Plants contain organic matter (proteins, fats, carbohydrates), minerals and water.
Water is essential for all vital processes in the plant organism. Therefore, cells in which vital processes are actively proceeding always contain a lot of water. Young growing organs contain up to 90 – 95% water, and lignified ones – only about 50%.
The organs of various plants contain an unequal amount of water, organic and mineral substances. So, in the leaves of cabbage – 90% of water, in the fruits of cucumbers it is even more – 96%, and in the ripe seeds of water contains only 5 – 15% of the total mass.
Mineral and organic matter
The seeds of mineral salts contain an average of 3%, in the roots and stems – 4 – 5%, in the leaves – 10 – 15% of the mass, the rest is organic matter.
The seeds of all plants contain much more organic matter than water and minerals.
The ratio of substances in plant organs may be different.
Example: proteins in wheat caryopses – 13%, carbohydrates – 69%, fats – 2%, and in sunflower seeds proteins – 26%, carbohydrates – 16%, fats – 44%.
Plants also contain very small amounts of other organic substances, such as vitamins.
The same parts of different plants can contain different amounts of substances.
Example: Wheat kernels contain twice as much water as sunflower achenes, and more organic matter in sunflower seeds.
Mineral and organic substances are used to build the body of plants, and also take part in various life processes in plants. Lack or absence of any substance disrupts the normal development of the plant and can lead to its death.
Man uses substances that make up plants. To obtain flour and cereals containing carbohydrates and proteins, wheat, rye, barley, corn, oats, millet, rice, and buckwheat are grown.
Seeds of peas, beans, soybeans, lentils are rich in proteins.
Sunflower, cotton, flax, hemp, peanuts, soybeans and other oilseeds are needed to obtain vegetable fats.
Plants are also used to obtain rubber, alcohol, turpentine, various medicinal and cosmetic preparations, and many other products important for humans.