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PART 9: Plants
1. Plants: multi-cellular, eukaryotic organisms that have a cell wall made of
cellulose. They are photosynthetic (they convert light energy to chemical energy
using chloroplasts primarily found in leaves), and they take up water via capillary
action. The phyla of Kingdom Plantae can be grouped as follows:
 Algal ancestor: it is believed that all plants evolved from algae.
 Non-vascular: bryophytes; low growing plants evolved next.
 Seedless-vascular: pterophyta, lycophyta, sphenophyta; seedless, semi-low
growing plants evolved next.
 Seeded-vascular: anthophyta (angiosperms), coniferophyta
(gymnosperms); tall vascular plants with seeds.
2. Vascular tissue: roots, xylem and phloem; material that transports water
against gravity using cohesive and adhesive properties.
 Xylem: tissue that conducts water and minerals up to a plant from its
roots. There are two types of xylem:
o Tracheids: long and thin
o Vessel elements: short and thick
 Phloem: tissue that carries nutrients (i.e., glucose) throughout the plant.
Phloem cells are made up of:
o Sieve tube elements: cells that carry the nutrients
o Companion cells: cells that assist the movement of the sieve tube
elements.
 Roots: where water is absorbed into a plant, usually underground. Roots
also help to anchor plants to the ground.
o Root hairs: stringed fibres that are attached to the roots in order to
increase the surface area of water absorption.
o Root tip: end of a root where constant cell division (growth of
meristems (#4) takes place.
o Epidermis: outer protective layer on roots
o Cortex: middle region of a root that stores starch and other minerals
o Stele: inner cylinder which contains xylems and phloems
o Apoplast: site where water and minerals enter the root through
pourous cell walls (holes in cell wall)
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o Symplast: site where water and minerals enter the root through
plasmodesmata
o Endodermis: inner layer of the cortex. After water and minerals
reach here, they pass through endodermal cells.
o Endodermal cells: cells that regulate the passage of water and
minerals into the vascular tissue.
 Casparian strip: a belt made of a fatty tissue called suberin
that blocks movement of water and minerals between the
endodermal cells.
3. Tracheophytes: any plant that has true vascular tissue; much more advanced
that bryophytes. Seeded vascular plants of the tracheophytes, as said in Vocab
#1, can be broken down into two groups: gymnosperms and angiosperms:
 Gymnosperms: “coned plants”; include the woody plants, huge lifespan,
can be very tall, and they are perennial (can survive through winters).
Every year they grow a new xylem layer as the old one dies. This creates a
tree-ring pattern. We can age trees by counting their rings. Their seeds are
enclosed and found on the scales of cones (e.g., evergreens, spruces, firs,
etc.).
 Angiosperms: the “flowering plants”; may be perennial or annual (die in
winter). The two types are monocots and dicots (both discussed in Part 8,
#5). Angiosperms have several organs and a unique reproductive system.
o Petals: brightly colored structures that attract potential pollinators
(organisms that feed on nectar in the flower and spread its pollen for
reproduction in return).
o Sepals: green, leaf-like structures that cover and protect the flower.
o Stamen: male reproductive organ of an angiosperm; consists of:
 Filament: thin stalk that supports the anther
 Anther: structure that produces pollen
 Pollen grains (AKA: microspores): sperm cells of plants
o Pistil: female reproductive organ in angiosperms; consists of:
 Stigma: sticky portion of the pistil that captures pollen grains.
 Style: stalk that supports the stigma and joins it to the ovary
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 Ovary: where fertilization occurs; sperm of pollen grains
captured by the stigma travel down the style and into the
ovary, and into the ovules:
 Ovules: contains the female eggs (AKA: megaspores) of
an angiosperm, found within the ovary. These eggs
undergo meiosis to produce 8 nuclei, include one egg
nucleus and two polar nuclei.
o Double fertilization: process of pollinated reproduction
(angiosperms). Pollen grains on the stigma form a tube to the ovary.
