Energy transfers in and between organisms

Question 1

Give 6 adaptations of the leaf

Answer 1

• Have a large surface area- absorbs as much sunlight as possible
• Leaves are thin- short diffusion distance for gases entering
• Leaves don’t overlap- Avoids shadowing which would reduce light absorption
• Transparent cuticle and upper epidermis- lets light through to the photosynthetic mesophyll cells.
• Long narrow upper palisade mesophyll- Many packed in, which increases the number of chloroplasts absorbing light
• Many stomata- maximises gas exchange

Question 2

Give 4 adaptations of chloroplasts

Answer 2

• Granal membrane- provides a large surface area for the attachment of chlorophyll
• Fluid Stroma- possesses all of the enzymes needed to make sugars in the 2nd stage of photosynthesis
• Contains DNA and ribosomes- can quickly and easily manufacture some of the proteins needed for photosynthesis
• Contains 2 types of chlorophyll- absorbs different wavelengths; maximum sunlight can be absorbed

Question 3

What are the 2 different chlorophyll present in the chloroplasts, and why are they advantageous?

Answer 3

• 2 types: chlorophyll a and b
• Absorb slightly different wavelengths
• light that is not significantly absorbed by one type, will be absorbed by the other
• Enables a plant to absorb a larger range of wavelengths- maximises photosynthesis

Question 4

Explain why a graph showing the “Absorbtion spectra of Chlorophyll a and b” has peaks at 400-499nm and 601-700nm but a dip at 500-600nm

Answer 4

• Plants obtain all their energy requirements from the blue and red parts of the spectrum
• hence the peaks
• However, there is still a large spectral region (b/t 500-600nm) where little light is absorbed
• Instead light is reflected
• This indicates the region of the green part of the spectrum
• Hence green colored plants

Question 5

Describe the structure of chloropyll

Answer 5

• Porphyrin ring

- attached to central atom

Question 6

State the equation for photosynthesis

Answer 6

6CO2 + 6H2O —> C6H12O6 + 6O2

Question 7

What is meant by the term ‘Rate limiting factor’

Answer 7

A variable that limits the rate of a chemical reaction

Question 8

State each factor that affects photosynthesis, and state whether the factor has a bigger effect on the LDR or the LIR

Answer 8

TEMPERATURE 
affects LIR more 
LIGHT INTENSITY
affects LDR more
CO2 CONCENTRATION
affects LIR more

Question 9

Why does an increase in Temperature, increase the rate of photosynthesis

Answer 9

Photosynthesis is mainly dependent on enzyme controlled reactions:
higher temp=
more KE=
More enzyme- substrate complex formed per second

Question 10

Why does an increase in Light intensity, increase the rate of photosynthesis

Answer 10

The light is absorbed by the chloropyll and causes electrons to be excited and emitted

Question 11

Why does an increase in Carbon Dioxide, increase the rate of photosynthesis

Answer 11

Carbon dioxide reacts with RuBP to form 2 molecules of GP in the LIR
So more co2 = More GP

Question 12

What is the Light Compensation point?

Answer 12

The light intensity when there are no gases being exchanged:

rate of photosynthesis = rate of respiration

Question 13

When CO2 is the factor being measured, why does the graph plateau?

Answer 13

-BEFORE the plateau, the CO2 concentration was the limiting factor
AFTER the plateau, another factor has become limiting
-Usually it is the quantity of RuBisCO: active sites are already occupied so excess CO2 has to wait to be converted to TP

Question 14

Why does the rate of photosynthesis start to decrease at very high temperature levels

Answer 14

After the optimum temp is reached:
-High temperature levels cause the bonds in the enzyme to be broken
-Changes the active site 
-The enzyme becomes denatured
-Decreases the rate of photosynthesis 
OR 
-Stomata close to prevent water loss
-Less CO2 enters the leaf
-Decreases the rate of photosynthesis

Question 15

State the 3 optimum conditions for photosynthesis

Answer 15

• High light intensity at the correct wavelengths
• Temperature around 25’C
• CO2 0.4% in the atmosphere

Question 16

State the different ways commercial users control the factors affecting photosynthesis in a greenhouse

Answer 16

• Made of glass for light to pass through
• Lamps left on when dark
• Heat energy is trapped in the greenhouse
• Heater and cooling systems used to maintain constant optimum temperature
• Air circulation systems- temp even throughout the greenhouse
• CO2 added by burning oil/ gas (propane)

Question 17

How can DCPIP be used to measure the rate of photosynthess in extracts of chloroplasts

Answer 17

• The DCPIP picks up electrons; it has been reduced and this causes it to turn colourless
• The electrons could come from the reduced NADP, or could come from the end of the electron transport chain in the Light Dependent reaction
• The faster the DCPIP turns colourless, the faster the rate of photosynthesis

Question 18

What are the products of the Light dependent reaction used for?

Answer 18

The ATP:
-provides energy to reduce GP to TP
-provides the energy to convert TP into RuBP in the light independent reaction
The Reduced NADP:
-Provides the hydroen to reduce GP to TP in the light independent reaction