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

Here are the answers to the True/False statements:

1. Unicellular organisms have one-celled body. (True) Explanation: Unicellular organisms, by definition, are composed of only a single cell that performs all life functions.

(b) Muscle cells are branched. (False)

Explanation: While some muscle cells can have complex structures, typical muscle cells are elongated and often spindle-shaped or fibrous, specialized for contraction, not generally described as branched in the way nerve cells are.

(c) The basic living unit of an organism is an organ. (False)

Explanation: The cell is considered the fundamental structural and functional unit of all living organisms, not an organ. Organs are made up of tissues, which are made up of cells.

1. Amoeba has irregular shape. (True) Explanation: Amoeba is a unicellular organism known for its ability to change its shape by forming 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.

Function of Nerve Cells: Nerve cells, also known as neurons, are specialized cells that form the nervous system. Their primary function is to receive stimuli from the internal or external environment and transmit electrical and chemical signals (nerve impulses) to other nerve cells, muscles, or glands. This communication allows the body to respond to changes and coordinate its various activities, enabling functions like thought, movement, and sensation.

1. Cytoplasm The cytoplasm is the jelly-like substance that fills the cell and surrounds the cell organelles, enclosed within the cell membrane but outside the nucleus. It is primarily composed of water, salts, and organic molecules. Various essential cell organelles, such as mitochondria, ribosomes, and endoplasmic reticulum, are suspended within the cytoplasm. The cytoplasm is the site where many metabolic reactions and cellular processes, like glycolysis, occur. It also plays a role in transporting substances between different parts of the cell and between organelles.

(b) Nucleus of a cell The nucleus is a vital, membrane-bound organelle found in eukaryotic cells, typically located near the center. It is often referred to as the 'control center' of the cell because it contains the cell's genetic material in the form of DNA, organized into chromosomes. The nucleus is enclosed by a double membrane called the nuclear envelope, which has pores that regulate the passage of molecules between the nucleus and the cytoplasm. Within the nucleus, there is a smaller, dense structure called the nucleolus, which is involved in ribosome synthesis. The chromosomes within the nucleus carry genes, which are responsible for heredity and the transmission of traits from parents to offspring. The nucleus controls all cellular activities, including growth, metabolism, and reproduction.