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Class 9 The Fundamental Unit of Life

Cell – Basic Unit of life

Introduction

As you all have learnt, the cell is the structural and functional unit of organisms. Unicellular organisms like Amoeba and Paramecium has a single cell in its body. The single cell performs all basic life activities like movement, intake of food, digestion, respiration, excretion, reproduction etc. However, in multicellular organisms, there are millions of cells. Each cell is specialized to perform different functions.They show the division of labour. Division of labour has been made possible by specialization of cells and their grouping with each specialized clusters of cells in a definite place in the body. Such a group of cells are called tissues.

What is tissue?

The tissue is a group of cells with common origin, structure and function that work together to perform a particular function. For example, Blood, bone, cartilage are some examples of animal tissues while xylem, phloem, parenchyma etc. are different types of tissues found in plants.

Did you know? The branch of science that deals with the study of tissue are called histology. The term histology was coined by Meyer.

Importance of Tissue

Now you must be wondering, what is the importance of tissues in multi-cellular organisms? Or why do we need tissues? Let us have a look.

Tissue brings about division of labour in multicellular organisms. The division of labour increases the survival rate of the multicellular organism.
Tissues become organized to form organs, which in turn form organ systems. It increases the efficiency of multi-cellular organisms.
Tissue decreases the workload of individual cells.

EXERCISE

Fill in the blanks

1. _____ is the structural and functional unit of life.
2. Cell theory was proposed by _______ and ______________.
3. The largest eggs are represented by eggs of ________.
4. In human body, _____________ cells can change their cells.
5. __________ controls all the activities of cell.
6. _____________ is called powerhouse of cell.
7. Chloroplasts are found only in _________ cells.
8. ___________ are the sites of photosynthesis.
9. _________ gives shape and support to the plant cells.
10. Amoeba is a/an _____________ organism.
Answers:
1- Cell, 2- Schwann and Schleiden, 3- Ostrich, 4- WBC, 5- Nucleus, 6- Mitochondria, 7- Plant, 8- Chloroplast, 9- Cell wall, 10- Unicellular
True or false
1. Chromosomes carry genes.
2. Nucleus lies towards the periphery due to the presence of large central vacuole in an animal cell.
3. Membrane-bound cell organelles are present in eukaryotes.
4. Mitochondrial and plastids are membranes with fewer organelles.
5. Leucoplasts are green colour plastids.
6. RER is the site of protein synthesis.
7. ER is the secretory organelle of the cell.
8. Lysosomes are protein factories of the cell.
9. Plants are an example of multicellular organisms.
10. The cell membrane is a selectively permeable membrane.
Ans.
1- True, 2- False, 3- True, 4- False, 5- False, 6- True, 7- False, 8- False, 9- True, 10- True