Bio 11 – Botany – Exercise 12 – Photosynthesis

A. Chlorophyll as a Factor in Photosynthesis

1. Examine young variegated leaves of coleus or caricature plant, Graptophyllum pictum (L.) Griff, and note the distribution of chlorophyll as indicated by the green area.

2. place the leaf in boiling water for a few minutes. Immerse it in a test tube containing 95% ethyl alcohol. Place the test tube in a warm bath until the pigments are extracted.

2.1 What is the purpose of boiling the leaf?

Burst the chloroplasts

3. Rinse the bleached leaf with water and place in a petri dis. Test for the presence of starch using dilute IKI solution. The presence of starch as shown by a bluish-black to purple coloration indicates the occurence of photosynthesis.

3.2 How does it compare with your sketch in 1.1?

Green ares – photosynthetic

Non-green areas – non-photosynthetic

3.3 Do the non-green areas of the leaf contain starch?

Yes although minimal

3.4 What can you conclude from this experiment?

Only those with chlorophyll can undergo photosynthesis

B. Light as a Factor in Photosynthesis

4. Place a potted coleus or bean plant in the dark. After 48-75 hours, warp one of the leaves with carbon paper or aluminum foil. Expose the plant to light for 6 to 10 hours. Detach the covered and one uncovered leaf of the same size and test for presence of starch as previously done in section A above.

4.1 Why was it necessary to place the plants in the dark for 48-72 hours?

Consume starch reserves in plant

4.2 Why was carbon paper or aluminum foil used?

Prevent light from reaching leaves

4.3 What areas in the covered and uncovered leaves showed a positive reaction to the starch test?

Uncovered areas contained starch

4.4 Can plants carry out photosynthesis under artificial light as well as natural or day light?

Yes

4.5 What can you conclude from this experiment?

Light is needed for photosynthesis

5. Immerse a hydrilla shoot with the cut end of the stem turned up in a clean test tube with tap water. To enrich the CO2 content of the water, add 10-15 drops of 1 percent NaHCO3. place the tube under dim light and count the number of bubbles released at 1 min intervals for 10 mins. Repeat the experiment under bright light.

5.2 How would you correlate the rate of gas evolution with the rate of photosynthesis?

directly proportional

5.3 What is the effect of light intensity on the rate of photosynthesis?

More intense light, higher rate of photosynthesis

C. Carbon Dioxide as a Factor in Photosynthesis

Half-fill each of three test tubes with water that has previously been boiled to remove dissolved air and cooled to room temperature. Add several drops of phenol red to each tube and shake gently. Phenol red is an indicator of p H. Indirectly it is an indicator of CO2 concentration since CO2 in water forms carbonic acid which lowers the pH of water. At low pH, the color of phenol red changes to yellow. With the aid of a soda straw, blow into the water in test tubes 1 and 2 until the solution just shows a change in color from red to yellow. Test tube 3 serves as control.

6.1 Account for any change in color in test tubes 1 and 2

Increase in acidity

7. Using the set-up prepared in section 6, place a shoot of hydrilla in test tube 1. place the 3 tubes in very bright light. After 20 to 30 minutes, note the color changes.

7.1 Which tubes show a change in color? Why?

Color in test tube 1 goes back to red since CO2 is being used for photosynthesis by the hydrilla plant. With less CO2, the water’s acidity goes back to normal level.

D. Separation of Pigments

8. Secure 5 mature leaves of papaya or 10 of hibiscus. Cut the lamina into small pieces and grind in a mortar to secure a deep green liquid extract and collect this into a small test tube. Place two or three drops of the leaf extract at about 1 to 2cm fromthe base of a strip of filter paper the width of which should not touch the sides of the test tubes. Carefully hang the strip on the lower or basal end of a cork with the use of a aper clip or adhesive and lower this into a clean dry test tube to which has been added 3-5ml of a solvent consisting of a mixture of 95 parts petroleum ether and 5 parts of acetone. The part of the strip containing the leaf extract should not be submerged in the solvent. Cork the test tube and observe the separation of the pigments. The development of the chromatogram is stopped when the solvent has travelled about 1 to 2 cm from the top of the strip. The chromatogram is stopped when the solvent has travelled about 1 to 2 cm from the top of the strip. The chromatogram should be observed at frequent intervals because if the separation continues for too long some of the pigments may be superimposed on each other near the top of the strip.

8.1 What colors are indicated in the chromatogramand what are the corresponding pigments they represent?

orange – carotene

yellow – xantophyll

yellow green/ light green – chlorophyll b

green / blue green – chlorophyll a

Note:

Some answers differ for each class/group.

Table 12.1 is based on your group’s data.

For 8.1, it is possible for the chromatogram to not show an orange color.

