B4b Flashcards
What is the word equation for photosynthesis?
carbon dioxide + water (light energy above) arrow (chlorophyll under) glucose + oxygen
Which is a waste product in the reaction?
Oxygen
What is the balanced symbol equation for photosynthesis?
6CO2 + 6H2O arrow C6H1206 +6O2
What is the order in the development of the understanding of the process of photosynthesis?
Greek Scientists - plants gain mass from soil minerals
Van Helmont - plants gain mass by taking in water
Priestley - plants produce oxygen
What did Greek scientists conclude?
Plants gain mass from soil minerals because they observed that the only thing touching plants was soil. They couldn’t see that air also touched plants.
What did Van Helmont conclude?
He set up the following experiment:
- He dried some soil, weighed it and put it in a pot.
- He planted a willow tree weighing 2.2kg in the soil.
- He added rainwater to the pot whenever it was dry.
5 years later Van Helmont removed the tree from the pot:
- The tree weighed 76.7kg - so it had gained 74.5kg of mass.
- He dried the soil and weighed it - its mass had changed very little (about 60g less)
Van Helmont concluded that because the weight of the soil had changed so little, the tree must have gained mass from another source. Because he only added water to the tree, he concluded the tree must have gained mass by taking in water.
What did Priestley’s experiments show?
Priestley did the following experiment:
- Placed a burning candle in a sealed container and observed that the flame went out after a short time The candle couldn’t have been re - lit.
- He then placed a burning candle and a living plant in the container. The flame went out after short time, but after a few weeks the candle could be re-lit.
He decided that the burning candle used up something in the container - and that this made the flame go out. He also decided that the living plant ‘restored the air’ so the candle could burn again.
He concluded that the plants restore something to the air that burning and breathing take out. Today we know this is oxygen.
How have experiments using isotopes increased our understanding of photosynthesis?
Scientists realised that plants release oxygen during photosynthesis, but they didn’t know whether oxygen came from carbon dioxide or water (both of which contain oxygen atoms).
To find out where the oxygen came from, a scientist supplied plants with water containing an isotope of oxygen called oxygen-18. The carbon dioxide the plants receive contained ordinary carbon-16.
It was found that when the plants photosynthesised, they released oxygen-18.
This showed that the oxygen came from the water that was supplied to the plant, not the carbon dioxide.
What are the two stages in photosynthesis?
Firstly, light energy is used to split water into oxygen gas and hydrogen ions.
Carbon dioxide gas then combines with the hydrogen ions to make glucose and water.
What is glucose made in photosynthesis transported as?
Soluble sugars but stored as insoluble starch.
What can glucose and starch be converted into ?
Other substances in plants to be used for energy, growth and storage products.
What are the five things glucose is used for?
Respiration Making cell walls Stored in seeds Stored as starch Making proteins
What is the conversion of glucose for respiration?
Plants use some of the glucose for respiration. This releases energy so they can convert the rest of the glucose into various other useful substances.
What is the conversion of glucose into cellulose?
Glucose is converted into cellulose for making cell walls, especially in a rapidly growing plant.
What is the conversion of glucose to be stored in seeds?
Glucose is turned into lipids (fats and oils) for storing in seeds. Sunflower seeds, for example, contain a lot of oil - we get coking oil and margarine from them.
