Photosynthesis and Plant Diversity

LEARNING OBJECTIVES

  1. Define: photosynthesis, autotroph, pigment, chlorophyll, and chloroplast.
  2. Write the generalized formulas for photosynthesis and aerobic respiration and fermentation.
  3. Relate the visible light range to photosynthesis and describe the absorption spectrum.
  4. Identify the pigments in a leaf pigment extract and describe a method of separating individual pigments.
  5. Use knowledge of photosynthesis to estimate a plant’s productivity.
  6. List the major plant groups and their defining characteristics.
  7. Identify the major plant organs and whether they are vegetative or reproductive

BACKGROUND & APPLICATIONS

Photosynthesis

The sun is the source of energy for nearly all of earth’s ecosystems.  But most organisms cannot utilize the sun’s energy until it has been converted and stored as a chemical (glucose).  The process by which light energy is converted to chemical energy (glucose) is called photosynthesis.  Organisms capable of performing photosynthesis are called photoautotrophs (“light-self-feeders”).   Plants, algae, and cyanobacteria are photoautotrophs.  Plants and algae are eukaryotic and use special organelles for photosynthesis called chloroplast.  Cyanobacteria perform photosynthesis within their cytoplasm.   The remaining organisms of the ecosystem such as animals and fungi (heterotrophs) must consume the plants in order to utilize the sun’s energy in the form of glucose or other molecule.   

Photosynthesis takes place in the chloroplast located in the cells of the leaves and/or the green stems of plants.   Photosynthesis begins when light energy stimulates chlorophyll a and water molecules split. The oxygen from the water molecule is released while the hydrogen left from the water are used to generate ATP and NADPH (energy carrying molecules). The second step is to use the energy carrying molecules (ATP and NADPH) from the first reaction to energize a series of enzyme-catalyzed reactions that to link together carbon dioxide molecules (from the air) to make glucose.   The following chemical reaction shows the major products and reactants of photosynthesis

6CO2     +       12 H2O        →     C6H12  O6+6O2+6H2O
(carbon dioxide)(water)(glucose) (oxygen) (water)


LABORATORY ACTIVITIES

Exercise 1: How Plants Affect Dissolved Oxygen

The hypotheses: If photosynthesis is taking place in the plant cells, then amount of oxygen around the plant will continuously increase over time.

Go to the Kaltura video link in this lab folder on blackboard to watch the “dissolved oxygen” experimental procedure performed in the face to face lab.  As you follow the video think about the chemical equations.  How does the data being collected reflect the chemical equations of photosynthesis?   You may want to make notes on the table and space below.

Table 1. Plant Oxygen Data

Time (min)Dissolved Oxygen Elodea Plant (ppm)
0 
5 
10 
15 
20 
25 
30 

This video is a variation of the lab procedure demonstrated in the Kaltura video. It uses algae instead of a plant and measures the amount of oxygen produced over a 24 hour  with different amounts of light.  The concept being demonstrated is the same.

Discussion Questions

  1. Did the data collected support the predicted statement of the hypothesis?
  2. Why can a researcher measure dissolved oxygen as an indicator of photosynthesis?
  3. Were there any measurements that did not follow the predicted trend? If so, which ones?
  4. What may cause the dissolved oxygen around the plant to decline even if for only one or two measurement?  There could be more than one. Think about the experimental design and other cellular process that are occurring at the same time (aerobic cellular respiration)


A CLOSER LOOK AT PHOTOSYNTHESIS

Title: vial of chlorophyll extract  - Description: Perceive color by wavelengths reflected
chlorophyll extract.JPGExercise 2: Interaction of Light and Chlorophyll

1. Visible light spectrum

Visible light is the portion of energy from the sun that is used by plants in photosynthesis and by the human eye for sight. The visible light spectrum is only a small portion of the energy the Earth receives from the sun. Energy from the sun travels through space in the form of waves. Energy with shorter wavelengths like ultra violet has higher energy levels than those with longer waves like infrareds. The wavelengths in the visible light spectrum range in length from 380 nm to 760 nm. A collection of all wavelengths between 380-760 nm produces white light. White light if passed through a prism can be split into the individual wavelengths or colors of light.

Observe the visible light spectrum below.  This is produced by passing white light through the prism in a spectroscope.

Title: Visible light spectrum as seen through a spectroscope - Description: notice shorter, higher energy, wavelengths are the violet to blue end and longer , lower energy wavelengths are the red end.
wavisible light spectrum.JPG

 According to the scale on the spectroscope, which colors are of higher energy (shorter wavelengths)?

