Cell - Structure and Functions Question Answers: NCERT Class 8 Science

(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.

(c) False

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.

Across:

1. Chlorophyll

3. Organelle

6. Protoplasm

8. Genes

Down:  

1. Chloroplast

2. Organ

4. Membrane

5. Vacuole

7. Tissue

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.

1. 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.
2. 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:

• 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.  

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.

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

Differences between eukaryotes and prokaryotes are as follows: 

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.

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.

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.