Directions: Study the following questions carefully and answers the questions given below:
Important for :
Which of the following factors inhibit weed seed germination and cause dormancy?

I. Low oxygen levels
II. Hard coating on seeds
III. Presence of light
» Explain it
Low oxygen levels and hard coating on seeds both inhibit seed germination and cause dormancy. Light may cause dormancy or lead to germination in different cases. Thus, it depends on the seed.

Hence, option D is correct.
Which of the following is associated with absence of primary dormancy?
» Explain it
A deficiency of ABA is associated with the absence of primary dormancy. High ABA content promotes seed dormancy. ABA is synthesized in the embryo and endosperm.

Hence, option B is correct.
Dormancy due to sudden changes in the environment is termed as –
» Explain it
Induced dormancy is also known as acquired dormancy. This is part of secondary dormancy. It is due to physiological changes like change in temperature, moisture and oxygen levels. This type may persist even after the environmental conditions have altered.

Hence, option C is correct.
» Explain it

Weed species that completes its life cycle over two growing seasons is a biennial weed. Eg: wild carrot, common mullein, musk thistle.

Hence, option A is correct.
Which of the following types of weeds occur only on cultivated land and never in wild form?
» Explain it
Obligate weeds occur only on land that has been cultivated and not in wild form.

Eg: Chenopodium, Convolves arvensis.

Hence, option D is correct.