8 and Cyclones Winds, Storms - NCERT

1 Reproduction in Plants8To produce its kind is acharacteristic of all livingorganisms. You have alreadylearnt this in Class VI. The productionof new individuals from their parents isknown as reproduction. But, how doplants reproduce? There are differentmodes of reproduction in plants whichwe shall learn in this MODES OF REPRODUCTIONIn Class VI you learnt about differentparts of a flowering plant. Try to list thevarious parts of a plant and write thefunctions of each. Most plants haveroots, stems and leaves. These are calledthe vegetative parts of a plant. After acertain period of growth, most plantsbear flowers. You may have seen themango trees flowering in spring. It isthese flowers that give rise to juicymango fruit we enjoy in summer. We eatthe fruits and usually discard the germinate and form new , what is the function of flowers inplants? Flowers perform the function ofreproduction in plants.

2 Flowers are thereproductive are several ways by whichplants produce their offspring. These arecategorised into two types: (i) asexual,and (ii) sexual reproduction. In asexualreproduction plants can give rise to newplants without seeds, whereas in sexualAsexual reproductionIn asexual reproduction new plants areobtained without production of propagationIt is a type of asexual reproduction inwhich new plants are produced fromroots, stems, leaves and buds. Sincereproduction is through the vegetativeparts of the plant, it is known asvegetative a branch of rose or champa with anode. This piece of branch is termed acutting. Bury the cutting in the soil. Anode is a part of the stem/branch atwhich a leaf arises (Fig. ). Water thecutting every day and observe itsgrowth. Observe and record the numberof days taken for roots to come out andPaheli thought that newplants always grow from , she has never seen the seedsof sugarcane, potato and rose.

3 Shewants to know how these , new plants are obtainedfrom 2023-24 REPRODUCTION IN PLANTS83new leaves to arise. Try the same activityby growing money plant in a jar of waterand record your you can also grow ginger(Fig. ) or (sprout leaf plant) hasbuds in the margins of leaves (Fig. ).If a leaf of this plant falls on a moistYou must have seen flower budsdeveloping into flowers. Apart fromflower buds, there are buds in the axil(point of attachment of the leaf at thenode) of leaves which develop intoshoots. These buds are called vegetativebuds (Fig. ). A bud consists of a shortstem around which immatureoverlapping leaves are present. Vegetativebuds can also give rise to new a fresh potato. Observe the scarson it with the help of a magnifying may find bud(s) in them. These scarsare also called eyes . Cut the potatointo small portions, each with an eyeand bury them in the soil.

4 Water thepieces regularly for a few days andobserve their progress. What do you find?Fig. Stem-cutting of roseFig. Potato plant sprouting from an eye Fig. Ginger with new plants sproutingfrom itsoil, each bud can give rise to a of some plants can also giverise to new plants. Sweet potato anddahlia are such as cacti produce newplants when their parts get detachedNodeBud inthe axilRationalised 2023-24 SCIENCE84 Activity (To be demonstrated by the teacher)Take a piece of yeast cake or yeastpowder from a bakery or a chemist a pinch of yeast and place it in acontainer with some water. Add aspoonful of sugar and shake to dissolveit. Keep it in the warm part of a an hour, put a drop of this liquidon a glass slide and observe under amicroscope. What do you observe? Youmay see the formation of new yeast cells(Fig. ).from the main plant body. Eachdetached part can grow into a Leaf of Bryophyllum with buds in themarginBoojho wants to know ifthere is any advantage ofvegetative produced by vegetativepropagation take less time to grow andbear flowers and fruits earlier than thoseproduced from seeds.

5 The new plantsare exact copies of the parent plant, asthey are produced from a single in this chapter you will learnthat plants produced by sexualreproduction have characters of both theparents. Plants produce seeds as a resultof sexual have already learnt about the tinyorganisms like yeast can be seen onlyunder a microscope. These grow andmultiply every few hours if sufficientnutrients are made available to that yeast is a single-celledorganism. Let us see how theyreproduce?The small bulb-like projectioncoming out from the yeast cell is calleda bud. The bud gradually grows andgets detached from the parent cell andforms a new yeast cell. The new yeastcell grows, matures and produces moreyeast cells. Sometimes, another budarises from the bud forming a chain ofbuds. If this process continues, a largenumber of yeast cells are produced in ashort might have seen slimy greenpatches in ponds, or in other stagnantwater bodies.

