define transpiration
loss of water vapor from leaves (and other aerial parts of the plant)
cuticle
outermost layer of wax that protects the plant against water loss and insect invasion
epidermis
protective cell layer of leaf
purpose of xylem
brings water to the leaves
purpose of phloem
carries the products of photosynthesis to the rest of the plant
what is the palisade mesophyll
-a densely packed region of cylindrical cells in the upper portion of the leaf, where light is most available
-chloroplast rich to carry out photosynthesis
what is the spongy mesophyll
-consists of loosely packed cells w/ few chloroplasts
-many air spaces to allow for gas exchange
what are stomata
openings on the bottom surface of leaves for gas exchange b/w the leaf and the environment
structure of Xylem
-dead cells with thick,
lignified wall
: provide
strength
under tension
- hollow tube: allow free movement of water
- attached end-to-end to form
continuous columns
- contains numerous pores or
pits
on the wall:
enable water transfer
between cells.
2 types of xylems
Xylems can be composed of tracheids (all vascular plants) and vessel elements (certain vascular plants only)
Tracheids
: tapered cells,
exchange water solely via pits
, leading to a
slower
rate of water transfer
Vessel elements
: the end walls fused to fo
why can stomata only be closed on a short-term basis
carbon dioxide must enter the mesophyll region of the leaf so photosynthesis can occur
describe the process by which guard cells regulate the
opening
of stomata
Guard cells become turgit -> stomata opens
Cells become flaccit -> stomata closes
describe the process by which Abscisic Acid causes the
closing
of stomata
1. Plant begins to
wilt
from water stress.
2. Dehydrated mesophyll cells
release the plant hormone abscisic acid
(ABA)
3. Abscisic acid
triggers
the rapid
efflux of potassium
from guard cells
4. The
water pressure is decreased
within these cells, making t
what is the main function of roots?
to provide mineral ion and water uptake for the plant
function of root hairs
-increase surface area for absorption of water & mineral ions
-have carrier proteins & ion pumps in their plasma membrane, and many mitochondria in cytoplasm, to aid active transport
function of root cap
protects the apical meristem during primary growth of the root through the soil
what is the zone of cell division
where new undifferentiated cells are forming, corresponding with the Mitosis phase of the cell cycle
what is the zone of elongation
where cells are enlarging in size, corresponding with the G1 phase of the cell cycle
what is the zone of maturation
where cells become a functional part of the plant
how does water move into root hairs from the soil
1. Root cells contain
proton pumps that actively
expel H+ ions into the surrounding soil
2. The H+ ions
displace the positively charged
mineral ions from the clay, allowing them to diffuse into the root along a gradient
3. Negatively charged mineral ions
Apoplastic vs Symplastic pathway
Symplastic
pathway: water moves through the
cytoplasm
Apoplastic
pathway: water moves through the cell wall. Water can't cross over the
Casparian strip
, hence there it will
join the symplastic pathway
.
3 ways for mineral ions to pass from the soil into the root
-diffusion
-active transport
-action of fungal hyphae
what is bulk flow/mass flow
passive flow of water and the minerals dissolved in it
how is
shedding leaves
a xerophyte adaptation for water conservation
become dormant in the driest months
Xerophytes adaptation to dry conditions
Reduced number of leaves
:
reduce the surface area
available for water loss
Rolled leaves
:
reduces
the exposure of stomata to the air* and hence reduces evaporative water loss
Thick, waxy cuticle
prevents water loss from the
leaf surface
Stomata in pits,
Halophytic adaptations to their environment
Adapted to
salinity
-May become succulent by storing water, thus diluting the salt concentrations
-
Secrete salt
through
salt glands
-
Separates
Na+ and Cl- in the vacuoles of their cells, thus preventing NaCl toxicity
-
Sunken stomata
on thickened leaves
Describe the experiments used to model water transport in xylem.
Capillary tubing
: explain
adhesion
property of water by showing that the narrower the tube, the more water rises up.
Filter paper
: explain the
cohesion and adhesion
property of water; water rises up along the length of the paper.
