Seed Germination and Dispersal PDF

Seed Germination and Dispersal 'J J, W I I ·--------: 1..,_ Mo...

Seed Germination and Dispersal 'J J, W I I ·--------: 1..,_ Most plants bear flowers. '..,. Structures of seeds..,. Flowers develop into fruits. 1..,. Types of seeds..,. Fruits have seeds. 1..,. Germination from seeds I L-- --- --- --- --- --- --- --~ ·,. Seed dispersal..,. Different dispersal agents ~-- --- --- --- --- --- --- --- --- --- ~ stem s and leaves in the We learn t abo ut vege tativ e prop agat ion thro ugh roots, e thro ugh seeds. previous chapter. Now we will see how plants repr oduc SEEDS we eat are seeds, for Seeds are an imp orta nt sour ce of food. All the grains that e of the spices we use, for example, rice, whe at, gram , kidney beans and peas. Som example cori ande r, mus tard and cum in are also seeds. castor, datu ra, man go are Seeds are of diffe rent shap es and sizes. Som e seeds like small. big while the seeds of mus tard , card amo m, cum in are very r names. 1. How man y of thes e seed s can you identify? Write thei for smo oth near them. fr\{) { 2. Which of thes e seed s have smo oth texture? Write 'S' l \f.', / ~ @, ti'! ti tr~{\~:h.. ~ eed Germ/notion and Dispersal  3. Which of these seeds are flat in shape? Write 'F' for flat near them. 4. Which of these seeds are round? Write 'R' for round near them. STRUCTURE OF A SEED A seed has the following parts in it. Seed Coat Good to Know Cotyledons are actually Young plant ~lumule (Embryo) I Rad',ce_.__----t modified leaves. 6M~~~;~i;---------- ------- Hilum WI I Radicle = Roots : Plumule = Plant (shoot of the planl) Structure of a dicot seed ------------------------------- Seed coat: A seed has an outer covering called the seed coat. It protects the from physical damage (being crushed), temperature-related damage (drying"-... water.damage. Hilum: The seed coat has a tiny opening called the hilum which absorbs Cotyledons: If we remove the seed coat, it reveals the fleshy part of. the sccc:i..: These fleshy parts or seed leaves are called cotyledons. These cotyledO.tlS for the growing embryo inside the seed. They also protect the embryt:i. Embryo: It is the baby plant inside the seed. The embryo baby·t>.1tn1 or food stored in cotyledons till it grows its own roots and leaves. from the cotyledons is used, the young plant starts making its OWi) photosynthesis. The embryo enclosed in the seed has two main parts - germination under favourable conditions, the radicle~~ plumule develops into the shoot of the baby plant. TYPES OF SEEDS There are two types of seeds depending upon the n storage. Monocotyledonous seeds Dicotyledonous seeds I ~  - Mo noc oty led ono us Seeds d mon oco tyle don s. For example, Some seed s hav e only one seed lea£ The y are calle wheat, bajra, mai ze and rice. Dic oty led ono us Seeds Baby Plant Some seed s hav e two seed leaves. The y are called Cotyledons dico tyle don s. For exam ple, man go, gram and pea. Oicot seed Monocot seed Cotyle don Cotyledons Position of PI um u Ie __,.,,,,,""" embryo Plumule Rad icle- ~= Positio n Radicle of radicle Position of embr yo in dicot seeds Posit ion of embr yo in mono cot seeds Go od to Kn ow Orchids have the smallest seeds. Each seed is the size of a speck of dust! Can ther e be seed s with no Coco-de-mer, also know n as doub le coco nut, h cotyledon at all? produces the largest seeds. Each seed can weig ----- ----: --:-- ---:- ~ -..... (Critical Thin king ) up to 18 kg!.-.-.-.-.-.-.-.-.-.- - - -...-.-.- ·.-.-. - - -.-.-.-....-.-.-..-.-.-.. -........ ~ ~ ~ ···························································· 4 ·················. ···································································································. L i f e lin k All food grain s like rice, whea t, mille t, pulses that we eat are seeds. A farm er does a lot of hard work to grow these seeds. It also takes a lot of time to grow and prep are these seeds so that & d You shou ld not you can cons ume them as 00 h waste a SINGLE grain of food. Take only as r:11uc food in your plate as you can finish......................................................................................................................................................................................... · ·.................................................. II  "'. - W- CJ l~ e --- --- --- --- --- --- --- --- --- --- --- --- --- - 0 ~a\G l·a_ Aim: To study the structure of seeds. Mater ials requir ed: Bean seeds, wheat seeds, dish, and muslin cloth Proce dure: 1. Soak some bean seeds and wheat seeds overnight in water in a dish. 2. Next morning, drain out all the water from the dish. Now, place the soaked seeds in a clean musi., cloth and tie a knot. Also sprinkle water on the cloth to keep it wet. 3. Open the knot after a day and observe the seeds. Remove the outer coat of the seed. Gently OJlen seed. Obser vation s: You will observe that- 1. The seeds absorbed water and became soft and swollen. They also started sprouting. 2. On removing the seed coat in a bean seed, you can see two fleshy cotyledons. In the wheat can only see one cotyledon. 3. On splitting open the bean cotyledons, you can see the baby plant with plumul e and radicle. Infere nce: Bean is a dicot plant with two cotyledons. Wheat is a monocot plant with one c cotyledons provide food for the embryo. ---- ---- ---- ---- ---- ---- ---- ---- - CERMINATION Plant s produ ce many seeds. But not all the seeds grow into new plants. So them are eaten by us or by birds and other animals. Some may get crush some may get destro yed by diseases. The seeds that survive require som condi tions to grow into baby plants. These right conditions are: 1. Water - The food in cotyledons is stored in dry conditions. Water activate chemicals called enzymes in the seed. These enzymes~.