Chordates are characterized by organisms that have at least a dorsal nerve cord, a notochord, pharyngeal pouches, and a tail.

C. fins

All nonvertebrate and verbrate chordates share a common invertebrate ancestor. The two nonvertebrate chordates include tunicates and lancelets. Therefore, the term cerebrum is the least closely related to chordate, invertebrate, and lancelet.

B. cerebrum

Fishes have acquired a pair of fins, scales, gills, and jaws as they evolved over time.

C. fishes

Fishes have acquired gills as an adaptation for living in an aquatic habitat. The gills facilitated in the gas exchange and allowed them to breathe underwater.

A. over the gill filaments

The brain of a fish contains a cerebellum, which coordinates all its body movements.

D. cerebellum

Fishes that lay eggs, wherein the embryos inside the egg grow and hatch outside the mother’s body are called oviparous.

A. oviparous

Sharks are classified as a cartilaginous fish that has large jaws and sharp teeth.

C. shark

Cloaca is a muscular cavity found at the end of the large intestine where the digestive wastes, eggs, or sperm cells pass through as they are released from the body.

A. cloaca

The three separate chambers of an amphibian heart include the left atrium, the right atrium, and the ventricle.

C. three chambers

The nictitating membrane is not a respiratory organ. It is a protective membrane that is present in the eyes of some animals.

D. nictitating membrane

The **notochord** is a flexible mesodermal structure that functions as an important element for the classification of chordate species. The notochord later develops as part of the vertebral column/vertebrae of the organism

Lancelets use their pharynx to filter the water and catch food. Once the sticky mucus trapped the food particles, the lancelet will swallow the mucus. In turn, the food gets to be broken down inside the digestive tract.

The two major groups that evolved from the early jawed fishes are the cartilaginous fishes (sharks and rays), and the bony fishes (ray-finned fishes and lobe-finned fishes).

**Fishes** are aquatic vertebrates that are characterized by having paired fins, scales, and gills. The fins are used for locomotion, scales for protection, and gills for respiratory function. Fishes’ adaptation to aquatic life includes the presence of various modes of feeding mechanisms. These species can be herbivores, carnivores, parasites, filter feeders, and detritus feeders.

Blood circulates in one continuous loop through a fish. Oxygen poor blood enters the sinus venosus and flows into the atrium. The blood then flows into the ventricle where it is pumped into the bulbus arterious. It is then moved into the ventral aorta and towards the gills.

Fishes excrete wastes in the form of ammonia. Since they are underwater, the fluid diffuses out of the gills and goes into the surrounding water.

**Fishes** have a well-developed and organized response mechanism because these species have already the presence of a defined nervous system (brain and spinal cord) and as well as the presence of sense organs. Fishes have these sensitive receptors called the **lateral line system**, which they use to detect the currents and vibrations in the water environment. Moreover, they also use this for protection and feeding(sensing predators and prey).

**Fishes** are vertebrate species that have well-adapted body forms for aquatic life. These organisms have paired fins for locomotion, various modes of feeding for survival, and specialized structures for gas exchange.

One important specialized feature in fishes is the presence of a **swim bladder**. This is a gas-filled internal organ present in bony fishes, which functions to maintain the organism’s buoyancy.

The muscles of a fish give it extra thrust when swimming. Paired sets of muscles on either side of the backbone contract alternately creating a series of s-shaped curves that move down the body. As the curve travels from head to tail it creates a backward force on the surrounding water propelling it forward with the action of the fins.

Both species have streamlined bodies due to their need to swim with the tails being used to propel them. Lampreys are jaw-less while sharks have powerful jaws. The lamprey latches onto a host and feeds off them while sharks grab and shred their prey.

Vertebrates had to breath air, protect themselves and their eggs from drying out as well as support themselves against the pull of gravity.

Please review explanation

During the tadpole stage of frogs, their diet consists of plants. Due to the kind of diet that they have, their intestines have a long coiled structure which can break down the plant materials.

Once the tadpole matures, adult frogs start to feed exclusively on meat. Their long intestines are transformed to shorter intestines and their feeding apparatus are now suited for their new diet.

An **amphibian** is a type of vertebrate species that has a life cycle that includes a larva that can live in an aquatic environment, and an adult stage that can live on land. One example of an amphibian organism is the **frog**

The frog is the most commonly known amphibian species. Its larval stage swims in a freshwater environment, where it uses its gills to breathe, while the adult stage of the frog lives in the terrestrial environment and breathes through its paired lungs.

A frog’s heart has three chambers that include two atria (left and right) and a single ventricle. The blood goes into two circuits. First, the blood goes into the lungs then back to the heart. The second circuit contains the blood that goes to the body and the organs then back to the heart.

The two atria receive blood from these two circuits. The right atrium receives deoxygenated blood from the veins that drain the organs of the body, while the left atrium receives the oxygenated blood coming from the lungs and skin. As soon as the blood goes into the ventricle, the blood from the two circuits is mixed.

