Living beings can be broadly classified into plants and animals. They both have common characteristics, and follow a universal circle of life that includes birth, reproduction, and death. They need all the basic nutrients for growth and development, and are prone to disturbances in their metabolism. They share a mutual bonding through the ecosystem in which they survive, i.e., plants depend on animals for carbon dioxide, and animals depend on plants for oxygen.
The basic and most fundamental component present in every living entity is the cell. Both plants and animals are made up of one to countless number of these units, which carry out different sets of functions. Life before evolution began from a single cell. Similarly even today, life is generated from a single cell, which then divides or multiplies to give rise to a complex living form. After fertilization, once the zygote is formed, the cells start differentiating into their types, and over a certain period of time, give rise to a fully developed, mature living entity.
Plants and animals use various forms of energy for the development of their bodies. The entire amount of chemical energy used by them to carry out their life processes is called metabolism. Plants use solar energy to carry out photosynthesis, which is the process for making their food (glucose). Hence, they are known as 'autotrophs'. However, animals cannot produce their own food, and are dependent on plants and other animals for their energy source. Hence, they are called 'heterotrophs'.
One of the rules of nature is growth, which is followed by all life forms. As development is an involuntary process, every cell in a living entity has to age. Growth and change is a part of all living organisms, as cells divide to give rise to new and identical ones. Sometimes due to some genetic defects, during differentiation, some cells mutate to form other types of cells, and result in complex organisms. This process of constant development and growth is also called organogenesis.
All organisms reproduce to continue their species' life. Plants and animals have a reproductive system, which is completely developed at puberty. There are two types of reproduction prevalent in nature, viz. sexual and asexual. The former involves the combination of genetic material to give rise to a single zygote, which further develops into a bigger organism. The latter type involves splitting of one organism or cell, to form two separate individuals of the same species.
Every living thing is highly organized when it comes to the pattern or structure of the body. Plants as well as animals have very complicated cell structures that are arranged uniquely in different organs. The cells form organelles, which in turn form organs. The organs make up the various parts of the organism. This is a network that is followed by every cell.
Whatever is created has to come to an end. Both plants and animals have limited life spans, during which they go through their life processes like development and reproduction. As the cells age over a particular time period, they start becoming weak and lose their functions. They can't survive, and this is called death. They all have a particular age they live up to, and then surrender to nature.
These include homeostasis, which is the process to maintain stable internal conditions for survival. These conditions have to be maintained for body temperature, heartbeat, water content, etc. When homeostasis is regulated, the metabolism of the body is also regulated, and the living things stay healthy and fit.
Movement is also one such characteristic. The type of movements depend on each species of plants and animals. Adaptation and defense are also considered as common traits. Every living entity has to adapt to certain conditions for survival, and if it can't, then it won't survive. It is their right to protect themselves from predators.
Evolution is a miracle that has accompanied us for billions of years, and is still in process. Eventually, all living entities complement each other through their characteristics.