Different parts of plants
Leaves
Most
plants' food is made in their leaves. Leaves are designed to capture sunlight
which the plant uses to make food through a process called photosynthesis.
Flowers
Flowers
are the reproductive part of most plants. Flowers contain pollen and tiny eggs
called ovules. After pollination of the flower and fertilization of the ovule,
the ovule develops into a fruit.
Roots
Roots
act like straws absorbing water and minerals from the soil. Tiny root hairs
stick out of the root, helping in the absorption. Roots help to anchor the
plant in the soil so it does not fall over. Roots also store extra food for
future use.
Stems
Stems
do many things. They support the plant. They act like the plant's plumbing
system, conducting water and nutrients from the roots and food in the form of
glucose from the leaves to other plant parts. Stems can be herbaceous like the
bendable stem of a daisy or woody like the trunk of an oak tree.
Plants tissues classification
Meristematic tissues
Meristematic
tissues at the growing tip that bring about growth in length are called as
apical meristematic tissues.
Tissues
present around the edges in a manner and giving rise to growth in the girth of
stem are called lateral meristematic tissues.
Areas
from which branching takes place Or a leaf or a flower stalk grows, we find a
kind of meristematic tissue called intercalary meristematic (also called
Cambium) tissue.
Dermal tissue
Dermal
tissue (Dermis) usually consists of a single layer of tissues showing
variations in the types of cells on the basis of their functions and location.
These tissues are divided into three different types. They are epidermis (outer
most layer), mesoclermis (The middle layer) and endodermis (the innermost
layer).
The
walls of the cells of dermal tissue Are comparatively thicker than the cells of
meristematic tissues. In desert plants it may be even more thick and waxy. Small
pores are seen in the epidermis of the leaf, called stomata. They are enclosed
by two kidney shaped cells, called guard cells. Cells of the roots have
long-hair like parts, called root hairs.
Stomata
and root hair are also dermal tissues that are essential for gaseous exchange,
transpiration as well as, absorption of water and minerals. Photosynthesis is
also carried out by certain cells of this tissue.
Ground Tissue
The
cells of the ground tissue. It forms the bulk of the plant body. The ground
tissue is useful for storing food and providing physical support to the plant
body. There are mainly three types of ground tissues. They are parenchyma,
collenchyma and sclerenchyma.
Vascular Tissue
Xylem
is responsible for the transportation of materials like water and salts from
the root. And phloem helps in the transportation of the food material prepared
by photosynthesis to the other parts of the plants. Hence they are known as
conducting or vascular tissues. Xylem and Phloem together form the vascular
bundles.
Reproduction Plants:
Artificial propagation
Cutting:
Some
plants grow individually when a piece of a parent plant having bud j cut from
the existing plant. The lower part of this cutting is buried in moist soil.
After few days the cut parts having buds grow as an individual plant after
developing roots. Ex: Rose, Hibiscus
Layering:
A
branch of the plant with at least one node is bent towards the ground and a
part of it is covered with moist soil leaving the tip of the branch exposed
above the ground. After some time, new roots develop from the part of the
branch buried in the soil. The branch is then cut off from the parent plant,
the part which has developed roots grows to become a new plant. Ex: Nerium.
Grafting:
Two
plants are joined together in such a way that two Stems join and grow as a
single plant. One which is attached to soil is called stock and the cut stem of
another Plant without roots is called scion. Both stock and scion are tied with
help of a twine thread and covered by a Polythene cover. Grafting is used to
obtain a plant with desirable characters. This technique is very useful in Propagating
improved varieties of various flowers and fruits (ex: Mango, citrus, apple,
rose).
Sexual reproduction in plants.
So
far we know about nearly 275,000 species of flowering plants. With a few
exceptions, all of them give rise to seeds enclosed in fruits. Most of the
plants you are familiar with are mostly flowering plants. Their characters are
quite remarkable. The plant size range from trees weighing many tonnes to tiny
water plants about the size of a rice grain. A sal tree growing in the
Himalayan mountains, a giant cactus in the Sahara desert, an orchid plant on
the branch of a jungle tree-all are flowering plants. Now let us examine the
sexual reproduction in flowering plants.
Observation of pollen grain
Take
a slide and put a few drops of water on it. Now take any flower like hibiscus,
tridax, marigold, etc. Tap the anther over the drop of water. You will see
small dot like structures in water. These are pollen grains. Observe these
first under hand lens then under a compound microscope. You may also see a
permanent slide of pollen grain from your lab. Observe under microscope.
