The Fundamental Unit of Life Class 9 Notes Science Chapter 5

Class 9 Science Chapter 5 Notes: Master the concepts of cells, their structure, and functions with our Science Revision Notes for Class 9 Chapter 5: The Fundamental Unit of Life. Crafted by experts these notes align with the latest CBSE syllabus and exam pattern. Dive into pointwise explanations of topics like animal cells, plasma membrane, lipids, cell wall, nucleus, Golgi apparatus, endoplasmic reticulum, plastids, chromoplasts, leucoplasts, plant cells, prokaryotic cells, and cell division. Whether you’re studying plant cells, prokaryotic cells, or cell division, these revision notes provide concise explanations for easy memorization.

CBSE Class 9 Science Notes Chapter 5 The Fundamental Unit of Life

Here, you’ll find concise notes for Class 9 Science Chapter 5 The Fundamental Unit of Life. This resource includes key points, summaries, images, and diagrams, making it ideal for quick revision. If you’re using the NCERT Textbook for Science, this chapter is a crucial one. After studying the lesson, having accessible notes can aid in memorization. For a deeper understanding, you can also refer to NCERT Solutions for Class 9 Science Chapter 5.

Also Refer:

• The Fundamental Unit of Life Class 9 Extra Questions
• The Fundamental Unit of Life Class 9 MCQ with Solutions
• NCERT Exemplar Class 9 Science Solutions Chapter 5

CBSE Class 9 Science Chapter 5 Notes PDF Download

Class 9 Science Chapter 5 Notes are available absolutely free. These notes cover Chapter 5 of the Class 9 Science syllabus comprehensively, helping your understanding of the subject. Whether you’re revising for exams or simply clarifying concepts, these notes are invaluable. Cover the topics like the fundamental unit of life, cell theory, and cell structure with ease. Plus, with the PDF format, you can access these notes anytime, anywhere, making studying more flexible.

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Cell – Introduction

Facts that Matter

The smallest functional unit of life is a cell, discovered by Robert Hooke in 1665. A cell can independently perform all activities to sustain life. Hence cell is the basic unit of life.

Structural Organization and Functions of Cells

There are two types of cells plant cell and animal cell. The different cell organelles and their functions are as follows:

1. Plasma/Cell membrane:

The outermost covering of a cell, known as the plasma membrane, serves as a barrier that separates the cell’s internal contents from its external environment. This membrane is selectively permeable, allowing certain substances to pass through while restricting others.

Substances like CO2 or O2 gases traverse the cell membrane via a process known as diffusion. Meanwhile, the movement of water molecules across this selectively permeable membrane is termed osmosis. Osmosis entails the flow of water from an area of high water concentration to an area of low water concentration through a semi-permeable membrane.

When the surrounding medium possesses a higher water concentration compared to the cell, the cell undergoes water uptake via osmosis. This scenario characterizes a hypotonic solution. Conversely, if the medium’s water concentration matches that of the cell, there’s no net water movement, resulting in an isotonic solution. Should the medium exhibit a lower water concentration than the cell, water loss occurs from the cell via osmosis, defining a hypertonic solution.

The plasma membrane, composed of organic molecules known as lipids and proteins, exhibits flexibility, allowing the cell to adapt to its surroundings. This characteristic enables the cell to engulf food and other materials from its external environment, a process known as endocytosis. This phenomenon is prominently observed in organisms like Amoeba.

Also Check: Animal Cell Diagram for Class 9

2. Cell wall (Protective wall): Plant cells possess a unique feature beyond their plasma membrane: the cell wall. This rigid outer covering lies exterior to the plasma membrane and primarily consists of cellulose, a complex substance providing structural support to plant cells. When a plant cell undergoes water loss through osmosis, its contents shrink away from the cell wall, a phenomenon termed plasmolysis.

3. Nucleus (Brain of a cell): The nucleus, often referred to as the “brain” of a cell, is enveloped by a double-layered structure known as the nuclear membrane. Pores within this membrane facilitate the transfer of materials between the nucleus and the cytoplasm.

Within the nucleus reside chromosomes, visible as rod-shaped structures during cell division. Chromosomes carry genetic information in the form of DNA molecules, comprising functional segments known as genes. The nucleus orchestrates cellular reproduction, playing a pivotal role in inheritance.

