Xylem and phloem Flashcards
What is larger, a phloem or a xylem?
Xylem
What has xylems?
vascular plants
What are vacular plants?
Plants that have speciali`ed tissue whih can move water and dissolved minerals (xylem)
and move sugards produced by photosynthesis(phloem)
What does the xylem do?
It moved water and dissolved minerals
What does the phloem do?
It moves sugars from photosynthesis from source to sink.
How do the roots passively absorb water?
They uptake mineral ions against their concentration gradient via active transport. This makes the roots have a higher solute concentration than the soil, the water passively moves from hypotonic to hyperonic solutions, up the root.
As soon as water is in the root, what two pathways can the water go in order to get to the xylem?
Apoplastic or symplastic
Describe apoplastic water transport
Water is moved between cells via their extracellular space
Describe sumplastic pathway of water
Water is transported in the cytoplasm of cells.
What is plasmodesmata?
The little corridor which connects the cytoplasm of the cells.
What is the symplast?
The continuum of the plants cytoplasm because of the plasmodesmata
From where to where does the xylem trasnport water?
From the roots to leaves.
What is the structure of a xylem?
It is a continuous pipe
stacked tubular cells
made up of dead cells
Explain why the cells in the xylem are dead?
When water passively moved into the plant as soon as it began growing vertically, the force into he xylem completely bursted the cells and any organelles within them. Only the cell walls remained which make up the exterior of the xylem.
What does the deadness of the xylem hint at?
All the water moves passively
How is the plant/xylem held upright?
The xylem is strengthened by lignin( a complex polymer) that forms rings and spirals in the xylem tube.
Where does water avaporate?
Via the stomata
What do stomata allow?
Gas exchange in and out of leaves
Explain the structure of stomata.
Each pore is surrounded by guard cells
What do guard cells do?
They open and close the pores
What organelles do guard cells have?
Vacuole, nucleus and chloroplasts
Define evaporation
The loss of H20 out of the leaf when stomata is open
Explain the transpirational pull.
There is a pull due to ongoing evaporation out of stomata. As water evaporates, it “pulls” the next one in line.
How does temperature effect evaporation?
Higher temperatures mean higher collisions, evaporation increase
Why does light intensity increase evaporation rate?
Higher light intensity means greater photosynthetic rate. If guard cells photosynthesize more, they become hypertonic. Water moves into the cells, causing them to cell, opening the pores, increasing evaporation.
How does humidity effect evaporation rate?
Water always moves down a concentration gradient. If the outside environment is packed with water (high conc. of water) water has less desire to move out and does so more slowly.
Explain the effect of wind speed on evaporation.
When water leaves the stomata, water can build up on the leaf. Wind removes this and increases the chance of water following its concentration gradient.
What are xerophytes?
Plants adapted to drought environment
Why is a deep root system important to xerophytes?
As much water as possible can be absorbed
Explain adaptation of xerophytes.
- reduced leaf size to reduce evaporation
- thick waxy cuticle for water retention
- deep root systems
- rolled leaves
- leaf hairs- capture water
- low growth to ground(less wind)
What is the effect of rolled leaves for xerophytes?
They trap evaporation and create a local humidity, reducing evaporation rate.
What is CAM photosynthesis?
When stomata only opens at night. They store and absorb CO2 during night to perform photosynthesis during the day without opening the stomata.
At night the temp is lower, reducing evaporation rates.
What devivce measured transpiration?
potometer- measures the loss of water. The top layer of water is covered in oil to reduce evaporation
mass potometer- loss of water mass
volume- loss of volume
pressure- as water moves into plant, pressure in tube decreases
Measuring the rate of evaporation
volume lost / time
What is the sugary water in the phloem?
Sap
what are the long tubes which sap flows through called?
Sieve tube cells. They have pores in teh bottom connecting them to otehr sieve tube cells which allow unobstructed flow of sap
What is teh structure of sieve tube cells like?
No nucleus or mitochondria which increase volume of sap, cell wall is thick and strong(allows pressure)
Explain companion cells.
They are adjacent to sieve tube cells, have many mitochondria, membrane has infoldings to increase surface area.
WHy is glucose converted into sucrose?
Glucose is too reactive.
What is translocation?
The movement of sap from source to sink
What is a source?
Any sygar exporting reigon that exceeds its own needs
What is a sink?
Any importing reigon whos sugar production doenst meet its needs
What is phloem transport?
Bidirectional
Step by step of translocation
Glucose is made during photosynthesis. In source, it is converted to sucrose). Sucrose is actively pumped into a companion cell via the sucrose H+ cotransport protein. From the companion cell, sucrose moves to sieve tube cell through plasmodesmata. This is caled phloem loading.
Phloem loading makes the sieve tube cell hypertonic at the site. Naturally, water from the xyem moves into the phloem via osmosis. Phloem sap is pushed along a pressure gradient to the sink.
“Phloem unloading”. Sucrose enters companion cells via plasmodesmata. Phloem becomes hypotonic and pressure reduces.
Sucrose is converted to starch for longer energy storage, or converted back into glucose to fuel metabolic reactions.
Explain how exactly the cotransporter works.
The cotransporter protein pumps sucrose into companion cell, along the way protons are taken with it. A concentration gradient is created and protons move back into source/sink thorugh atp synthase where ATP is passively generated.
What are aphids?
Animals which feed on sap, they easily locate phloems.
Describe how aphids feed on sap.
