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BIOLOGY OF PLANTS
Kingdom of Plants
• Plants are alive, just like people and animals.
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They grow and die.
They need energy, nutrients, air, and water.
They produce young.
They are made up of cells.
They react to what's around them.
Specialized Structures
• Specialized Structures
1. Some plant parts are greatly modified, and these may look very different from
the "typical" plant part. For example:
a. A potato is an underground stem, modified for storage.
b. Cactus spines are leaves, modified to protect the plant.
c. A radish is a root, modified for storage.
d. Some orchids perform photosynthesis only with their (above-ground) roots.
2. Structures that look the same to us may be made of different plant parts in
different kinds of plants. For example, spines, thorns, and prickles are all sharp
plant parts that protect the plant from herbivores. Depending upon the kind of
plant, spines may be made from many different plant parts:
a. Leaves - e.g., cacti
b. Stipules - e.g., Euphorbia (African plant that looks very much like a cactus)
c. Shoots - e.g., buckthorn
d. Epidermal Hairs - e.g., roses
e. Roots - e.g., some tropical trees
Plant Physiology
A. Plants are photosynthetic -- they gather
their food energy directly from sunlight
B. To perform photosynthesis, plants need to
have a supply of:
1.Sunlight
2.Carbon dioxide gas from the atmosphere
3.Water
4.Mineral nutrients
What Do Plants Need to Make Food?
• Plants need several things to make their own food.
They need:
• chlorophyll, a green pigment found in the leaves of plants (see the layer
of chlorophyll in the cross-section of a leaf below)
•light (either natural sunlight or artificial light, like from a light bulb)
•carbon dioxide (CO2)(a gas found in the air; one of the gases people and
animals breathe out when they exhale)
•water (which the plant collects through its roots)
•nutrients and minerals (which the plant collects from the soil through its
roots)
What Do Plants Need to Make Food?
Plants make food in their leaves. The leaves contain a
pigment called chlorophyll, which colors the leaves
green. Chlorophyll can make food the plant can use from
carbon dioxide, water, nutrients, and energy from
sunlight. This process is called photosynthesis.
Basic Plant Structure
• Plants have
three vegetative
organs:
– roots,
– stems,
– and leaves.
Shoot System
1.
2.
Shoots are made of leaves attached to a stem.
Leaf (singular; plural is leaves)
Leaves are often the primary site of photosynthesis.
a. Leaf Blade - large, flat part of leaf that collects sunlight.
b. Petiole - narrow stick that holds leaf blade away from
the stem.
c. Leaf Base - slight broadening at base of petiole, protects
bud when leaf is young, and may include stipules.
d. Simple Leaves - leaf blade is composed of only one
piece.
e. Compound Leaves - leaf blade is divided into two or
more leaflets. In some plants the leaflets of compound
leaves look very similar to leaves, but only true leaves
have buds in their axils
Root System
1. The root anchors the plant in the soil, absorbs water and
mineral nutrients from the soil, and often serves for storage.
2. Roots are underground, so people don't think very much
about them, but they are very important.
3. Branch Roots
a. Roots do not have leaves or axillary buds
b. Branch roots emerge from the inside of the root
c. Root Hairs
d. Absorption
e. Found just behind growing tip of root
f. Root Cap
g. Protects the delicate tip of the root as it grows through the
soil.
h. Found in front of the root apical meristem.
Stem System
Holds leaves, transports and stores water and
nutrients, and is sometimes photosynthetic.
Tissue System
and Its Functions
Component
Tissues
Dermal Tissue
System
• protection
• prevention of
water loss
Ground Tissue
System
• photosynthesis
• food storage
• regeneration
• support
• protection
Epidermis
Periderm (in older
stems and roots)
Vascular Tissue
System
• transport of
water and
minerals
• transport of food
Xylem tissue
Phloem tissue
Parenchyma tissue
Collenchyma
tissue
Sclerenchyma
tissue
Location of Tissue Systems
Dermal Tissues
• The dermal tissue system protects the
soft tissues of plants and controls
interactions with the plants'
surroundings.
