People often wonder at the differences between animals and plants. Just how do you define what a plant is as opposed to a fungus or an animal? Well, there are three kingdoms of life, animals, plants and fungi and in each kingdom the organisms making it up have common characteristics which associate one to another. PLants have several common characteristics..
All the kingdoms show characteristics which define them as 'alive' with processes of reproduction, locomotion, nutrition, exretion and respiration. How they do this varies and it is not always breathing in air as we think of it for example or reproducing sexually -a good many organisms don't need another to reproduce thank you very much and manage fine on their own.
However, while many understand that plants, fungi and animals differ, it is difficult to pinpoint common characteristics of plants specificaly.
Perhaps the easiest common characteristic to identify is that plant cells are unique in that, as well as possessing a cell membrane, they have a cell wall. This is an outer layer of the cell, against which cytoplasm pushes to maintain the tissue shape. This is important in plants because, as they photosynthesise, they need to have their leaves held in the best position to obtain light and to do this, cells must be rigid so they support leaves and stems.
Other characterictics common to plants are the abilities to photosynthesise. Many plants do this using all of the light spectrum wavelengths apart from green (we see them as green plants as they reflect the green part of the wavelength). However, many plants including seaweeds, many water plants and algae do not use the same part of the light spectrum. We may see these as blue, red, brown or different shades of green because they use different parts of light wavelength and reflect the parts they do not use. It is a common characteristic of plants that they can use light energy to make food (photosynthesis).
It is however wrong to say all plants are green as many are not and also some animals possess cells, in association with algae) which photosynthesise to boost energy levels and enable them to fix carbohydrate from sunlight to some extent.
Similarly, it is wrong to suggest all plants have leaves. Many do not and many animals have leaf-like appendages as camaflouage. It is also wrong to say plants are immobile - so are some animal life forms and some plants move a lot more than you might expect as their roots forage for nutrients and water. The plant cell wall remains the one characteristric which is indicative of the organism being a plant.
Genetics will obviously tell us if an organism is animal or plant or fungi but characteristics tend to be those things which show themselves easily so the cell wall is a good way of telling if an organism is a plant or animal as only plant cell sposess it and it is common to all plants.