Unit 10: Reproduction in Plants — Short Questions

This method is very common in yeast (a unicellular fungus). During budding a part of the parent organism grows out from its body. This part is called a bud.
When the bud has grown big, it may separate from parent body or may remain attached.

Examples
Some animals e.g. hydra also reproduce asexually by budding.

Spores are thick-walled asexual reproductive cells. Most fungi (e.g. Rhizopus: bread mold) produce spores in special sac-like structures called sporangia (Singular: sporangium). When spores are mature, the sporangium bursts and spores are released.

Spores can tolerate unfavorable conditions due to their thick walls. When favorable conditions are available the spores germinate to produce new fungus.

Example
Some bacteria reproduce by forming endospores (spores produced inside the cell). They form endospores in unfavorable environmental conditions. Even if the original cell dies, the endospore survives. When conditions improve, the endospore grown into a new bacterium.

It is a horizontal stem that grows above the ground. A stolon has nodes where new leaves and roots grow. The leaves grow upwards and roots grow down. In this way, a new plant is formed at the node.

Example
Strawberry reproduces by using its stolon.

Potatoes reproduce by tubers. If is fleshy stem that grows underground. It has "eyes" which are actually its buds. Eyes can grow into new plants.

Advantages
i. Vegetative propagation allows to produce many new plants in a short time.
ii. The new plants are exactly like the parent plant, so they all have same good characteristics. This means useful qualities, like good fruit or strong growth, are passed on to the next generation.

Disadvantage
i. Plants produced through vegetative propagation do not have genetic differences.
ii. In other words all the offspring are identical. Due to it, they are equally sensitive to environmental changes and prone to the same diseases or pests.

Floral Parts
Floral parts are in the form of the following four concentric whorls, or rings.

1. Calyx: It is the outermost whorl. It is made of green leaf-like sepals.

2. Corolla: It is the second whorl and made of petals. Most flowers have coloured petals.

3. Androecium: It is the third whorl and is made of male reproductive structures called stamens. Each stamen consists of an anther and a filament. Anther contains pollen sacs (microsporangia), which produce microspores.

4. Gynoecium: It is the innermost whorl made of female reproductive structures called carpels. A carpel consists of three parts.
i. The enlarged base of carpel is called ovary, where ovules are produced.
ii. The stalk-like part attached to ovary is called style.
iii. The tip of style is called stigma.

The ovule acts as mega sporangium. It contains diploid megaspore mother cell which undergoes meiosis, and produces four haploid megaspores.

Only one megaspore remains alive. Inside megaspore, eight haploid nuclei are formed by mitosis.
Two nuclei migrate to the center and fuse to form a fusion nucleus.
One nucleus out of the remaining six forms the female gamete i.e. egg cell.

i. Asexual and sexual reproduction

Asexual Reproduction The reproduction that does not involve the fusion of gametes is called asexual reproduction
Sexual Reproduction: The reproduction that involves the fusion of male and female gametes is sexual reproduction.

Asexual Reproduction The offspring produced by asexual reproduction are genetically identical to the parents.
Sexual Reproduction: In sexual reproduction, the offspring have variations among themselves and with the parents.

ii. Binary Fission in bacteria and amoeba

Binary Fission in Bacteria During binary fission the bacterial DNA replicates and the daughter DNA molecules move to opposite sides. Cell membrane pinches in. New cell's wall is synthesized in the middle and so two identical daughter cells bacteria are produced.
Binary Fission in Amoeba: During binary fission in amoeba, the nucleus of parent organism divides into two. This is followed by the division of Cytoplasm. So two daughter protists are formed.

iii. Stolon and Rhizome

Stolon It is a horizontal stem that grows above the ground. A stolon has nodes where new leaves and roots grow.
Rhizome: It is a horizontal stem that grows below the ground. It has nodes where new leaves and roots grow. In this way, a new plant grows from each node

iv. Bulb and Corm

Bulb It is a very short stem that grows underground. It has bud and fleshy leaves.
Corm: It resembles the bulb but does not have fleshy leaves. Almost all of a corm consists of stem, with a few brown non-functional leaves on the outside.

