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14.1: Plant Organs, Tissues and Cells

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Saberina Ahmed

on 10 January 2014

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Transcript of 14.1: Plant Organs, Tissues and Cells

Plant Organs
Flowers and Sexual Reproduction
A Plant's Main Tissue Systems
Types of Plant Cells
The Cellular Structure of a Leaf
Vegetative Reproduction
Plants are capable for both sexual and asexual reproduction
Asexual reproduction is also know as
Vegetative reproduction
(Offspring produced are genetically identical)
Occur naturally or with human help -->
Plant cells that are grown under right conditions are capable of forming all the tissues and organs of the adult plant
First cloned plant were carrots
Vegetative reproduction provides a way to propagate useful crops in a short period of time
On woody species a branch from an plant can be "grafted" onto the stem of another plant that belongs to the same or closely related specie
Grafting: Widely used by fruit growers, allowing them to combine a high quality fruit-bearing stem with a tough and hardly root or to put several varieties of fruit on one plant
Roots:
Structures that anchor a plant in the soil, absorbing minerals and water, and providing structural support

Different angiosperms have different root systems
oDicotyledons have taproot system:
one large vertical root with many smaller branches
oMonocotyledons have a fibrous root system:
a mat of many thin roots spread below the soil surface to provide an increase exposure to soil and nutrients

However not all roots are underground, some roots that have adapted to the plants certain environment have interesting structures
oE.g.: Mangrove trees have above-ground roots that help bring oxygen into the roots.
Plant Organs, Tissues, and Cells
Dermal Tissue
The top and bottom part of a leaf are covered by
epidermal tissues
(dermal)
, which in turn are covered by a layer of
waxy cuticle
(this reduces the amount of water lost by the leaf).
There are
guard cells
flanking the
stomata
on the bottom layer of the epidermal tissues.
The guard cells controls the diffusion of gasses into the leaf and the amount of water vapour coming from the leaf.
The ground tissue is made of
mesophyll
(parenchyma cell)

which specializes in gas exchange.
There are two layers of mesophyll cells:
palisade mesophyll
(top) and
spongy mesophyll
(bottom)
.
The palisade mesophyll captures light energy and carries out photosynthesis.
The spongy mesophyll (also called
aerenchyma
) allows gas exchange to occur in the leaf.
Vascular tissues transport nutrients and water throughout the plant.
Chapter 14.1
Root and Shoot Systems
The primary organ systems of plants are:
Roots
Shoots
Leaves
Flowers
These organ systems vary between two groups of angiosperms:
The Leaf
Seed Development
Seed Germination
Vascular Tissue
Ground Tissue
Comparing Monocots and Dicots
Outer covering or "Skin" of the plant
The "
epidermis
" is a dermal tissue on non-woody plants
It covers and protects all young parts of the plant
Epidermis can be specialized (e.g. epidermis on leaves and stems secrets a waxy cuticle, an adaptation the helps plants retain water)
Many plants have epidermal hairs to trap or poison insect, protecting the plant from insect herbivores
Stomata
(Plural, stoma): Locate in epidermis of leaves and some other tissues are pores
Gas exchange between between environment and interior of the plant occurs through stoma
Transport water, minerals nutrients, and organic molecules between roots and shoots
Contributes to structural support of the plant
2 types pf vascular tissue
Xylem:
Transport water and dissolve minerals upward from roots into shoots
Phloem:
Transports food made in mature leaves to the roots and the parts of the shoot system that don
'
t carry out photosynthesis, such as developing leaves, flowers, and fruits
Vascular tissues are located in the centers of roots but in the stems it is arranged on many separate stands called vascular bundles
E.g. Monocot stem has vascular bundles scattered throughout its tissue
Vascular bundles if a dicot stem are arranged in a ring
Filling the spaces between the dermal and vascular tissue
Makes up most of young, non-woody plant and functions in photosynthesis in shoot and in storage and support throughout the plant

Cortex:
ground tissue consist of primary of a mass cells
E.g. Naturally
Cati, drop stems or other out shoots that establish new crones
Strawberry plant and grasses send out runners
Some trees and stubs send out shoots from their trunks or from underground stem
E.g. Human help
Simplest way to clone plants is to cut off a leaf or stem and place the cut in water or soil
Cells at the cut end of petiole or stem becomes undifferentiated (Genetically identical form original one)
Parenchyma
It is the most abundant cell
Has thin cell walls
Typically has large central vacuoles
Performs photosynthesis and cellular respiration
ex. Fruits
Collenchyma
Has uneven thick walls
Provides support for the parts of the plant that is still growing
Grouped together in strands or cylinders
ex. the strings in celery
Sclerenchyma
Specialized for support
Grows and dies in the mature part of a plant
The cell wall that is left behind is called a
skeleton
and it provides support for the plant
Angiosperms make up about 90% of the world's plants and are a very successful group of plants.
Two types of angiosperms are the
monocots
and
dicots
(together they represent 97% of the world's modern flowering plants).
The terms refer to the presence of 1 or 2
cotyledons

(the first leaves to appear on a plant)
in the developing embryo.
See Table 14.1 on page 390 in the textbook for more details.

Leaves
The primary manufacturing sites of a plant
oCapturing sunlight and converting light energy into chemical energy during photosynthesis.

Most leaves are flattened and thin, allowing them to intercept and capture sunlight effectively.

Some plants also have modified leaves
oE.g.: the tendrils on a pea plant or grape are modified so that they allow the plant to attach and climb along a surface.

