Choices B, C, and D are incorrect. Invertebrates do not have a notochord, which is a flexible rod that lies on the ventral side of a chordate’s body. This structure is the defining characteristic of chordate animals.

A. a notochord

Choices A, B, and C are incorrect. Members of the subphylum Vertebrata are vertebrates that have a vertebral column. This structure acts as the backbone that supports the body.

D. vertebrates

Choices A, C, and D are incorrect. An animal exhibits cephalization if its sense organs and nerve cells are concentrated in front of its body. This characteristic allows the animal to detect stimuli in their environment more quickly.

B. cephalization

Here are the characteristics that are shared by all animals:

a. multicellular eukaryotes that lack cell walls
b. heterotrophic
c. asexual and sexual reproduction
d. complex structure: contain differentiated and specialized tissues
e. exhibits body plans

Feedback inhibition is a mechanism that is often seen when an organism maintains homeostasis. This mechanism is referred also as a negative feedback that occurs when the end result of a reaction limits or interferes with the process.

For example, when the temperature is very cold, our body tends to shiver. This reaction is actually the body’s way of triggering the muscles to generate heat. The shivering stops when the temperature becomes warm again.

The term invertebrate is used to describe an organism that lacks a vertebrate. In this case, this category indicates that the organisms lack a characteristic, instead of telling us that they share a similar characteristic from a common ancestor. For this reason, invertebrates are not classified as a clade.

The sea star exhibits a radial symmetry, wherein its 5 identical arms are extended outward from the center of the body.

Choices A, C, and D are incorrect. According to the current fossil records, the earliest animals first appeared during the Precambrian Era (before the Cambrian Explosion) that happened 600 million years ago. The fossils that were found comprised of eggs, embryos, and body parts. Some indirect evidence from the past which is in the form of trace fossils like tracks and burrows were also discovered.

B. Precambrian Era

Choices A, C, and D are incorrect. According to the cladogram of chordates in figure 24-11, the terrestrial chordates have four limbs.

B. four limbs

Choices A, B, and D are incorrect. According to the fossil records, the evolution of jaws and paired appendages first appeared in cartilaginous fishes, such as sharks.

C. fishes

The body plan characteristics that are shared by arthropods and vertebrates include:

1. bilateral symmetry (the body’s left and right side are the mirror images of each other)
2. cephalization (sensory organs and nervous control are concentrated on the anterior part of the body)

Cambrian animals had shells, skeleton and other hard body parts, such as appendages. These body structures consist of compact tissues and bones that were able to fossilize quite well.

The main defining characteristic that sets the birds different from other living animals is the presence of feathers.

According to the cladogram in figure 24-11, the early jawed fishes evolved into cartilaginous fishes and bony fishes. These are the two major groups of fishes that were able to survive.

Newborn Monotremes:
Monotremes lay eggs. Once the young monotremes hatch from the eggs, the parent produces milk to feed them.

Newborn Marsupial:
Marsupials lack a placenta. Instead, they have marsupium to nourish their newborn young after birth. Marsupium is the protective pouch found in female marsupials in which their newborn marsupials are placed and carried in order to nourish and to continue its growth and development.

Newborn Placental Mammal:
The embryo develops inside the mother with the help of the placenta for nourishment. After birth, the mother cares for the young by nursing.

Choices A, B, and C are incorrect. The anthropoids include the monkeys, apes, and humans. This branch of primates is split into two different groups–the new world monkeys and the old world monkeys and great apes.

D. humans

Choices A, C, and D are incorrect. Primates have fingers, toes, and rotating shoulders that allows them to grip objects and swing on trees. They also have binocular vision that enables them to have depth perception and a three-dimensional view of the surroundings. More importantly, they have a large and well-developed brain. Because of this, they are able to perform different functions and display complex behaviors than other mammals.

B. rotation at the shoulder joint

Choices B, C, and D are incorrect. The Homo sapiens species is the only surviving member of the hominin clade as of today.

A. one

Primates have a flat face structure that allows the eyes to face forward. This is the reason why they have a binocular vision that enables them to have depth perception and a three-dimensional view of the surroundings.

Primates have grasping fingers and toes that allow them to grip and climb on tree branches. They also have rotating shoulders that allow them to swing on trees.

Hominins have a larger brain inside a skull that is attached to the S-shaped spine. They have a bowl-shaped pelvis and thigh bones that are faced inward. They have arms that are shorter than the legs and hands that evolved into an opposable thumb that allowed them to grasp objects. In addition, their legs are used for walking on the ground, which improved their locomotion and enabled them to become bipedal.

