A review on Crop Sciences (Plant Biology)

By: Mark Lawrence B. Edullantes
Cavite State University Indang, Cavite
Philippines

Topics to be discussed:
• Plant Biology
• Agriculture and Crop Science
• Basic Physiological processes of crops

Review Questions to be Answered
Define calyx, corolla, receptacle, peduncle,
pedicel, pistil, filament, ovary and carpel.
Distinguish monocots from dicots.
What is the difference between a fruit and a
vegetable?
What causes an embryo to develop into a fruit?
What are the various parts of a fruit?
How do fleshy fruits differ from dry fruits?

Distinguish among simple, aggregate and multiple
fruits.
Distinguish achenes, grains and nuts.
What adaptation do seeds and fruits have for
dispersal by water and animals?
Define plumule, radicle, coleoptile, coleorhizae,
hypocotyls, after-ripening, stratification and vivipary.

The Leaves
 The leaves are the lateral outgrowth of the
plant’s stem.
 They are flattened surfaces which are covered
by a transparent layer of cell called epidermis,
which allows sunlight to enter in the leaf tissues.
 Leaves are usually green in color due to the
presence of substance called chlorophyll.

Parts of typical
leaf:
• Blade or lamila
• Petiole or leaf stalk
Petiolated leaf
Sessile leaf
• Midrib
• Stipule
Stipulated leaf
Ex-stipulated
leaf

Other leaf parts & function
• Lower epidermis – outmost tissue on the lower side of the
leaf; protects the leaf
• Upper epidermis – outmost tissue on the upper side of the
leaf; protects the leaf
• Palisade layer – rows of elongated cells in the upper center
of leaf; site of photosynthesis
• Cuticle – waxy layer on the covering the epidermis; holds in
moisture, prevents too much absorption of water
• Stoma – opening between the guard cells; allows for gas
exchange and some water
• Guard cells – surround the stoma; control the opening and
closing of the stoma
• Vein – supply support for the leaf; contain the xylem and
the phloem

• Spongy layer – irregular shaped cells in lower center of
leaf; absorbs gas & some water
• Air space – space in the spongy layer; contain gases
• Xylem – found in the vein; transports minerals and
water from roots to shoots
• Phloem – found in the vein; transports sugar & other
products of photosynthesis from leaves to other parts
of the plant
• Chloroplast – cells in the leaves that contain
chlorophyll; trap light energy and convert it to chemical
energy
• Mesophyll – all of the middle tissue of the leaf

Leaf Phyllotaxy
Phyllotaxy refers to the arrangement of
leaves in a stem of a plant.
Alternate- when there is only one leaf at a node
Example. Gumamela
Opposite- when there are two leaves at a node
Example. Santan
Whorled- when there are 3 or more leaves at a
node
Example. Adelfa

Leaf venation
It refers to the arrangement of the veins in a leaf.
Parallel venation- veins run parallel to each other from the base to
the apex, of from the midrib to the margin (as in corn and banana).
Netted venation- veins branch out repeatedly and form a network
over the blade
Includes:
Pinnate venation
Palmate venation

Kinds of leaves
Simple leaf- the blade is made up of only one
piece
Compound leaf- the blade is made up of two
or more pieces. Each piece is called a leaflet
and their individual stalks are called
petiolules.
• Pinnately compound leaves- when there are two rows
of leaflets on both sides of the rachis (odd or evenly
pinnate)
• Palmately compound- when the leaflets radiate from a
common point.

Functions of the leaf
1. Photosynthesis. Leaves make food for the plants in the
process called photosynthesis. The collected solar
energy from the sunlight together with inorganic
substances such as water and carbon dioxide produce a
hexose sugar (called glucose) which is used in plant
metabolism.
2. Transpiration and Guttation. Leaves take part in other
plant functions as well including transpiration and
guttation, both of which remove excess water from the
plant.
3. Respiration. This is the process by which a plant obtains
oxygen and energy.
4. Food and water storage. Leaves may also store food and
water.
5. Structural support.

The Stem
-It is the part of the vascular plants that
commonly bears leaves and buds.
-Usually aerial, upright and elongated, but
may be highly modified in structure.

Parts of stem:
• Nodes- those
points on the stem at
which leaves or buds
arise
• Internodes- the
regions of the stem
between the nodes

Functions of the stem:
1. Production and support of leaves and
reproductive structures
2. Conduction of water and nutrients
3. Translocation of food substances to other
plant parts
4. Food and water storage (such in cactus)
5. Propagation materials as stem cuttings in
cassava and fruit crops through grafting.

