Plants: Lecture 5 Flashcards
Types of Meristems?
There are two types of meristems:
Apical Meristems
Lateral Meristems
Apical meristems?
Responsible for primary growth in roots and shoots. They are in all vascular plants.
Lateral meristems?
Composed of the vascular cambium and cork cambium, in change of secondary growth in all woody plants - not monocots. Only in woody eudicots and conifers. They make wood and bark.
What is there product of secondary growth and what does it occur in?
Secondary growth produces wood and bark, and occurs in conifers and woody eudicots.
Where is the vascular cambium?
It is located between the xylem and phloem of the primary tissues in the vascular bundle.
What is made by the vascular cambium?
The vascular cambium makes secondary xylem and secondary phloem.
What is the secondary xylem?
It is the tissue made inward from the vascular cambium. It is also what we traditionally call wood and is made by the vascular cambium
What is the secondary phloem?
Secondary phloem is made outward from the vascular cambium, and controls the flow of sugar water.
Primary phloem and xylem after vascular cambium development?
The primary xylem and phloem are fully non-functional after the development of the secondary xylem and phloem. They are also completely split apart at this point.
What does the cork cambium make?
The cork cambium is what makes the protoderm (bark/cork of the tree). Both the secondary phloem and everything outward from it make up the bark of a tree.
Palm trees not being a real tree?
They have lignin but don’t go through the process of making a vascular and cork cambium so they are not actually woody.
Creation of secondary xylem and phloem?
- Secondary xylem is to the inside and makes wood
- Secondary phloem is to the outside and part of bark.
- More Vascular cambium added to increase in circumference.
- Rays of parenchyma are present for lateral transport
How do trees thicken?
Most of the thickening is from the secondary xylem, and each year it thickens much more than the phloem does, causing the creation of rings.
What else does the vascular cambium make?
The vascular cambium is also charged with making rays.
What do fusiform initials make?
Fusiform initials make tracheids and vessel elements (xylem) alongside sieve elements (phloem).
- They are tapered cells that make these items.
What do ray initials make?
Ray initials make rays in both xylem and phloem. Rays are tissues that help move fluids laterally across the plant.
Heartwood vs. Sapwood?
Heartwood is darker and older wood, whereas sapwood is younger and lighter wood.
- It is thought that heartwood might have materials that aren’t very good for the cell within them.
What is wood and what polymer is in it?
Wood is secondary xylem.
- The polymer lignin is in the secondary walls of tracheids and vessel elements.
- In other words, wood is woody because the walls of tracheids and vessel elements are impregnanted with large quantities of lignin.
Why are there growth rings?
Growth starts and stops based on what season it is. This rhythm creates the rings we see, which represent 1 year each.
What is lignin?
Lignin is deposited in cell walls, filling spaces and binding cellulose, hemicellulose, and pectin.
- It gives strength to bark and wood
- It can be seen in the cell walls of non-woody plants as well (bamboo, palms, wheat straw)
What trend do we see when looking at tree rings under a microscope?
We see that there are bigger cells at the beginning of the year, which is why we are able to differentiate years. They get smaller as the meristems split more and more.
What is the cork cambium?
It is a new type of lateral meristem.
- It arises from the cylinder of cortex cells outside the vascular cambium and secondary phloem.
- It produces the 3 layers of the periderm.
What are the three layers of the periderm?
- Phelloderm to the inside (a thin layer of parenchymal cells)
- The cork cambium itself
- Cork to the outside (Suberized, dead cells that protect the woody plant from pathogens and losing water).
Components of bark?
All tissues outside of the vascular cambium.
- Living phloem
- Cork Cambium
- Cork
*latter two also make up the periderm
What is the technical (biological) meaning of sap?
Sap is composed of the water and minerals that go upward from the soil through the xylem.
1st Law of thermodynamics?
We cannot create nor destroy energy, it can only change from one form to another
- electricity to light
What is the 2nd law of thermodynamics?
Energy spontaneously tends to flow from being concentrated in one place to becoming spread out
- In other words: for a combined system and surroundings, entropy will never decrease.
The second law in life?
The movement of fluid in plants follows the second law of thermodynamics.
- The most equitable distribution of energy corresponds to maximum entropy
Examples of the second law in life?
- Osmosis
- Diffusion
- Fluid movement because of differences in hydrostatic (water) pressure
Baking soda + water example?
Water goes to the baking soda spontaneously. This is what happens in plants. Adding solute causes water to want to go there because of a difference in potential energy
Transport overview?
