Download Chapter 09

Chapter 9
Nutrition in plants: Plants as autotrophs
Photosynthesis
Need for minerals
Absorption of water and minerals
Gas exchange in plants
Occurrence of gas exchange in different parts of plant; Gas exchange in leaves
1.
What is the mode of nutrition of green plants?
Autotrophic nutrition. Green plants are called autotrophs
2.
What substances are required to make food in green plants? What energy is needed?
Carbon dioxide, water are needed to make sugars, fats, vitamin and so on. Minerals such as nitrates, phosphate, and sulphate
are needed to make amino acid, protein, and nucleic acid, Light energy is needed. Other minerals are needed for metabolism.
3.
What is the importance of green plants in ecosystem?
To produce organic food by photosynthesis. The plants store food in their body. It is the food of consumers. Therefore,
energy is transferred from the sun to the consumers through feeding. Plants also produce oxygen for aerobic respiration of
other organisms.
4.
Name 7 major elements for plants. How do the plants obtain these elements
C, H, O, N, K, P, Mg. Plants get C from carbon dioxide in air, get H from water in soil; get O from carbon dioxide in air; get
K from potassium ion in soil; get P from phosphate in soil; get Mg from magnesium ions in soil.
5.
In water culture experiment, why do we cover the flask with aluminium foil? Why do we bubble air into the solution? Why
we use seedlings instead of bigger plant? Why do we refresh nutrient solutions every week?
Aluminium foil: prevent growth of algae
Bubbling air: provides dissolved oxygen for the roots to carry out respiration
Seedling: it has less food store; therefore its growth is much more affected by the nutrient solution; its growth rate is faster
Refreshing nutrient: plants will use up some nutrients after some times; the minerals may be deficient after some times.
6.
What are the uses of nitrogen, phosphorus, potassium and magnesium? What are the deficiency symptoms of these elements?
N: making amino acids, proteins, chlorophyll and nucleic acid
(poor growth, yellow leaf)
P: making phospholipid, and nucleic acid
(poor growth, purple leaf)
K: promote transport in plants and activate enzymes
(poor growth, curled-up leaf with dark-coloured edges)
Mg: making of chlorophyll
(poor growth, yellow leaf)
Page 1
7.
Describe the adaptive features of roots in absorption of water.
There is no cuticle on root surface. Water and minerals can easily pass. There is only one layer of thin-walled epidermis. This
reduces diffusion distance for water can pass through. Root hair is finger-like to increase surface area for absorption. The root
hair is long and fine and can grow between soil particles to absorb more water.
8.
What is the use of epidermis, cortex and vascular bundle in roots?
Epidermis: protect the root from infection, allow water can pass through
Cortex: store food, allow water to pass through
Vascular bundle: xylem transports water upwards and phloem transports food
9.
Describe how water is absorbed into the root hair cell.
Root hair cells are surrounded by a layer of water film. Root hair cells have a lower water potential than soil water. Water
moves into root hair cell by osmosis.
10. Describe how water is transported from root hair cell to xylem.
When water enters, the cells have higher water potential than other cortex cells. Water moves into the root across the cortex
down the water potential gradient. Finally, water moves into the xylem.
A lot of water moves along the cell walls of the cortex cells without entering their cytoplasm.
Transpiration pull pulls up the water, aiding the water moving into the xylem.
11. Describe how mineral salts are absorbed.
Most minerals are absorbed by active transport. The epidermal cells uses energy to uptake the minerals against concentration
gradient. Some minerals are absorbed by diffusion. In most cases, both processes occur. The minerals dissolve in water and
moves in together with the water.
12. Where does gas exchange occur in plant?
Stomata in leaf and young stem; lenticels in woody stem; the whole epidermis of root (no cuticle)
13. What is the use of cuticle, epidermis, mesophyll cells, guard cells and stomata?
Cuticle: Reduce loss of water;
epidermis: allow light to pass, protect against infection
Guard cells: control opening and close of stomata
mesophyll cells: photosynthesis
stomata: allow gases exchange
14. How is the leaf adapted to gas exchange?
Leaf is broad and flat, providing a large surface area for gas exchange
There are many air spaces among the spongy mesophyll cells. These allow gas diffuse freely.
The surface of mesophyll cells is moist to dissolve gases.
There are many stomata for gases exchange.
The guard cells can control opening and close of stomata to control the rate of gas exchange.
Page 2
15. Describe what gases get in and come out during daytime and at night.
Gas diffuses into air space. It dissolves in the water film on mesophyll cells. Dissolved gas diffuses into the cells. During
daytime, oxygen and water vapour comes out, carbon dioxide gets in. At night, oxygen gets in, carbon dioxide and water
vapour comes out.
16. Describe the distribution of stomata on leaves.
Normal leaf: upper less, lower more (to hide away from direct sunshine to reduce water loss rate)
Floating leaf: upper more, lower zero (lower side touching water; no cuticle on lower epidermis)
Submerged leaf: upper zero, lower zero (no cuticle on all surface)
17. How do we know the distribution of stomata on leaves?
Method 1: observe under microscope: count the number in the area of view; calculate the stomata density
Method 2: put dry cobalt (II) chloride paper; measure the time to change colour to estimate the rate
Method 3: put leaves in hot water; air in air space expands and come out, sees where air bubbles come out
18. What is compensation point?
The light intensity at which rate of photosynthesis is equal to rate of respiration
19. During daytime, explain why the plant gives out oxygen instead of carbon dioxide.
During daytime, the rate of photosynthesis is faster than the rate of respiration. There is a net production of oxygen.
20. What happens at compensation point?
No net release of carbon dioxide and oxygen. No net uptake of carbon dioxide and oxygen. No net food is made or used.
No growth at the moment.
21. What is the colour of hydrogencarbonate indicator in different concentrations of carbon dioxide?
>0.03% yellow
=0.03% red
<0.03% purple
22. In daytime, a plant absorbs 10 units of carbon dioxide from the air in one hour. Can we say its actual photosynthetic rate is 10
units of carbon dioxide per hour?
Plants carry out respiration and photosynthesis at the same time in daytime. Respiration produces some carbon dioxide which
is also used in photosynthesis. This amount of carbon dioxide is not enough. The plants have to absorb 10 units more from
outside. Therefore, the actual photosynthesis needs more than 10 units of carbon dioxide.
Page 3