Question Video: Identifying Plant Hormones from Their Descriptions | Nagwa Question Video: Identifying Plant Hormones from Their Descriptions | Nagwa

Question Video: Identifying Plant Hormones from Their Descriptions Biology • Second Year of Secondary School

Join Nagwa Classes

Attend live Biology sessions on Nagwa Classes to learn more about this topic from an expert teacher!

Which of the following tables correctly summarizes the major plant hormones and some of their roles in a plant? [A] Table A [B] Table B [C] Table C [D] Table D

03:15

Video Transcript

Which of the following tables correctly summarizes the major plant hormones and some of their roles in a plant?

The question asks us about plant hormones, which are chemical messengers that travel throughout the plant in order to help it respond to stimuli. Although there are many different hormones in plants, the tables we are given include just three of the major types. So, let’s have a quick discussion of these.

Auxins are plant hormones that are produced in the tips of roots and shoots. They have many roles, but their main function is to promote tropisms through cell elongation. Tropisms are directional growth responses toward or away from a stimulus. The most dominant tropism is phototropism, the plant’s movement in response to light.

When exposed to light, most plant species will accumulate auxin on the shaded side of a plant shoot. The high concentration of auxin promotes cell elongation in that region of the shoot, causing the plant to bend towards the light. This is termed positive phototropism, and it allows more light to enter the shoots, which in turn can increase the plant’s rate of photosynthesis.

Next, let’s review gibberellins. These hormones are first produced by seeds when they are under ideal growth conditions. For most plant species, this means warm, wet, well-oxygenated soil.

Gibberellins break seed dormancy and stimulate germination by helping the starchy food stores in the seed to break down into simple sugars and amino acids. The sugars allow the cells in the plant embryo to initiate cellular respiration, and the amino acids allow them to build proteins, leading to germination. The energy from respiration and the proteins from amino acids allow roots to begin growing and the stem to reach above the soil so photosynthesis can occur.

Gibberellins continue to play a role throughout the plant’s life by encouraging stem elongation and cell division so that the plant grows taller.

The fruit of a plant, such as the unripe strawberry shown here, contains its seeds. In order for its genes to be passed down to a new generation, a plant must ensure that its seeds are dispersed. Ethylene is a gaseous hormone that promotes the ripening of fruit. Ripe fruit is more likely to be eaten by animals, which increases the chances of seed dispersal.

Now that we have discussed the three plant hormones in the tables, let’s check which one correctly summarizes their roles.

Auxins are not involved in seed germination and do not directly promote fruit ripening, so we can rule out tables (A) and (C). We can see that tables (B) and (D) both give the correct description of auxins as promoters of cell elongation and tropisms. However, table (B) gives incorrect descriptions for the role of both gibberellins and ethylene.

The correct summary of the roles played by these plant hormones is found in table (D). Auxins promote cell elongation and mediate positive phototropism in shoots, gibberellins promote stem elongation and initiate seed germination, and ethylene promotes fruit ripening.

Join Nagwa Classes

Attend live sessions on Nagwa Classes to boost your learning with guidance and advice from an expert teacher!

  • Interactive Sessions
  • Chat & Messaging
  • Realistic Exam Questions

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy