Describe What Occurs During the Process of Seed Development

Describe What Occurs During the Process of Seed Development.

Learning Outcomes

  • Depict the process that leads to the development of a seed
  • Describe the process that leads to the development of a fruit

Development of a Seed

The mature ovule develops into the seed. A typical seed contains a seed coat, cotyledons, endosperm, and a single embryo (Figure one).

 Illustration shows the structure of a monocot corn seed and a dicot bean seed. The lower half of the monocot seed contains the cotyledon, and the upper half contains the endosperm. The dicot seed does not contain an endosperm, but has two cotyledons, one on each side of the bean. Both the monocot and the dicot seed have an epicotyl that is attached to a hypocotyl. The hypocotyl terminates in a radicle. In the dicot, the epicotyl is in the upper middle part of the seed. In the monocot, the epicotyl is in the lower cotyledon. Both the monocot and dicot seed are surrounded by a seed coat.

Figure 1. The structures of dicot and monocot seeds are shown. Dicots (left) accept two cotyledons. Monocots, such as corn (right), have i cotyledon, called the scutellum; information technology channels nutrition to the growing embryo. Both monocot and dicot embryos accept a plumule that forms the leaves, a hypocotyl that forms the stalk, and a radicle that forms the root. The embryonic axis comprises everything between the plumule and the radicle, not including the cotyledon(s).

Practice Question

What is of the following statements is truthful?

  1. Both monocots and dicots have an endosperm.
  2. The radicle develops into the root.
  3. The plumule is part of the epicotyl
  4. The endosperm is part of the embryo.

Statement b is true.

The storage of food reserves in flowering plant seeds differs between monocots and dicots. In monocots, such equally corn and wheat, the single cotyledon is called a
scutellum; the scutellum is connected directly to the embryo via vascular tissue (xylem and phloem). Food reserves are stored in the large endosperm. Upon germination, enzymes are secreted by the
aleurone, a single layer of cells simply within the seed coat that surrounds the endosperm and embryo. The enzymes degrade the stored carbohydrates, proteins and lipids, the products of which are absorbed by the scutellum and transported via a vasculature strand to the developing embryo. Therefore, the scutellum tin be seen to be an absorptive organ, not a storage organ.

The two cotyledons in the dicot seed besides have vascular connections to the embryo. In
endospermic dicots, the nutrient reserves are stored in the endosperm. During germination, the ii cotyledons therefore human activity as absorptive organs to accept up the enzymatically released nutrient reserves, much like in monocots (monocots, by definition, as well have endospermic seeds). Tobacco (Nicotiana tabaccum), tomato (Solanum lycopersicum), and pepper (Capsicum annuum) are examples of endospermic dicots. In
not-endospermic dicots, the triploid endosperm develops normally following double fertilization, only the endosperm food reserves are quickly remobilized and moved into the developing cotyledon for storage. The two halves of a peanut seed (Arachis hypogaea) and the split peas (Pisum sativum) of split pea soup are private cotyledons loaded with food reserves.

The seed, along with the ovule, is protected by a seed coat that is formed from the integuments of the ovule sac. In dicots, the seed glaze is further divided into an outer coat known as the
and inner coat known as the

The embryonic axis consists of three parts: the plumule, the radicle, and the hypocotyl. The portion of the embryo between the cotyledon attachment indicate and the radicle is known equally the
(hypocotyl means “below the cotyledons”). The embryonic centrality terminates in a
(the embryonic root), which is the region from which the root will develop. In dicots, the hypocotyls extend above basis, giving rise to the stem of the establish. In monocots, the hypocotyl does not prove above footing because monocots do not showroom stalk elongation. The function of the embryonic centrality that projects to a higher place the cotyledons is known as the
epicotyl. The
plumuleis composed of the epicotyl, young leaves, and the shoot upmost meristem.

Upon germination in dicot seeds, the epicotyl is shaped like a hook with the plumule pointing downwards. This shape is chosen the plumule hook, and it persists equally long as germination proceeds in the night. Therefore, equally the epicotyl pushes through the tough and abrasive soil, the plumule is protected from damage. Upon exposure to low-cal, the hypocotyl hook straightens out, the young foliage leaves face the sun and expand, and the epicotyl continues to elongate. During this time, the radicle is too growing and producing the primary root. As it grows downward to form the tap root, lateral roots branch off to all sides, producing the typical dicot tap root system.

 Illustration shows a round seed with a long thin radicle, or primary root, extending down from it. A yellow tip , the coleorhiza, is visible at the end of the root. Two shorter adventitious roots extend down on either side of the radicle. Growing up from the root is a thicker coleoptile, or primary shoot.

Figure 2. Every bit this monocot grass seed germinates, the primary root, or radicle, emerges starting time, followed by the primary shoot, or coleoptile, and the adventitious roots.

