Topic 9 Flashcards
Sieve elements
sieve elements form tubes which transport water & solutes
- to be efficient at transport, they have reduced quantities of the cytoplasm and have no nucleus, ribosomes or vacuole
Fibres of Sclerenchyma cells
provide structural support for the plant
Paranchyma
acts as a packaging material between other cell types & helps transfer materials to the sieve elements & companion cells
Companion cells
are “life support” for the sieve element cells as they perform certain metabolic functions for sieve elements
- also why plasmodesmata(microscopic pores in the cell walls) between companion cells & sieve element cells are larger than in most plant cells to allow for the exchange of metabolites (e.g ATP)
How are sieve tubes structured to its function?
- Rigid cell walls of sieve tube
→ allow for the building of high pressures needed to generate hydrostatic pressure (the flow inside the tubes) - The ends of sieve element cells are connected with other sieve elements together to form a sieve tube
- Sieve plates are found
What is hydrostatic pressure?
the pressure exerted by a liquid due to the force of gravity
- in the phloem it causes the sugar & the water to be pushed towards the source cell (translocation)
What are the functions of transpiration?
- carries water to various parts of the plant
- carries minerals along w the water
- cools down the plant when water evaporates through the stomata
cuticle
- protects the plant against water loss & insects
- if no cuticle is present, the epidermis protects the leaf
- waxy, so its good for water loss prevention
Epidermis
- provides a protective barrier if no cuticle is present
- flat, tightly packaged cells on the leaf
Palisade mesophyll
- cells that are near the top of the leaf that are most responsible for light absorption & photosynthesis (why they are at the top & not the bottom)
- contain a lot of chloroplast (bc thats what’s needed for photosynthesis)
Spongy mesophyll
- a layer of sparsely spaced cells where there are channels for gas exchange
- air pockets allow for efficient gas exchange ->the gases that are coming in & out of the cell are oxygen & carbon dioxide
What is the rate of transpiration in xerophytes & why?
Xerophytes will have high rates of transpiration due to the high temperatures and low humidity of desert environments
What are xerophytes?
Xerophytes are plants that can tolerate dry conditions (such as deserts) due to the presence of a number of adaptations
What are the adaptions of xerophytes?
- Reduced leaves
- rolled leaves
- thick, waxy cuticle
- stomata in pits
- low growth
- CAM physiology
What are halophytes?
Halophytes are plants that can tolerate salty conditions (such as marshlands) due to the presence of a number of adaptations
What are the adaptions of halophytes?
- Cellular sequestration
- Tissue partitioning
- root level exclusion
- salt excretion
- altered flowering schedule
What is a photometer?
a device that is used to estimate transpiration rates by measuring the rate of water loss / uptake
What are the models of water transport?
- capillary tubing
- filter paper
- porous pots
Capillary tubing
- Water has the capacity to flow along narrow spaces in opposition to external forces like gravity (capillary action)
- This is due to a combination of surface tension (cohesive forces) and adhesion with the walls of the tube surface
- The thinner the tube or the less dense the fluid, the higher the liquid will rise (xylem vessels are thin: 20 – 200 µm)
Filter paper
- Filter paper (or blotting paper) will absorb water due to both adhesive and cohesive properties
- When placed perpendicular to a water source, the water will hence rise up along the length of the paper
- This is comparable to the movement of water up a xylem (the paper and the xylem wall are both composed of cellulose)
Porous pots
- Porous pots are semi-permeable containers that allow for the free passage of certain small materials through pores
- The loss of water from the pot is similar to the evaporative water loss that occurs in the leaves of plants
- If the porous pot is attached by an airtight seal to a tube, the water loss creates a negative pressure that draws more liquid
What is translocation?
is the movement of organic compounds (e.g. sugars, amino acids) from sources to sinks
What is a source?
a source is where organic compounds are synthesised - this is the photosynthetic tissue (e.g leaves)
What is the sink?
the sink is where the compounds are delivered to for use or storage - this includes roots, fruits & seeds
Why are sugars transported as a disaccharide?
transported as sucrose bc it is soluble but metabolically inert
What are aphids?
are a group of insects, belonging to the order Hemiptera, which feed primarily on sap extracted from phloem
What are the factors affecting translocation rate?
