plants: their forms and functions

Plants: Their Forms and Function 1

Plants: Their Forms and Functions

Garcia, Pauline Jessica M.

Bautista, Analin DR.

Salonoy, Mary Sheil S.

BSA 2-20

Adrian Guinto

August 10, 2012


Abstract

Plants are found everywhere but people often do not notice them. These organisms play

an extremely important part in the existence of life on earth. Virtually, all land animals depend

on them for food, either eating plants directly or eating other animals that eat plants. Above and

below the ground, plants provide food, shelter and breeding areas for animals, fungi and

microorganisms. Plant roots also prevent soil erosion, and photosynthesis in plant leaves helps

reduce carbon dioxide levels in the atmosphere and adds oxygen to the air. This paper will give

its audience little information about plants, mainly about their parts with their certain functions

and bodily processes. It aims to enlighten people of what they have to know about the most

important organism on earth.


Plants: Their Forms and Function

Plants are eukaryotic, multicellular, photosynthetic and non-motile organisms. These

include angiosperms, gymnosperms ferns, bryophytes and green algae which is recently included

in the plant kingdom.

Flowering plants or Angiosperms

Angiosperms or flowering plants are the most varied set of land vegetation. The

distinguishing trait of flowering plants or angiosperms is the flower. The chief role of the

flower is to make certain that fertilization of the ovule occur and that result in the growth

of fruit containing seeds.

Conifers or Gymnosperms

Gymnosperms or conifers are plants that have cones instead of flowers. Their seeds grow

within female cones. The seeds develop on scales inside cones. The majority of

gymnosperms are trees or shrubs. The cones are not as diverse as flowers but they can be

brilliantly colored and attractive.

Ferns

Ferns are the most superior spore bearing type of plants. Many ferns grow in cool, dry

places but the largest ones are found in the hot, damp tropic regions. Around 15,000

species of ferns are there in existence now according to scientific researches

Mosses

Mosses and most liverworts have simple stems and tiny, slender leaves. They can be

found growing on the plain land, on rocks, and on other plants. They habitually live in

mild, damp regions, but some can live in very cold places.

Algae

The simplest plant type is algae. They do not have leaves, stems or roots. Algae thrive in a

moist or wet environment. Many are tiny single celled plants, but some seaweeds are

huge.


The main focus of this discussion is about angiosperms. Angiosperms are classified into

two groups called monocots and dicots. The names “monocot and “dicot” refer to the first leaves

that appear on the plant embryo. These embryonic leaves are called seed leaves or cotyledon.

Monocots

As the name implies, a monocot embryo has one seed leaf. Most monocots have leaves vith

parallel veins and their stem have vascular tissues arranged in a complex array of bundles.

The flowers of most monocots have their petals in multiples of three. The fibrous root system

of a monocot provides broad exposure to soil, water and minerals as well as firm anchorage.

Dicots

You can see two cotyledons in a typical dicot seed. Multibranched network of veins are

found in dicot leaves. Unlike in monocot stems, the vascular bundles of a dicot stem are

arranged in a ring. The dicot flower usually has petals in multiples of four or five. The root

system of a dicot has many small secondary roots growing out from one large taproot.


Plant Structure

Plant cells like animal cells are eukaryotic, i.e. they contain membrane bound nuclei and cell

organelles. A plant cell differs from an animal cell in having certain distinctive structures - cell

wall, vacuoles, plasmodesmata and plastids. On the contrary, plant cells lack centrioles and

intermediate filaments, which are present in animal cells. Despite these, plant and animal cells

share several similarities in structure, parts and their roles.

Different Parts of a Plant Cell

Plant cells are classified into three types, based on the structure and function, viz. parenchyma,

collenchyma and sclerenchyma. The parenchyma cells are living, thin-walled and undergo

repeated cell division for growth of the plant. They are mostly present in the leaf epidermis, stem

pith, root and fruit pulp. Mature collenchyma cells are living, and provide stretchable support to

the plant. Lastly, sclerenchyma cells (e.g. fiber cells) are hard, non-living and give mechanical

support to plants. Now, let us see the different parts of a plant cell with their significant roles.

