Plant Responses to Stimuli (Tropisms) Kuyankha kwa Zomera pa Zosintha (Tropisms)
For plants to survive, they must be able to detect changes in their environment and respond to them. While plants do not have a nervous system or muscles like animals, they can still adjust their growth in response to specific external stimuli. This growth response is known as a tropism.
Types of Tropisms A tropism is a directional growth response, meaning the direction of the plant's growth is directly determined by the direction of the stimulus. If a plant grows towards a stimulus, it is a positive tropism; if it grows away from it, it is a negative tropism.
Phototropism: This is the growth response to light. Plant shoots exhibit positive phototropism, growing directly towards the light source to maximise photosynthesis. Roots exhibit negative phototropism, growing away from the light and deeper into the soil.
Geotropism (Gravitropism): This is the growth response to gravity. Plant roots show positive geotropism, growing downwards with gravity to anchor the plant and access water. Shoots show negative geotropism, growing upwards against gravity to reach the sunlight.
Hydrotropism: This is the growth response to water. Roots exhibit positive hydrotropism, actively growing towards areas of higher soil moisture.
The Mechanism of Tropisms: The Role of Auxin Tropisms are controlled by plant hormones, the most important being auxin. Auxin is synthesised in the very tips of the shoots and roots. It controls the rate at which plant cells elongate (stretch and grow). When light shines on a shoot from one side, the auxin moves to the shaded side of the shoot. The increased concentration of auxin on the shaded side causes those cells to elongate much faster than the cells on the sunny side. This uneven growth causes the shoot to bend towards the light. Scientists use a rotating device called a clinostat to investigate tropisms by slowly turning a plant to cancel out the directional effects of gravity or light.
Nastic Responses Unlike tropisms, nastic responses are non-directional. The plant responds to a stimulus, but the direction of the movement does not depend on the direction of the stimulus. These responses are usually much faster and are caused by sudden changes in cell turgor pressure (water pressure) rather than slow growth. A classic example is the Mimosa pudica (the sensitive plant), whose leaves rapidly fold inwards and droop when touched. Carnivorous plants, such as the Venus flytrap, also utilise rapid nastic responses to snap their traps shut when an insect touches their sensory hairs.
Kuti zomera zipulumuke, ziyenera kuzindikira zosintha m'malo omwe zili ndikuchitapo kanthu. Ngakhale zomera zilibe ubongo kapena minofu ngati nyama, zitha kusintha kakulidwe kawo potengera zinthu zakunja zomwe zikuzikhudza. Kukula uku poyankha chinthu chakunja kumatchedwa tropism.
Mitundu ya Tropisms Tropism ndi kakulidwe kolunjika gulu, kutanthauza kuti njira yomwe chomera chikukulira imadalira mwachindunji komwe chinthu chosonkhezeracho chikuchokera. Ngati chomera chikukulira kumene kuli chinthucho, ndi tropism yotsata (positive); ngati chikukulira kuthawa, ndi tropism yotsutsa (negative).
Phototropism (Kutsata kuwala): Uku ndi kukula poyankha kuwala kwadzuwa. Mphukira za zomera zimasonyeza positive phototropism, zikukulira komwe kuli kuwala kuti zipange chakudya chambiri. Mizu imasonyeza negative phototropism, ikukulira kuthawa kuwala kulowa pansi panthaka.
Geotropism (Kutsata mphamvu yokoka): Uku ndi kukula poyankha mphamvu yokoka ya dziko lapansi (gravity). Mizu ya zomera imasonyeza positive geotropism, ikukulira pansi kutsata mphamvu yokoka kuti igwire bwino nthaka ndikupeza madzi. Mphukira zimasonyeza negative geotropism, zikukulira mmwamba kuthana ndi mphamvu yokoka kuti zipeze dzuwa.
Hydrotropism (Kutsata madzi): Uku ndi kukula poyankha madzi. Mizu imasonyeza positive hydrotropism, ikukulira mwamphamvu m'madera omwe nthaka ili ndi chinyontho chambiri.
Kachitidwe ka Tropisms: Ntchito ya Auxin Ma tropism amalamuliridwa ndi mahomoni a zomera, ndipo yofunika kwambiri ndi auxin. Auxin imapangidwa kunsonga zenizeni za mphukira ndi mizu. Imalamulira liwiro lomwe maselo achomera amatambalala (elongate) ndi kukula. Kuwala kukawala pamasamba kuchokera mbali imodzi, auxin imasamukira kumbali ya mthunzi yotsutsana ndi kuwala. Kuchuluka kwa auxin kumbali ya mthunzi kumapangitsa maselo a kumeneko kutambalala mwachangu kwambiri kuposa maselo akumbali ya dzuwa. Kukula kosagwirizanaku kumapangitsa mphukira kupindika kulunjika kukuwalako. Asayansi amagwiritsa ntchito chipangizo chozungulira chotchedwa clinostat kufufuza ma tropism pozunguliritsa chomera pang'onopang'ono kuti athetse zotsatira zolunjika za dzuwa kapena mphamvu yokoka.
Mayankho Osadalira Kulunjika (Nastic Responses) Mosiyana ndi ma tropism, mayankho a nastic samadalira komwe chosonkhezera chachokera. Chomera chimayankha, koma mayendedwe ake sadalira komwe chinthucho chachokera. Mayankho amenewa nthawi zambiri amakhala achangu kwambiri ndipo amayamba chifukwa cha kusintha kwadzidzidzi kwa kuthamanga kwa madzi (turgor pressure) m'maselo m'malo mokula pang'onopang'ono. Chitsanzo chodziwika bwino ndi Mimosa pudica (gundamwala kapena tsekera-tsekera), yemwe masamba ake amapindana mwachangu kulowa mkati ndi kufota akakhudzidwa. Zomera zodya tizilombo zimagwiritsanso ntchito mayankho a nastic achangu kuti zitseke misampha yawo tizilombo tikakhudza tsitsi lawo lozindikira.
Exercise RequiredMasewera Ofunikira
You must pass this exercise to complete the lesson. Questions are randomly selected each attempt. Muyenera kupambana masewera awa kuti mumaliza phunziro. Mafunso amasankhidwa mwachisawawa nthawi iliyonse.