#48 Summary of plant nutrition
Here is a brief summary of previous topics.
- Photosynthesis
takes place in chloroplasts in the leaves of plants.
- The
word equation for photosynthesis is:
- The
balanced equation is:
- Chlorophyll
traps energy from light. In photosynthesis, this energy is
converted to chemical energy in carbohydrates.
- Photosynthesis
takes place in the cells of the mesophyll layer, especially the
palisade mesophyll. Leaves are thin and have a large surface
area, to speed up the supply of carbon dioxide to the
palisade cells and to maximise the amount of sunlight that hits the
leaf and can be absorbed by chlorophyll. Stomata and air
spaces allow carbon dioxide to diffuse quickly
from the air to the chloroplasts. Xylem vessels bring
water, and phloem tubes take away the products of photosynthesis.
- Some
of the glucose that is made is used in respiration, to
provide energy to the plant cells. Some is stored as starch. Some
is used to make cellulose for
cell walls. Some is transported around the plant in the form of
sucrose, in the phloem tubes. Some is combined with
nitrate or ammonium ions to make proteins. Some is used to make
other substances
such as fats. With the addition of magnesium ions,
chlorophyll can be made.
- When
testing a leaf for starch, it must first be boiled to
break down cell membranes and allow iodine solution to make contact
with any starch inside the cells. Hot alcohol will remove
chlorophyll from the leaf, making it easier to see
any colour changes.
- Plants
need light and carbon dioxide for photosynthesis.
- If
either light or carbon dioxide are in short supply, they
limit the rate of photosynthesis and are said to
be limiting factors. The rate of photosynthesis
is also affected by temperature.
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