Frank Brothers Solutions for ICSE Class 9 Biology Chapter 17 The Skeletal System

PAGE NO: 162

Solution 1: 
Bones of skull, vertebral column, sternum and ribs.
These bones form the central axis of the human body and are part of the axial skeleton. They are responsible for protecting the most important organs like the brain, spinal cord, and heart.
Think of the "Axis" of the Earth; these bones are the center line that everything else hangs on.
Exam Tip: Make sure to list all four parts - skull, vertebral column, sternum, and ribs - to get full marks for identifying the axial skeleton.

Solution 2: 
Longest bone - Femur
Smallest bone - Stapes of middle ear.
The femur is your thigh bone and is incredibly strong to support your weight. The stapes is a tiny bone in your ear that helps you hear sound vibrations.
Remember "F" for Femur is "F"ound in the thigh; "S" for Stapes is "S"mallest.
Exam Tip: Always specify that the stapes is located in the "middle ear" to show precise knowledge.

Solution 3:
There are seven cervical vertebrae. First vertebra is called atlas, second is axis while the rest are called typical cervical vertebrae.
These seven bones are located in your neck and allow for head movement. The atlas helps you nod "yes," while the axis helps you shake your head "no."
Think of the giant Atlas from Greek mythology who held up the world; your atlas holds up your head!
Exam Tip: Learn the names "Atlas" and "Axis" for the first two neck bones as they are frequently asked in exams.

Solution 4: 
The skeletal system performs the following functions in an animal:
1. It provides a framework to support the body and gives a definite shape and form to the body.
2. It helps to protect some of the vital organs like heart, lungs, brain and spinal cord.
3. It provides the base for attachment of muscles and several bones so as to make body movements possible.
4. Bones act as storehouse of some minerals like calcium and phosphorus.
5. Red bone marrow of long bones of limbs produces red blood cells and granulated white blood cells in their hollow cavities.
The skeleton acts like the steel frame of a building, keeping us upright and structured. It is also a chemical factory and a shield for our soft internal parts.
Use the word "SHAPE" to remember: Support, Hematopoiesis (blood making), Attachment, Protection, and Energy/minerals.
Exam Tip: Mention the production of Red Blood Cells (RBCs) in the bone marrow to score higher on the functions of bones.

Solution 5:
1. Axial skeleton
2. Appendicular skeleton
The human skeleton is divided into these two main categories based on the position of the bones. One group forms the center pillar, and the other group consists of the limbs that attach to it.
Axial is the "axis" (middle), and Appendicular is for the "appendages" (arms and legs).
Exam Tip: Use these exact terms when asked to classify the human skeletal system.

Solution 6: 
The various parts of a human skeleton are:
1. Axial skeleton: This consists of skull, vertebral column, sternum and ribs
2. Appendicular skeleton: It consists of pectoral and pelvic girdles and bones of limbs.
The axial skeleton is like the trunk of a tree, while the appendicular skeleton is like the branches. Together, they allow us to stand tall and move around easily.
Touch your head and chest for Axial; move your arms and legs for Appendicular.
Exam Tip: Do not forget to include the "girdles" (shoulders and hips) when describing the appendicular skeleton.

Solution 7: 
A typical vertebra has a main body or centrum and a neural canal in the centre of the neural arch, arising from the sides of the centrum. Neural spine is a flat, longitudinal projection. There are side projections called transverse processes. The articular facets help in joining the two adjacent vertebrae.
Every single bone in your spine is specially shaped to protect the spinal cord. The projections allow muscles to pull on the bones so you can bend and twist.
Centrum means "center" - it is the big, solid part of the vertebra.
Exam Tip: Label the "Neural Canal" as the hole where the spinal cord passes through in diagrams.

Solution 8:
On the basis of position, endoskeleton is divided into two main parts:
Axial skeleton: This consists of skull, vertebral column, sternum and ribs. Human skull has 22 bones of which 8 are present in the cranium and 14 on the face. Brain is present in the cavity called cranium. In the occipital region is an opening called foramen magnum through which spinal cord passes. Cranium has 8 bones which covers the brain from all sides.
Facial bones: These bones form the face and protect the sensory organs present in the head. It has 14 bones.
Vertebral Column:
It makes the axis of the body and provides support like a pillar. Vertebral column is divided into following five parts:
1. Cervical Region. It has 7 cervical vertebrae. First vertebra is called atlas, second is axis and rest are called typical cervical vertebrae.
2. Thoracic Region. It has 12 thoracic vertebrae. Neural spine of these vertebrae is long and pointed, which provdes surface for muscle and attachment.
3. Lumber Region. It has 5 lumber vertebrae.
4. Sacral Region. It has 5 sacral vertebrae which are permanently fused to each other. These are situated on both halves of pelvic and form a joint with pelvic girdle.
5. Caudal Region. It has 4 caudal vertebrae. These are also fused to form a triangular structure which is called coccyx.
Sternum and Ribs
Sternum is the bone at the mid-ventral line of the thorax to which most of the ribs are attached at their ventral ends. Ribs are formed by vertebral and sterna part. First seven pairs of ribs are called true ribs. These are joined on one side with sternum and on second side with thorax.
Appendicular skeleton: It consists of limbs, shoulder or pectoral girdle and hip or pelvic girdles and bones of limbs.
The skull is a biological helmet made of many fused bones. The vertebral column is like a flexible pillar that supports your head and protects your nerves.
Remember the number of vertebrae as a phone number: 7-12-5-5-4.
Exam Tip: The foramen magnum is a very important opening in the skull that allows the spinal cord to connect to the brain.

