chapter 29

Question 1

what are the major components of a plant’s organic compounds

Answer 1

carbon, oxygen, hydrogen – obtained from carbon dioxide and water (3 of the 9 macronutrients)

Question 2

what are the three minerals macronutrients that are found in greatest amounts in plant fertilizers

Answer 2

nitrogen, phosphorus, & potassium

**nitrogen shortage is very common in plants

Question 3

what are the two processes in soil formation

Answer 3

weathering of rock & decomposition of organic matter

Question 4

what are five soil components

Answer 4

1) minerals – breakdown of rocks
2) soil water –size of the soil particles affects capacity of water held [smaller particles like clay hold water better; large particles like sand do not hold water well] best soil is a mixture of both
3) organic matter – also called humus
4) living organisms – numerous & varied [i.e. bacteria, fungi (decomposers) worms, insect larvae]
5) oxygen – important for respiration of roots & soil organisms

**minerals- inorganic chemical elements

Question 5

what type of soil particle holds the most water, what type holds the least water

Answer 5

clay holds more; sand holds least

Question 6

what is the best soil pH for most plants

Answer 6

6 to 7.5 pH

Question 7

why is organic matter (humus) better as a fertilizer than inorganic (commercial) fertilizers

Answer 7

–>soaks up water & releases it as needed

–>helps to keep soil loose

–>organic mulch on top of soil acts as a sunscreen & as a reservoir of nutrients which are released slowly – thus organic matter is better than commercial fertilizer because organic matter provides soil conditioning and slow release of minerals prevents fertilizer burn

Question 8

how does transport occur in plants at the cellular level

Answer 8

–>diffusion – movement of molecules from a region where they are more concentrated to a region where they are less concentrated

–>osmosis – diffusion of water through a differentially permeable membrane from a region where it is more concentrated into a region where it is less concentrated

–>active transport – movement of molecules from a region where they are less concentrated into a region where they are more concentrated – this requires energy

Question 9

how does transport occur in plants at the tissue and organ level

Answer 9

• ->cell wall pathway

- ->cytoplasmic pathway, through the plasmodesmata

Question 10

how does transport occur in plants at the whole plant level

Answer 10

• ->bulk flow – movement due to pressure differences moves water and minerals through xylem and
• ->food through the phloem
• *involves the vascular tissues

Question 11

what are the three factors involved in the ascent of water and minerals in xylem vessels

Answer 11

–>capillary – movement of fluid into a narrow tube because of the attraction of water to cellulose molecules in the walls of the xylem cells (adhesion) molecules of water adhere to the sides of the tube and these water molecules pull other water molecules up (cohesion)
[by capillary alone water can rise only a few feet (2-5 feet) , so if the sap cannot climb on its own, it must either be pushed from the bottom or pulled from the top]

–>root pressure (the push from the bottom) – root pressure results from the active transport of ions followed by osmosis of water – thus building up hydrostatic pressure in the xylem – this can be demonstrated in some plants by cutting off the plant near the ground, sealing the stump in a glass tube and watching the sap rise in the tube in small plants guttation (loss of liquid water from leaves) may occur as a result of root pressure –
[greatest root pressures measured can push sap only a few feet so capillarity and root pressure alone are not sufficient to account for movement of sap in large plants]

–>transpiration (the pull from the top) – loss of water vapor (by evaporation) from pores in the leaves

Question 12

of these three factors, which is the most important in tall plants

Answer 12

root pressure

Question 13

what is the transpiration-cohesion-tension mechanism & how does it work?

Answer 13

–>evaporation of water from the upper plant (transpiration) creates a negative pressure (tension) in xylem that pulls water molecules from the lower plant (cohesion)

–>continuous transpiration stream moves water up from the roots, through the xylem, and out through the stomata
[water lost from the leaves is continuously replaced as soil water is taken up by the roots]

Question 14

what are structural factors that affect the rate of transpiration

Answer 14

density of stomata; thickness of cuticle

Question 15

what are environmental factors that affect the rate of transpiration

Answer 15

availability of soil water; sunlight; temperature; humidity; wind

Question 16

what is translocation

Answer 16

movement of sugars and other nutrients in phloem following a source to sink pathway source – where sugar is produced, e.g. leaves

Question 17

what is the pressure flow mechanism, how does it work

Answer 17

solutes move in solutions that move because of differences in water concentration (pressure) caused by differences in solute concentration

Question 18

what are three differences in plant and animal hormones

Answer 18

–>plants–>hormones are produced in various organs that have other functions
animalsdistinct hormone producing glands (endocrine)

–>plants–>hormones can affect virtually any tissue
animalstarget specific hormones

–>plants–>hormones affect changes such as growth, differentiation, & responses to the environment
animalshormones maintain homeostasis

Question 19

what are the five major plant hormones, what is the main function of each

Answer 19

—>auxins – first plant hormones discovered, functions include:
promote meristematic growth and cell elongation
prevent leaves, flowers, and fruits from falling off prematurely
in apical buds – partially responsible for apical dominance
phototropism – auxin causes stems to bend toward light (because auxin is light sensitive, it accumulates on the darker side of the stem, causing it to grow faster, thus bending the plant toward the light)
gravitropism – auxin causes roots to grow down and shoots to grow up
[synthetic auxins are used commercially in rooting preparations and as weed killers (2,4-D)]

-->cytokinins – functions include:
	stimulate cell division
	inhibit aging of leaves – florists spray cut greenery and flowers with cytokinin to keep them fresh
	interact with auxin to produce the total growth pattern of the plant

--->gibberellins – functions include:
	promote stem elongation
	stimulate leaf and flower growth – florists use to stimulate early flowering

-->abscisic acid – functions include:
	inhibition of growth (it opposes the three growth-promoting hormones)
	promotes dormancy in shoots and seeds
	promotes closing of stomata during water stress

-->ethylene –functions include:
	fruit ripening
	counteracts some of the effects of auxin (acts as a check and balance system)
	promotes dropping of leaves, flowers, and fruits

Question 20

what is phototropism

Answer 20

response to the length of day & night

Question 21

what is gravitropism

Answer 21

response to gravity