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NCERT Solutions for Class 8 Science - Cell Structure and Functions

Exercises

Q1. Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have a one-celled body. ( )
(b) Muscle cells are branched. ( )
(c) The basic living unit of an organism is an organ. ( )
(d) Amoeba has an irregular shape. ( )

Ans:

(a) True

  • Organism made up of one cell is called unicellular or unicellular organism.

(b) True

  • Muscle tissue is of three types- Striated muscle, Cardiac muscle, Smooth muscle. Muscle cells usually branched cells.

(c) False

  • Cell is the basic, structural and fundamental unit of life.

(d) True

  • Amoeba has no definite shape.

Q2. Make a sketch of the human nerve cell. What function do nerve cells perform?
Ans:

Human Nerve CellHuman Nerve Cell
The function of a nerve cell is to transmit messages to the brain and also to take away messages from the brain to the receptor organs.


Q3. Write short notes on the following:

(a) Cytoplasm
(b) Nucleus of a cell

Ans:
(a)
 Cytoplasm 

  • The cytoplasm is the jelly-like substance present between the cell membrane and the nucleus. Various other components or organelles like Mitochondria, Golgi bodies, Ribosomes, etc. are present in the cytoplasm.NCERT Solutions for Class 8 Science - Cell Structure and Functions
  • Cytoplasm helps the exchange and storage of substances among cell organelles.
  • Most of the metabolic activities occur inside the cytoplasm.

(b) Nucleus of a Cell

  • The nucleus is an important component of the living cell. It is mostly spherical and located in the center of the cell.Plant and Animal Cell
    Plant and Animal Cell
  • It is separated from the cytoplasm by a membrane called the nuclear membrane. 
  • In addition, 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. 
  • The nucleus, in addition to its role in inheritance, acts as the control centre of the activities of the cell.

Q4. Which part of the cell contains organelles?
Ans: Cell organelles are suspended in the cytoplasm of the cell . Cytoplasm is the gel 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.

Q5. Make sketches of animal and plant cells. State three differences between them.
Ans:
NCERT Solutions for Class 8 Science - Cell Structure and Functions

NCERT Solutions for Class 8 Science - Cell Structure and Functions


Q6. State the difference between eukaryotes and prokaryotes.
Ans:
NCERT Solutions for Class 8 Science - Cell Structure and Functions

Q7. Where are chromosomes found in a cell? State their function.
Ans. 

  • Chromosomes are found inside the nucleus of a typical cell. 
  • Chromosomes contain genes that are carriers of genetic information. 

ChromosomeChromosome

  • Chromosomes govern distinct features of an organism.
  • Chromosomes take part in cell division.

Q8. ‘Cells are the basic structural units of living organisms’. Explain.
Ans: Cells are the smallest units from which a living organism is made. A cell contains all the necessary structures which are required to carry out various biological processes. A group of cells makes a tissue which further makes organs and finally an organism. Thus, cells are called the basic structural unit of living organisms.

Q9. Explain why chloroplasts are found only in plant cells?
Ans: Chloroplasts are a type of plastids that contain chlorophyll. Chlorophyll is a green colour pigment that plays important role in photosynthesis. Since green plants need to prepare their food, hence chloroplast is present in them.Structure of ChloroplastStructure of Chloroplast


Q10. Complete the crossword with the help of clues given below:
Across-
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.
Down-
1. Green plastids.
2. Formed by a collection of tissues.

4. It separates the contents of the cell from the surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.

NCERT Solutions for Class 8 Science - Cell Structure and FunctionsAns:
Across:
1. Chlorophyll
3. Organelle
6. Protoplasm
8. Genes
Down:
1. Chloroplast
2. Organ
4. Membrane
5. Vacuole
7. Tissue

NCERT Solutions for Class 8 Science - Cell Structure and Functions

The document NCERT Solutions for Class 8 Science - Cell Structure and Functions is a part of the Class 8 Course NCERT Textbooks & Solutions for Class 8.
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FAQs on NCERT Solutions for Class 8 Science - Cell Structure and Functions

1. What is the cell theory?
Ans. The cell theory states that all living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells arise from pre-existing cells. This theory was proposed by Matthias Schleiden and Theodor Schwann in 1839.
2. What are the differences between prokaryotic and eukaryotic cells?
Ans. Prokaryotic cells are smaller and simpler in structure, lacking a true nucleus and membrane-bound organelles. Eukaryotic cells are larger and more complex, with a true nucleus and various membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus.
3. What is the function of the cell membrane?
Ans. The cell membrane is a selectively permeable barrier that separates the cell from its external environment. It controls the entry and exit of substances into and out of the cell, maintains the integrity of the cell, and plays a role in cell signaling and communication.
4. What is the role of ribosomes in cells?
Ans. Ribosomes are the site of protein synthesis in cells. They are composed of RNA and proteins and are found in both prokaryotic and eukaryotic cells. Ribosomes translate the genetic information from the DNA to synthesize proteins according to the sequence of nucleotides.
5. What is the function of mitochondria in cells?
Ans. Mitochondria are the powerhouse of the cell and are responsible for generating energy in the form of ATP through cellular respiration. Mitochondria are found in eukaryotic cells and possess their own DNA and protein-synthesizing machinery. They also play a role in calcium signaling and programmed cell death.
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