For “8.2. Which pigment is the least soluble or moves the slowest along the strip? The most soluble and travelling farthest up the strip?” Least soluble would be the color at the bottom and the most soluble would be the one at the topmost.

NaHCO3 was used to supply CO2 in order to drive photosynthesis.

Bio 11 – Botany – Exercise 2 – The Plant Cell

1. Place a drop of water at the center of the clean slide and place a thin layer of skin peeled off from the inner surface of onion bulb, Allum cepa L. With a dissecting needle, put a cover slip on the specimen by tilting it along one side of the slide so that one edge touches the water. Gently lower the cover slip by withdrawing the needle slowly to prevent air bubbles.

2. Examine one cell under the HPO.

2.1 Is the cell wall uniform in thickness?

Yes

2.2 Can you observe the narrow canals or depressions along the walls? If yes, identify these structures.

Plasmodesmata

2.3 Can you distinguish the protoplast clearly?

No

2.4 Can you see the cytoplasmic strands? No

3. Using filter paper as absorbent, remove the water from the slide by gently pressing one side of the coverslip. Immediately apply a drop of iodo-potassium iodide solution on the opposite side of the coverslip. The solution will slowly replace the water. After a minute or two,wipe off the excess solution

3.1  Do you observe the cytoplasmic strands now?

Yes

3.2 In what part of the cell is the nucleus found?

Cytoplasm

3.3 Do you see more than one nucleolus?

Yes

3.4 What structure(s) is/are between the cytoplasmic strands?

Organelles

4. Take a leaf from the actively growing shoot of a water plant, hydrilla, Hydrilla verticillata (Roxb.) Royle which has been previously exposed to bright light. Make a water mount by placing the upper surface of the leaf next to slide. By moving the  LPO up and down, you can see two layers of cells. Under the HPO observe the streaming protoplast (cyclosis) and note the direction of its movement.

4.1 What structure in the cell contains the green pigment?

Chloroplast

4.2 What is the shape and arrangement of the structure?

In stacks (grana)

4.3 Do they move along with the streaming protoplast?

Yes

6. On a slide, make separate mounts of the skin and pulp of a ripe fruit of tomato, Lycopersicon lycopersicun (L.) Karsten and red pepper, Capsicum frutescens L.

6.1 What structure in the cell contains the pigments?

Chromoplast

7. Make water mounts of both upper and lower surfaces of the leaf of boat of Moses, Rhoeo discolor (Hert.) Hence. One surface contains a vacuole pigment and the other a plastid.

7.1 What types of pigment are found on each surface?

Anthocyanin – vacuole

Chlorophyll – chloroplast

7.2 How do these pigments differ from those of the tomato pulp and hydrilla leaf?

Differ in location and color.

8. Prepare free-hand sections of any 5 of the following specimens representing the different types of crystals: petioles of Begonia sp.; castor oil plant, Ricinus communis L.; the laminae of santan, Ixora sp.; bowstring hemp, Sanseviera zeylanica Roxb.; the midribs of fringed waterplant, Raphidophora merili Engl.; dumbcane, Diefferenbachia sp.; guava, Psidum guajava L.; pigweed, Amaranthus viridus l.; purslane, Portulaca oleracea L.; sweet potato, Opomoea batatas Lam. and stem of Pilea cadieri.

8.1 Identify and sketch the types of crystals observed.

9. Examine prepared slides of a cross-section of any stem or root and fresh surface sections of the lower epidermis of the leaf of the boat of Moses under the LPO and HPO. Locate cells that ar bounded by a single cell wall called the primary cell wall. Locate the middle lamella (the intracellular layer) between the primary walls of adjacent cells.

9.1 What must be the function of the middle lamella?

Cement adjacent walls together

10. Examine fresh sections of green and ripe tomato fruits.

10.1 Compare the appearance of the cells

Cells in the unripe tomato fruit are closer together

10.2 What happens to the middle lamella when fruits ripen

Loss of cell wall components particularly pectin, which makes up the middle lamella

11. Scrape cells from a shell of a coconut, Cocos nucifera L. and stain with 18% alcoholic phloroglucinol-sulfuric acid solution. Examine under the compound microscope. Lignin will turn red with this solution. These cells have both the primary and secondary walls.

11.1 Draw a cell and label parts

a basic sketch of cell from coconut husk (sclereid cells)

Notes:

Some questions are dependent on the specimen and therefore differs for each student. Questions 2.2,. 2.4, 3.1, 3.3 may be answered yes/no dependent on what you observed.

For the types of crystals:

CaC₂O_4:

prismatic

raphides

druses

styloids

CaCO_3:

cystolith

wormlike cystolith

Your instructor will draw a basic sketch of what these crystals look like and that’s pretty much it.