Solution 9: 
1. Bones of the fore arm: Humerus, radius, Ulna, Carpals, Metacarpals, finger bones, etc.
2. Bones of the hind limb: Femur, Tibia, Fibula, Tarsal, Metatarsal, etc.
3. Pectoral Girdle: In mammals, two halves of pectoral girdle are situated at equal distance from the ribs on the dorsal plane. Each of it is called shoulder bones. Each half of it made up of a triangular flat bone called scapula. From its outer side a projection arises called acromion and has a cavity called glenoid cavity.
4. Pelvic Girdle: It consists of two similar halves. In each, three bones are found, ilium, ischium and pubis. Pubis bones of both halves are joined and are called pubic sysmphysis. Ilium and ischium form acetabulum cavity in which head of femur articulates by forming ball and socket joint. A hollow space is found between pubis and ischium, which is called obdurate foramen, which provides passage for obturatry artery, vein and nerve.
Your arms and legs have matching bones; for example, the wrist carpals match the ankle tarsals. The girdles are the connectors that let your limbs swing and rotate.
The "Pectoral" girdle helps you "Pick" things up (arms); the "Pelvic" girdle helps you "Pedal" a bike (legs).
Exam Tip: Name the "Scapula" as the shoulder blade and "Femur" as the thigh bone to show detailed understanding.

Solution 10: 
The five regions of the vertebral column are:
(i) Cervical region - It has seven cervical vertebrae. First vertebra is called atlas, second is axis while the resta re called typical cervical vertebrae.
(ii) Thoracic region - It has 12 thoracic vertebrae. Neural spine of these vertebrae is long and pointed, which provides surface for muscle attachment.
(iii) Lumbar region - Has 5 lumbar vertebrae.
(iv) Sacral region - Has 5 sacral vertebrae which are permanently fused to each other.
(v) Caudal region - Has 4 caudal vertebrae, which are fused to form a triangular structure called coccyx.
These regions divide our backbone into the neck, ribs, lower back, hips, and tailbone. Each section has a specific number of bones designed for different levels of strength and flexibility.
C-T-L-S-C: Cervical, Thoracic, Lumbar, Sacral, Caudal.
Exam Tip: Be prepared to draw the vertebral column and label these five regions correctly.

Solution 11:
Importance of pectoral girdle:
1. It provides support to the anterior portion of the body.
2. Provides surface articulation of fore arms.
3. Provides surface for muscle attachment.
4. Provides protection to vital organs like heart and lungs.
Importance of pelvic girdle:
1. Provides surface articulation of hind limbs.
2. Provides surface for joining of muscles.
3. Provides protection to the uterus.
4. Protects from shocks.
These girdles act as bridges between the central axis of the body and our limbs. They are strong bones that take the impact when we fall or jump.
Pectoral is for the chest/shoulders; Pelvic is for the lower belly/hips.
Exam Tip: Mention that the pelvic girdle protects internal organs like the uterus in females to score full marks.

Solution 12: 
The place of joining of two or more than two bones is called joint.
Joints are the points where our skeleton becomes flexible. Without joints, our bodies would be as stiff as a piece of wood.
A "Joint" is where bones are "Joined" together.
Exam Tip: Define a joint as a site of connection between bones that usually allows movement.

Solution 13: 
Flexor is a muscle that causes bending of a limb or other part e.g. thigh muscle.
Extensor is the muscle that causes the straightening of a limb or other part. E.g. for extending the foot
Levator is the muscle that raises any part of the body.
Rotator is a muscle that rotates one part on another.
Muscles work in teams to pull bones in different directions. These names describe exactly what kind of movement the muscle produces.
"Flex" means to bend, and "Extend" means to straighten out.
Exam Tip: Use the example of biceps (flexor) and triceps (extensor) to explain how limb movement works.

