2 Hormones and Plant Growth Plant cells send signals to one another that indicate when to divide, when not to divide, and when to develop into a new kind of cellWhen animals reach adulthood, they stop growingEven when plants reach adulthood, they keep growingMeristems allow plants to remain “forever young”
3 What do plants grow in response to? LightMoistureTemperatureGravity
4 What is a plant hormone?A substance that is produced in one part of an organism and affects another part of the same individualControl a plant’s patterns of growth and development, and the plant’s responses to environmental conditions
5 Plant HormonesTo respond to a hormone, the target cell must contain a receptor to which the hormone bindsIf the receptor is present, the hormone can influence the target cell by:-changing its metabolism-affecting its growth rate-activating the transcription of certain genesA single hormone may affect two different tissues in different ways
6 AuxinsPhototropism – tendency of a plant to grow toward a source of lightAuxins are produced in the apical meristem and are transported downward into the rest of the plantAuxins stimulate cell elongationResponsible for gravitropismGravitropism – response of a plant to the force of gravityInvolved in the way roots grow around objects in the soil
7 Auxins Regulate cell division in meristems Apical dominance is the phenomenon in which the closer a bud is to the stem’s tip, the more its growth is inhibitedCompounds that mimic auxins are used as herbicides to kill weedsHerbicides – compounds that are toxic to plants
8 CytokininsCytokinins – plant hormones that are produced in growing roots and in developing fruits and seedsStimulate cell division and the growth of lateral budsCause dormant seeds to sproutDelay the aging of leavesInhibit elongation and cause cells to grow thicker
9 Plant Hormones BOTH: Determine how a plant grows Auxins Cytokinins Stimulate cell elongationInhibit growth of lateral budsInhibit elongationStimulate lateral bud growthBOTH: Determine how a plant grows
10 Gibberellins Gibbberellin – growth-promoting substance Produce dramatic increases in size, especially in stems and fruitsProduced by seed tissueResponsible for rapid early growth of plants
11 Ethylene Ethylene – plant hormone that stimulates fruits to ripen Plants produce their own ethyleneIn response to auxins, fruit tissues release small amounts of ethylene, which then stimulates fruits to ripenUsed to control the ripening process of fruit
13 Plant tropisms include gravitropism, phototropism, and thigmotropism Plant tropisms include gravitropism, phototropism, and thigmotropism. Each of these responses demonstrate the ability of plants to respond to external stimuli
14 25-2 Plant ResponsesTropism= the response of plants to external stimuliPhototropism: response to lightAuxin controls itAuxin=hormoneMaximizes plant exposur to sunlightGravitropism: response to gravityAuxin controlsRoots grow with gravityStem grows against gravity
15 More tropism!!! :D Thigmotropism=Response to touch Plants that are touched regularly may be stunted in growthVines and climbing plants grow around anything that they touch.
16 EVEN MORE Tropisms!!!:D Hydrotropism: response to water E.g. plant grows towards where water is abundantChemotropism: response to chemicalsThermotropism: response to temperatureHeliotropism: response to the position of the sun
17 Rapid Response Plant movements that are not tropisms Tropisms involve plant growthTropisms DO NOT happen rapidly!!!Ex. Venus fly trap
18 PhotoperiodismPhotoperiodism: plants ability to respond to periods of light and darknessShort-day plants: flower when days are shortLong-day plants: flower when days are longPhytochromes are plant pigment that absorbs red light is responsible for photoperiodism.
19 Winter DormancyDormancy: is the period during which an organism’s growth and activity decrease or stopShorter days and colder temperatures reduces rate of photosynthesisKeeping the leaves would be costly in terms of water lossThe leaves have little chance of surviving the winter
20 Leaf AbscissionPlant reduces auxin production, and increases ethylene productionLeaf stops making chlorophyllRemaining chlorophyll breaks down and exposes accessory pigmentsNutrients are transported from the leaf to the plantAbscission Layer – seals off the leaf from the rest of the plant
21 Plant Adaptations By Jenny Song Angiosperms can survive in many different locations. How is this possible?Plant AdaptationsBy Jenny Song
22 Through natural selection, plants have evolved different adaptations to live successfully in each environment.
23 Adaptations are special features that allow a plant or animal to live in a particular place or habitat
24 Aquatic Plants Often live in MUD(contain little oxygen) To get enough oxygen, many aquatic pants have air-filled spaces in their tissues.Oxygen diffuses through these spaces from the leaves to the roots.Example of an Aquatic Plant: Waterlillies
25 Salt-Tolerant PlantsPlants that grow in salt water or in very salty air near the ocean.These plants have special cells that pump salt out of the plant tissues and onto the leaf surfaces.Then, the rain washes off the salt.Ex. Lampranthus spectabilis (trailing iceplant)
26 Xerophytes (Desert Plants) These plants often have extensive roots, reduced leaves, and thick stems that can store water.Seeds of many desert plants can remain dormant for years.These seeds will germinate only when enough moisture guarantees them a chance to survive.
27 Nutritional Specialists Plants that grow in soil with little nutrients.Ex. Carnivorous plants and parasitesCarnivorous plants trap and digest insects to get nitrogen.Parasites get water and nutrients directly from a host plant.These plants HARM their host plants
28 Epiphytes Plants that are not rooted in soil. They grow directly on the bodies of other plants.Are NOT parasites.They gather their own moisture from the rain.They make their own food.Most live in Rain Forests.
29 Chemical DefensesMany plants produce chemicals that are poisonous to the animals that eat them.Chemical defenses protect plants from potential predators.Digitalis (Foxglove)ispoisonous when eaten.