Equations + General
Word - Carbon Dioxide + Water = Glucose + Oxygen
Symbol - CO2 +nH2O = C6H12O6 + O2
Balanced - 6CO2 + 6H2O = C6H12O6 = 6O2
Photosynthesis uses sunlight energy to transform it into chemical energy in the bonds of glucose.
CO2 + H2O produces glucose, O2 = waste product
- stored as starch
- used in respiration for the release of energy
- turned into sucrose = transported in the phloem to the rest of the plant
- turned into cellulose = cell walls
- with nitrates, produces protein for growth
- Thin = shorter path for diffusion of carbon dioxide
- Large surface area = maximise light absorption
- perpendicular to the sun
- contain palisade cells = many chloroplast + chlorophyll for photosynthesis
Cross section of a leaf
Upper Epidermis -
- upper layer of cell
- NO chloroplast
- secrets a waxy cuticle = barrier
Palisade Layer -
- long + thin ^ chloroplast = ^ photosynthsis
- close to surface = absorbs more sunlight
Spongy Layer -
- main gas exchange surface, absorbs CO2 + releases O2 by diffusion
Vascular Bundles -
- xylem: transports water from root to the rest of the plant
- phloem: transports sucrose + amino acids from leaves to the rest of the plant
Lower Epidermis -
- lower layer of cell contains guard cells (with chloroplasts)
- guard cells surround the stomata, where gases diffuse in and out
Palisade Cell -
- long + thin to pack more in close to upper surface = ^ sunlight absorption
- contain chloroplasts = ^ photosynthesis
- where photosynthesis takes place
- contain chlorophyll green pigment: absorbs sunlight = provides chloroplast with energy
- chlorophyll contains magnesium(Mg)
- reflects green light
- each stomata is surrounded by a guard cell
- in low light guard cells lose water = flaccid , causing stoma to close, this normally only happens in the dark when no CO2 is needed for photosynthesis
- in light, the guard cells become turgid = stoma opens
A limiting factor is a factor that limits the rate of photosynthesis.
- light intensity, CO2, temperature
Effect of light on gas exchange by a leaf
- Hydrogencarbonate indicator solution can be used to show the effect on the exchange of CO2 by a leaf.
- If we place the same volume in a boiling tube the colour change would tell us how fast photosynethsis or respiration would be occuring; the colour change depens on the concentration of CO2 [CO2].
Condition: Indicator colour:
^CO2 (>0.04%) Yellow
CO2 of normal air (0.04%) Orange
decrease CO2 (<0.04%) Purple
Rate of photosynthesis
- How much CO2 enters or O2 leaves the leaf depends on the rate of photosynthsis - the more sunlight = more photosynthesis and the more CO2 will enter and the more O2 will be released
- Net uptale of CO2 = rate of photosynthesis is greater than the rate of respiration
- Net release of CO2 = rate of respiration is greater than the rate of photosynthesis
- this will depend on the light intensity
- low light intensity = respiration but low rate of photosynthesis
- as light intensity increases- rate of photosynthesis increases
Testing a leaf for starch(1)
Testing a leaf for starch(2)
Which factor is limiting the rate of diffusion at point X on the diagram? See next slide for the answer
Exam question answer
Answer :Light intensity. This is because the factor on the x axis will remain the limiting factor as long as the lline continues to rise. At the point at which it starts to level off some other factor becomes the limiting factor such as temperature, or carbon dioxide availability.
Explain why the rate of photosynthesis increases as the temperature is increased from 20 to 30 degrees Centigrade.
Answer See next slide
exam question answer 2
Answer: Photosynthesis is controlled by enzymes. As the substrate molecules move more quickly as temperature increases then the enzyme and substrate will collide more often and the rate will increase. The enzyme will be near its optimum temperature.
Name another factor that can limit the rate of photosynthesis at point Y on the graph.
See next slide for the answer
Exam question answer 3
Answer: Carbon dioxide concentration.