Chapter Notes and Summary
• All living organisms are made up of cells.
• Cells are building blocks of an organism.
• skeleton is framework formed by bones of our body.
• skeleton of a normal adult human is made up of 206 bones.
• Functions of Skeleton :
• It forms framework of our body, provides shape and support and holds body upright.
• It helps in movement of various parts of body.
• It protects internal organs of our body.
• Bones are filled with a spongy mass from inside called bone marrow where blood cells are formed.
• skeleton comprises four main parts–– skull, back bone or spine, rib cage and limbs.
• skull comprises bones of face and head region.
• skull protects our brain, which is an extremely vital organ of our body.
• skull is made up of 22 bones. Out of these, 14 form face and jaw. Rest of 8 bones are present in upper part of head.
• Most bones of skull are fixed and can not move except that of lower jaw.
• movement of lower jaw makes it possible for us to chew food.
• There are 12 pairs of ribs, that is total of 24 bones, forming a cage-like structure called rib cage.
• ribs are flat, thin and curved bones which are joined with back bone at back and with breast bone in front.
• last two pairs of ribs are not attached in front and are called floating ribs.
• rib cage protects heart and lungs as well as parts of stomach and kidneys.
• long, hard and uneven structure in back is called backbone or spine. It is also called vertebral column. It is made of 33 small bones called vertebrae. These vertebrae are joined to each other.
• All animals that have a vertebral column are called vertebrates. e.g., Fish, amphibians, reptiles, birds and mammals.
• Limbs allow us to perform various types of movements.
• Two pairs of limbs are found in our body–– fore limbs (arms) and hind limbs (legs).
• upper arm has one long bone called humerus and lower arm has two bones called radius and ulna.
• humerus is attached to vertebral column by collar bone and shoulder blade.
• longest bone in our body is femur which is thigh bone.
• lower leg has two bones called tibia and fibula.
• pelvis or hip bone supports legs which is attached to lower end of back bone.
• Bones are rigid and can not bend. However, our body is very flexible and we can move our body parts at specific locations due to presence of joints.
• A joint is a place where two bones are joined together.
• bones are held in position at joints because these are connected together by tissues called ligaments.
• At place of joint, ends of two bones are covered with a soft tissue called cartilage.
• In ball and socket joint, end of one bone is like a ball and it fits perfectly into a cavity (socket) in other bone.
• Hinge joints allow movement of bones in only one direction i.e., either forward or backward.
• In pivot joint, end of one bone is in form of a cylinder. end of other bone is in form of a ring.
• bones in our head that protect our brain are joined together by fixed points. They can not move.
• Muscles are attached to bones with help of a tissue called tendon.
• On contraction, muscle becomes shorter, thicker and stiffer.
• Muscles work in pairs and can only pull bone .
• Earthworm does not have legs and bones. It moves by alternate expansion and contraction of body affected by muscles.
• Earthworm is very useful for farmers as it increases fertility of soil.
• body of snail is covered with hard shell. body is soft and consists of head, foot and shell.
• snail moves with help of a muscular organ known as foot. It makes wave-like movements by expanding and contracting muscles in foot.
• A cockroach can walk, run, climb and even fly short distances.
• body of a cockroach is made up of three parts-head, thorax and abdomen.
• body of a fish is specially designed for swimming.
• A fish has streamlined body.
• Birds have a streamlined body, which makes it easy for them to move through air.
• Snakes slither or crawl on ground in a wave-like motion.
• back bone of snakes is very flexible.