v. Cutting and Grafting

Cutting Cuttings are widely used to propagate house plants, ornamental trees and shrubs, and some fruit crops. Roses and grapevines are grown from stem cuttings.
Grafting: Grafting is the joining of two or more plant parts of the same type to form a single plant. In grafting, a bud or small stem of one plant is attached to the roots or stems of a second plant.

vi. Vegetative and Artificial Propagation

Vegetative Propagation It is a methods of sexual reproduction in plants. In this method, new plant is produced from vegetative part (root, stem or leaf) of the present plant. Vegetative propagation takes much less time to produce new generation as compared to the sexual method. Secondly, the offspring are genetically identical to the parent plant. Vegetative propagation may be natural or artificial.
Artificial Propagation: Artificial propagation includes the methods in which humans produce new plants by using the vegetative parts of plants. It includes techniques such as cutting, grafting, or tissue culture. Artificial propagation is used to cultivate plants with desirable characteristics or to increase crop production. The following two are the most common methods of artificial propagation.

vii. Male and Female Gametophytes

Male Gametophytes The pollen sacs present in anther act as microsporangia. Each pollen sac contains many diploid microspore mother cells.
Female Gametophytes: The ovule acts as mega sporangium. It contains diploid megaspore mother cell which undergoes meiosis, and produces four haploid megaspores. Only one megaspore remains alive.

viii. Calyx and Corolla

Calyx It is the outermost whorl. It is made of green leaf-like sepals. Sepals protect the inner parts of a developing flower before it opens.
Corolla: It is the second whorl. It is made of petals. Most flowers have coloured petals. Play role in pollination.

ix. Stamen and Carpel

Stamen It is the third whorl and is made of male reproductive structures called stamens. Each stamen consists of an anther and a filament. Anther contains pollen sacs (microsporangia), which produce microspores. The stalk-like filament supports the anther
Carpel: The enlarged base of carpel is called ovary. It is the part where ovules are produced. Ovules produce megaspores during reproduction. The stalk-like part attached to ovary is called style.

Stigma, Anther, Petal, Style, Filament, Ovary, Sepal, Receptacle

Spore In most of fungi like Rhizopus, when they reach at reproduction age, then body cells produce by forming thick walled sacs called sporangia. Inside each sporangia, a cell divides many times and forms many daughter cells called spores.

Endospore Under unfavorable conditions, some species of bacteria reproduce by forming spores e.g. Clostridium and bacillus. Thick walled spores are formed inside bacterial cell. These are called endospores.

After pollination pollen grains germinate to develop a pollen tube containing a tube nucleus and two sperm nuclei. Inside the ovule macrospore undergo three consecutive mitosis to produce female gametophyte containing an egg (1N), fusion nuclei (2N) and other associated cells. Pollen tube enters the ovule and transfer both the sperms for fusion with two different cells of female gametophyte so called "double fertilization".

A spore is seen as an adaptation for surviving harsh environmental conditions because it is a durable reproductive structure capable of withstanding extreme factors like drought, heat, and cold. They can also remain dormant for a long time and grow into a new organism when conditions become favorable. That is why they are considered as an adaptation for survival in harsh environmental conditions.

Asexual Reproduction produces offsprings that are genetically identical to the parent, as there is no mixing of genetic material. This enables rapid population growth, but it restricts the ability to adapt to shifting environmental conditions.

Sexual Reproduction increases genetic diversity in plants by combining genes from two parents. This genetic recombination leads to variation which helps the organisms to adapt according to changing environmental conditions, which supports long-term survival.

So Asexual reproduction produces identical offspring, making it suitable for stable environments, whereas sexual reproduction promotes genetic diversity, helping populations in adapting to new challenges.

The pollen tube facilitates fertilization in flowering plants because it grows from pollen grain on stigma through the style to the ovary. When the pollen grain lands on the stigma, it absorbs water and begins to grow, forming a pollen tube. This tube extends down the style, through the ovary, and into the ovule. It carries the male gametes to the ovule, where one gamete fuses with the egg cell to form a zygote, completing the fertilization process. In short, the pollen tube serves as a transport system, ensuring the sperm reaches the egg for fertilization.