Embryogeny: Definition, Meaning, Diagram, Plants

The development of the embryo from the zygote is known as embryogeny. Embryogeny is a series of mitotic divisions of the zygote and then undergoes differentiation. In plants, structures such as radicle, plumule, cotyledons, and hypocotyl are formed as a result of embryogeny. On the other hand, in animals, cleavage of the zygote occurs, forming the germ layers, and then goes on to form the organs and the whole organism.

This Story also Contains

1. What is Embryogeny?
2. Embryogenesis in Animals
3. Duration and Stages of Pregnancy in Animals
4. Embryogeny in Plants
5. Factors Affecting Embryogeny
6. Common Anomalies of Embryogenesis
7. MCQs on Embryogenesis
8. Recommended Video On 'Embryogeny'

The embryogeny in plants differs in the case of monocots and dicots, particularly in the number and position of cotyledons. The knowledge of embryogeny is essential to understand developmental biology, plant breeding and creates a foundation for techniques like somatic embryogenesis. Embryogeny is a topic in the field of biology.

What is Embryogeny?

Embryogeny is the process by which the zygote—an already fertilised egg—develops into a completely formed embryo. Being such a complex process, it involves multi-staged cell divisions, differentiation, and morphogenesis, finally forming the onset of different tissues and organs of the organism.

Major, general stages of embryogenesis present themselves with the following: fertilisation, zygote formation, blastula stage, gastrula stage, and organogenesis. To single out each process at every stage, one can mention certain cellular processes and structural changes that give rise to the developing embryo.

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Embryogenesis in Animals

Embryogenesis involves a series of coordinated stages wherein a single-celled zygote transforms into a multicellular embryo.

Fertilisation

• A process where a sperm and an egg combine to form a zygote.

• A sperm cell penetrates an egg (ovum) cell, and the egg then becomes activated and its genetic material combines with that of the sperm.

Zygote Formation

• The single cell is formed from the combination of the sperm cell and the egg cell during fertilisation.

• Rapid mitosis of the zygote, without intervening cell growth.

• Formation of a multicellular structure called a morula.

Stage of Blastula

• This is the process of the development of a hollow sphere composed of cells, known as a blastocyst.

• A fluid-filled cavity formed inside a spherical layer of cells: blastocoel.

• The central cavity is formed within the blastula.

Gastrula Stage

• Gastrulation is a process that rearranges the blastula into a three-layered formation called the gastrula.

• The cell movement leads to the development of the primary germ layers.

Formation Of The Germ Layers

• Ectoderm: The outer layer of skin and the nervous system.

• Mesoderm: It forms the middle layer, such as muscles and bones.

• Endoderm: it forms the inner layer, like the digestive tract and organs.

Organogenesis

• Organogenesis is the process through which germ layers develop into the organs and tissues of the organism.

• Cells from germ layers become specific to form particular organs, such as the heart, lungs, and brain.

Duration and Stages of Pregnancy in Animals

Pregnancy is the most important period in human development, normally ranging to about 40 weeks from the first day of the last menstrual period to childbirth. It is divided into three trimesters that have quite significant developmental milestones.

First Trimester: Weeks 1-12

The developments in this period are given below:

• Fertilisation ensues, resulting in a zygote.

• The zygote divides and is implanted in the uterine wall.

• Major organs and structures start to form.

• The heartbeat is detectable by the end of week 6.

Second Trimester (Weeks 13-26)

The developments in this period are given below:

• Rapid growth and development of body systems.

• Movement of the fetus (quickening) is felt by the mother.

• Formation of skeletal structure and facial features.

• Development of sensory organs; The fetus can hear and respond to stimuli.

Third Trimester (Weeks 27-40)

The developments in this period are given below:

• Rapid weight gain and maturation of lungs and other vital organs.

• Positioning of the fetus for birth (head down).

• Braxton Hicks's contractions can be felt.

• More frequent prenatal visits will be booked to make sure the baby is healthy.

Key Milestones In Pregnancy

• Week 4: Implantation complete

• Week 8: All major organs start to develop

• Week 12: The chance of miscarriage greatly decreases

• Week 20: Ultrasound can detect the sex of the baby

• Week 24: The Baby has a survival chance outside the womb if a medical intervention is made

• Weeks 37-40: Fully developed pregnancy; the baby is ready to come out of the mother's body.

Embryogeny in Plants

Plant embryogeny consists of stages and processes particular to both monocots and dicots. The differences and similarities between embryogeny in monocots and dicots are described in table below-

Embryogeny Stages in Detail

Proembryo Stage

The proembryo stage begins when the zygote divides into two cells: an apical small cell that gives rise to the embryo proper and a large basal cell that grows to form the suspensor.

