4.4.1 Photosynthesis

Question 1

Photosynthesis equation

Answer 1

Water + carbon dioxide -> glucose + oxygen

Question 2

Photosynthesis: exo or endo

Answer 2

Endothermic
It takes in energy (in the form of light)
From the environment

Question 3

Features of photosynthesis

Answer 3

Leaves are thin and broad
Palisade cells are long and thin
Palisade cells contain many chloroplasts
The spongy mesothelioma contains air spaces
Stomata are surrounded by guard cells
Network of vascular tissue in the veins

Question 4

Give adaptation for feature of photosynthesis: leaves are thin and broad

Answer 4

Thin - Short diffusion pathway for CO2
Broad - increases SA for light absorption

Question 5

Give adaptation for feature of photosynthesis: palisade cells are long and thin

Answer 5

To increase SA to absorb CO2

Question 6

Give adaptation for feature of photosynthesis: palisade cells contain many chloroplasts

Answer 6

To absorb light for photosynthesis

Question 7

Give adaptation for feature of photosynthesis: spongy mesophyll contains air spaces

Answer 7

For fast/rapid diffusion of gases

Question 8

Give adaptation for feature of photosynthesis: stomata are surrounded by guard cells

Answer 8

To open and close stomata

Question 9

Give adaptation for feature of photosynthesis: network of vascular tissue in veins

Answer 9

Transport water via xylem from roots to leaves

Question 10

Limiting factors affecting the rate of photosynthesis: light intensity

Answer 10

As the intensity of light increases, the rate increases

When increasing the intensity of light has no further effect on the rate—the limiting factor is now CO2 or temperature

Question 11

Limiting factors affecting the rate of photosynthesis: temperature

Answer 11

As temp increases so does the rate because photosynthetic enzymes have more kinetic energy

Most plant enzymes are denatured about 45 degrees —here photosynthesis stops and the rate falls to 0

Question 12

Limiting factors affecting the rate of photosynthesis: CO2 concentration

Answer 12

As the concentration of CO2 incr, so does the rate—limiting factor is CO2

Here increasing CO2 has no further effect on the rate—limiting factors are now temp/ light intensity

Question 13

How to control limiting factors to get the maximum yield from crops

Answer 13

Raising CO2 concentration: combustion heater
Controlling temperature: heaters (expensive), fan, open the windows
Controlling light intensity, wavelength and duration: electric lighting in winter/night, use coloured lighting (red/purple)

Question 14

BI RP6: investigating the effect of light intensity on the rate of photosynthesis in pondweed
Control variables

Answer 14

Temperature concentration of CO2
Size of pondweed
Light intensity of surroundings
Species of pondweed

Question 15

BI RP6: investigating the effect of light intensity on the rate of photosynthesis in pondweed
Method

Answer 15

1. Set up test tube rack containing a boiling tube at a distance of 10 cm away from the the light source
2. Fill the boing tube with sodium hydrogen carbonate solution (not to the very top, you also need to add your pondweed)
3. Put the piece of pondweed into the boiling tube with THE CUT END ON TOP. Gently push the pondweed down with the glass rod to ensure the cut end is submerged
4. Leave the boiling tube for 5 minutes to allow the rate of photosynthesis to stabilise
5. Start the stop watch and count the number of bubbles produced in one minute
6. Repeat the count twice more. Then use the data to calculate the mean number of bubbles per minute
7. Repeat steps 1-6 with the test use rack and boiling tube at distances of 20cm, 30cm, 40cm and 50cm from the light source
8. Record the results in a suitable table

Question 16

BI RP6: investigating the effect of light intensity on the rate of photosynthesis in pondweed
Sources of error

Answer 16

Bubbles are not equal in volume - collect the gas in a syringe or inverted measuring cyclinder

Other light sources - switch them off

Might miscount - use computer program or video it and play it back

Question 17

Light intensity and the inverse square law

Answer 17

Light intensity δ 1/d^2
Where d = distance from light source

If you double the distance between the light and plant, the light intensity falls to 1/4 of original value

Question 18

Plant’s uses of glucose

Answer 18

Converted into fats + oils for energy storage in seeds
Combined with nitrates from the soil—amino acids—proteins
Converted into sucrose for transport around the plant
Used in respiration to release energy for active transport, synthesis reactions
Many glucose molecules joined together—starch for storage, Cellulose for strength in cell wall, dna using phosphates

Glucose used in respiration, and the rest is converted into other organic substances a plant needs—biosynthesis