Sources
the sites where organic compounds are loaded into the phloem
What is the movement in the phloem?
translocation
Sinks
it’s where organic compounds are unloaded from the phloem
Where is sucrose made?
in the mesophyll of cells
What is a meristem?
a group of undifferentiated cells which have the ability to continually divide by mitosis
What are the 3 types of meristems?
- apical meristems
- lateral meristems
- intercalary meristems
What is transpiration?
- the loss of water vapour from the stems & leaves of plants
- -> it is the inevitable consequence of gas exchange
Xerophytes
plants that are adapted to grow in dry conditions
e.g cactus
what are the adaptions of xerophytes
- less leaves/spines
- water storage cells in the stem
- vertical branches
- extensive shallow root system
- CAM physiology
- thick waxy cuticle
how are spines an adaption in xerophyites?
less surface area for water loss
CAM physiology
allows cacti to fix co2 at night & release it for photosynthesis during daylight hours
they only open their stomata at night when temp is much lower
how are sugars transported in plants?
- transported in the phloem sap as sucrose
- sucrose is made in mesophyll cells & transported into companion cells, which are found next to sieve elements
- sucrose is then loaded from the companion cells into sieve elements by active transport
- this creates a proton-sucrose symport protein driven by a proton gradient generated by a protein pump
- active transport creates a high concentration of sucrose in the sieve tubes at the source
- this causes water to move from the xylem by osmosis
- this leads to an increase in volume which causes a high hydrostatic pressure in the phloem at the source
- at the sinks, water is unloaded by active transport
- the low solute concentration causes the water to return back to the xylem by osmosis
- this causes a low hydrostatic pressure at the sink
- due to the incompressibility of water, phloem sap travels from a region of high hydrostatic pressure(source) to the region of low hydrostatic pressure(sink)
what type of transport move sucrose from the companion cells into the sieve elements?
active transport
where is the region of high hydrostatic pressure?
at the source
where is the region of low hydrostatic pressure
at the sink
How is the growth of the shoot apex controlled?
by plant hormones
- this includes auxin
Describe the production of plants by micropropagation
- nearly all plants have the ability to develop into a new plant (they are totipotent)
- micropropagation is carried out in sterile conditions
1. a small tissue sample is excised from the shoot apex & sterilised
2. it is placed onto nutrient agar containing equal concentrations of auxin & cytokinin
3. the callus can be split & each part allowed to grow
4. the callus is then transferred onto nutrient agar containing more auxin than cytokinin to promote root development
5. the shoots are then transferred onto utrient agar containing more auxin than cytokinin to promote root development
6. plantlet formed are transferred onto soil
What are the advantages of micropropagation?
- new plants can rapidly be produced in large numbers from a small amount of starting material
- virus-free plants can be produced
- orchids & other rare species can be produced in large numbers
How can short-day plants be made to flower at other times of the year?
- an example of a short-day plant is chrysanthemum
- they flower when nights are long; in the late summer 7 autumn
- they can be covered to achieve longer periods of darkness (at least 12 hrs) during the summer to simulate the day & night periods of autumn
- the plants will then flower in the summer
