Life Processes in Plants: questions with answers

A tomato plant makes food through photosynthesis in its green leaves. It uses water and carbon dioxide in the presence of sunlight and chlorophyll. Its roots absorb water and minerals from the soil, rather than ready-made food.

Both plants receive water every day, but only Pot A receives sunlight. Water alone does not support normal plant growth. In the chapter's experiment, Pot C has fewer leaves than Pot A.

Each pair differs in exactly one thing, and that one thing is what the pair can speak to. Pot A against Pot C removes only the sunlight, so it establishes that sunlight is needed. Pot A against Pot B removes only the water, so it establishes that water is needed. Neither pair on its own establishes that only one of the two matters.

In photosynthesis, carbon dioxide and water are used to make glucose and oxygen. Carbon dioxide is taken in as a gas. Oxygen is produced as a gas. The answer is carbon dioxide.

Blue-black colour with iodine indicates starch. Destarching removed old starch, so the test detected starch formed during the experiment. Both halves had sunlight, water and chlorophyll. Caustic soda removed carbon dioxide around the enclosed half. Only the half with carbon dioxide formed starch. This supports the conclusion that carbon dioxide is needed for starch formation.

Oxygen supports burning, so the intense flame identifies the collected gas as rich in oxygen. The plant releases oxygen during photosynthesis.

Some leaves appear red, violet or brown because they contain MORE of those coloured pigments than chlorophyll, which hides the green rather than replacing it. Some of those pigments also help in photosynthesis. The chapter says so directly: an iodine test can be used on such leaves to check for starch, indicating that photosynthesis has indeed taken place.

The plant had chlorophyll all along -- the green patches are still green. What it did not have was sunlight. Table 10.2 records the result: the leaf from the plant kept in the dark shows no blue-black anywhere, not even on its green patches. Chlorophyll is essential for making starch, but it is not sufficient; the sunlight has to be there too.

Iodine is a test for STARCH: a blue-black colour indicates that starch is present. It says nothing directly about chlorophyll -- the leaf taken from the plant kept in the dark has chlorophyll in its green patches and shows no colour at all. And the alcohol step removes the leaf's colour, not its starch; if it removed the starch, no leaf could ever test positive.

The seed and the leaf carry out respiration. All living plant parts respire, whether green or non-green. Photosynthesis makes food, while respiration breaks down food to release energy.

The two processes run in opposite directions, and the table makes that visible. Photosynthesis: carbon dioxide and water in, glucose and oxygen out. Respiration: glucose and oxygen in, carbon dioxide, water and energy out. What one takes in, the other gives out -- and it is respiration, not photosynthesis, that releases the energy the plant actually uses.

Photosynthesis needs chlorophyll, along with sunlight, water and carbon dioxide. A leaf is the main site because leaves hold most of the chlorophyll. Other parts of the plant that have chlorophyll also make food, so being a leaf is not the test. A root underground has neither chlorophyll nor light. So the answer is no.

Carbon dioxide + Water gives Glucose + Oxygen, in the presence of sunlight and chlorophyll. Photosynthesis produces glucose, which can later be converted into starch for storage. Sunlight and chlorophyll are needed for photosynthesis but are not raw materials used up to make food. X and Y are Glucose; oxygen, respectively.

The coloured water travels up the stem through the xylem, staining it blue. The cut is above the water level, so this part of the stem was not dipped in the ink.

The twig from tumbler B stands in water with red ink in it; the twig from tumbler A stands in plain water. A day later the twig from B shows red in its stem, its leaves and its flowers, and the twig from A shows nothing. The two tumblers differ only in the ink. So the red must have travelled up with the water. That is what tells us water moves from the base to every part of the plant. The experiment says nothing about food, which was never put in the tumbler.