Download How Plants Use Sugars

Name __________________ Per ____
How do plants use the sugar they produce during photosynthesis?
During photosynthesis, plants capture carbon dioxide molecules from the air to
build sugar molecules and other carbohydrates. These carbohydrates can be
used as building blocks that add to the total mass of the plant as it grows bigger,
or they can be used for cellular respiration to make ATP for processes that
require energy.
The following figure represents data from an investigation of how plants use the
carbohydrates they produce during photosynthesis. The graph at left shows
carbohydrate use for plants grown with a limited supply of nitrogen (nitrates), and
the graph at right shows carbohydrate use for plants grown with an unlimited
supply of nutrients. Biomass is used to measure the amount of growth.
Limited nitrates in soil
root respiration
shoot respiration
biomass
Unlimited soil nutrients
root respiration
shoot
respiration
biomass
Figure 1. The black section of the pie refers to carbon invested in growth (measured as biomassthe total mass of the plant); the other two sections refer to carbon used in shoot respiration (white
sector) and root respiration (gray-shaded sector). [Adapted from Plant Physiological Ecology, by
Lambers, H., et al. page 123. Original source by Van der Werf et al. 1992.]
Figure 2. Identifying
parts of a plant. The
shoot refers to all
parts of a plant
above ground,
including leaves,
stems, and flowers.
The root refers to all
parts of a plant
below ground.
Shoot
Root
Name __________________ Per ____
Answer the following questions on a SEPARATE PIECE OF PAPER.
For plants grown in limited soil nitrates
1. About what percent of the total carbohydrates produced in photosynthesis is
used for each of the following processes?
a. Increasing biomass
b. Shoot respiration
c. Root respiration
2. Which of the 3 processes uses the largest proportion of the glucose produced
during photosynthesis?
3. What molecule is the source of chemical energy for cellular processes like
active transport?
4. What process produces the molecule mentioned in question #3?
5. The molecule mentioned in question #3 cannot be transported between cellsit must be used by the cell that produces it. Which tissues are using more of
this molecule for active processes- the roots or the shoots?
6. Plants use active transport to pump solutes into their roots to make the roots
hypertonic compared to the soil. Write a paragraph to explain why cellular
respiration in the roots of plants is extremely important for the plants to stay
alive. [HINT: Think about osmosis and the direction water tends to move
across a membrane]
For plants grown in unlimited soil nutrients
7. About what percent of the total carbohydrates produced in photosynthesis is
used for each of the following processes?
a. Increasing biomass
b. Shoot respiration
c. Root respiration
8. Which of the 3 processes uses the largest proportion of the glucose produced
during photosynthesis?
9. How is the use of carbohydrates in plants with unlimited nutrients different
from the use of carbohydrates in plants with a limited nitrate supply?
10. Nitrates are nitrogen-containing compounds that are needed to produce
molecules like protein and DNA for new tissues of a growing plant. Write a
paragraph to explain why the use of carbohydrates in plants with unlimited
nutrients is different from the use of carbohydrates in plants with a limited
nitrate supply.