CBSE Class 8 Science Chapter 8: Cell - Structure and Functions NCERT Solutions

Let's evaluate each statement:

1. Unicellular organisms have one-celled body. This statement is True (T). Unicellular organisms are defined by their single-celled structure, where all life processes occur within that one cell.
2. Muscle cells are branched. This statement is False (F). While some cells are branched (like nerve cells), muscle cells are typically elongated and spindle-shaped, designed for contraction.
3. The basic living unit of an organism is an organ. This statement is False (F). The fundamental structural and functional unit of all known living organisms is the cell, not an organ. Organs are composed of tissues, which are made of cells.
4. Amoeba has irregular shape. This statement is True (T). Amoeba is a unicellular organism known for its ability to change its shape due to the formation of pseudopodia, giving it an irregular outline.

A sketch of a human nerve cell (neuron) typically shows a cell body, dendrites, and an axon ending in nerve endings. The main function of nerve cells is to receive stimuli from the environment or other nerve cells and to transmit signals (messages) throughout the body. This allows for rapid communication and coordination of bodily functions, enabling responses to stimuli and control over various activities.

Function of Nerve Cells: Nerve cells are specialized to transmit information in the form of electrical and chemical signals. They receive signals, process them, and then transmit them to other nerve cells, muscles, or glands. This communication network is crucial for coordinating actions, sensing the environment, and controlling bodily processes.

1. Cytoplasm: The cytoplasm is the jelly-like substance found within the cell membrane, surrounding the nucleus. It is composed mainly of water, salts, and organic molecules. Various essential cell organelles, such as ribosomes, mitochondria, endoplasmic reticulum, and Golgi apparatus, are suspended in the cytoplasm. The cytoplasm serves as the medium for many metabolic reactions and biochemical processes that occur within the cell. It also plays a role in the transport and storage of substances between different cell organelles.
2. Nucleus of a cell: The nucleus is a vital, typically spherical organelle found near the center of eukaryotic cells. It is enclosed by a double membrane called the nuclear membrane, which has pores to regulate the passage of substances between the nucleus and the cytoplasm. The nucleus contains the cell's genetic material in the form of chromosomes, which are thread-like structures made of DNA. These chromosomes carry genes that determine hereditary traits. Within the nucleus, there is also a smaller, denser body called the nucleolus, which is involved in ribosome synthesis. The nucleus controls all the activities of the cell, including growth, metabolism, and reproduction.