Structure of stem
Conducting tissues within the plant stems
are arranged in columns called vascular
bundles. These bundles are composed of
xylem, which conducts water up the stem,
and of phloem, which transports sugars
produced during photosynthesis from leaves
down the stem. Vascular bundles extend into
leaves, in which they are called veins as the
stem grows longer, new cells are added to the
vascular system, providing conductive tissues
for new leaves and branches

The arrangement of vascular bundles
differs in the stems of two major groups of
angiosperms or flowering plants: the
monocotyledons and dicotyledons. In
monocotyledons, such as corn, the vascular
tissue occurs in many scattered bundles
throughout the cross section of the stem. In
dicotyledons, such as the pea, the vascular
bundles are arranged in a cylindrical ring.

Cross section of a woody plant

The reminder of the stem constitutes the
fundamental tissue and is usually divided into
the cortex, or portion outside the ring of
vascular bundles, and the pith, the portion
inside the cylindrical ring. The outer layer of
the stem of herbaceous plants is called
epidermis.

Cambium
thin layer of cells between the xylem and
phloem
 During the growing season, these cells divide
actively, producing new cells that
differentiate into xylem, or wood, toward the
inner side of the cambium and phloem
toward the outer side
As the cambium grows, the diameter of the
stem increases, and the new phloem presses
outward upon the soft tissues of the cortex,
which become distorted and die.

Kinds of stem:
1. Herbaceous stems- stem lacking in woody
growth. May derived strength by other
means (e.g bamboo by the presence of
numerous fibers).
2. Woody stems- are thickened and hard stems
covered by periderm.

Specialized stems:
Thorns- rose, citrus
Tendrils- cucurbits and
some legumes
Corms- gladiola and
gabi
Tubers- white potato
Rhizome- ginger
Photosynthetic stem-
cacti
Economic importance
of stem:
• Source of raw
materials for
industry (e.g.
gummy exudates,
rubber sap etc.)
• Source of building
materials ( e.g.
timber)
• Source of food (e.g
sugarcane, labong)

The Root System
• The root is the vegetative part which
originally goes into the soil or growing media. It is
a cylindrical in structure, normally without
chlorophyll, not divided into nodes and
internodes and does not bear leaf or floral bed.
• Upon seed germination, a part of embryo
within it (radicle) grows out and develops into the
first root. This may develop either into a
thickened taproot, from which thinner branch
roots arise, or into numerous adventitious roots.

• A fibrous root system (monocot) with
numerous fine roots of similar diameter then
develops from the adventitious roots. Many
mature plants have a combination of taproot
and fibrous root system.

Classification of roots according to origin:
1. Primary root- located at the base of the stem,
developed from radicle.
2. Secondary root- arises from the primary root
and may give rise to other roots.
3. Adventitious root- those that grow from
bulbs (e.g. onion), rhizomes (e.g. ginger),
tubers (e.g. potatoes) and plant cuttings
(asexual reproduction).

Functions of the root system:
Anchorage of the plants into the soil
Absorption of water and mineral from the soil
For food and water storage (as in sweet
potatoes and yams)
Provide means for asexual reproduction
For hormone production of plants

Kinds of root system:
Fibrous (monocot) vs. Taproot (dicot) roots systems:
1. Fibrous root system- composed of a mass of similar-
sized roots with numerous smaller root branches.
Examples are food staples rice and corn.
2. Taproot system- composed of one, or occasionally,
more primary roots which remain dominant from
which secondary roots develop. Examples are mango
and mongo (legume),
If the taproot is enlarged so as to serve as storage
for food and water, it is termed fleshy taproot.
Examples include carrot and radish.

Specialized roots
Metamorphosed or specialized roots are roots which are
modified to perform functions other than for absorption or
anchorage.
1. For support of other plant organs
– Brace roots- when the part of the stem near the ground is very small
and incapable of supporting the weight of the whole plant, large roots
grow out from the main stem and serve as the brace of the plant (as in
corn)
– Prop roots- adventitious roots that grow from the branches of the
plant and prop them up (as in pandan plant).
– Aerial adventitious roots- develop into attach branches to their
supporting structures such as trellis or posts. (As in Ivy).
– Buttress roots- plant-like extension growing from the upper portion of
a large root ( as in narra, and Ficus benjamina)

2. For photosynthesis
 Roots to expose light or aerial roots produce
chlorophyll and thus, trough photosynthesis,
cam manufacture with them, are called
photosynthetic roots. (As in orchids).
 For reproduction through asexual propagation
 Many plants produce adventitious buds along
the roots that grow near the surface of the
grounds. The buds grow into aerial stems
called suckers which become rooted and thus,
develop as new plants. Examples include
grasses and weeds.