• The epidermis is a dermal tissue that is
usually a single layer of cells covering
the younger parts of a plant. It secretes
a waxy layer called the cuticle that
inhibits water loss.
Dermal Tissues
• Most epidermal
cells lack
chloroplasts.
Most epidermal cells lack chloroplasts.
Guard cells contain
chloroplasts and regulate
gas exchange between the
inside of the leaf and the
surrounding air.
Dermal Tissues
Glandular hairs
prevent herbivory
by storing
substances that
are harmful to
insects.
Epidermal hairs lower water
loss by decreasing the flow of
air over the plant surface,
which in turn, slows the loss
of water from the plant.
Vascular Tissue
Xylem Tissue
Phloem Tissue Function •
Function
•Conduct water and dissolved
minerals
• Support
•Conduct food and other
organic substances
Cell Types Unique to
This Tissue
Additional Cell Types in
This Tissue
Tracheids
Vessel members
Companion
Cells
Parenchyma cells Fibers
Sieve-tube
elements
Parenchyma cells Fibers
Primary Growth
• Primary growth is the lengthening of the stem
and roots.
– All plant growth occurs by cell division and cell
elongation. Cell division occurs primarily in regions of
undifferentiated cells known as meristems.
– Cell division in the apical meristems and subsequent
elongation and maturation of the new cells produces
primary growth.
– The other type of growth, secondary growth, is the
increase in girth of stems and roots.
Primary Growth of Stems
• The apical meristem produces the three primary meristems, protoderm,
procambium, and ground meristem, which develop into dermal tissues,
vascular tissues, and ground tissues respectively.
Primary Growth of Stems
• Meristems are regions of embryonic tissue capable of growing into
new plant parts. Meristems are found in both roots and shoots.
1. Primary meristems make the shoot or root grow longer. This kind of
growth is called primary growth.
a. A shoot apical meristem is found within each bud.
b. A root apical meristem is found at the tip of each root, and is protected by
the root cap.
2. Secondary meristems make the stem or root grow larger in diameter.
This kind of growth is called secondary growth. Not all kinds of plants
are capable of secondary growth. Secondary growth gives rise to
wood, and plants that are not capable of secondary growth do not
develop wood.
Plant Reproduction
A. Asexual Reproduction
1. Because plant growth is indeterminate, each meristem can
potentially develop into a complete plant. This means that it is very
easy to clone plants, and many plants can grow from cuttings or
broken plant parts. This is asexual reproduction (also called
vegetative reproduction).
B. Sexual Reproduction
1. Alternation of Generations - plant sexual reproduction is unusual,
and involves an alternation between two partially independent life
stages. We will discuss this later in the course.
2. Flowers are special reproductive structures found in the Flowering
Plants (=Angiosperms)
3. A flower is a specialized shoot, adapted for sexual reproduction.
4. A fruit develops from a flower following fertilization.
5. Other plants perform sexual reproduction, but do not use flowers,
and do not form fruit.
Pollination
• Pollination is the transfer of pollen from a
stamen to a pistil. Pollination starts the
production of seeds.
• To be pollinated, pollen must be moved from a
stamen to the stigma. When pollen from a
plant's stamen is transferred to that same plant's
stigma, it is called self-pollination.
Helpful terms
• Herbaceous:
Plants with stems that are usually soft and bendable.
Herbaceous stems die back to the ground every year.
• Woody:
Plants with stems, such as tree trunks, that are hard and do
not bend easily. Woody stems usually don't die back to the
ground each year.
• Photosynthesis:
A process by which a plant produces its food using energy
from sunlight, carbon dioxide from the air, and water and
nutrients from the soil.
• Pollination:
The movement of pollen from one plant to another.
Pollination is necessary for seeds to form in flowering
plants.
Plant Adaptations
• Plants have adaptations to help them survive (live and
grow) in different areas. Adaptations are special features
that allow a plant or animal to live in a particular place or
habitat. These adaptations might make it very difficult for
the plant to survive in a different place. This explains why
certain plants are found in one area, but not in another. For
example, you wouldn't see a cactus living in the Arctic.
