Module/Chapter 10 Reproductive Organs: Seeds PDF

Bio 17 Botany BS Bio I-A Benguet State University MODULE/ CHAPTER 10 **Reproductive Organs: SEEDS** MOTIVATION It is expected by now that the preparatory knowledge on plant cells and tissues are embedded in your understanding. You will need those understanding for the upcoming chapters. We would...

Bio 17 Botany BS Bio I-A Benguet State University MODULE/ CHAPTER 10 **Reproductive Organs: SEEDS** MOTIVATION It is expected by now that the preparatory knowledge on plant cells and tissues are embedded in your understanding. You will need those understanding for the upcoming chapters. We would shift now our focus from predominantly microscopic to somewhat macroscopic study of plants. We would deal now with plant organs, studying its structure and functions. In this chapter, we will deal with the plant SEEDS. But before we go down to business, let's have some laughs (if you would care to understand it first)! In the Bible, a lot of parables and stories involves the seed. If we look at plants, seeds seem to be insignificantly small or unimportant but given proper conditions, the seeds will eventually grow into majestic trees or bountiful harvest. Same could be said on what we are doing here, we are planting seeds of information into you but it would be up to you to nurture that. If you nurture that with the right mentality, say you value it and try to internalize it (or much better apply it) then through time, coupled with discipline; it would eventually blossom into a fruitful and satisfying career. But if your mentality in schooling is just to go with the flow, or to just to enjoy life and see the seeds we are painstakingly inculcating in you through these lenses, then you will eventually reap what you sow. You might be connected to those in power or you maybe rich but if you would not allow yourself to be equipped with proper knowledge and skills, your connection and your richness would not save you in this ever-becoming competitive world. Hope, you enjoyed this but we have to go now to the topic at hand. Again, I present to you the plant SEEDS! LESSON PROPER **CHAPTER X. Reproductive Organs: SEEDS** **Seeds** ⮚ These are mature or ripened ovule ⮚ Functions: 1\. The completion of sexual reproduction in flowering plants, it contains the next generation of plants **Parts of a Typical Seed** Bio 17 Botany BS Bio I-A Benguet State University A typical seed consists of three main parts: 1) seed coat, 2) endosperm, and 3) embryo. 1. **Seed Coat** - the protective outer covering of a seed that is usually hard, thick, and brownish in color. The seed coat is formed from the outer covering of the ovule called the integument. It usually contains **two layers**: a\. **testa** -- the thick outer layer, b\. **tegmen** -- the delicate inner layer. A seed coat has the following four parts: a) **Micropyle** -- the small opening present at one end of the seed coat, b) **Funiculus** -- the seed stalk with which the seed is attached to the fruit body, the integument, c) **Hilum** -- the region from which the seed breaks off from the fruit, leaving a scar, and d) **Raphe** -- the base of the funiculus that is fused with the integument. Functions of the seed coat: ∙ Protecting the seed from physical and mechanical damage ∙ Preventing the seed from germination even under favorable conditions of growth (seed dormancy) ∙ Preventing the excessive loss of water from the seeds ∙ Acting as a physical barrier against the entry of parasites **2. Endosperm -** It is a tissue that is rich in oil, starch, and protein. Depending on the presence or absence of endosperm, seeds are of **two types**: i\) **Non-endospermic** or **exalbuminous seeds** -- Characterized by the complete absence of the endosperm, such as the seeds of the pea plant, groundnut, and gram. ii\) **Endospermic** or **albuminous seeds** -- Characterized by the presence of the endosperm, such as the seeds of millets, palms, and lilies. Functions: ∙ Storing of reserve foods that provide nourishment to the developing plant ∙ Protecting the embryo, the next part of the seed, by acting as the mechanical barrier Bio 17 Botany BS Bio I-A Benguet State University 3\. **Embryo -** the young plant that is developing inside the seed coat. An embryo contains the underdeveloped tissues of [leaves], stem, and roots of a plant. Parts of an Embryo of a Seed a\. **Epicotyl** -- The tiny shoot of an embryo, from which the entire shoot system develops. The tip of the epicotyl is called plumule. b\. **Hypocotyl** -- The stage of transition for the growing shoot and [root] of the embryo c. **Radicle** -- The tiny root of the embryo d\. **Cotyledons** -- They are the leaves of the embryo that provide nourishment to the developing plant. There are two types