3. For food and water storage
Underground roots may become very
much thickened and enlarged. They serve as
storage sits for large quantities of starch and
other carbohydrates. Examples include sweet
potatoes and yams

Root structure
Longitudinal section of a young root
a. The root cap- Composed of thimble-shaped mass of
parenchyma cells covering the tip of each root, Protects
from damage the delicate tissues behind it as the young root
tip pushes through the soil particles.
b. The meristematic region- This is the region of cell division or
mitosis. The root cap is produced by the cells in this region,
which is the center of the root tip and surrounded by the
root cap. It is composed of an apical meristem. Cells are of
then cube-shaped, with relatively large centrally located
nuclei and few small vacuoles.

c. The region of elongation- This region is
composed of the mass of cell recently formed in
the merismatic region and undergoing
enlargement, particularly in length. Cell alls also
increase in length, new protoplasm is formed
and vacuoles merge and increase in size.
d. The region of maturation- This region is called
the region of differentiation or root-hair one. It
is composed of cells which have become
differentiated into the mature tissues of the
root. Root hairs develop from many epidermal
cells in this region.

2. Cross section of a root through the region of maturation
• Epidermis: The outermost region of the root made up of
a single layer of non-cutinized cells. The surface tissue
absorbs water and minerals from the soil and offer
protection to the inner tissues of the root. It has
specialized structures that is in work of absorption called
root hairs.
• Cortex: A tissue composed of parenchyma cells adjacent
to the epidermis. It is comprised of irregularly shaped
parenchyma cells with many intercellular spaces. This is
chiefly a water and food storage site.

• Endodermis: innermost
layer of the cortex with
inner and side walls
thickened with suberin.
Such thickenings usually
take the form of thin
waxy strips called
Casparian strips.
• Pericycle: a cylinder of
parenchyma cells inside
the endodermis and
immediately adjacent to
it. It is composed of cells
which retain their
capacity to divide even
after they have matured.
Lateral or branch roots
arise from the pericycle.

• Primary xylem: Composed of water conducting cells
which form a solid core in the center of the roots of
most dicot and conifers. In monocots, the primary
xylem forms a cylinder of tissue.
• Primary phloem: Composed of food conducting cells.
It forms in discrete patches between xylem arms of
both monocot and dicot roots.

The Reproductive System of the Plants
The Flower
Flower- name applied to reproductive organs
of certain plants which produce fruits
containing seeds. Not all seed plants have
flowers; conifers, for example produce seed
on scales united to form a cone.

Parts of a Flower
• Receptacle or floral axis- terminal
branch consisting of a modified
stem, the floral axis, or receptacle.
The floral axis bears one to four
types of specialized appendages, or
modified leaves, usually arranged
in whorls in the more advanced
flowers and spirally arranged in the
more primitive ones.
• Calyx- the outermost whorl
consists of a number of sepals that
protect the flower bud before it
blooms.
• Corolla- composed of a number of
petals, often bearing nectar-
producing glands that aid in
attracting pollinators. The calyx
and corolla are collectively known
as the perianth.

• Androecium- consists of a number of stamens
that produce in anthers the pollen necessary
for reproduction. Two whorls of stamens may
be present.
• Gynoecium- consists of several carpels
frequently fused to form a pistil. Each carpel
contains at least one ovary to which is
attached ovules, or immature seeds.

Flowering plants are divided into two major
classes, the dicots and the monocots. In the dicots,
floral organ in multiples of five or four predominate, in
the monocots, multiples of three are usual.

Types of flower
1. Complete flowers- bear sepals, petals, stamens and
pistils
2. Incomplete flowers- lack any of the mentioned parts
– Imperfect flower- lack the parts involved in reproduction-
the stamens or pistils-
– Perfect flower- both pistils and stamens are present but
lack the other parts.
If only pistils are present the flower is said to be
pistillate; with stamens only, staminate. Typical
flowers are bisexual. When staminate and pistillate
flowers occur on one plant, it is said to be monoecious
when they occur on different plants, dioecious.

