Seed germination

activity In your groups list the requirements needed for seed to germinate 2mins

Learning outcomes Identify the process involved in pollination and distinguish the stages of seed germination Compare the seed types epigeal and hypogeal Explain the requirements for successful germination

Seed germination requirements Water Temperature Oxygen Food Light time

water Seeds hold very little water. It is one of the reasons that seeds can stay dormant for a long time

temperature The requirements of individual seeds vary within an overall range of 5-35ºC. In our climate 10-20º C is typical Heat will speed up the process which is why we use greenhouses and propagators to assist germination

Oxygen A supply of oxygen is necessary for respiration

food A supply of food is necessary to fuel the process until the plant is able to photosynthesise. The food is stored in the seed in the cotyledons of the endosperm. If seeds are planted too deep they can die by exhausting their food supply before reaching the point at which they can photosynthesise

light Some seeds require light to germinate

time Some seeds have a chemical inhibitors which needs to diminish before germination is possible

Stages in germination Imbibition: The initial step in the development of seed germination is to absorb water or imbibition The seed absorbs water and as a  result it swells. The swelling of seed causes the seed coat to rupture and allows the radicles to move downward  forming the  root. Respiration: When the seed absorbs water, it also respires. While in the beginning the respiration is anaerobic and later it becomes aerobic.

Inducing germination Some seeds are difficult to germinate either because of their tough coat, or because of chemical inhibitors, or because they must be exposed to certain temperatures before germination will occur.

Seed stratification The purpose of this is to expose the seed to a period of cold such as it would encounter under natural conditions. Placing the seed in a refrigerator for a period of time as indicated on the seed packet Some seeds may require periods of high heat to germinate

Seed scarification The purpose of this is to weaken the seed coat and allow water to enter. Large seeds such as those of peas and beans may be nicked with a knife. smaller seeds can be rubbed with an abrasive substance such as sandpaper.

activity In your group using the learner resource centre research the following to produce a hand out including diagrams: Seed stratification Seed scarification 20mins

epigeal In this type of germination the seed/cotyledons remain inside the soil The cotyledons play the role in photosynthesis There is a greater elongation of the epicotyl The terminal part of the plant of the epicotyl is curved to protect the plumule from friction Example bean

hypogeal In this type of germination the seed/cotyledons emerges out of the soil The cotyledons turn green and act as the first true leaves of the plant There is a great elongation of the hypocotyl The terminal part of the hypocotyl is curved to protect the plumule from the friction of the soil Example pea