Monday, February 29, 2016



Connective tissue helps in binding the other tissues and organs together and provides a frame work and support to various organs in the body.

This tissue also plays a major role in the transport of material from one tissue to another. 
It also helps in the body defense, body repair and in the storage of fat.

There are different types of connective tissues each performing a different function.

Areolartissue is one type of connective tissue which joins different tissues. It helps in packing these tissues and thus help to keep the organs in pace.
These Cells called fibroblasts are the major components in this type of connective tissue. These cells secrete fibrous material which holds the other tissues in position. These cells also help in repair of the tissues when they are injured.

Cartilage is a type of connective tissue found in the joints of bones, tip of ribs, of the nose, external ear and in trachea. Embryos of several vertebrates do not have bone but have cartilage. The entire skeleton of fishes like sharks is made of cartilage. Cartilage is hard but not as hard as bone.
 Boneis another type of connective tissue. It is a major component of the skeletal system of  several vertebrates. Bone is made calcium, phosphate and calcium carbonate.
These salts are secreted by cells called osteocytes. These are present in the central hollow portion of the bone called marrow.
Ligament is yet another types of connective tissue that connects bones at the joints and holds them in position. It is made us. These fibres are made of a protein called collagen.
 Tendon is a type of connective tissue which is also made of fibres. The tendon joins the muscles to the bone. It is also made of collagen.

Adipose or fat tissue is a type of connective tissue which store fat. This tissue is present beneath the skin, around the kidneys and in bone marrow. This tissue is made of large numbers of cells called adipocytes or fat cells.

Cytoplasm of these cells is filled with fat is used for the production of energy required by the body during starvation. The layer of fat, especially, below the skin, prevent heat loss from the body.
Blood is called fluid connective tissue. It differs from other from types of connective tissues. There are several different types of cells in blood each one has a different function.
All the cells in the blood float freely in the plasma. Extracellular space is filled with a fluid called plasma. There are no fibres in blood. A normal adult humans being has about 5 liters of blood. Chief component of blood is water.

Besides water, it also has several nutrients such as glucose, amino acids, proteins, vitamins, and hormones etc. required for the body and excretory products such as lactic acid, urea, salts etc.

plasma also contain factors responsible for blood clotting. Cells present in blood are called corpuscles and they are of three types- red blood cells, white blood cells and blood platelets.
 Red blood cells, also known as erythrocytes, are red in color . In mammals, red blood cells do not have mitochondria, nucleus, endoplasmic reticulum, lysosomes and ribosomes.
 In fishes, amphibians and reptiles, they have a nucleus. These cells are concave on both the sides.
 They have red colored protein called hemoglobin, which helps in the transport of oxygen and carbon dioxide .One ml of human blood has about 500 crores of red blood cells. In adults humans, red blood cells are formed in bone marrow and live for 120 days I blood.

The second type of cell present in blood are white blood cells. These cells do not have hemoglobin, hence they are colorless. These cells are less in number.

There are two kinds of white blood cells, they are granulocytes and a granulocytes.

There are three types of granulocytes, neutrophils, basophils and eosinophils. These three kinds of cells attack and destroy the micro organisms that enter the blood . all these types of cells have granules in their cytoplasm. Hence they are called granulocytes.

There are two types of a granulocytes- they are lymphocytes and monocytes. Lymphocytes secrete antibodies towards foreign material that enter into blood . monocytes move like amoeba and along with granulocytes they attack the foreign materials and engulf them. The foreign material are destroyed inside these cells.

Blood platelets are a separates group of cells which do not have a nucleus. They are disk  like bodies. Whenever a blood vessel is injured, platelets accumulate at the site of injury and help in the formation of a blood clot.
The clot seals the wound in the blood vessel and prevent blood loss. Several chemicals present in the blood required for clot formation.




On the basis of their function, animal tissues are of four major types. They are epithelial tissue, connective tissue, muscle tissue and nervous tissue.

Let us examine the structure the structure and functions of these four kinds of tissues in animals ( including man).

Epithelial tissue: epithelial tissue forms a covering over the surface of the body as well as on the outside and inside of several internal organs example skin is an epithelial tissue on the outer side of the body. Lining of the digestive tract is a covering of epithelial cells on the internal organ.
Epithelial cells perform several functions- they offer protection, produce structure like hair, nails, feather and horns, in the form of gland cells, they secrete a variety of chemical and may involve in receiving external stimuli.
Cells in the epithelial are very close to each other and are joined together by a cementing substance. Epithelial cells occur in various shapes, flat, cube like, long and cylindrical.
Epithelialcells lining the digestive and respiratory system of several animals have hair like projections called cilia. They help in moving the food particles or mucus.
Epithelial cells may be present in a single layer or may occur in multiple layer stratified epithelium.



