1.2 Photosynthesis

Photosynthesis

endothermic process by plants to create glucose, oxygen and remove carbon dioxide

Uses of glucose from photosynthesis

• Respiration- used to provide energy

• Storage- converted into starch and oils

• Useful substances- creates cellulose for cell walls, protein for growth and chlorophyll

Chlorophyll

green pigment that absorbs light energy to carry out photosynthesis made from magnesium ions

Photosynthetic rate

speed which plants carry out photsynthesis

Testing leaves for starch

adding iodine solution after leaf has been heated and submerged in ethanol

Photosynthesis word equation

Carbon Dioxide + Water (Light/Chlorophyll) → Glucose + Oxygen

Balanced equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Endothermic reaction

energy is taken in from surrounding environment

Temperature effect on photosynthesis

rate increases to an optimum before decreasing due to denaturing enzymes

Cellulose

Carbohydrate component of cell walls made from glucose

Amino acids

Building blocks of protein made from photosynthesis

Enzymes

should be maintained in optimal conditions for efficient rates of photosynthesis

Limiting factors

as factor increases, so does rate of photosynthesis until a certain point where it plateaus (another factor must be limiting)

Maximum rate of photosynthesis

all limiting factors must be at optimum level, else rate will be determined by factor in shortest supply

Three main limiting factors

Temperature, light intensity and carbon dioxide concentration

Plateau

graph levels off and no longer increases past a certain point

Purpose of photosynthesis

products used for respiration and to make new molecules

When photosynthesis occurs

light conditions during the day

When respiration occurs

all the time in animals and plants, but plant respiration is more observable at night

Hydrogencarbonate indicator

detect increases and decreases of carbon dioxide concentration

Hydrogencarbonate indicator low concentrations (midday)

• purple

• rate of photosynthesis is faster than respiration

• CO₂ produced from respiration is used, then plateaus as no longer limiting factor

• Decreases net levels of CO₂

Hydrogencarbonate indicator normal concentrations (dusk/ dawn)

• red

• rates of photosynthesis and respiration are equal

• volume of CO₂ produced is the same as the volume used by photosynthesis

• known as compensation point

Hydrogencarbonate indicator high concentrations (midnight)

• yellow

• photosynthesis has stopped due to no light being available

• respiration still occurs, producing CO₂

• Increases net levels of CO₂

Structure of leaf

• Cuticle

• Upper epidermis

• Palisade mesophyll

• Chloroplast

• Spongy mesophyll

• Intercellular air space

• Lower epidermis

• Stomata

• Guard cell

Mesophytic leaf

adapted to general conditions, not too dry or too humid

Adaptations of the leaf for light absorption

• Each leaf is not in the shade of another

• Thin to ensure all cells receive light

• Large surface area

• Transparent waxy cuticle

• Epidermis transparent

• Palisade mesophyll layer

Waxy cuticle

protective layer that is transparent to allow light to pass through and waterproof to reduce loss by evaporation

Epidermis

physical defence layer containing no chloroplasts so it is transparent and allows light into leaf

Palisade mesophyll

regularly shaped, so can pack closely together at top of the leaf, and contains many chloroplasts to trap as much light as possible

Adaptations of the leaf for gas exchange

• Spongy mesophyll

• Intercellular air spaces

• Stomata

Spongy mesophyll

have very few chloroplasts and packed loosely for efficient gas exchange with increased surface areas

Intercellular space

space between to provide room for an increased rate of diffusion

Stomata

Small pores on underside of leaf to allow gases to pass through

Guard cells

pairs of cells that surround stomata and control opening to optimise gas exchange and reduce water loss

Activity of guard cells

usually open during the day and closed at night