9 Nutrition and gas exchange
in plants I
2nd WS 08
1.
(a) W: cuticle 1m
X: palisade mesophyll 1m
Y: chloroplast 1m
Z: lower epidermis 1m
(b) Carbon dioxide from the environment diffuses
through the stomata into the air space
due to the higher carbon dioxide
concentration outside. 1m
Carbon dioxide dissolves in the moist
surface of the mesophyll cells. 1m
Dissolved carbon dioxide diffuses to the
neighbouring cells due to the concentration difference
until it reaches the palisade mesophyll
cells. 1m
(c) Leaves are broad and flat, providing a large
surface area for gas exchange.
/ Leaves are thin. This reduces the diffusion distance
of gases.
/ There are many air spaces among the spongy mesophyll cells. This allows
gases to diffuse freely.
/ The surface of the mesophyll cells is moist. This allows gases to
dissolve in the moisture and then diffuse into the cells easily.
/ There are stomata on the epidermis. This allows gases to pass into and
out of the leaves freely.
/ Guard cells are present to control the opening and closing of stomata.
The rate of gas exchange can be regulated.
(any 2) 1m x 2
2.
(a) To
prevent the growth of algae in the nutrient solutions,
which may use up the minerals in
the nutrient solutions and affect the results. 1m
(b) This
provides oxygen for the root cells to carry out respiration. 1m
(c) Plant
X grew poorly. 1m
Nitrogen is essential for the synthesis
of proteins.
/ Proteins are made up of amino
acids which contain nitrogen.
Plants cannot grow healthily
without proteins. 1m
(d) Its
leaves would turn yellow. 1m
Magnesium is important for the
synthesis of chlorophyll /
forms part of the chlorophyll
molecules. 1m
(e) Nitrogen,
phosphorus and potassium 1m
(f) Magnesium / sulphur / calcium / iron / copper / zinc / cobalt (any 2 or
other correct answers) 1m
沒有留言:
張貼留言