“The Cell” is Chapter 16 taken from the JKBOSE textbook of Science for students of Class 8th. In the previous post, I provided you with Questions and Answers for Chapter 15 Stars and the Solar System. This post is about The Cell Chapter 16 Class 8 Question Answers. Before we move on to solutions you must have your basics clear. So, let me begin by giving you a brief overview of what you have studied in this chapter.
The Cell Chapter 16 Class 8 Question Answers
Overview of Chapter
- INSTRUMENTS USED TO MAGNIFY OBJECTS.
- HOW TO MAKE A MICROSCOPIC SLIDE?
- CELL STRUCTURE.
- PARTS OF A CELL.
- Cell Membrane.
- DIVERSITY IN CELLS.
- Cell number.
- Cell Size.
- Cell shape.
- Basic Facts of Cell Structure and Functions.
INTRODUCTION All living organisms are made up of cells but we cannot see these cells from an external examination of a living organism. We can see these cells only by studying the internal structure of different parts of living organisms. In this chapter, we have studied how we can see cells, the basic structure of a cell and diversity in cells.
INSTRUMENTS USED TO MAGNIFY OBJECTS: There are two main instruments which are used to magnify objects. These are a hand lens and a microscope.
HOW TO MAKE A MICROSCOPIC SLIDE: We can prepare a microscopic slide in the following manner:
1) Take a clean glass slide.
2) Put a drop of water in the middle of a slide using a dropper.
3) Now, gently put the object to be viewed in the drop of water with help of a brush. (Stain the object before putting it on a glass slide if it is transparent)
4) Hold the coverslip over the water in such a way that it touches the edge of the drop of water. Gently lower the coverslip onto the water.
5) Dry the extra water that may come out from under the coverslip with the help of a blotting paper. Take care that the slide thus prepared is clean and dry.
CELL STRUCTURE: Each organ in the system performs different functions such as digestion, assimilation and absorption. Similarly, different organs of a plant perform specific/specialised functions. For example, roots help in the absorption of water and minerals. Leaves are responsible for the synthesis of food. Each organ is further made up of smaller parts called tissues. A tissue is a group of similar cells performing a specific function. Tissues are made up of cells.
PARTS OF THE CELL: Each cell has a number of smaller parts in it. Some parts are present in all types of cells but certain parts are found only in plant cells, they are not present in animal cells.
- Cell Membrane: Every cell is covered by a thin sheet of skin which is called a cell membrane or plasma membrane. The cell membrane separates a cell from one another and also from the surrounding medium. The plant cells have an outer rigid thick layer outside the cell membrane called the cell wall. It is made up of cellulose.
- Cytoplasm: It is the jelly-like substance present between the cell membrane and the
nucleus. Various other components, or organelles, of cells are present in the cytoplasm. These are mitochondria, Golgi bodies, ribosomes, etc.
- Nucleus: It is a large, spherical and most important cellular component present in all cells. The nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. There is a smaller spherical body in the nucleus. The nucleus contains thread-like structures called chromosomes. These carry genes and help in the inheritance or transfer of characters from the parents to the offspring.
DIVERSITY IN CELLS: There are millions of living organisms. They are of different shapes and sizes. Their organs also vary in shape, size and number of cells. The various organisms differ in the number of cells in their bodies, shapes of cells and size of cells in their body.
- Cell Number: All organisms are made up of cells but the number of cells varies from organism to organism. Depending upon the number of cells organisms can be unicellular (single cell) like bacteria, Amoeba, Paramecium, Euglena etc. or multicellular (many cells) higher organisms.
- Cell Size: Cells are of different sizes. It may be as small as a millionth of a metre or may be as large as a few centimetres. Most of the cells are microscopic and need to be enlarged by a microscope to be viewed.
- Cell Shape: Cells can be of different shapes depending on their functions. Cells can also vary their shape according to their requirement. For example, Amoeba can change its shape according to its need. Similarly, white blood cells of human blood can change their shape.
In multicellular organisms, cells have specific functions to perform, so they have different shapes.
