What do CO4 plants use to minimize cost of photorespiration? What does it yield?
They incorporate CO2 into 4 carbon compounds in mesophyll cells
What enzyme is required to do this?
Why does this enzyme work?
PEP carboxylase has a higher affinity for CO2 even when concentrations are low.
Where are the 4 carbon compounds exported to once produced?
Bundle sheath cells
What is the main role of the bundle sheath cells?
Hold 4 carbon compounds which release Co2 that goes into calvin cylcle.
Where are C4 plants most abundant? Give an example of one...
High light, high temp, semi-arid environments Corn
What does CAM stand for and what is a characteristic of plants that have it...
Crassulacean Acid Metabolism Plants capture CO2 at night, release CO2 into Calvin cycle during day
What happens during the day for CAM plants?
Stoma closed, plants use stored CO2
What does water use efficiency depend on?
rate of carbon gained via photosynthesis vs water lost through transpiration
Carbohydrates are transported across long distances in the form of ...
Most green plants store carbohydrates in the form of ...
What is sucrose?
disaccharide of glucose and fructose
What is starch?
polysaccharide of glucose monomers
What is the difference between the glucose monomers in starch vs cellulose?
starch - linear, alpha glucose cellulose - one rightside up, one righside down, beta glucose
Name 2 different forms of starch...
1. amylose 2. amylopectin
process of moving sugars in the phloem
Name 3 important components of translocation in the phloem...
1. sieve tube element 2. sieve plate 3. companion cells
What is the purpose of the sieve plates?
Facilitate movement of fluids between cells.
Name 2 important features of both sieve tube element and companion cells...
1. Sieve tube elements - living, contain no nucleus, ribosomes, vacuole, and cytoskeleton 2. Companion cells - living, do contain nucleus, ribosomes, and many mitochondria
Name 2 pathways through which sucrose may enter sieve tube element...
Across membrane, or plasmodesmata in companion cell
Name the 4 steps of translocation...
1. load sugar 2. load water 3. unloading sugar 4. recycle water
What kind of pressure drives translocation?
positive pressure, flow goes down
Describe the movement of sucrose across a membrane...
Sucrose moves through cotransporter which also channels H+ ions from high concentration to low concentration. Proton pump on the other hand uses ATP energy to transport H+ ions from low to high concentrations.
What happens at the sink?
Concentration of sucrose is higher than outside of sieve tube so sucrose leaves via diffusion.
What 3 other things can be transported via the phloem?
What is the effect of plant viruses on plasmodesmata?
What drives plant growth?
What does being annual mean for a plant?
It completes its growth cycle in a year.
What does biennial mean?
the plant requires two or fewer growing seasons
What are meristems made of ?
What kind of growth do meristems allow for?
Where are apical meristems located?
tips of roots and shoots at axillary buds of shoots
What is the function of apical meristems?
elongate shoots and roots primary growth
Where are lateral meristems located?
What is the purpose of lateral meristems?
add thickness to woody plants secondary growth
What two things do meristems give rise to?
Initials and derivatives
What happens to initials?
They stay in the meristem
What happens to derivatives?
They become specialized in developing tissues
What is the role of the apical bud?
protection of main shoot meristem
What is the role of the axillary bud?
protection of branch shoot meristem
Name the 3 zones of a root...
1. zone of differentiation 2. zone of elongation 3. zone of cell division (root cap and apical meristem)
What is the function of the root cap?
protection of the root apical meristem
From where do lateral roots arise?
from the pericycle
From where do leaves arise?
leaf primordia along sides of apical meristem
What happens to the meristematic cells left at the base of leaf primordia?
They develop into axillary buds
Name 2 types of lateral meristem?
Vascular and cork cambium
What is the role played by vascular cambium?
adds layers of vascular tissue called secondary xylem(wood) and pholem
What is the function of the cork cambium?
Replaces epidermis with periderm, which is tougher and thicker
Describe the cells that make up the vascular cambium...
