TROPISMS, HORMONES, &FLOWERING RESPONSES

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TROPISMS• LTS react to changes in environment—plants

are LTS so their reactions (RESPONSE) is called a TROPISM.•POSITIVE TROPISM—to grow TOWARD the STIMULUS

(light, water, gravity)NEGATIVE TROPISM—growing AWAY from the stimulus.

• Kinds of — ’ tropisms A PLANT S GROWTHRESPONSE• GRAVITROPISM--a plant’s growth response to GRAVITY+ roots grow TOWARD gravity; - stem grows away HYDROTROPISM—a plant’s growth response to WATER

+ roots grow towardPHOTOTROPISM—a plant’s growth response to LIGHT

+ stem grows toward; - roots grow away from lightTHIGMOTROPISM—a plant’s growth response to TOUCH

• PLANT TROPISMS are controlled by plant !!HORMONES

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TROPISM(CONTUED)• HORMONES include AUXINS with cause the

stem and

leaves of plants to grow TOWARD the light ---which is a

+ .PHOTOTROPISM• ETHYLENE GAS is another plant HORMONE. It causes thefruit to ripen on the plant. It doesn’t matter where the ethylene gas comes from so the growers pick fruit “green” and treat it with ethylene gas on the

.way to the s tore Fruit arrives ripe, ready to buy and eat.•PHOTOPERIODISM is the flowering res pons e of a plant to changes in the length of light and dark in a day—since we have SEASONS due to the tilt o f

the Earth on its axis , the hours of light and dark in a season changes.•Mos t plant require a s pec ific amount of light to flower.• - LONG DAY PLANTS require s hort nights to flower (spinach, lettuce, and potatoes)• - SHORT DAY PLANTS need long nights to flower (poinsettias, strawberries, ragweed)• - DAY NEUTRAL PLANTS are plants that have a wide range of flowering times -not so sensitive like marigolds and corn.

SEC. 3 TRANSGENIC CROPS

• A method of improving crops by moving DNA from one LT to

another is called BIOTECHNOLOGY. DNA can come from a different

species of plant OR it could come from the same species.

TRANSGENIC CROPS are crops that have DNA from one kind of crop

Inserted into another plant to improve the crop. EXAMPLESinclude

herbicide insensitive cotton plants, insect-resistance tobacco plants

and tomato plants with firmer fruit not spoiling as quickly. pp. 332

• There are TWO methods of moving the DNA to the other plant:

• Coat tiny metal balls with the DNA and s hoot them into the .target ce lls hoping to hit the nucleus

• Us ing an empty VIRUS coat or a bacterium with the DNA, ins ide let thes e things trans fer ( the DNA to the LT ls t us ed

1987).inBENEFITS : Tomatoes do not spoil as quickly and so more are able to be used as food. Other fruits

could also be altered for the same reason. Some trans genic potatoes PRODUCE their own pesticide reducing the need for pesticides. None of it remains when the potato reached the market because it was the LEAVES that made the pesticide, not the

UNDERGROUND STEM. With INCREASING populations, scientists HOPE that transgenic crops will ease WORLD HUNGER.