- Basic Facts of Cell Structure and Functions: 1) Cells are the basic structural units of all organisms.
2) Cells are functional units of all organisms, as cells carry out all body functions of an organism.
3) All cells contain cell organelles.
4) Functioning of cells is responsible for the functioning of organisms.
Class 8 Science Chapter 16 The Cell Questions
- Define a cell.
Ans. A cell is the basic structural and functional unit of all living organisms. All living organisms are made up of cells.
- Who discovered the cell?
Ans. Robert Hooke, an English scientist discovered a cell in 1665 in a slice of cork.
- Give three examples of unicellular organisms.
Ans. Amoeba, Paramecium and Bacteria are three examples of unicellular organisms.
- Answer the following questions:
(i) Why cells could not be observed before the 17th century?
Ans. Cells could not be observed before the 17th century because of their small size and lack of magnifying instruments like a microscope.
(ii) Why cork could not be observed as such by Hook?
Ans. Cork could not be seen as such because it is a solid structure.
(iii) Where did Hook demonstrate his observations on cork slices?
Ans. He demonstrated his work to scientists at the Royal Society of London.
(iv) Name the outermost layer of an animal cell?
Ans. The outermost layer of an animal cell is the cell membrane.
(v) Name the layer which is present outside the plasma membrane in a plant cell?
Ans. The cell wall is the layer which is present outside the plasma membrane in the plant cell.
(vi) Where are chromosomes present in a cell?
Ans. Chromosomes are present in the nucleoplasm of the cell.
(vii) Name the cell part that has tiny holes?
Ans. Cell membrane and nuclear membrane are the part of a cell that has tiny holes.
(viii) Name the cell organelles which are found in the plant cell?
Ans. Cell organelles which are present in a plant cell are chloroplasts, mitochondria, endoplasmic reticulum, vacuoles, ribosomes, and Golgi bodies.
(ix) Name the cells having branched structure?
Ans. Nerve cells have a branched structure.
(x) Which cell can be observed with the unaided eye?
Ans. Ostrich egg cells can be observed with the unaided eye.
- Mention the functions of the following;
(a) Cell membrane
Ans. The cell membrane performs the following functions for the cell.
- It protects the cell.
- It gives shape to the cell.
- It allows the exchange of material in the cell.
Ans. Chromosomes perform the following functions for an organism.
- It helps in the transmission of character from parents to offspring.
- It controls all the life functions taking place inside the cell.
- Why are the following important to a plant cell?
(i) Cell wall.
Ans. It is an extra covering that surrounds the cell membrane of a plant cell. It is made up of stiff and non-living material called cellulose. It provides rigidity and protection to the plant cell.
Ans. It is a cell organelle which contains green colouring pigment chlorophyll in it, It helps in the process of photosynthesis in plants and it also imparts green colour to the leaves of the plant.
Ans. It is called the powerhouse of the cell because the process of respiration takes place here. It provides energy to the cell.
Ans. The nucleus is the head of the cell. It controls all the functions of a cell. The nucleus has chromosomes in it which contain genetic material which is transmitted from one generation to another.
- Draw an outline diagram of an animal cell. Label the different parts.
- Mention three differences between plant cells and animal cells.
|Plant Cell||Animal Cell|
|1. It contains a cell wall.||1. It does not have a cell wall.|
|2. Chloroplasts are present.||2. Chloroplasts are absent.|
|3. Vacuoles are large and mostly single.||3. Vacuoles are smaller and more numerous.|
- What features are possessed by both plant cells and animal cells?
Ans. Following are the features present in both plant cells and animal cells.
- Plasma membrane is present in both cells
- Nucleus is present in both plant cells as well as animal cells.
- Mitochondria is present in both cells.
- Endoplasmic reticulum, Golgi complex, lysosomes and ribosomes are present in both plant cells and animal cells.
- Why are nerve cells long? Why do these cells have projections?
Ans. Nerve cells are long, branched and have thread-like projections because they have to convey the message to different parts of the body.
- Why are mitochondria known as the powerhouse of the cell?
