Food Supply, Plant Growth and Productivity

Question 1

What is food security?

Answer 1

Food security is the ability of human
populations to access food of sufficient
quality and quantity.

Question 2

Why do we need to increase global food production?

Answer 2

Increase in human population and
concern for food security leads to a
demand for increased food production.

Question 3

Why should food production be sustainable?

Answer 3

Food production must be sustainable and
not degrade the natural resources on
which agriculture depends.

Question 4

How is all food production dependent on photosynthesis?

Answer 4

Agricultural production depends on
factors that control photosynthesis and
plant growth. The area to grow crops is
limited. Increased food production will
depend on factors that control plant
growth — breeding of higher yielding
cultivars, use of fertiliser, protecting crops
from pests, diseases and competition.

Question 5

What are the fates of light when it strikes a leaf?

Answer 5

Absorbed- pass into leaf and be converted into other energy

Transmitted- pass through the lead unaffected

Reflected- bounce off the surface

Question 6

What is an absorption spectra?

Answer 6

The degree of absorption at each wavelength of light.

Question 7

What is an action spectrum?

Answer 7

Shows the rate of photosynthesis of the plant.

Question 8

What are the 2 stages of photosynthesis?

Answer 8

Light reactions
Carbon fixation

Question 9

What happens in the light reactions stage?

Answer 9

Absorbed light energy excites electrons in
the pigment molecule. Transfer of these
electrons through the electron transport
chain releases energy to generate ATP by
ATP synthase. Energy is also used for
photolysis, in which water is split into
oxygen, which is evolved, and hydrogen
ions, which are transferred to the
coenzyme NADP.

Question 10

What happens in the carbon fixation stage?

Answer 10

In the carbon fixation stage (Calvin cycle),
the enzyme RuBisCO fixes carbon dioxide
by attaching it to ribulose bisphosphate
(RuBP). The 3-phosphoglycerate (3PG)
produced is phosphorylated by ATP and
combined with hydrogen ions from NADPH to form glyceraldehyde-3-
phosphate (G3P). G3P is used to
regenerate RuBP and for the synthesis of
glucose.

Question 11

What are the fates of glucose?

Answer 11

Used in respiration.

Passed to other biosynthetic
pathways.

Synthesised into starch or
cellulose.