Bone is very strong and non-flexible tissue. It is porous, highly vascular, mineralized, hard and rigid. Its matrix is made up of proteins, and rich in salts of calcium and magnesium. It forms the framework that supports the body. It also anchors the muscles and supports the main organs of the body. However, cartilage is specialized connective tissue which is compact and less vascular. It has widely spaced out cells. Its matrix is composed of proteins and sugars, and is slightly hardened by calcium salts. Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx.

The number of bones a person has in their body generally depends on their age.  A human newborn baby has approximately 270 bones in his or her body.  As the person ages and develops, some of the bones fuse together to make larger bones.  By the time a person is an adult, they have the standard 206 bones in their body. 

Serum is the fluid and solute component of blood which does not play a role in clotting. It may be defined as blood plasma without fibrinogens. Serum includes all proteins not used in blood clotting; all electrolytes, antibodies, antigens, hormones; and any exogenous substances (e.g., drugs or microorganisms). Serum does not contain white blood cells (leukocytes), red blood cells (erythrocytes), platelets, or clotting factors.

An ecosystem is a community of plants, animals and smaller organisms that live, feed, reproduce and interact in the same area or environment.
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An ecosystem includes all of the living things in a given area, interacting with each other, and also with their non-living environments.

• Pivotal joints allow for rotation, twisting, extension, and flexibility.
• This type of joint allows movements in many planes, viz. up and down, side to side movements. The joint between the skull and the vertebral column is an example of pivot joint.
• It is moreover like a cylindrical bone moving in a ring.

Electricity is an energy. This energy can be used to power electrical items such as toasters, kettles, cookers, televisions and computer tablets.  Electrical energy is caused by electrons (the particles in atoms) moving about to make a current.

Cartilage: Cartilage is a stiff yet flexible connective tissue. It is not as hard and rigid as bone but is stiffer and less flexible than a muscle. Cartilage is and elastic tissue that covers the end of the bones at a joint. Cartilage acts as a cushion or sponge and absorbs shock at the joints. It is present at joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs.
Tissue: A group of cells with similar shape and function are termed as tissues. They form a cellular organizational level intermediate in between the cells and organ system. Organs are then formed by combining the functional groups of multiple tissues.

The part of plants which prepares food is the leaf. Leaves of a plant prepare food in the presence of sunlight. The process of making food by utilizing water and carbon dioxide in the presence of sunlight is called photosynthesis.

Aquatic habitat: It refers to the region covered with water where plants and animals survive. Aquatic habitat is further divided into freshwater habitat, marine habitat and coastal habitat. Water is the medium for the organisms living in aquatic habitats.
a) Freshwater habitat: These are the water bodies filled with fresh water. These include rivers, lakes, ponds, streams etc. Water present has very low concentration of salts. Plants growing in water are called as hydrophytes.
b) Marine habitat: Ocean and seas are termed to be marine habitat. These are full with life. Different varieties of organisms exist in marine habitat. Organisms like, corals, shelled animals, sponges, jelly fish, sharks and many others are found in this habitat.
c) Coastal habitat: This is the region represented by the place where land meets the sea. Estuaries are formed when the saltwater mixes with freshwater. These habitats are unique Special type of trees called as mangroves are found in this region. Animals are also well adapted to live in these regions.

All living things have some common characteristics which help them to survive and distinguish them from non-living things. They are:

i. Food: All living things require food to survive. They also need water and air to stay alive.

ii. Growth: All living things grow by increasing their body size with the passage of time.

iii. Movement: All living things move themselves or their body parts. For example – birds fly in the sky.

iv. Response to stimuli: All living things respond to changes around them. Such changes in the environment to which living things respond are called stimuli. Examples of external stimuli are heat, light, touch, sound, etc. for example – if a man touches a very hot object accidentally, he quickly pulls his hand away from the hot object. In this case heat is a stimulus.

v. Respiration: All living things need energy for their growth, movement and their life processes. They get energy from the food they eat by the process of respiration.

vi. Excretion: Excretion is the process of getting rid wastes by living beings. All living organisms need to excrete waste products from their body which mainly includes the removal of carbon dioxide, urea, water and faeces.

vii. Reproduction: All living organisms reproduce to produce new members of their species. Animals reproduce their own kind. The mode of reproduction may differ in different kinds of organisms. Some animals reproduce by giving birth to their young ones like human beings. Some animals produce their young ones through eggs like hens, pigeons, etc.

viii. Life span: All living things have a definite life span. The living things start their life when they are born as babies or hatched from eggs. 

Adaptation in lion:

The lion is a carnivorous animal which eats only meat. Its special features which help it to survive in grasslands are as follows:

1. It is a strong, fast and agile animal which can hunt and kill its prey like deer.
2. It has long, sharp and strong claws in its front legs to catch its prey.
3. It has eyes in front of its head which enable it to have a correct idea of the location of its prey.
4. It is light brown in colour which helps it to hide in dry grassland while hunting.

Adaptation in deer:

The deer is a herbivorous animal which eats only plants. Its special features which help it to survive in grasslands are as follows:

1. It has eyes on the sides of its head which enable it to see in all directions at the same time and helps it to see animals like lion which kill it.
2. It has big ears for hearing which helps it to protect it from its predator animals.
3. It is a fast and agile animal which helps it to run away from the predators.
4. It has brown colour which helps it to hide in dry grasslands without being noticed by the predators like lion.
5. It has strong teeth for chewing hard parts of the forest plants like stems.

Fish in the Pisces classification have these three characteristics as adaptations to living in water.
1. Skin with scales to let water run over the body easily when swimming.
2. Gills under covers or free, to increase the surface area for gas exchange during breathing.
3. A streamlined body shape with fins to allow easy swimming through water.