There are simple and complex tissues in plants. Parenchyma, collenchyma, sclerenchyma, are examples of simple tissues . PlantTissues fall into two large categories: Meristematic, or Permanent (Non-Meristematic)
Xylem and phloem are example for complex tissues. Simple tissues have only one type of cell while complex tissues have several different types of cells.
Parenchyma: parenchyma is the fundamental and simple tissue in plants. Almost all the primary structure like leaves, flowers and young stem made up of parenchyma.
Cells in parenchyma are living cells. They can be either round, suare or polyhedral. There are different types of parenchymatous cells.
Chlorechyma: cells in this type of parenchyma have chloroplasts and are commonly seen in leaves.
Aerenchyma: air spaces are present between cells in this type of parenchyma

This type of parenchyma is seen in plants which float on water such plants are called hydrophytes.
Storage tissue: cells in this type of parenchyma store food materials. This type of parenchyma is seen in tubers and rhizomes.
Water storage: cells in this type of parenchyma store water – such cells are seen in desert plants.
Collenchyma : collenchymas is  a simple living tissue. This tissue is present in the stems of herbs and shrubs. It gives mechanical strength and support. Cells may have chloroplasts. Cells in collenchymas are short and square or long and fibre like with pointed ends. Cell wall is made up of cellulose and pectin which gives. Collenchyma  gives flexibility and tensile strength to the plants.
Sclerenchyma : sclerenchyma is a tissue with dead cells and is designed to give mechanical strength to the plant. It also protects the parenchyma from damage due to stretching, bending and pressure lignin is the major component in cell walls of the cells present in sclerenchyma.
Xylem:  xylem is a conductive tissue which has both living and non-living cells. It conducts water and minerals from roots to other parts of the plant. A part  from this xylem gives mechanical strength to plant. Xylem tissue is also helpful in identifying the plant species.
There are three kinds of non-living cells in xylem- they are fibers, tracheas and vessels. Xylem parenchyma is the living component in xylem. Cell walls of the xylem cells are thick because of lignin deposition. It is also commercially very useful.
Phloem: phloem is also called bast or leptome. Unlike xylem, phloem is a living tissues. Cell walls have lignin deposition. Phloem is composed of five types of cells. They are sieve cells, sieve tubes, companion cells, phloem fibres and phloem parenchyma.
Sieve cells and sieve tubes are long with tapering ends. Sieve plate with one to many sieve pores is present at the ends of sieve tubes. The conductuion of food material from leaves to other parts takes place through phloem tissues. Besides, phloem has commercial value- bast fibres present in phloem are used for making ropes.


Sunday, February 28, 2016


Unlike plants, animals cannot prepare their own food. Instead, they procure food by feeding on other organisms.
Hence, they are called Heterotrophs. Heterotrophic nutrition is of two types. Saprozoic and Holozoic.

Saprozoic  nutrition in very primitive animals, especially some protozoans, and parasites exhibit saprozoic mode of nutrition. They absorb food materials dissolved in water through their body surfaces. 
Some animals secrete enzymes into the external medium. These enzymes breakdown the complex organic molecutes into simple organic molecules. These are then absorbed by the animal through its body surface. As the food is already digested and in the form of small molecules, some of these animals may not have special digestive organs. Even if present, the digestive system in these animals is very simple.
Holozoic nutrition  Majority of animals take solid particulate food or liquid food through special feeding mechanisms and digest them with the help of digestive enzymes. This mode of nutrition is know as holozoic nutrition.

The size of food particles varies considerably ranging from microscopic organisms to large animals and plants. Depending on the size of the food, different mechanisms to capture the food.
Some animals use pseudopodia (Amoeba), tentacles (Hydra) for capture the food. These animals do not cut the food into small pieces and swallow the entire food at one time. Other animals which feed on solid food have mechanisms to cut the food into small pieces before they consume it.
For example, snails have snarp teeth like structures on their tongue called Radula with which they scrape the surface of food and swallow the food particles.

Some animals, like lions and tigers, are equipped with organs to chase, seize (capture) kill, cut and cat the prey.
Some animals feed only on liquid food. For example scorpions and spiders kill the prey and inject digestive enzymes into the body of the dead animal. These enzymes digest the food and convert it into liquid form which the animal will feed.
Houseflies, butterflies, mosquitoes, aphids, leeches etc.,also feed on liquid food. Butterflies have long tube like proboscis which is inserted into the flowers and nectar is sucked.
Mosquitoes have special organs to pierce through the skin and suck the blood. Blood sucking animals such as mosquitoes and leeches secrete substances into the blood to prevent blood from clothing while they are feeding.
Animals like earth worms feed on soil containing decomposed organic material.
Thus,a variety of feeding mechanisms are seen in animal kingdom and the type of feeding mechanisms in the animal depends on the type and nature of the food.

Mono and Polyphagous animals:
Some animals feed on only one type of food material and these are called monophagous animals.
A typical example for this is the caterpillar larva of silkworm which feeds only on mulberry leaves.
Several animals feed on plant material are called herbivores while those feeding on other animals are called carnivores. Animals which eat both plants and animals are called omnivores.  
Diet of an animal may be different in different sexes or at different stages of its life. For example, male mosquito feeds on plant juices white female mosquito feeds on blood. Similarly, caterpillar larva feeds on leaves while the butterfly feeds on the nectar.
Thus, there is a great variation in the type of food consumed and the method by which it is consumed in holozoic animals.