Seed: Germination, Dispersal, and Structure

Study Notes

Seed

Seeds play a crucial role in plant reproduction and survival. They contain all the necessary components for a new plant to grow from a single cell called a zygote. There are three main aspects of seeds: germination, seed dispersal, and seed structure.

Germination

Germination is the process by which a seed begins to develop into a young plant. It involves several stages: imbibition, embryo growth, radicle emergence, and shoot elongation. Imbibition occurs when water enters the seed's dry cells, causing them to expand. Embryo growth follows, where the embryo starts to increase in size, forming a root (radicle) and a stem (epicotyl). Radicle emergence marks the start of the visible growth phase, with the radicle breaking through the seed coat. Finally, shoot elongation continues until a complete plant has emerged.

Seed Dispersal

Seed dispersal is the method plants use to spread their offspring over a larger area. This ensures genetic diversity, reduces competition between siblings, and helps colonize new areas. Some common methods of seed dispersal include wind, water, animals (zoochory), insects (entomochory), bacteria (bacteriochory), and gravity (barochory). For example, dandelion seeds can fly great distances due to puffballs filled with wind-blown seeds.

Seed Structure

Seed structure refers to the physical characteristics of a seed that determine its ability to survive and establish itself as a new plant. There are two main types of seeds based on structure: naked seeds and enclosed seeds. Naked seeds lack a protective covering (testa) around their embryo, while enclosed seeds have a testa that protects them from desiccation. Other factors affecting seed structure include dormancy, light requirements, and temperature sensitivity.

Dormancy and Light Requirements

Dormancy refers to the period during which a seed cannot germinate, while light requirements indicate whether a seed needs light to initiate germination. Some seeds, like avocado seeds, need light to break dormancy before they can begin germinating. Others, such as sweet potato seeds, require darkness to break dormancy and germinate.

Temperature Sensitivity

Temperature sensitivity determines the range of temperatures under which a seed can germinate successfully. Temperature plays a vital role in determining germination rate, directionality, and depth. For instance, northern lupine seeds will only germinate if the soil temperature remains consistently below freezing.

Description

Learn about the key aspects of seeds: germination, seed dispersal, and seed structure. Explore the stages of germination, methods of seed dispersal, and the different types of seed structures. Understand concepts like dormancy, light requirements, and temperature sensitivity in seeds.