NCERT biology notes for class 9 chapter 5 The Fundamental units of life

This chapter is very important for children who want to pursue their future in a biology-related field. This chapter forms the basics of Biology. Following are NCERT biology notes for class 9 chapter 5 – The Fundamental units of life.

Biology notes for class 9 chapter 5

1. Discovery of a Cell

1. The cell was first discovered by Robert Hooke in the year 1665
2. He mentioned this discovery in his book Micrographia.
3. He saw cork cells under a self-designed microscope.
4. He saw small boxes or honeycomb-like structures.
5. Robert Hook named them “Cell“.
6. Cell means ‘A little room.’
7. These cells combine to form tissues.

Extra information about cell;

• Smallest cell organelles – Ribosomes
• Largest cell organelles – Nucleus
• Largest living cell – Egg of Ostrich
• Cell that lack nucleus – RBCs

2. Preparation of Onion peel

Step 1. Take a small piece of onion.

Step 2. Remove the peel from the concave side (inner side) of the onion with the help of forceps.

Step 3. Put some water in the watch glass and put onion peel in it, to prevent it from drying and folding.

Step 4. Now add a drop of water to the glass slide and put the onion peel on it.

Step 5. Put safranine dye and remove the excess.

Step 6. Now add a coverslip and view it under a microscope.

3. Important names, discoveries, and dates to remember

1. Name Cell was coined by – Robert Hooke in 1665
2. The first living cell was discovered by – Antonie van Leeuwenhoek (1674) from pound water.
3. Nucleus was first discovered by – Robert Brown (1831)
4. Protoplasm was discovered by – Purkinje (1839)
5. The Cell Theory wad proposed by – Schleiden (1838) and Schwann (1839)
6. Cell theory was expanded by – Virchow (1855)

4. Plasma Membrane

1. The plasma membrane is also known as Cell Membrane.
2. Outermost covering of the cell.
3. It is the boundary of the cell which separates the content from the external environment.
4. It is flexible and is made up of lipids and proteins.
5. It is selectively permeable as it allows the entry and exit of certain material in and out of the cell.
6. Allows diffusion of CO2 and O2 through it.
7. Also, it allows the entry and exit of liquid through the process of osmosis.

5. Cell Wall

1. Discovered by Robert Hook.
2. The cell wall is present outside the cell membrane.
3. It is only present in plants, fungi, and bacteria.
4. Absent in Animal Cell.
5. It is a rigid, porous, and non-living structure.
6. Made up of cellulose.
7. The joint between two adjacent cell walls is known as “Middle Lamella.“
8. The main function of the cell wall is to provide strength and definite shape to the cell.
9. It is permeable and allows substances of different sizes to pass through it.

6. Nucleus

1. The nucleus is known as the “Headquarters of the cell.“
2. It controls all the cellular activity.
3. The nucleus is generally stained by – Safranin and iodine.
4. The nucleus contains genetic material which is responsible for inheritance.
5. It consists of the nuclear membrane which is double-layered. (Inner and outer membrane)
6. The membrane has pores called Nuclear pores.
7. The nucleus contains Nucleolus, chromosome, and chromatin material (DNA + Protein).
8. A well-defined nucleus is absent in Prokaryotes and is present in Eukaryotes.

Class 9 Biology notes for Chapter 6 Tissues and important points for the exam

7. Cytoplasm

1. The semi-fluid liquid is present inside the cell.
2. It is the liquid part of the cell in which other organelles float and perform their functions.
3. The cytoplasm has its own genetic material.

8. Cell Organelles

1. Cell organelles are membrane-bound structures present inside the cell.
2. Found in Eukaryotic cells only.
3. These usually float in the cytoplasm of the cell.
4. Different cell organelles perform different functions.
5. Following are the types of cell organelles;

• Endoplasmic Reticulum (ER)
• Golgi Apparatus
• Lysosomes
• Mitochondria
• Plastids

8.1 Endoplasmic Reticulum

1. Commonly known as ER.
2. It is basically a complex network of tubes that is present in the cytoplasm of the cell.
3. It looks like tubes, oblong bags (vesicles), or bags.
4. ER helps in the transport of substances (especially protein) in various regions of cytoplasm and between cytoplasm and nucleus.
5. ER is of two different types – Rough Endoplasmic Reticulum and Smooth Endoplasmic Reticulum.
6. Rough Endoplasmic Reticulum: It has small organelles present on it which are commonly known as Ribosomes. Due to the presence of ribosomes, these look like rough surfaces on the tubes. Ribosomes are the site of the manufacture of protein, which can be sent to different parts of the body depending on their functions.
7. Smooth Endoplasmic Reticulum: Ribosomes are absent and hence it appears smooth under a microscope. It helps in the manufacture of fat molecules or lipids. This is known as Membrane biogenesis.

Note: SER present in liver cells helps in the detoxification of poisons and drugs from liver cells. (biology notes for class 9 chapter 5)

8.2 Golgi Apparatus

1. First Discovered by “Camillo Golgi.“
2. Appear like membrane-bound vesicles (Flattened sacs)
3. Golgi Apparatus contains vesicles parallel to each other in stacks called “Cisterns.”
4. ER secrete protein and lipids which are packed and stored by GA.
5. Golgi Bodies also help in the formation of Simple Sugar from Complex Sugar molecules.
6. GB plays an important role in the formation of Lysosomes.

8.3 Lysosomes

1. Lysosomes play a very important role in cells.
2. These are bounded by Single Membrane.
3. The main function of lysosomes is digestion.
4. The main function of lysosomes is waste disposal.
5. Lysosomes contain digestive enzymes important for the digestion process.
6. Lysosomes are also known as “Suicidal bags” because, during cellular metabolism, lysosomes may burst to release their digestive juice and the enzymes to digest their own cell.

8.4 Mitochondria

1. These are known as the “Powerhouse of the cell.“
2. Mitochondria are rod-shaped structures present in the cytoplasm.
3. These are present in the Eukaryotic cell.
4. It consists of 2 membranes – The outer and inner membrane.
5. The inner folding of the membrane is known as Cristae.
6. The space between the inner and outer membrane is known as Matrix.
7. It plays an important role in the formation of ATP (Adenosine Triphosphate).
8. It has its own DNA and Ribosomes.

8.5 Plastids

1. It is only present in a plant cell.
2. Plastids are of three types.

• Chromoplast – Red, and Brown in color
• Chloroplast – Found in aerial parts and is green in color
• Leucoplast- Colourless and is usually found in underground parts of the plant. Also, it helps in the storage of starch, oil, and protein granules.

8.6 Vacuoles

1. The membrane-bound region in the cytoplasm contains water, amino acids, sugar, and various organic acids.
2. Vacuoles are small in size in animal cells whereas plant cells have large vacuoles.
3. Amoeba – Food Vacuoles that contain food items.

I hope there notes for Biology notes for class 9 chapter 5 were helpful for you.

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