Chapter 8 Cell - Structure and Functions

Cells are the basic structural and functional unit of life.
Organs are the smaller parts which collectively made a full organism.
Robert Hook in 1665 observed cells in the cork for the first time.
Cells are of different shapes and size.
Number of cells are also differ from organisms to organisms.
Some cells are of large size and some are of small size.
The organisms which contains large number of cells are known as multicellular organisms.
In unicellular organisms, all the basic functions are performed by the single cell.
In multicellular organisms, all the basic functions are performed by the various cells.
Cells have mainly three parts: cell membrane, cytoplasm and nucleus.
A cell without nuclear membrane is known as prokaryotic cells.
Cells with the nucleus is known as eukaryotic cells.
A green pigment chloroplast is present in the body of plants that contains chlorophyll.
Cell membrane is thin sheet of skin around the cell. It controls the movement of substances “into the cell” and “out of the cell”.
A thick layer around the cell membrane is present, is known as cell wall. It helps in giving the shape of the cell.
Thread like structures are present in the nucleus of the cell that are known as chromosomes. And, they carry genes.
Cytoplasm is the jelly like substances which is present between the cell membrane and the nucleus.
Genes are the unit of inheritance in the organisms.
Nucleus is covered by a membrane called nuclear membrane.
In a nucleus a dense stained structure is found which is known as nucleolus.
Group of tissues which are adapted to perform the specialized functions in the body known as organs.
In amoeba, false feet are known as pseudopodia.

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Exercise 1 ( Page No. : 100 )

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)

Ans:

(a) True

This statement is true because unicellular organism have one cell present in their body, in unicellular organisms, all functions are performed by a single cell.

(b) False

This statement is false because the muscle cells are striated cells. These are not branched.

This statement is false because the basic unit of living organisms is cell. Group of tissues are called as organ.

(d) True

This statement is true because amoeba is irregular in shape. It has pseudopodia. Amoeba is single celled organism.

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

Ans:

nerve cell

Nerve cell has dendrite, axon and a nucleus. It has branched cells.

Nerve cells transmit message to the brain and it also receives message from the brain to the receptor organs. It controls and coordinate the working of different parts of the body.

Write short notes on the following: (a) Cytoplasm (b) Nucleus of a cell

Ans:

Cytoplasm: Cytoplasm is a fluid like substance which fills the cell and it is present between the plasma membrane and the nucleus. In cytoplasm, cell organelles like ribosomes, mitochondria and golgi bodies are suspended. Exchange of material between cell organelles is done with the help of cytoplasm.
Nucleus of a cell: The spherical structure is present in the center of the cell called as nucleus. It is composed of the following components:

chromosome

Nuclear membrane: A double layered membrane which separates the contents of the nucleus from the cytoplasm is known as nuclear membrane. Pores that are present in the nuclear membrane which allows the transfer of specific substance in and out of the nucleus.
Nucleolus: The spherical bodies which are not bounded by a membrane called as nucleolus.
Chromosomes: The thread like structure which carry genes. Genes have the necessary information for the transfer of different characteristics from parents to the offspring. Therefore, inheritance mainly depends on the chromosomes.

Which part of the cell contains organelles?

Ans:

Cytoplasm is a fluid like substance which fills the cell and it is present between the plasma membrane and the nucleus. In cytoplasm, cell organelles like ribosomes, mitochondria and golgi bodies are suspended. Exchange of material between cell organelles is done with the help of cytoplasm.

Make sketches of animal and plant cells. State three differences between them.

Ans:

The difference between plant cell and animal cell are as follows:

plant and animal cell

Plant cell	Animal cell
These cells are large in size.	Cells are small in size.
Cell wall is present.	Cell wall is absent.
Vacuoles are larger in size.	Vacuoles are small in size.
Plastids are present.	Plastids are absent except Euglena.
Plasma membrane is present.	Plasma membrane is absent.
Mitochondria are present in small number.	Mitochondria are present and are numerous.

State the difference between eukaryotes and prokaryotes.

Ans:

Differences between eukaryotes and prokaryotes are as follows:

Eukaryotes	Prokaryotes
These are multicellular.	These are unicellular.
Nucleus is well developed and well defined.	Nucleus is poorly defined.
Nucleolus is present in the nucleus.	Nucleoid is present.
Cell organelles are present in this cell like: Ribosomes, Endoplasmic Reticulum, Golgi apparatus etc.	Cells organelles are absent except Ribosomes. Ribosome is the only organelle that is present in both the cells.
Flagella is absent.	Single flagella is present.

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

Ans:

Chromosomes are found in the nucleus. These are thread like structures. Chromosomes carry genes which are responsible for the transfer of different characters from parents to the offspring. It plays an important role in inheritance.

‘Cells are the basic structural units of living organisms’. Explain.

Ans:

Various components of plants and animals are made up of cells. The basic and smallest unit of living organism is a cell which is responsible for all the functions. These are also known as the building blocks of the life. Cells are different in shape, size and contains specific functions. That is why cells are known as “the basic structural and functional units of life.

Explain why chloroplasts are found only in plant cells?

Ans:

Chloroplast only found in the plant cells. The leaves of a plant seems as green due to presence of the pigment chlorophyll. Chloroplast contains the pigment called chlorophyll. Photosynthesis is done by green leaves. The solar energy is trapped by the chlorophyll and utilize in making the food for plants.

chloroplast