Cell Wall

Cell wall is the outermost tough and rigid layer, which comprises cellulose, hemicellulose, pectin

and at other times, lignin. As expected, it remains connected with the cell walls of other cells.

The prime functions of cell wall are protection, giving structural support and helping in the filter

mechanism.

Plasmodesma

Plasmodesma (plural plasmodesmata) is a small opening, which connects plant cells with each

other. Present only in some types of algal cells and plants cells, this connecting channel enables

transport of materials and allows communication between the cells. In a single plant cell, about

1,000-100,000 plasmodesmata are present.

Nuclear Membrane

The nuclear membrane and the nuclear envelope mean one and same thing. As the name reveals,

it is the outer covering of the nucleus. It separates the cytoplasmic contents from the nuclear


contents. Nonetheless, minute pores (nuclear pores) are present for exchanging materials

between the cytoplasm.

Nucleus

Nucleus is a specialized organelle, which contains the plant's hereditary material i.e. DNA

(Deoxyribonucleic Acid). Inside the nucleus, a dense, spherical body called nucleolus is present.

The nucleus contains structures, which regulates the cell cycle, growth, protein synthesis and

reproductive function.

Vacuole

Vacuoles are large membrane-bound compartments, which store water and compounds. They

function as storage, excretory and secretory organelles. The membrane surrounding a vacuole is

called tonoplast. A mature plant cell has a single vacuole at the near center of the cell (central

vacuole), which contributes to about 30-80 percent of the cell's volume.

Cytoplasm

Cytoplasm is filled up by cytosol, which is a gelatinous and semitransparent fluid. All the

organelles of the plant cell are present in this cytoplasm. This part of the plant cell is the site for

cell division, glycolysis and many other cellular activities. Also, the cytoskeleton elements

(microtubules and microfilaments) are present in the cytosol.

Plastid (Chloroplast)

Plastids are organelles responsible for photosynthetic activity, manufacturing and storage of

chemical compounds in plants. Chloroplast is an important form of plastid containing

chlorophyll pigment, which helps in harvesting light energy and converting it to chemical

energy. Likewise, chromoplast and other plastids are present in a plant cell.

Mitochondria

Mitochondria (singular mitochondrion) are oblong shaped organelles, which are also known as

'the powerhouse of the cell'. They are responsible for breaking down complex carbohydrate and

sugar molecules to simpler forms, which the plants can use. Other than this, mitochondria are

crucial for cell signaling, cycle, division, growth and death.


Endoplasmic Reticulum

The endoplasmic reticulum (ER) organelle plays a major role in manufacturing and storage of

chemical compounds, like glycogen and steroids. It is also involved in translation and

transportation of protein. ER is also connected to the nuclear membrane, so as to make a channel

between the cytoplasm and the nucleus.

In the overall functioning of a plant cell, the above cell parts coordinate in a specific

manner. As you have seen, lysosomes are absent in plant cells. While vacuole is large and single

in a plant cell, the animal cell houses smaller vacuoles in larger numbers. Likewise, for

understanding the differences between plant and animal cells, you can study the cells separately

along with the types of organelles present in them.

Tissue Organization in Angiosperms

There are three types of tissue in an angiosperm, the dermal, ground and vascular tissue. Dermal

tissue is composed of epidermal cells, closely packed cells that secrete a waxy cuticle that aids in

the prevention of water loss. The ground tissue comprises the bulk of the primary plant body.

Parenchyma, collenchyma, and sclerenchyma cells are common in the ground tissue.

Vascular tissue transports food, water, hormones and minerals within the plant. Vascular tissue

includes xylem, phloem, parenchyma, and cambium cells.

