Photosynthesis A summary of what you should know.

photosynthesis

A summary of what you should know

Revision of third form photosynthesis

PhotosynthesisWhat happens to the glucose formed in photosynthesis?

PHOTOSYNTHESIS

GLUCOSE STARCH

CELLULOSE

LIPIDS

PROTEINS

CARBON DIOXIDE AND

WATER

Required to make plant cell walls. It is made of 100s of glucose molecules bonded together.

Glucose is chemically converted to fatty acids and glycerol to make lipids, which are needed to make plant cell membranes and seed storage oils.

Is used by roots and leaves to store excess glucose in an osmotically inactive form. It is made of 100s of glucose molecules.

Using nitrate ions absorbed by plant roots, glucose is converted first to amino acids then to protein.

The carbon dioxide can be used again in photosynthesis or may diffuse out of the leaf via the stomata

respiration

ATP

Factors necessary for photosynthesisFactors affecting the rate of photosynthesis

light intensity

The main external factors affecting the rate of photosynthesis are:

Rat

e o

f p

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temperature (degrees C)

Heat energy increases kinetic energy. More

collisions, with more force, thus the rate increases

Enzyme protein denatures. They lose their catalytic ability to

catalyse photosynthesis

Optimum

Increasing light intensity increases the energy entering chlorophyll and thus the amount of ATP

and produced to drive photosynthesis

The effect of light intensity on photosynthetic rate

The effect of temperature on photosynthetic rate

The rate is limited by another factor such as carbon dioxide

concentrationLight intensity limiting.

light wavelength

light intensity

temperature

carbon dioxide

Notice how increasing the light intensity beyond a certain point causes no further

increase in rate of photosynthesis. Something else is now ‘holding the reaction back’. Light is no longer the limiting factor.

Photosynthetic sugar production is catalysed by enzymes. If the temperature is raised too high

the enzymes denature and photosynthesis stops.

Factors necessary for photosynthesisLimiting factors

25O C and 0.04% CO2

25O C and 0.4% CO2

15O C and 0.04% CO2

Ra

te o

f p

ho

tos

yn

the

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Light intensity

0 5 10 15 20 25

Rat

e o

f p

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temperature (degrees C)

High light intensity

Low light intensity

The effect of temperature and light

At low light intensities increasing the temperature has little effect on the rate of photosynthesis.

At high light intensities the rate of photosynthesis increases much more rapidly over the same temperature range.

This is an example of the law of limiting factors.

THE LAW OF LIMITING FACTORS If a process is influenced by more than 1 factor, the rate will be limited by the

factor nearest its lowest value

Here is another example of the law of limiting factors

What 3 factors are limiting in regions A, B, C respectively?

ANSWERS:

At B temperature limiting

At A CO2 limiting

A

B

C

At C light limiting

Plant mineral requirements

Plants require small quantities of minerals for healthy growth

Minerals are absorbed by the root hairs, either by diffusion or active transport, depending on their concentration in the soil – see next topic.

The most important minerals for plants are:

Nitrogen

Potassium

Magnesium

Iron

Phosphorous

usually as nitrate, nitrite or ammonium ions, NO3- , NO2

-, NH4+

often in the form of phosphate ions, PO4- ions.

in the form of K+ ions.

in the form of Mg2+ ions

in the form of Fe2+ ions

Mineral requirements of plants

Nitrogen (nitrate ions: Needed to make proteins and

chlorophyll

Deficiency: Poor growth and leaf yellowing

NO3-

Potassium: Helps enzymes in photosynthesis and respiration

Deficiency: Yellow leaves with dead spots

K+

Phosphorous: Required for photosynthesis and respiration

Deficiency: Poor root growth and purple younger leaves

PO4-

Iron is required by the enzymes that make chlorophyll

Deficiency: Leaf yellowing

Fe2+

Magnesium is required as part of the chlorophyll molecule

Deficiency: Yellowing of leaves and poor growth

Mg+

REMEMBER THESE ARE REQUIRED

IN IONIC FORM!

The photosynthesis word equation. That light energy is absorbed by chlorophyll in chloroplasts and used to make sugar from carbon dioxide. Oxygen is a bye-product.

The rate of photosynthesis may by limited by: low temperature, shortage of carbon dioxide, shortage of light.

The glucose produced in photosynthesis may be converted to insoluble starch. Start does not attract water by osmosis.

The energy from respiration is used to build smaller molecules into larger ones, including: sugars into starch, sugars into cellulose for cell walls, sugars, nitrates and other nutrients into amino acids and then proteins. Sugars into lipids for seed storage.

For healthy growth plants need mineral ions including: nitrate for protein synthesis, phosphate and potassium for photosynthesis and respiration.

Symptoms shown by mineral ion-deficient plants include:

Any 1 of light, temperature and carbon dioxide will be limiting the rate of photosynthesis at any particular time.

WHAT YOU SHOULD KNOW AT THE END

OF THIS UNIT

Plant cells use some of the photosynthetic glucose for respiration. In addition, nitrates, absorbed by the roots, are needed for healthy growth.

Stunted growth and yellow older leaves if nitrate ions are deficient

Poor root growth and purple younger leaves if phosphate ions are deficient

Yellow leaves with dead spots if potassium ions are deficient.