In this article, we shall study asexual reproduction in plants.

Reproduction:

Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself. The offspring grow, mature and in turn produce new offspring. Thus, there is a cycle of birth, growth and death. Reproduction enables the continuity of the species, generation after generation.

Types of Reproduction:

• Asexual Reproduction: When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual.
• Sexual Reproduction: When two parents (opposite sex) participate in the reproductive process and also involve the fusion of male and female gametes, it is called sexual reproduction.

Characteristics of Asexual  Reproduction

• In this method, a single individual (parent) is capable of producing offspring. A
• As a result, the offspring that are produced are not only identical to one another but are also exact copies of their parent.
• These offspring are genetically and morphologically identical to parents
• The term clone is used to describe such morphologically and genetically similar individuals.
• Usually followed by organisms with relatively simpler organizations

Types of Asexual  Reproduction:

Binary Fission:

In Protists and Monerans, the organism or the parent cell divides into two to give rise to new individuals. Thus, in these organisms cell division is itself a mode of reproduction. Many single-celled organisms reproduce by binary fission, where a cell divides into two halves and each rapidly grows into an adult. e.g., reproduction in Amoeba, Paramecium, Viruses.

Budding:

In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which, eventually gets separated and mature into new yeast organisms (cells). e.g reproduction in  Yeast and hydra.

Spores Formation:

Members of the Kingdom Fungi and simple plants such as algae reproduce through special asexual reproductive structures. The most common of these structures are zoospores that usually are microscopic motile structures. Other common asexual reproductive structures are conidia (Penicillium), buds (Hydra) and gemmules (sponge).In fungi and algae, specialized asexual reproductive units are formed.

Natural Methods of Vegetative Propagation (Asexual reproduction):

Vegetative Propagation is an asexual method of reproduction in plants. In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offspring. These structures are called vegetative propagules. Since the formation of these structures does not involve two parents, the process involved is asexual.

Tuberous Roots:

The roots of such plants have adventitious buds on their surface which sprout under favourable conditions to produce leafy shoots. In Commercial Production these sprouts are separated and planted. Thus many plants can be obtained from a single root. e.g. Sweet potato, Asparagus (Shatavari), Dahlia.

Stem Tubers:

A stem tuber has many notches called ‘eyes’ on their surface. Each eye actually a node and consists of one or more small axillary buds and reduced scale leaves. After dormancy period the eyes which sprout under favourable conditions to produce leafy shoots.

In Commercial Production the tuber is cut into pieces, such that each piece has at least one eye. Then they are grown separately. Thus many plants can be obtained from a single tuber. e.g. Potato, Ginger.

Runners:

Runner develops from the lower axillary bud of the stem and thin elongated cylindrical wire-like structure with long internodes. It creeps on the ground and becomes rooted at the nodes. Shoots are produced from the upper sides of nodes. After getting detached from a parent, such shoots grow as an independent plant. e.g. Cynodon (doobgrass), Fragaria (strawberry), Oxalis.

Leaf:

In bryophyllum, the leaf is succulent with crenate or notched margins. Adventitious buds called epiphyllous buds or foliar buds are formed at notches at the tip of lateral veins. These buds sprout and form leafy shoots and adventitious roots. When such sprout falls on wet soil, they develop into independent plants. e.g. Bryophyllum, Kalanchoe, Begonia.

Hazard due to Water Hyacinth (Terror of Bengal)

• One of the most invasive weeds
• Grows wherever there is standing water
• Drains oxygen from water- leads to the death of fishes.
• Introduced in India because of its pretty flowers & shape of leaves
• Vegetative propagation occurs at a phenomenal rate

Artificial Methods of Vegetative Propagation  (Asexual reproduction):

Vegetative methods offer many advantages. As the new generation produced by asexual reproduction is exactly the same as the parent (clone), the good qualities of a race or variety can be preserved indefinitely. If plants have poor viability or prolonged seed dormancy, then vegetative propagation is a rapid, easier and less expensive method of multiplying plants.

The process of growing plants using artificial methods is called artificial propagation.

Layering:

In this method, a young branch is bent and pressed into moist soil. After some time roots develop from the covered part. This is called a layer. Now the branch can be cut from the parent and a new plant is produced. This method is used to propagate plants such as jasmine, black raspberries.

Cutting:

In this method, a branch of plant part (stem, root or leaves) is cut with a node (primary meristem) on it. This piece of a branch is termed a cutting. This cutting is buried in the soil and is watered continuously. This method is the cheapest and convenient method of vegetative propagation.

Grafting:

In this method, the parts of two different plants are joined together in such a way that they unite and continue their growth as one plant. The plant rooted in the soil and on which the part of the other plant is inserted is called a stock. The other plant which is inserted on the stock is called Scion or graft. Budding is a special case of grafting in which a single bid with a small part of bark and living tissue is grafted on another plant.

Tissue culture:

This is a modern method of vegetative reproduction. In this method, a piece of tissue is cut from the plant the removed tissue is called explant. The explant is kept in a nutrient medium under controlled condition. This tissue grows into a mass of cells called a callus. Cells of callus are separated and each cell can give a new plant. These cells are called plantlets.  Now the plantlets are grown in a pot of soil. Plants like chrysanthemum and orchids have been propagated by this method.

The significance of Vegetative Propagation:

• It is easy and cheaper method of multiplication.
• The plants like banana, pineapple and grapes which do not produce viable seeds can be propagated by vegetative propagation only.
• In this method, genetically similar plants are formed.
• The yield can be increased by grafting high-yield variety on less yielding variety but which is adapted to the region.
• This is a rapid method of propagation particularly for the plants having a long dormancy period.
• It can be used to get clones of rare plants.