Parts of the Leaf:

oBlade:
the main usually flattened part of the leaf
oPetiole:
s
talk that connects the leaf to the steam
oVenation:
ar
rangement of veins on the leaf. They vary in dicot and monocot leaves.
-Dicot leaves have a network of branching veins.
-Monocots have several major veins that run parallel along the length of the leaf’s blade.
Most mammals have a characteristic adult form
However, a plants adult appearance can differ
•E.g.: a rose bush may have one stem or fifty

But, like animals, plants have specialized organs that also have specific functions.
Plant embryo begins to grow when conditions are favourable, and this process is called
germination.
Most seeds soak up water to germinate, so that the seed expands and splits the seed coat, and metabolic changes are triggered so it may grow.
The conditions for germination vary among species.
Garden vegetables need as little as a warm moistened environment
Some desert plants need heavy rainfall, which allows seedling to push through the now softened-soil
Plants in cold climates germinate after a long period of cold, to prevent germination during warm spell in winter
Some need exposure to extreme heat, (i.e: brush fires) so that plants that would have competed with it are eliminated

Flowers
are a specialized shoot (exclusive to angiosperms) made of four different rings of modified leaves
Sepal
: covers and protects flower bud before it blossoms
Petals
: Strikingly colorful organ that attracts insect pollinators
Stamens
: Male reproduction organ located in the center of the flower and Pistils. They have a long stalk topped by a sac called
anther
, where meiosis occurs and generates spores that develop into
pollen grains
.
Pistils
: Female reproduction structure.
Pollen
: male gametophyte containing two cells surrounded by a protective wall.
Ovules
are found inside ovaries which are at the base of each tissue.
Style
is a narrow structure leading to the ovary, that has

a sticky tip called the
stigma
(plural:
stigmata
)
During pollination, pollen grains released from anthers land of stigmata of flowers
Pollen is carried by wind or insects and land on the stigmata of flowers.
Water is absorbed by the pollen grain and a structure (
pollen tube
)
is developed.
The pollen tube has two sperm nuclei that move towards the ovary through the style.
When the pollen reaches the ovule, a zygote is developed and then turn into an embryo.
A nutrient-rich tissue called
endosperm
nourishes the growing embryo.
Monocot Flowers:
have sepals, petals, and reproductive parts in multiples of three. (eg: lilies)
Dicot Flowers:
have organs dispersed in multiples of four or five.
Reproductive Process
1.Dicotyledons/ Dicots:
The larger group, containing species with broad-leaves •E.g.: Dandelions, canola, and maple trees
2.
Monocotyledons/Monocots:
Species with long thin leaves
•E.g.: Grasses, orchids, and lilies
After fertilization, the ovule develops into a seed
A
seed coat
(tough outer layer) helps to protect the tiny embryo and endosperm
The endosperm serves as a food source for the embryo, containing starch, proteins and oils
Many plant products (wheat and popcorn) made from endosperm
Within the embryo, a miniature root, shoot, and embryological leaf
(cotyledon
)
develops.
The cotyledon functions in storage and transfer of nutrients to the embryo and is important in seeds without an endosperm.
Dicots have two cotyledons, and monocots have one.
After several cycles of mitosis, the growth and development of the plant embryo is temporarily halted.
This is when the seed is usually dispersed from the parent plant.
In many flowering plants, a fruit develops from the ovary of an angiosperm. Fruits protect seeds and help disperse seeds from the parent plant. Eg: green peppers, walnuts, cucumbers, apples, melons, coconuts, and corn.
Shoots:
Usually above ground structures that consist of:
oStems:
Part of the plant that supports the leaves and flowers, and also play an important role in transporting materials to all parts of the plant.
oNodes:
Points on the stem where the leaves are attached
oInternodes:
The portions of the stem between nodes.

A bud is an undeveloped shoot and are found in different areas

oTerminal buds
are found in the tip of the stem

oAxillary buds
are found in angles called axis formed by a leaf and the main stem.

Shoots also have modified roles and may vary significantly in their appearance. E.g.: stems of cacti are specialized to store water•
Structure of Sex Organs (Flower)
O
Seed Dispersal
Seed dispersal occur in many ways
Fruit:
flesh of fruit is digested, passing through the digestive tract, and indigestible seed coat protects embryo. It is deposited sometimes very far away from the parent plant. Some seeds benefit from this, because the digestive enzymes help break down the coating of the seed coat, enabling root and shoots to emerge easily.
Animal:
some seeds travels by sticking onto a passing animals fur, as burrs
Water:
seeds land in moving bodies of water and are swept ashore far downstream.
Wind:
some are light and small enough to be carried by wind (eg: dandelion)
Projectile:
some plants propel the seed several metres away from the plant (eg: touch-me-not)
Checkpoint

#1
1. Compare and contrast the functions of roots and shoots.

2. Compare the arrangement of veins in monocot and dicot leaves.

3. Draw the reproductive structures of a flower. For each structure, include a label stating a brief description of its function.
?
?
Checkpoint #2
?
?
1. Describe three methods of seed dispersal.

2. Explain how two different adaptations of seed germination in dicots and monocots protect the developing root.

3. Give two examples of vegetative reproduction in plants.
Checkpoint #3
?
?
1. List one function of dermal, ground and vascular tissue.

2. Describe characteristics of the three main plant cell types.

3. Which cell types provide structural support to the plant body?
After germination, the plant shoot attempts to break through the soil to the surface.
However, sand and other abrasive materials make this difficult, and so the plants have special methods in combating this issue.
Some dicots:
(eg: bean plant) Have a hooked shoot tip which protects the delicate shoot tip by holding it downwards. Once the plant breaks the surface, the shoot is lifted and straightened out. (eg: bean plant)
Most monocots:
(eg: corn plant) Sheath surrounds the shoot, providing a protective tunnel for the shoot to grow straight up through. Once it emerges from the soil, the first leaves expand and start photosynthesis.
Now called a
seedling
.
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