Environmental Factors

Question 1

Which factors influence plant growth?

Answer 1

o Environment
o Irradiation, Day-length, Temperature, Water availability, Gases
o Soil.
o Water.
o Nutrients.
o Pests & Diseases.
o Weeds

Question 2

Why is the ozone important to life on earth?

Answer 2

o Ozone in the upper atmosphere serves as a protective shield by absorbing
most of the harmful ultraviolet radiation.
o Atmospheric gases do not absorb much of the sun’s radiation between 400
and 700 nm.
o This is notable because this band of radiation is called photosynthetic
active radiation.
o This is the most important for life on Earth.

Question 3

Why is light quality important to healthy plant growth?

Answer 3

o Light affects plant processes in the range of 380 to 800 nm.
o Photosynthesis requires a narrower band than this.
o Blue light (440 um) and red light (680 um) are more effective than green
light (520 um)
o As a result green light is reflected more – hence green plants.

Question 4

Define photoperiodism

Answer 4

the response of an organism to seasonal changes in day length; long day plants (LDP), short day plants (SDP), day neutral plants (DNP)

Question 5

What is the proportion of nitrogen (N2), oxygen (O2) and carbon dioxide (CO2) in
the earth’s atmosphere?

Answer 5

o Atmospheric gasses are composed of 78% nitrogen (N2) = 780,000 ppm.
o 21% oxygen (O2) = 210,000 ppm.
o 0.035% carbon dioxide (CO2) = 350 ppm.