Dermal Tissue

Generally a single layer of cells

The "skin" of the plant

Primarily parenchyma cells

Main role is protection of the plant

The dermal tissue system consists of the epidermis and the periderm.

http://www.nsci.plu.edu/~jmain/b359web/pages/periderm.htm

http://www.nsci.plu.edu/~jmain/b359web/pages/epiderm.htm


The epidermis is generally a single layer of closely packed cells. It both covers and

protects the plant. It can be thought of as the plant's "skin." Depending on the part of the plant

that it covers, the dermal tissue system can be specialized to a certain extent. For instance, the

epidermis of a plant's leaves secretes a coating called the cuticle that helps the plant retain water.

The epidermis in plant leaves and stems also contain pores called stomata. Guard cells in the

epidermis regulate gas exchange between the plant and the environment by controlling the size

of the stomata openings.

The periderm, also called bark, replaces the epidermis in plants that undergo secondary

growth. It is multilayered as opposed to the single layered epidermis. It consists of cork cells

(phellem), phelloderm, and phellogen (cork cambium). Cork cells are nonliving cells that cover

the outside of stems and roots to protect and provide insulation for the plant. The periderm

protects the plant from pathogens, injury, prevents excessive water loss, and insulates the plant.

Ground Tissue

Makes up the bulk of the plant

Predominately parenchyma, but collenchyma and schlerenchyma cells are found

Diverse functions including photosynthesis, storage, and support

The ground tissue system synthesizes organic compounds, supports the plant and

provides storage for the plant. It is mostly made up of parenchyma cells but can also include

some collenchyma and sclerenchyma cells as well. Parenchyma cells synthesize and store

organic products in a plant. Most of the plant's metabolism takes place in these cells.

Parenchyma cells in leaves control photosynthesis. Collenchyma cells have a support function in

plants, particularly in young plants. These cells help to support plants while not restraining

growth due to their lack of secondary walls and the absence of a hardening agent in their primary

walls. Sclerenchyma cells also have a support function in plants, but unlike collenchyma cells,

they have a hardening agent and are much more rigid.

http://biology.about.com/od/plantbiology/a/aa050605a.htm



Parenchyma

A generalized plant cell type, parenchyma cells are alive at maturity. They function in

storage, photosynthesis, and as the bulk of ground and vascular tissues. Palisade parenchyma

cells are elogated cells located in many leaves just below the epidermal tissue. Spongy

mesophyll cells occur below the one or two layers of palisade cells. Ray parenchyma cells occur

in wood rays, the structures that transport materials laterally within a woody stem. Parenchyma

cells also occur within the xylem and phloem of vascular bundles. The largest parenchyma cells

occur in the pith region, often, as in corn (Zea ) stems, being larger than the vascular bundles. In

many prepared slides they stain green.

The cells of parenchyma are large, thin-walled, and usually have a large central vacuole.

They are often partially separated from each other and are usually stuffed with plastids. In areas

not exposed to light, colorless plastids predominate and food storage is the main function. The

cells of the white potato are parenchyma cells. Where light is present, e.g., in leaves, chloroplasts

predominate and photosynthesis is the main function of parenchyma cells.

Sclerenchyma

Sclerenchyma cells support the plant. The walls of these cells are very thick and built up

in a uniform layer around the entire margin of the cell. Often, the cell dies after its cell wall is

fully formed. Sclerenchyma cells are usually associated with other cells types and give them

mechanical support. They are usually found in stems and also in leaf veins. Sclerenchyma also

makes up the hard outer covering of seeds and nuts. They often occur as bundle cap fibers.

Sclerenchyma cells are characterized by thickenings in their secondary walls. They are dead at

maturity. They, like collenchyma, stain red in many commonly used prepared slides. A common

type of schlerenchyma cell is the fiber. Some of these cells occur in the fruits of pear which gives

pears their gritty texture.

Collenchyma

Collenchyma cells have thick walls that are especially thick at their corners. These cells

provide mechanical support for the plant. They are most often found in areas that are growing

rapidly and need to be strengthened. The petiole ("stalk") of leaves is usually reinforced with

collenchyma.

