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Main Ideas from Ch. 28 & 30 (Angiosperm Life Cycle :check: (Formation…
Main Ideas from Ch. 28 & 30
3 Plant Organs
:check:
2. Stems (part of shoot system)
:star:
Definition:
organ to which leaves are attached that elongates the shoot to maximize photosynthesis and elevates reproductive structures for wider range of dispersal
Consists of...
Nodes
:sparkles: --> points at which leaves are attached
Internodes
:sparkles: --> stem segments between nodes
Apical/terminal bud
:sparkles: --> bud at the tip of a plant stem
Axillary bud
:sparkles: --> bud formed between leaf and stem
3. Leaves (part of shoot system)
:star:
Definition:
organ responsible for photosynthesis, gas exchange, heat dissipation, and defense against pathogens and herbivores
Consists of...
Flattened blade
:sparkles:
Stalk (petiole)
:sparkles: --> joins leaf to stem at node
Veins (vascular tissue)
:sparkles: --> transports supplies for photosynthesis
Mesophyll
:sparkles: --> contains specialized cells for photosynthesis
Stomata
:sparkles: --> allows for gas exchange between air and photosynthetic cells; located in epidermis
Guard cells
:sparkles: --> regulate opening and closing of stomata (and thus, influencing water loss)
Vascular tissue (xylem and phloem)
--> transports nutrients and photosynthetic products
:!!:
There is tremendous variation in leaf morphology to suit different functions!
1. Roots (root system)
:star:
Definition:
organ that anchors as vascular plant in the soil, absorbs water and minerals, and stores carbs
Includes 2 systems...
Taproot system
:sparkles: --> one main vertical root (taproot) that helps prevent plant from toppling over and allows plant to grow tall; water absorbed through lateral roots branching off
Fibrous root system
:sparkles: --> many thin, small roots spread out from stem
Adventitious
:sparkles: --> describes plant organ growing in an unusual location
Root hairs
:sparkles: --> thin, finger-like extensions of root epidermal cells; increase surface area for absorption
:!!:
In a mycorrhizal relationship: fungi increase plants' ability to absorb minerals, plants supply fungi with nutrients!
3 Plant Tissue Systems
:check:
1. Dermal tissue system
:star:
Functions:
outer protective covering, defense against pathogens and physical damage
Features:
For non-woody plants...
Epidermis
:sparkles: --> tightly packed cells
Cuticle
:sparkles: --> waxy coating to prevent water loss
For woody plants...
Periderm (instead of epidermis)
:sparkles: --> offers more protection
2. Vascular tissue system
:star:
Functions:
helps transport materials through plant, provides mechanical support
Features:
2 types of tissue...
Xylem
:sparkles: --> transports water and minerals from roots into shoots
Phloem
:sparkles: --> transports sugars to roots and sites of growth
Stele
:sparkles: --> vascular tissue of root or stem
Vascular cylinder
:sparkles: --> solid central bundle of vascular tissue (in root)
Vascular bundles
:sparkles: --> separate strands of xylem and phloem (in stems and leaves)
3. Ground tissue system
:star:
Functions:
contains cells that help in photosynthesis, short distance transport, storage, or support
Features:
Pith
:sparkles: --> ground tissue that is
internal
to vascular tissue
Cortex
:sparkles: --> ground tissue that is
external
to vascular tissue
Primary Growth
:check:
Definition:
growth in
length
due to more sun and soil exposure, occurring in
all plants
(woody + non-woody) at
apical meristems
Apical meristems
:sparkles: --> located at tip of roots and shoots and axillary buds of shoots; enable growth in length
Apical dominance
:sparkles: --> phenomenon in which an active apical bud inhibits growth from axillary buds
:question:
How?
Through plant hormones
Removal of
JUST
apical bud
--> axillary bud grows laterally
Removal of apical bud
AND
addition of plant hormones (emitted by apical bud)
--> axillary bud is inhibited from growing
Pollination
:check:
Definition:
act of placing pollen (containing male gametophyte) on the stigma of a carpel so that the male gametophyte can travel to the female gametophyte inside embryo sacs of ovule
Types of pollination...
