Bovard Josh Biology 111 Thursday, September 25th, 2008 Professor
PLANT BODY: STRUCTURE AND NUTRITION
Growth:
Seed Germination is the process by which seeds begin growth into plants Generally dormant just after being shed
Wont germinate even if temperature, soil and moisture conditions are optimal Dormancy is most frequently due to the presence of the hormone abscisic acid (ABA)
ABA has to degrade before the seed will germinate
Frequently need a light signal to make them germinate
Because most seeds have only a small amount of stored food, they have to germinate close to the soil surface If they see the light they are close to the surface If they germinate deep down below the soil, they run out of food before then can perform photosynthesis above the surface
Different types of light affect germination Red or white light encourages germination
Pr is the phytochrome that absorbs red light and gets converted to Pfr
The stimulation of Pfr causes germination, leaf expansion, hook unfolding, stimulation of chlorophyll synthesis
Deep red light restricts germination
Pfr is the phytochrome that absorbs deep red light and gets converted to Pr
Auxin is a hormone that controls plant shape Through apical dominance, the axillary buds control whether or not branches grow Coleoptiles has parts that sees the light and another one parts due to the light An experiment was done where blindfolds were put on the tips of the plants, resulting in no
bending at the tip
Without the blindfolds, bending occurred Proved that the tip of the plant is the part that responds to light
Another experiment was done where the tip of the plant was cut, place in an agar block so it
can diffuse
Determined that the isolated hormone called was auxin
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Josh Bovard Biology 111 Thursday, September 25th, 2008 Professor
The movement of auxin is controlled by the light and gravity The auxin moves away from the plant, thus causing the plant to bend towards the light Negative Geotropic Growth occurs when the auxin moves to the lower side of the plant,
bending it upwards and away from gravity Reproduction:
Asexual: Vegetative reproduction Sexual: Flowering
Angiosperms have a stigma, style, ovary, ovule, and anther making up their reproductive system Inflorescence is a branch that bears flowers (ex. Sunflowers) Plants always flower at a particular time of the year because they obtain a certain 24-hour cycle (depending on the species) ex. Potato tubers are underground stems that store food for the potato; they sometimes turn into new shoots Some plants have leaves that fall off and grow into new plants
Combo of light-length and day-length that induces a plant to flower is an inductive photoperiodic cycle Exposure of a single leaf can induce the cycle, thus there must be some movement of hormones from the leaf to the shoot (where the flowers are produced)
Pollination & Fusion of gametes
Gametes fuse in the ovule, a triploid nuclei is also formed
Responses to the Environment:
Drought Desert ephemerals avoid drought by growing during the brief rainy season
Restricted their lifestyle to the rainy time of the year; very brief
Large trees have deep tap roots Flooding During flooding, plants do not get enough oxygen
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Josh Bovard Biology 111 Thursday, September 25th, 2008 Professor
Roots produce pneumatophores to stick out of the water and take up air through the tiny
pores
Hypoxia Aquatic plants have air spaces
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