6 These are the algae. WhenFig. Reproduction in yeast by buddingYeast cellDeveloping budChain of budsNew budNew plantsRationalised 2023-24 REPRODUCTION IN PLANTS85air. As they are very light they can coverlong are asexual reproductivebodies. Each spore is covered by ahard protective coat to withstandunfavourable conditions such as hightemperature and low humidity. Sothey can survive for a long time. Underfavourable conditions, a sporegerminates and develops into a newindividual. Plants such as moss andferns (Fig. ) also reproduce by meansof SEXUAL REPRODUCTIONYou have learnt earlier the structure ofa flower. You know that the flowers arethe reproductive parts of a are the male reproductive partand pistil is the female reproductive part(Fig. ).water and nutrients are available algaegrow and multiply rapidly byfragmentation. An alga breaks up intotwo or more fragments. These fragmentsor pieces grow into new individuals(Fig.)

7 This process continues andthey cover a large area in a short periodof Reproduction through spore formationin fungusSpore formationIn Chapter 1 you learnt that the fungion a bread piece grow from spores whichare present in the air. Repeat Observe the spores in the cotton-like mesh on the bread. When sporesare released they keep floating in theFig. Reproduction through spore formationin fernHyphaSporangiumSporesSori(Spore formingbodies)Fig. Fragmentation in spirogyra (an alga)Rationalised 2023-24 SCIENCE86 Boojho wants to know how themale gamete in the pollen grainreaches the female gamete presentin the , pollen grains have a toughprotective coat which prevents themfrom drying up. Since pollen grains arelight, they can be carried by wind orActivity a mustard/China rose/petuniaflower and separate its reproductiveparts. Study the various parts of astamen and which contain either onlypistil or only stamens are calledunisexual flowers.

8 Flowers whichcontain both stamens and pistil arecalled bisexual flowers. Corn, papayaand cucumber produce unisexualflowers, whereas mustard, rose andpetunia have bisexual flowers. BothFig. Pollination in flowerFig. Reproductive parts(b) PistilStigmaStyleOvaryAntherFilament(a) StamenOvule(a) Self-pollination(b) Cross-pollinationAntherStigmaStigmamale and female unisexual flowers maybe present in the same plant or indifferent you identify the anther andthe filament of a stamen? [Fig. (a)].Anther contains pollen grains whichproduce male gametes. A pistil consistsof stigma, style and ovary. Ovarycontains one or more ovules. Thefemale gamete or the egg is formed inan ovule [Fig. (b)]. In sexualreproduction a male and a femalegamete fuse to form a 2023-24 REPRODUCTION IN PLANTS87water. Insects visit flowers and carryaway pollen on their bodies. Some ofthe pollen lands on the stigma of a flowerof the same kind.

9 The transfer of pollenfrom the anther to the stigma of a floweris called pollination. If the pollen landson the stigma of the same flower oranother flower of the same plant, it iscalled self-pollination. When the pollenof a flower lands on the stigma of a flowerof a different plant of the same kind, itis called cross-pollination [Fig. (a)and (b)].FertilisationThe cell which results after fusion ofthe gametes is called a zygote. Theprocess of fusion of male and femaleBoojho wants to know whyflowers are generally so colourfuland fragrant. Is it to attractinsects?Fig. (a) Section of an apple, (b) Almondgametes (to form a zygote) is calledfertilisation (Fig. ). The zygotedevelops into an FRUITS AND SEED FORMATIONA fter fertilisation, the ovary grows intoa fruit and other parts of the flower falloff. The fruit is the ripened ovary. Theseeds develop from the ovules. The seedcontains an embryo enclosed in aprotective seed fruits are fleshy and juicy suchas mango and orange.

10 Some fruits arehard like almonds and walnuts[Fig. (a) and (b)]. SEED DISPERSALIn nature same kind of plants grow atdifferent places. This happens becauseseeds are dispersed to different after a walk through a forestor a field or a park, you may have foundseeds or fruits sticking to your Fertilisation (Zygote formation)Pollen grain (germinating)OvumZygoteformationPollen tube(a)(b)(a)(b)Rationalised 2023-24 SCIENCE88 Did you try to observe how these seedswere clinging to your clothes?What do you think will happen if allseeds of a plant were to fall at the sameplace and grow there? There would besevere competition for sunlight, water,minerals and space. As a result the seedswould not grow into healthy benefit by seed dispersal. Itprevents competition between the plantand its own seedlings for sunlight, waterand minerals. It also enables the plantsto invade new habitats for and fruits of plants are carriedaway by wind , water and seeds such as those of drumstickand maple [Fig.]