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Developmental biology is the branch of biology that studies the processes by which organisms grow and develop from a single cell into a complex multicellular organism. Developmental biologists investigate how genes and environmental factors interact to shape the structure, function, and behavior of organisms.


is the progre­ssion from earlier to later stages in matura­tion. It is the process whereby tissues, organs, and whole plants are produced.
involves: growth, morpho­genesis (the acquis­ition of form and struct­ure), and differ­ent­iation.
refers to an irreve­rsible increase in mass.
The process in which the cells of the apical meristems mature to perform specific functions.
is the acquis­ition of form, how a plant or organ acquires its distin­ctive shape or form.
is the ability to change form or shape in response to a change in enviro­nment; no genetic change is involved.
Plant develo­pment is highly plastic

Types of growth in Plants

Indete­rminate growth
Plant organ grow contin­uously
Plant organ grow contin­uously Ex. Root and stem
Determ­inate growth
Organs stop growing after reaching a certain size.
Ex. Leaves, flowers and fruits


Primary growth
is an increase in stem and root length
Secondary growth
is an increase in the girth of plant.

Structural and functional unit

basic structural and functional unit of plants
basic structural and functional unit of plants
Plant tissue systems fall into one of two general types:
merist­ematic tissue
permanent (or non-me­ris­tem­atic) tissue


plant regions of continuous cell division and growth
merist­ematic tissue
is a group of identical cells that are in a continuous state of division
Cells that remain as sources of new cell.
The new cells displaced from the meristem.

Types of Merist­ematic Tissues

apical meristem
interc­alary meristem
interc­alary meristem

Apical meristem

Apical meristem
A small mitoti­cally active zone of cells found at the shoot tip or root tip
Primary growth occurs as a result of the activity of apical meristem
primary tissues
Tissues derived from the apical meristems are
Form primary meristems that produce the tissues of the stem and root
a. Protoderm (which forms the epidermis)
b. Procambium (which forms phloem and xylem)
c. Ground meristems (which form parenc­hyma)

Lateral Meristem

are known as secondary meristems because they are respon­sible for secondary growth, or increase in stem girth and thickness
Give increase in girth (secondary growth)
Produces secondary vascular tissues
Two lateral meristems: the vascular cambium and the cork cambium are respon­sible for secondary growth

Vascular Cambium

sometimes known just as cambium) is a cylinder of cells that forms new phloem and xylem.
Division of the cells of the vascular cambium adds more cells to the wood(s­eco­ndary xylem) and inner bark (secondary phloem).
You can find out the age of a tree by counting the number of dark rings

Cork Cambium

the outermost lateral meristem.
It produces cork cells, which contain a waxy substance that can repel water.
The phloem together with the cork cells form the bark.
The cork cambium also produces a layer of cells known as phelloderm
The cork cambium, cork cells, and phelloderm are collec­tively termed the periderm.

Interc­alary meristem

Regions of merist­ematic tissue between regions of more mature tissues
Occur only in monocots, at the bases of leaf blades and at nodes (the areas where leaves attach to a stem).


Permanent tissue
consists of plant cells that are no longer actively dividing
Three main types:

Plant Reprod­uction and Embryo­genesis

Altern­ation of generation
All land plants (and some green algae) reproduce via the altern­ation of genera­tions life cycle, where both the haploid and the diploid stage are multic­ell­ular.
Sporophyte (Diploid stage)
produces spores
Gameto­phyte (Haploid) stage)
formed from the spore and give rise to the haploid gametes
Haploid (n)
the quality of a cell or organism having a single set of chromo­somes
Diploid (2n)
a cell or organism that has paired chromo­somes
a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reprod­uction to form a zygote
a minute, typically one-ce­lled, reprod­uctive unit capable of giving rise to a new individual without sexual fusion


The reprod­uctive structure found in flowering plants which is specia­lized for sexual reprod­uction
Pollin­ation and Reprod­uction


Male Gameto­phyte (The Pollen Grain)
is the male gameto­phyte in angios­perms and gymnos­perms.
micros­por­angium (micro = small)
this is where ollen develo­pment occurs, located within the anthers.
micros­por­angia (P of micros­por­angium)
are pollen sacs in which the micros­pores develop into pollen grains.

Female Gameto­phyte (The Embryo Sac)

Embryo sac / female gameto­phyte
is an oval structure present in the ovule of flowering plants.
It possesses two haploid nuclei and six haploid cells which do not have cell walls.

How does pollin­ation and fertil­ization occur?

