EXPERIMENT 17.2 3e__ AIM OF THE EXPERIMENT MRAIMOF THE EXPERIMENT and analogous organs, To observe flash cards or models showing examples of homologous ¥R_ MATERIALS REQUIRED MR_MATERIALS REQUIRED, i locally available plants, ci ing tendrils, thorns, etc., of Flash cards or models of plant specimens showing te 4 aL plant with normal stem, potato and onion bulb, prickly pear, a on gs ird, cockroach and bat, and cervical, thoracic and lumbar vertebrae of am: 2 THEORY @ A. Homologous Organs: Tend Trom— Bougainvitea CCucurita Man Cheetah Whale @) ) Fig. 17.8 Examples of homologous organs in (a) plants and (b) animals Bat (@) The organs with same structural design and origin but different functions are called homologous organs. For example, the forelimbs of some animals like whales, bats, cheetah and humans have similar anatomical structure, i.e. all ave humerus, radius, ulna, carpals, metacarpals and phalanges. (©) Due to different needs, some structures developed differently. Thi (6) Homology indicates common ancestry. called divergent evolution. (@) Other examples include vertebrate hearts or brains in animals, thorn and tendril invillea and Socn ae and tendrils of Bougainvi © B. Analogous Organs: 3 \F Dilerontskeltal stuctires Fig. 17.9 Analogous organs ‘Same function 116 (& scanned with OKEN Scanner(a) The organs which are anatomically different but functionally simil example, wings of butterfly and birds, ir are called analogous organs. For (b) Due to same function, different structures evolve similarly, This is called convergent evolution. (©) Other examples include eye of octopus and mammals, Flippers of penguins and dolphins, Sweet potato (root modification) and potato (stem modification). (6) Similar habitat resulted in selection of sinillar adaptive features in different groups of organs but towards the same functions, @® PRoceDURE 1. Observe the specimens and movtels 2. Note down the observations and draw the diagrams in your notebook. a OBSERVATION Homologous organs in plant ©) Tendrils of passion fruit and thorns of pomegranate: Tendrils of passion fruit different but they hay ate are structurally and functionally ¢ from axillary bud @ ) Fig. $7.0 (a) Tendris of passion fut (b) Thorns of pomegranate (ii) Tendrils of Vitis and thorns of Carissa: Tendrils of Vitis and thorns of Carissa origi functionally different. ate from the terminal bud, but they are at ‘Thomns (a) () Fig. 17.14 (a) Tendrits of Vitis (b) Thorns of Carissa (i) Tendsits of baloon vine (Cardiospermum) and bulbils of Agave: : 117 (& scanned with OKEN ScannerBoth are modifications of floral bud, but they perform different functions. Tendrils help ig x climbing but bulbils are meant for reproduction. Fig, 17.42 (a) Tendrils of baloon vino (b) Bulbils of Agave (iv) Scale leaves of onion and spines of prickly pear (Opuntia): Both the scale leaves and spines are modifications of leaves but are structurally and functionally different, Scale leaves of onion are thick and fleshy and store food. On the other hand spines of cactus are defensive organs. Spines Scale Leaves. @ ©) Fig. 17.13 (a) Scale leaves of onion (b) Spines of Opuntia 2. Analogous Organs in Plants: (# Stem tendrils and leaf tendrils: All tendrils are analogous with one another, being structurally and functionally similar, irrespective of their origin. Example: Tendtils of pea and tendrils of Vitis. Tendrils of pea are modification of leaf and in Vitis itis the modification of terminal bud @ ° Fig. 17-44 (a) Tendrits of pea (b) Tends of Vitis (ii) Thorns and spines: 118 (& scanned with OKEN Scannerish) as Modified stems (rhizome, corm, tuber) are analogous 7 ee fee {carrot radish) funeti rage but their ori they perform similar function of storage of food peony singer, potato tuber, colocnsin arc tees ond beetroot, radish, etc. are roots. (a) ® Fa 17.45 () Moditied root of earzot (b) Rhizome of ginger (iv) Phylloclade, cladode and leaves: ‘They perform the same fi modifications of stem. Phylloct plant like mango are n, i they photosynthesise but phylloclade and cladode are lice of Opuntia, Parkinsonia, asparagus and leaves of any local analogous organs. Spine fa) (b) Fig. 17.16 (a) Phylloctade (b) Cladode of ruscus 3. Homologous Organs in Animals: Wings of birds, and forelimb (humerus, radius, ulna, carpals, birds, for holding or walking, etc. of mammals/reptiley/ frog: All have the metacarpals and phalanges), . in other). same bony elements but perform different (flying in (@) ) Fig. 17.17 Forelimb of (a) human (b) bat 4. Analogous Organs in Animals: (© Wings of dragonfly/cockroach/butterfly and of birds. @) (>) Fig. 17.18 Wing of (a) dragonfly (b) bird () Mandible of cockroach and mandible (lower jaw) of a vertebrate. 119 (& scanned with OKEN Scanner(a) (b) Fig. 17.19 Mandible of (a) cockroach (b) rabbit © scanned with OKEN Scanner