Collenchyma cells support the plant. They are alive at maturity. They tend to occur as

part of vascular bundles or on the corners of angular stems. In many prepared slides they stain

red.


Vascular Tissue

Involved in the transport of water, ions, minerals, and food

Also has a secondary role in support

Composed of xylem, phloem, parenchyma, schlerenchyma

Xylem and phloem throughout the plant make up the vascular tissue system. They allow

water and other nutrients to be transported throughout the plant.

Xylem consists of two types of cells known as tracheids and vessel elements. Tracheids

and vessel elements form tube-shaped structures that provide pathways for water and minerals to

travel from the roots to the leaves. While tracheids are found in all vascular plants, vessels are

found only in angiosperms.

Phloem is composed mostly of cells called sieve-tube cells and companion cells. These

cells assist in the transport of sugar and nutrients produced during photosynthesis from the leaves

to other parts of the plant. While tracheid cells are nonliving, sieve-tube and companion cells of

the phloem are living. Companion cells possess a nucleus and actively transport sugar into and

out of sieve-tubes.

Guard Cells

Guard cells contain chloroplasts and regulate gas exchange between the inside of the leaf

and the surrounding air. To facilitate gas exchange between the inner parts of leaves, stems, and

fruits, plants have a series of openings known as stomata (singular stoma). Obviously these

openings would allow gas exchange, but at a cost of water loss. Guard cells are bean-shaped cells

covering the stomata opening. They regulate exchange of water vapor, oxygen and carbon

dioxide through the stoma.

The "Typical" Plant Body

The Root System

Underground (usually)

Anchor the plant in the soil

Absorb water and nutrients

Conduct water and nutrients

Food Storage

http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookglossG.html#guard%20cells

http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookglossS.html#stomata

http://biology.about.com/od/cellanatomy/p/nucleus.htm


http://www.nsci.plu.edu/~jmain/b359web/pages/phloem.htm

http://www.nsci.plu.edu/~jmain/b359web/pages/xylem.htm


The Shoot System

Above ground (usually)

Elevates the plant above the soil

Many functions including:

o photosynthesis

o reproduction & dispersal

o food and water conduction

Note: the shoot system includes the leaves and the reproductive organs, although these

will be covered in more detail separately

Transport System in Plants

Plant cells need water, minerals and sugars to live. Usually the tissues that are devoted

for energy capture are not necessarily where this energy is most needed. So plants need transport

systems to move substances to and from individual cells quickly.

Vascular tissues system is made up of xylem and phloem which run through the leaf,

stem and roots. It‘s main function is to transport water and nutrients throughout the plant.

The leaf’s vascular tissue system is made up of a network of veins which support it. Each vein is

a vascular bundle composed of xylem and phloem surrounded by a sheath of parenchyma cells.

The veins’ xylem and phloem, continuous with the vascular bundles of the stem, are near the

outside to provide a sort of scaffolding to reduce bending; they are in close contact with the

leaf’s photosynthetic tissues. This ensures that those tissues are supplied with water and mineral

nutrients from the soil and that sugars made in the leaves are transported throughout the plant.

Unlike in the leaves and the roots, monocot and dicot stem differ in the arrangement of

their tissues. The dicot stem has a distinct ring of vascular bundles and a two-part ground tissue

system. The dicot cortex fills the space between vascular ring and the epidermis. Monocot stem

has no defined cortex. The pith, composed of parenchyma cells occupies the center. The vascular

tissues are scattered at the outer layer of the pith near the cortex.

In the root, vascular tissue occupies the center forming a cylinder providing support for

the root as it pushes through the soil, with the xylem cells radiating from the center like spokes

of a wheel, and phloem cells filling in the wedges between the spokes.


Xylem and Phloem

Xylem vessels carry water and minerals from the roots up to the leaves. They are thick

walled cells that are not alive. It consists of two types of water-conducting cells namely,

tracheids and vessel elements. Tracheids are long cells with tapered ends. Vessel elements are

wider, shorter and less tapered. Chains of tracheids or vessel elements are arranged end-to-end

forming a system of tubes that convey water from the roots up to the stems and the leaves. The

tubes are hollow because when mature, both tracheids and vessel elements are dead, and only

their cell walls remain. They also have a woody substance called lignin which help support

zylem vessels and stops them collapsing inwards.

