Lecture 6

Question 1

Two main tissues for transport

Answer 1

Xylem: transports sap, upward only, tracheids and vessel elements
Phloem: transports sugar water, all directions, sieve tube elements

Question 2

Transpiration Tension Cohesion Hypothesis

Answer 2

1) Water is being pulled out of moist cells in leaf by the atmosphere. Atmosphere has really low water potential
2) As water is being pulled out of cells, causes water to be pulled out of adjacent tissues, causing tension in the xylem
3) Water sticks together via hydrogen bonds (cohesion)
4) Tension in xylem creates negative pressure. Pressure potential at top of plant is lower (more negative) than at bottom
5) Water flows up the plant via tracheids and vessel elements
6) Water enters roots via osmosis

Question 3

Facts about Transpiration Tension Cohesion Hypothesis

Answer 3

-Passive process, doesn’t require energy because tracheids and vessel elements are dead
highest to lowest in water potential

Question 4

Stomates

Answer 4

where gas exchange occurs

-flanked by guard cells

Question 5

Guard cells

Answer 5

• open and close the stomate
• turgid/ filled with fluid, stomate open
• flaccid/ no fluid, stomate is closed

Question 6

How to open stomate

Answer 6

Guard cells to pump K+ ions into cell. Increases osmotic potential, water flows inside cell and stomate open

Question 7

Cues to open stomates

Answer 7

• light
• CO2 depletion
• circadian rhythm

Question 8

Close stomate

Answer 8

Abscisic acid (hormone) pumps K+ out of cell, closes stomate

Question 9

Phloem flow: Pressure-flow hypothesis

Answer 9

• from source to sink
  1) Companion cell has sucrose, sucrose enters phloem. Phloem increases in solute potential, water enters phloem from nearby xylem.
  2) Water entering creates positive pressure, sugar water flows down to sink where pressure is lower
  3) Sucrose goes out of phloem into companion cell at the sink
  4) Sink is decreasing in osmotic potential, water spontaneously flows to xylem where water potential is the lowest
  5) Water moves up xylem due to negative pressure

Question 10

Source and sink depend on the time of year

Answer 10

summer and fall right hand side, spring left hand side

Question 11

aphids

Answer 11

eat phloem fluid

Question 12

Photosynthesis

Answer 12

Source of oxygen in atmosphere
50% terrestrial plants
50% marine phytoplankton and macroalgae
First step in moving energy into the living world, the source of all energy in ecosystems

Question 13

Photosynthesis equation to make one glucose

Answer 13

6CO2 + 12H2O —-> C6H12O6 + 6O2 +6H2O

Question 14

CO2

Answer 14

electron accepter/gets reduced

Question 15

H2O

Answer 15

electron doner/ gets oxidized

Question 16

2 Stages of photosynthesis

Answer 16

1) Light reactions: occur in thylakoid, need light

2) Calvin cycle: occur in stoma, don’t need light

Question 17

Light reaction steps

Answer 17

1- Light hits chlorophyll
2- electrons bounce to higher energy level and off of chlorophyll
3- Chl steals electrons from H2O, causing photolysis: splitting water to release O2
4- NADP+ + 2e +H+ reacts to produce NADPH
5- ADP + Pi yields ATP

Question 18

Overview of light reactions

Answer 18

Converts light into:

• NADPH
• ATP via photophosphorylation
• O2 from photolysis of water

Question 19

Light reaction equation

Answer 19

Light + H2O + ADP + P + NADP+ + 2E + H+ —> ATP + NADPH + O2

Question 20

NADP+ AND NAD+

Answer 20

-oxidizing agents
-gain electrons
NADP+ + 2E +H+ —> NADPH

Question 21

NADPH and NADH

Answer 21

• reducing agents

- lose electrons

Question 22

Why is chlorophyll green

Answer 22

doesn’t absorb green wavelengths, reflects green wavelength
chl a: all photosynthetic organism
chl b: accessory pigment, extends wavelengths

Question 23

Dark Reactions/ Calvin cycle

Answer 23

• doesnt require light
• occur in stroma
• produce sugar
• supply light rxns with NADP+ AND ADP +P

Question 24

Calvin cycle steps

Answer 24

CO2 comes in, rubisco takes C off and puts in on RuBP (ribulose bi-phosphate) making it a 6 carbon sugar.
RuBP breaks into two three carbon sugars called 3-Phosphoglyerate, C3 photosynthesis.
3-Phosphoglyerate + NADPH + ATP–> G3P glyceraldehyde-3-phosphate
makes 6 G3P, one gets shunted off
5 G3P turn into 5 glucose
5 glucose turn into 3 RuBP
Produces ADP + P and NADP+ to give to light reactions cycle

Question 25

Dark reactions equation

Answer 25

CO2 + ATP + NADPH —> sugar + ADP + P + NADP+

Question 26

Rubisco

Answer 26

-most abundant and important protein
-dual nature
-Ribulose 1, 5-biphosphate carboxylase oxygenase
grabs co2 makes o2

Question 27

A plant experiencing dry conditions

Answer 27

-Not enough water to supply