Water and minerals are taken up the roots - the ascent of sap. CO2 goes in and O2 goes out. When light comes in, sugar is transported downward toward the roots. Root respiration also has CO2 out and O2 in as a gas exchange.
What are the different routes of water movement?
Apoplastic: travels within the cell membranes
Symplastic: travels within the cytosol
Trans-membrane: travels both within and alongside the membrane at different times.
What is cytoplasm vs. cytosol?
Cytoplasm: all material inside the cell membrane
Cytosol: the part of the cytoplasm excluding the organelles.
Cell walls hydrophilic?
Cell walls are generally hydrophilic and soak a lot of water up.
What is cellulose?
- main component of cell walls
- highly water absorbent
- polysaccharide
- most abundant organic compound on earth
Uses of cellulose?
- Rayon
- Cotton
- Paper
- Cellulose sponges
Water potential energy (Psi)?
Water potential energy is measured in megapascals (MPa)
- 1 MPa = ~10 atmospheres (bars)
What does water potential consist of?
It combines the effects of solute concentration and pressure.
What direction does water flow in?
Water flows from regions of higher to lower water potential.
When is Psi = 0?
it equals 0 MPa for pure water at sea level and at room temperature.
- It determines the direction of the movement of water.
Adding solutes - Water potential?
Adding solutes lowers water potential where the solutes are.
Positive pressure - water potential?
Positive pressure means that pressure is being put on one side - therefore it will move to the opposite side.
negative pressure - water potential?
This is also known as tension and pulls toward, creating lower water potential in the direction of the pulling
Cell in sugar water?
If the potential is less than the cellar rest than the water in the cell will go into the sugar water, causing the membrane to shrivel inwards.
Adding to pure water?
Adding to pure water will mean that the potential inside the ell is greater, therefore more water will be pulled into the cell.
What is plasmolysis?
Plasmolysis is the loss of water from the cell by osmosis. This results in the cell membrane becoming separated from the cell wall.
Lateral transport of water and minerals?
Water enters the root hairs and travels toward the xylem in the middle of the cell. It cannot pass the casparian strip and instead goes around and has to cross the cell membrane - this gives it the opportunity to turn away unwanted/unneeded components that the cell does not benefit from.
Apoplast?
nonliving continuum outside the cytosol, including:
- Cell walls
- Xylem cells
- Extracellular spaces
Symplast?
Continuum of cytosol is connected by the plasmodesmata.
The endodermis?
A cylinder that is one cell thick
Stele?
All the material inside the endodermis.
- Xylem and phloem
- Pith
- Pericycle (origin of lateral roots)
Casparian Strip?
- Where primary walls and middle lamella were
- Waterproof and impermeable to ions: suberin
- All water and ions entering the xylem must pass through the endodermal cells, and must cross the cell membrane
What is Mycorrhizae (mycorrhizal fungi)?
A mutualism between plants and fungi.
- They increase root surface area
- Aid the absorption of materials into the roots.
- known as a mycorrhizal association.
Pathway of water and minerals?
- Soil
- Root hair or micorrhizae
- Cortex
- Endodermis
- Xylem
- Atmosphere
- Every step has a lower water potential and therefore moves spontaneously without any energy expended.
Theoretical possibilities of water and mineral movement?
- Capillary Action
- Pumps
From above: atmospheric pressure.
From below: root pressure - Transpiration - Cohesion - Tension mechanism
Steps of the transpiration-cohesion- tension mechanism?
- Water evaporates from moist cells in leaf stomates (low atmospheric pressure) through transpiration
- Water potential is lowered at air-water interface, causing negative pressure (tension) in the xylem
- Hydrogen bonds hold water molecules together (cohesion)
- Xylem under tension gradient: pressure potential is lowest at the top
- Thus, water is pulled up by pressure gradient (difference in pressure potential not solute)
- Water and minerals enter root by osmosis.
Generation of transpirational pull?
Negative pressure (tension) at the air-water interface in the leaf is the basis of transpirational pull, which draws water out of xylem.
TTC mechanism: Facts?
- total path in xylem from highest to lowest water potential
- Passive process
- Tracheids and vessel elements are dead cells
- Moves upward only.
2 main components of TTC?
1) water spontaneously moves from higher to lower pressure
2) air has lower pressure and creates a strong pull creating the most pressure (most negative) at the top.
Stomates open?
Cues to open include:
- Light
- CO2 depletion
- Circadian rhythm
Dry conditions effect on stomata?
Abscisic acid: hormone
- Causes potassium to leave guard cells
- Stimulates stomate closure
Xylem movement?
Passive, only moves in one direction.
Phloem movement?
Requires energy and active.
