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Theory - To Prepare Stained Temporary Mount of Onion Peel, Biology, Science, Class 9 | Science Class 9 PDF Download

Our Objective

Our aim is to prepare stained temporary mounts of onion peel and human cheek cells and to record the observations.


The Theory

Before exploring the details of cell structure, let's understand the differences in the structure of an onion cell and a human cheek cell.


Onion Cell

An onion is a multicellular (consisting of many cells) plant organism.As in all plant cells, the cell of an onion peel consists of a cell wall, cell membrane, cytoplasm, nucleus and a large vacuole. The nucleus is present at the periphery of the cytoplasm. The vacuole is prominent and present at the centre of the cell. It is surrounded by cytoplasm. The presence of a cell wall and a large vacuole are indicators that help identify plant cells, such as seen in the onion peel.


Human Cheek Cell

As in all animal cells, the cells of the human cheek do not possess a cell wall. A cell membrane that is semi-permeable surrounds the cytoplasm. Unlike plant cells, the cytoplasm in an animal cell is denser, granular and occupies a larger space. The vacuole in an an animal cell is smaller in size, or absent. The nucleus is present at the centre of the cytoplasm.The absence of a cell wall and a prominent vacuole are indicators that help identify animal cells, such as cells seen in the human cheek.

Theory - To Prepare Stained Temporary Mount of Onion Peel, Biology, Science, Class 9 | Science Class 9 Theory - To Prepare Stained Temporary Mount of Onion Peel, Biology, Science, Class 9 | Science Class 9

 

Cell Organelles

Have you ever wondered what the inside of a cell looks like? If you think about the rooms in our homes, the inside of any animal or plant cell has many similar room-like structures called organelles. Here are some names and descriptions of organelles and other parts commonly found in cells.

Theory - To Prepare Stained Temporary Mount of Onion Peel, Biology, Science, Class 9 | Science Class 9

Cell Wall: Protective Coat in Plant Cells

The presence of a cell wall is what provides the most significant difference between plant and animal cells, as it is present only in plant cells and covers the cell membrane.The cell wall is rigid and is composed of cellulose fibre, polysaccharides, and proteins. Despite the rigidity of the cell wall, chemical signals and cellular excretions are allowed to pass between cells.
 

Cell Membrane: Protective Coat in Animal Cells

The cell membrane is found in both plants and animals, and it is the outer most layer in the animal cell, that separates the contents of the cell from the outside world. It consists of both lipids and proteins and is selectively permeable, which means it permits only some molecules to pass through it.


Cytoplasm: Cell’s Inner Space

Cytoplasm is a jelly-like material that is eighty percent water and is usually clear in colour. It is also called cytosol. Cytoplasm contains all the organelles inside the cell membrane. The cytosol contains dissolved nutrients, helps break down waste products, and moves material around the cell through a process called cytoplasmic streaming.


Nucleus: The Control Centre

The nucleus is known as the control centre of the cell.It contains the regulatory machinery responsible for all the activities inside the cell. It is the largest organelle in the cell and it contains the DNA of the cell. DNA contains all the information that helps cells live, perform their functions and reproduce.The nucleus has a double layered covering called nuclear membrane.


Vacuoles: Cell’s Storage Space

A vacuole is a membrane-bound organelle that stores solid and liquid contents.Vacuoles are found in both animal and plant cells, but are much larger in plant cells. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these. The organelle has no basic shape or size; its structure varies according to the needs of the cell.


Similarities and Differences between Plant and Animal Cells

Animal and plant cells have a number of key similarities, but also some noted differences. Here are some of the common similarities and differences between plant and animal cells.

Features

Animal Cell

Plant Cell

Cell Shape

Round (irregular shape)

Rectangular (fixed shape)

Cell Wall

Absent

Present and is formed of cellulose

Cell Membrane

Present

Present and is covered by the cell wall

Nucleus

Present

Present

Vacuole

One or more small vacuoles

A large central vacuole taking up 90% of the cell volume

Plastids

Present

Present

Chloroplast

Absent 

Present and make their own food 

Endoplasmic Reticulum

Present

Present

Ribosomes

Present

Present

Mitocondria

Present

Present


Learning outcomes:

  • Students understand the different organelles inside the cell and their functions.

  • Students understand difference between animal cells and plant cells.

  • Students acquire skills to do the temporary mounts of cells by observing animation and simulation. 

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FAQs on Theory - To Prepare Stained Temporary Mount of Onion Peel, Biology, Science, Class 9 - Science Class 9

1. What materials are needed to prepare a stained temporary mount of onion peel?
Ans. To prepare a stained temporary mount of onion peel, you will need the following materials: - Fresh onion bulb - Microscope slide - Cover slip - Dropper - Iodine solution or safranin stain - Distilled water - Microscope
2. Why is staining necessary when preparing a temporary mount of onion peel?
Ans. Staining is necessary when preparing a temporary mount of onion peel to enhance the visibility of the cell structures. Onion cells are usually transparent, making it difficult to observe their internal components under a microscope. Staining helps to highlight specific parts of the cells, such as the nucleus and cell walls, making them easier to study.
3. What is the purpose of adding a cover slip to the stained temporary mount of onion peel?
Ans. The purpose of adding a cover slip to the stained temporary mount of onion peel is to protect the specimen and prevent it from drying out. The cover slip also helps to flatten the onion peel, allowing for a clearer view under the microscope. It creates a thin, uniform layer between the slide and the objective lens, ensuring optimal focusing and reducing distortion.
4. Can any stain be used to prepare a stained temporary mount of onion peel?
Ans. Yes, different stains can be used to prepare a stained temporary mount of onion peel. The most commonly used stains are iodine solution and safranin. Iodine solution stains the cellulose cell walls of the onion cells, making them more visible. Safranin stain, on the other hand, stains the cell nuclei, highlighting them for better observation. The choice of stain depends on the specific components of the onion cells that need to be studied.
5. How can the stained temporary mount of onion peel be observed under a microscope?
Ans. The stained temporary mount of onion peel can be observed under a microscope by placing it on the stage and adjusting the focus. Start with the lowest magnification objective lens and gradually increase the magnification as needed. Use the microscope's fine focus knob to sharpen the image. Observe the stained cells by looking through the eyepiece and adjust the light intensity if necessary. Take note of the cell structures, such as the cell walls, nuclei, and any other components of interest.
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