Phloem vessels carry food in the form of a sugar called sucrose to all parts of the plant in

either direction. They are build up of food-conducting cells, also known as sieve-tube elements,

which are also arranged end-to-end, forming tubes. Unlike water-conducting cells however,

sieve-tube elements have thin primary walls and no secondary walls and they remain alive at

maturity. Sieve tube elements don’t have nucleus, but contain a very thin layer of cytoplasm and

few organelles. Their end walls are perforated by pores which form sieve plates, through which

sugars, other compounds, and some mineral ions move between adjacent food-conducting cells.

Each sieve tube element is flanked by at least one companion cell, which is connected to the

sieve-tube elements by numerous plasmodesmata. The nucleus and ribosomes of the companion

cells may make certain proteins for the sieve-tube member, which loses its nucleus and

ribosomes during development.

Phloem and xylem also contain schlerenchyma cells that provide support to keep plants

upright and parenchyma cells that store various materials.

Water Transport in Plants

Water and minerals needed by plants are found in the soil, which are absorbed by the

roots through their epidermis in the process of osmosis. Some of these epidermal cells will grow

outward and form root hairs, which will increase the absorptive surface area of the epidermis and

in turn will ensure more efficient absorption of water.

Nutrients then move through the cortex and into the stele via endodermis. From the stele

most minerals moved along with the water up to the stem through the xylem vessels and

tracheids by root pressure, a force produced by the uptake of water because of osmosis.

Root pressure can push water a few centimeters up a short stem but is not sufficient to

bring water up a big tree. Transpiration provides the needed pull to do this. It is the loss of water


from the plant in the form of vapor. As water escapes from the leaves, water below moves up to

replace it.

Factors affecting Transpiration

Light. Light stimulates the stomata to open allowing gas exchange for photosynthesis,

and as a side effect this also increases transpiration. This is a problem for some plants as

they may lose water during the day and wilt.

Temperature. High temperature increases the rate of evaporation of water from the

spongy cells, and reduces air humidity, so transpiration increases.

Humidity. High humidity means a higher water potential in the air, so a lower water

potential gradient between the leaf and the air, so less evaporation.

Air movements. Wind blows away saturated air from around stomata, replacing it with

drier air, so increasing the water potential gradient and increasing transpiration.

Many plants are able to control their stomata, and if they are losing too much water and their

cells are wilting, they can close their stomata, reducing transpiration and water loss. So long

periods of light, heat, or dry air could result in a decrease in transpiration when the stomata close.

Solute Transport in Plants

The phloem contains a very concentrated solution of dissolved solutes, mainly sucrose, but

also other sugars, amino acids, and other metabolites. This solution is called the sap, and the

transport of solutes in the phloem is called translocation.

Unlike the water in the xylem, the contents of the phloem can move both up and down a plant

stem, often simultaneously. It helps to identify where the sugar is being transported from (the

source), and where to (the sink).

During the summer sugar is mostly transported from the leaves, where it is made by

photosynthesis (the source) to the roots, where it is stored (the sink).

During the spring, sugar is often transported from the underground root store (the source)

to the growing leaf buds (the sink).

Flowers and young buds are not photosynthetic, so sugars can also be transported from

leaves or roots (the source) to flowers or buds (sinks).

Surprisingly, the exact mechanism of sugar transport in the phloem is not known, but it is

certainly far too fast to be simple diffusion. The main mechanism is thought to be the mass flow


of fluid up the xylem and down the phloem, carrying dissolved solutes with it. Plants don’t have

hearts, so the mass flow is driven by a combination of active transport (energy from ATP) and

evaporation (energy from the sun). This is called the mass flow theory or pressure flow model

The mass flow theory works like this:

1. Sucrose produced by photosynthesis is actively pumped into the phloem vessels by

the companion cells.