In monocot seeds (Figure 2), the testa and tegmen of the seed coat are fused. As the seed germinates, the primary root emerges, protected by the root-tip covering: the
coleorhiza. Adjacent, the primary shoot emerges, protected by the
coleoptile: the covering of the shoot tip. Upon exposure to low-cal (i.east. when the plumule has exited the soil and the protective coleoptile is no longer needed), elongation of the coleoptile ceases and the leaves expand and unfold. At the other end of the embryonic axis, the primary root soon dies, while other, adventitious roots (roots that do not arise from the usual place – i.e. the root) sally from the base of the stem. This gives the monocot a fibrous root organisation.

Seed Germination

Many mature seeds enter a period of inactivity, or extremely depression metabolic action: a process known as
dormancy, which may terminal for months, years or fifty-fifty centuries. Dormancy helps keep seeds viable during unfavorable conditions. Upon a render to favorable weather, seed germination takes place. Favorable conditions could exist as diverse as moisture, light, cold, burn down, or chemical treatments. Afterward heavy rains, many new seedlings emerge. Woods fires besides lead to the emergence of new seedlings. Some seeds require
(common cold handling) earlier they can germinate. This guarantees that seeds produced past plants in temperate climates volition non germinate until the spring. Plants growing in hot climates may have seeds that need a estrus handling in order to germinate, to avoid germination in the hot, dry out summers. In many seeds, the presence of a thick seed glaze retards the power to germinate.
Scarification, which includes mechanical or chemical processes to soften the seed coat, is often employed before formation. Presoaking in hot water, or passing through an acrid environs, such every bit an animal’s digestive tract, may also exist employed.

Depending on seed size, the fourth dimension taken for a seedling to emerge may vary. Species with big seeds accept plenty nutrient reserves to germinate deep below basis, and still extend their epicotyl all the mode to the soil surface. Seeds of pocket-size-seeded species usually require light equally a germination cue. This ensures the seeds only germinate at or nigh the soil surface (where the lite is greatest). If they were to germinate too far underneath the surface, the developing seedling would non have enough nutrient reserves to attain the sunlight.

Evolution of Fruit and Fruit Types

After fertilization, the ovary of the blossom usually develops into the fruit. Fruits are usually associated with having a sweet gustation; nevertheless, not all fruits are sugariness. Botanically, the term “fruit” is used for a ripened ovary. In most cases, flowers in which fertilization has taken place will develop into fruits, and flowers in which fertilization has not taken place volition not. Some fruits develop from the ovary and are known equally true fruits, whereas others develop from other parts of the female gametophyte and are known as accompaniment fruits. The fruit encloses the seeds and the developing embryo, thereby providing it with protection. Fruits are of many types, depending on their origin and texture. The sweet tissue of the blackberry, the red flesh of the tomato, the shell of the peanut, and the hull of corn (the tough, sparse part that gets stuck in your teeth when yous eat popcorn) are all fruits. Equally the fruit matures, the seeds also mature.

Fruits may be classified as simple, amass, multiple, or accessory, depending on their origin (Figure 3). If the fruit develops from a single carpel or fused carpels of a single ovary, it is known as a
simple fruit, as seen in nuts and beans. An
aggregate fruit
is one that develops from more than one carpel, but all are in the same flower: the mature carpels fuse together to course the unabridged fruit, as seen in the raspberry.
Multiple fruit
develops from an inflorescence or a cluster of flowers. An case is the pineapple, where the flowers fuse together to form the fruit.
Accompaniment fruits
(sometimes called false fruits) are non derived from the ovary, simply from another part of the blossom, such as the receptacle (strawberry) or the hypanthium (apples and pears).

 Photos depict a variety of nuts in their shells, an apple, raspberries and a pineapple.

Figure 3. There are iv main types of fruits. Simple fruits, such equally these nuts, are derived from a unmarried ovary. Aggregate fruits, like raspberries, form from many carpels that fuse together. Multiple fruits, such as pineapple, class from a cluster of flowers called an inflorescence. Accessory fruit, like the apple, are formed from a part of the plant other than the ovary. (credit “basics”: modification of work by Petr Kratochvil; credit “raspberries”: modification of work by jill111; credit “pineapple”: modification of piece of work by psaudio; credit “apple”: modification of work by Paolo Neo)

Fruits more often than not take 3 parts: the
(the outermost peel or covering), the
(middle part of the fruit), and theendocarp
(the inner part of the fruit). Together, all 3 are known as the
pericarp. The mesocarp is ordinarily the fleshy, edible part of the fruit; all the same, in some fruits, such as the almond, the endocarp is the edible part. In many fruits, two or all three of the layers are fused, and are indistinguishable at maturity. Fruits tin be dry or fleshy. Furthermore, fruits tin can exist divided into dehiscent or indehiscent types. Dehiscent fruits, such as peas, readily release their seeds, while indehiscent fruits, like peaches, rely on decay to release their seeds.

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Describe What Occurs During the Process of Seed Development