The dont suck on it, it bursts into their mothpieces.
How are aphids used to sudy sap.
Humans cant find phloem manually, aphids can. Scientists let aphids feed on sap and then cut off their mouthpeace. The mouth remains in the phloem, insect is removed and phloem sap is bursting out. Scientists can now analyze the sap
How were aphids used together with radioactive carbon to study translocation?
Only one leaf was exposed to radioactive C14. The plant photosynthesized , C14 became a part of glucose. It gets converted into sucrose and enters the phloem. Aphids are allowed to feed on sap at different distances from the source. The style is removed and sap is analyzed for C14. Scientists see how long it takes the C14 to reach certain distances, understanding the speed of translocation.
What are the regions from which plants grow called?
Meristems
What are features of meristems?
- can become any cell type
- can divide as often as desired
What are the two types of meristems?
apical and lateral meristems
When cell divides, what happens to totipotent features?
One of the cells always maintains it.
When parts of a meristem grow, remaining meristem tissue does what?
It turns into an inactive axillary bud.
When can axillary buds grow?
Eitehr when they are far away enough from the apical meristem, or if the apical meristem is removed (low hormone concentrations)
What plant hormone influences plant growth?
Auxin
How does auxin function?
By turning on transcription
How is the distribution of auxin important?
When auxin simulates growth in roots, lateral buds are dormant.
List roots, lateral, and apical bud from their ability to utilize high au≈in concentration from least to most
roots, lateral, and apical bud
What is apical dominance
When the main stem(shoot) grows the most due to high auxin concentrations. This inhibits lateral growth nearby, therefore the tsems furthest away from the apical shoot are the longest
What is pruning?
Cutting off the apical meristem to allow lateral growth.
What distributes auxin?
Efflux pumps.
What can effluc pumps change?
Their position in the membrane, They can move.
What is tropism
The turning of all parts of a plant in a particular direction in desponse to external stimulus. (eg. sunlight)
What is gravitropism?
The growth of a plant in response to gravity “pulling” on it. (roots growth downwards).
Compare the presence of auxin in roots versus stems/ branches?
In roots, high concentrations of auxin mean inhibited growth, If auxin sinks to the bottom of the tip, the the lower horizontal side is inhibited. The upper half elongates. Therefore, the tip turns downwards.
In stems/branches, higher concentration promote growth. So if, via gravity, auxin is in the bottom of the branch horizontally, then that side elongates, and the top inhibits. Branches grow upwards.
What is phototropism?
Plants growing towards the sun.
Explain phototropism.
Auxin moves to the shady side of the shoot. Auxin loosens up cellulose in the cell wall. This allows them to elongate. Beding towards the sun.
Explain how auxin makes cells grow.
It loosens up the cellulose material, allowing more flexible growth,
Explain micropropagation.
Mristem tissue is seected from parent plant. This is called the explant. The explant is gron on sterile nutrient agar and treated with growth hormones.
Different hormone conc. allow shoot and root growth. When the plant is ready, it can be transferred again.
What does micropropagation allow?
- breeding of desireable species
- fast growth
- virus free
How can you cut a plants stem in order to grow an entire new plant?
But beneath node
remove leaves
dip into auxin
insert into water
Examples of natural cloning in plants
Bulbs
vegetative propagration
Tubers
Runners
What is florigen?
The hormone which stimulates transcription in order to stat flowering
Explain flowering
A change in season alters teh time of day and night. Phytochrome (pigment protein) in the leaf recognizes this and activates florigen. Florigen moves through the shoot to the apical meristem and triggers cell differentiation(trigger genes related to flowering). Meristem shifts from making stems and leaves to flowers.
Where is florigen made?
In the companion cell
What are the differences between phytochrome red and phytochrome far-red?
PT red is activated by red light (day)
PT far red is activated by far red light (night)
How are PT red and PT far -red related?
They are the same molecule which shifts between two shapes.
What causes the shift from PR to PFR?
a reaction with light from the day
Wha happens to PR when it absorbs light from the day?
It immediatey shifts to PFR.
What happens to PFR when it absorbs far-red light?
It slowly shifts to PR
What happens to PR in summer?
There is more time to convert PR quickly to PFR.
What happens to Pfr in the winter?
Its dark for longer so Pfr has more time to turn back into Pr.
In short day plants:
They require less exposure to light. Pfr inhibits flowering as the flower only flowers when the night is long and Pfr is low.
In long day plants:
They require lots of Pfr to flower. The nights are short so that less Pfr is converted back into the inactive version of the molecule. Needs low concentrations of Pr
How is phytochrome understanding used in real life?
Plants are often grown off season to increase agricultureal yield. Greenhouses with speciallights are used to trick plants.
What is pollinization?
Moving pollen from an anther to a stigma,
What is fertilization?
The fusion of a haploid egg and haploid sperm cell cell to create a diploid zygote.
How does pollen on the stigmae promote fertilization?
After pollen has been placed on the stigma, a long tube is grown by the pollen down into the ovary and ovules where one of the sperm cells fertilizes the egg. The other sperm fertilizes the two polar nucleii, forming a triploid food source for the embryo.
What is a seed?
A small embryonic plant enclosed in a cover called seed coar eith some stored food.
What is the hylum?
The “scar” in the seed from bein attached to bellybutton.
What is a pumule
A pair of minature leaves from the seed
What is a micropyle?
Where the sperm entered the ovule
- this is where water enters during germination