2. This decreases the water potential in the leaf phloem, so water diffuses from the

neighbouring xylem vessels by osmosis.

3. This is increases the hydrostatic pressure in the phloem, so water and dissolved

solutes are forced downwards to relieve the pressure. This is mass flow: the flow of

water together with its dissolved solutes due to a force.

4. In the roots the solutes are removed from the phloem by active transport into the cells

of the root.

5. At the same time, ions are being pumped into the xylem from the soil by active

transport, reducing the water potential in the xylem.

6. The xylem now has a lower water potential than the phloem, so water diffuses by

osmosis from the phloem to the xylem.

7. Water and its dissolved ions are pulled up the xylem by tension from the leaves. This

is also mass flow.

This mass-flow certainly occurs, and it explains the fast speed of solute translocation. However

there must be additional processes, since mass flow does not explain how different solutes can

move at different speeds or even in different directions in the phloem. One significant process

is cytoplasmic streaming: the active transport of molecules and small organelles around cells on

the cytoskeleton.

Plant Reproduction, Growth and Development


Plant Reproduction

Plant reproduction is the production of new individuals or offspring in plants, which can be

accomplished by sexual or asexual means.

Asexual Vegetative Reproduction

Plants are able to produce new plants without reproducing sexually when there is an outgrowth

of old vegetative structures. Vegetative Propagation may occur in two ways:

Natural Process

Artificial Process

Natural Processes of Vegetative Propagation

Most times, asexual reproduction in plants occurs naturally, without human influence. New

plants may be formed from rhizomes, corms, stem tubers, runners, plantlets and bulbs.

Rhizomes

Rhizomes are horizontal underground stems. This is made evident by their physical properties

which greatly reflect the properties of a stem. For example, there are scale leaves or scars where

leaves were once attached to the stem and buds grow in the axils of these leaves. It is from these

bids that the shoots of the new plant develop and grow. Adventitious roots form from the nodes

of the rhizome. There newly developed shoots and adventitious roots form a newly produced

plant. Examples of rhizomes are ginger and devil's grass.

Corms

Corms are short, swollen underground stems which look like short, upright rhizomes. Like most

stems, the corm has a bud(s), which serves as its point of growth. In the case of the corm, the

bud(s) can be found at the top of the corm and it is from this bud that a shoot begins to grow,

eventually forming a new plant. Examples of these corms include dasheen and garlic.

Stem Tubers

http://en.wikipedia.org/wiki/Asexual

http://en.wikipedia.org/wiki/Plant


Stem Tubers are the swollen ends of slender rhizomes. New plants develop from buds and roots

growing at the nodes in the stem tubers. Buds grow into shoots and leaves at the top and on the

side of tubers. Roots grow at the bottom. Examples of stems tubers are Irish Potatoes and yams.

Bulbs

Bulbs are underground vertical shoots which have modified leaves. A modified stem forms the

base of the bulb and it is from this stem that the new plant emerges. Roots emerge from under the

base of the bulb. Shoots and leaves emerge from the top of the base. This root and shoot system

forms a new plant. Example of bulbs includes onion and tulip.

Runners

Runners are also horizontal stems growing from the parent plant, but they grow above ground.

When their terminal buds touch the ground they take root and produce new plants.

Plantlets

Plantlets are a plant asexually reproduced by tissue culture. A plantling is a plantlet growing in a

soil mixture that has attained sufficient size and hardiness to be outplanted.

Artificial Processes of Vegetative Propagation

Gardeners have learned to use the asexual reproduction of plants to their advantage and are now

using artificial methods of vegetative propagation to increase the stock of a plant. Two ways in

which this is done is via cuttings and grafting. These methods are considered to be artificial as

they do not occur naturally

Cuttings

Cuttings are the most common method of artificial vegetative propagation used as many plants

can be produced from just one parent plant. In this method, cuttings may be taken mainly from

the stems and roots of the parent plant. Identical offspring produced by vegetative cuttings are

clones.