Forms of Flower
1. Radially symmetrical flowers- sepals and
petals are uniform in size and arranged in a
star-shaped or radially symmetrical form.
2. Bilaterally symmetrical flowers- have petals
that differ in size and shape. The five petals
the sweet pea, for example, include a large,
showy banner, or standard petal, two smaller
wing-like petals at the side of the flower, and
between them the keel, two petals that
encase the pistils and stamens. These are
united along their edges.

Figure 12. Types of flower inflorescence

Pollination
The transfer of pollen from the stamen, or male structures of a flower, to the
region of the pistil or female structure, of the same or different flower.
Kinds of pollination
Self-pollination or autogamy- the pollen is transferred from the stamen to
the stigma of the same flower.
Cross-pollination or allogamy- pollen is transferred from one flower to
another on the same plant (geitonogamy) or to a flower of another plant
of the same species (xenogamy).
Agents of pollination
 Wind
 Bees and other insects
 Birds and bats
 Man (hand pollination)
Opening of flowers is termed anthesis.

The Fruit
A fruit is mature ovary on flowering plants, together with
all inseparably connected parts of the flower. It is normally
produced only after fertilization of ovules taken place. In
some plants, largely cultivated varieties such as seedless citrus
fruits, bananas and cucumbers, fruit matures without
fertilization, a process known as parthenocarpy. The
maturation of the ovary results in the withering of stigmas
and anthers and enlargement of the ovary or ovaries. Ovules
within fertilized ovaries develop to produce seeds. In
unfertilized varieties, seeds fail to develop, and the ovules
remain their original size.

Function of the Fruits
The major function performed by fruit is
the protection of the developing seeds. In
many plants fruit also aids in seed distribution
as in coconut and other species where fruits
themselves function as propagating material.

Structure of Fruit
 Pericarp
As the ovary matures, its wall develops to form the pericarp,
divided into three layers. The outermost, exocarp, is usually
a single epidermal layer. The extent of the middle layer,
mesocarp, and the inner layer, endocarp, varies widely, but
in any single type of fruit one of the layers may be thick,
the others thin. In fleshy fruits the pulpy layer is usually the
mesocarp, as in peaches or grapes.
 Seed/Seeds
The seed or seeds, which lie immediately within the pericarp,
in some cases constitute the entire edible portion of the
fruit. For example, the hard outer husk of a coconut is the
complete pericarp, and the edible part inside, including the
“milk”, is the seed.

Structure of the fruit wall
The fruit consists of the wall and the seed.
The wall could be dry (has a very low moisture
content) or fleshy (succulent). A dry fruit could
be either dehiscent (splits apart when ripe) or
indehiscent. Thus beans become dry and
dehiscent at maturity while the mango is
fleshy. The fruit may show three distinct
layers: exocarp or pericarp, the outermost
layer; mesocarp, the middle part and
endocarp, the inner part.

Caryopsis- the pericarp or seed coat is a very
thin layer and is fused with the ovary (e.g
corn kernel).

Types of Fruit
1. Simple fruit- formed from a single ovary, developed
from the pistil of a single flower which may be
single or compound
2. Aggregate fruit- composed of many ovaries
attached to a single receptacle, as in soursop and
strawberry.
3. Multiple fruit- formed from the coalesced ovaries of
an entire inflorescence as in pineapple.

Sub-division of simple fruit
 Dry simple fruit
 Fleshy simple fruit
Ovary walls that develop into simple fruits are
succulent when young, but as they mature, those of
dry fruits lose most of their moisture, whereas those of
fleshy fruits increase in size and moisture capacity.
Sub-classes of dry fruits
1. Dry dehiscent fruits- dry fruits that split when ripe
2. Dry indehiscent fruits- those that do not split when
ripe

Types of fleshy fruits
• Berry- typified by the tomato
possesses seeds dispersed
throughout the fleshy mesocarp
and endocarp; the exocarp is thin
and skinlike.
• Hesperidium- all citrus fruits.
These have leathery rinds
composed of exocarp and
mesocarp and juicy section of
endocarp.
• Pepo- fruits of the Cucurbitacae,
includes cucumber, pumpkins
and melons. The outer layer of
the pepo is receptacle tissue
covering the exocarp; the pulpy
portion of the fruit is mostly
endocarp and mesocarp.
endocarp, the fleshy portion is
mesocarp.

