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IB Biology 5/6
PLANTS
I.
Classification (9.1.2)
A. Divisions
1. bryophyte-nonvascular plants; mosses
2. pteridophyta-seedless vascular plants; ferns
3. gymnospermophytes-naked seed vascular plants; conifers
4. angiospermophytes-flowering vascular plants;
a. monocots
1) one cotyledon (leaf) contained in the embryo
2) floral organs (petals) in multiples of 3
3) parallel leaf veins
4) leaves attach around the whole stem circumference
5) vascular bundles are spread throughout the stem
6) apical meristems only
7) examples: palms, gingers, lilies, irises, grasses, orchids
b. dicots
1) two cotyledons
2) floral organs of four or five
3) branching network of leaf veins
4) leaves attach on one side of stem by a leaf stalk
5) vascular bundles arranged in a ring
6) apical and lateral meristems (stem can widen)
7) examples: most trees and shrubs
II.
Structure (9.1.1, 9.1.3, & 9.1.4)
A. Roots (9.2.1)
1. anchor plant and absorb water and mineral ions
a. root hairs increase surface area (specialized epidermal cells)
b. mutualism with fungi may aid mineral absorption
1. fungi grow on roots and extend hyphae to absorb
minerals; fungi often receive sugars in return
2. may be generally fibrous in appearance or as a tap root
3. modifications-may grow above soil level to prop up tree; mangrove
roots are important for “breathing”; root tubers store food (carrot)
B. stems (9.2.4)
1. draw and compare monocots vs. dicots
2. produce leaves and sometimes branches
3. support
a. with turgid cells
b. with cells that have thickened cellulose cell walls
c. with xylem tissue that has lignin-impregnated cell walls
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C. leaves
1. leaf diagram
2. relate structure to functions
a. absorption of light
b. gas exchange
c. support
d. water conservation
e. water and sugar transport
III.
IV.
Growth
A. meristems (9.1.5-9.1.6)
1. groups of stem cells that allow plants to grow indefinitely
2. types
a. apical
1. also called primary meristems
2. located at the tips of roots and shoots
a) grows the stem as well as the leaves
3. allow for vertical growth
b. lateral
1. grows in a complete circle around the stem
2. allows the stem to grow thicker
3. found in dicots, not monocots
4. xylem cells grow inward, phloem cells grow outward
B. control (9.1.7)
1. hormones are used to control growth
a. can control rate and direction
2. gravity and light influence growth
a. stems grow toward light or away from gravity
3. phototropism-growth toward bright light
a. light is absorbed by phototropins (photoreceptive proteins)
b. light causes a conformational change
c. phototropins bind to receptors which influence the
transportation of auxin from cell to cell
d. auxin promotes the elongation of cells
e. auxin produced by the tips of shoots is transported down the
shoot
f. detection of brighter light on one side causes auxin to be
transported to the side away from the bright light
g. this causes those cells to elongate more, thus bending the shoot
toward the light
transport
A. water (9.2.1, 9.2.5-9.2.10)
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1. branching and root hairs increase surface area for osmosis
2. solute concentration is always greater inside root cells
3. constant influx of water generates root pressure forcing water
upward
4. xylem
a. long, continuous tubes with cell walls containing lignin
b. cells are joined end-to-end with pores in cells walls
c. cells are dead at functional maturity
d. there are a few side-to-side pores
5. transpiration pull
a. transpiration-loss of water vapor from the leaves and stems of
plants
b. generates an area of low pressure
c. water from xylem moves to replace evaporated water from the
leaf
d. cohesion (water to water) pulls water up the plant
1. adhesion-allows water to adhere to cellulose
e. guard cells regulate transpiration by opening/closing the
f. stomata
1. abscisic acid
2. low water in guard cells causes them to close the
stomata
3. absorbing water increases the pressure in the
guard cells and forces them apart
6. factors influencing transpiration
a. light-increases transpiration (causes stomata to open for CO2)
b. temperature-increases transpiration (higher evaporation, higher
rates of diffusion)
c. wind-increases transpiration (decreases humidity immediately
around the leaf)
d. humidity-decreases transpiration (humidity in leaf spaces is
nearly 100%, it is lower outside the leaf)
7. adaptations of xerophytes (outline)
a. C4 and CAM physiology
1. C4-store CO2in oxaloacetic acid (a 4-carbon
molecule) to release directly to rubisco
2. CAM-store CO2in malic acid to release to rubisco
b. reduced leaves
c. rolled leaves
d. reduced number of stomata
e. increased cuticle
f. stomata in pits surrounded by hairs
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g. water storage tissue
h. low growth form
B. minerals (9.2.2-9.2.3)
1. diffusion into the root
2. fungal hyphae
3. mass flow of water in the soil carrying ions
4. active transport
a. protein pumps in plasma membranes of root cells are unique for
each mineral ion
C. sugars (9.2.11)
1. active transport loads sugars into the phloem at sugar sources
a. sucrose is the most common form
2. water flows into the phloem via osmosis (generates high pressure)
3. this generates higher pressure, forcing the sugars toward the sugar
sinks
4. active transport unloads sugars
5. water flows out of phloem via osmosis (creates lower pressure)
6. sources-photosynthetic organs, storage organs
7. sinks-fruits, seeds, roots, storage organs
V.
Reproduction (9.3.1-9.3.6)
A. terms
1. pollination-pollen from one flower comes into contact with the stigma
of another
2. fertilization-male gametes fertilize the ovary
3. seed dispersal-travel of the seed away from the parent plant
a. dry and explosive
b. feathery or winged
c. covered in hooks
d. attractive to animals for food
4. germination-cell division of the zygote and growth of the embryo root
and shoot
B. flower structure-be able to draw and label
1. Figure
a. sepal, petal, anther, filament, stigma, style, ovary
C. seed structure-be able to draw and label
1. Figure
a. testa, micropyle, embryo root, embryo shoot, and cotyledons
D. conditions for germination
1. all sees need water
a. may need to rehydrate cells
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b. may need to cleanse the seed of a germination-inhibiting
hormone
c. water raises metabolic rate from near zero
2. oxygen is required for cellular respiration
3. warmth is necessary for enzyme function
E. germination
1. absorption of water
2. this triggers the synthesis of gibberellin in the cotyledons
a. stimulates mitosis and the production of amylase (breaks down
starch to maltose for energy production)
3. sucrose and glucose diffuse to the embryo
F. flowering
1. growth of roots, stems and leaves are the vegetative phase
2. flowering phase occurs when meristems begin producing flowers
3. trigger is length of darkness, not light
a. long-day plants bloom in summer when nights are short
b. short-day plants bloom in autumn when nights are longer
4. phytochrome-plant pigment responsible for measuring dark periods
a. PR absorbs red light (660nm) and is converted into PFR
b. PFR is slowly converted back to PR in darkness
c. PFR is the active form and binds to receptor proteins that
promote the transcription of flowering genes
d. during short nights, PFR remains in the cell to trigger flowering
in long-day plants
e. in short-day plants, the PFR-receptor proteins complex acts as
an inhibitor; long nights break down PFR so that the inhibition
fails