lecture 12

Question 1

primary growth

Answer 1

• lengthens roots and shoots
• most plant species experience indeterminate growth meaning that they continue to grow for the duration of their life
• most animals have determinate growth meaning that the cease growing after a certain length
• this indeterminate growth growth allows plants more exposure to sunlight, soil, and air

Question 2

plants are not immortal and angiosperms are characterized according to life cycle duration

Answer 2

1. annuals: complete life cycle in one year or less (most important crops)
2. biennials: complete life cycle in two years ex) beats and carrots
3. perennials: live and reproduce for many years ex) trees and shrubs
   - plants do not die from old age but rather from environmental trauma such as fire or infection

Question 3

plant growth

Answer 3

• made possible by tissues called meristems
• meristems consist of cells that divide frequently generating more cells
• some of these new cells remain in the meristem and continue to divide while other differentiate being incorporated into the tissues of the growing plant

Question 4

apical meristems

Answer 4

• are located at the tips of the roots and the buds of shoots
• cell division here produces new cells allowing the plant to grow in length: a process called primary growth
• enables roots to push through the soil and shoots to increase exposure to light and CO2
• roots and shoots lengthen using different mechanisms

Question 5

root growth

Answer 5

• the tip of the root is covered by a root cap which protects the cells of the apical meristems which are actively dividing
• growth in length occurs just behind the root tip with three areas of distinct cells
  1. the zone of cell division
  2. zone of elongation
  3. the zone of maturation (differentiation)
• there are no sharp boundaries between these three areas

Question 6

the zone of cell division

Answer 6

• contains the cells of root apical meristem and cells that derive from it
• new cells of the root produced here including root cap cells

Question 7

the zone of elongation

Answer 7

• root cells here elongate (as much as ten times their original length)
• pushes the root tip further into the soil
• cells lengthen and do not expand becasue of cellulose fiber arrangement
• cells take up water and the cellulose fibers separate expanding like an accordion

Question 8

zone of differentiation

Answer 8

• all three plant tissues complete their development here
• dermal, ground and vascular tissues
• cells in the vascular cylinder differentiate into primary xylem and primary phloem
• differentiate occurs because of differential gene expression

Question 9

secondary growth

Answer 9

• woody plants continue to grow in girth once primary growth is complete
• referred to as secondary growth
• occurs because of activity in dividing lateral meristrems
• arranged into cylinders called vascular cambium and cork cambium
• when secondary growth begins the epidermis sloughs off and is replaced by cork-the new outer layer
• mature cork cells are dead and have thick waxy-cell walls that protect the underlying layers from water loss, pathogens, and physical damage
• cork is produced by the cork cambium which first forms from parenchymal cells within the cortex
• as the stem thickens the secondary xylem expands the original cork and cork cabium falls off only to be replaced by new cork cambium that has formed on the inside
• when no cortex remains it forms from parenchymal cells in phloem

Question 10

vascular cambium

Answer 10

• cylinder of meristem cells one cell thick between the primary xylem and primary phloem
• secondary growth adds layers of vascular tissue on either side of the vascular cambrium
• gives rise to two new tissues: secondary xylem (to the interior of the vascular cambrium) and secondary phloem (to the exterior of the vascular cambrium)
• each year the new that are proposed are larger in circumference than the previous year-thickening roots and stems
• secondary xylem composes the wood of the tree-cell walls are rich in lignin providing characteristics wood strength

Question 11

wood rays

Answer 11

• consists of parenchymal cells that transport water and nutrients
• they also function in nutrient storage

Question 12

heart wood

Answer 12

• trunk cells
• older secondary xylem
• no water transport
• clogged with resin
• will not rot

Question 13

sapwood

Answer 13

• younger secondary xylem

- conducts xylem sap

Question 14

everything outside of the vascular cambium is called

Answer 14

• bark
• main components are secondary phloem, cork cambium, and cork
• youngest secondary phloem functions in sugar transport and older secondary phloem dies
• bulk of the tree is dead tissue
• living tissue includes: vascular cambium, youngest secondary phloem, cork cambium, and cells in the wood rays (move out from the center)

Question 15

fertilization

Answer 15

• diploid plant body is the sporophyte (roots, stems, leaves and most reproductive structures are all diploid)
• sporophyte produces specialized sturctures-anthers and ovules in which cells undergo meiosis in order to become a multicellular gametophyte
• the gametophyte is the plant haploid generation which produces gametes by mitosis
• spores in the anthers give rise to a male gametophytes: pollen grains which produce sperm
• a spore within an ovule produces the embryo sac which is the female gametophyte containing an egg cell
• pollination is the arrival of pollen grains onto a stigma
• a pollen tube grow into the ovule and sperm pass through it fertilizing both egg and a second cell called double fertilization

Question 16

the ovule develops into a seed

Answer 16

the now triploid (3n) nucleus divides by mitosis and produces an endosperm

• nutrient rich
• the zygote divides by mitosis producing the embryo
• the ovule looses most of its water and develops a resistant seed coat enclosing the endosperm and the embryo
• the seed may remain dormant and only begin to grow when favorable environmental conditions occur (seed dormancy)

Question 17

euicots vs monocot

Answer 17

eudicot:
-two cotylendons
-apical meristems lack protection shealths
-endosperm is absorbed by the cotylendons
monocot:
-single cotylendon
-apical meristems have a protection shealth
-endosperm is present

Question 18

the ovary develops into a fruit

Answer 18

• hormonal changes which occur as a result of fertilization trigger the ovary to develop into a fruit
• the fruit functions to protect the seed and to aid in dispersal
• mature fruits may either be fleshy or dry
• fleshy: oranges
• dry: beans

