Question

Define the term "tissue".

Answer 1

Hint: These are a group of cells of similar structure that functions together as a single unit. These are different in plants and animals.

Complete answer:
A tissue is a group of similar or identical cells that are derived from the same germ cells and act together to perform a specific function. Tissues are absent in unicellular organisms and even in some simplest multicellular species such as sponges. But multicellular animals and plants have specialised tissues that can organise and regulate the responses of an organism to its environment.
Plant tissue:
In vascular plants such as angiosperms and gymnosperms, special tissues known as meristems are present. The apical meristems are located at the tips of roots and shoots in the vascular plant giving rise to three types of primary tissues of the plant. These three types of tissues are dermal tissue, ground tissue, and vascular tissue.
1)Dermal tissue: these tissues make the outer covering of the herbaceous plants. Dermal tissues are composed of closely packed epithelial cells. They secrete a waxy cuticle that helps in the prevention of water loss during transpiration, and also in an invasion by insects and microorganisms.
2)Ground tissue: The ground tissue constitutes the bulk of the primary plant body. These consist of parenchyma, collenchyma, and sclerenchyma cells. The ground tissues provide various support, storage, and helps in photosynthesis.
3)Vascular tissue: This tissue includes xylem, phloem, parenchyma, and cambium cells. The vascular tissues are mainly responsible for the transport of food, water, hormones, and minerals within the plant. Vascular tissues are absent in bryophytes such as liverworts, hornworts, and mosses.
Animal tissue:
There are generally four different types of tissues in animals: connective tissue, muscular tissue, nervous tissue, and epithelial tissue.
1)Connective Tissue: This tissue binds different tissues to form an organ and also connects the small organs of the body. The main feature of this tissue is the presence of a large quantity of intercellular space (matrix). It also contains different types of fibres which bind bones to tissues.
2)Muscular Tissue: These tissues are required for locomotion and performing different kinds of movement. These are made up of muscle fibres that develop from myoblasts cells.
3)Nervous tissue: These are made up of nerve cells or neurons and neuroglia, which are cells that help nerve impulses to travel. These tissues receive, transmits and discharges various kinds of stimuli. The brain, spinal cord, and the peripheral nerves, which are all parts of the nervous system are made up of nervous tissue.
4)Epithelial tissue: This tissue consists of self which covers either external or internal surfaces of the body skin and lining of the alimentary canal. There is no intercellular space between the cells of epithelial tissue. These are of two types of simple epithelial tissue when the tissue is only of one layer and compound epithelial tissue when the tissue is having several layers of thickness.

Note: -Connective tissue has an elasticity that allows the organ, such as the lungs to move. They also provide physical support to cells and ground substances.
-Based on structure and function, muscular tissues are of three kinds: unstriped muscle, striped muscles and cardiac muscles.
-Unstriped muscles are made up of fusiform muscle fibres, each fibre with a centrally placed nucleus.
-Striped muscles are made up of long cylindrical fibres. These are multinucleated muscle fibers.