Meristematic cells one cell layer thick Develops from undifferentiated parenchyma cells
An interesting note, xylem typically consists of either vessels or tracheids. However both can be found in where?
flowering plants (vessel elements)
Why does wood formed in the spring have thin cell walls?
To maximize water delivery
Why does late wood in the fall have thicker cell walls?
What does the bark consist of ?
everything from periderm to cork cambium (includes secondary phloem)
What is the role of lenticels? and where are they located?
allow for gas exchange between living stem or roots and outside, located in periderm
What are the 3 steps in the signal transduction pathway?
1. reception 2. transduction 3. response
What is the one main component in reception?
Who are the main players in transduction and what 2 things do they do?
Second messengers 1. transfer signals 2. amplify signals from receptors to proteins that will trigger responses
What are the 2 ways that the signal transduction pathway can increase enzyme activity?
transcriptional regulation post translational modification
What is etiolation?
When plants are grown without exposure to light
What does cGMP mean? What is its role in the signal transduction pathway?
cyclic Guanosine Monophosphate Phytochrome is a receptor protein activated by light, it communicates with cyclic Guanosine Monophosphate ( a second messenger) which transfers signal and activate a specific protein kinase
What is the role of Ca2+ levels in the signal transduction pathway?
Phytochromes activated by light communicate with Ca2+ channel, opening it and allowing ions to transfer signals again to a specific protein kinase specifically cytoskeletal proteins and enzymes
What is the response step then?
Protein kinases activate transcription factors in nucleus triggering transcription, then translation outside of nucleus, then de-etiolation (greening response proteins)
What 2 things does transduction often involve?
1. Protein kinases that phosphorylate proteins 2. Protein phosphates that de-phosphorylate proteins
What are the 2 effects of such enzyme activities?
1. Can regulate transcription 2. Can modify proteins post-translation
What is the difference between positive and negative transcription factors?
Positive transcription factors are proteins that increase the transcription of specific genes while negative TF are proteins that decrease the transcription of specific genes
What does post-translational modification involve ?
modification of existing proteins in signal response phosphorylation of specific amino acids
What function do hormones play in signal transduction pathway? What 3 key aspects do they affect?
plant growth regulators they affect division, elongation, and differentiation of cells tropism
greek tropos - to turn any response resulting in curvature of organs towards or away from a stimulus
What was the main topic of Charles Darwin and his son Francis' experiment in late 1800s?
What were the results?
Postulated that coleoptile tip hit by sunlight will cause grass seedling to bend toward light because coleoptile transmits signal to zone of elongation.
What did Peter Boysen-James demonstrate in 1913?
The signal to the elongating zone is a mobile chemical substance.
Who took the experiment even further? What did he discover?
Frits Went. Extracted chemical messenger for phototropism known as auxin
Define auxin and 3 noteworthy characteristics...
Any chemical that promotes elongation of coleoptiles 1. Auxin transporter proteins move the hormone from the basal end of the cell to the apical end of the neighboring cell 2. moves from tip of shoot to base 3. only certain concentrations of auxin work in cell elongation
Give an example of a common auxin...
indoleactic acid (IAA)
Where are auxin transporter proteins located? What is their function?
In xylem parenchyma at base of cells. Function is to move auxin out of cells.
Describe the acid growth hypothesis...
Auxin stimulate proton pumps that lower the pH in the cell wall. This causes expansins to be released that break the hydrogen bonds between cellulose microfibrils and crosslinking polysaccharides. The microfibrils are loosened and can slide so the cell elongates.
How does expansion rely on turgor pressure?
Increasing the proton gradient increases ion uptake into the cell. This lowers water potential and caused water to flow in. The increase in turgor pressure and the plastic cell wall allows for cellular expansion.
What other 5 functions does auxin perform?
Root formation Root branching Herbicide (overdoses kill eudicots) Affects secondary growth by increasing cell division vascular cambium and promoting differentiation in secondary xylem Gravitropism
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