Question 19

seedling germination

Answer 19

when a seed absorbs water germination occurs

• the seed begins to expand as a result of water absorbation causing the seed coat to rupture
• the embryo now begins to grow and produce enzymes
• the enzymes function to digest the endosperm releasing nutrients that can be used as energy

Question 20

asexual reproduction

Answer 20

• vegetative reproduction
• involved fragmentation of the plant body
• each fragment gives rise to a genetically identical daughter plant
  ex) garlic

Question 21

plant importance

Answer 21

• provide shelter for animals, fungi, and bacteria
• provide food for animals
• roots function to prevent the erosion of soil
• photosythesis reduces atmospheric CO2 and provides the atmosphere with oxygen
• plants benefits humans immensely:
• lumbar, paper, food, industrial chemicals

Question 22

plants acquire nutrients from soil and air

Answer 22

• plant roots absorb water, minerals such as inorganic ions and a small amount of oxygen from the soil
• leaves take CO2 from the air
• photosynthesis uses water, CO2, and minerals to produce sugars composed of carbon, oxygen, and hydrogen
• inorganic ions such as nitrogen and magnesium are components of the photosynthetic pigment chlorophyll which gives plants their characteristic green color
• inorganic ion phosphorus is a major component of DNA and RNA as well as ATP and phospholipids

Question 23

control of solute uptake

Answer 23

-the absorptive surface area of the root is dramatically increased by the presence of root hairs
-water and solutes must first enter the xylem before they can be transported by the plant body
-to enter the xylem the water may either move through cells (intracellular route) to move through the epidermis and the cortex
-or it may move between the cells
(extracellular route)
-the intracellular pathway of uptake moves through the cell membrane of a root hair
-through to the plasmodesmata, then through the cytoplasmic content of the cortex cells and endodemal cells
-finally into the xylem vessels
-the extracellular pathway moves through the cell wall of all epidermal and cortex cells and within intracellular spaces
-the waxy barrier called the caspiran strip in the walls of the endodermal cells forces the water through the endodermis and into the xylem

Question 24

transpiration

Answer 24

• pulls water up the xylem vessels
• xylem sap: inorganic nutrient solution that travels up xylem from a plants root to shoot
• root pressure can only push the xylem sap up a few meters
• solute transport raises the water pressure in the xylem
• the xylem sap is pulled upward from the soil through a transpiration-cohesion-tension mechanisms
• transpiration: loss of water from a leaf
• exerts a pull on xylem sap
• cohension causes the water molecules to adhere to one another
• relays the pull of transpiration along a string of water molecules all the way up to the roots
• the adhension of water molecules to the exterior of xylem cells aids to combat the force of gravity

Question 25

guard cells

Answer 25

• the guard cells surround stoma and control the opening, thus controlling transpiration
• the opening and closing of the stoma help the plant to control water content and adapt to changing environmental conditions
• as the guard cells open the stoma they actively pump potassium in increasing the solute concentration with the cell
• water consequently follows by osmosis
• when the stomata lose potassium the guard cells close

Question 26

cues for the stomata opening

Answer 26

1. increased sunlight cause the guard cells to take up potassium
   - if water is lost too fast the guard cell close
2. decreased internal CO2 has the same effect as increased sunlight
   - an internal daily timing mechanism trigger potassium uptake and stomata opening in the morning and stomata closing in the evening

Question 27

phloem

Answer 27

• transport sugars made by photosynthesis via a pressure-flow mechanism
  1. sugar is loaded into pholem tube at the source which raises the solute concentration within the tube
  2. water is then drawn into the tube by osmosis, raising the tube pressure
  3. sugar and water leave the tube at the sugar sink
• the increases in pressure at the sugar source and decrease in pressure at the sugar sink causes the sap within the phloem to move from source to sink

Question 28

fertilizers

Answer 28

• help prevent nutrient deficiencies
• the availability of nutrients within the soil affect plant growth and health
• the absence of certain nutrients lead to particular plant symptoms which can be identified
• the addition of inorganic fertilizer or compost to soil can alleviate these deficiencies
• stunting of growth, wilting of the plant and changes in color all indicate nutrient deficiencies

Question 29

nutrient deficiencies

Answer 29

nitrogen:
-most common
-stunted growth and yellow/green leaves
-affects the older leaves first
phosphorus:
-second most common
-sometimes a purplish color
-reduced growth rate
-spindly and brittle new growth
potassium:
-yellow leaves with brown margin
-localize symptoms 
-stunted growth

Question 30

mycorrhizal fungi

Answer 30

• relationships with other organisms help a plant to obtain essential nutrients
• many plants form mycorrhizae
• a network of fungi threads that act to increase the plants absorptive capacity
• in exchange the fungus receives some nutrients from the plant
• two types:
  1) sndomycorhizae: found inside of the root (most common)
  2) ectomycorrhizae: fungus is located on the root surface
• associated with woody plant species

Question 31

nitrogen dependency

Answer 31

• plants depend on bacteria to supply
• atmospheric nitrogen is in the form N2 which plants cannot use
• nitrogen supplies in the soil are use instead
• soil bacteria convert N2 from the air into forms utilizable by the plant
• ex) nitrate ions (NO3)2- and ammonium ions (NH4+)
• this process of converting nitrogen form the atmosphere into alternate forms is called nitrogen fixation

Question 32

plant parasites

Answer 32

• some plants have evolved parasitic ways of obtaining food from other plants
• parasites:
• a plant that is not capable of photosynethesis may tap into anothers plants vascular system and absorb organic molecules from the plant
• carnivorous plants obtain some nutrients from animal tissue ex) use insects as a source of nitrogen
• epiphytes are non-parasitic but use other plants to anchor themselves
• for support
• orchids