Examples of hominins are Ardipithecus, Australopithecus, Paranthropus, and Homo. Under the genus Homo is the species called Homo sapiens, which is known as the modern human.

Choices B, C, and D are incorrect. The reaction to the changes within an internal or external stimulus is called a behavior.

A. behavior

Choices A, B, and C are incorrect. The behavior is often shaped by natural selection. The behavior that is favored by nature will increase the organism’s fitness. As a result, the organism will survive and such behavior, which is influenced by the genes, are passed on to the next generation; hence, it will spread through a population. Therefore, D is the correct answer.

D. genes that influence behavior that increases an individual’s fitness can be passed on to the next generation

Choices B, C, and D are incorrect because they are all social behaviors. Operant conditioning is not a social behavior. It is actually a learned behavior.

A. operant conditioning

An example of a stimulus and response in the animal behavior is the way ducklings crouch when they see a predator bird overhead. The stimulus is the moment they see the body shape of the flying predator, whereas the response is the crouching behavior.

Operant conditioning refers to the learning that occurs when a particular behavior is associated with a consequence (reward or punishment).

One example is the experiment wherein a rat receives food when a button is pressed. In this case, since a reward is given right after the button is pressed, the rat learns how to get food.

According to the kin selection theory, animals have the tendency to stay with their relatives to protect them and their territory against predators. This behavior ensures the survival of their own genes, which increases the chances of passing the traits to the next generation.

Vertebrates have a spinal cord instead of a dorsal, hollow nerve cord that is found in non-vertebrate chordates. When young vertebrates start to mature, their vertebrae are formed. This structure is an endoskeleton that serves as the backbone of a vertebrate.

Bilateral symmetry is a body plan in which the body’s left and right sides are the mirror images of each other. This is an important step in cephalization, wherein the sensory organs and nervous control are concentrated on the anterior part of the body. Due to this evolution, animals have quicker responses to stimuli and they were able to exhibit a forward and directional movement.

The characteristics of the primate that are shown in the photo include:
1. grasping hands and toes (for gripping on the branches)
2. rotating shoulders (shoulder joint attached to the collarbone for swinging on trees)
2. binocular vision (eyes forward for depth perception)

Operant conditioning can be applied when you are training your new pet dog to sit in situations where you would like him to be seated and calm. First, hold a treat close to the dog’s nose. Then move your hand up and allow the dog to follow the treat. This would make the dog lower his bottom. The next thing to do is say, “sit.” Then, give the dog a reward–the treat and some affection. Repeat this for a few times until the dog mastered it.

If the developments during evolution are arranged according to the order of appearance, the sequence is multicellularity, tissues, mouth-first development, and anus-first development.

A bilaterally symmetrical body plan has one plane of symmetry that results to a body that has a head and back end. It also exhibits a body with left and right sides that are the mirror images of each other. This means that cephalization occurs in organisms that have a bilaterally symmetrical body.

The evolution of the 3 germ layers, which are the origin of the main organ systems, allowed the organisms to have specialization of body segments and parts during embryological development. The concentration of sense organs and nerve cells in the anterior end of the body allowed cephalization.

According to the cladogram of chordates in figure 24-11 of the book, all non-vertebrate and vertebrate chordates share a common chordate ancestor. Chordates are characterized by organisms that have a notochord. Both non-vertebrate chordates and vertebrates have notochord as a part of their life cycle. However, the notochord of vertebrates is replaced by vertebrae once the embryo matures.

Here are some of the major adaptations of animals that allowed them to thrive in terrestrial life are:
a. Lungs – for breathing air on land
b. Limbs – for propping on land
c. Neck – allows the head to be flexible
d. Teeth – for feeding on land

The type of learning showed by the baby is operant conditioning. The baby learned to smile whenever his mother comes near. The reason the baby behaves this way is that he is always picked up and cuddled as a result of smiling, which is a sort of reward for him.

One advantage of the solitary living is the absence of competition among his own species for food and resources. In this case, the survival advantage of the animal increases because it only needs to find enough food to sustain itself.

Ideally, animals migrate to different places on a seasonal basis in order to mate, to escape harsh living conditions and climate, and to find food. In this case, if the animals randomly moved into another place that contains the exact conditions of their old habitat, then it is not considered a migration. It is only a local dispersal. A true migration must be done seasonally or annually.

Animals that occupy a particular area, especially those that live in solitary, are often aggressive and territorial. Whenever they see other animals, they treat them as rivals and attack them in order to drive them away and to protect their food resources and territory. Their aggressiveness is the result of them being protective or territorial to their own space and being dominant over other animals.