Science · World of living · chapter 7 of 13

Class 10 Science Chapter 7: How do Organisms Reproduce? case study question with answers

One case-based question of the kind the board asks in Section E: a passage, then 3 parts worth 4 marks in all, with the answer and the marking scheme for each. Written from the NCERT chapter.

Case study · 4 marks

Green Leaf Nursery near Pune sells plants raised without seeds. Along one bed, rose stems are bent down and pegged into the soil until they root, and grape branches from a strong vine are joined onto young plants. In a separate room, a technician takes a few cells from the growing tip of an orchid, places them in a nutrient medium in glass jars, and later moves the growing mass to another medium before the tiny plantlets go into pots. The owner says buyers trust her plants because each one turns out just like the plant it came from.

Part 1 · 1 mark

The methods used for the roses and the grapes along the bed are examples of

(a) vegetative propagation(b) spore formation(c) regeneration(d) germination

Show answer

Answer: (a) vegetative propagation

Bending a stem into the soil to root and joining a branch onto another plant use a plant's ability to grow new plants from its parts: vegetative propagation, the method used for plants such as sugarcane, roses and grapes.

Part 2 · 1 mark

Why are the owner's plants just like the plants they came from?

Answer and marking scheme

Plants produced by vegetative propagation are genetically similar enough to the parent to have all its characteristics.

genetically similar to the parent, so they keep all its characteristics (1)

Part 3 · 2 marks

Describe the steps the technician follows with the orchid cells, naming the mass formed and what the second medium contains.

Answer and marking scheme

Cells from the growing tip are placed in an artificial medium, where they divide rapidly to form a callus. The callus is moved to a medium containing hormones for growth and differentiation; the plantlets formed are then placed in soil.

tip cells divide rapidly in artificial medium to form a callus (1)
callus moved to a hormone medium for growth and differentiation, then plantlets to soil (1)

Give two reasons why a nursery would raise orchids by the technician's method rather than one plant at a time, and name the kind of plant for which it is commonly used.

Answer and marking scheme

Many plants can be grown from one parent, and they are grown in disease-free conditions. The method is commonly used for ornamental plants.

many plants from one parent, in disease-free conditions (1)
commonly used for ornamental plants (1)

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