Grafting


Grafting occurs this way; Piece of stem is cut from the plant which is being propagated, that is

the plant which is being grafted onto root stock. This piece of stem is inserted into the root stock

and bound tightly in place. After a while, after the vascular bundles of the stem and the root

stocks have been connected to each other, the stem and root stock begin to grow together. The

new plant has all the features of its parent plant but its size is controlled by the root stock which

it has been grafted onto.

Layering

Layering is a practice of propagating a plant by rooting a branch before severing it from the

mother plant. Typically the branch is bent and a section that has been slit or broken on the

underside is covered with soil and held in place by means of stakes or pins.

Sexual Reproduction

Happens primarily in the flower which can take place through pollination, whether self-

pollination or cross-pollination.

Self- pollination

When a plant is self-pollinating, it has the ability to pollinate and fertilize itself. This means that

the plant does not need another plant of the same species for pollination. Pollen is moved from

the male anther of the plant to the female stigma on the same plant.

Cross-Pollination

Cross-Pollination requires two plants of the same species for pollination of the flowers. Without

another plant close by in the same species, the plant is not fertilized. Seed and fruit development

does not occur.

Plant Development


Plants need material resources and energy to grow and develop. Material resources are used as

reactants in chemical reactions involved in the synthesis of new body parts. Energy is needed to

drive these chemical reactions forward.

a.) Optimum Temperature

b.) Sunlight

c.) Water

d.) Mineral Nutrients such as:

-Nitrogen

-Phosphorus

-Potassium

-Calcium

-Magnesium

-Sulfur

-Micronutrients

e.) Gases such as:

-Oxygen

-Carbon Dioxide

Basic Requirements for Plant Growth

Plants produce certain chemical substance that regulates growth and development. These plant

regulators are known as hormones. The following are substances and condition required to

achieve continuous and optimum growth in plants:

a.) Auxins


- is produced by the shoot apical meristem.

- diffuses from the shoot tip where it is produce below the shoot apical meristem.

- is sensitive to light and tends to move away from it.

- promotes cell elongation.

b.) Cytokinins

-are plant regulators that work in combination with auxins to stimulate cell

division and differentiation.

- generally promote cell division and growth of lateral buds but inhibit the

formation of lateral roots.

c.) Gibberellins

- are plant regulators produced in seeds and juvenile plants.

- they promote seed germination in response to water availability and flowering in

response to day length.

- also stimulate the growth of stems and leaves, thereby promoting stem

elongation.

d.) Abscisins (or Abscisic Acid)

- are synthesized mainly in the root cap, mature leaves and fruits.

- promote bud dormancy and affect the closing of the stomata in the leaf.

- help the plant cope with environmental stresses, such as extreme cold and

drought.

e.) Ethylene

- is a gaseous plant regulator that inhibits stem and root elongation.

- it also promotes ripening of fruits, wilting of flowers and aging of leaves.

References


Allen, Robert D. (1995). Biology a Critical Thinking Approach. Dubuque, IA: Wm. C. Brown Publishers

Campbell, Mitchell, Reece, Addison. (1997). Biology: Concepts and Connections. Canada. Wesley Longman Inc

Campbell, Neil A. Biology (Fourth Edition). California: The Benjamin/ Cummings Publishing Company, Inc.

Grolier International Encyclopedia. Plant. Vol. 15 pp. 333-343. 1994

Hadsall, A. (2009). High School Science Today. Makati City: Diwa Learning Systems, Inc.

McMahon, Levin. (2008). Plants and Society (Fifth Edition)

Miller, K., & Levine, J. (1998). Biology the Living Science. New Jersey: Prentice Hall Inc.

Payawal, R., Alvarez, L & Coronado, A. et. al. (2012). Practical Biology: A Modular Approach 2nd edition. Manila

Radford, Albert E. Fundamentals of Plant Systematics

Essenfeld, Gontang, Moore. (2004). Biology. Adison-Wesley Publishing Company

plants: their forms and functions

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