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PhotosynthesisIB MYP Sciences: Flashcards

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What is the word equation for photosynthesis?

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What is the word equation for photosynthesis?
Carbon dioxide + water → glucose + oxygen (in light, with chlorophyll).
What is the balanced symbol equation for photosynthesis?
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Where does photosynthesis take place in a plant cell?
In the chloroplasts.
What does chlorophyll do?
It absorbs light energy for photosynthesis.
Why are leaves green?
Chlorophyll reflects green light and absorbs mainly red and blue light.
What energy change happens in photosynthesis?
Light energy is transferred to chemical energy stored in glucose.
Give four uses of glucose in a plant.
Respiration, starch (storage), cellulose (cell walls), proteins.
Why is glucose stored as starch?
Starch is insoluble, so it does not affect water movement in cells.
Which substance from the soil is needed to make proteins?
Nitrates.
Why is a leaf boiled in water in the starch test?
It kills the leaf cells and makes them permeable so that iodine can enter.
Why is a leaf heated in ethanol in the starch test?
It removes the chlorophyll so the colour change is visible.
What colour does iodine turn if starch is present?
Blue-black.
Why is ethanol heated in a water bath?
It is flammable, so a naked flame must not be used.
Why is a plant kept in the dark before a starch investigation?
To use up its starch store (destarch it) so any starch found was made during the test.

Exam questions on Photosynthesis

  1. A greenhouse grower in the Netherlands grows tomato plants. The leaves make glucose from carbon dioxide and water using energy from light, in a process that also releases a gas into the greenhouse air.
    State the role of chlorophyll in photosynthesis.2 marks
  2. Photosynthesis can be summarised by an incomplete symbol equation in which two of the numbers have been left out: ? CO₂ + 6 H₂O → C₆H₁₂O₆ + ? O₂. The glucose produced is used by the plant in several ways.
    State two ways in which a plant uses the glucose made in photosynthesis.2 marks
  3. A student wants to find out whether light is needed for photosynthesis. She keeps a geranium plant in a dark cupboard for 24 hours. She then covers one leaf completely with aluminium foil and places the plant in bright light for two days. She removes the covered leaf and an uncovered leaf and tests both for starch. She boils each leaf in water, heats it in hot ethanol, rinses it and adds iodine solution. The uncovered leaf turns blue-black. The covered leaf stays orange-brown.
    Describe the purpose of each of the following steps in the starch test: boiling the leaf in water, heating the leaf in hot ethanol, and adding iodine solution.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).