Nor would you see lots of really tall trees living in
grasslands.
Tundra
Desert
Grassland
In Water
Temperate Rain Forest
Taiga
Temperate Deciduous Forest
Tropical Rain
Forest
Major Plant Groups
• We are going to examine
several groups that show
these trends:
– 1. bryophytes: nonvascular plants
including liverworts
and mosses
– 2. seedless vascular
plants such as ferns
and horsetails
– 3. gymnosperms,
which have seeds and a
vascular system, such
as the conifers
– 4. angiosperms, the
flowering plants that
dominate the world
today.
Bryophytes
• The bryophytes include
the mosses, liverworts,
and hornworts. They are
short plants mostly
growing in wet
environments.
• Bryophytes have a waxy
cuticle on their leaves to
prevent dessication.
• Bryophytes have no
internal vascular system.
•Bryophytes spend most of their lives as
haploids: the body of the moss plant is
haploid.
•The only diploid structure is a stalk and
spore capsule, which grow out of the
haploid plant body.
Bryophyte Life Cycle
• The haploid gametophyte
plant bodies are either
male or female. Each
produces a different kind
of gamete (eggs or sperm).
• The sperm are motile: they
swim through drops of
water (rain or dew) to
reach the eggs. The eggs
are encased within the
female gametophyte’s
body.
Bryophyte Life Cycle
•After fertilization, the
diploid sporophyte grows
as a stalk out of the
female gametophyte’s
body.
•After the diploid
sporophyte matures, the
cells in it undergo
meiosis, forming haploid
spores.
•The haploid spores
disperse in the wind, and
go on to form new
gametophyte plants.
Seedless Vascular Plants
• The seedless vascular plants
include ferns and horsetails.
• A vascular system to distribute
nutrients throughout the plant
allows them to grow tall.
Some ferns grow up to 80 feet
tall, and some extinct
horsetails were also tree-sized.
• Being seedless means that the
diploid sporophyte grows out
of the fertilized egg, attached
to the gametophyte.
Fern Life Cycle
• The main plant body in the
diploid sporophyte.
Specialized structures on
the underside of the leaves
develop, and inside them
meiosis occurs.
• The haploid meiotic
products are released as
spores, which are dispersed
to new locations and
germinate into
gametophytes.
Fern Life Cycle
•The haploid
gametophytes are quite
small, a few millimeters
in diameter. They
contain structures that
produce sperm and
eggs.
•The sperm swim to the
eggs and fertilize them
•The fertilized eggs are
diploid, and they grow
into the sporophyte
plant body.
Seeds and Pollen
• A major development in plant
evolution was the development of
pollen grains and seeds.
• Pollen grains are the male
gametophyte packaged in a hard coat
that allows it to reach the female
without having to swim through water.
This is a large advantage on dry land.
• Seeds are diploid sporophyte embryos,
packaged to survive a period of
dormancy and bad environmental
conditions. Seeds develop from the
fertilized egg.
Gymnosperms
• Gymnosperms were the first
plants to have pollen grains
and seeds.
• Gymnosperm means “naked
seed”: their seeds develop on
the outside of the plant,
instead of inside an ovary as
in the flowering plants.
• The most important
gymnosperms today are the
conifers: pines, redwoods,
cedars, etc. All are woody
plants with needles or scales
as leaves.
• Conifers are our main source
of wood and paper.
• Ginkos and cycads are other
gymnosperms.
Angiosperms
• Angiosperms are flowering plants. Most
of the plants we see are angiosperms.
• Unlike the other plant groups,
angiosperms are often fertilized with the
aid of animals: insects, birds, bats, that
carry the pollen from one plant to another.
The plants and their pollinators have coevolved in a symbiotic relationship.
• Flowers produce the visual signals and
the scents that pollinators use to find the
plants. Flowers secrete nectar which is
eaten by the pollinators. The pollen is
carried from flower to flower on the body
of the pollinator, as a consequence of its
going into the flower in search of nectar.
• Some angiosperms have wind-dispersed
pollen. Flowers on these plants are
usually small and inconspicuous.