Theory:

As we have already seen the characteristics of living organisms briefly, let us focus in detail here.
Food
Nutrition is the process through which living organisms obtain food, and use the food to give energy to the organism. 
Energy is required for growth of the organism, as well as for life processes which takes place inside them.
Growth and Development
Cells in the body divide and grows to attain growth of the organism from the young one to an adult.
Example:
A chick hatches from an egg, which further develops into a cock or a hen.
Respiration
  • Breathing in living organisms is through the process of respiration.
  • Our body consumes the oxygen (from air) as we breathe in, and the carbon dioxide is sent out in the process.  
  • Through respiration, body obtains energy from the food that we consume.
Some animals have a different mechanism for the exchange of gases in the respiration process.
Example:
1. An earthworm breathe through its skin. The skin of an earthworm is so thin, and moist through which it absorbs the oxygen required.
 
2. Fishes have gills that use dissolved oxygen present in water.
 
3. In plants, the gaseous exchange takes place through stomata (tiny pores) that present in leaves.
 
4. Humans respire by taking in oxygen, and giving out carbon dioxide.
Response to the Environment and Stimuli
Changes in the surroundings which makes livings things respond to it are called, stimuli.
All living things respond and behave differently according to stimuli.
Example:
Don't we behave active or differently when we see our favorite food? Or, we use fans or air conditioners to cool the temperature of the surroundings when the climate is too hot.
Important!
Plants too respond to stimuli. Plants grow towards the direction of sunlight. Mimosa or "touch-me-not" plant leaves closes when someone touches them.
Excretion
All the living organisms consume food. And, remember that the body will not utilizes all the consumed food. The remaining unused food is waste, and need to be excreted through the body.
The body also produces waste in the form of urea in other processes.
The process of removal of wastes from the body is known as excretion.
Important!
Plants also excrete! Plants remove waste products through secretions.
Reproduction
Living organisms produce a new organism of their own kind through the process of reproduction.
There are various modes of reproduction.
  • Some animals produce young ones through eggs, while some give birth to young ones.
  • In plants, the mode of reproduction is through seeds. The seeds germinate into a new plant.
  • In some plants like potato, reproduction occurs through parts other than seeds - a bud which can grow into a new plant.
Movement
  • The animals move from one place to another and also displays other body movements.
  • Plants are fixed to the soil, and thus do not move.
  • However, water, minerals, and the food prepared in the plant moves from one part to another.
  • Plants also display other movements like the opening and closing of buds, movement of plant towards sunlight.
Adaptation to environment
The presence of certain features in a habitat which enables an animal or a plant to live in a particular surrounding is called adaptation.
 
Depending on the place where it is present, different animals adapt in different ways.
Example:
Fish have slippery scales on their bodies. The scales protect the fish and helps in easy movement through water.
Acclimatisation
Adaptations are very slow changes that takes place in the bodies of the organisms over thousands of years. However, some changes can occur in the organisms over a short period of time so that the body can adjust to the sudden changes that occur in the environment.
 
For example, a person lives in plain, and suddenly he goes to a mountain region; the body may experience difficulties in breathing as the air is thin at the altitude, and the person breathes faster to obtain the sufficient amount of oxygen.
 
After a few days, the body automatically adjusts or gets acclimatized to the new environment.
 
The process of getting adjusted to the surrounding over a short period of time is termed as acclimatisation.
Important!
The changes that happen during the acclimatisation process is reversible and temporary. In contrast, the changes that take place during adaptation are permanent and not reversible.