4.5.4.2 Use of Plant Hormones (HT only)

Question 1

What are plant growth hormones used in?

Answer 1

• plants use hormones to control and coordinate growth in response to light and gravity
• in agriculture and horticulture - e.g. to increase yield, obtain desirable features and to lower costs

Question 2

What are auxins used for?

Answer 2

• as weedkiller
• as rooting powders
• to promote growth in tissue cultures

Question 3

How are auxins used as weedkillers?

Answer 3

• many weeds are broad-leaved
• weedkillers, containing auxin, have been synthesised so they only affect broad-leaved plants (selective weedkiller)
• the increased amount of auxin causes the cell to grow too rapidly
• this results in the weed dying

Question 4

How are auxins used as rooting powders?

Answer 4

• plants with desirable features are cloned to make more plants with the same feature
• one way to clone a plant is to take a cutting from the original plant
• rooting powder containing auxin is applied to it and it is placed in the ground
• roots grow and the new plant begins to grow very quickly

Question 5

How are auxins used to promote growth in tissue cultures?

Answer 5

• another way to clone a plant is to use tissues culture
• cells from the plant are taken and placed in a growth medium containing lots of nutrients
• hormones such as auxins are added
• used to stimulate cell division and elongation
• the cells begin to form roots and shoots

Question 6

What is ethene used for?

Answer 6

• ethene is used in the food industry to control ripening of fruit during storage and transport
• fruit is picked when it is not ripe
• it is firm which means that during transport it gets less bruised and damaged
• when it is needed to be sold, it is exposed to ethene and warmer temperatures
• ethene is involved in controlling cell division and stimulates enzymes that result in fruit ripening
• this reduces wastage as more fruit is suitable to be sold and it does not ripen too early
• ethene inhibitors can also be used to delay ripening during transport and storage

Question 7

What are gibberellins used for?

Answer 7

• ending seed dormancy
• promoting flowering
• increasing fruit size

Question 8

How do gibberellins end seed dormancy?

Answer 8

• in the brewing industry, the germinate rate of barley seeds is increased to make malt
• ends seed dormancy
• important for initiating seed germination
• low conc can be used to increase seed germination

Question 9

How do gibberellins promote flowering?

Answer 9

• responsible for growth and development of plant
• instead of requiring certain conditions such as longer days and lower temperatures to flower, applying this hormones allows it to flower in any conditions with bigger flowers

Question 10

How do gibberellins increase fruit size?

Answer 10

• responsible for growth and development of plant
• the seeds in fruit produce gibberellins to increase fruit size
• this means that seedless fruit is generally smaller
• seedless fruit can be sprayed with gibberellins to increase their size