Porous Pots
: semi-perm
define translocation
the movement of organic molecules from
sources to sinks
Steps of translocation
1. Sugars are
transported as sucrose
(soluble form) in the
phloem sap
2. Sugars are
actively loaded
into the phloem by
companion cells
, creating a
high concentration
which draws water from the xylem via
osmosis
3. This increases the sap volume & pressure
Structure of a Phloem Sieve tube
1. Transports water and food
2. Composed of
sieve element cells
which connect to form a tube
3. Connected sieve cells share a highly
perforated sieve plate
4. Supported by
companion cells
that help with loading and unloading
5. Movement of sap is mediated
The process of phloem loading
Symplastic loading
: passing materials through the
plasmodesmata
Apoplastic loading
into the companion cell :
1.
H+ are actively transported
out of phloem cells by proton pumps
2. The
concentration of H+ builds up outside
of the cell, creating a
proton gr
Outline the mass flow in vascular bundle transportation
At the Source
1. The active transport of solutes into the phloem makes the sap solution hypertonic; causes water to be drawn from the xylem via osmosis
2. Due to the incompressibility of water, this causes the
hydrostatic pressure to increase
; forcing th
dermal tissue
outer covering protecting against physical & pathogenic agents
ground tissue
thin-walled cells that function in storage, photosynthesis, support, and secretion
difference between determinate & indeterminate growth
determinate = growth stops one a certain size has been reached
indeterminate = show growth throughout their life
Outline the different types of meristematic tissues
Apical meristem
: root & shoot apex; responsible for
primary growth
(lengthening); non-woody stems and roots.
Lateral meristem
: occurs at the
cambium
, responsible for
secondary growth
(widening).
2 types of lateral meristem:
i)
vascular cambium
: produc
define tropism
growth or movement in response to directional external stimuli
what are auxins
-plant hormones that cause
positive photo/geotropism
-increase flexibility of cell walls (to allow cell elongation on the side of the shoot to cause growth towards the light)
Steps of phototropism
1. Auxin is produced by all cells in the stem on the light side;
auxin influx
into the shady side of the apex
2. Auxin
activates a proton pump
in the plasma membrane which causes the secretion of H+ ions into the cell wall
3. pH within the cell wall decre
Process of micropropagation and its uses.
1. Specific plant tissue (typically the undifferentiated shoot apex) is selected from a stock plant and
sterilised
2. The tissue sample (called the
explant
) is
grown on a sterile
nutrient agar gel
3. The explant is treated with
growth hormones
(e.g. auxi
compare monocots & dicots
Monocots
-parallel venation
-flower parts in 3's
-seeds contain one cotyledon
-mainly fibrous root system
-pollen grain w/ one opening
Dicots
-branched or netlike venation
-flower parts in 4's or 5's
-seeds contain two cotyledons
-root system involves tap
define pollination
The transfer of the male pollen to the female stigma
define fertilization
The fusion of a male and a female gamete nuclei to form a zygote (diploid)
Steps of fertilization
1. Pollen germinates to produce a pollen tube
2. Pollen tube grows down the style of the carpel
3. Pollen tube completes its growth by entering an opening at the bottom of the ovary
4. Sperm moves from the tube to combine w/ the egg of the ovule to form a
Structure of flower
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
The role of phytochrome in flowering of plant
P-red
: active during the day; rapidly converted to P-fared.
P-fared
: active during the night; slowly converted to P-red.
Long Day Plant (flower when the days are long): P-fared
activate
flowering.
Short Day Plant (flower when the days are short): P-fare
Horticulturalists
Methods used to induce short-day plants to flower out of season by controlling the exposure to light.
Structure of seed and their function
Testa
- an outer seed coat that protects the embryonic plant
Micropyle
- a small pore in the outer covering of the seed, that allows for the passage of water
Cotyledon
- contains the food stores for the seed and forms the embryonic leaves
Plumule
- the em
define germination
development of the seed into a functional plant
Steps of maturation/germination, following successful seed formation
-Seed will dehydrate until water content is 10-15% of its weight.
-Seed will become dormant.
-Once
water
is supplied to rehydrate the seed,
-Enough
oxygen
is present for aerobic respiration,
-And the
temperature
is favorable for enzymatic activity ( suita
define photoperiodism
plant's response to light involving the length of day & night