XII BIOLOGY
CH-1 - Reproduction in lower and higherplants
Part-Asexual.Reproduction-
Reproduction-
Reproduction is an essential process as it leads to the continuation of species as well as to maintain the continuity of life. Hence, reproduction is one of the most important characteristics of all living organisms.
Types of reproduction:-
Two types of reproduction:-
1)Asexual reproduction
2)Sexual reproduction
1)Asexual
Reproduction:
This involves a single organism creating a genetically identical or very similar copy of itself. It does not require the fusion of gametes. Examples include binary fission in bacteria, budding in yeast, and fragmentation in some plants and animals.
2)Sexual
Reproduction:
This typically involves the fusion of two specialized reproductive cells, called gametes, from two different parents. This process results in offspring with a unique genetic makeup derived from both parents, which introduces genetic diversity.
1) Asexual
Reproduction-
Modes of
Asexual reproduction-
Binary
Fission-
Binary fission is a method where a single organism, typically a single-celled one, divides into two identical daughter cells. The process involves the replication of the organism's DNA, followed by the division of the cytoplasm. This is the most common form of reproduction in prokaryotic organisms like bacteria and archaea, and it also occurs in some eukaryotic single-celled organisms like amoeba.
In budding, a new organism develops from "bud" on the parent organism. The bud grows and eventually detaches from the parent to live independently, or sometimes, it remains attached to form a colony.
This is seen in organisms like yeast, and some animals like hydra and corals.
Fragmentation is a new organism grows from a fragment or a piece of the parent organism.
The parent's body breaks into multiple fragments, and each fragment is capable of developing into a new, complete individual.
This is observed in organisms such as starfish, planarians (flatworms), and some algae and lichens.
1.Spore
Formation
Spore formation is a method where an organism produces specialized cells called spores.
These spores are reproductive units that can develop into new individuals without fusion with another cell.
This is a common mode of reproduction in fungi ;Chlamydomonas.
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2.Vegetative
Propagation-
It involves a new plant growing from a part of the parent plant, such as a stem, root, or leaf, without the involvement of seeds or spores. Examples
Runners: Horizontal stems that grow along the ground, like in strawberries.
Tubers: Underground storage organs that can sprout new plants, like potatoes.
Bulbs: Fleshy leaves that store food and can produce new plants, like onions and garlic.
Rhizomes: Underground stems that grow horizontally, like ginger and iris.
A.Natural
Vegetative Propagation -
Natural vegetative propagation is a form of asexual reproduction in plants where a new plant grows from a part of the parent plant, such as the stem, roots, or leaves.
There are several ways this occurs naturally in plants:
By Roots: Some plants develop new shoots from their roots, which can then grow into new individual plants. Sweet potatoes and dahlias are examples of plants that propagate this way.
By Stems: Modified stems, both above and below the ground, are common for vegetative propagation.
Runners/Stolons: Horizontal stems that grow along the surface of the soil. in strawberry plants.
Rhizomes: Underground horizontal stems that can produce new .Ginger and bamboo spread this way.
Tubers: underground stems that store food. "Eyes" on the potato tuber are buds that can sprout into new plants.
Bulbs: underground stems surrounded by fleshy leaves that store food. Onions, garlic, and tulips.
By Leaves: In new plantlets can grow directly from the leaf margins. For example, the Bryophyllum plant.
B.Artificial vegetative propagation-
is the human-assisted process of producing new plants from a part of an existing plant.
1. Cutting
This is one of the simplest methods. A portion of the stem, root, or leaf of a plant is cut and placed in a suitable medium to grow a new plant.
The cut end develops roots and shoots, eventually becoming a new, independent plant.
Examples: Rose, hibiscus, sugarcane, and money plant.
2. Layering
In layering, a stem still attached to the parent plant is bent and buried in the soil. The buried part of the stem develops roots while it's still connected to the parent plant, receiving nutrients and water. Once the roots are well-developed, the new plant is cut from the parent and transplanted.
Examples: Jasmine, lemon, and guava.
3. Grafting
Grafting involves joining two different plant parts to grow as a single plant. The upper part, called the scion, is attached to the lower part with the roots, called the stock. The goal is for the two parts to fuse together and grow. This method is used to combine the desirable traits of two different plants, such as a strong root system from the stock and high-quality fruit from the scion.
Examples: Mango, apple, citrus fruits, and rose.
4. Tissue
Culture
Also known as micropropagation, tissue culture is a modern technique used in a laboratory.
A small piece of plant tissue, like a cell or a small fragment of a leaf, is placed in a sterile, nutrient-rich medium. Under controlled conditions, this tissue grows and develops into a full plant.
This method allows for the rapid production of thousands of plants from a single parent plant, and it's also used to produce disease-free plants.
Asexual Reproduction
1. Many plants are able to propagate themselves
using asexual reproduction.
2. This method does not require the investment
required to produce a flower, attract pollinators, or find a means of seed
dispersal.
3. Asexual reproduction produces plants that are
genetically identical to the parent plant because no mixing of male and female
gametes takes place.
4. Traditionally, these plants survive well under
stable environmental conditions when compared with plants produced from sexual
reproduction because they carry genes identical to those of their parents.
Plants have two main
types of asexual reproduction:
1. vegetative reproduction and apomixis.
2. Vegetative reproduction results in new plant
individuals without the production of seeds or spores. Many different types of
roots exhibit vegetative reproduction.
3. The corm is used by gladiolus and garlic.
4. Bulbs, such as a scaly bulb in lilies and a
tunicate bulb in daffodils, are other common examples of this type of
reproduction.
5. A potato is a stem tuber, while parsnip
propagates from a taproot.
6. Ginger and iris produce rhizomes, while ivy uses
an adventitious root (a root arising from a plant part other than the main or
primary root), and the strawberry plant has a stolon, which is also called a
runner.
7.
Some plants can produce
seeds without fertilization.
8.
Either the ovule or part
of the ovary, which is diploid in nature, gives rise to a new seed. This method
of reproduction is known as apomixis.
9.
An advantage of asexual
reproduction is that the resulting plant will reach maturity faster.
10. Since the new plant is arising from an adult
plant or plant parts, it will also be sturdier than a seedling.
Key Points
- Asexual reproduction produces
individuals that are genetically identical to the parent plant.
- Roots such as corms, stem
tubers, rhizomes, and stolon undergo vegetative reproduction.
- Some plants can produce seeds
without fertilization via apomixis where the ovule or ovary gives rise to
new seeds.
- Advantages of asexual
reproduction include an increased rate of maturity and a sturdier adult
plant.
- Asexual reproduction can take
place by natural or artificial means.
Key Terms
- stolon: a shoot that grows along the ground and produces
roots at its nodes; a runner
- apomixis: process of reproduction in which plants produce seeds
without fertilization