HKDSE Biology Ch.9 Nutrition and Gas Exchange in Plants Worksheet Answer Key PDF

HKDSE Biology Ch.9 Nutrition and gas exchange in plants Answer 9.1 Nutrition in plants: A. Plants as autotrophs Plants carry out autotrophic nutrition. They can make their own food through the process of photosynthesis. They are described as autotroph. Question: Complete the overall word eq...

HKDSE Biology Ch.9 Nutrition and gas exchange in plants Answer 9.1 Nutrition in plants: A. Plants as autotrophs Plants carry out autotrophic nutrition. They can make their own food through the process of photosynthesis. They are described as autotroph. Question: Complete the overall word equation for the process of photosynthesis in the diagram above. Light absorbed by carbon dioxide + water carbohydrate + oxygen chlorophyll Question: State the raw materials of photosynthesis and products of photosynthesis. Raw materials: carbon dioxide, water Products: carbohydrate, oxygen (by product) Question: Photosynthesis is a catabolic process. Comment on this statement with explanation. Photosynthesis involves the building-up of complex organic food (carbohydrate) from simple inorganic substances (carbon dioxide and water). Light energy is converted to chemical energy in organic food. Therefore, photosynthesis should be an anabolic process but not catabolic process. Question: How can lipids and proteins be synthesized from the photosynthetic products? Lipids: Proteins: With the presence of enzyme, carbohydrates are With the presence of enzyme, carbohydrate is changed to the intermediate form and then lipids. changed to the intermediate form, with the addition of nitrogen from minerals, amino acids are formed. Proteins are formed with the condensation of amino acids. 1  HKDSE Biology Ch.9 Nutrition and gas exchange in plants B. Importance of minerals to plants For healthy growth, plants need to absorb a variety of minerals in the form of ions from the soil. Element Major forms in soil Main function Deficiency symptom Nitrogen nitrate (NO3–),  For the synthesis of  Poor growth (N) ammonium (NH4+) amino acids, proteins,  Yellow leaves nucleic acids and chlorophyll Phosphorus phosphate ions (PO43−)  For the synthesis of cell  Poor growth (P) membrane, ATP (adenosine triphosphate) and nucleic  Leaves turn purple acids  Roots poorly  Required in some enzymatic reactions developed Magnesium magnesium ion (Mg2+)  For the synthesis of  Poor growth (Mg) chlorophyll  Yellow leaves Question: Which element is in abundance upon the digestion of insects? Nitrogen. (Insects is mainly made up of protein, which is a source of nitrogen). 9.2 Gas exchange in plants 2  HKDSE Biology Ch.9 Nutrition and gas exchange in plants Question: Identify the cell types in dicotyledonous Question: What is/are the function(s) of guard cells? leaf that contain chloroplast. Palisade mesophyll cell, spongy mesophyll cell and Control the opening and closing of stomata, guard cell. hence the rate of gas exchange. Question: Contrast the two mesophyll layers in the leaf. The palisade mesophyll cells are cylindrical and closely packed while spongy mesophyll cells are irregular in shape and loosely packed. Palisade mesophyll layer is located at the upper part while spongy mesophyll layer is located at the lower part. There are more air space among spongy mesophyll cells (which allow gases to diffuse freely). There are more chloroplasts in palisade mesophyll cells than spongy mesophyll cells ((which allow the efficient absorption of sunlight). Question: Label all the cell type(s) below. B. Gas exchange in leaves of terrestrial plants Question: Identify the gases involved. Oxygen and carbon dioxide Question: What is the process for gases move from the environment into the air space through the stoma? Gases from the environment diffuse into the air space through the stoma. Question: Describe what happen in stages 2 and 3. Stage 2: Gases dissolve in the water film on the surface of the mesophyll cells and diffuse directly into the cells. Stage 3: Gases in these cells diffuse to the neighbouring cells (Remark: Gases may diffuse through the air space to dissolve in the water film on the surface of the palisade mesophyll cells and diffuse directly into the cells.) C. Gas exchange in leaves of aquatic plants Submerged plants Floating plants Their leaves do not have cuticle. They are Their leaves have stomata in the usually very thin and have few or no stomata upper epidermis only. The lower epidermis is in the epidermis on both sides. not covered by cuticle. Gas exchange can take place over the leaf surface. 3  HKDSE Biology Ch.9 Nutrition and gas exchange in plants D. & E. Gas exchange in stems and roots: Stem Root Herbaceous plants Woody plants Herbaceous and woody plants The stems also have Gas exchange also takes place through Roots are not covered by cuticle. stomata for gas small broken parts in the cork layer called Gas exchange takes place all over exchange. lenticels on the stem. their surfaces. F. Effect of light intensity on gas exchange in plants Respiration takes place all the time at a rather constant rate. However, the rate of photosynthesis is greatly affected by light intensity. Therefore, the net uptake or release of gases by a plant would be affected by light intensity. Daytime  The rate of photosynthesis is higher than that of respiration.  As a result, there is a net uptake of carbon dioxide and a net release of oxygen. At night  Photosynthesis stops and only respiration occurs.  As a result, there is a net uptake of oxygen and a net release of carbon dioxide. Question: What is the implication of having a positive net uptake of carbon dioxide for plant? It implies that the rate of photosynthesis is higher than that of respiration. The food production is higher than that of food consumption and hence there is a net food production for growth. Question: Use ‘P’ for rate of photosynthesis and ‘R’ for the rate of respiration to indicate and compare these two processes (< , = , >) in each of the conditions from A to E. A: R only B: P < R C: P = R D: P > R E: P >>> R Question: What does compensation point represent? The rate of photosynthesis is equal to the rate of respiration. There is no net uptake or release of carbon dioxide. Question: Match the letters (A – E) with the following diagrams. CO2 CO2 CO2 CO2 No net gas O2 O2 O2 O2 exchange C A B E D Question: During which period did the plant carry out the processes below? (i) Photosynthesis 0600 - 2000 (ii) Respiration All the time Question: Calculate the highest rate of photosynthesis of the plant in terms of the rate of carbon dioxide uptake. (6 + 2) mg h-1 = 8 mg-1 4