Science > Biology > Botany > Reproduction in Plants > Asexual Reproduction in Plants

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Biology is a branch of science which studies living beings that all plants and animals including humans. Biology examines the structure, function, growth, origin, evolution, and distribution of living things. It classifies and describes organisms, their functions, how species come into existence, and the interactions they have with each other and with the natural environment. Four principles form the foundation of modern biology are cell theory, evolution, genetics, and homeostasis. In this article, we shall study the characteristics of life.

Growth and Change:

All living organisms have the ability to grow and change. An increase in mass and an increase in the number of individuals are two characteristics of the growth. Multicellular organisms grow by cell division. A seed under the right conditions will sprout and form a seedling that will grow into a larger plant.  

Even the smallest bacteria grow by binary fission. The growth is also required for the persistence of the species. The growth of plants takes place throughout life and at a specific portion of the body but the growth in the animal is time-bound and overall. After some period, the growth in animals occurs by cell division of certain tissues to replace the lost cells. In unicellular organisms, the growth is by the increase in the mass.

Nonliving objects like mountains, boulders and sand dunes also grow but this growth is due to the accumulation of substance on their surface. Thus both the living and non-living grow. Hence growth cannot be considered as characteristic of life.

Reproduction:

All living organisms (multicellular and unicellular) have the ability to reproduce. Living things make more organisms like themselves. If a species does not reproduce the next generation, the species will go extinct. Reproduction is the process of producing the next generation. Reproduction may be a sexual or asexual process. Sexual reproduction involves two parents and the fusion of gametes, haploid sex cells from each parent. Sexual reproduction produces offspring that are genetically unique and increases genetic variation within a species. Asexual reproduction involves only one parent. It occurs without a fusion of gametes and produces offspring that are all genetically identical to the parent. Genetic variation is not possible in asexual reproduction.

Many organisms like mules, sterile worker bee, warblers, infertile human couples, etc. do not reproduce. Thus reproduction cannot be considered as a characteristic feature of living organisms.

Cellular Organization:

All living organisms, whether made up of one cell or many cells, have some degree of organization. A cell is the smallest unit that can perform all life’s processes. Some organisms, like bacteria, are made up of one cell and are called unicellular organisms. Other organisms, such as humans or higher-level plants, are made up of multiple cells and are called multicellular organisms.

Complex multicellular organisms at the highest level, the organism is made up of organ systems, or groups of specialized parts that carry out a certain function in the organism. For example, the digestive system of humans. Organ systems are made up of organs. For example, the digestive system is made of organs like mouth, esophagus, stomach, liver, gall bladder, small intestine, large intestine, etc. Organs are structures that carry out specialized jobs within an organ system. Thus in the digestive system, the stomach performs the function of churning the food and add acid to it. All organs are made up of tissues. Tissues are groups of cells that have similar abilities and that allow the organ to function. Tissues are made up of cells. A cell is covered by a membrane, contains all genetic information necessary for replication, and be able to carry out all cell functions. Within each cell are organelles. Organelles are tiny structures that carry out functions necessary for the cell to stay alive. Organelles are made up of biological molecules, the chemical compounds that provide physical structure and that bring about movement, energy use, and other cellular functions. All biological molecules are made up of atoms. Atoms are the simplest particle of an element that retains all the properties of a certain element.

Beyond the organism level, organisms form populations which make up parts of an ecosystem. Different ecosystems collectively form the biosphere. Thus the cellular organization is a defining feature of living organisms.

Metabolism:

Metabolism is essentially a collection of chemical reactions occurring within the body (or cell). In body two activities are continuously taking place anabolic activities (making up) and catabolic activities (breaking up). All living organisms are made up of chemical substances. These chemical substances belong to different classes like carbohydrates, lipids, proteins, etc. Collectively they are called biomolecules. During anabolic activities, the food material is digested, absorbed and assimilated in the body. In catabolic activities, the stored substances are broken down by hydrolysis or oxidation to produce energy in the form of ATP which is required for doing regular activities by the body. Metabolism includes processes such as protein synthesis, chemical digestion, cell division, or energy transformation.

Metabolism is observed in all living organisms. Hence metabolism is a defining feature of all living beings.

Maintain Homeostasis:

All living things, from single cells to entire organisms, have mechanisms that allow them to maintain stable internal conditions despite changes in their external environment. This process is called homeostasis and is an important characteristic of all living organisms. By this process, the body temperature, sugar level in the body is maintained at a constant level. Multicellular organisms usually have more than one way of maintaining important aspects of their internal environment.

Without these mechanisms, organisms can die. For example, a cell’s water content is closely controlled by the taking in or releasing water. A cell that takes in too much water will rupture and die. A cell that doesn’t get enough water will also shrivel and die. It is a vital characteristic of life. If it is disturbed, it will result in diseases and if not controlled can threaten the life of the organism.

Responding to the Environment:

All living organisms respond to their environment. Living things know what is going on around them (consciousness) and respond to the changes in the environment. The response may be physical, chemical or biological. Human beings are only animals with self-consciousness. When touch me not plant is touched its leaves close. The Venus flytrap traps insects.

The stem of the plant moves in the direction of light and above the ground. (positively phototropic and negatively geotropic. The Root grows towards the soil and away from light (positively geotropic and negatively phototropic).

Heredity:

Heredity means that our genetic information can be passed from one generation to another. This way characteristics are transferred from one generation to the other.

Adaptation:

An adaptation refers to the process of becoming adjusted to an environment. Adaptations may include structural, physiological, or behavioral traits that improve an organism’s likelihood of survival.

Conclusion: Characteristics of Life of Living Organisms?

Thus the main characteristics of life (living organisms) are the self-replicating, evolving and self-regulating interactive systems that can respond to external stimuli.

Next Topic: Biodiversity

Science > Biology > General Biology > Introduction to Biology > Characteristics of life

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