Abcission

Question 1

What are abiotic factors?

Answer 1

non-living chemical and physical parts of the enviornment

Question 2

Why does abcission occur in deciduous plants?

Answer 2

• amount of glucose required for respiiration to maintain the leaves and anti-freeze chemical is greater than the amount produced by photosynthesis
  
  • in time of low sunlight and temperatures
• trees that are in leave are more vulnerable to damage or being blown over
• lose leaves in winter and lay dormant until days and temperatures rise

Question 3

How are plants sensitive to day length?

Answer 3

• results from a light-sensitive pigment called phytochrome
• exists in 2 forms - P_r and P_fr
• each absorbs a different type of light
• and the ratio of the 2 forms changes depending on the level of light

Question 4

What does the falling light level result in?

Answer 4

• falling conc of auxin

Question 5

How do plants respond to the falling auxin conc?

Answer 5

by producing gaseous hormone ethene

Question 6

What is the abcission zone?

Answer 6

• 2 layers of cells sensitive to ethene

Question 7

What does ethene do?

Answer 7

• initiate gene switching in these cells resulting in the production of new enzymes

Question 8

What is the purpose of the enzymes ?

Answer 8

• digest and weaken the cell walls in the outer layer of the abcission zone, known as the separation layer

Question 9

What are the other events during abcission?

Answer 9

• vascular bundles sealed off at leaf
• fatty material deposited in the cells on the stem side of the separation
  
  • forms a protective scare when the leaf forms
• cells deep in sepparation zone respond to hormonal cues by retaining water and swelling
  
  • puutting more strain on the already weakend outer layer