of cotyledons present in flowering plants: i\) **monocotyledonous** or monocots -- embryo with one cotyledon ii\) **dicotyledonous** or dicots -- embryo with two cotyledons. (In monocot seeds, there are additional structures of the embryo such as the **coleoptile** -- the tubular protective covering of  epicotyl, and the **coleorhiza** -- the protective outer covering of the radicle.) Functions of the embryo ∙ Giving rise to a new complete new plant ∙ Storing food and nourishing the baby plant **Seed Dispersal** **Seed dispersal** is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their propagules, including both abiotic vectors such as the wind and living (biotic) vectors like birds. Seeds can be dispersed away from the parent plant individually or collectively, as well as dispersed in both space and time. The patterns of seed dispersal are determined in large part by the dispersal mechanism and this has important implications for the demographic and genetic structure of plant populations, as well as migration patterns and species interactions. There are five main modes of seed dispersal: gravity, wind, ballistic, water, and by animals. **Modes of Seed Dispersal** **A. Autochory** - dispersal is attained using the plant\'s own means **1) *Barochory*** or the plant use of gravity for dispersal is a simple means of achieving seed dispersal. The effect of gravity on heavier fruits causes them to fall from the plant when ripe. Fruits exhibiting this type of dispersal include apples, coconuts and passionfruit and those with harder shells (which often roll away from the plant to gain more distance). Gravity dispersal also allows for later transmission by water or animal **2) *Ballochory*** is a type of dispersal where the seed is forcefully ejected by explosive dehiscence of the fruit. Often the force that generates the explosion results from turgor Bio 17 Botany BS Bio I-A Benguet State University pressure within the fruit or due to internal tensions within the fruit. Some examples of plants which disperse their seeds autochorously include: *Impatiens spp.*, *Arceuthobium spp.*, *Ecballium spp.*, *Geranium spp.*, *Cardamine hirsuta*, *Sucrea spp*, *Raddia spp.*and others. An exceptional example of ballochory is *Hura crepitans*---this plant is commonly called the dynamite tree due to the sound of the fruit exploding. The explosions are powerful enough to throw the seed up to 100 meters. **B. Allochory** - dispersal through external means **1) *Anemochory*** - Wind dispersal is one of the more primitive means of dispersal. Wind dispersal can take on one of two primary forms: seeds can float on the breeze or alternatively, they can flutter to the ground. The classic examples of these dispersal mechanisms, in the temperate northern hemisphere, include dandelions, which have a feathery pappus attached to their seeds and can be dispersed long distances, and maples, which have winged seeds (samaras) and flutter to the ground. **2) *Hydrochory***, or seed dispersal through water. Seeds can travel for extremely long distances, depending on the specific mode of water dispersal; this especially applies to fruits which are waterproof and float on water. **3) *Epizoochory*** *-* Seeds can be transported on the outside of vertebrate animals (mostly mammals). Plant species transported externally by animals can have a variety of adaptations for dispersal, including adhesive mucus, and a variety of hooks, spines and barbs. **4) *Endozoochory*** - Seed dispersal via ingestion by vertebrate animals (mostly birds and mammals). This is the dispersal mechanism for most tree species. Birds and mammals are the most important seed dispersers. The exact percentage of tree species dispersed by endozoochory varies between habitats, but can range to over 90% in some tropical rainforests **5) *Anthropochory*** *-* Dispersal by humans. It's most widespread and intense cases account for the planting of much of the land area on the planet, through agriculture. In this case, human societies form a long-term relationship with plant species, and create conditions for their growth. **Seed Germination** **Seed germination** is the sprouting of a seed or the resumption of growth, usually after a period of dormancy. The absorption of water, the passage of time, chilling, warming, oxygen availability, and light exposure may all operate in initiating the process. 2 Major Types of Seed Germination 1\. **Epigeal Germination** -- type of germination where the cotyledons are lift up the soil/ ground. This is common in dicot seeds 2\. **Hypogeal germination** -- type of germination where the cotyledon/s is/are retained under the soil/ground Bio 17 Botany BS Bio I-A Benguet State University EVALUATION **(will be given at the same time for equal grounding)**