BISC 101 Lecture Notes - Lecture 21: Palisade Cell, Axillary Bud, Eudicots

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BISC 101 – Lecture 21 – Plant Structure, Growth, and Development
Plant Groups
Terrestrial plants can be divided into two broad groups
The terrestrial (land) members of the plant kingdom are generally organized or
divided into two broad groups:
oVascular Plants
Ex: Ferns, conifer trees and flowering plants
Have roots, stems and leaves
Have vascular tissue
Vascular Tissue: Consists of special cells for transport of water
and nutrients within a plant that run continuously through roots,
stems and leaves
Can grow tall
oNon – Vascular Plants
Ex: Mosses, hornworts, liverworts
Lack of roots, stems and leaves
Do not have vascular tissue
Water under soil is not reached and actively taken up
Water can only be taken in by direct absorption through their cell walls
and the water moves from cell to cell via osmosis
Cannot grow tall
There are two main types of vascular plants
oGymnosperms
Non-flowering plants
Plant seeds are not enclosed in an ovule
Ex: Pinecone
“Naked Seeds”: Plant seeds not enclosed in ovule
No leaves
Usually have needles that stay green throughout the year
Ex: Pine, cedars, spruces, first)
Wind pollination is most common
Pollination: The process by which pollen is transferred from the
anther to the stigma of plant, thereby enabling fertilization and
reproduction
Anther: Male part of a plant
Stigma: Female part of a plant
oAngiosperms
Flowering plants
Mature seed is surrounded by ovule (usually in a fruit)
Have flat, broad leaves that usually change color and die every
autumn
Ex: Oaks, maples
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Insect pollination is most common
More abundant than gymnosperms
Two basic types: Eudicots and Monocots
Plant Body
The plant body has a hierarchy of organs, tissues, and cells
Like multicellular animals, plants have organs composed of different tissues,
which in turn are composed of cells
Three basic organs evolved
1. Roots
2. Stems
3. Leaves
They are organized into a root system and a shoot system
Roots rely on sugar produced by photosynthesis in the shoot system
Shoots rely on water and minerals absorbed by the root
Roots
Roots are multicellular organs with important functions
1. Anchoring the plant
2. Absorbing minerals and water
3. Storing organic nutrients
The roots of eudicot plants form a taproot
oTaproot: Consists of one main vertical root that gives rise to some large
lateral roots, or branch roots
The roots of monocot plants form a fibrous root system
oFibrous Root: Many thin lateral roots with no main root
In most plants, absorption of water and minerals occurs near the root hairs, where
vast numbers of tiny root hairs increase surface area
o Root hairs often form on fine roots and improve water absorption by
increasing root surface area and by improving contact with the soil
After water and minerals enter the root hair, they travel through either the:
oSymplastic Route: Via the continuous connection of cytosol between
cells through plasmodesmata
oApoplastic Route: Via the cell walls and intercellular spaces
Endodermis: Also known as the root’s border guard is the innermost layer of cells
in the root cortex
oThis is the last checkpoint for selective passage of minerals from the
cortex into the vascular cylinder
oStele: Vascular cylinder
Casparian strip: Waxy strip found on the endodermal wall which blocks apoplastic
transfer of minerals from the cortex to stele
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oThis forces polar molecules taking the apoplastic route to enter
endodermal cells using the symplastic route
In eudicots, the xylem forms a cross or star while the phloem is found between
the arms
In most monocot stems, xylem and phloem form a ring with a core of parenchyma
oPith: Core of parenchyma cells
Stems
Stems are plant organs consisting of nodes and internodes
oNodes: The points at which leaves are attached
oInternodes: The stem segments between nodes
Axillary Bud or Lateral Bud: Embryonic structure found at the junction of the stem
and petiole that has the potential to form a lateral shoot, or branch
Apical Bud or Terminal Bud: Embryonic structure located near the shoot tip and
causes elongation of a young shoot
In most eudicots, the vascular tissue consists of vascular bundles (xylem and
phloem group together) that are arranged in a ring
In most monocot stems, the vascular bundles are scattered randomly throughout
the ground tissues
Leaves
Leaves: Main photosynthetic plant organs
They generally consist of a flattened blades and a stalk called the petiole
oPetiole: Joins the leaf to a node of the stem
Monocots and eudicots differ in the arrangement of veins, the vascular tissue of
leaves:
oMost monocots have parallel veins
oMost eudicots have branching
There are differences in terms of leaf shape
oSimple: Leaf has a single undivided blade
oCompound: Leaf blade consists of multiple leaflets
A leaflet has no axillary bud at its base
oDoubly-compound: Each leaflet is divided into smaller leaflets
Many leaves, such as those of poison ivy, are compound or doubly-compound
Advantages of compound or doubly-compound:
oEnable leaves to withstand strong wind with less tearing
oConfine some pathogens (disease-causing organisms and viruses) that
invade the leaf to a single leaflet, rather than allowing them to spread to
the entire leaf
The epidermis in leaves is interrupted by stomata
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