Title: vial of chlorophyll extract  - Description: Perceive color by wavelengths reflected
chlorophyll extract.JPG2. Reflected and transmitted light.

Individual wavelengths (colors) of light may be transmitted, reflected, or absorbed when light strikes an object. If particular wavelengths are absorbed, they are removed from the spectrum. Our eyes perceive the wavelengths that are transmitted (pass through) or reflected (bounced off) as colors. Chlorophyll and accessory pigments absorb specific wavelengths of light. These wavelengths provide the energy source for photosynthesis.

Observe the pigments extracted from leaves.

What color does the solution appear to you?

Why did you perceive the solution as the color answered above?

Title: visible light spectrum as light is shone through green pigment - Description: note only green light is visible because green wavelengths are reflected by chlorophyll.  Chlorophyll when energised by light fluoresces red

reflected visible light spectrum chlorophyll absorption.JPG

The following, is the visible spectrum when a tube of plant pigment extract is placed between a light source and a spectroscope and observe the spectrum.

What color(s) are missing compared with the first spectrum observed? 

In what way does chlorophyll interact with light?

Exercise 3: Chlorophyll and Accessory Plant Pigments

The chlorophyll pigment is absolutely necessary for photosynthesis to go forth and utilizes energy from both ends of the visible spectrum, while reflecting the green wavelengths in the middle of the spectrum, as demonstrated in Exercise 3. Most plants, however, also possess other pigments in addition to chlorophyll. These pigments are called accessory pigments and they enable the plant to use wavelengths from the visible spectrum that chlorophyll may miss. Normally, accessory pigments are masked by the abundance of chlorophyll until the fall of the year when the temperature drops and day length shortens. At this time, the chlorophyll begins to degrade and the leaves begin to turn color. The fall colors are caused by the accessory pigments in the leaves of the tree.

Paper chromatography is a method used to separate and observe the different pigments in spinach leaves. Chromatography uses the varying solubility and attraction to paper of the pigments present in a leaf to separate the pigments into bands on the paper. As the solvent moves up the paper, pigments that are highly soluble will travel farther. Conversely, pigments that are less soluble and have a greater attraction to the paper molecules will move more slowly.

  1.  Link to  http://www.youtube.com/watch?v=u6jD0hJO-28  for video on separation of photosynthetic pigments by paper chromatography

2.   Observe the movement of the solvent up the paper strip. During this time, the different pigments will separate from each other based on their relative solubility in the solvent. The more soluble the pigment in the solvent, the faster and farther the pigment will move up the paper. Carotene, a bright yellow pigment, should be seen toward the top of the paper. Xanthophylls are a pale yellow pigments. Chlorophyll a is a yellow- green line just above chlorophyll b, a olive-green color.

3.  Use colored pencils to diagram and label your chromatography results.

Beginning pigment line  

Diversity in the Plant Kingdom

The organisms included in the plant kingdom are sessile (except for sperm cells), have cell walls composed of cellulose, mostly obtain their nutrient by photosynthesis, and demonstrate cellular specialization into tissues. The primary tissues of plants are epidermal tissue (covering and water conservation), ground tissue (photosynthesis and storage), and vascular tissues (xylem and phloem for the transport of water and photosynthesis products).  These tissues are arranged into vegetative structures and reproductive structures.  The vegetative structures are more commonly known as roots, stems, and leaves.  Some reproductive structures may ultimately lead to the production of seeds which contain an embryonic plant, nutritional material, and protective covering.   Another form of reproduction simply disseminates spores which will germinate into structures that produce egg and sperm, fertilization and the development of the embryo without the dormancy period associated with seeds. 

Four major groupings of the plants will be covered in this lab.  These groups include the nonvascular plants (bryophytes), seedless vascular plants, plants that have flowers and fruit covered seeds (angiosperms) and those that produce seed without flowers and fruits (gymnosperms).   These major groups are divided largely on the extent of the development of the three tissues into the roots, stems and leaves, the production seeds, and production of flowers and fruit.

Nonvascular plants or bryophytes have the most simple tissue development of the plant kingdom.  Without vascular tissue, they do not develop true characteristics of roots, stems, and leaves but they do have structures that emulate these structures to varying degrees.  The most recognizable members of this group are the mosses.  Mosses tend to be short existing close to the surface they grow on and are closely tied to water particularly for reproduction.    They do not produce seeds rather they reproduce by spores.  Their inability to conserve water means these plants will easily dry out and they respond quickly to changes in the environmental conditions.  When conditions are right, they undergo sexual reproduction within a few days.  When conditions dry out, some species will shrivel up and look dead but will green up within a few hours after it rains.  Mosses are often associated with disturbed areas and cool moist areas.  They can be found as part nearly all ecosystems but thrive in cool moist environments.