Solution 14: 
Axial skeleton: This consists of skull, vertebral column, sternum and ribs. Human skull has 22 bones of which 8 are present in the cranium and 14 on the face. Brain is present in the cavity called cranium. In the occipital region is an opening called foramen magnum through which spinal cord passes. Cranium has 8 bones which covers the brain from all sides.
Facial bones: These bones form the face and protect the sensory organs present in the head. It has 14 bones.
Vertebral Column:
It makes the axis of the body and provides support like a pillar. Vertebral column is divided into following five parts:
1. Cervical Region. It has 7 cervical vertebrae. First vertebra is called atlas, second is axis and rest are called typical cervical vertebrae.
2. Thoracic Region. It has 12 thoracic vertebrae. Neural spine of these vertebrae is long and pointed, which provdes surface for muscle and attachment.
3. Lumber Region. It has 5 lumber vertebrae.
4. Sacral Region. It has 5 sacral vertebrae which are permanently fused to each other. These are situated on both halves of pelvic and form a joint with pelvic girdle.
5. Caudal Region. It has 4 caudal vertebrae. These are also fused to form a triangular structure which is called coccyx.
Sternum and Ribs:
Sternum is the bone at the mid-ventral line of the thorax to which most of the ribs are attached at their ventral ends. Ribs are formed by vertebral and sterna part. First seven pairs of ribs are called true ribs. These are joined on one side with sternum and on second side with thorax.
Appendicular skeleton: It consists of limbs, shoulder or pectoral girdle and hip or pelvic girdles and bones of limbs.
1. Bones of the fore arm: Humerus, radius, Ulna, Carpals, Metacarpals, finger bones, etc.
2. Bones of hind limb: Femur, Tibia, Fibula, Tarsal, Metatarsal, etc.
3. Pectoral Girdle: In mammals, two halves of pectoral girdle are situated at equal distance from the ribs on the dorsal plane. Each of it is called shoulder bones. Each half of it made up of a triangular flat bone called scapula. From its outer side a projection arises called acromion and has a cavity called glenoid cavity.
4. Pelvic Girdle: It consists of two similar halves. In each, three bones are found, ilium, ischium and pubis. Pubis bones of both halves are joined and are called pubic sysmphysis. Ilium and ischium form acetabulum cavity in which head of femur articulates by forming ball and socket joint.
This section summarizes the entire skeletal architecture of a human being. It shows how the protection of the axial skeleton works with the mobility of the appendicular skeleton.
Your skeleton is like a puzzle of 206 pieces that fit perfectly together.
Exam Tip: Differentiate clearly between "True Ribs" (first 7 pairs) and other ribs in your answers.

Solution 15: 
Forelimbs consists of one humerus (anterior arm bone), one radius and one ulna (posterior arm bones), 8 carpals (wrist bones), 5 metacarpals ( palm bones) and 14 phalanges (finger bones).
Hindlimb consists of one femur bone or thigh bone, one tibia and fibula which are bones of the leg, 8 tarsals (bones of ankle), 5 metatarsals (bones of feet), and 14 phalanges (bones of fingers).
Both your arms and your legs have a single bone at the top, two in the middle, and many small bones for the hands or feet. This pattern is shared by many animals with backbones.
"Carpals" are for the wrist, and "Tarsals" are for the ankle.
Exam Tip: Use the term "Phalanges" for both fingers and toes to be scientifically accurate.

Solution 16: 
The three levers found in the human skeleton are:
1. First order levers
2. Second order levers
3. Third order levers
Our bones and joints act as simple machines to help us lift things and move our bodies. Most of the movements in our limbs are third-order levers where the muscle pull is between the joint and the weight.
Think of your elbow as a hinge that works like a mechanical lever.
Exam Tip: Identify the elbow joint as a common example of a third-order lever in humans.

Solution 17: 
1. Ball and socket joint
2. Pivot joint
These are two different types of movable joints that allow us to rotate or turn our parts. The pivot joint is what allows you to turn your head from side to side.
A "Pivot" joint works like a gate hinge that lets things rotate.
Exam Tip: Name the neck joint (atlas/axis) as the primary example of a pivot joint.

Solution 18: 
In a ball and socket joint, the ball of one bone is fitted into the socket of another bone such that the ball can move in the socket. Such a joint always involves a long bone, which can move in all planes. This type of joint is found in pectoral girdle, glenoid cavity, femur and acetabulum of pelvic girdle.
This joint gives you the largest range of movement, like a joystick on a game controller. You can swing your arms in a full circle because of this specific joint design.
Imagine a bowl (socket) with a ball sitting inside it - that is exactly how your shoulder works!
Exam Tip: Use the shoulder and hip as classic examples of the ball and socket joint.

