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Plant Tissues
Plant Tissues Types
All plant organs (roots, stems, leaves) are composed
of the same tissue types. The tissues that
originated in embryo’s body are called primary
tissues.
There are three types of tissue:
1. Dermal – outermost layer
2. Ground – bulk of inner layers
3. Vascular – conducting tissue, transport
1. Dermal tissue
• Epidermis is the outermost layer of cells. It
is a single layer of cells without
chloroplasts.
• The functions of the epidermis includes,
absorption, protection and gas exchange.
• In stems and leaves, the epidermis has a
cuticle, a waxy layer that prevents water
loss. Its thickness varies in the different
plants.
The Cuticle
The Stomata
In addition, the epidermis
may have specialized cells
with different functions.
In the epidermis of leaves
and sometimes stems, you
find a specialized group of
cells called stomata.
These are specialized
for gas exchange.
Dermal tissue
• Another group of specialized cells found
in leaves and stems are the Trichomes or
hairs (fuzzy look).
These may release chemicals
(for aroma, defense), reflect light, etc.
More trichomes
Surface of Lavender, including hairs and glands.
And more.....
Functions
Nutrition and
Absorption.
The trichomes of
carnivorous plants
such as sundew and
butterwort secrete
enzymes that help
the plant liquefy
their prey.
Functions
Defense
•In many plants, root hairs deterred meroding animals
creating a very dense inaccessible surface.
•In many plants the trichomes are filled with essential oils
and other substances that deters predators.
In many other plants, the
trichomes protect plants
from larger prey. The leaves of
Urtica or stinging nettle when
touched breaks the hair,
producing a syringe-like needle
that penetrates the skin and
injects penetrating
Uses
• The most economically important
trichomes are those of the seeds of
cotton. These are 6cm (2.5 inch.)
long and soft (95% cellulose).
• In the case of Strychnis nuxvomica, strychnine tree, the
trichomes of the seeds are lignified
and hard. They produce strychnine
which is highly poisonous.
Uses
• The trichomes of Mentha piperita or
peppermint produce Menthol a volatile
oil.
• The trichomes of Lavander (Lavandula)
produce an essential oil that has
antiseptic and anti-inflammatory
properties. It was used in hospitals
during World War I to disinfect floors
and walls. These extracts are also used
as fragrances for perfumes, cosmetics
and bath products.
Uses
• The trichomes of Pelargonium
citrosum a type of geranium
produces some essential oil that
works as a natural mosquito
repellent.
• The trichomes of Cannabis sativa
produce tetrahydrocannabinols
(THC) responsible for marihuana
soothing effects. The purified
THC is hashish, a most powerful
psychoactive drug.
Ground tissues
• Makes up the bulk of plant organs.
• Functions: Photosynthesis, storage and support
• Three different ground tissues are present in
plants:
• Parenchyma
• Collenchyma
• Sclerenchyma
The Parenchyma
Photosynthetic parenchyma
makes the main tissue in
the leaves of plants. Ex:
Elodea
Photosynthetic parenchyma
in Syringa (lilac) leaf cross
section.
Ground tissue
In roots and seeds, parenchyma tissue often
stores sugars and starch. This is storage
parenchyma. (for example: yams, sweet
potato, etc.)
Storage in Bean Seeds
(endosperm). IKI stain
Parenchyma in
storage cells with
starch grains
known as
AMYLOPLASTS.
Parenchyma in Capsicum (red
pepper) with licopene pigment
granules known as
CHROMOPLASTS.
Uses
Photosynthetic Parenchyma:
• The photosynthetic parenchyma contributes all the
photosynthetic energy to the food chain. It provides
all the energy for herbivores (first consumers) at the
bottom of the food chain.
• It provides a large amount of the fiber in the human
diet.
• It contribute a considerable amount of water to the
diet.
• The photosynthetic parenchyma is a major source
of Phytochemicals.
Phytochemicals
Phytochemicals can be defined as chemicals produced
by plants. The term is generally used to describe
chemicals from plants that may affect health, but are
not essential nutrients.
While there is evidence to support the health benefits
of diets rich in fruits, vegetables, legumes, whole
grains and nuts, evidence that these effects are due to
phytochemicals is limited.
Because plant-based foods are complex mixtures of bioactive
compounds, the information on the potential health effects of individual
phytochemicals is linked to information on the health effects of foods
that contain those phytochemicals.
For example Flavonoids, a subgroup of phytochemicals known as
polyphenols. Flavonoids are phytochemicals that work as anti-oxidants.
Antioxidants are thought to rid the body of harmful molecules known as
free radicals, which can damage a cell's DNA and may trigger some
forms of cancer and other diseases. These compounds are commonly
found in the leaves of tea (Camellia sinensis) and in vegetables such as
broccoli, Brussels sprouts, cabbage, and cauliflower.
Another example: In Cruciferous vegetables (broccoli, brussel sprouts,
cabbage and cauliflower) are unique in that they are rich sources of
glucosinolates, sulfur-containing compounds that impart a pungent
aroma and spicy (some say bitter) taste. Scientists think that high intakes
of cruciferous vegetables as to prevent cancer.
Uses
Storage Parenchyma:
The storage parenchyma
feeds the world. The starch
and in the case of legumes
proteins, accumulated in
this tissue is the number
one source of energy of
the world. All major crops
are starchy crops.
The Chollenchyma
The collenchyma is
made of cells with
unequally thickened
walls. It provides mild
support. For example
the ribs in a celery
stalk. This mild
protection maintain
plants upright in rain
storms and strong
winds.
The Sclerenchyma
Vascular tissues
Transports water and organic materials
(sugars) throughout the plant
Xylem – transports water and
dissolved ions from the root
to the stem and leaves.
•
Phloem – carries dissolved sugars
from leaves to rest of the plant
The Xylem
The Phloem