The life of our fellow plant starts here. It is a small seed. It is a new recruit, just dispatched from its parent. It is buried in the soil, waiting for the right conditions. At last, it finds the right temperature, water, oxygen, and light source for the plant to start germinating. It now has to ready its systems, use its energy, and grow through the soil and towards the light.
Anatomy of a Seed
Before we talk about germination, we have to look at the anatomy of the seed to understand what is required for germination and its process. The seed is divided into three main parts: the embryo, the storage tissues, and the seed coat. The embryo is a baby plant. It consists of different parts. The epicotyl is the shoot of the plant. This is the part that first comes out of the ground. Then there is the hypocotyl. This is the part of the plant that transitions the epicotyl to the radicle and vice versa. The radicle is the embryonic root, and it first emerges out of the seed to absorb water. There is also one last part of the embryo called the cotyledons. This will be talked about later.
The second part of the seed has the most volume. This is the storage tissue. The storage tissue is like a starter pack. Since the plant does not have leaves yet, it can not photosynthesize (the way mature plants obtain energy). The storage tissue provides temporary energy with proteins, carbohydrates, and fats. This is used along with oxygen to provide energy for the seed to emerge out of the soil to begin photosynthesis.
The third section of the seed is the seed coat. As the name suggests, this is the outer layer of the seed. The texture of the seed covering can vary depending on the species. It can range from being wrinkled to winged. Most seeds are thickened, brownish, hard and mostly impermeable. This makeup is designed for protection from water (because excess water can drown the seed) and parasites. The seed coat also allows dormancy, so if it is in desert or tundra, then the seed can survive longer until the right conditions are set. Seeds can be able to germinate from a mere 20 days to a colossal 2,000 years.
Now that we know how our seed works, what are the conditions for seeds to germinate? There are four essential factors a seed needs to germinate effectively. The first one is water. Water must be present in the soil for the seed to maintain its health. The water also causes the seed to swell up. This is called imbibition. Imbibition makes the dry seed absorb the water. The cells inside the seed enlarge as water is now present in their system. The cells expand until the seed ruptures, causing the radicle (embryonic root) to emerge.
Following water, oxygen is important as well. The seed uses oxygen to commence cellular respiration and to create energy. This is the process of using oxygen and glucose to produce carbon dioxide, water, energy. If the seed is buried too deep within the soil, then the seed will die from lack of oxygen or stay dormant in the soil, never to germinate.
The third and fourth factor are not necessary, but instead will improve on its growth. The third factor is warmth. When a seed picks up warmth, it breaks out of its dormant stage and can begin germination if there is oxygen or water present. The fourth factor is light. Seeds rarely germinate in the dark. Light is used for photosynthesis and it is their main energy source. Seeds can detect light from the soil and will grow towards it. They germinate knowing that they can gain a light source. However, if the seed is planted too deep, the energy required to reach the surface is not enough for the seed.. Therefore, once the energy from the storage tissue runs out, it will die from being unable to photosynthesise with the sun.
Seed Germination Process
Our seed has warm temperature, light, water and oxygen. It is ready to germinate. The water swells up the seed. The radicle slowly emerges from the seed. The radicle plants itself into the soil, absorbs water, and holds the plant in place. Later, the hypocotyl emerges from the seed. The seed almost seems like it’s lifting through the soil. The epicotyl is the first one to rise to the surface. It carries a seed coat hat. When the seed coat comes off, we see a green pad or another pad with it. These green pads are called cotyledons. These act like miniature leaves in the sense that they can photosynthesize.
Cotyledons are in the embryo from the beginning. Their job is to produce energy from the sun, so it has enough to produce a true leaf. Species of plants can be classified by how many cotyledons they have when sprouting. A monocotyledonous (or monocot) plant means it has one cotyledon. A dicotyledonous (or dicot) plant means it has two cotyledons in its embryo. When the cotyledon(s) complete their purpose, the true leaves take over and photosynthesize.
Our seed has overcome the hurdle of germination, and is now growing its first true leaves. A few days later it is now a fully functional plant. The whole process from finding the right environment, to the cotyledons has finished here. The plant grows and later gives seeds of its own. These seeds go off to faraway lands, and those seeds are ready to germinate.
“BBC – Standard Grade Bitesize Biology – Growing Plants : Revision, Page 2.” BBC News. BBC, 2014. Web. 09 Feb. 2017.
Kumar, Sirinibas. “Process of Seed Germination: 5 Steps (With Diagram).” Biology Discussion. N.p., 26 Oct. 2015. Web. 09 Feb. 2017.
Bareja, Ben G. “Parts of a Seed and Their Functions.” CropsReview. N.p., Nov. 2011. Web. 09 Feb. 2017.
“Cotyledon.” ScienceDaily. ScienceDaily, n.d. Web. 09 Feb. 2017.
“Process Of Seed Germination | Germination Process Step By Step.” Biology. Byjus Classes, 17 Sept. 2016. Web. 09 Feb. 2017.
Bot, Am J. “Role of Warm Stratification in Promoting Germination of Seeds of Empetrum Hermaphroditum (Empetraceae), a Circumboreal Species with a Stony Endocarp.”American Journal of Botany. U.S. National Library of Medicine, n.d. Web. 09 Feb. 2017.
“Parts Of A Seed (Word Search).” My Jhs Science. N.p., n.d. Web. 10 Feb. 2017.
“Cotyledon.” Cotyledon Stock Photos, Royalty-Free Images & Vectors – Shutterstock. N.p., n.d. Web. 10 Feb. 2017.