plants Flashcards
3 reasons why plants require transport systems
- many plants are large multicellular organisms with a low surface area to vol ratio
- plants photosynthesise and exchange gasses at the leaves but get water and minerals from the roots- water needs to go up and sugars need to go down
- plants have high metabolic rates and need nutrients delivered efficiently to their cells
co2 is taken up by the leaves and used to produce…
sugars in photosythesis
what does the vascular bundle include
xylem , phloem, cambium, parenchyma
sclerenchyma fibres?
provide additional support to the vascular bundle and the plant as a whole
parenchyma
are living cells that act as packing tissue to separate xylem vessels from phloem and provide them with support
compared to phloem what does xylem look like
larger and non living
state notes about the xylem
- xylem vessels are dead and are stacked end-to-end.
- xylem vessels have no cytoplasm or organelles and no cell walls at their ends that would slow the flow of water
- xylem cells are lined with a waterproof coat made of the polysaccharide lignin
- xylem cells are continuous hollow tubes
talk abt the formation of xylem vessels
- immature xylem vessels are waterproofed when lignin is deposited on the inside of their cell walls.
- this process of lignification kills the cells and allows for max flow of water through the hollow tubes
state adaptations of the xylem
- there are holes in the xylem with no lignification- these are bordered pits
- these bordered pits allow water to move between vessels.
- these vessels are narrow enough to ensure water travels in an unbroken column
- there are no end walls or organelles to impede water flow
what does the phloem transport
assimilates
before h20 can get to the xylem, it must enter through the root. water moves through the plant tissue in the roots in two main ways:
- through the spaces in and between cells- this is the apoplast/cell wall pathway
- through the cytoplasm travelling between cells through pores called plasmodesmata- this pathway is symplastic or vacuolar
talk about root hair cells and how they allow water in
- root hair cells are adapted for the uptake of water and mineral ions, mineral ions are actively transported from the soil into the root hair cell.
- these minerals reduce the water potential of the root hair cell cytoplasm.
- water then enters the root hair cell from the surrounding soil by osmosis ( mineral ions drive osmosis)
once h20 is inside the root cortex, where must it travel to meet the xylem vessels and the medulla.
must travel through the endodermis
what are the 3 routes water can travel through the root cortex
-the apoplastic, vacuolar or symplastic pathway…
what does the casparian strip do
the casparian strip in the endodermis blocks the apoplast/cell wall pathway
what do the cells of the endodermis do
they actively transport mineral ions into the xylem.
water enters the endodermis cells and then the medulla and xylem by osmosis
what are two purposes of the casparian strip
1- creates a checkpoint for plant immune systems before transport through the rest of the plant
2- it blocks water from passing back into the cortex from the xylem (don’t want water going in the wrong direction)- keeps water flowing forwards
what happens once water reaches the leaf
water exits the xylem vessels located in the spongy mesophyll, water travels through the plant tissues of the spongy mesophyll (s,a,v).
- water evaporates off the high sa of the spongy mesophyll.
- water vapour diffuses out the stomata down a water vapour gradient.
what are stomata
pores on the underside of a leaf that allow the leaf to exchange gasses with the external environment.- allow co2 to enter, allows 02 to exit- allows h2o vapour out
whats transpiration
the loss of water from the aerial (parts with air connected to it) parts of the plant mainly through the stomata in the leaves
whats the transpiration stream
there is a constant stream of water travelling from the roots, through the stem and out of the leaves- its an inevitable consequence of gas exchange and doesn’t require ATP.
what are the benefits of a constant supply of water to the leaves.