- the rate of photosynthesis
- the rate of cellular respiration
- the rate of transpiration
- the diameter of the sieve tubes
What are meristems?
Meristems are tissues in a plant consisting of undifferentiated cells capable of indeterminate growth
What is micropropagation?
Micropropagation is a technique used to produce large numbers of identical plants (clones) from a selected stock plant
Micropropagation is used to rapidly produce large numbers of cloned plants under controlled conditions:
- rapid bulking
- virus free strains
- propagation of rare species
Rapid Bulking
- Desirable stock plants can be cloned via micropropagation to conserve the fidelity of the selected characteristic
- This process is more reliable that selective breeding because new plants are genetically identical to the stock plant
- This technique is also used to rapidly produce large quantities of plants created via genetic modification
Virus-free strains
- Plant viruses have the potential to decimate crops, crippling economies and leading to famine
- Viruses typically spread through infected plants via the vascular tissue – which meristems do not contain
- Propagating plants from the non-infected meristems allows for the rapid reproduction of virus-free plant strains
Propagation of Rare Species
- Micropropagation is commonly used to increase numbers of rare or endangered plant species
- It is also used to increase numbers of species that are difficult to breed sexually (e.g. orchids)
- It may also be used to increase numbers of plant species that are commercially in demand
What is pollination?
- The transfer of pollen grains from an anther (male plant structure) to a stigma (female plant structure)
What is fertilisation?
- Fusion of a male gamete nuclei with a female gamete nuclei to form a zygote
What is seed dispersal?
- Fertilisation of gametes results in the formation of a seed, which moves away from the parental plant
What is the stamen composed of?
- anther
- filament
What is the pistil (or carpel) composed of?
- stigma
- style
- ovule
Anther
- pollen producing organ of the flower (pollen is the male gamete of a flowering plant)
Filament
- slender stalk supporting the anther (makes the anther accessible to pollinators)
Stigma
- the sticky, receptive tip of the pistil that is responsible for catching the pollen
Style
the tube-shaped connection between the stigma and ovule (it elevates the stigma to help catch pollen)
Ovule
the structure that contains the female reproductive cells (after fertilisation, it will develop into a seed)
Petals
function to attract pollinators
Sepal
Outer covering which protects the flower when in bud
What are phytochromes?
Phytochromes are leaf pigments which are used by the plant to detect periods of light and darkness
What is photoperiodism?
The response of the plant to the relative lengths of light and darkness
Phytochromes exist in two forms – an active form and an inactive form:
- The inactive form of phytochrome (Pr) is converted into the active form when it absorbs red light (~660 nm)
- The active form of phytochrome (Pfr) is broken down into the inactive form when it absorbs far red light (~725 nm)
Additionally, the active form will gradually revert to the inactive form in the absence of light (darkness reversion)
Why is the active form predominant during the day?
Because sunlight contains more red light than moonlight, the active form is predominant during the day
- Similarly, as the active form is reverted in darkness, the inactive form is predominant during the night
What will a typical seed possess?
- testa
- micropyle
- cotyledon
- plumule
- radicle
Testa
an outer seed coat that protects the embryonic plant
Micropyle
a small pore in the outer covering seed, that allows for the passage of water
Cotyledon
contains the food stores for the seed and forms the embryonic leaves
Plumule
the embryonic shoot (also called the epicotyl)
radicale
the embryonic root
For germination to occur, a seed requires a combination of:
- oxygen
- temp
- water
- pH
How can germination be measured?
germination can be measured by the rate of seed growth over a set period of time
