Introduction
All living organisms are made up of tiny building blocks called cells, which are the smallest units of life. These cells combine to form tissues, which further unite to form organs and organ systems. So, what is tissue in science?
All biotic organisms in the world are classified into two major categories: unicellular and multicellular organisms.
In higher multicellular organisms such as dogs and human beings, cells cluster together to form groups that perform a particular function. Each group performs a specific function and is known as a tissue.
To put it simply, a tissue is a group of cells that play a similar role. These are present in both plants and animals and represent levels of organization in living organisms.
The study of tissues is called histology, and for plants, the subject is called plant anatomy.
Read on to know more about tissue and its types.
Classification of Tissues
Tissues form an intermediate organizational structure between cells and organ systems. Different groups of tissues with diverse functions group together to form an organ. In animals, therefore, a group of muscle cells combines together to form muscle tissue.
The classification of tissues in animals falls under four major categories. These are:
Connective tissues.
Muscle tissues.
Nervous tissues.
Epithelial tissues.
Before you learn more about what is the function of tissue, here’s a quiz for you to try:
Pop Quiz 1:
The study of tissues is known as ________.
Plant anatomy.
Morphology.
Histology.
Natural history.
Connective Tissues
In connective tissue, a group of cells separated by a non-living extracellular matrix combine to form a tissue. Connective tissues help provide mechanical strength, shape and rigidity to the organs and keep them in place. Examples of connective tissues include tendons, ligaments, bones, blood, adipose and areolar tissues. Further, there are three types of connective tissues. These are:
Skeletal Connective Tissue.
Fluid Connective Tissue.
Fibrous Connective Tissue.
Connective tissues have several different functions in the human body, namely:
They provide insulation and protection against cold to the body.
They help bind the organs together and provide mechanical support to them.
Connective tissues help transport gases, water, hormones, nutrients and waste materials within the body.
Muscle Tissue
Muscle tissues help us to perform different actions and engage in activities like walking, running and locomotion. There are three types of muscle tissue:
Skeletal muscles.
Cardiac muscles.
Visceral or smooth muscles that line the inner walls of organs.
Firstly, muscle tissues help us to maintain our posture. Secondly, they also aid in our involuntary and voluntary movements. For example, cardiac muscles help pump blood and regulate its flow in arteries and capillaries.
Muscle tissues can also be classified on the basis of the conscious control a person has over those muscles. On this basis, there are two types of muscles in existence which are - Voluntary muscles and Involuntary muscles. Voluntary muscles move according to the will of the person and involuntary muscles move freely irrespective of the will of the person.
Nervous Tissue
Nervous tissues are present in the central nervous system that comprises the brain and spinal cord. In the peripheral nervous system, nervous tissues make up the cranial and spinal nerves.
Nervous tissues perform several vital functions, such as:
They control and coordinate metabolic activities in the body.
They help transmit information within the body.
They help maintain stability and create an acute awareness of the environment around us.
They also help us respond to external stimuli.
These tissues also play a key role in the management of various emotions, memory, and the reasoning skills of an organism.
Epithelial Tissue
Epithelial tissues consist of cells that form the external covering of the body. These cover the organ surfaces such as the skin, the airways, the inner walls of our digestive tract as well as the reproductive tract.
Epithelial tissues provide support and mechanical strength to the cells and tissues. They also help in the transportation of materials through diffusion, secretion, and filtration.
Moreover, epithelial tissues such as the ones beneath our skin help us in sensory reception and protect us against pathogens and physical trauma. They also secrete hormones, mucus, and enzymes from various endocrine organs.
Now that you have gone through the classification of tissues, it’s time to revise a few concepts with the following exercise.
Classification of the tissue present in the plants
Plants also have various types of tissues and can be classified into two categories. The first is based on the parts of plants whose tissue is present in the plant and the second is on the basis of types of cells.
By the first category, the plant tissues can be classified into three major groups, these three groups are:
a) Epidermis Tissues: These tissues are present on the outer surfaces of the leaves.
b) Vascular Tissues: They help in the transportation of the various fluids and nutrients. They are generally present at the middle of the stem and trunk and are spread all over the plant's body.
c) Ground Tissues: Ground tissues are the ones that assist in the process of photosynthesis.
With the help of the second category, the plant tissue can be divided into two sub-categories.
a) Meristematic Tissues: These cells keep on producing new copies of themselves.
b) Permanent Tissues: These tissues have lost their ability to divide and recreate themselves.
Pop Quiz 2
What are the types of tissues?
Connective Tissues.
Nervous Tissue.
Epithelial Tissue.
Muscle Tissue.
All of the above.
Here is a classification of tissues chart to help you understand better.
(Image will be Uploaded soon)
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FAQs on Classification of Tissues
1. What is a tissue in biology?
In biology, a tissue is defined as a group of cells that are similar in structure, origin, and work together to perform a specific function. The study of tissues is known as histology. In multicellular organisms, tissues are the foundational level of organisation between cells and complete organs.
2. What are the main types of tissues found in animals and plants?
Tissues are broadly classified based on the organism.
