Lessons 9–10 · 2 lessons · O. Pratov, A. Tukhtaev, F. Azimova, I. Saparboev, M. Umaraliyeva. Biology (Botany), Grade 6. O‘zbekiston Publishing House, Tashkent, 2017
9
Modified roots
Textbook: p. 26
GoalDistinguish modified roots (storage roots, prop roots, aerial roots) and state their jobs.
New words
metamorphosis (change of form for a new job) · metamorfozstorage root (root vegetable) · ildizmevaprop (support) root · tayanch ildizaerial root · havo ildizi
Explanation
Roots can change shape to fit their job; such a change is called metamorphosis and the roots are called modified roots. Storage roots form when the main root thickens and stores reserve food (sugar, starch): carrot, turnip, black radish, beet, radish. They are the first-year reserve of biennial plants, and in the second year it is spent on flowering and seed production. Prop roots are adventitious roots growing from the stem that hold the plant upright: in maize and sorghum they grow from the lower nodes. In tropical forests some plants have aerial roots; for example, the banyan tree has roots hanging from its branches that reach the ground and become extra supports. Even when a root changes its shape, its origin does not change.
Worked examples
Carrot and beet are storage roots: the thickened main root stores reserves. The orange colour of carrot comes from pigment in chromoplasts.
Maize grows prop roots from its lower nodes and so does not fall over in the wind.
Class activity
Laboratory 1 (root types): identify and draw taproot and fibrous systems on herbarium and live plants; look at adventitious roots in maize, strawberry and couch grass; look at storage roots in carrot, beet, radish, turnip and black radish and draw them. Safety: cut root vegetables with a knife only with an adult’s help and wash hands after handling plants and soil.
Practice
1
Give 4 examples of storage roots.
Carrot, turnip, beet, black radish (radish).
2
In which plants are prop roots found and what do they do?
Maize, sorghum; they hold the plant upright.
3
Why is carrot seed obtained in the second year from a replanted storage root?
Carrot is biennial: it stores food in the first year and uses it in the second to bloom and form seeds.
4
What is metamorphosis? Explain with a root example.
A change of an organ’s form to suit its job; e.g. the main root thickens into a storage root.