Plants – Growth and development is a process that is always experienced by all living things. Growth is the increase in the size of a living cell in terms of mass, height, or volume. Not only humans and animals, but plants also go through this phase through several stages of plant growth.
Growth events are essentially irreversible, meaning they cannot return to their initial state due to the increase in the number and size of cells in the process. In the process of growth, the plant will go through several stages that are quite long
The stages of plant growth consist of 4 stages, namely the stages of embryonic development, germination, primary growth, and secondary growth.
Growth and development in plants begin with the stage of fertilization (fertilization) of pollen in the pistil through double fertilization. After fertilization occurs, the ovule contains the nucleus of the secondary institution and the zygote.
The nucleus of the secondary institution will develop into the endosperm which functions as a food reserve. While the zygote develops into an embryo, where embryonic development begins when the zygote divides into 2 cells. The ovule will then develop into a seed.
If the environmental conditions are favorable and the seeds do not experience dominance, then the seeds will start germination. Seed germination begins through the process of imbibition (the entry of water into the seed).
The imbibition breaks the seed coat and triggers the activation of the gibberellin hormone in the embryo. Where this hormone will activate the enzyme amylase to break down food reserves in the endosperm or cotyledons and send it to the growing point of the embryo.
The simpler molecules resulting from the breakdown of food reserves will enter into catabolic metabolic pathways to produce ATP energy which is used by seeds to grow. In plants, germination is divided into 2 types, namely:
Epigeal germination occurs when the hococots elongate which causes the plumules and cotyledons to emerge on the soil surface. This allows photosynthesis to occur as a substitute for unformed leaves. For example, green beans.
The cotyledons remain underground during hypogeal germination. For example, corn.
Primary growth is growth that occurs due to the activity of primary meristem cells which are abundant at the tips of roots and stem tips (shoots). This meristem activity causes roots and stems to increase in length.
At the tip of the root, there are 3 zones, namely the cleavage zone, the elongation zone (elongation), and the differential zone (maturation). In the cleavage zone, there is an apical meristem that is actively dividing to produce new cells. While the elongation zone is a place where cells grow lengthwise.
Meanwhile, in the zone of differentiation, the cells undergo specialization in structure and function. There are 3 tissue systems in the zone of differentiation, namely dermal tissue (epidermis), ground tissue, and vascular tissue.
The growth that allows for an increase in the diameter of the stem and roots is called secondary growth. Secondary growth occurs in dicot plants and gymnosperms. Where, this growth occurs due to lateral meristem activity, namely the vascular cambium and cork cambium (phellogen).
The division of the vascular cambium towards the inside will form the secondary xylem while the division outward forms the secondary phloem. The longer due to the activity of the vascular cambium, the xylem gets bigger and harder to form a layer called the annual circle.
Meanwhile, the cleavage activity of the cork cambium (phellogen) produces cork tissue that functions as a protector. Folgen will divide inward to form felem and split out to form phelloderm.
The cork tissue will replace the damaged and peeling epidermal tissue. The cork layer, cork cambium, and secondary phloem together form the bark.