ICSE Class 10 Biology Chapter 01 Cell The Structural and Functional Unit of Life

Are you looking for the ICSE Class 10 Biology book PDF free download. You have come to the right place as we have provided the PDF for Chapter 1 Cell The Structural and Functional Unit of Life here. You can refer to the link below to download the ICSE Class 10 Biology Book in PDF Chapter 1 Cell The Structural and Functional Unit of Life which is highly recommended textbook for students following the ICSE syllabus for this year. This book has been published by Selina Concise for this academic year and covers important concepts in a detailed manner. Students of ICSE Class 10 will be easily able to understand all concepts and will help students to build a strong foundation in the subject. One of the key chapters in this book is Chapter 1 Cell The Structural and Functional Unit of Life which explains all the important topics in lot of detail. The Biology book for Class 10 follows the latest ICSE syllabus for the current year thus ensuring that students get updated with the most relevant content for their studies. By downloading the Selina Concise Biology Class 10 Textbook PDF, students can conveniently access the book anytime and study without needing a physical copy.

Cell - The Structural and Functional Unit of Life [For Revision Only]

All organisms, including ourselves, are made of microscopic cells. These cells perform activities which contribute to the overall tasks of an individual. It is also to note that every organism starts its life as a single cell. The same cell undergoes repeated divisions to give rise to a large mass of cells. Further, the cells get specialised for various tasks such as those of giving support, producing digestive enzymes and carrying out photosynthesis.

1.1 CELLS - A BASIC STUDY IN BIOLOGY

You have already read about cells in some detail in Class IX. However, it is necessary to refresh your knowledge for a proper understanding of several aspects of biology which specially constitute the Class X syllabus. Some of the main points about cells are as follows:

• All living beings are made up of cells.
• The cell is the structural and functional unit of the body.
• All living beings develop from a pre-existing cell.

1.2 CELLS - HOW NUMEROUS?

Larger an organism, greater the number of cells in its body.

• Single-celled: Many small organisms are made up of just one single cell. Examples: Bacteria, yeast and amoeba.
• Few-celled: Some very small organisms are made up of just a few hundred or a few thousand cells. Examples: Spirogyra, Volvox.
• Multi-celled: Most plants and animals we see around are made up of millions and billions of cells. Examples: Humans, mango.

An average-sized adult human constitutes approximately:

• 1000 million million cells in the whole body.
• 10,000 million nerve cells in the brain cortex.
• 25 million million red blood cells.
• 30 thousand million white blood cells.

1.3 CELLS - HOW SMALL?

Cells are very small and can be seen only with a microscope.

• Smallest cells are certain bacteria, red blood cells in the human body, etc.
• Longest cells are the nerve cells.
• Largest cells are the birds' eggs (actually the central yellow sphere). Ostrich egg, before development begins in it, is the largest single cell of the living world today. The white (albumen) of the egg and the egg-shell are extra parts added on the actual egg as it passes down the reproductive tract.

1.4 CELL SHAPES

Different shapes of cells are often related to the different functions they perform.

• Human red blood cells are circular and biconcave, for easy passage through blood capillaries and to transport oxygen.
• White blood cells are amoeboid (amoeba-like movement, with pseudopodia) that can squeeze out through capillary walls.
• Nerve cells are long to conduct "impulse" from distant parts of the body to the brain and vice-versa.
• Guard cells of stomatal pore in the leaves are bean-shaped to open and close it.

1.5 GROSS STRUCTURE OF CELL - THE THREE ESSENTIAL PARTS

1. Cell membrane (or plasma membrane) encircles the cell.

• It is a living membrane having fine pores.
• It is semi-permeable (also called selectively permeable or differentially permeable) meaning that it allows only certain substances to pass through while preventing others.
• In the plant cell, an additional outermost non-living layer called the cell wall, surrounds the cell membrane.
• The cell wall is mostly made up of cellulose.
• It gives shape and rigidity to the cell.
• It is freely permeable (allowing substances in solution to enter and leave the cell without hindrance).

2. Cytoplasm is the part of the cell inside the cell membrane and outside the nucleus.

• It is a semiliquid substance.
• Many chemical reactions catalyzed by enzymes occur in it.
• It contains several organelles, each concerned with some specific function.
• The part of the cytoplasm other than the organelles (mitochondria, etc.) is called cytosol, which constitutes mainly the liquid medium.

3. Nucleus is a large somewhat spherical body lying nearly in the centre of the cytoplasm.

• It is surrounded by a double layered nuclear membrane with nuclear pores.
• The ground substance of the nucleus is a semi-solid substance (nucleoplasm) containing one or more round-shaped nucleoli (sing. nucleolus).
• The nucleoplasm contains a network of dark-coloured fibres called chromatin fibres. These chromatin fibres condense into short thick chromosomes during cell division.
• Chromosome number varies from one organism to another.

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