart rate (beats per minute) has significantly increased. Therefore, increased exposure to caffeine causes the Daphnia’s heart to pump faster.

If five or drops of caffeine were added to the water, the heart rate of the Daphnia would continue to increase. This event can be very fatal for the water crustacean. It might strain the heart and cause the organism to lose consciousness, or in worst cases, a cardiac arrest.

The snake was able to reach its food at 35 seconds when it was exposed to a temperature of 27 degrees Celsius. According to the data on the table, this was the fastest rate in which the snake hunted its food.

The snake reached the food within 51 seconds when the temperature was set to 4 degrees Celsius. However, when the temperature was changed to 27 degrees Celsius, the time was reduced to 35 seconds.

In this case, the time to reach the food has decreased when the snake was exposed to a higher temperature.

According to the experiment, time and temperature have a negative correlation. In this case, the time decreases when the temperature increases. Therefore, we can say that snakes move faster when they are exposed to a warmer environment.

The circulatory system of fishes undergoes a single-loop circulation, which is characterized by a single pump that moves the blood in a unidirectional flow. Their hearts have two chambers: an atrium and a ventricle. Once the heart receives the blood from the body capillaries through the atrium, the blood is pumped out of the heart and into the gill capillaries through the ventricle.

On the other hand, mammals have a four-chambered heart–two atria and two ventricles. Their circulatory system undergoes a double-loop circulation, which is characterized by a two-pump system. The first loop, which is located on one side of the heart, pumps oxygen-poor blood into the lungs. The second loop, which is on the other side of the heart, receives the oxygen-rich blood and pumps it into the rest of the body. through the systemic capillaries.

Despite being relatively small, the lungs of the birds are considered as the most efficient respiratory structure when compared to other animals. Once the fresh air is inhaled, the air sacs allow the oxygen to move in a unidirectional flow; hence, more oxygen is diffused in the blood and no old or stale air is trapped into the lungs. The high oxygen intake of the birds allows them to fly and power up their flight muscles for an extended period of time.