An amphibian is a type of vertebrate species that has a life cycle that includes a larva that can live in an aquatic environment, and an adult stage that can live on land. Early amphibians organisms evolved various several adapting mechanisms that enable and helped them to thrive and live the adult stage of their life out of water.

The **amphibian limb bones and limb girdles became stronger, allowing more efficient and effective movement**. The presence of lungs for terrestrial respiration, and the presence of bony cavity that protects its internal organs.

Most amphibians are not able to tolerate an arid environment. Since they live underwater during their early life stage and on land during their adult stage, they are well-suited to thrive in moist places like wetlands and rainforests. They have a moist skin that helps in respiration. Their skin is prone to water loss if they are exposed to extreme heat. This is why they tend to stay in damp areas so their skin would not dry out.

Saltwater fishes have a special adaptation to avoid water loss due to the high concentration of salt in the marine ecosystem. They can tolerate the saltwater because they have kidneys which help balance and control the amount of water in their body by excreting the salt.

It would be impossible for a saltwater fish to survive in a freshwater ecosystem due to the low concentration of salt there. Since saltwater fishes have cells that are hypertonic, they will become hypotonic once they are placed in freshwater. Once the cells absorb too much freshwater, they have the tendency to burst.

Salmon species exhibit a unique characteristic that is not usually observed in other saltwater fish. When the Salmon matures, it moves upstream to the freshwater river to spawn. This is also referred to as the “Salmon Run.”

Salmons on maturity return back to their hatching grounds for spawning. Here it lays eggs and then dies. These eggs then hatch in the same fresh water and baby salmons begin their journey towards the salty seawater. On its journey back to the salty waters, it takes up the smell and tastes of the water on its path and thus they remember its route for the completion of the life cycle. It matures in the seawater for around 3 to 4 years and then returns back to its home ground of fresh water for spawning.

The construction of dams might act as a hurdle in their migration process. They will not be able to make their way from the salt water into the river water. Thus will not be able to complete their life cycle.

**Amphhibian** species have evolved various adaptations that could aid them to leave their life out of the water and survive in terrestrial habitats. These adaptations include the presence of moist skin, development of lungs, stronger bones, etc. However, even though they are already adapted to the land environment, the excessive presence of pollution causing a drastic increase in global warming and climate change can still bring chaos to their population.

Their moist skin that maintains the body’s physiological balance may not be able to handle the increased heat in the land, and their skin might dry up because of this. As a result, there will be lesser protection for their body hence causing fatality. Moreover, because their eggs are not protected by shells, they are more prone to desiccation and danger, especially since most water environments are already drying up because of global warming.

These are the few reasons connected to why there is a decline in the amphibian population nowadays.

Using the graph, the given questions are answered as follows:

a. Amphibians evolved during the Devonian period. They have evolved from the Osteichthyes. which evolved from the jawless fishes.

b. Amphibians evolved from early bony fishes (Osteichthyes). However. Osteichthyes evolved from jawless fishes. Thus, the amphibians have indirectly evolved from jawless fishes.

c. Numbers of species have increased from Osteichthyes in recent times. The Osteichthyes started increasing in number from the Cretaceous period of the Mesozoic era and they are flourished in the Cenozoic era.

d. Placoderms are now extinct. They were seen only upto the Permian period. They flourished in the Devonian period and started diminishing in the Carboniferous period.

The experiment can be performed in two parts. They are part A and part B.

– Part A: Herbivore diet:

1. Identify a tadpole for the experiment.

2. Create a stimulating environment for the experiment.

3. Provide the tadpole with food resources comprising of **plant diet**

4. Repeat the process for several weeks.

5. Observe the development rate of a tadpole (you can check the size, and the weight for this).

– Part B: Carnivorous diet:

1. Identify a tadpole for the experiment.

2. Create a stimulating environment for the experiment.

3. Provide the tadpole with food resources comprising of the **carnivore diet.** (you may feed the tadpole with small fish, or small seafoods)

4. Repeat the process for several weeks.

5. Observe the development rate of the tadpole.
(you can check the size, and the weight for this).

Since tadpole **feeds only on plants as a food source**, both will have different developmental rates. The variables that need to be controlled include biotic components like sunlight, water salinity, temperature, etc.

To be called a chordate an animal needs to exhibit the following four characteristics at least at one stage during its life cycle. These features include **the presence of nerve cord, notochord, pharyngeal cavity, and tail**.

There are two groups of non-vertebrate chordates. They are tunicates and lancelets. **Tunicate larva exhibits all the chordate characteristics**. However, as it *matures to become an adult, it loses its notochord and tail*.

**Adult lancelet** on the other hand **contains all four characteristics of chordates**. It has a hollow nerve cord, a notochord, a pharynx with gills, and also a tail. It is because they share common ancestors, that they resemble chordates for at least a part of their life stage.