Class 9 Science Chapter 11: Reproduction – How Life Continues — Important Questions & Sample Paper

Tissue culture

Meiosis halves the chromosome number in gametes, and fertilization restores the diploid number.

Hydra

Offspring are genetically identical to the parent.

A is false but R is true.

Refrigeration lowers the temperature, which slows down the reproduction and growth of microorganisms like moulds and bacteria that spoil food. These microorganisms require warmth and moisture to reproduce rapidly; cold conditions inhibit their activity.

The gardener can use grafting. In this method, a stem cutting (scion) from the plant with beautiful flowers is inserted into a slit made in the rooted plant (rootstock) with strong roots. The tissues join, and the resulting plant will have the strong roots of the rootstock and the attractive flowers of the scion.

Bread mould reproduces by spore formation. Spores are produced in large numbers inside sporangia. They are light, can be easily carried by air, and can survive dry conditions, enabling widespread dispersal. Yeast reproduces by budding, where a small bud grows on the parent and eventually detaches. This allows rapid local multiplication when nutrients are plentiful, but the offspring are not necessarily dispersed over long distances. Thus, spores aid in long-distance dispersal, while budding aids in quick colonization of a local niche.

Cutting – sugarcane; Grafting – mango; Layering – lemon. (Accept any valid examples like rose for cutting or grafting, jasmine for layering, etc.)

Layering is a vegetative propagation method where a flexible young stem is bent and a part of it is buried in the soil while still attached to the parent plant. The buried portion develops adventitious roots after some time, and once roots are established, the stem is cut off from the parent to grow as an independent plant. For example, lemon plants are often propagated through layering. This method is useful for plants that do not produce viable seeds because it allows the production of new plants that are genetically identical to the parent without depending on seed formation and germination.

Tissue culture is a technique where a small piece of plant tissue (explant) is taken from the apical meristem and grown in a sterile nutrient medium under controlled conditions. The cells divide and form a mass of undifferentiated cells called callus, which is then transferred to a medium with hormones to induce shoot and root formation, resulting in tiny plantlets. These plantlets are hardened and transplanted into the field. This method produces disease-free plants because the apical meristem is usually free from viruses due to rapid cell division. It allows mass propagation of desirable plants in a short time. An application in agriculture is the large-scale production of virus-free banana plants, which ensures high yields.

Grafting involves joining a scion from the sweet variety onto a hardy rootstock. Advantage: combines good fruit with strong roots. Disadvantage: requires skill and may not always succeed.