Lesson 1, Topic 2
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A characteristic feature of all organisms for continuation of species

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Living organisms are made up of cells. Cells are the structural and functional units of all the living organisms. In 1665, Robert Hooke discovered the existence of cells using a microscope, which further paved the way for the discovery of various other microscopic organisms. Some organisms consist of a single cell, for example, the amoeba. Other organisms are multicellular, having millions of cells.

A single cell is able to produce many cells through a process known as cell division. Different organisms have different kinds of cells. A human body alone shows various kinds of cells such as – blood cells, nerve cell, fat cell etc. Shapes and sizes of cells depend upon the functions they perform. Amoeba has an ever-changing shape as it changes form to locomote. Some cells have a fixed shape and perform a specific function, such as nerve cells, which are usually shaped like trees.

An organism is any being that consists of a single cell or a group of cells, and exhibit properties of life. They have to eat, grow and reproduce to ensure the continuation of their species. Organ systems collectively work together for the proper functioning of a living organism, failure of even one of these systems has an impact on our lives.

Characteristics Of Living Things

Following are some key features:

  • Living things eat food. They take in nutrition in different forms to lead a healthy life
  • They respire. Respiration is one of the key aspects of living organisms. It happens within cells and releases energy as a result of a chemical reaction.
  • Food eaten is digested and eliminated out of the body through the excretory system
  • An organism is said to be living if it is sensitive to touch. It can be light-sensitive or sensitive to chemicals.
  • All living organisms exhibit some form of movement.
  • All living organisms grow. Growth is one of the most important aspects of a living organism.
  • Living organisms reproduce via asexual or sexual methods.

What are Cells made up of?

Cells are the building blocks of every living organism. Two-thirds of a cell is composed of water and are made up of biological molecules such as proteins and lipids. They provide a definite structure to the body, help to break down food and release energy which is used up by our body to perform multiple tasks throughout the day. Also, our body performs many other important functions such as manufacturing nerve cells, carrying out chemical reactions, producing blood cells, etc. All these activities require energy which is provided by cells after breaking down food.

Components of a Cell:

The cell structure of plants and animals are different. However, they do have common features such as a nucleus, mitochondria, and the endoplasmic reticulum.

A human cell is primarily made up of the following:

  • Nucleus
  • Cytoskeleton
  • Cytoplasm
  • Golgi Apparatus
  • Endoplasmic reticulum
  • Lysosomes
  • Mitochondria
  • Ribosomes
  • Plasma membrane
  • Secretory Vesicles
  • Centriole
  • Centrosome
  • Peroxisome