B1.4 Photosynthesis

Question 1

Photosynthesis

Answer 1

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

Question 2

Photosynthesis equation

Answer 2

. Reactants Products
word: water + carbon dioxide——(light energy)——> Glucose + oxygen
balanced symbol: 6H2O + 6CO2——(light energy)——> C6H12O6 + 6O2

Question 3

Endothermic

Answer 3

Chemical reaction in which energy is transferred from the surrounding to the reacting mixture
Takes in energy

Question 4

Why are plants and some algae termed producers

Answer 4

They are organisms that make their own food through photosynthesis

Question 5

2 main stages of photosynthesis

Answer 5

Light dependent
Light independent

Question 6

What happens in stage 1 of photosynthesis

Answer 6

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

Question 7

What happens in stage 2 of photosynthesis

Answer 7

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)

Question 8

What happens to the glucose produced in photosynthesis

Answer 8

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

Question 9

Test for starch to prove photosynthesis has taken place

Answer 9

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)

Question 10

How can a leaf be destarched before a photosynthesis experiment

Answer 10

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

Question 11

Proving chlorophyll is needed for photosynthesis

Answer 11

Take a variagated plant and destarch
Place destarched plant in sunlight for several hours
Test one leaf with iodine for presence of starch

Question 12

Prove light is needed for photosynthesis

Answer 12

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

Question 13

Proving carbon dioxide is needed for photosynthesis

Answer 13

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

Question 14

Proving oxygen is given off during photosynthesis

Answer 14

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

Question 15

Limiting factor

Answer 15

Factors which can prevent an increase in rate of photosynthesis

Question 16

Main limiting factors which affect rate of photosynthesis

Answer 16

Light intensity
Carbon dioxide availability
Temperature

Question 17

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

Answer 17

Volume of rain / water concentration

Question 18

Effect of light intensity on the rate of photosynthesis

Answer 18

As light intensity increases, rate of photosynthesis increases until another limiting factor has an effect

Question 19

Effect of temperature on the rate of photosynthesis

Answer 19

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

Question 20

Effect of carbon dioxide concentration on rate of photosynthesis

Answer 20

As carbon dioxide concentration increases,
rate of photosynthesis increases until another limiting factor has an effect

Question 21

What is happening at point x on the graph?
Rate of photosynthesis
I
I . - ———————
I / x
I/____________________
Light intensity

Answer 21

Another limiting factor is preventing an increase in rate of photosynthesis

Question 22

Why should a farmer keep careful control of limiting factors for photosynthesis in their greenhouse

Answer 22

To maximise rate of photosynthesis in most efficient way possible

Question 23

Why commercial growers increase carbon dioxide concentration in a greenhouse

Answer 23

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

Question 24

Inverse square law

Answer 24

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

Question 25

Increase rate of photosynthesis

Answer 25

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

Question 26

Rate of photosynthesis

Answer 26

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)

Question 27

Rate of photosynthesis to light intensity graph

Answer 27

Rate of photosynthesis
| ________
| .—
| .-
| /
|/_________________
Light intensity

Graph has a smooth curve
Levels off as light intensity is no longer a limiting factor

Question 28

Rate of photosynthesis to temperature graph

Answer 28

Rate of photosynthesis
| ___
| .— \
| .- \
| / |
|/______________|__
Temperature

Graph must have SMOOTH CURVES
Drops sharply as high temperature causes enzymes essential for photosynthesis to denature