What is photosynthesis?
- uses energy from the sun
- takes place in chloroplasts in plant cells–they contain pigments like chlorophyll that absorb light energy
- carbon dioxide+water—>glucose+oxygen
How is photosynthesis a two-stage process?
1-light energy is used to split water into oxygen gas and hydrogen ions
2-carbon dioxide gas combines with hydrogen ions to make glucose and water
-but more water gets used up in the first stage than made in the second, so water is not a product
What to plants convert glucose into?
- glucose for respiration, this releases energy so they can convert glucose into other substances
- glucose is turned to lipids (fats and oils) and stored in the seeds
- glucose combines with nitrates (collected in the soil) to make amino acids, which then are made into proteins, used for growth and repair
- glucose converted to cellulose for making cell walls, especially in rapidly growing plants
- glucose turned into starch and stored in the roots, stems and leaves ready for use when photosynthesis is not happening
How did Van Helmont decide that plants gain mass by taking in water?
- he set up an experiment as followed:
- he dried some soil, weighed it, and put it in a pot
- he planed a willow tree weighing 2.2kg in the soil
- he added rain water to the pot whenever it was dry
What did people used to think made plants gain mass?
- Greeks scientists observed the only thing touching plants was soil
- so they decided that plants much grow and gain mass by taking in minerals from soil
How do plants actually gain mass?
-using C02 from the air
Hoe did Priestly show that plants produce oxygen?
- his experiment was as followed:
- burning candle in a sealed container and observing that the flame went out after a short time and couldn’t be re-lit in the container
- burning candle and a living plant in a container, the flame went out after a short while but after few weeks could be re-lit
- he did the same experiment with a mouse
- he decided that the burning candle and mouse use something in the air because they couldn’t survive for long
- he decided plants restored something in the air
- today we know this is oxygen
What are isotopes?
-different forms of the same element
How does oxygen produced in photosynthesis come from water?
- to find this scientists:
- supplied plants with water containing an isotope of oxygen called oxygen-18
- the carbon dioxide the plant receive was ordinary oxygen-16
- is was found that when plants photosynthesis they release oxygen-18
- this shows oxygen came form the water that was supplied to the plant
What are the three limiting factors that control the rate of photosynthesis?
- light
- carbon dioxide
- temperature
How does a lack of light slow down the rate of photosynthesis?
- light provides energy needed for photosynthesis
- when light levels raises, rate of photosynthesis raised to only a certain point
- beyond a certain point it will make no difference because either temperature or C02 will now be the limiting factor
How does a lack of carbon dioxide slow down the rate of photosynthesis?
- one of the raw materials needed for photosynthesis
- increase C02 levels and photosynthesis will increase to a certain point
- after this point there will be no difference, as CO2 is no longer the limiting factor
Why does the temperature have to be just right for photosynthesis?
- photosynthesis works best warm but not too hot
- as the temperature increases so do photosynthesis
- but too high will denature the enzymes and the rate will rapidly decrease (45C)
- usually temperature is the limiting factor because it is too low
Why is starch good for storing?
- it is insoluble
- it can’t be dissolved in water and move away from storage areas in a solution
- it doesn’t affect water concentration inside cells (soluble substances would bloat the storage cells by drawing in water)