Ans. Mitochondria are known as the powerhouse of the cell because it performs the function of respiration and supplies energy to the cell.
- Which four basic elements constitute more than 90% of protoplasm?
Ans. The four basic elements which constitute more than 90% of the protoplasm are carbon, hydrogen, oxygen and nitrogen.
- Write in brief about the variation in shape and size of cells?
Ans. There are millions of organisms on earth which differ in shape and size of cells in their body. Some plant and animal cells are visible to the naked while most of the cells are microscopic and are not visible to the naked eye. The largest cell is the ostrich egg cell which is 170 × 13 mm and is easily visible to the naked eye while the smallest cell is a bacterium (mycoplasma) which is about 0.1 microns. Cells also have diverse shapes and the shape of cells is also linked to the function performed by them. Some cells are oval in shape, some are rectangular and some are branched like that of the nerve cell. Some cells continuously change their shape while most cells maintain a constant shape throughout their life.
- Name the different cell organelles and the functions of these organelles.
|Name of organelle||Functions|
|1. Mitochondria||1. Performs functions of respiration.|
|2. Supplies power to the cell.|
|2. Chloroplasts (Plants)||1. It imparts green colour to the leaves of the plant.|
|2. It helps in the process of photosynthesis.|
|3. Endoplasmic reticulum||1. It provides a large surface area for life functions to take place|
|4. Golgi complex||1. It collects and distributes the material made in the cell.|
|2. It synthesises and secrete many materials.|
|5. Lysosomes||1. It has enzymes which help in destroying toxic and unwanted materials from the cell.|
- What is meant by protoplasm? How does it differ from cytoplasm?
Ans. Protoplasm refers to all the living matter present inside the cell membrane. It includes cytoplasm and nucleoplasm.
The cytoplasm is a jelly-like substance which is present in between the cell membrane and nucleus of a cell. It contains cell organelles such as mitochondria, chloroplasts, Golgi complex, ribosomes etc.
- Fill in the blanks, using the words given below:
(mycoplasma, microscope, nucleus, ostrich egg, cytoplasm, lysosome, mitochondria, Robert Hook; plant, cell membrane)
(i) The lysosomes are also called suicide bags.
(ii) The term ‘cell’ was given by Robert Hooke.
(iii) The instrument used to see tiny objects is called a microscope.
(iv) Smallest cell is that of a mycoplasma.
(v) An ostrich egg cell is a cell that can be seen without a microscope…
(vi) The nucleus and cytoplasm and cell membrane are parts of a cell.
(vii) Energy is produced in mitochondria.
(viii) Cell wall is present in plant cells.
- Write ‘True ‘or ‘False ‘in front of the statement given below:
(i) Most of a cell is the nucleus. (True)
(ii) Only the nucleus of a cell represents the protoplasm. (False)
(iii) Most cells are microscopic. (True)
(iv) All living organisms are made of cells. (True)
(v) Every cell has a cytoplasm. (True)
(vi) All cells in a multicellular organism can live independently. (False)
(vii) The outermost covering in an animal cell is called the cell wall. (False)
- Match the statements in Column A with those in Column B.
|Column A||Column B|
|1. Cell.||a. Outermost covering in plant cells.|
|2. Nucleus||b. Tiny structures inside cells.|
|3. Cell wall||c. Unit of a living body.|
|4. Chloroplast||d. Boss of the cell.|
|5. Cytoplasm||e. Photosynthetic units.|
|6. Organelles||f. Jelly-like substance between cell membrane and nucleus.|
|Column A||Column B|
|1. Cell.||c. Unit of a living body.|
|2. Nucleus||d. Boss of the cell.|
|3. Cell wall||a. Outermost covering in plant cells.|
|4. Chloroplast||e. Photosynthetic units.|
|5. Cytoplasm||f. Jelly-like substance between cell membrane and nucleus.|
|6. Organelles||b. Tiny structures inside cells.|
- Label the different parts numbered 1 to 6 of the cell indicated by guidelines in the figure shown below: