topic 14.2 - plant nutrition biology 1001 - november 16, 2005
TRANSCRIPT
Topic 14.2 - Plant Nutrition
Biology 1001 - November 16, 2005
1. Introduction Nutrition involves obtaining energy, carbon, and
other essential organic and inorganic compounds for metabolism
Plants require sunlight, CO2, water and certain minerals
Sunlight & CO2 are obtained from the aerial environment through the shoot, especially leaves
Water & minerals are obtained from the subterranean environment, through the roots
Plants perform photosynthesis to synthesize organic molecules
They perform cellular respiration to derive energy from these organic molecules
Photoautotrophs
2. Chloroplasts: The Sites of Photosynthesis Chloroplasts are located in mesophyll cells
of the leaf (30-40 chloroplasts per cell) Chloroplast internal structure includes a
dense fluid called stroma and stacks of thylakoid sacs called grana
Chlorophyll in the thylakoid membrane absorbs the light energy necessary for photosynthesis
Green wavelength light is reflected, which is why chloroplasts & leaves are green
Stomata on the leaf surface allow CO2 to enter, O2 & H2O to leave the leaf
Vascular veins transport water & minerals to the leaf and the organic products of photosynthesis away from the leaf
Figure 10.3!!
3. Overview of Photosynthesis Overall equation of photosynthesis
An anabolic pathway of endergonic reactions 6CO2 + 12H2O + light energy C6H12O6 + 6O2 6H2O
About the process Water is consumed and new molecules of water are formed Water is split during photosynthesis, not carbon dioxide The enzymes required for photosynthesis are located in the
stroma or embedded in the thylakoid membrane Photosynthesis does not occur as the reverse of cellular
respiration, but as two sets of many reactions each
The Two Stages of Photosynthesis The Light Reactions
The “photo” part of photosynthesis, these reactions occur in the thylakoid membrane
Light energy drives a transfer of electrons and hydrogen from water to NADP+, producing NADPH
H2O 2H+ + 2e- + 1/2O2
NADP+ + H+ + 2e- NADPH This is reducing power
Light energy also phosphorylates ADP to ATP ADP + P ATP This is chemical energy
Water is split and oxygen released during these reactions ATP and NADPH are used in Calvin cycle
The Two Stages of Photosynthesis The Calvin Cycle
The “synthesis” part of photosynthesis, occurs in the stroma The reactions of the Calvin Cycle do not directly require light, but they
require the products of the light reactions, so they generally occur in the light
Carbon enters the Calvin Cycle as CO2 and leaves as sugar It first gets added to already existing organic molecules, a process called
carbon fixation It then gets reduced to a carbohydrate using the reducing power of
NADPH and the chemical energy of ATP The carbohydrate produced by photosynthesis is actually the three
carbon sugar glyceraldehyde-3-phosphate, not glucose
ADP and NADP+ released from the Calvin Cycle are returned to the thylakoid membrane and used again in the light reactions
The cooperation of the light reactions and the Calvin cycle - Figure 10.5!,!!
4. The Relationship of Photosynthesis to Cellular Respiration Energy enters the ecosystem as sunlight
and gets stored as chemical energy in the organic products of photosynthesis which also releases oxygen as a by-product
During cellular respiration the organic molecules react with oxygen and are broken down to release the energy that phosphorylates ATP and powers cellular work - some of the energy dissipates as heat
The products of cellular respiration are used as the reactants of photosynthesis
Note the recycling of molecules but the flow of energy through the ecosystem
Figure 9.2!
An Overview of Cellular Respiration A catabolic pathway of exergonic reactions
Mostly occurs in the mitochondria; enzymes for cellular respiration are embedded in the mitochondrial membranes
Cellular respiration is the combustion of organic compounds by oxygen Organic compounds + oxygen carbon dioxide + water + energy C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP & heat)
Fermentation is a partial degradation of organic compounds that does not involve oxygen Glucose carbon dioxide + ethanol + energy (ATP & heat)
The three stages of cellular respiration are glycolysis, the citric acid cycle and oxidative phosphorylation ATP is produced at each stage, but mostly by oxidative phosphorylation
An Overview of Cellular Respiration
Glycolysis, which occurs in the cytosol, converts glucose to pyruvate
Pyruvate is converted to CO2 during the citric acid cycle which occurs in the matrix of the mitochondria
Also during the citric acid cycle, electrons are added to NAD and FAD converting them to NADH and FADH2
These carry electrons to the inner membrane where they are added to oxygen to release energy during oxidative phosphorylation
Figure 9.6!
O2
H2O
Link to Video
Comparing Photosynthesis & Cellular Respiration
Feature Photosynthesis Cellular Respiration
Water Used Produced
Oxygen Produced Used
Carbon dioxide Used Produced
Energy Used Produced
Organic molecules Produced Used
When does it occurs In the light Anytime
Organelle involved Chloroplast Mitochondrion
Which organisms use it?
Photoautotrophs including plants and algae
Most (all?) eukaryotes
Certain prokaryotes
Compare and contrast photosynthesis and cellular respiration for each of the following characteristics