Solution 19: 
Forelimbs consists of one humerus (anterior arm bone), one radius and one ulna (posterior arm bones), 8 carpals (wrist bones), 5 metacarpals (palm bones) and 14 phalanges (finger bones).
Hind limb consists of one femur bone or thigh bone, one tibia and fibula which are bones of the leg, 8 tarsal (bones of ankle), 5 metatarsals (bones of feet), and 14 phalanges (bones of fingers).
These are the precise names for every bone in your arms and legs. Knowing these helps doctors and scientists talk about specific injuries or growth patterns.
The "Femur" is in the leg, while the "Humerus" is in the arm.
Exam Tip: List the exact number of bones (like 8 carpals) if the question asks for a detailed description.

Solution 20: 
Biceps muscles first contract to bend the arm, following which the triceps muscles act to straighten the arm. Thus act in opposite ways and are antagonistic muscles, since they counteract each other’s action. The muscles of biceps are called flexor muscle while that of the triceps is the extensor muscle. This whole coordination of muscular action is under the nerve impulse and brain control.
Muscles can only pull, they cannot push, so they must work in pairs to move bones back and forth. This coordination is like a "tug-of-war" that is perfectly timed by your brain.
"Antagonistic" means they work against each other, like a hero and a villain in a story.
Exam Tip: Use the word "antagonistic" to describe muscle pairs like the biceps and triceps.

Solution 21:
Muscles which counteract each other’s actions are known as antagonistic muscles. Biceps and triceps are two such muscles.
This type of muscle arrangement is found throughout the body to control movement. When you bend your knee or move your fingers, antagonistic pairs are at work.
Think of "Antagonists" as muscles that do the "opposite" of each other.
Exam Tip: Define antagonistic muscles clearly as pairs that perform opposite movements at a joint.

Solution 22: 
Biceps cause bending of a limb or other part. Triceps cause straightening of a limb or other part.
These two muscles are the most famous examples of how we move our limbs. The biceps pull the forearm up, and the triceps pull it back down.
Biceps for "bending" - both start with the letter B!
Exam Tip: Specify that the biceps is a "flexor" and the triceps is an "extensor."

Solution 23: 
Striped, Unstriped and cardiac muscles.
Striped muscles are what we use to move our bones, and unstriped muscles control our internal organs. Cardiac muscles are special and are only found in the walls of the heart.
Striped (Voluntary), Unstriped (Involuntary), Cardiac (Heart).
Exam Tip: Remember that cardiac muscles never get tired throughout your entire life.

Solution 24: 
1. Synovial joint is a movable joint present between the adjoining bones which can move independently. The articulating surfaces of the two bones are covered with articular cartilage. The joint is covered with a synovial membrane which secretes synovial fluid for lubrication.
2. These are found in elbow joint, knee joint, femur and pelvic girdle, etc.
3. The cartilages cover the ends of the adjoining bones. They function to absorb shock and reduce friction during movement.
4. 1 and 5 -epiphyseal bone, 2- synovial cavity, 3- synovial fluid, 4- synovial membrane
This type of joint is designed for smooth, pain-free movement over millions of cycles. The fluid inside acts as oil for a biological hinge, preventing the bones from grinding together.
Synovial fluid is like the "WD-40" or oil for your body's joints.
Exam Tip: List "synovial fluid" and "articular cartilage" as the main parts that help reduce friction in joints.

Solution 25: 
1. (a) Scapula; 2. Shoulder joint; 3. Humerus; 4. Bicep; 5. Tricep; 6. Radius; 7. Tricep; 8. Elbow Joint; 9. Ulna.
(b) Bicep muscles and triceps are antagonistic muscles.
(c) Bicep muscles.
(d) Shoulder bones.
(e) Ball and socket joint.
These terms help identify the anatomy of the human arm and its associated joint. It shows how bones, joints, and muscles all work together to create movement.
The Scapula is the "Shoulder blade" you can feel on your back.
Exam Tip: When labeling a diagram, always ensure you identify the Radius on the thumb side and the Ulna on the pinky side.

PAGE NO: 163

Solution 26: 
1. (d) all the above
2. (c) 24
3. (b) 7
4. (a) Parietals of skull
5. (d) stapes
6. (b) Cranium
7. (c) It allows movement in all directions.
These multiple-choice questions cover the most important facts about the skeletal system. For example, humans have 12 pairs of ribs, which makes a total of 24 ribs.
12 pairs of shoes = 24 shoes; 12 pairs of ribs = 24 ribs!
Exam Tip: Read each option carefully in MCQs to avoid simple mistakes with numbers like 7 vs 12.