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Keywords: Asteraceae | Helianthus annuus hybrid
This is the backlit leaf of a giant sunflower growing in the Food Garden here at UBC Botanical Garden. Despite the general cloudiness of this past summer, a few of these plants have easily exceeded 3.5m (~12ft) in height.
What is immediately obvious is the network of veins in the leaf. While the veins are essential for nutrient and water transportation, in many leaves they also help to provide a structural skeleton. Each vein consists of xylem (water-conducting) tissue and phloem (sap-conducting) tissue surrounded by a protective wrapping of structural tissues, including collenchyma. In the spaces between the veins (and bounded by the upper and lower epidermi of the leaves) is the tissue called parenchyma. In leaves, parenchyma cells are packed with chloroplasts, the organelles that are responsible for photosynthesis. It should be noted that other parenchyma cells may have different functions elsewhere in the plant, such as storage or secretion. This is why the chloroplast-laden parenchyma of leaves is sometimes referred to as chlorenchyma, so as to better reflect the specific purpose of this tissue.
I don't mention photosynthesis often enough on BPotD, considering the fact that nearly all complex life on Earth depends on this process in one way or another. The evolution of photosynthesis approximately 3.5 billion years ago and subsequent alteration (with some lag time) of the Earth's atmosphere to the present day concentration of oxygen in the air permitted the evolution of complex life.
Posted by Daniel Mosquin at August 24, 2007 12:00 AM
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Posted by: A Jablanczy at August 24, 2007 4:25 AM
Daniel;
Thanks for another excellent and educational post. I hope (but doubt, at 56) to live long enough that we discover life on other planets that has evolved using a different mechanism than photosynthesis; wouldn't that be interesting?
Posted by: bev at August 24, 2007 6:07 AM
I am a new member as of about 2-3 weeks ago and this is now, by far, one of my favorite pictures. In response to Bev, I agree and am amazed at the diversity not just in shape or form but in life processes that exist within this biosphere. For example, the hydrothermal vent/cold seeps deep along the ocean floor have organisms that evolved to metabolize sulfur for energy - it's amazing.
Posted by: Rach at August 24, 2007 7:19 AM
Perhaps you should have complemented it with a picture of a field of oil producing sunflowers, from the Prairies.
Posted by: Big Al at August 24, 2007 2:47 PM
I think by the time I get to the prairies this year, the sunflowers will be over.
Posted by: Daniel Mosquin 
at August 24, 2007 2:48 PM
Terrific image and post Daniel. Thank you.
Posted by: Katy S at August 26, 2007 6:29 PM
Please share your comments about the photograph(s) and accompanying write-up. Telling a story about the subject of the photograph(s) is also much appreciated! If you have a gardening question, the best place to ask is on the UBC Botanical Garden Forums. Thank you!
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Botany Photo of the Day is a project of the UBC Botanical Garden and Centre for Plant Research, located in Vancouver, British Columbia Canada. UBC BGCPR is a department of the Faculty of Land and Food Systems within The University of British Columbia.
A very nice summary of intermediate metabolism especially the function of chloroplast in O2 and CO2 use.
To go further green plants are green and vertebrate even annelid and mollusc blood is red
and insect exoskeletonous animal blood is yellow because Fe or Cu or Mg atom sits like a spider in the centre of its web in the heme or chlorophyll molecule which are almost identical and carry grab and release O2 or CO2 as needed.
Light resonates at different wavelengths in Fe O
rust being red and Cu O being yellow and Mg O being green as magnesium flares.
Thats why plants are green vertebrate blood red and insect blood yellow. Iron copper or magnesium carrying O2.