• Pome- fruits with a pericarp limited to the so-called
core and the inner fleshy portion of the fruit, as in
apples and pears. The outer portion of the fleshy
part of a pome is tissue developed from the fusion of
the other floral parts and the ovary.
• Drupe- the stone fruit of such plants as mango,
avocado, plum, cherry and peach. The single seed is
surrounded by a stony

The Seed
Seed, term applied to the ripened ovule.
Seeds of the angiosperms or flowering plant
differ from those of the gymnosperms or
conifers and related plants, in being enclosed
in the ovary that later forms a fruit;
gymnosperm seeds lie on exposed scales of
the cones.

Parts of a dicot seed:
• Seed coat- protective
covering
• Plumule- embryo shoot
• Hypocotyle-radicle axis
• Hilum- marks the point at
which the ovule was
attached to the ovary.
• Microphyle- visible pore
adjacent to the hilum
• Cotyledons- food-storage
organs
• that also function as the
first leaves of the seedling
plant.

Parts of a monocot seed:
• Pericarp- From the wall of
the embryo sack (mother
tissue)
• Endosperm- Food supply
containing 3 sets of
chromosomes (2 from the
mother and 1 from the
father)
• Embryo - Immature plant
• Cotyledon- Seed leaf
• Coleoptile-
• Plumule-shoot
• Radicle- root
• Coleorhiza-

Seeds remain viable for periods that vary
greatly, depending on the species and the
condition of the storage.
Vivipary- the embryo develops from the
zygote continues to grow without pause. No
dormancy of the seed.

CHAPTER 2: AGRICULTURE AND CROP
SCIENCE

Agriculture defined
Agriculture is the art, science and business of
growing crops and raising livestock for food,
shelter and raw materials for processing essential
to mankind. It also involves primary processing of
farm produce.
The science, art, or practice of cultivating the
soil, producing crops, and raising livestock and in
varying degrees the preparation and marketing of
the resulting products (Merriam-Webster).

Crop production defined
According to Lantican (2001), Crop production may
be defined as the art and science of producing crops,
aimed at increasing productivity and quality of the
products in order to maximize monetary returns but at
the same time minimize, if not completely eliminate,
the negative effects on the environment.
Crop production covers principles underlying crop
growth and development, production practices of
economically important agronomic and horticultural
crops, harvesting, and primary aspects of crop
processing. Long term objective of crop production is
to enhance the environment.

Branches of Crop Science
• Agronomy
Agronomy is a term derived from the Latin
words, “Agros”, meaning field or farm and
“Nomos”, pertaining to management. It
involves annual herbaceous plant grown on
large-scale or extensive culture.

Classification of major agronomic crops
• Cereal or grain crops- Graminaceae, which are food staples. It
includes important grains such as corn, rice, sorghum, wheat, millet
and rye.
• Grain legumes or pulses – belong to family Leguminoseae, which
are consumed in dry seed form. It includes mungbean, peanut and
soybean.
• Fiber crops- sources of commercial fiber which includes: kenaf, jute,
ramie and cotton.
• Root crops- which are rich sources of carbohydrates. It inclides
cassava and sweet potato.
• Forage legumes and grasses for animal fodder- Important grasses
are: napier, guinea grass, paragrass, and pangola grass. Important
legume forage are cento, ipil-ipil, Townville style and siratro.
• Crops for industrial processing- The economic species include
sugarcane, tobacco and castor bean.

Horticulture
The term horticulture derived from the
Latin words, “hortus”, meaning garden and
“colore”, meaning to cultivate. It involves
annual and perennial species which are grown
under a system of “intensive” culture or
special care. Intensive cultivation refers to
higher unit of input in terms of labor and
capital is invested per cultivated land area.

Classification of major horticultural crops:
• Olericulture or vegetable group- It consists of
broad range of crops including leafy, fruit and
root vegetables.
• Pomological or fruit crops- Are consumed
fresh or processed form. It includes mango,
pineapple, papaya, lanzones, rambutan,
pummel and durian.
• Ornamental plants- Includes cutflowers,
cutfoliage, flowering pot plant, landscape
plant and dry and processed ornamentals.