Self-fertilizing
:sparkles: --> plants combine their own pollen + ovule to form a zygote
:+1:
Pro:
ensures every ovule will develop into a seed
:-1:
Con:
no genetic diversity
But...
:!!:
Most angiosperms have evolved mechanisms to prevent self-fertilization
:question:
How?
Some plants lack
either
carpels or stamens
Some plants have carpels and stamens that mature at different times
Self-incompatibility
:sparkles: --> plant rejects its own pollen and pollen of closely related plants
Abiotic pollination
:sparkles: --> by wind
Pro:
no selective pressuring by favoring colorful or scented flowers (aka success doesn't depend on attracting pollinators)
Biotic pollination
:sparkles: --> by insects (moths, butterflies, bees, flies), bats, birds
Driven by color and/or odor
Secondary Growth
:check:
Definition:
growth in
thickness
at parts of roots and stem, occurring in
only woody plants
at
lateral meristems
Lateral meristems
:sparkles: -->
vascular cambium
adds layers of vascular tissue (secondary xylem and phloem);
cork cambium
replaces epidermis with thicker periderm; enable growth in thickness
:checkered_flag:
Think:
Secondary growth occurs in older regions where primary growth has ceased
:!!:
Primary growth and secondary growth occur
simultaneously
Angiosperm Life Cycle
:check:
:checkered_flag:
Think:
2n sporophyte --> n spores --> n gametophyte --> n gametes --> fertilization --> 2n zygote
Formation of female gametophyte
:star:
In megasporangium of ovule... megasporocyte (
2n
) undergoes meiosis --> produces 4 megaspores (
n
)
Only 1 megaspore (
n
) survives and becomes female gametophyte (
embryo sac
)
Formation of male gametophyte
:star:
In microsporangium of anther... microsporocyte (
2n
) undergoes meiosis --> produces 4 microspores (
n
)
Each microspore undergoes mitosis to produce male gametophyte (
pollen grain = 2 cells [generative cell + tube cell] + spore wall
)
Pollination
:star:
Pollen grain is transferred to stigma surface
Generative cell passes into tube cell
Tube cell produces pollen tube
Pollen tube elongates and delivers sperm to female gametophyte
Double fertilization
:star:
Definition:
union of two sperm cells with different nuceli of female gametophye
1 sperm fertilizes egg --> becomes embryo (
2n
)
1 sperm fertilizes 2 polar nuclei --> becomes
endosperm
aka food storing tissue of seed (
3n
)
Endosperm contains stored proteins, oils, starch
Each fertilized ovule develops into a
seed
Seed = result of double fertilization = embryo (
2n
) + endosperm (
3n
)
Each ovary develops into a
fruit
enclosing the seed
Asexual vs. Sexual Reproduction in Plants
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Sexual reproduction
:star:
Male gametophyte + female gameotphyte = zygote
Male gametophyte = pollen grain
Microspore = spore that produces male gametophytes
Female gametophyte = embryo sac
Megaspore = spore that produces female gametophytes
Does
NOT
require water to transfer sperm
:+1:
Pros:
increased viability, long-term evolutionary persistence, offspring survival; rapid removal of harmful genes, rapid adaptation to new parasites
:-1:
Cons:
new individuals not produced as rapidly, takes time to mate/find pollinators
Asexual reproduction
:star:
Definition:
generation of offspring from a single parent
without
fusion of gametes (aka vegetative reproduction for plants)
:question:
How?
Budding, division of single cell, or division of entire organism into two or more parts
Plant growth can be renewed or sustained by
meristems
(aka sites of indeterminate growth)
Fragmentation
:sparkles: --> detached plant fragment develops into new plant
Apomixis
:sparkles: --> plant produces seeds without pollination or fertilization
:!!:
Offspring are genetically identical to the parent
:!!:
Many angiosperms can do
both
sexual and asexual reproduction
:+1:
Pros:
no need to find pollinator, successful genotypes are mass-produced, less "costly" for parent's resources, new individuals produced rapidly
:-1:
Cons:
no genetic diversity, offspring not dispersed far away from parent, offspring must grow in current environment
