Reproduction in Plants: CBSE Class 7 Science Guide

What is Reproduction in Plants?

Reproduction is one of the most important life processes. It is the biological process by which new individual organisms – or 'offspring' – are produced from their 'parents'. For plants, this means creating new plants. This ensures that the species continues to exist, generation after generation. Imagine if mango trees couldn't make new mango trees! We would eventually run out of mangoes. Plants have developed two major strategies to reproduce:

1. Asexual Reproduction: In this method, only a single parent is involved. The new plant that grows is an exact copy, or clone, of the parent plant. It happens without the production of seeds.

1. Sexual Reproduction: This method usually requires two parents (or two different parts). It involves special reproductive cells called gametes. The new plant that grows inherits characteristics from both parents, so it is not an exact copy. This process involves the formation of seeds.

Types of Asexual Reproduction

Key Parts of a Flower for Sexual Reproduction

Sepals

The green, leaf-like parts at the base of the flower that protect the bud before it opens.

Petals

The brightly coloured parts of a flower that attract insects and birds for pollination.

Stamen (Male Part)

Consists of the anther, which produces pollen grains (containing male gametes), and the filament, which is the stalk that holds up the anther.

Pistil/Carpel (Female Part)

Consists of the stigma (the sticky top part that receives pollen), the style (the tube connecting the stigma to the ovary), and the ovary (which contains one or more ovules, and each ovule has a female gamete or egg cell).

The Process of Sexual Reproduction in Flowering Plants

1. Step 1: Pollination — This is the transfer of pollen grains from the anther to the stigma. If it happens on the same flower, it's called self-pollination. If pollen from one flower lands on the stigma of another flower, it's cross-pollination. Pollination is carried out by agents like wind, water, insects, and birds.
2. Step 2: Fertilization — After pollen lands on the stigma, it grows a tube called a pollen tube down through the style to the ovary. The male gamete travels down this tube and fuses with the female gamete inside the ovule. This fusion of male and female gametes is called fertilization.
3. Step 3: Zygote and Embryo Formation — The fertilized egg is now called a zygote. The zygote divides many times to form an embryo, which is a tiny, baby plant contained within the ovule.
4. Step 4: Fruit and Seed Formation — After fertilization, the ovary grows and develops into a fruit. The other parts of the flower, like petals and sepals, usually fall off. The ovules develop into seeds. The seed contains the embryo and a food store, all protected by a tough outer seed coat.
5. Step 5: Seed Dispersal and Germination — The fruit helps in spreading the seeds to different places (dispersal) by wind, water, animals, or even by bursting open. When a seed lands in a place with the right conditions (water, oxygen, and warmth), it germinates, and the embryo grows into a new plant (seedling).

Exam Tip: Distinguishing Asexual and Sexual Reproduction

A very common question in exams is to list the differences between asexual and sexual reproduction. Remember these key points:

• Number of Parents: Asexual involves one parent; Sexual involves two parents (or fusion of male and female gametes).
• Offspring Genetics: Asexual produces offspring that are genetically identical to the parent (clones); Sexual produces offspring with a mix of genes from both parents, leading to variation.
• Reproductive Units: Asexual reproduction happens through vegetative parts, buds, or spores; Sexual reproduction happens through the fusion of gametes.
• Seeds: Seeds are produced in sexual reproduction but not in asexual reproduction.

Practice Questions with Solutions

• Q: Describe the process of budding in yeast. A: Step 1: Budding is a type of asexual reproduction commonly observed in organisms like yeast. Step 2: In this process, a small bulb-like projection, called a bud, grows out from the parent cell. Step 3: The nucleus of the parent cell divides, and one of the daughter nuclei moves into the bud. Step 4: The bud then detaches from the parent cell and grows into a new independent yeast cell. Sometimes, a chain of buds may form before detaching. Final answer: Budding is an asexual reproduction method where a small outgrowth (bud) forms on the parent cell, receives a daughter nucleus, detaches, and grows into a new organism.
• Q: Identify the male and female reproductive parts of a flower and state their primary functions. A: Step 1: The male reproductive part of a flower is called the Stamen. It consists of two main parts: the anther and the filament. Step 2: The primary function of the anther (part of the stamen) is to produce and store pollen grains, which contain the male gametes. Step 3: The female reproductive part of a flower is called the Pistil or Carpel. It consists of three main parts: the stigma, style, and ovary. Step 4: The primary function of the stigma is to receive pollen grains. The ovary contains ovules, which develop into seeds after fertilization, and the ovules contain the female gametes (egg cells). Final answer: Male reproductive part: Stamen (anther produces pollen). Female reproductive part: Pistil/Carpel (stigma receives pollen, ovary contains ovules with egg cells).
• Q: Differentiate between self-pollination and cross-pollination. A: Step 1: Pollination is the transfer of pollen grains from the anther to the stigma of a flower. Step 2: Self-pollination occurs when pollen grains are transferred from the anther to the stigma of the same flower, or to the stigma of another flower on the same plant. Step 3: Cross-pollination occurs when pollen grains are transferred from the anther of a flower on one plant to the stigma of a flower on a different plant of the same species. Step 4: Self-pollination leads to less genetic variation, while cross-pollination promotes genetic diversity and stronger offspring. Final answer: Self-pollination is pollen transfer within the same flower or same plant. Cross-pollination is pollen transfer between flowers of different plants of the same species.
• Q: Explain why seed dispersal is important for plants. Name two methods of seed dispersal. A: Step 1: Seed dispersal is the process by which seeds are moved away from the parent plant. Step 2: It is important because it reduces competition for sunlight, water, and nutrients between the parent plant and its offspring. It also helps in colonizing new areas, increasing the chances of survival and propagation of the species. Step 3: One method of seed dispersal is by wind. Seeds dispersed by wind are often light, small, or have wing-like structures (e.g., dandelion, maple). Step 4: Another method of seed dispersal is by animals. Seeds dispersed by animals can be eaten and passed through their digestive system (e.g., berries), or they can have hooks or spines that attach to animal fur (e.g., Xanthium, Urena). Final answer: Seed dispersal is important to reduce competition and colonize new areas. Two methods are wind dispersal (e.g., dandelion) and animal dispersal (e.g., berries, Xanthium).

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