The transfer of pollen from a male part of a plant to a female part of a plant, later enabling fertil­ization
is pollin­ation of a carpel by pollen from the same flower or another flower on the same plant
is the pollin­ation of a carpel by pollen from a different individual
Methods of Pollin­ation
Biotic Pollin­ation
◻ involves pollin­ators (also called pollen vectors)
Abiotic Pollin­ation
◻ wind, water and rain
Double Fertil­ization
Double fertil­ization involves two sperm cells; one fertilizes the egg cell to form the zygote, while the other fuses with the two polar nuclei that form the endosperm.


is the first stage of the develo­pment of a new organism from its first cell named zygote, which appears as a result of the sexual fertil­iza­tion.

Seed develo­pment

After double fertil­ization.
each mature ovule develops into a seed
the ovary develops into a fruit enclosing the seed(s)
are protective structures that contain plant embryos and nutritive tissue to support the embryo until it can survive on its own
A typical seed contains:
a. Seed coat
b. Endosp­erm­/co­tyledon
c. single embryo


1. Seed coat
They are the protective outer covering of a seed. The seed coat is formed from the outer covering of the ovule called the integu­ment.
It usually contains two layers:
testa – the thick outer layer
tegmen – the delicate inner layer.
Protecting the seed from physical and mechanical damage
Preventing the seed from germin­ation even under favorable conditions of growth (seed dormancy)
Preventing the excessive loss of water from the seeds
Acting as a physical barrier against the entry of parasites
2. Endosperm
It is a tissue that is rich in oil, starch, and protein.
Non-en­dos­permic or exalbu­minous seeds
Charac­terized by the complete absence of the endosperm, such as the seeds of the pea plant, groundnut, and gram.
Endosp­ermic or albuminous seeds
Charac­terized by the presence of the endosperm, such as the seeds of millets, palms, and lilies.
-Storing of reserve foods that provide nouris­hment to the developing plant
-Prote­cting the embryo, the next part of the seed, by acting as the mechanical barrier
3. Embryo
the young plant that is developing inside the seed coat.
contains the underd­eve­loped tissues of leaves, stem, and roots of a plant.
The tiny shoot of an embryo, from which the entire shoot system develops. The tip of the epicotyl is called plumule.
The stage of transition for the growing shoot and root of the embryo
The tiny root of the embryo
They are the leaves of the embryo that provide nouris­hment to the developing plant.
Giving rise to a new complete new plant
Storing food and nourishing the baby plant
two types of cotyledons
monoco­tyl­edonous or monocots
embryo with one cotyledon and
dicoty­led­onous or dicots
– embryo with two cotyle­dons.


The single cotyledon
is connected directly to the embryo via vascular tissue (xylem and phloem).
Food reserves are stored in the large endosperm


The two cotyledons in the dicot seed also have vascular connec­tions to the embryo.
In endosp­ermic dicots
the food reserves are stored in the endosperm.
non-en­dos­permic dicots
The triploid endosperm develops normally following double fertil­iza­tion, but the endosperm food reserves are quickly remobi­lized and moved into the developing cotyledon for storage

Seed Germin­ation

mature seeds enter a period of inacti­vity, or extremely low metabolic activity:
is the develo­pment of a plant from a seed after a period of dormancy.
Germin­ation depends on imbibi­tion, the uptake of water due to the low water potential of the dry seed


Any structure that develops from a fertilized ovary and contains seeds of the plant.
The ovary surrou­nding the ovules develops into a fruit that contains one or more seeds.
is actually not a scientific term and simply refers to the edible part of the plant: roots/­tubers, stems, leaves, etc.
is the seed-c­ont­aining part of a plant
is the fleshy or dry ripened ovary of a plant.


While the seeds are developing from ovules, the ovary of the flower is developing into a fruit, which protects the enclosed seeds and, when mature, aids in their dispersal by wind or animals.
Fertil­ization triggers hormonal changes that cause the ovary to begin its transf­orm­ation into a fruit. If a flower has not been pollin­ated, fruit typically does not develop, and the entire flower usually withers and falls away

Parts of a fruit

the ovary wall becomes the pericarp, the thickened wall of the fruit.
the outer layer
middle layer
inner layer


The shoot system consists of two portions:
the vegetative (non-r­epr­odu­ctive) parts of the plant,
leaves and the stems,
the reprod­uctive parts of the plant,
flowers and fruits.
The root system
which supports the plants and absorbs water and miis usually underg­round.


primary plant body
derived from shoot and root apical meristem
composed of primary tissues
consti­tutes the herbaceous parts of a plant
secondary plant body
derived from meristems other than apical meristem
composed of secondary tissues


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