• Plantation crops for industrial processing- crops
need processing for consumption includes coconut
(oil), cacao (chocolate), coffee (beverage), abaca
(textile) and rubber.
It also includes:
- Spice producing crops - black pepper and vanilla
- Aromatic or essential-oil producing crops, lemon
grass, citronella and ilang-ilang
- Medicinal and biocidal plants, are sources of
pharmaceutical or insecticidal compounds. It
includes lagundi, yerba Buena and sambong.

Crop Protection
Encompasses the discipline of 1.)
entomology, study of insects; 2.) plant
pathology, the study of plant diseases; 3.)
weed science, the study of weed; and 4.) the
study of other vertebrate pests (e.g. rats and
birds).

CHAPTER 3: BASIC PHYSIOLOGICAL
PROCESSES OF CROPS

Crop Growth and Development
Growth is the irreversible increase in size and in
dry matter due to increase in vegetative or
reproductive parts. It includes increase in number of
cells, weight and enlargement of the cells in terms of
width, length, diameter and area.
Development refers to all the changes that the
plant undergoes from germination up to before
death.
Differentiation is the process by which cells
become specialized into recognizable tissues and
organs.

Photosynthesis
Photosynthesis is the process in which carbon dioxide and
water, to the presence of light and chlorophyll, are converted to carbon-
containing energy rich organic compounds needed for plant metabolism.
The process of photosynthesis can be generalized by the following:

Consequences:
1. Conversion of light energy into chemical
energy, for metabolic processes by plants;
2. Inorganic compounds are converted into
essential foodstuffs and other products
useful to man;
3. The release of oxygen into the atmosphere
which is used in respiration of both plants
and animals.

Light Dependent Reaction
The light dependent reaction happens in the
thylakoid membrane and converts light energy to
chemical energy. This chemical reaction must,
therefore, take place in the light. Chlorophyll and
several other pigments such as beta-carotene are
organized in clusters in the thylakoid membrane and
are involved in the light reaction. Each of these
differently-colored pigments can absorb a slightly
different color of light and pass its energy to the
central chlorphyll molecule to do photosynthesis. The
central part of the chemical structure of a chlorophyll
molecule is a porphyrin ring, which consists of several
fused rings of carbon and nitrogen with a magnesium
ion in the center.

Light Independent Reaction (Dark reaction)
The energy harvested via the light reaction
is stored by forming a chemical called ATP
(adenosine triphosphate), a compound used
by cells for energy storage. This chemical is
made of the nucleotide adenine bonded to a
ribose sugar, and that is bonded to three
phosphate groups. This molecule is very
similar to the building blocks for our DNA.

The dark reaction takes place in the stroma
within the chloroplast, and converts CO2 to sugar.
This reaction doesn’t directly need light in order
to occur, but it does need the products of the
light reaction (ATP and another chemical called
NADPH). The dark reaction involves a cycle called
the Calvin cycle in which CO2 and energy from
ATP are used to form sugar. Actually, notice that
the first product of photosynthesis is a three-
carbon compound calledglyceraldehyde 3-
phosphate. Almost immediately, two of these join
to form a glucose molecule.

C3 and C4 pathways
C3 pathway
Most plants like rice, wheat, potato cotton
and tobacco put CO2 directly into the Calvin
cycle. Thus the first stable organic compound
formed is the glyceraldehyde 3-phosphate.
Since that molecule contains three carbon
atoms. On hot summer weather the amount
of water that evaporates from the plant
increases.

Plants lessen the amount of water that
evaporates by keeping their stomates closed
during hot, dry weather. Unfortunately, this
means that once the CO2 in their leaves
reaches a low level, they must stop doing
photosynthesis. Even if there is a tiny bit of
CO2 left, the enzymes used to grab it and put
it into the Calvin cycle just don’t have enough
CO2 to use.

C4 pathway
Other plants like corn and sugarcane
capture CO2 in a different way: they do an
extra step first, before doing the Calvin cycle.
These plants have a special enzyme that can
work better, even at very low CO levels, to
grab CO2 and turn it first into oxaloacetate,
which contains four carbons.

CAM Plants (Crassulecean acid metabolism)
Some plants (for example, cacti and pineapple) that live
in extremely hot, dry areas like deserts, can only safely open
their stomates at night when the weather is cool. Thus, there
is no chance for them to get the CO2 needed for the dark
reaction during the daytime. At night when they can open
their stomates and take in CO2, these plants incorporate the
CO2 into various organic compounds to store it. In the
daytime, when the light reaction is occurring and ATP is
available (but the stomates must remain closed), they take
the CO2 from these organic compounds and put it into the
Calvin cycle.

