Living things are made up of cells.

Cells are the smallest units of an organism that can be considered alive.

Living things can reproduce.

Organisms reproduce either sexually or asexually in order to produce offspring.

Living things are able to develop and grow.

Every organism has a certain pattern of growth and development. For example the pattern of development for a caterpillar is to metamorphose into a butterfly.

Living things respond to environmental stimuli

Organisms have ways to detect environmental stimuli and then formulate a response. For example, birds will migrate when the weather gets cold.

Living things are unified by a universal genetic code.

Organisms store genetic information in DNA molecules that are passed onto the next generation.

Please click for explanation.

Due to a large number of life-forms found on Earth, they are studied on different levels. For an instance, molecular and cellular biologists study the smallest forms of living things. On the other hand, ecologists and population biologists study larger systems in the level of organization. Since community refers to all the populations of different species living in a particular area, ecologists and population biologists can study this system. The scope of their study would include the topics on how the groups of species interact with each other, and how these life-forms interact with the environment and vice versa. Other topics like demography, statistics, and ecosystem ecology are also studied at the community level of organization.

Living organisms are able to reproduce either by *sexual* or *asexual* reproduction. This allows them to produce offspring that will inherit a part or all of their genetic information in their DNA.

**Sexual** reproduction involves the union of two sex cells or *gametes* such as sperm and egg cells. Therefore, this type of reproduction typically involves two parents from the same species.

On the other hand, **asexual** reproduction requires only one parent, and thus does not involve the union of gametes. This would produce offspring that is genetically identical to the parent.

One of the characteristics of living things is to obtain and use energy in order to sustain life through a process called metabolism. Metabolism is the chemical process in which living things break down and convert food and other materials into energy. In turn, this energy is used by the cell for its processes such as growth, development, and reproduction.

Since the external environment can constantly change, there is a need for the organism to maintain a constant and stable internal environment in order for its cells to function properly.

The process by which organisms expend energy in order to maintain a constant and stable internal environment is called **homeostasis**. This process is essential for their survival.

One example of homeostasis is how birds fluff up their feathers in order to keep themselves warm during cold weather. This helps maintain their internal body temperature at a stable level.

Living things have the ability to respond to stimuli from the body’s internal conditions and the external environment. For an instance, you haven’t eaten breakfast today. When your stomach growls, it is an internal stimulus that says you are hungry and you need food. When you see the peach in the fruit bowl, it triggers an external stimulus in which the appearance, smell, and texture of such food tells you to eat it. As a result, your body will react to the stimuli by telling you to get and eat the peach to satisfy your hunger.