Characteristics of living things

Structural Organization:

• Living things have a definite structural organization.
• Their bodies are made of cells, which are the building blocks of the body.
• A cell is the smallest living structure that is able to function independently.
• A group of similar cells that perform a particular function form a  tissue .
• A group of tissues performing a particular function in the body form an  organ .
• A group of organs interacting with one another to perform a particular process form an  organ  system.

Structural organization of living things

• An organism can be made of one cell or more than one cell.
• An organism consisting of a single cell which performs all its functions is called a  unicellular  organism.
• In a unicellular organism, all life processes are carried out by a single cell. ( Life  process:  Different processes that help an organism to stay alive, e.g. Digestion, Respiration, etc.)
• E.g. Amoeba, Euglena, Paramoecium, etc

• An organism consisting of several cells is called a multicellular organism.
• E.g. Human beings, plants, animals

Movement and response to stimuli:

• Most living things are capable of moving on their own.
• Animals move from place to place in search of food and water, to escape from danger, and for various other reasons.
• Plants cannot move from one place to another on their own.
• However, they exhibit movement of certain parts, such as leaves and roots, in response to changes in their immediate environment.

• A change in the immediate environment of an organism, which produces change in the activities of the organism, is called a stimulus (plural: stimuli).
•  An organism's reaction to a stimulus is called a response. Leaves of touch-me-not (lajwanti) curl up when touched.
• Here, touch is the stimulus and curling up of leaves is the response.
• The movement of leaves, roots, etc., of a plant in response to external stimuli such as light and gravity is called tropism.

• Shoot of a plant grows towards the light and the root grows towards gravity.

Growth:

• Living things grow.
• For example, a child grows into an adult and a seedling grows into a tree.
• Growth in living things is irreversible.
• We cannot get the seedling back from a tree. We cannot become a baby again.

Excretion:

• Excretion is the process of removal of wastes from the body of a living organism.
• Living things remove waste from their body through excretion.
• Most animals excrete solid wastes in the form of faeces, liquid wastes in the form of urine, and gaseous wastes in the form of carbon dioxide.
• Plants get rid of wastes in the form of gum, resins, latex, etc.

Respiration:

• The process by which living things utilize the oxygen to release energy stored in the food they eat is called respiration.
• Breathing is a part of respiration.
• By breathing, we inhale air which contains oxygen.
• It is through respiration that this oxygen is used by the body to obtain energy from food.
• Plants also respire to obtain energy from the food they make by photosynthesis. Thus, respiration is a vital process for all living organisms.

Reproduction:

• Living things have the ability to produce more of their kind through reproduction.
• Different organisms have different means of reproduction.
• Plants reproduce mostly through seeds.
• Animals reproduce by either laying eggs or giving birth to young ones.

Feeding:

• All living things need food.
• Green plants manufacture their own food in their green leaves by photosynthesis. So, they are called autotrophs {auto, self; trophe, food).
• Animals cannot manufacture their own food. So, they are called heterotrophs (hetero, different; trophe, food). They depend on plants and other animals for food.

Life span and death:

• All living things follow a cycle of growth and development, in which an organism takes birth, grows into an adult, grows old, and dies.
• This is known as the life cycle of an organism.