Seedless vascular plants have greater development of some vascular tissues which allows them to obtain some size but they do not produce woody structures, flowers, or seeds.   Seedless vascular plants dominated the landscape during the carboniferous period and were converted after being covered for millions years to coal, oil and gas we use today to fuel electricity, homes, and cars.    The most recognizable of these plants are the ferns but there is a wide variety of this type of plant.  Ferns have stems that run horizontally (rhizome) along the ground that produce leaves (fronds) aerially and roots down into the soil.  Like mosses, this group is closely tied to water for fertilization and sexual reproduction.  They do not produce flowers or seed but reproduce by spores that are born directly on the leaves or in cone-like structures called a strobilus. 

The word gymnosperm means “naked seed”.  This group includes the Sequoia trees of the Pacific Northwest which are the largest trees on Earth.  The development of seeds was a major advantage to the survivability and dispersal of these plants.  It enabled plants to break free of the ties of water for fertilization and reproduction that kept the seedless vascular plants and nonvascular plants from colonizing areas far from the moist environments.  Gymnosperm use pollen and wind to carry sperm to the female organs which may be on the same tree or different trees.   Seeds have a tough outer covering that protects the embryo until conditions are favorable for growth and development.   The seed also provides stored nutrient for the young tree until it can develop leaves and make its own nutrients.  Pines and the needle-leaf conifers are the most identifiable members of this group but it also include Ginkgo and the Junipers. 

Angiosperms are by far the most diverse group of plants.    They range in size from less than 2mm (duck weed, Wolfia sp.) to over 100 meters (Mountain Ash, Eukalyptus sp.) tall.  Member of Angiosperm can be found anywhere you can go…deserts, mountains, plains, fresh water, and salt water.  The one thing member of this group have in common is they all produce flowers and fruit that contain seeds.   Flowers have four basic parts and depending on the species of plants these parts can be of different shapes, colors, or be missing entirely.   The four flower parts are the sepals, petals, carpels (female parts), and stamen (male part).  Sepals are the protective outer covering of the flower bud. The petals are modified leaves generally for the purpose of attracting pollinators.   The carpel is made up of the stigma, style and ovary. 

 The stigma and style are to capture pollen and direct the pollen tube and sperm down to the ovary where the ovules containing egg cells await fertilization.  The stamen are made up of the anthers and filaments.  Pollen is released from the anthers and ultimately transport sperm to the egg cell for fertilization.  After fertilization fruit develops from the outer covering of the ovary.  The organs that are roots, stems, and leaves are vegetative (non-reproductive) structures while fruits are reproductive structures for the purpose of seed dissemination. 

Exercise 4: Plant diversity

https://www.khanacademy.org/partner-content/crash-course1/partner-topic-crash-course-bio-ecology/crash-course-biology/v/crash-course-biology-135
https://www.khanacademy.org/partner-content/crash-course1/partner-topic-crash-course-bio-ecology/crash-course-biology/v/crash-course-biology-136

Observe examples of mature vascular and nonvascular plats from the major groups (Google images).  Some may have reproductive structures present some not.  Use the descriptions above and the information in the Crash Course Biology Videos to identify the characteristics of the major plant groups.  

Is it a vegetable or fruit? 

Many arguments have been waged over whether a particular item in the produce department at the supermarket is a vegetable or a fruit…particularly when it comes to tomatoes.  Using your knowledge of plant structure and definitions, identify these common items from the produce department as a vegetable or fruit.

 ItemIdentityJustification
1Green beans  
2Spinach  
3Onion  
4Squash  
5Cucumber  
6Broccoli  
7Banana  
8Carrot  
9Corn  
10Pepper  
11Cabbage  
12Apple  

Exercise 5: Fungi: (Special Mention)

https://www.khanacademy.org/partner-content/crash-course1/partner-topic-crash-course-bio-ecology/crash-course-biology/v/crash-course-biology-138

The kingdom Fungi are often studied with the Plant kingdom even though they have very little in common.   Actually, Fungi have more in common with animals than plants.  Fungi are primarily saprobes which mean they consume dead things (decomposers).  By obtaining their nutrient from their environment they do not perform photosynthesis, have no chlorophyll are not green.  Their cell walls are composed of a chitin (a protein) rather than cellulose (a carbohydrate).  The mushroom structures so often associated with fungi are actually their reproductive structure which release spores.   The vegetative structure is rarely seen as it grows in a filamentous mass (mycelium) beneath the soil surface.  Some fungal mycelium can grow to cover very large surface areas. 

Perform a search to see the diversity in Fungi.

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