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The structures and functions of plants tissues
and organs
1. The structures and functions of plants tissues and organs
First, let’s review the structure of
monocot and dicot seeds
Second, let’s review the steps of monocot
seed germination.
1. Enzymes activate growth within the seed.
2. The embryo of the seed begins to grow, using its
endosperm for energy.
3. The seed coat bursts open and the root tip emerges.
4. The leaf sheath of a monocot shoots up as the root tip
grows deeper into the soil.
5. The leaf sheath of a monocot hits the light, the leaves
escape from their covering.
1. The structures and functions of plants tissues and organs
Next, let’s review the steps of dicot
seed germination.
1. When conditions are right, the embryo of the seed
begins to grow, using its endosperm for energy.
2. The seed coat bursts open. The tip of the root, the
hypocotyl, emerges from the embryo.
3. The root tip anchors the seed in the soil. It absorbs
water and minerals.
4. In a dicot, the hypocoytl lengthens until it rises above
the soil, taking the seed cotyledons with it.
5. Two leaves emerge from between the cotyledons.
After germination, the new seedling
differentiates into 3 main types of tissues:
Dermal, Ground, and Vascular.
For example, see the cross section of a
Dicot root below
Cross-section of Dicot Root System
Epidermis- dermal tissue for protection
Cortex- ground tissue responsible for storage of glucose,
assists in the uptake of water and minerals
Vascular Cylinder- vascular tissue forms an X-shaped
pattern in very center of the root of xylem and phloem
Cross Section of Monocot Root System
Endodermis – a cylinder one cell thick that
forms a boundary between the cortex and the
vascular cylinder
Vascular Cylinder - forms a ring in very center
of the root of xylem and phloem
Tissue Type
Dermal
Tissue
Function
Protection of
plant from
water loss
Location
It covers most
plant parts with a
single layer of
cells, almost like a
“skin.” These cells
excrete a waxy
cuticle.
Cell Type
It consists of parenchyma cells, which have the
ability to differentiate into many different cell
types. They have flexible cell walls and carry on
most of a plant’s metabolic functions.
Ground
Tissue
Serves all types
of functions
including
photosynthesis,
storage, and
support.
Makes up the
bulk of the plant.
It consists predominately of parenchyma cells, but
collenchyma cells and schlerenchyma cells can be
in ground tissue too. Collenchyma cells have
thicker cell walls and are responsible for support of
herbaceous plants.
Ground
Tissues
Schlerenchyma cells die at maturity and provide
structural support for woody plants.
Vascular
Tissue
Transports
water, minerals,
and food, but
also supports
the plant as it
grows.
It is present in all
plant parts, but
dominates in
roots, stems,
leaves.
Vascular tissues have two types: Xylem and
Phloem.
Xylem cells transfer water and ions from the soil
through the roots. They are dead cells at maturity
and have thick cells walls.
Phloem cells transport sucrose and other organic
compounds in plants. They are living at maturity a
may lack some organelles of standard cells in order
to aid in their transport function.
1. The structures and functions of plants tissues and organs
Like the roots, the stems consist of all types of plant cells and tissues. However,
unlike the roots, the stem has a higher percentage of collenchyma cells to aid in
structural support. Stems also have a different distribution of vascular tissue than
in roots.
In a monocot, vascular bundle is scattered throughout the stem.
In a dicot, the vascular bundle is a ring, with the larger xylem cells in the center and
the smaller phloem cells to the outside.
Vascular bundles of xylem and phloem make up the
vein system of a leaf. In dicots, the vein system is
netted and branching.
The large vein is called a
midvein. The smaller
veins that branch off are
secondary veins.
Most cells of plants have chloroplasts, but the cells of
leaves have the most. They lay open to the sun and
can adjust position to optimize their absorption of
solar radiation. Chloroplasts are responsible for
photosynthesis, so the more a leaf cell has the more
food it can make for the plant.
Stomata and Guard cells
Stomata are microscopic pores in the epidermis of plants
that allow water and gas exchange with the environment.
They take in carbon dioxide and water for photosynthesis
and release oxygen as a by-product of the reaction.
Stomata consist of a stoma, a small pore, and guard cells
that control the opening and closing of the stoma in response to environmental
conditions, such as temperature or moisture.
• Most stomata are located in leaves, since leaves are responsible for much
of the photosynthesis in plants.
• Plants that live in tropical, moist environments will have more stomata than
those in hot and arid climates.
• Having less stomata prevents undesirable water and gas loss to the plant.
How do seeds form from cones in a gymnosperm?
A sporophyte is a plant in its asexual reproduction phase. It consists of cells that
are diploid (2n). This means all their cells have a full set of chromosomes for that
organism. A full set of is different for every species. Pine trees have 24
chromosomes in their diploid cells, while cycads have only 22.
A gametophyte is a plant in its sexual reproduction phase. All the cells of a
gametophyte are haploid (1n). A haploid cell has half the number of
chromosomes as the diploid cell (2n) of the same species. For example, humans
have 46 chromosomes in their diploid cells and 23 chromosomes in their haploid
cells. Haploid cells used for sexual reproduction are called gametes.
How do seeds develop from flowers in angiosperms?
Flowers develop from the sporophyte phase of an angiosperm. The male and
female gametophytes form within the flowers the sporophytes create.
Petals: colorful structures at the top of the flower stem responsible for attracting pollinators
Pistil/Carpel: the female part of the flower
(multiple carpels are called a pistil)
Stigma: the sticky part of the pistil that traps
pollen
Style: tube-like structure that supports pistil
Ovary: contains the female gametophytes (eggs)
Stamen: the male part of the flower
Anther: contain the male gametophytes (pollen)
Filament: thread-like support for stamen
Sepals: modified leaves that enclose the petals
Steps to seed formation:
1. The petals attract pollinators to the anthers.
2. When a bird or insect sips the nectar, it brushes against the anthers, and the
pollen sticks to their bodies. They carry the pollen to another flower, resulting in
pollination.
3. When a pollen (1n) grain containing two haploid nuclei reaches the pistil, it
sticks to the stigma.
4. A pollen tube grows through the pistil into the ovary, and then into the ovules
(1n).
5. The male gametes (two haploid sperm) join with the female gametes within the
ovule. This is known as double fertilization.
6. One sperm must fertilize the main egg, the other sperm joins the polar nuclei
inside the embryo sac to make the endosperm tissue that will provide energy for
the embryo's growth and development. This double fertilization creates a diploid
zygote or seed (2n).
Sample questions:
1. What happens when the stomata on a plant's leaves are open?
a) Oxygen and water escape the leaves and carbon dioxide enters it.
b) Water enters the leaves and carbon dioxide escapes from the leaves.
c) Sunlight is able to enter the leaves and photosynthesis takes place.
d) Sugars and nutrients are transported up to the leaves from the roots.
2. When water and nutrients from the soil travel up from the roots of a plant
through the stem to the leaves, they do so in which of the following structures?
a) Cortex
b) Epidermis
c) Phloem
d) Xylem
3. Which of the following best describes the reproductive life cycles of
angiosperms?
a) Angiosperms need moisture to bring together male and female gametes to
form a seed.
b) Angiosperms depend on soil to transfer male gametes to the female gametes
during sexual reproduction.
c) The dominant sporophyte phase in the life cycles of angiosperms includes the
formation of flowers.
Answers: 1. A; 2. D; 3. C