13 worked answers · short steps first, explanations when you need them
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Textbook pages 150–152
Question 1
Complete a comparison table for photosynthesis and respiration, including raw materials, products, word equations, and importance.
Steps only
Photosynthesis makes glucose; respiration breaks glucose down and releases energy.
Answer
Photosynthesis: CO₂ + water → glucose + O₂. Respiration: glucose + O₂ → CO₂ + water + energy.
Question 2
What would happen to living organisms if all organisms that photosynthesise disappeared from Earth?
Steps only
Food chains would collapse and oxygen would no longer be replenished by photosynthesis.
Answer
Most life depends directly or indirectly on photosynthesis.
Question 3
Where does potato starch come from? Where is plant food made, and how does it reach the potato?
Steps only
Leaves make food; phloem carries it to the potato, where it is stored as starch.
Answer
Potato starch comes from food made in leaves by photosynthesis.
Question 4
Does the broad, flat structure of leaves make plants more efficient at photosynthesis? Justify your answer.
Steps only
A broad surface catches light; stomata allow gas exchange.
Answer
Broad, flat leaves help capture light for photosynthesis.
Question 5
In X + Y → carbon dioxide + Z + energy, glucose is broken down. What do X, Y, and Z stand for?
Steps only
Compare the letters with the respiration word equation.
Answer
X: glucose; Y: oxygen; Z: water.
Question 6
Krishna places two similar potted plants, one in sunlight and one in a dark room. (i) What idea is being tested? (ii) What visible differences may appear? (iii) Which leaves should test positive for starch with iodine?
Steps only
Sunlight supports photosynthesis; starch is expected in the sunlit plant’s leaves.
Answer
(i) Tests sunlight’s role.
(ii) The dark-kept plant may become pale.
(iii) The sunlit leaf should turn blue-black with iodine.
Question 7
Plants are placed in four conditions: (a) sunlight with CO₂, (b) sunlight without CO₂, (c) dark with CO₂, (d) dark without CO₂. In which will starch form and oxygen be generated?
Steps only
Photosynthesis requires both light and CO₂.
Answer
Only (a) forms starch and releases oxygen by photosynthesis.
Question 8
A snail is placed in tube A, a water plant in B, both in C, and only water in D. All contain a carbon-dioxide indicator. What is being investigated, and how can the result be checked?
Steps only
Compare indicator changes: the snail releases CO₂; a plant in light uses CO₂.
Answer
The setup tests how plants and animals change CO₂ in water.
Question 9
Design an experiment to find out whether water moves through plants faster in warm or cold conditions.
Steps only
Compare similar twigs in coloured water at two temperatures, keeping other conditions the same.
Answer
Measure colour movement in equal time to compare water transport.
Question 10
Discuss how photosynthesis and respiration help maintain balance in nature.
Steps only
Photosynthesis uses CO₂ and releases O₂; respiration uses O₂ and releases CO₂.
Answer
Together they cycle gases and support food chains.
Exploratory Projects
Textbook pages 152
Question Project 1
Make a bottle garden with a growing plant such as a spider plant or jade plant. After the plant is established, seal the large transparent bottle and observe its growth. How can its growth show that gases are exchanged?
Steps only
Observe an established plant in a sealed, clear bottle over time.
Answer
Photosynthesis and respiration exchange carbon dioxide and oxygen.
Question Project 2
Explain how photosynthesis, respiration, and water and food transport help crops grow. What may happen to a crop if any one of these processes is missing or slowed down?