&,~ food into soluble form that the embryo can use. 2. Air - To get energ y from food, oxygen is required. The seed get& the air. 3. Warm th - Most seeds require a temperature of 25-30 de~ germination. Very low or very high temperatures can destro Can boiled gram seeds germin ate? Why? The embryo inside a seed can rest witho ut growing for a long growing when it gets all the right conditions. The process of plant from a seed is called germ inatio n. The Pro ces s of Ge rm ina tio n the seed coa t bec ome s soft. 1. Wh en the see d rece ives wat er, it swells up and yme s cha nge food into a solu ble 2. Thi s acti vate s enz yme s in the seed. The enz inat ion. form tha t the emb ryo uses to get ene rgy for germ seed coa t and grow s dow n into the 3. The radi cal star ts gro win g first. It bur sts the soil to bec ome the roo t. sun ligh t to form the sho ot. 4. The n the plu mul e star ts gro win g up tow ards small gree n leaves insi de the seed. 5. As the bab y pla nt gro ws, it star ts dev elop ing and pus hes the coty ledo ns The gro win g hoo k-sh ape d sho ot stra ight ens out abo ve the gro und. stem and its leaves unfo ld. At Gradually, the sho ot elon gate s to form a pro per. The leaves star t mak ing foo d by this stag e the bab y plan t is kno wn as a seed ling ns shri nk and fall off as the foo d pho tosy nthe sis. As the leav es grow, the coty ledo stored in the m is fully use d up by the bab y plan t. Seed Coat Stages of grow th of a seed to a baby plant II  Aim:To study the conditions necessary for seed germination. Materials required: Beaker, water, three bean seeds, glass slide Procedure: Fill three-fourths of a beaker with water. Take a glass slide I and tie three bean seeds over it. Place this slide in a beaker half full of water, in such a way that one seed is completely immersed in water, the ---- ·'f-;~'~ middle one is half immersed in water and the upper one is in air. Leave , /~} I ' the beaker in a warm place. Keep adding water in the beaker to keep the level of water the same. Observations: After a few days, you will observe that germination has taken place only in the middle seed. Inference: Germination takes place only in the seed which is half immersed as it gets all three , conditions necessary for growth - air, water and warmth. --------------- --------------- ---- DISPERSAL OF SEEDS What do you think will happen if all seeds produced by a plant fall below the oarcn1 plant? Many plants will then start growing at one place. You know that each seed requires proper amount of air, water, minerals, warmth to germinate. If they all to grow at one place, they will not get enough space, air, water, minerals and Su.u&111w11J and hence will not be able to grow well. Many of them would die. Nature has therefore arranged some methods by which the seeds of a plant are scattered over large distances. This is called dispersal of seeds. Seeds are dispersed by 1. Wind ------------------------------------------ 2. Water 0 Mnemonics W, Have you heard about WWE? Its full ~ 3. Animals Wrestling Entertainment, known for orofel1IQI wrestling. You can use this to~ 4. Explosion of fruits 3 out of 4 dispersal agents, These are called agents of dispersal. Explosion. Isn't it cool? Let us learn more about them. Dispersal by Wind Some seeds are carried to a new place by the wind. Such seeds are usually small and light. They also have other adaptations. Some seeds such as those of orchid are so small that they loo~ They are blown away by the wind.  li d ,vhich ac t as So me se ed s like th at of da nd e on an co tto n ha ve hairs on the m av.ray in th e \.V·Ind. pa rach ute s an d ca rry th em far lp the m mo re an d ma pl e ha ve wi ng ed att ac he d to the m, wh ich he Th e ~eed_s of sy ca float in air. Sycamore seeds Orc hid seeds Dandelion seeds Dispersal by W at er wa ter or ne ar it are dis pe rse d by pla nts tha t gr ow in Th e seeds an d fru its of so me at ca n flo at in water. Th e co co nu t ha s a ha ve fru its or se ed s th water. Th es e pl an ts in wa ter. Th e lot us fru it ha s a sp on gy en ab les it to flo at thick co at of fib re wh ich wh ich it ca n flo at. W ate r carries th em to far of f places. pa rt be ca us e of Coconut fru it Lotus fru it in coastal areas. Ho w does this he lp the tre es ?, I Cocon ut tre es are mo stl y fou nd Thinking) ,.,,.,.12 EE VSW @lfQKIINHiU?_~o o '.:t/:?.-?!.:£(Refl~iv~ Dispersal by A ni m al s he r an im als ea t. Af ter ea tin g th e th at hu ma ns an d ot Some pla nts ha ve fle sh y fru its its su ch as ma ng o, pa pa ya an d ch er ry wn aw ay. Se ed s of fru fruits, the se ed s are th ro in thi s way. get dis pe rse d to fa r of f pla ce s Birds and other animals eat some fruits which have small and hard seeds called stones and pips. These cannot be digested and are excreted unharm ed. They produce new plants where they fall. Seeds of fruits like blackberry, cherry and Agric ultur apples are dispersed in this way. We get nutnn plants and re Some fruits like that of xanthium and tiger nail have seeds with hooks or spines. plants are gro These help the seeds stick to our clothes and to the bodies of animals. They are crops such as carried to far off places with the animal. They germinate where they fall off. animals. They ,,, '- ·\."'' f;.._'.._ LE: - ~ -.. there are two ~~:\.\1, ,ttll~\r;I '., --.' , Kharif crops I/. '(-~~y Z- ~ ·,, -- ---~-.-·-,.~ u - ~--..,,~ , ~~"" the south-wes1 , ~----f. ~-~ ~I , ) , ' -·. '.. - ,. ~'.:·