B1.4 Flashcards
Formula for photosynthesis
Water + carbon dioxide -> oxygen + glucose
Define photosynthesis
Photosynthesis is the process in which green parts of the plants use carbon dioxide and water in the presence of sunlight and chlorophyll to produce glucose as food and in this process oxygen gas is released as a byproduct.
What kind of reaction is photosynthesis?
Endothermic
State reactants and products of photosynthesis
Reactants: carbon dioxide + water
Products: oxygen + glucose
What does carbon dioxide do?
This diffuses through from the air into the plant through the stomata
What does water do?
This enters the roots from the soil through the root hair cells
Where does photosynthesis occur?
Chloroplasts (leaf)
What are leafs green?
Because they contain the pigment chlorophyll
What happens in photosynthesis
Light transfers energy from the Sun to chlorophyll, where carbon dioxide and water react to make glucose.
Glucose stores energy within its chemical bonds.
Name the 2 stages of photosynthesis
- Light dependant
- Light independent
State what happens in the first stage if photosynthesis
The first stage is the light dependent stage of photosynthesis where energy transferred from light is used
to split water molecules into oxygen gas and hydrogen ions
State what happens in the second stage of photosynthesis
The second stage isthe light independent stage of photosynthesis where carbon dioxide gas combines with the hydrogen ions produced in stage 1 of photosynthesis to make glucose
State the uses of glucose
-Stored as starch - food store
-Used for respiration
-Stored in fruit as sucrose
-Used to build cellulose cell walls
- Combined with nitrogen to build protiens for grow and repair
-Biosynthesis into fats and oils for food and growth
How can you test for starch when photosynthesis has taken place
1.Place leaf in boiling water for 1 minute to kill it
2.Place in boiling tube with ethanol
3.Place boiling tube in a water bath an boil until white (chlorophyll removed)
4.Wash leaf with water to remove ethanol and soften
5.Place on white tile and add 1-2 iodine drops
6.Watch for colour change in iodine.
How do you destarch a plant
Keep it in the dark for a minimum of 24 hrs
How do you prove chlorophyll is needed for photosynthesis
Take a variagated plant and destarch
Place the destarched plant in sunlight for several hours
Test oneof the leave with iodine for the presence of starch
How do you prove light is needed for photosynthesis?
To prove light is needed for photosynthesis take a destarched plant and cover part of one of its leaves with black card or tin foil.
Light cannot reach the covered area of the leaf.
Place the plant in sunlight for several hours. Finally, remove the card from the leaf and test the leaf for the presence of starch
How can you prove carbon dioxide is needed for photosynthesis
Take a destarched plant, and place it inside a polythene bag.
Before you seal the bag add a pot of soda lime .
This is a chemical that absorbs carbon dioxide and water vapour.
Place the plant in sunlight for several hours, before testing one of its leaves for the presence of starch.
How can you prove oxygen is needed for photosynthesis
Place an upturned test tube above an aquatic plant such as the pondweed Elodea
. Put the apparatus in the light for maximum photosynthesis.
When you have collected a full tube of gas, place a glowing splint inside the tube.
It will relight because of the oxygen present.
What 3 factors affect the rate of photosynthesis
- light intensity
- temperature
- carbon dioxide
What is meant by limiting factor
A limiting factor is a condition, that when in shortage, slows down the rate of a reaction.
- Light intensity, carbon dioxide concentration and temperature are limiting factors of photosynthesis. They all affect the rate of the photosynthetic reaction, but in different ways
How do we calculate rate of photosynthesis
Rate = 1/T
T = time
- measure how much glucose of oxygen a plant makes in a given time
How does light intensity affect the rate of photosynthesis
The higher the light intensity, the faster the rate of photosynthesis. This continues until photosynthesis reaches its maximum rate.
In very low light levels or if there is no light, photosynthesis stops.
How does carbon dioxide affect the rate of photosynthesis
The greater the carbon dioxide concentration, the faster the rate of reaction
However, the atmosphere only contains about 0.04% carbon dioxide.
This means that carbon dioxide is most commonly the limiting factor.
.
How does temperature affect the rate of photosynthesis
Photosynthesis is a series of enzyme-controlled reactions. Therefore, the higher the temperature the faster the reactions occur. However, if the temperature is too high the enzymes will denature the reactions will stop.
Why does the rate of photosynthesis drop if the temperature gets too high?
The enzymes will denature
How to investigate the 3 factors’ effect on photosynthesis
Light intensity - place a light source at a different distances
Carbon dioxide - add different masses of potassium hydrogen carbonate powder to the water. Potassium hydrogen carbonate releases carbon dioxide to the atmosphere.
Temperature - place the apparatus in water baths at different temperatures
What is inverse square law
Relative light intensity = 1/ (distance from light source)^2
How do limiting factors interact?
When you investigate each of the limiting factors separately you see that, at some point, increasing the factor no longer makes a difference to the rate of photosynthesis. This is because one of the other factors is now in short supply - it becomes the limiting factor.
