NCERT Solutions for Class 8th Science Chapter 16 The Cell textual questions and answers based on the latest syllabus of CBSE and JKBOSE NCERT Books
Excercise of The Cell
1. Define a cell.
Answer: A cell is the basic structural, functional, and biological unit of all living organisms. It is the smallest unit of life that can replicate independently.
2. Who discovered the cell?
Answer: The cell was discovered by Robert Hooke in 1665.
3. Give three examples of unicellular organisms.
Answer: Three examples of unicellular organisms are Amoeba, Paramecium, and Bacteria.
4. Answer the following questions:
4.1 Why cells could not be observed before the 17th century?
Answer: Cells could not be observed before the 17th century because microscopes, which are essential for viewing cells, had not yet been invented.
4.2 Why could cork not be observed as such by Hooke?
Answer: Cork could not be observed as such by Hooke because he observed the dead cell walls of plant tissue, not living cells.
4.3 Where did Hooke demonstrate his observations on a cork slice?
Answer: Hooke demonstrated his observations on a cork slice using a compound microscope.
4.4 Name the outermost layer of an animal cell.
Answer: The outermost layer of an animal cell is the cell membrane.
4.5 Name the layer which is present outside the plasma membrane in a plant cell.
Answer: The layer present outside the plasma membrane in a plant cell is the cell wall.
4.6 Where are chromosomes present in a cell?
Answer: Chromosomes are present in the nucleus of a cell.
4.7 Name the cell part that has tiny holes.
Answer: The cell part that has tiny holes is the nuclear membrane.
4.8 Name the cell organelles which are found in the plant cell.
Answer: The cell organelles found in the plant cell are chloroplasts, mitochondria, nucleus, endoplasmic reticulum, Golgi apparatus, and vacuoles.
4.9 Name the cells having a branched structure.
Answer: Nerve cells (neurons) have a branched structure.
4.10 Which cell can be observed with the unaided eye?
Answer: The ostrich egg cell can be observed with the unaided eye.
5. Mention the functions of the following:
5.1 Cell membrane
Answer: The cell membrane regulates the entry and exit of substances, protects the cell, and provides structure.
5.2 Chromosomes
Answer: Chromosomes carry genetic information and are involved in the process of cell division and replication.
6. Why are the following important to a plant cell?
6.1 Cell wall
Answer: The cell wall provides structural support, protection, and helps maintain the shape of the cell.
6.2 Chloroplast
Answer: Chloroplasts are responsible for photosynthesis, allowing plants to convert sunlight into energy.
6.3 Mitochondria
Answer: Mitochondria are the powerhouses of the cell, generating ATP through cellular respiration.
6.4 Nucleus
Answer: The nucleus controls cell activities and stores genetic information.
7. Draw an outline diagram of an animal cell. Label the different parts.
Answer: (Diagram to be drawn by the student, labeling parts such as the cell membrane, nucleus, cytoplasm, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and ribosomes.)
8. Mention three differences between a plant cell and an animal cell.
Answer:
- Plant cells have a cell wall; animal cells do not.
- Plant cells contain chloroplasts for photosynthesis; animal cells do not.
- Plant cells usually have a large central vacuole; animal cells have small vacuoles.
9. What features are possessed by both plant cells and animal cells?
Answer: Both plant cells and animal cells possess a cell membrane, nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and ribosomes.
10. Why are nerve cells long? Why do these cells have projections?
Answer: Nerve cells are long to transmit signals over long distances within the body. The projections (dendrites and axons) help in receiving and sending signals to other cells.
11. Why are mitochondria known as the ‘powerhouse of the cell’?
Answer: Mitochondria are known as the ‘powerhouse of the cell’ because they generate most of the cell’s supply of ATP, used as a source of chemical energy.
12. Which four basic elements constitute more than 90% of protoplasm?
Answer: The four basic elements are carbon, hydrogen, oxygen, and nitrogen.
13. Write in brief about the variation in the shape and size of cells.
Answer: Cells vary greatly in shape and size depending on their function. For example, nerve cells are long and branched for transmitting signals, while red blood cells are small and biconcave to carry oxygen efficiently. Plant cells can be rectangular for structural support, while white blood cells are flexible to move through tissues.
14. Name the different cell organelles and the functions of these organelles.
Answer:
- Nucleus: Controls cell activities and contains genetic material.
- Mitochondria: Produces energy through cellular respiration.
- Endoplasmic Reticulum: Synthesizes proteins and lipids.
- Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
- Lysosomes: Digests cellular waste and foreign materials.
- Chloroplasts (in plant cells): Conducts photosynthesis.
- Vacuoles: Stores nutrients, waste products, and helps maintain turgor pressure.
15. What is meant by protoplasm? How does it differ from cytoplasm?
Answer: Protoplasm refers to the living content of a cell, including the cytoplasm and nucleus. Cytoplasm is the jelly-like substance within the cell membrane, excluding the nucleus, where various cell organelles are suspended.
16. Fill in the blanks, using the words given below:
(mycoplasma, microscope, nucleus, ostrich egg, cytoplasm, lysosome, mitochondria, Robert Hook, plant, cell membrane)
16.1 The lysosome is also called as suicide bags.
16.2 The term ‘cell’ was given by Robert Hook.
16.3 The instrument used to see tiny objects is called a microscope.
16.4 The smallest cell is that of a mycoplasma.
16.5 An ostrich egg is a cell that can be seen without a microscope.
16.6 The nucleus, cytoplasm, and cell membrane are parts of a cell.
16.7 Energy is produced in mitochondria.
16.8 Cell wall is present in plant cells.
17. Write ‘True’ or ‘False’ in front of the statement given below:
17.1 Most of a cell is the nucleus.
Answer: False
17.2 Only the nucleus of a cell represents the protoplasm.
Answer: False
17.3 Most cells are microscopic.
Answer: True
17.4 All living organisms are made of cells.
Answer: True
17.5 Every cell has cytoplasm.
Answer: True
17.6 All cells in a multicellular organism can live independently.
Answer: False
17.7 The outermost covering in an animal cell is called a cell wall.
Answer: False
18. Match the statements in Column A with those in Column B:
| Column A | Column B |
|---|---|
| 1. Cell | c. Unit of 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 |
19. Label the different parts numbered 1 to 6 of the cell indicated by guidelines in the figure shown below:
Answer: (The diagram will need to be labeled based on the given numbers and cell structure. Common parts to label include the nucleus, cell membrane, cytoplasm, mitochondria, endoplasmic reticulum, and Golgi apparatus.)
