Have you ever wondered what the human body is made up of? Cells are the fundamental unit of life. All organisms are made of cells. Organisms may be single cell (unicellular) or made up of several cells (multicellular). We are multicellular organisms. 

The smallest known cells in the world are Mycoplasmas. Cells are the building blocks of all living things. Cells provide structure to the body and convert nutrients taken from food to energy.

They are complex and serve different functions in the body. Cells are of different shapes and sizes, almost like the bricks of the buildings. Our body has cells of varying shapes and sizes – they are the lowest organisation level in all life forms.

Protoplasm is defined as organic and inorganic substances that make up the cell’s living nucleus, cytoplasm, plastid, and mitochondria. The protoplasm is the living part of a cell that is made up of different cellular organelles. It is a jelly-like, colourless, transparent and viscous living substance present within the cell wall.

However, at the microscopic level, all living organisms are made up of the same fundamental unit – the cell.

• Prokaryotic Cell
  Prokaryotic cells are relatively smaller and much simpler than eukaryotic cells. The other distinguishing trait of prokaryotic cells is that they do not have membrane-bound organelles, such as the nucleus. Reproduction takes place in a binary fission process.
  Structurally, prokaryotes have a capsule that envelops the whole body and acts as a defensive coat. Pilus is a hair-like appendage present on most prokaryotes’ outer surface, which allows the body to bind itself to different environments.
• Eukaryotes
  Eukaryotes are more complex and much larger than prokaryotes. They comprise nearly all major kingdoms except the monera kingdom. Structurally, eukaryotes have a cell wall that surrounds and defends the plasma membrane. The cell is surrounded by a plasma membrane which regulates the entrance and exit of certain compounds. Chloroplasts are present only in plant cells and are subcellular sources of photosynthesis.
  The nucleus comprises DNA that is responsible for preserving all genetic material. Eukaryotic cells also contain mitochondria responsible for the generation of energy, which is then used by the cell.

The presence of a nucleus is the basic difference between prokaryotic and eukaryotic cells. In prokaryotic cells, the true nucleus is absent, and the membrane-bound organelles are found only in eukaryotic cells. Other main distinctions between prokaryotic and eukaryotic cells are that prokaryotic cells are exclusively unicellular, while eukaryotic cells are not.

Source: science.howstuffworks.com

In basic terms, tissue can be described as a group of cells with a similar shape and function, called tissues.

Animal tissues are divided into four types:

• Connective Tissue: A set of tissues formed by cells divided by a non-living medium called an extracellular matrix.
• Muscle Tissue: It is engaged in the production of force and the generation of motion, either for locomotion or for other body movements within internal organs.
• Nervous Tissue: These are the primary brain and spinal cord tissue elements of the central nervous system.
• Epithelial tissue: It is created by cells that cover the outer sections of the body’s organs and line the organ surfaces, such as the surface of the skin, the reproductive tract, the airways and the inner lining of the digestive tract.

The classification of plant tissues is primarily based on the following two relevant criteria:

• Based on the various parts of the plants.
• Based on the various cell types.

Plant Tissues are generally classified into three tissue systems. This classification is based on the parts of the plants they are present in.

• Epidermis Tissues – cells developed from the outer surface of the leaves.
• Vascular tissues – involved in the internal transfer of fluids and nutrients.
• Ground Tissue – involved in the production of nutrients through photosynthesis and the preservation of nutrients.

The plant tissue is classified into two groups. This classification is based on the type of cells that they contain.

• Meristematic tissues: They are a collection of young cells, consisting of continuously dividing cells and expanding the length and width of the plant.
• Permanent tissues: A collection of cells that are identical in origin, shape and function. They are engaged in total growth and differentiation during inadequate meristematic activity.

Source:researchgate

In this chapter, we developed a basic understanding of the cell. We also learned about the types of plant and animal tissues and the primary difference between them.

1. What is a prokaryotic cell?
   A prokaryotic cell is a primitive type of cell characterised by the lack of a nucleus. Also, prokaryotes do not have membrane-bound cellular organelles. Prokaryotes are unicellular only.
2. What is a eukaryotic cell?
   Eukaryotic cells are cells that have a real nucleus along with membrane-bound organelles. Eukaryotes can be either unicellular or multicellular.
3. Define cell.
   It is the fundamental physical and structural unit of life.
4. List the functions of chloroplasts.
   Chloroplasts are plastics used in all plant cells. These cells consist of a photosynthetic pigment called chlorophyll and are involved in the synthesis of food through photosynthesis.
5. Who has discovered cell and cell theory?
   The cell was first discovered in 1665 by Robert Hooke, an English natural philosopher. The cell theory was demonstrated in 1830 by Theodor Schwann and Matthias Jakob Schleiden.