B1.4 Photosynthesis Flashcards
Photosynthesis
Process by which plants harness the energy from sun and transfer this energy into a useable food source in the form of glucose that can be stored as starch that is insoluble
ENDOTHERMIC
Photosynthesis equation
. Reactants Products
word: water + carbon dioxide——(light energy)——> Glucose + oxygen
balanced symbol: 6H2O + 6CO2——(light energy)——> C6H12O6 + 6O2
Endothermic
Chemical reaction in which energy is transferred from the surrounding to the reacting mixture
Takes in energy
Why are plants and some algae termed producers
They are organisms that make their own food through photosynthesis
2 main stages of photosynthesis
Light dependent
Light independent
What happens in stage 1 of photosynthesis
First stage is the light dependent stage of photosynthesis
Energy transferred from light is used to split water molecules into oxygen gas and hydrogen ions
What happens in stage 2 of photosynthesis
Light independent stage of photosynthesis
Carbon dioxide gas combines with hydrogen ions produced in stage 1 of photosynthesis to make glucose
(HAPPENS IN ABSENCE OF LIGHT SO CAN HAPPEN AT NIGHTTIME)
What happens to the glucose produced in photosynthesis
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 growth and repair
Biosynthesis into fats and oils for food and growth
Test for starch to prove photosynthesis has taken place
Place leaf in boiling water for 1 minute to kill it
Place in boiling tube with ethanol
Place boiling tube in a water bath an boil until white (chlorophyll removed)
Wash leaf with water to remove ethanol and soften
Place on white tile and add 1-2 iodine drops
Watch for colour change in iodine for presence of starch (orange to blue - black)
How can a leaf be destarched before a photosynthesis experiment
Keep it in the dark for a minimum of 24 hours, in dark room and covering with foil
Starch present will be used up in respiration and without light no further glucose can be produced by photosynthesis to be converted to starch
Proving chlorophyll is needed for photosynthesis
Take a variagated plant and destarch
Place destarched plant in sunlight for several hours
Test one leaf with iodine for presence of starch
Prove light is needed for photosynthesis
Take destarched plant and cover part of one of its leaves with black card or tin foil
Place destarched plant in sunlight for several hours
Remove and uncover partially covered leaf
Test the leaf that was partially covered with iodine for presence of starch
Proving 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 - chemical that absorbs carbon dioxide and water vapour
Place destarched plant in sunlight for several hours
Remove one of the covered leaves and test with iodine for the presence of starch
Proving oxygen is given off during photosynthesis
Place upturned FUNNEL and TEST TUBE over an aquatic plant in beaker of water
Put the apparatus in the light for maximum photosynthesis
Collect a full test tube of gas
Place a glowing splint into the test tube to test for oxygen
Relights = oxygen present
Limiting factor
Factors which can prevent an increase in rate of photosynthesis
Main limiting factors which affect rate of photosynthesis
Light intensity
Carbon dioxide availability
Temperature
Which of the following is NOT a limiting factor of photosynthesis:
Temperature
Light intensity
Amount of chlorophyll
Carbon dioxide concentration
Volume of rain / water concentration
Volume of rain / water concentration
Effect of light intensity on the rate of photosynthesis
As light intensity increases, rate of photosynthesis increases until another limiting factor has an effect
Effect of temperature on the rate of photosynthesis
As temperature increases rate of photosynthesis increases
Increases up to a specific point and then any further increase in temperature,
decreases the rate of photosynthesis - high temperatures cause enzymes involved in photosynthesis to denature
Effect of carbon dioxide concentration on rate of photosynthesis
As carbon dioxide concentration increases,
rate of photosynthesis increases until another limiting factor has an effect
What is happening at point x on the graph?
Rate of photosynthesis
I
I . - ———————
I / x
I/____________________
Light intensity
Another limiting factor is preventing an increase in rate of photosynthesis
Why should a farmer keep careful control of limiting factors for photosynthesis in their greenhouse
To maximise rate of photosynthesis in most efficient way possible
Why commercial growers increase carbon dioxide concentration in a greenhouse
Greenhouse is warm and light so temperature and light intensity are therefore not limiting factors
As CO2 concentration is limiting factor in this situation therefore increasing CO2 concentration with increase photosynthesis and therefore plant growth/yield
Inverse square law
Relative light intensity = 1 / distance from light source²
When you double distance from light source, light intensity falls by a factor of 4
Light intensity is inversely proportional to square of distance from the light source
Increase rate of photosynthesis
Light intensity - place a light source at different distances from the plant
CO2 conc - add different masses of potassium hydrogen carbonate powder to the water, releases carbon dioxide to the surroundings
Temperature - place the apparatus in water baths at different temperatures
Rate of photosynthesis
Measure of how much photosynthesis occurs in a given time.
Rate = 1 / time
Units: s ⁻¹(per second), min ⁻¹(per minute), h ⁻¹(per hour)
Rate of photosynthesis to light intensity graph
Rate of photosynthesis
| ________
| .—
| .-
| /
|/_________________
Light intensity
Graph has a smooth curve
Levels off as light intensity is no longer a limiting factor
Rate of photosynthesis to temperature graph
Rate of photosynthesis
| ___
| .— \
| .- \
| / |
|/______________|__
Temperature
Graph must have SMOOTH CURVES
Drops sharply as high temperature causes enzymes essential for photosynthesis to denature