- In plants, the two primary types of tissues are Meristematic Tissue (dividing cells) and Permanent Tissue (differentiated cells).
- In animals, there are four fundamental types of tissues: Epithelial Tissue, Connective Tissue, Muscular Tissue, and Nervous Tissue.
3. How are plant tissues classified based on their dividing capacity?
Plant tissues are classified into two main groups based on their ability to divide:
- Meristematic Tissues: These consist of actively dividing, undifferentiated cells responsible for plant growth. They are found in the growing regions of a plant, such as the tips of roots and stems.
- Permanent Tissues: These are derived from meristematic tissues but have lost their ability to divide. Their cells are fully differentiated to perform specific functions like support, protection, and transport.
4. What are the four major types of animal tissues and their primary functions?
The four major types of animal tissues are classified based on their functions:
- Epithelial Tissue: Forms a protective layer or lining on the body's surfaces, such as the skin and the lining of the mouth. It also functions in absorption and secretion.
- Connective Tissue: Binds, supports, and protects other tissues and organs. Examples include bone, cartilage, blood, and ligaments.
- Muscular Tissue: Composed of cells that can contract, enabling movement. This includes skeletal, smooth, and cardiac muscles.
- Nervous Tissue: Responsible for communication within the body by transmitting electrical signals. It is made up of nerve cells called neurons.
5. Why are blood and bone considered types of connective tissue?
Blood and bone are considered connective tissues because they fit the fundamental definition: cells suspended within an extracellular matrix. In bone, the cells (osteocytes) are embedded in a hard, rigid matrix made of calcium and phosphorus salts. In blood, the cells (red blood cells, white blood cells, and platelets) are suspended in a fluid matrix called plasma. Despite their different appearances and functions, this shared structural characteristic classifies them both as specialised connective tissues.
6. What is the difference between simple and complex permanent tissues in plants?
The main difference lies in their cellular composition. Simple permanent tissues, such as parenchyma, collenchyma, and sclerenchyma, are made up of only one type of cell. In contrast, complex permanent tissues, such as xylem and phloem, are composed of multiple types of cells that work together as a single unit to perform a specialised function, like the transport of water and food.
7. How does the structure of a neuron relate to its function in the nervous tissue?
The structure of a neuron is highly specialised for transmitting information. The cell body (cyton) contains the nucleus and manages the cell. The branched dendrites receive signals from other neurons. The long, slender axon carries the electrical impulse away from the cell body, often over long distances, to another neuron or a muscle. This unique structure allows for rapid, precise, and long-distance communication, which is the core function of the nervous system.
8. What are the three types of muscle tissues and where are they located in the human body?
The three types of muscle tissues are:
- Striated (Skeletal) Muscle: These are voluntary muscles attached to bones, responsible for body movement. They are found in the limbs, face, and trunk.
- Unstriated (Smooth) Muscle: These are involuntary muscles found in the walls of internal organs like the stomach, intestines, and blood vessels.
- Cardiac Muscle: This is an involuntary, striated muscle found exclusively in the wall of the heart. It is responsible for pumping blood throughout the body.
9. Why do plants have meristematic tissues at specific locations like the root and shoot tips?
Placing meristematic tissues at specific locations allows plants to grow in a targeted and efficient way. Apical meristems are located at the tips of roots and shoots and are responsible for increasing the plant's length (primary growth). This positioning helps the shoot grow towards sunlight and the roots to penetrate deeper into the soil for water and nutrients. Lateral meristems, found along the sides of stems and roots, increase the plant's girth, providing the necessary support as it grows taller and heavier.
10. What are the functions of xylem and phloem in plants?
Xylem and phloem are the two complex conducting tissues in vascular plants.
- The primary function of xylem is to transport water and dissolved minerals from the roots up to the rest of the plant. It also provides mechanical strength to the plant body.
- The main function of phloem is to transport sugars (food) produced during photosynthesis from the leaves to other parts of the plant, such as fruits, seeds, and roots, for use or storage.
11. How does the arrangement of cells in epithelial tissue determine its function?
The arrangement of cells in epithelial tissue is directly linked to its function.
- Simple epithelium, which is a single layer of cells, is thin and allows for easy passage of substances. It is ideal for processes like absorption, secretion, and filtration, and is found in the lining of the intestines and air sacs of the lungs.
- Stratified epithelium, which has multiple layers of cells, is thick and durable. Its primary function is protection against mechanical abrasion and chemical damage, which is why it is found in the skin and the lining of the mouth.
12. Can you provide examples of parenchyma, collenchyma, and sclerenchyma tissues in plants?
These three are types of simple permanent tissues with distinct roles:
- Parenchyma: A living tissue that forms the bulk of a plant's non-woody structures, like the pulp of fruits and the cortex of stems. It functions in photosynthesis and food storage.
- Collenchyma: A living tissue that provides flexible support to growing parts of the plant, such as the stalks of leaves (petioles) and young stems.
- Sclerenchyma: A non-living tissue with very thick, lignified walls that provides rigid mechanical support. Examples include the gritty texture in pear fruit and the hard shell of nuts.
