Life cycles of plants describe their development from birth through growing, flowering and seed production to maturity and death.
All plants start as seeds. After being planted and germinating, each seed produces two leaves known as cotyledons before breaking open to grow roots and shoots.
Seed
Seeds are the fruit of plants, each one containing DNA from both pollen grains (male parent) and an ovule (female parent). After reaching maturity, seeds are dispersed through wind, water, animals or people to land where conditions are optimal for them to begin their growth process. When this happens, germination starts and eventually the seed transforms into a plant producing more seeds of its own to continue this cycle over and over.
An outer coating, or seed coat, protects and provides nourishment to an embryo inside a seed. It may have a smooth, glossy, textured or varied surface texture and come in various shapes and sizes. Some seeds feature wings for airborne dispersal while others, like burdock seeds with their hooks, barbs or prickles (used to attach themselves to fur and feathers of birds and mammals) can easily travel to new locations via fur or feather attachment. Still others, like dustlike seeds of orchids are easily transported by wind currents while other seeds dispersed when eaten by wildlife that helps dispereing them further in new habitats.
Once a seed germinates and develops into a young plant, it becomes known as a “seedling”. For optimal growth and success, seedlings require sunlight, soil nutrients, water and air for survival; photosynthesis converts solar energy to energy for the plant to use for growing. When mature, mature seedlings will produce flowers and then seeds to continue their lifecycle cycle.
As a seedling grows into maturity, it will begin producing flowers and fruits, filled with seeds that can start the lifecycle all over again. The process is known as alternation of generations: an asexual haploid phase called gametophytes transforms into a sexual one containing two sets of chromosomes known as sporophytes that will reproduce more directly.
Once a seedling has produced flowers and seeds, it will mature into an established plant with roots, shoots, and leaves. If the species produces flower buds that eventually open into full flowers that require pollination by bees or another animal. Pollination fertilizes an ovule to produce more seeds, which will eventually be dispersed by wind, animals or water and restart their life cycles elsewhere. Some plants, like ferns and mosses, don’t produce flowers or seeds for reproduction but instead rely on spores for propagation. Spores are tiny cells that form into new plants without producing identical offspring to their parents – these sporophytes are known as “sporophytes.” Spores that have been floating in the air for an extended period eventually settle down and form into new plants, producing additional spores which continue this cycle – an incredible cycle to watch happen! Algae and fungi use similar processes. It’s truly remarkable!
Germination
Most plants begin their lives as seeds. A seed contains the embryo of a plant along with food and an outer coating for protection, ready to germinate once placed on rich soil with enough water and the appropriate temperature. When placed on such an environment, this process known as germination begins and eventually the seedling develops into an adult plant with leaves sprouting before blooming into flowers that produce pollen that, once fertilized by pollen, produce seeds which then dispersed by wind, moving water or animals back out into fertile ground where they can germinate and start the cycle all over again.
Germination is the initial stage in a plant’s life cycle. Most seeds require oxygen, water and an ideal temperature in order to germinate successfully; legumes (beans and peas) are particularly susceptible; when water enters an empty bean seed pod it swells up, pushing through its hypocotyl into sunlight to expose its embryo and absorb energy from sunlight.
Seeds may remain dormant for months before conditions are right to initiate growth. A seed may become dormant while still on its parent plant (primary dormancy), or after it has left (secondary dormancy). Germination is controlled by several plant hormones such as gibberellins, abscisic acid, ethylene, jasmonates and nitric oxide which help control this process.
Seeds typically consist of dense packs of starch for energy and have thick, tough seed coats to provide protection. As such, these seeds can withstand significant mechanical restraint – for instance cress seeds will germinate on moist paper towels or cotton wool; and bean seeds sprout when taped to windows if they possess extremely thick seed coats. However, this form of mechanical limitation should only ever be necessary if their seedcoat has extremely tough protective features.
Germination occurs when a seed absorbs water through its seed coat, softening and swelling as a result. Water uptake then activates enzymes within the seed that convert starch to sugar for sprouting purposes and initiates biochemical processes within it that convert starch to sugar and enable sprouting.
Once a seed has enough energy, it begins producing its own food through photosynthesis. When growing its own food is done right, photosynthesis produces oxygen which feeds its roots which then use their roots to find nutrients in the soil while its cotyledons pull in moisture from the air. Once enough energy has been collected by a plant, it will produce flowers which attract pollinating insects that fertilize its pollen into more seeds – thus multiplying and spreading out across new territories.
Most plants produce fruits that contain their seeds. Birds, ants or other animals carry these away to be planted somewhere for them to germinate – or sometimes by wind, moving water or plants themselves; some are dispersed via raindrops falling directly on the ground – eventually finding fertile ground where life begins anew.