Tissues

Tissue formation takes place, when a group of cells specialised to do similar function. Examples are blood, xylem, muscle, etc.

The main function of the meristematic tissue or meristem is to divide and produce new cells. It is responsible for growth in length (primary growth) in plants.

Small pores present in the epidermis of the leaf are called stomata. Stomata are enclosed by two kidney-shaped cells called guard cells.

Function of stomata includes:

(a) Exchange of gases such as O₂ and CO₂ with the atmosphere.

(b) Transpiration (loss of water in the form of water vapour) occurs through stomata.

Sclerenchyma is the tissue used for making ropes. It is the tissue which makes the plant hard and stiff. For example, the husk of a coconut.

The sclerenchyma tissue is made of dead cells. The cells are without cytoplasm and nucleus that are devoid of cytoplasm and nucleus. Space between cells (intercellular space) absent due to deposition of lignin.

Simple permanent tissue such as parenchyma, collenchyma and sclerenchyma are a few layers of cells located beneath the epidermis.

Parenchyma and collenchyma are the simple permanent tissue whose cells are living.

The diagram shows the two tissues present.

The tissues in plants are divided as:

Nervous tissue is present in the brain. Nervous tissue is consists of nerve cells or neurons.

The covering or protective tissues in our body are epithelial tissues which protects our entire body.

(i) Skin, oesophagus and lining of mouth is made of squamous epithelium.

(ii) Columnar epithelium is present in the respiratory tract.

The diagram is given below:

Bone is an example of connective tissue whose matrix is solid. Bone cells or osteocytes are present in a hard matrix that is composed of calcium and phosphorus compounds.

Areolar tissue is connective tissue which hold organs in place and attaches epithelial tissue to other underlying tissues.

Cilia are hair-like projections on the outer surfaces of epithelial cells called ciliated epithelium. Ciliated epithelium is found in the upper respiratory tract, the Fallopian tubes, the uterus, and the central part of the spinal cord.

(i) Multinucleate muscle fiber :

Skeletal or striated muscles have many nuclei.
Skeletal muscles are attached to bones by tendons, and they produce all the movements of body parts in relation to each other.

(ii) Spindle-shaped muscle fiber :
Smooth or unstriated muscles are spindle shaped with single nucleus.
Spindle cell sarcoma is a type of connective tissue cancer in which the cells are spindle-shaped when examined under a microscope.

Smooth muscle tissues are located in the iris of the eye, in ureters and in the bronchi of the lungs.

The smooth muscle tissue forms organs which shape to perform various bodily functions.

Permanent tissues possess the following characteristics:

(i) Cells of this tissue can be living or dead.

(ii) Cell walls may be thin or thick.

(iii) Intercellular spaces may be present or absent.

(iv) Metabolic activities are relatively slow.

(v) Vacuoles in the cells are prominent.

Examples of permanent tissues are parenchyma, collenchyma and sclerenchyma (simple tissues) and xylem and phloem (complex tissues).

A simple tissue is made up of one type of cells forming a uniform mass. The simple tissues are of the following three types: parenchyma, collenchyma, and sclerenchyma.

The collenchyma is a simple permanent tissue. The cells of this tissue are living, elongated and irregularly thickened at the corners and have very little intercellular space. It provides mechanical support to the plant parts. It gives flexibility and allows bending of various parts of a plant like tendrils and stems of climbers without breaking.

Vascular tissues are complex permanent tissues. Examples are xylem and phloem. They are conducting tissues, xylem conducts water and dissolved mineral from roots to the leaves and phloem conducts food from leaves to the roots.

A Nissl’s granules are rough endoplasmic reticulum (RER) with free ribosomes attached to their walls. The main function of these ribosomes is protein synthesis. Thus, Nissl’s granules help in protein synthesis and provides proteins to the cyton.

Mast cells are also known as a mastocytes. It is a type of white blood cell (WBC). Mast cells release histamine and other substances during inflammatory (redness and swelling) and allergic reactions.

The diagram is given below:

Fibres and sclereids are the type of sclerenchyma based on shape and size of the cells.

(a) Tissue that forms the inner lining of our mouth is epithelial tissue. It forms a barrier to keep different body systems separate.

(b) Tissue that stores fat in our body. Adipose tissue, it stores excess fat in the body found abundant in the abdomen and in the hip.

(c) Tissue that transports food in plants. Xylem is a complex permanent tissue. It conducts water from roots to the different parts of a plant.

Bone a skeletal connective tissue. It forms the framework that supports the body. Bone is a strong and nonflexible tissue made of cells called osteocytes. Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds. Two bones can be connected to each other by another type of connective tissue called the ligament. Another type of connective tissue associated with bone is cartilage. Cartilage smoothens bone surfaces at joints. Our nose, ear, trachea and larynx are made of cartilage.

Lining all the external surfaces such as skin and internal cavities of an animal's body are covered with a continuous sheet called epithelium.

Following are the functions of epithelial tissues:

(a) It protects underlying tissues of the body.

(b) Columnar epithelial cells present in the intestine absorb the digested food.

(c) It secretes enzymes.

(d) It receives sensory stimuli.

Blood is considered a fluid (liquid) connective tissue because it has a matrix and living cells. The matrix is called the plasma which liquid part. The plasma contains proteins, salts, and hormones. Blood flows and transports gases, digested food, hormones and waste materials to different parts of the body. The living cell types are red blood cells (RBC) are also called erythrocytes, white blood cells (WBC) are also called leukocytes and platelets are suspended in the plasma.

Blood plasma is a light yellow liquid, similar to the color of straw. It is the largest component of your blood, making up about 55% of blood content. Blood plasma also contains glucose and other dissolved nutrients.

Functions of plasma:

(a) The primary function of plasma is to transport nutrients, hormones, and proteins to the parts of the body that need it.

(b) Cells also deposit their waste products into the plasma and it helps remove this waste from the body.

(c) Plasma contains proteins that help blood in clotting.

(d) Plasma also contains antibodies. The proteins and antibodies in plasma are used to treat rare disorders such as haemophilia.

Epithelial cells of following types:

(a) Simple squamous epithelium:

It located in the lining of Air sacs of lungs and the lining of the heart and blood vessels. It allows materials to pass through by diffusion and filtration and secretion.

(b) Simple cuboidal epithelium:

It is present in ducts and secretory portions of small glands and in kidney. It function is to secretes and absorbs.

(c) Simple columnar epithelium:

It is present in respiratory tract such as bronchi, lining of uterus and in the digestive tract. It absorbs and secretes mucous and enzymes.

(d) Stratified cuboidal epithelium:

It is present in different glands such as sweat, salivary and mammary glands. It helps in protection.

(e) Stratified columnar epithelium:

It is present in the male urethra and in the ducts of some glands. It helps in secretion and protection.

There are four types of tissues found in animals. These are epithelial tissue, connective tissue, muscular tissue, and nervous tissue.

(a) Epithelial tissue: The cells of the tissue are of various shape and closely connected to each other via cellular junctions. This tissue lines body surfaces, cavities and forms glands. The function of epithelial tissue in protection, absorption and secretin.

(b) Connective tissues: The cells of connective tissue are embedded in extracellular material. This material is called matrix is secreted by the cells. The extracellular matrix is non-living material composed of protein fibres and ground substance. It helps in transportation, protection and body defence and storage.

(c) Muscular tissue: The cells are elongated and contain the contractile proteins actin and myosin. It brings about contraction and movement of organs.

(d) Nervous tissue: The tissue consists of two major cell types: neurons and glial cells. Neurons are specialized for the conduction of nerve impulses. This tissue composes the brain, spinal cord, and peripheral nerves.