Plants are one of the five kingdoms of living organisms on our planet. They belong to eukaryotes, that is, creatures whose cells contain a nucleus.
Structure of a plant
They can be either unicellular or multicellular. The latter are divided into such departments as green, brown and red algae, spore, gymnosperms and angiosperms. The organism of algae can consist of both one cell and many, however, there are no organs in their structure, the body is continuous - called a thallus. In spores, gymnosperms and angiosperms (flowering), the presence of differentiated tissues and organs is observed. The latter are divided into vegetative and generative.
The first includes the shoot (stem and leaves), as well as the root. Many are interested in the question: "Why are the leaves green?" Why this particular color? Also, many children ask the question: “Why are the leaves green?” And we will start this article with this topic.
Why are the leaves green?
This color is due to the presence of chlorophyll. In autumn, this pigment is lost and the green leaf turns red, orange, or yellow. Why is this substance needed? It is simply vital for the plant. Without it, the process of photosynthesis cannot proceed, due to which nutrients are produced. Organic plant chemicals are usually obtained only from this process. However, some species living in the lower layers of tropical forests do not receive enough light for full-fledged photosynthesis, so they resort to hunting small insects, thus compensating for the lack of organic compounds. These include sundew, lady's slipper, etc.
Briefly about the structure of a plant cell
It consists of a plasma membrane, a cellulose cell wall, a cytoplasm containing organelles, and a nucleus containing DNA. The cytoplasm contains the following organelles: mitochondria, ribosomes, endoplasmic reticulum, vacuole (one large in an old cell, several small in a young one), the Golgi complex and plastids (chloroplasts, leukoplasts, chromoplasts).
Each of them performs its functions. Mitochondria produce energy, ribosomes synthesize proteins, the endoplasmic reticulum (reticulum) produces lipids, vacuoles accumulate unnecessary substances, since it is impossible to bring them out because of the solid cell wall, photosynthesis takes place in chloroplasts, chromoplasts contain pigments, leukoplasts store reserve nutrients (mostly starch).
How does photosynthesis work?
This process is carried out in chloroplasts, which are located in the cytoplasm of the cell. These organelles are single-membrane, in their structureincludes thylakoids - thin plates collected in grains - piles. It is in them that chlorophyll is contained - that is why the leaves are green. In addition, chloroplasts contain ribosomes involved in the production of proteins, starch grains, and circular DNA molecules that contain information about substances that should be synthesized in the cell.
During photosynthesis, plants absorb solar energy, water and carbon dioxide, and release oxygen as a by-product of the reactions. Enzymes that help carry out chemical interactions are located directly in the chloroplast matrix (the substance that fills it).
What are leaves made of?
Several types of plant tissue can be found in this organ, there are four of them. These are the epidermis, mesophyll, conductive tissues (xylem and phloem), as well as mechanical tissues. Photosynthesis takes place in the mesophyll, or parenchyma. You can see the cells of a green leaf under a microscope. This is the top ball - the epidermis.
Its cells are located closely to each other, but in this layer there are pores that allow you to absorb carbon dioxide and release oxygen, as well as regulate water and temperature balance. The parenchyma (mesophyll) is divided into two layers - one of columnar cells, the other of spongy. The former contains more chloroplasts than the latter. The xylem is represented by vessels through which the liquid is supplied from the roots to the leaves, that is, upwards, and the phloem consists of sieve-like tubes, alongwhich water is transported downward. Mechanical fabrics provide the sheet with rigidity and stability, a certain shape.
