PHOTOSYNTHESIS

CO₂ + H₂O -----> C₆ H₁₂ O₆ + O₂
               light energy

• production of sugars, eventually other organic compounds
• source of ATP energy for plants and all heterotrophs
• reverse of cellular respiration in general way

Question: Where does the water come from? Be as specific as possible.
 
 
 
 
 

Question: Where does the carbon dioxide come from? How does it get there? How does this relate to the competing needs of plants?
 
 
 
 
 
 
 
 

Fate of photosynthate

• glucose + fructose ------> sucrose, transported to other parts of plant
• used in cellular respiration to generate ATP for cellular work
• used as raw material for production of other molecules to build plant tissue

Question: Name several processes that ATP would be used for.
 
 
 
 
 
 
 

Question: Consider a living pine tree. Over the course of its life so far, how much carbon dioxide has the tree used in photosynthesis relative to the amount it has produced by cellular respiration - the same, more, or less? Explain.
 
 
 
 
 
 
 
 

OTHER NUTRITIONAL NEEDS OF PLANTS

Nitrogen

• needed in fairly large amounts
• large amt in atmosphere (79%) but inert to most organisms including plants

Nitrogen fixation - see figure 37.9 in text (p.775) for pathways of fixation, nitrification, denitrifying, etc.

Question: What is the first step when nitrogen from the atmosphere gets converted to a useable form?
 
 
 
 

Question: What happens to ammonium in the soil?
 
 
 
 

Question: What form of nitrogen do plants take up the most?
 
 
 
 

Question: What do plants do with the nitrogen they take up from the soil?
 
 
 
 

Question: What happens to the nitrogen in dead plant (or animal) material?
 
 
 
 

Question: How does nitrogen gas get returned to the atmosphere?
 
 
 
 
 
 
 

Symbiosis of some plants and nitrogen fixers

• bacteria attracted by chemical produced by plant

• bacteria induce curling of root hairs around bacteria
• infect root, stimulate cell division, formation of nodule where bacteria live and grow

Question: What benefit do the bacteria get from the plant?
 
 
 
 
 
 
 

• nitrogenase of bacteria requires low oxygen for enzyme to function
• plant and bacteria produce leghemoglobin - similar to animal hemoglobin

Carnivorous plants - Examples: Venus flytrap, pitcher plant

• live in low N soil; obtain N and some minerals from trapping and digesting small animals

Minerals - many different minerals required in relatively small amounts

General method of determining mineral requirements

• control - grow in medium containing full complement of minerals
• experimental - grow others in medium lacking one or a combination of them
• observe effects on plant (yellowing, flowering, root development...)

Question: Based on the first set of experiments, rank the minerals from highest to lowest in terms of their importance for growth.
 
 
 
 

Question: Based on the second set of experiments, what conclusions can be drawn about the specific roles of any of these minerals? Explain your conclusions based on your knowledge of plant nutrition.
 
 
 
 
 
 
 
 

Some agricultural considerations

• growing one ton of wheat results in loss of 18.2 kg N, 3.6 kg P, 4.1 kg K from the soil
• in natural setting, nutrients typically are not lost from the soil

• fertilizers replenish nutrients in depleted soil
• inorganic ("chemical") fertilizers - immediately available to plants; less stable in soil
• organic fertilizers - less immediate availability to plants; more stable in soil; add to soil structure

Question: Why is there a difference between the two types of fertilizer in stability and availability? What must happen to organic fertilizers before they become available?
 
 
 
 
 
 
 
 
 
 
 

• both types - can end up in surface water and ground water