Globular Stage

At this stage, the developing embryo becomes globular in shape. Cellular differentiation matures, and the suspensor is extended to allow the embryo to grow further into the nutrient-containing tissue. Cells begin to differentiate into various tissue types.

This establishes the basis for future development of the plant organs and structures. The suspensor becomes larger and continues growing to deliver the nutrients ingested from the endosperm into the growing embryo.

Heart Stage

At this stage, the heart-shaped structure is developed in dicots. In monocots, a single cotyledon starts to develop, that is, the scutellum, with the initiation of the root and shoot meristems. The scutellum develops from the apical part of the embryo and acts as a nutrient-absorbing organ, which in turn supports the development of seedlings after germination.

Torpedo Stage

During the torpedo stage, the embryo becomes elongated as the tissues become even more specialised. The cotyledon becomes elongated, and the shoot and root systems become more developed. The cells in the embryo start to elongate and further differentiate into definite tissues to prepare the embryo for its future transition to the seedling stage.

Factors Affecting Embryogeny

Embryogenesis is subject to control by genetic, environmental, and hormonal factors. Some of the factors controlling embryogenesis are described below-

• Developmental processes are controlled by inherited genetic information.

• Furthermore, mutations can affect embryonic development.

• Extrinsic factors like temperature, nutrition, and toxins affect development.

• Hormones regulate the proliferative and differentiation processes in embryogenesis.

Common Anomalies of Embryogenesis

A variety of factors may truncate or abort the process of embryogenesis. Below are a few factors that are can go aberrant during the development of embryo-

• Gene mutations, environmental stress, and nutritional deficits.

• Neural tube defects, Congenital heart defects, and Limb malformation are some developmental disorders.

• Understanding the mechanisms of birth defects.

• Advances in regenerative medicine and stem cell therapy.

• Helps in developing self-incompatible plants with desired traits.

• Enhancement of plant breeding

• Improved yield of crops with disease resistance.

MCQs on Embryogenesis

Q1. Which of the following statements is true?

Statement 1: The growth and development of an embryo from a zygote in flowering plants is known as embryogenesis.

Statement 2: The phases of embryo development are the same in monocot and dicot plants.

Option 1: Statement 1 is correct, but Statement 2 is incorrect

Option 2: Statement 2 is correct, but Statement 1 is incorrect

Option 3: Both statements are correct

Option 4: Both the statements are incorrect

Correct answer: (3) Both statements are correct

Explanation:

Statement 1: The growth and development of an embryo from a zygote in flowering plants is known as embryogenesis. Embryogenesis is a fundamental process in the life cycle of flowering plants, where a zygote formed through fertilization develops into a mature embryo within a seed. This process involves various stages and cellular changes, leading to the formation of different tissues and organs in the developing embryo.

Statement 2: The phases of embryo development are generally the same in monocot and dicot plants. Although there may be some variations and differences in timing, the overall sequence and major events of embryo development are conserved among flowering plants, regardless of whether they are monocots (e.g., grasses) or dicots (e.g., roses, beans). Both types of plants undergo processes such as the formation of the embryo proper, differentiation of cotyledons, and development of the embryonic root and shoot systems.

Hence, the correct answer is option 3) Both statements are true

Q2. The process of formation and development of an embryo is called.

Option 1: Fertilisation

Option 2: Embryo cleavage

Option 3: Embryogeny

Option 4: Sporulation

Correct answer: (3) Embryogeny

Explanation:

Embryogeny refers to the formation and development of an embryo. Embryogeny refers to the formation and development of an embryo from a fertilized egg or zygote. It involves a series of cell divisions, differentiation, and tissue formation to establish the body plan of the organism. The process typically includes key stages such as cleavage, blastula formation, gastrulation, and organogenesis. Embryogeny ensures the proper arrangement of cells and tissues necessary for the growth and functionality of the mature organism.

Hence, the correct answer is option 3) Embryogeny.

Q3. During the development of the embryo in angiosperms, the suspensor cell is derived from

Option 1: Basal cell

Option 2: Terminal cell

Option 3: Coeloptile

Option 4: Coleorhiza

Correct answer: (1) Basal cell

Explanation:

During the development of an embryo in angiosperms, the suspensor cell originates from the basal cell of the zygote after its first division. The zygote undergoes an asymmetric division, resulting in a terminal (apical) cell and a basal cell. While the terminal cell contributes to the formation of the embryo proper, the basal cell develops into the suspensor. The suspensor plays a crucial role in anchoring the developing embryo to the endosperm and facilitating the transfer of nutrients from the endosperm to the embryo.

Hence, the correct answer is option 1)Basal cell.

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