Structure of the ovule
An
ovule is an egg-shaped structure attached by a stalk to the inner side of the
ovary. Depending upon the species of plant involved, an ovary may have one,
two, several, or even hundreds of ovules. At the center of each ovule there is
a microscopic embryo sac filled with food and water. The embryo sac is composed
of gametophyte cells. The majority of flowering plants have an embryo sac
consisting of seven cells and eight nuclei. Two of which are important to our
discussion. One is a large central cell containing two nuclei. These are called
polar nuclei. The other cell is the egg. It is located at the end of the embryo
sac closest to the opening through which the pollen tube enters. Cells on the
surface of the stigma secrete a sticky nutrient fluid Contains Sugars and other
substances. This will help the pollen grain to germinate. Then it forms pollen
tube, It bears two nuclei. Soon after the tip of the pollen tube enters the
embryo sac, the end of the tube ruptures and releases the two sperms into the
embryo sac.
One
of the two sperms fuses with the egg to form a Zygote. By the time the egg cell
has been fertilized, the two polar nuclei combine to form a single fusion
nucleus. Now the second sperm deposited in the embryo sac by the pollen tube
moves to the center and unites with the fusion nucleus. The zygote will develop
into an embryonic plant within the ovule. Fertilization of the fusion nucleus
stimulates the formation of a new tissue the endosperm. In which, food
materials are stored as development of the ovule proceeds.
Soak few groundnut or Bengal gram
(chana) seeds overnight.
Leave them for
a day. Keep sprinkling water at regular intervals so that they do not dry up.
Photosynthesis:
Photosynthesis is the process by which plants
containing the green pigment ‘chlorophyll’ build up complex organic molecules from
relatively simple inorganic ones, using sun light as an energy source.
Van Neil first worked on purple Sulphur
bacteria and found light plays a specific role in photosynthesis. Instead of
H20 they used H2S as a starting material. Here no oxygen is liberated during
photosynthesis instead, elemental sulphur is evolved. Later he envisioned a
similar process for photosynthesis in plants and proposed the above mentioned
equation. Later Robert Hill showed 02 is released from water. Then the equation
was modified as follows (Modifications are still being made).
Light
6CO2
+12H2O -----------------à C6H12O6
+ 6H2O+6O2
Chlorophyll
Respiration
in Plants
You already know about stomata in leaf
where gaseous exchange takes place in plants. There are other areas on the
plant body as well through which gaseous exchange take place like surface of
roots, lenticels on stem etc. (Fig showing stomata and lenticels). Some plants
have specialized structures like breathing roots of mangrove plants as well as
the tissue in orchids that produces oxygen is also required by plants to
produce energy and carbon dioxide is released. But CO2 is required elsewhere in
the plants try to identify them.
Conduction
within the plant
The stomata openings lead to a series
of spaces between the cells inside
the plant. Which form a continuous
network all over the plant? The spaces are
very large in the leaves, much smaller in other parts of the plant. The air spaces are lined with water where the oxygen is dissolved in this
and passes through the porous cell walls into the cytoplasm. Here the sugar is
broken down into carbon dioxide and water with the liberation of the energy.
The carbon dioxide passes out into the air spaces by a similar method.
The whole system works by diffusion; as
the oxygen is used up by the cells a gradient develops between the cells and
the air in the spaces. Similarly between the air in the spaces and the air
outside the stomata and lenticels, so oxygen passes in the same way, as more
carbon dioxide is released by the cells a gradient occurs in the reverse
direction and it passes out to the environment.
Aeration
of roots
Most plants can aerate their roots by
taking in the oxygen through the lenticels or through the surface of their root
hairs (as their walls are very thin). They obtain oxygen from the air spaces
existing between the soil particles. But, plants which have their roots in very
wet places, such as ponds or marshes, are unable to obtain oxygen. They are
adapted to these water-logged conditions by having much larger air spaces which
connect the stems with the roots, making diffusion from the upper parts much
more efficient.
The most usual adaptation is to have a
hollow stem. Next time when you are by a pond or marsh cut the stems of some of
the plants which are growing there and see how many are hollow compared with a
similar number of species of plants growing in normal soil. The problem of air
transport is more difficult for trees and not many survive with their roots
permanently in water. An exception is the mangrove tree of the tropics which
forms aerial roots above the soil surface and takes in oxygen through these
roots.