- maintenance of cell turgidity- gives plant support and strength
- water for metabolic purposes- DNA replication requires H20, so does photosynthesis and respiration
- transport of mineral ions to plant cells- mineral ions wouldn’t be able to dissolve in any solution up the xylem
- evaporating water keeps plant leaves cool in the sun- water takes away latent heat of vaporisation causing the plant to cool.
what type of pressure is the column of water pulled up the xylem under?
negative pressure
whats negative pressure
where something is being pulled to an area of less pressure- draws up water- gradient of there being a lot of it to less of it
what happens if xylem vessels are broken
- then air gets sucked in
- the plant loses its ability to draw water up
why does the transpiration stream operate without energy from the plant
because adhesion and cohesion keeps the water moving upwards
what is the evaporation at the leaf facilitated by
by high surface area and exposure
water molecules pull other water molecules with them due to…
cohesion
whats cohesion
the attraction between water molecules due to hydrogen bonds
what do water molecules adhere to in the xylem
hydrophilic polysaccharides
whats adhesion
the attraction of water molecules to hydrophilic substances
whats capillary action, talk abt this force and where its useful
the forces of adhesion push water along narrow vessels in a process called capillary action, packing thin xylem vessels at high density maximises this effect, overall this force is quite weak- its more useful in short plants
talk about root pressure- include stuff about Caspian strip
the roots of the plant generate positive pressure at the base of plant stems.
- mineral ions are actively transported from the endodermis into the xylem and water follows by osmosis
- the Caspian strip prevents water from travelling back into the roots
- water is constantly being pushed into the xylem via osmosis
- root pressure generates forces that can push water a few meters up the xylem
what are the factors affecting transpiration rate
LIGHT- the lighter, the faster the transpiration rate- stomata opens when it gets light so co2 can diffuse into the leaf for photosynthesis. when its dark=closed stomata=little transpiration
TEMPERATURE- higher temp= faster transpiration- warmer water molecules=more energy so evaporate faster- increases water pot grad between inside and outside of leaf making water diffuse out faster
HUMIDITY- lower humidity= faster transpiration-increases water pot grad between inside and outside of leaf making water diffuse out faster
AIR FLOW- more wind= faster transpiration rate. lots of air movement blows away water molecules around the stomata, increases water pot grad so faster transpiration rate
what is transpiration a consequence of
gas exchange
what can be used to estimate transpiration rates
a potometer
plants are highly metabolically active so what do they need to carefully regulate
their water level
whats the main point of water loss in plants
leaves
leaves are adapted to maximise their gas exchange, what negative does this lead to
increased water loss
what are xerophytes
plants adapted to living in dry conditions
what are general features of xerophytes
- thick waxy cuticle
- few stomata (less gas exchange)
- hairs on leaves
- small or needle shaped leaves
- stomata located in pits sunk into the epidermis
why do xerophytes have a thick waxy cuticle
for increased diffusion distance=less water loss
why do xerophytes have hairs on leaves
-slows air movement, humidity is with kept so less water loss
why do xerophytes have small or needle shaped leaves
to reduce sa to vol ratio so less area for water to be exchanged so less water loss
why do xerophytes have stomata located in pits sunk into the epidermis
creates a local environment in the pit
-the pit can maintain humidity (water trapped)
…so less water loss
what are the two examples of xerophytes
cacti and marram grass
what typical xerophyte adaptations do cacti have
- fewer and sunken stomata
- hairy leaves
- small/ needle shaped leaves
what are additional adaptations that cacti have to help them cope with dry conditions (in terms of water storage)
-water storage ( fleshy body to retain water)
-spines to deter animals stealing water
-small growth, doesn’t flower much= low metabolic rate
Thick= reduces sa to vol ratio-less able for water to leave
what are additional adaptations that cacti have to help them cope with dry conditions (in terms of water collection)
wide roots and extensive roots- increases sa for them to gather water
what is marram grass
a xerophyte adapted to living in costal sand dunes
whats the most common trait of marram grass and why is this an advantage
the rolled leaf:
- reduces sa to vol ratio= less water loss
- humidity is trapped in the leaf so less water loss
what are other adaptations apart from a rolled leaf of marram grass that helps reduce water loss
- sunken stomata in pits
- many hairs (trap air and humidity)
- thick waxy cuticle (reduce diffusion)
what are hydrophytes
plants specifically adapted to live in water rather than soil
what are the challenges that hydrophytes face
- hydrophytes have to get oxygen to submerged tissue
- hydrophytes have to keep afloat to get sunlight
- high humidity above the surface of the water greatly reduces the rate of transpiration
what are the adaptations of hydrophytes
- the leaves have large air spaces in their spongy mesophyll to give them buoyancy.
