How do plants grow? Surprisingly, what makes plants grow is very similar to what makes humans grow... all the way down to sexual reproduction for many plant species.
Just as humans have essential needs for survival, all plants require several basic elements to grow and thrive, including…
How much a plant needs of each element initially depends on the plant's original habitat. For example, a rainforest plant that requires consistently moist and warm conditions could obviously not survive in a desert.
But with human coercion, a plant’s ability to survive doesn't have to completely depend on nature. Organic farmers, gardeners, scientists and researchers before you have “changed” the characteristics of many desirable plants in order to allow them to thrive in other environments.
Continuing with the rainforest plant example, if a grower notices that one plant of her crop doesn't need quite as much water in order to thrive, she can cross-pollinate that plant with another more draught-tolerant plant in an attempt to begin a new "line" (called "variety" in the gardening world) of more draught-tolerant rainforest plants. Over time and continued cross-pollination of more and more draught-tolerant plants, that rainforest plant can "learn" to survive in conditions that are much different than its native lands.
This intentional cross-pollination can apply to any characteristic of the plant... from draught-resistance to flower color, fruit flavor and root depth.
Now let's move on to what happens inside and between the plants that allows them to grow, thrive and reproduce...
At the risk of over-simplifying, following are the seven stages of a plant’s growing cycle…
While some plants can reproduce asexually (for example, plant a root cutting or a stem cutting, and a new plant will emerge), most plants reproduce sexually through pollination.
During pollination, pollen grains carrying the male sperm (gametes) are carried by insects or animals to the female part of the plant where the gametes come into contact with the female’s ovule. This can occur either between two plants (cross-pollination) or within the same plant (self-pollination). A sexually reproducing plant’s sexual organs are contained in what is commonly known as its flowers.
In some types of plants, when a pollen grain containing the male’s gamete comes into contact with the female part of the flower (called the carpel), a tube extends from the pollen grain and down into the female parts in an attempt to reach the female plant’s ovule.
In some plants, the tube can extend from the pollen grain by up to 12 inches! When it does, the gametes travel through the pollen tube to reach the ovule and fertilize the egg cell within.
In other types of plants, the female parts contain a watery fluid through which flagellate sperm swim on their way to fertilize the egg cells.
Seed formation begins inside the mother plant or plant part. It then continues its growth inside a fruit in some plant types (angiosperms) or out in the open on the bracts of cones in other types (gymnosperms).
After a plant’s fruit has ripened or cone has been dropped, its seeds are spread by wind, water, animals or insects at a time when conditions are ideal for plant’s seed to germinate and grow.
Germination occurs when the plant sprouts from its seed and starts to grow, producing its familiar parts including roots, stems and leaves. Germination happens after the plant’s seed has landed on or been pushed down or buried into a growing medium (i.e. soil).
Unlike animal stem cells that can only create new types of cells early in the animal’s development, plants are always creating new parts based on the need at the time from special tissue called meristem. The meristem comes in two types - one for the roots and one for the shoot - and consists of various cell types that are “triggered” to perform the action-at-hand (or should we say, action-at-root/stem).
The process of the plant’s continued growth is made possible through several processes including photosynthesis, nutrient transfer and transpiration (see our Why Do Plants Need Water? page for more information about these).
After the plant has grown into maturity, it produces its own flowers for pollination and fertilization. Let the cycle continue!
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