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Plant Cell and
Tissues 1
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
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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
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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.
Root Hairs: Absorb
minerals and water from
the soil
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
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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 nux-vomica,
strychnine tree, the trichomes of the
seeds are lignified and hard. They
produce strychnine which is highly
poisonous.
Uses
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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
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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
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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
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In roots and seeds, parenchyma tissue
often stores sugars and starch. This is
storage parenchyma.
(for example: yams, sweet potato, etc.)
You’re not a
yam, you’re a
sweet potato!
Storage in Bean Seeds
(endosperm). IKI stain
Hey!
I yam
what I
yam,
man!
Parenchyma in
storage cells with
starch grains
known as
AMYLOPLASTS.
Parenchyma in Capsicum (red
pepper) with Licopene pigment
granules known as
CHROMOPLASTS.
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.