Germination of Cress Seeds

Only available on StudyMode
  • Download(s) : 591
  • Published : April 17, 2011
Open Document
Text Preview
Background point 1:

There are several conditions that affect the germination of seeds. Most factors are external but there are also some internal conditions that affect the germination of seeds, even though this is quite rare. The most common and the most important external conditions and factors that affect the germination of seeds are oxygen, water, temperature and also in some cases light or darkness. Some plants require several variables for successful seed germination. As this is quite rare, this often depends on the individual seed and its natural habit.

Let’s focus on the most important factors that affect germination of seeds.

Firstly we have oxygen which is required by the seed that is germinating for metabolism. The O2 is used in the process of aerobic respiration which is the seedling’s source of energy until it grows. Oxygen can be found in soil pore spaces, as it is an atmospheric gas. If, for some reason, a seed is buried and placed too deeply within the soil or if the soil is waterlogged, the seed could be lacking oxygen. This means that the seed can be oxygen starved.

A second main factor that affects germination of seeds is water, also called the source of human existence. Water is required for germination of seeds. Many well-grown seeds often become extremely dry and need to absorb vital amounts of water until it is in equilibrium with the dry weight, after that cellular metabolism and growth of the seeds can proceed. There are also some other types of seed that only need enough of water to moisten themselves instead of enough to soak themselves. This process of uptake of water by seeds is defined as imbibition which later on leads to the swelling and the breaking of the seed coat. At the time when seeds are formed, most plants store an area for food reserve with the seed; this can be starch, proteins, or oils. This reserve of food provides the vital nourishment to the now growing embryo. Water is also important, because when the seed imbibes water, as explained above, so called hydrolytic enzymes are enabled and activated. These enzymes then break down the stored food resources into metabolically very useful chemicals. After the seedling is done and emerges from its seed coat and starts growing roots and leaves these food resources no more provides the seed with water. Normal photosynthesis starts take place and provide the energy, the nutrients, the light and the water needed for continuous growth.

A third factor that affects the germination of seeds is temperature. The temperatures of the environment affect the cellular metabolic and also the growth rates of the seeds. Obviously seeds from different species germinate over a wide range of temperatures, but what is surprising is that even seeds from the same plant can germinate in different temperatures. Most seeds have a temperature range right above room-temperature, between 16 and 24 degrees Celsius, within they will germinate. If the temperature rises above or falls below this range, the seed will not germinate. There are also some exceptions. There are seed that only germinate when exposed to temperature alternations, seeds that germinate when the soil is cold (-2 – 4 degrees Celsius) and also some seeds that germinate only when the soil is warm (24 – 32 degrees Celsius). Temperature also affects the seed when breaking dormancy. There are some seed that requires exposure to cold temperatures in order to break its dormancy. Worth noticing is that seeds that are in a dormant state will never germinate even if the conditions are on their side.

A last thing that affects the germination of seeds is the amount of light and darkness the seed is exposed to. Light or darkness can be an environmental trigger for the germination of the seed. Yet, many seeds are not affected by the amount of light or darkness it is exposed to, but there are some exceptions, such as species in forest settings. They will not germinate until an opening in...
tracking img