Reproduction (Lecture 3)
Reproduction is the process of “production of new individuals or offspring”, which can be accomplished by sexual or asexual means.
“The process by which living beings/organisms propagate or duplicate.”
For a specie to survive, it must reproduce successfully in every generation.
Some organisms reproduce individually; their offspring are genetically identical to the parent.
Others reproduce sexually, producing offspring that receive genetic information from two parents.
Methods of Reproduction
Vegetative, Asexual and Sexual Reproduction
- In asexual reproduction special cells or asexual units are produced by the parent body which grow themselves into new individuals. Therefore development of new individual without fusion of male and female gametes is known as asexual reproduction e.g. binary fission, fragmentation, spore formation and budding.
requires only 1 parent and the offsprings are an exact copy of the parent—a clone
Asexual reproduction is natural “cloning.” Parts of the plant, such as leaves or stems, produce roots and become an independent plant.
A group of genetically identical cells or organisms produced through asexual reproduction is called a clone.
Types of asexual reproduction
1) binary fission
* the equal division of nuclear material and cytoplasm resulting in 2 new organisms
* carried out by paramecium, amoeba, bacteria, and many algae
- A) in unicellular organisms
* similar to binary fission BUT has an unequal division of cytoplasm; offspring is smaller than the parent
- B) in multicellular organisms
* a bunch of cells form a smaller organism on the original if conditions are favorable
* the bud develops into a fully functional organism which may or may not detach from the parent
* spores are single, specialized cells that are released from the parent and can develop into new individuals if the conditions are favorable.
* occurs in molds and mushrooms
Learning objectives of asexual reproduction
1.Define Asexual/vegetative reproduction (or propagation) in plants
2.List the specialized plant structures which help in vegetative propagation. and describe their general morphology with examples.
3.Differentiate between natural and artificial ways of vegetative propagation.
4.Differentiate between cuttings, layering, gootee and grafting by giving examples.
5.Define micropropagation and describe methods employ in it.
6.State advantages of micropropagation.
7.Describe the advantages of vegetative propagation.
Learning objective 1
Define Asexual/vegetative reproduction (or propagation) in plants
- Part of the plant becomes separated from the parent plant and divides by mitosis to grow into a new plant
- As a result the offspring are genetically identical to the parent
- in plant cells, a CELL PLATE forms after mitosis between each new cell, like a cell wall
Vegetative/Asexual Reproduction In Lower Plants
- Vegetative Reproduction is the production of new plants from any vegetative part of the plant except seed (“vegeta” = body)
- The reproduction takes place through vegetative parts such as bulbils, corms, rhizome, bulbs, stem cuttings and root cuttings.
Vegetative reproduction followed by growth. In certain filamentous algae like spirogyra if the filament gets broken into two or more portions, each portion is capable of growing into an independent individual by cell divisions.
Vegetative Reproduction In Higher Plants
- A common experience : Most of the plants which reproduce vegetatively in nature usually have small daughter plants growing around them. e.g. banana, canna, ferns.
- These plants have aerial portions with green leaves and they also have a thickened modified stem (rhizome) growing horizontally under the soil. From this underground stem new young plants grow out like the “babies of the mother plant“. These young plants develop their own root system. When separated from mother plant they grow independently.
- Vegetative parts which reproduce have primary or secondary meristems, capable of active cell division, and thus can give rise to new plants.
Learning Objective 2
List the specialized plant structures which help in vegetative propagation and describe their general, morphology with examples.
* when new plants develop from roots, stems or leaves of the parent organism
* many different types
- A) cuttings
* a new plant grows from a piece of the parent
* ex. coleus, geraniums
- B) bulbs
* bulbs bud from parent plants
* can grow into new individuals
* ex. onions, tulips
- C) tubers
* stem-like structures that grow underground from the parent
* can form new individual organisms if the conditions are right
* ex. potatoes
* stem-like structures that grow above the soil from the parent
* when it reaches a favorable spot (enough light, water…) it will grow into a new individual
* ex. strawberries, ivy
- E) grafting
* special tissues–called cambium (embryonic) tissues can be attached to a cutting of a parent plant
* ex. seedless oranges
* can artificially grow plants with different characteristics that are desirable!
(a) Vegetative reproduction by roots
- Tuberous roots or fasciculated roots of sweet potato and asparagus.
- when get detached from the parent plant can grow into a new plant.
- These swollen roots have abundant stores of reserve food which is used during active growth at the time of sowing.
- Such roots can also be called roots stocks because they can be stocked for sowing in the next season.
(b) Vegetative reproduction by stem
Vegetative propagation by various kinds of stem is quite common. A few examples with the technical names of such stems are as follows
- Runners (lawn grasses)
- Suckers (mint)
- Rhizome (ginger)
- Tuber (potato)
- Corms (arvi)
- Bulbs (onion)
(c) Vegetative reproduction by leaf (Adventitious buds)
- Leaves of a number of plants produce adventitious buds in their marginal notches (Bryophyllum).
- These buds usually remain dormant (inactive) in intact plants.
- When leaves are detached or touch the soil with proper moisture, dormancy of the buds ends and each notch is able to produce a small new plant.
- Vegetative propagation by fleshy leaves of different kinds of rose cactus (kind of succulents) are also very common.
- When leaves get detached from the main plant and moisture is available the leaf base produces a new plant.
(d) Vegetative reproduction by Bulbils
- In some plants such as certain varieties of pineapple, some of the upper and lower flowers of the inflorescence instead of producing fruit and seeds become modified into small tufts called bulbils.
- These fall on the ground and grow into new plants.