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Cell-Structure and Functions - Class 8 : NCERT Exercise Questions


Q.1 Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have one-celled body.                                         (T/F)
(b) Muscle cells are branched.                                                                     (T/F)
(c) The basic living unit of an organism is an organ.                                  (T/F)
(d) Amoeba has irregular shape.                                                                  (T/F)
Sol. (a) Unicellular organisms have one-celled body.                                 (True)
(b) Muscle cells are branched.                                                                     (False)
(c) The basic living unit of an organism is an organ.                                   (False)
(d) Amoeba has irregular shape.                                                                  (True)

Q.2 Make a sketch of the human nerve cell. What function do nerve cells perform?
Sol. The function of nerve cells is to receive and transfer messages, thereby helping to control and coordinate the working of different parts of the body.
Q.3
Write short notes on the following:
(a) Cytoplasm
(b) Nucleus of a cell
Sol. (a) Cytoplasm:
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. Cytoplasm helps exchange and storage of substances among cell organelles. Most of the metabolic activities occur inside cytoplasm.
(b) Nucleus of a cell:
Nucleus is an important component of the living cell. It is mostly spherical and located in the centre of the cell. It is separated from the cytoplasm by a membrane called the nuclear membrane. In addition, nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. Nucleus, in addition to its role in inheritance, acts as control centre of the activities of the cell. The entire content of a living cell is known as protoplasm. It includes the cytoplasm and the nucleus. Protoplasm is called the living substance of the cell.

Q.4 Which part of the cell contains organelles?
Sol. Cytoplasm is the part of cell which contains organelles such as mitochondria, ribosomes, golgi bodies, etc.

Q.5 Make sketches of animal and plant cells. State three differences between them.
Sol. The differences between plant cell and animal cell are:

Parameter

Plant Cell

Animal Cell

Sketch  

 

Cell wall

Present

Absent

Size

Small

Large

Vacuole

Large

Small or Absent

Plastids Present

Absent


Q.6 State the difference between eukaryotes and prokaryotes.
Sol. The differences between eukaryotes and prokaryotes are:

Eukaryotes

Prokaryotes

The cells having a well-organized nucleus with a nuclear membrane are termed as eukaryotic cells

The cells having nuclear material without nuclear membrane are termed as prokaryotic cells.

Most eukaryotes are multi-cellular.

Most prokaryotes are unicellular.

Cell organelles such as mitochondria, plastids, golgi bodies, etc. are present.

Cell organelles such as mitochondria, plastids, golgi bodies, etc. are absent.

Example: Fungi, onion cells, etc.

Example: Bacteria and blue green algae

Q.7 Where are chromosomes found in a cell? State their function.
Sol. Chromosomes which are thread-like structures are found in the nucleus of the cell. They carry genes that help in inheritance or transfer of characters from the parents to the offspring.

Q.8 ‘Cells are the basic structural units of living organisms’. Explain
Sol. A cell is the smallest unit of life and is capable of all living functions. All basic functions for the organism survival take place inside cells. They are the building blocks of life. This is the reason why ‘Cells are the basic structural units of living organisms’.

Q.9 Explain why chloroplasts are found only in plant cells?
Sol. Chloroplasts are found in plant cells only because chloroplasts contain chlorophyll which is essential for photosynthesis. Chlorophyll traps solar energy and utilize it to manufacture food for plants.

Q.10 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 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.Sol. Across:
1. Chlorophyll
3. Organelle
6. Protoplasm
8. Genes
Down:
1. Chloroplasts
2. Organ
4. Membrane
5. Vacuole
7. Tissue



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