- the leaf stems have many air spaces to allow oxygen to diffuse to the roots
- stomata are on the upper surface of the leaves to allow gas exchange
how do many hydrophytes increase their transpiration rates
by using hydathodes
what are hydathodes
structures in plants that release water droplets which may then evaporate from the leaf surface
explain why non xerophytic plants are able to photosynthesise despite evaporation of water from their leaves
water for photosynthesis can be provided by osmosis from the xylem, driven by the transpiration stream which is driven by the evaporation of water from the leaves in non-xerophytic plants.
what two things need to both travel up and down in a plant
assimilates and sugars
what two things need to both travel up and down in a plant
assimilates and sugars
what tissue are the two transport systems grouped inti
the vascular bundle
what does the phloem transport
assimilates and sugars
phloem tissue consists of two types of cell:
sieve tube elements and companion cells
how are sieve tube elements aligned and what does this allow for
lined end to end to allow the flow of sap
how do sieve tubes maximise space for sap
they have little cytoplasm’s and no nucleus- they’re still alive
they also have sieve plates
what do companion cells do
control transport in the sieve tube elements
what do companion cells contain and why
-they contain many mitochondria because the phloem requires active transport to move sap in translocation
whats translocation
the transport of assimilates through a plant
simple: what is active loading
the process of loading sucrose into the sieve tube elements
outline the steps of active loading
1) H+ ions are pumped out (active transport (requires atp)) from the companion cells to the surrounding leaf tissue creating a diffusion gradient of H+ (later on H+ will diffuse back into the companion cell as there is a lot in leaf tissue)
2) H+ ions diffuse back into the companion cells through cotransporter (takes two thing)proteins bringing sucrose with them.
3) high concentrations of sugar in companion cells cause sucrose to diffuse in to the sieve tube elements
- high hydrostatic pressure (link to source and sink)
what do companion cells actively load sucrose and assimilates into
sieve tube elements
what are sources
parts of plants that load materials into the transport system-( the leaves are a source of assimilates that are transported in the phloem)
what are sinks
parts of the plant where materials are removed from a transport system- roots are a common example
what are sources and sinks connected by
by the phloem
how does a source of material move to a sink
- when the assimilates are actively loaded into the sieve tube element, the water potential at the source decreases
- water from the xylem vessels in the source follows into the sieve tube elements by osmosis
- loading of assimilates and water at the source creates a high hydrostatic pressure.
- sucrose removed at the sink (used by cells now) reduces the water potential of the surrounding cells( they are using the sucrose from the sink)
- water then leaves the sieve tube elements by osmosis
- unloading of assimilates and water reduces the hydrostatic pressure at the sink.
- the difference in hydrostatic pressure between a source and sink creates a pushing force that moves sap to the location it is needed
- this is mass flow
what ahs a high hydrostatic pressure and what has a low hydrostatic pressure
high hydrostatic pressure=source
low hydrostatic pressure= sink
What creates the pushing force that moves sap from the source to the sink of a plant?
a hydrostatic pressure gradient
state why swelling occurs if there is a cut damaging the phloem
sugars cannot pass the cut so they accumulate above it. This decreases the water potential of the tissues above the cut and water moves in by osmosis. this causes the cells to swell and become turgid
can early leaves photosynthesise
no-they use sugars from stores
describe how guard cells are adapted to their role
- have an unevenly thickened cell wall
- able to change shape/ bend
- has transport proteins
- presence of chloroplasts
- mitochondria for energy
use the cohesion-tension theory to explain how water moves from the roots to the leaves
evaporation at the top of the plant creates tension in the xylem. water molecules stick together to form a chain/ column. The chain is pulled up by tension
give examples of assimilates that are loaded into sieve tube elements
sucrose and amino acids
what’s transpiration
the loss of water vapour from a plant
what’s the transpiration stream
movement of water up xylem vessels from roots to leaves
talk about cross walls in the xylem and phloem
xylem: no end/ cross walls
phloem: perforated cross walls
what are the gaps called between companion cells and sieve tube elements called
plasmodesmata
what type of diffusion is the movement of sucrose and H+ ions through cotransporter ions
facilitated diffusion
