Chapter 14: Plant Tropisms and Hormonal Control

Question 1

Environmental Cues

Answer 1

Plants grow wherever the seed germinates and they have evolved to deal with the varying environmental conditions they experience. The environment also provides many cues to a plants growth and development.

Question 2

Hormone functions in plants

Answer 2

Plants use hormones to send messages, however, they don’t have many hormones and they are not as highly specific as animal hormones

Question 3

hormone production in plants

Answer 3

Plants don’t have endocrine glands and hormones are produced by cells receiving environmental stimuli

Question 4

what is a tropism

Answer 4

If the direction of a growth response is related to the direction the stimulus came from it is called a tropism.

Question 5

Three types of tropisms hormones are responsible for and what are their functions?

Answer 5

• Phototropism: growth in response to light - Geotropism: growth in response to gravity. - Apical dominance: one stem grows big and strong and up (trunk).

Question 6

Auxins

Answer 6

• Responsible for phototropism as it causes cells furthest from the light source to elongate resulting in shoot tip bending.
• Auxin also responsible for geotropism, root grow down and negative geotropism, stems growing away from gravity ie. Up.
• Apical dominance also caused by auxin.

Question 7

Gibberellins

Answer 7

Promote cell elongation and the growth of the entire plant.

Question 8

Cytokonins

Answer 8

With auxin responsible for cell division and cell differentiation. More cytokinin than auxin – stems and leaves grow. More auxin than cytokinin roots grow.

Question 9

Abscisic Acid

Answer 9

Growth-inhibiting hormone responsible for the dropping of fruit and leaves. Also controls stomatal opening and closing.

Question 10

Ethylene (gas)

Answer 10

Results in fruit ripening, increase cellular respiration, converts starch and oil into sugar.

Question 11

5 ways plants respond to physical and chemical factors in their environment

Answer 11

• Light
• Gravity
• Touch
• Movements and plant rhythms
• Temperature

Question 12

Light

Answer 12

Phototropism (plants grow towards light), Photoperiod (Length of Day/Night) affects flowering – some plants need long days others need long nights.

Question 13

Gravity

Answer 13

Shoots are negatively geotropic, Roots are positively geotropic.

Question 14

Touch

Answer 14

Thigmotropism is growth that occurs as a result of contact. Eg. Vines coiling around things.

Question 15

Movements and plant rhythms

Answer 15

o Sleep movements: Flower petals close at night, Stomata close at night. Results from turgor (amount of liquid) in cells. o Solar tracking: Leaves follow light. o Nodding in seedlings to help shoot get to surface. o Contractile movements to get bulb into deeper soil. o Rapid response: Some carnivorous plants are capable of rapid movements in response to touch

Question 16

Temperature

Answer 16

Temperature: affects enzymes and plants have an optimal temperature range. o Seed dormancy: Seeds are triggered to germinate in spring after winter/a period of expose to the cold (vernalisation). o Bud dormancy: Some plants become dormant over winter.