The biochemical substances produced in
plants are of two types, primary metabolites and secondary metabolites. The
materials like carbohydrates, fats and proteins are primary metabolites. The
materials which do not require for normal growth and development are secondary
metabolites. e.g.: Alkaloids, Tannins, Resins, Gums, and Latex etc. Though
plants produce these chemical for their own use. Man found the usage of these
chemicals for own benefits. They are generally coloured and fragrant.
Alkaloids:
These are nitrogenous by- products and
poisonous. These are stored in different parts of the plants. Common alkaloids
in plants and their uses are given below.
Tannins: Tannins are carbon compounds. These
are stored in different parts of the plant and are deep brown in colour.
Tannins are used in tanning of leather and in medicines e.g. Cassia, Acacia.
Resin: Occur mostly in Gymnosperms in
specialized passages called resin passages. These are used in varnishes-
e.g.Pinus.
Gums: Plants like Neem, Acacia oozes out a
sticky substance called gum when branches are cut. The gum swells by absorbing
water and helps in the healing of damaged parts of a plant. Gums are
economically valuable and used as adhesives and binding agents, in the preparation
of the medicines,
food etc.
Latex: is a sticky, milky white substance
secreted by plants. Latex is stored in latex cells or latex vessels. From the
latex of Hevea braziliensis (Rubber plant) rubber is prepared. Latex from
Jatropa is the source of bio-diesel. Do you know which part of jatropa used in
production of bio diesel.
Plant
Diseases:
Bacteria
Not all bacteria are bad for plants and
soil. In fact, most are beneficial, and there are millions! However, there are
approximately 200 types of bacteria that cause diseases in plants. They are
most active in warm and humid environments, so this is when you’ll see the most
evidence of their presence.
There are several symptoms of bacterial
infection. One is leaf spot. In this case, the bacteria that attacks the
plants, produces a toxic chemical that kills the surrounding plant cells. The
plant then reacts defensively by killing off the surrounding plant cells,
thereby isolating the infected cells. In some cases, these dead cell areas drop
out, creating what looks like “shot holes” in the leaves.
Fungi
Like bacteria, many more fungi are
actually good for the garden. But, unlike bacteria, there are thousands of
fungi that are harmful to plants. For this reason, you are likely to encounter
fungal problems most often. Because fungi are present in the soil and above
ground symptoms of fungal attack can appear above and below ground. These
include rotting or dead roots, or large swelling on roots below ground. At the
soil level, new seedling stems can rot and flop over. Above the soil line,
plants can display leaf spots, mildews (white or gray powdery patches on
foliage), rusts, and wilts.
Fungal spores are very small and light,
and can travel great distances through the air to infect other plants or trees.
They are also spread by water, animals and insects, and people.
Viruses
Even viruses on occasion can be
beneficial, but for the most part, they are bad news in the garden. They can
persist for many years, before they appear as a problem, and when they do, they
often show up in one of a few primary ways. First, plant foliage may appear
yellow, or they may appear as mosaic patches of yellow, light green, or white.
Next, the plant may appear stunted. In addition, the plants are often misshapen
or malformed. Specifically, the leaves may be rolled, or swollen or puckered,
or they may be abnormally narrow.
Economic
Importance of Plants
Plants are extremely important in the
lives of people throughout the world. People depend upon plants to satisfy such
basic human needs as food, clothing, shelter, and health care. These needs are
growing rapidly because of a growing world population, increasing incomes, and
urbanization .
Plants provide food directly, of
course, and also feed livestock that is then consumed itself. In addition,
plants provide the raw materials for many types of pharmaceuticals, as well as
tobacco, coffee, alcohol, and other drugs. The fiber industry depends heavily
on the products of cotton, and the lumber products industry relies on wood from
a wide variety of trees (wood fuel is used primarily in rural areas).
Approximately 2.5 billion people in the world still rely on subsistence farming
to satisfy their basic needs, while the rest are tied into increasingly complex
production and distribution systems to provide food, fiber, fuel, and other
plant-derived commodities . The capability of plants to satisfy these growing
needs is not a new concern. The Reverend Thomas Malthus (1766-1834) in his
Essay on the Principle of Population in 1798 argued that population growth
would exceed nature's ability to provide subsistence. According to the U.S.
Census Bureau, the world population was about one billion in 1800, doubled to
two billion in 1930, doubled again to four billion in 1975, and reached six billion
people in 2000. World population is expected to be nine billion by the year
2050. The challenge to satisfy human needs and wants still exists.