9 Nutrition and gas exchange in plants I
2nd WS 08
(a) W: cuticle
X: palisade mesophyll
Z: lower epidermis
(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
(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