laboratory

Assignment 13: Transport Systems

Downloads:
Work sheet for assignment 13
Work sheet as a pdf file (in case you cannot open a doc file)

Activities:
ACTIVITY 1. GAS EXCHANGE AND WATER TRANSPORT IN PLANTS
Stomata and gas exchange
Introduction to transpiration and water transport
  Transpiration Experiment
ACTIVITY 2. TRANSPORT SYSTEMS OF ANIMALS
  Open vs. closed circulatory systems
  Circulation in vertebrate animals
ACTIVITY 3. PHYSIOLOGY OFTHE HUMAN CIRCULATORY SYSTEM
  Blood pressure
  Electrocardiograms

Parts of this laboratory is based on material taken from the lab manual for the on-campus BIO 181 laboratory. 

Before you attempt this exercise you should have a thorough understanding of the material in the topics "Transport Systems I" and "Transport Systems II".

ACTIVITY 1. GAS EXCHANGE AND WATER TRANSPORT IN PLANTS

Stomata and gas exchange

Leaves are the primary photosynthetic organs of most plants. The exchange of oxygen and carbon dioxide in the leaf, as well as the loss of water vapor, occurs through pores called stomata (singular = stoma). The evaporation of water from the leaf is called transpiration.

stomata Cross section of a leaf showing gas movement through stomata

The number of stomata on leaf surfaces varies widely among different species of plants. The lower epidermis of the leaf tends to have a higher total than the upper surface. The average number of stomata is about 300 per square mm of leaf surface. The smallest number is found on Tradescantia (spiderwort) leaves which have 14 per square mm. The highest number of stomata is1200 per square mm on leaves of the Spanish oak tree. Stomata are found on conifer needles as well as on the broad leaves of angiosperms.

pine stoma

Stomata found on the bottom surface of a pine leaf.

(from http://sols.unlv.edu/Schulte/
Anatomy/Leaves/Leaves.html)

There are several environmental factors that affect the number of stomata on a leaf. Researchers have evidence which indicates that stomata densities change in response to changing atmospheric levels of carbon dioxide. This suggests that as global warming progresses (due to rising levels of atmospheric carbon dioxide) the number of stomata per leaf may increase, allowing the plant to absorb more carbon dioxide. Other factors that can increase stoma density are an increase in light or amount of rainfall. Why would these changes occur? The following data was collected by calculating the number of stomata on the underside of Holly tree leaves. View this image of a holly tree and note its shape.

Leaves were collected and a thin layer of nail polish placed on the underside of a leaf and allowed to dry. A strip of packaging tape was placed on the dried nail polish and both were gently peeled away from the leaf.  The impression obtained was viewed under a microscope so that the number of stomata per square mm could be counted.

stoma impression

View of the leaf impression under the microscope at 400X

The field of view is estimated to be 0.152 square mm.

Tables 1 and 2 contain the results from 8 samples taken from leaves near the center and the periphery of a Holly tree. (Bruce W. Grant and Itzick Vatnick 2004 Environmental Correlates of Leaf Stomata Density TIEE 1)

Table 1. Stomata observed on the bottom of leaves collected from areas near the
center of the tree
.

Slide Stomata/field Stomata/mm2
1 41 270
2 55 362
3 40 263
4 40 263
5 42 276
6 40 263
7 38 259
8 40 263
Average (stan. dev.) 276 (35.3)

Table 2. Stomata observed on the bottom of leaves collected from areas near the
periphery of the tree
.

Slide Stomata/field Stomata/mm2
1 43 283
2 42 276
3 47 309
4 72 474
5 59 388
6 52 342
7 53 349
8 53

349

Average (stan. dev.) 346 (63.6)

When you have examined the data, answer questions 1-3 on your work sheet.

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