Animal, Plant & Soil Science E4-1 Seed Germination Processes and Requirements

Interest Approach Fill a clean mayonnaise or pickle jar one-half full with soybeans. Add fine textured sand. Shake the jar until the beans and sand are evenly distributed and the contents fill the jar to the top. Place the jar on a pan at the front of the class. At the start of class, ask students to present hypotheses as to what will happen when the contents are completely saturated with water. List the predictions on the board. Fill the jar with water as you collect the student hypotheses. Use warm water to speed the process. Within 30 to 45 minutes, expect the glass to crack due to the build up of osmotic pressure caused by the seeds’ imbibition of water.

Objectives 1 Identify the parts of seeds and describe their functions. 2 Describe the process of seed germination. 3 Discuss the conditions required for seed germination. 4 Explain the importance of seed quality.

Terms amylase cotyledon embryo endosperm epicotyl germination hilum

Terms hypocotyl imbibition micropyle phytochrome plumule protease radicle

Terms scarification seed coat stratification suspensor turgid viability vigor

What are the parts of seeds and their functions? I. Seeds contain everything necessary for the growth and development of a new plant. The three primary parts of a seed are the embryo, endosperm, and seed coat. The embryo is the young, multicellular organism before it emerges from the seed. The endosperm is a source of stored food, consisting primarily of starches. The seed coat consists of one or more protective layers that encase the seed.

What are the parts of seeds and their functions? A. Seeds begin to form an embryo following fertilization and the start of a zygote. The initial division of the zygote results in two cells. The bottom cell develops into a multicellular structure, called the suspensor. The suspensor anchors the embryo and helps to obtain nutrients from the endosperm. The top cell develops into the embryo.

What are the parts of seeds and their functions? 1. The first cell divisions from this top cell create a chain of cells called the proembryo. As the cell divisions continue, a globular embryo takes shape. 2. At this point of development, cells begin to differentiate. Cotyledons begin to form. The cotyledon is a seed leaf that stores food in the form of starch and protein for use by the embryo.

What are the parts of seeds and their functions? 3. Embryos of monocotyledon (monocot) plants have one cotyledon, while those of dicotyledon (dicot) plants have two cotyledons. 4. Monocot plants store the bulk of their energy in the endosperm. Dicots store their food in the two cotyledons. 5. The cotyledons grow and elongate. As the embryo matures, the pressure of the expanding embryo crushes the suspensor.

What are the parts of seeds and their functions? B. The mature embryo consists of an embryonic root known as the radicle, an embryonic shoot, and one or two cotyledons. The embryonic shoot, known as the plumule, has two main parts: the epicotyl and the hypocotyl. 1. The epicotyl is the portion of the embryonic stem above the point at which the stem is attached to the cotyledon(s). 2. The hypocotyl is the portion below the point of attachment. The hypocotyl is connected to the radicle.

What are the parts of seeds and their functions? C. The seed is encased in a protective seed coat. It protects the embryo and the endosperm from drying and from physical injury. 1. A scar, called the hilum, can be seen at the end or along the side of the seed coat. The hilum marks the point of attachment of the seed to the ovary wall. 2. The seed coat has a tiny opening, sometimes visible near the hilum, called the micropyle.

What is seed germination? II. Germination is the process by which the seed embryo begins growth. A seed is considered to have germinated when the embryonic root emerges from the seed coat. Many important crops are grown from seeds. Corn, soybeans, cotton, and vegetables are started from seeds. Seed germination is a complex process that begins when conditions are favorable for growth.

What is seed germination? A. Some plants produce seeds, which germinate immediately once they are released. Others produce seeds that have internal dormancy mechanisms and remain dormant until conditions are favorable for growth.

What is seed germination? 1. Stratification is a dormancy mechanism that involves temperature. Seeds with this mechanism must experience a period of cold temperature before the seed can germinate.

What is seed germination? 2. Scarification is a dormancy mechanism that involves the breakdown of the seed coat. Some plants have very thick and tough protective seed coats. These seed coats prevent water and oxygen from entering the seed. The seed coat must be broken before germination can begin. The seed coat can be damaged or broken by the acid produced in the animal stomach, by soil microorganisms, by repeated freezing and thawing, by mechanical stress from the grinding in the gizzard of birds, by being stepped upon, and by being chewed.

What is seed germination? B. There are three major stages in the germination process. 1. Germination begins with the seed’s absorption, or imbibition, of water. Most dormant seeds have 5 to 10 percent moisture content. When conditions are right, water is imbibed very rapidly. Most water is imbibed through the micropyle. As the cells hydrate, they swell and become turgid, or rigid. The moisture triggers an increase in cellular respiration. Oxygen must be present for cellular respiration.

What is seed germination? 2. In stage two, metabolic activity surges. Proteins are synthesized. Gibberellins stimulate the production of enzymes. The enzyme amylase converts stored starches to sugars. The enzyme protease breaks down stored proteins into amino acids. The sugars and amino acids are directed toward cell division, growth, and differentiation sites at the root and shoot meristems, or tips.

What is seed germination? 3. Metabolic processes increase in the third phase of germination. The swelling of cells causes the seed coat to rupture. The radicle emerges downward, and the stem grows upward. The shoot begins manufacturing food through photosynthesis. The roots absorb water and nutrients.

What conditions are required for seed germination? III. Germination begins when favorable conditions exist for the survival of the developing plant. The conditions for germination include moisture, air, optimal temperatures, and possibly light or darkness.

What conditions are required for seed germination? A. Water triggers germination processes and is necessary as the embryo grows and develops.

What conditions are required for seed germination? B. All seeds need oxygen to germinate. Oxygen is required for cellular respiration, a process necessary for converting stored food into energy. Seeds germinate at a wide range of temperatures, ranging from 32° to 105°F. However, the optimal temperature for most seeds lies between 65° and 80°F. Temperature influences the speed of metabolic activities. Metabolism is faster when temperatures are warm than when temperatures are cool.

What conditions are required for seed germination? C. Seeds of some plants need exposure to light before they will germinate. Seeds of other plants require darkness in order to germinate, and there are those that are not influenced by light or darkness. Seeds that are light-sensitive have a photoreceptor pigment, called phytochrome, found in the seed coat. This pigment sends messages to the seed, instructing it to initiate or to stop germination.

Why is seed quality important? IV. Seed quality and the proper storage of seeds are crucial to achieving desired high germination rates. High-quality seeds produce healthy seedlings. Seed quality refers to both viability and vigor.

Why is seed quality important? A. Viability is the ability of seeds to germinate under optimal conditions. B. Vigor is the ability of seeds to germinate under different conditions and still produce healthy plants.

Why is seed quality important? C. Seed producers test seeds to determine the percentage of seeds that will germinate. Germination rates from the tests are printed on the seed container label. D. Until the seeds are sold and planted, they must be kept in storage. The goal is to maintain seed viability and vigor during the storage period. The best seed storage conditions typically consist of cool temperatures (about 40°F) and low humidity (approximately 15%).

REVIEW 1. What are the parts of seeds and their functions? 2. What is seed germination? 3. What conditions are required for seed germination? 4. Why is seed quality important?