Requirements of photosynthesis
Carbon dioxide and water. These are the raw materials for
photosynthesis. Carbon dioxide comes from the air and enters trough the stomata
of the leaves. On the other hand, water is supplied through the soil in the process
called absorption.
Sunlight. Photosynthesis requires the expenditure of large amounts of
energy. It uses the light energy from the sun (as photo means sun, in the word
photosynthesis).the more intense and the longer the light duration the greater the
chances to capture adequate light for crop growth and development. Light
requirement varies among plant species. Light intensity is the most important
factor that affects photosynthesis.
Chlorophyll. The green pigment of plants, which is found in the chloroplast of
the leaves that traps light energy necessary for photosynthesis. For the synthesis
of chlorophyll, carbon, hydrogen, oxygen, nitrogen, magnesium and manganese
are needed as building blocks.
Enzyme. A protein molecule that is necessary for each complex reaction to
proceed during photosynthesis. Each enzyme is specific for a particular reaction.
The presence or absence of a specific enzyme tells whether a reaction will proceed
or not.

Translocation
Translocation refers to the movement of
photosynthates within the plant.
Photosynthates are most needed in the roots,
developing flowers, fruits and seeds and the
growing region of the stem and roots.

Respiration
In respiration, the stored food from
photosynthesis is broken down and energy is
released to power necessary processes within the
cells. Like photosynthesis, respiration also involves
complex reactions.

Energy required for growth and
development is released in respiration. The
complex carbohydrates are broken down first
through a process called glycolysis into an acid
with three carbons in its structure. Then, this
enters into a cycle (Kreb’s cycle), in which it is
changed from one organic acid to another.

In the process, Adenosine triphosphate
(ATP) is released as a source of energy, CO2 is
given off, and the hydrogen removed from the
acids combines with oxygen to form water.
Some of the acids formed in the cycle may
separate and serve as building blocks for other
plant constituents like plant growth
regulators.

The process of plant respiration requires
1.) the products of photosynthesis or
photosynthates;
2.) oxygen;
3.) enzymes. Enzymes are synthesized in all
plant parts.

Transpiration
Water in the roots is pulled through the
plant by transpiration (loss of water vapor
through the stomata of the
leaves). Transpiration uses about 90% of the
water that enters the plant. The other 10% is
an ingredient in photosynthesis and cell
growth.

Transpiration serves three essential roles:
• Movement of minerals up from the root (in the xylem) and
sugars (products of photosynthesis) throughout the plant
(in the phloem). Water serves as both the solvent and the
avenue of transport.
• Cooling – 80% of the cooling effect of a shade tree is from
the evaporative cooling effects of transpiration. This
benefits both plants and humans.
• Turgor pressure – Water maintains the turgor pressure in
cells much like air inflates a balloon, giving the non-woody
plant parts form. Turgidity is important so the plant can
remain stiff and upright and gain a competitive advantage
when it comes to light. Turgidity is also important for the
functioning of the guard cells, which surround the stomata
and regulate water loss and carbon dioxide
uptake. Turgidity also is the force that pushes roots
through the soil

Factors affecting Growth and Development
Internal factors
Yield potential. Yield potential is usually a reflection of the
ability of the plant to utilize and adapt to its aerial environment in
terms of its morphology, anatomy or biochemical nature.
Relative susceptibility to unfavorable environmental conditions.
Unfavorable environmental conditions include presence of harmful
insects and diseases, water logging, drought, too high or low
temperature and too much or low of nutrients.
Natural size. A plant that is naturally small at maturity
either lacks the genes that manufacture the enzyme necessary to
convert the initial products of photosynthesis into gibberellins,
which is necessary for “normal” or typical plant growth.

External factors
External or environmental factors includes:
• Physical factors
• Includes light, temperature, soil relative
humidity and rainfall
• Chemical factors
• Presence or absence of gases and nutrients
• Biological factors
• Insects, microorganisms, weeds, animals or
even humans

Biotic factors
All life forms existing around the
immediate vicinity of the crop are considered
biotic factors. Most of them compete for
space, food, water, light and nutrients such as
weeds.

A review on Crop Sciences (Plant Biology)

A review on Crop Sciences (Plant Biology)

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