Plant Nutrition and Photosynthesis

Reading Quiz Get out a small sheet of paper and write your name at the top. Answer the following questions in silence Get out a small sheet of paper and write your name at the top. Answer the following questions in silence 1)What is the chemical process that plants use to make energy from sunlight? 2) What reactants do plants need to do this reaction? 3) Why are plants green? 4)What is the organelle that absorbs sunlight? 6CO 2 +6H 2 O+sunlight  C 6 H 12 O 6 +6O 2 CO 2, H 2 O, and sunlight Only color they don’t absorb well Chloroplasts

ATP: The Energy unit of the Cell ATP (adenosine triphosphate, 三磷酸腺苷） O O O O CH 2 H OH H N HH O N C HC N C C N NH 2 Adenine Ribose Phosphate groups O O O O O O CH

Cell Energy use in Active Transport

Energy is released from ATP ( kJ/mol) –When the 3rd phosphate bond is broken

Trapping Energy from Sunlight The process that uses the sun’s energy to make simple sugars is called photosynthesis Bases of all ecosystems on Earth 6 CO H 2 O + Light energy  C 6 H 12 O O 2

Tissue of a Leaf Plant tissue: Plant tissue: Upper epidermis  water proof outer covering; covered with cuticle Upper epidermis  water proof outer covering; covered with cuticle Palisade mesophyll  photosynthetic cells; lots of chloroplasts Palisade mesophyll  photosynthetic cells; lots of chloroplasts Spongy mesophyll  space for CO 2 /O 2 circulation Spongy mesophyll  space for CO 2 /O 2 circulation Phloem  transport solutes Phloem  transport solutes Xylem  transport water and salts Xylem  transport water and salts Lower epidermis  stomata for gas exchange Lower epidermis  stomata for gas exchange

Vein Leaf cross section Mesophyll CO 2 O2O2 Stomata Where Does CO 2 come from? Enters leafs through the stomata Where does H 2 O come from? Absorbed by roots and pulled up to the leaves by cohesion and adhesion (transpiration)

The Problem with Gas Exchange How does CO 2 and O 2 get in and out of a plant? –Stromata under the leaves What else can escape through a stromata that the plant needs? –H2O–H2O What problems must plants in dry, hot climates deal with? –The plant needs to take in CO 2 and release O 2, but the open stromata will also release H 2 O H 2 O out

Where does Light Energy come from? Energy from the sun must be absorbed by pigments, light absorbing molecules (chlorophyll) Inside a chloroplasts are thylakoids and inside their membranes are pigments What wavelength of light do the pigments not absorb? –Green; reason why plants are green

Photosynthesis: 2 Reaction Set 1)Light-dependent reactions  chemical reactions driven by light energy absorbed by pigments 2)Light-independent reactions  chemical reactions that use ATP and NADPH to create sugars out of CO 2

H2OH2O CO 2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH 2 O] (sugar) NADPH NADP  ADP + P O2O2 ATP

The Light-Dependent reactions Light Reflected Light Chloroplast Absorbed light Granum Transmitted light Pigments- light absorbing molecules Chlorophyll  main light absorbing pigment Light-dependent reactions use chlorophyll to trap light energy. This energy produces ATP, NADPH, and O 2

The Light-Dependent reactions Photolysis

H2OH2O CO 2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH 2 O] (sugar) NADPH NADP  ADP + P O2O2 ATP

The Light-Independent reactions

Final Numbers UseProduce Light-Dependent Reactions SunlightNADPH H2OH2OATP O2O2 UseProduce Light-Independent Reactions (Calvin Cycle) NADPH RuBP (recycled to keep cycle going) ATPPGAL (Which form sugars) CO 2

Photosynthetic Rates

Structure of a Leaf If photosynthesis occurs mostly in the leaf, what factors must be considered when designing a leaf? 1)Amount of sun exposure –More surface area = more photosynthesis 2)Movement of CO 2 and O 2 –Space for exchange 3)Movement of H 2 O and products of photosynthesis –Water from the roots and organic molecules to other areas

Photosynthetic Rates: Light What factors could affect photosynthetic rate? –Light intensity –Amount of CO 2 / H 2 O –Too much O 2 –Temperature Increase Light Intensity = Higher Photosynthetic rate –BUT there is a max. limit; Why? Limit to how fast enzymes can work

Photosynthetic Rates: Temperature If just temperature is increased, rates go up Why? –More kinetic energy = faster enzymatic rates Why is there only a small increase in rate? –Light-dependent stage is limited by light intensity What would be create the best photosynthetic rate? –High temperature and high light intensity Why do rates drop after raising the temperature too high? –Enzymes (proteins) denature

Photosynthetic Rates: Limiting Factors Even with high temps and high light intensity, what factors must be considered? –Availability of CO 2 and H 2 O –Too much O 2 (limits enzymes in high conc.) Limiting factor  the factor least available or having the strongest affect on reactions rates –Can be light, temperature, CO 2, H 2 O, or O 2 depending on the situation

Limiting Factors Practice What is the limiting factor for : 1)Plants in the rain forest? –Light intensity; Rain forests have plenty of rainfall and humidity but limited space; plants fight for sunlight 2)Plants in the deserts? –Water; Deserts have plenty of sun and open space but very little rain 3)Plants underwater? –CO 2 /Sunlight; Dissolved CO 2 harder to access and sunlight loses strength as it passes through water 4)Plants in the arctic? –Temp/Sunlight; Cold temperatures and little direct sunlight limits growth

Limiting Factors on Growth We have plant that gets plenty of sunlight, water, and CO 2. However it seems to grow very slowly and looks unhealthy. Why? –Missing other nutrients –Soil does not contain enough mineral salts Mineral salt  plant nutrients needed for growth and repair –Nitrates –Phosphates –Ions like Mg and K

Mineral Salts Nitrates  nitrogen based compounds like NH 3, NO 2 -, and NO 3 - which are used to build amino acids –Most nitrogen is N 2 which is unusable –Nitrogen fixation by bacteria make nitrates –Animal urine has urea which is similar to NH 3 Phosphates  PO 4 3- which is used to build DNA and RNA Magnesium ions  Mg 2+ which is used to build chlorophyll Potassium ions  K + which is used to make stable cells all over the plant

Getting Mineral Salts Mineral salts must be present in the soil for plants to grow. How can we add mineral salts? 1)NPK fertilizers  mix of material containing NPK ions which are absorbed by the roots –Can wash away and cause algae blooms  rapid growth of algae in lakes that causes the ecosystem to crash 2)Humus  natural decomposition of material (compost) that slowly added mineral salts to soil –Farms can never be sure if enough of each Ion is present in compost