The sperm then divides into 2 nuclei. One of these sperm nuclei joins
with the 2 polar nuclei (the structure resulting from this provides
food for the embryo). The embryo itself is developed from the
second sperm nucleus and the one egg nucleus.
o Early seedling development: the cotyledons are the first to develop.
There are two small important structures of the cotyledon here
(epicotyl and hypocotyl), and there is also an interesting reproductive
stimulant (photoperiodism) and alternative method (vegetative
propagation).
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 Epicotyl: tip of the cotyledon which becomes the stem and
leaves of the plant.
 Hypocotyl: the stem below the epicotyls which becomes the
roots of the plant.
 Radical: a well-defined embryonic root in the cotyledon
of a seed.
 Photoperiodism: the phenomena of plants flowering in
response to changes in the amount of daylight and darkness.
The pigment involved with this is called phytochrome. This
phenomena subdivides into three groups:
 Short-day plants: plants that require more darkness and
bloom in late summer or fall.
 Long-day plants: plants that require only short periods
of darkness and bloom in late spring or summer.
 Day-neutral plants: plants that flower in response to
changes in nutrients, water, temperature, etc., rather
than to solar light.
 Vegetative propagation: asexual reproduction of
angiosperms; when pieces of the parent plant can
produce a new organism. Examples of these plant parts
are bulbs, runners, and tubers, and grafting can also be
used to reproduce asexually.
o Bulbs: short stems underground (e.g., onions)
o Runners: horizontal stems that run along the
ground (e.g., strawberries)
o Tubers: underground stems (e.g., potatoes)
o Grafting: cut a stem and attach it to a closelyrelated plant and it will continue to grow.
4. Meristems: plant cells with no other purpose but to grow. They grow in two
ways:
 Primary growth: increases the length of the plant. The meristems here are
called apical meristems and are located in the tips of roots and stems.
 Secondary growth: increases the width of a plant. The meristems here are
called lateral meristems and are located on the sides of stems and roots.
Lateral meristems have two types of cells:
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o Vascular cambium: produce secondary xylem and phloem to replace
the primary (tree rings).
o Cord cambium: produces the outer bark and its cork and sap layers.
 Lenticels: holes in bark that allow gas exchange.
5. Leaves: leaves have multiple functions:
 Photosynthesis: discussed in Part 4.
 Spinal: leaves can be modified to form spines in order to store water and
to protect the organism (e.g., cacti).
 Storage: leaves can be modified to behave like a pouch to store water;
usually found in climates with low water supplies.
 Carnivorous: leaves can be modified to trap prey and digest them. This
adaptation happens in areas with low nitrogen in the soil (e.g., marsh
[where water diffuses nitrogen], swamps [where water diffuses nitrogen
and organic matter does not decay quickly]). Two forms of this adaptation
are:
o Sloped: when a bell-shaped bowl with slippery sides is formed with
nectar at the bottom. The nectar attracts insects that slip in and
can’t get out (e.g., Pitcher Plant).
o Triggered: when leaves have tiny hairs that, when touched twice,
trigger stiff leaves to clamp around an insect where it releases
digestive juices (e.g., Venus Flytrap)
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6. Tropism: a turning and/or moving response to a stimulus. These movements
are controlled by hormones.
 Phototropism: movement of plants to face light (similar to
photoperiodism, which opens petals)
 Gravitropism: how plants respond to gravity. Stems are negativegravitropic (push up and away from gravity) whereas roots are positivegravitropic (push down towards gravity)
 Thigmotropism: how plants respond to touch, such as how climbing plants
(e.g., ivy) climb walls as they grow.
 Auxins: hormone that promotes growth and tropism. Found in the tips of
the plant.
 Gibberellins: hormone that promotes stem elongation.
 Cytokinins: hormone that promotes cell division and differentiation.
 Ethylene: hormone that induces leaf abscission and promotes fruit
ripening.
 Abscisic acid: hormone that inhibits leaf abscission and promotes bud and
seed dormancy.
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