NCERT Class 9 Science Chapter 5 Notes - The Fundamental Unit of Life PDF Notes

Download NCERT Notes for Class 9 Science Chapter 5 PDF

The notes for The Fundamental Unit of Life are available in a clear and simple PDF format. These notes help students revise all key points in less time. Students can use the NCERT notes for class 9 Science chapter 5 PDF during offline. It’s a quick and effective way to study. The NCERT Notes for Class 9 and solutions together prove to provide conceptual clarity and improve retention.

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The Fundamental Unit of Life Class 9 Notes

This chapter helps students understand how cells form the basic building blocks of life. The notes cover important topics such as cell structure, functions of cell organelles, and differences between plant and animal cells. The Fundamental Unit of Life Class 9 Notes are great for quick last-minute revision before exams.

Cell

A cell is the smallest functional and structural unit of life. The history of cells started when Robert Hooke examined a thin piece of cork using a microscope in 1665 and found tiny compartments that he referred to as 'cells.' He likened these compartments to a honeycomb and set the stage for future research in cell biology.

Cell Theory

The cell theory was developed through the work of various scientists:

• Matthias Schleiden (1838) asserted that all plants consist of cells.
• Theodor Schwann (1839) noted that all animals are made up of cells and suggested that cells constitute the fundamental unit of life.
• Rudolf Virchow (1855) established that new cells develop from pre-existing cells as a result of cell division.

This resulted in the development of the Cell Theory, which argues:

• All living organisms consist of cells.
• Cells are the structural and functional unit of living organisms.
• All cells come from existing cells.

The establishment of the cell theory was a significant breakthrough in the concept of the continuity of life.

Cell Shape, Size, and Number

The form of cells is different based on their function. For instance, nerve cells are elongated to carry signals, whereas an Amoeba is irregularly shaped and constantly changing.

The cells vary in size from 0.5 to 20 micrometers in most organisms. Sperm cells are the smallest cells in the human body, whereas nerve cells are the longest.

Unicellular organisms are made up of one cell, while multicellular organisms contain many cells specialized for various functions.

Structure of a Cell

A cell consists of three major parts:

• Plasma Membrane (Cell Membrane)
• Cytoplasm
• Nucleus
• Plasma Membrane (Cell Membrane)

The outermost portion of the cell that isolates the interior of the cell from the outside world.

It is selectively permeable since it lets through some substances but not others.

Movement of molecules across the plasma membrane is by:

Diffusion – Movement of gases such as oxygen and carbon dioxide.

Osmosis – Movement of water across a selectively permeable membrane.

Cell Wall (Only in Plant Cells)

• An inelastic outer sheath is present in plant cells, fungi, and bacteria.
• The Cell wall is mainly made of cellulose, which gives strength to the structure as well as shields it.
• Puts a block on excess absorption of water and prevents the explosion of the cell when placed under hypotonic conditions.

Nucleus

• The central organizing point of the cell, with a nuclear envelope covering it.
• Has chromosomes consisting of DNA along with proteins.
• The nucleus is responsible for heredity and cell reproduction.
• The nucleolus inside the nucleus functions to synthesize ribosomes.

Cytoplasm

• A jelly-like substance that holds cell organelles and allows them to move.
• It is the location of most biochemical reactions that sustain cells.
• Organelles within the cytoplasm are specialized in function and are vital for cell metabolism.

Cell Organelles and Their Functions

The cell organelles and their functions are described as:

Endoplasmic Reticulum (ER)

Rough ER (RER): Ribosomes are attached, and it is involved in protein synthesis.

Smooth ER (SER): Does not have ribosomes, synthesizes lipids, and detoxifies toxic substances.

Golgi Apparatus

• Alters, sorts, and packages proteins and lipids.
• Aids in the creation of lysosomes and the movement of substances across the cell.

Lysosomes

• Have enzymes for digestion to destroy waste products, diseased organelles, and foreign materials.
• Lysosomes digest damaged organelles and can cause self-destruction of the cell under certain conditions, so they are called suicidal bags.

Mitochondria

The energy-generating part of the cell produces energy from cellular respiration.

Manufactures ATP (Adenosine Triphosphate), the cell's energy currency.

Has its own DNA and ribosomes, so it can reproduce itself.

Plastids (Only in Plant Cells)

Chloroplasts: Have chlorophyll, which is needed for photosynthesis.

Leucoplasts: Store starch, oils, and proteins.

Chromoplasts: Give color to flowers and fruits.

Vacuoles

• Vacuoles are the sacs filled with fluid that store nutrients, waste products, and other materials.
• Larger in plant cells, they assist in maintaining turgidity and cell shape.

Cell Division

Cells divide to provide for growth, repair, and reproduction. There are two primary types of cell division:

Mitosis

• Happens in body (somatic) cells.
• Creates two identical daughter cells.
• Has the same number of chromosomes as the parent cell.
• It is vital for growth, repair, and asexual reproduction.

Meiosis

• Takes place in reproductive cells (gametes).
• Forms four daughter cells with half the number of chromosomes.
• Results in genetic variation, which is critical for evolution.

Also, Read

• NCERT Books for Class 9
• NCERT Books for Class 9 Science
• NCERT Syllabus for Class 9
• NCERT Syllabus for Class 9 Science

Key Features of Class 9 Science Chapter 5 Notes

These notes have several features and are useful for daily revision as well as during eczema preparation. Some of the key features are listed below:

• Class 9 Science Chapter 5 Notes include concepts such as cell structure, types of cells, and the function of each organelle.

• These notes follow the latest syllabus, so students don’t miss any topic.

• All the topics are explained in easy and simple language, making it easier to understand.

• The Class 9 Science Chapter 5 Notes include well-labeled diagrams of plant and animal cells for visual learning.

• Highlights all the important definitions and terms for quick reference.

Chapter 5 Science: Previous Year Questions and Answers

The previous years’ questions given below help students know the exam pattern and test their level of preparation. To answer these questions easily, students are advised to read the NCERT Class 9 Science Chapter 5 Notes The Fundamental Unit of Life.

Question 1: What are the structures performing different functions in the cell called?

Option 1. Organs

Option 2. Organelles

Option 3. Cytoplasm

Option 4. Cell membrane

Answer:

All the functions of the cell are assigned to different structures of the cell, such as mitochondria, endoplasmic reticulum, Golgi apparatus, etc. These are called organelles of the cell.

Hence, the correct answer is option (2), Organelles

Question 2: The Function of the vacuoles is

Option 1. Storage of food

Option 2. Storage and excretion of waste material

Option 3. Storage of secondary metabolites

Option 4. All of the above.

Answer:

Function of the vacuole:

• The primary function of the vacuole is to store excess food and secondary metabolites in plants
• It is also used as an excretory organelle in some of the unicellular organisms
• It is used to store food material in the Amoeba

Hence, the correct answer is option (4), All of the above

Question 3: Chloroplasts contain color pigments

Option 1. Green

Option 2. Yellow

Option 3. Orange

Option 4. All of the above

Answer:

Chromoplasts that contain green color pigments are called chloroplasts, and the green color pigments are called chlorophyll. Chloroplast also shows the presence of yellow and orange pigments.

Hence, the correct answer is option (4), All of the above

Subject-Wise NCERT Exemplar Solutions

• NCERT Solutions for Class 9

• NCERT Solutions for Class 9 Maths

• NCERT Solutions for Class 9 Science

Chapter-Wise NCERT Class 9 Notes Science

Below are the links to detailed notes for each chapter, designed to help you quickly revise and understand key concepts.