Prokaryotic Cells: In contrast, prokaryotic cells, such as bacteria, lack a nuclear membrane and membrane-bound organelles. Instead, their genetic material is housed in a region called the nucleoid, and they typically contain a single chromosome. Eukaryotic cells, on the other hand, feature a well-defined nucleus and membrane-bound organelles, often possessing multiple chromosomes.

4. Cytoplasm: The cytoplasm, the fluid interior enclosed by the plasma membrane, hosts numerous specialized organelles, each executing specific cellular functions. These organelles are essential components of the cell, collectively contributing to its diverse activities and processes.

5. Cell Organelles: Each cell is encapsulated by a membrane, serving to maintain separation between its internal contents and the external environment. These internal components, known as cell organelles, fulfill distinct functions within the cell, collectively contributing to its various processes and activities.
(i) Endoplasmic Reticulum (ER) (Channels, Network for transport):

The endoplasmic reticulum (ER) comprises a vast network of membrane-bound structures, appearing as elongated tubules or rounded, oblong bags. It exists in two main forms: the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER). The RER is distinguished by the presence of ribosomes, small particles attached to its surface. The ribosomes Endoplasmic Reticulum are the sites of protein manufacture.

The smooth endoplasmic reticulum (SER) plays a crucial role in producing lipid molecules, vital for cellular function. Among these lipids are those involved in constructing the cell membrane, a process termed membrane biogenesis. Additionally, certain proteins and lipids synthesized by the SER serve as enzymes and hormones, contributing to various cellular activities.

The function of ER is to serve as channels for the transport of materials between various regions of the cytoplasm or between the cytoplasm and the nucleus. The ER also functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.

(ii) Golgi Apparatus (Packaging):

The Golgi apparatus, originally described by Camillo Golgi, is comprised of a series of membrane-bound vesicles organized into stacks known as cisterns. This intricate structure serves as a pivotal hub for processing and distributing materials synthesized near the endoplasmic reticulum (ER) to various destinations within and outside the cell.

Functionally, the Golgi apparatus is involved in a range of tasks, including storage, modification, and packaging of cellular products within vesicles. Notably, it can facilitate the conversion of simple sugars into complex sugars. Additionally, the Golgi apparatus plays a key role in the formation of lysosomes, specialized organelles responsible for cellular digestion and waste management.

(iii) Lysosomes [Suichge bags] (Cleanliness of cell): Lysosomes are a kind of waste dispatch and disposal system of the cell. Lysosome help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. Foreign materials entering the cells such as bacteria or food, as well as old organelles, end up in the lysosome, which break them up into small pieces. They are able to do this because they contain powerful digestive enzymes capable of breaking down all organic material. Under abnormal condition, when the cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Therefore they are also known as “suicide bags”

(iv) Mitochondria (Powerhouse, Energy provider): Mitochondria are known as powerhouses of the cell. The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP [Adenosine Triphosphate] molecules. ATP is known as energy currency of the cell. Mitochondria have two membrane coverings instead of just one. The outer membrane is very porous while the inner membrane is deeply folded. They are able to make some of their own protein.

(v) Plastids: Plastids are present only in plant cells. There are two types of plastids chromoplasts and leucoplasts. Chromoplasts are the coloured plastids present in leaves, flowers and fruits. Plastids containing the pigment chlorophyll are known as chloroplasts. They are important for photosynthesis in plants. Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll. Leucoplasts are found primarily in organelles in which materials such as starch, oils and protein granules are stored.

The internal organisation of the plastids consists of numerous membrane layers embedded in a material called stroma. Plastids are similar to mitochondria in external structure. Plastids have their own DNA and ribosomes.

(vi) Vacuoles (Storage): Vacuoles are storage sacs for solid or liquid contents. Vacuoles are small-sized in animal cells while plant cells have very large vacuoles [50% to 90% cell volume].

In plant cells, vacuoles are full of cell sap and provide turgidity and rigidity to the cell. In Amoeba, the food’vacuole contain the food items that is consumed it and contractile vacuoles expels excess water and some wastes from the cell.