7/22/2019 Student Worksheet on Stomata

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Course:Science 10 Name: Date:

Topic:Structure and Function of Stomata/Densityof Stomata

Unit: Cycling of Matter in LivingSystems

Grade: 10

A. PurposeTo generate and analyze SEM images of leaf stomata from various species of plants to determine correlations

between stomata density and the environment.

7/22/2019 Student Worksheet on Stomata

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1. Background

All plant leaves need to breathe. The exchange of atmospheric gases is essential to photosynthesis, the process

by which plants use sunlight to convert carbon dioxide and water into oxygen and fuel (carbohydrates). Leaves

have special pores calledstomata that make gas exchange possible while helping to control the loss of water. The

stomata operate through the use of two tiny jellybean shaped cells called guard cells located in the outer layer of

tissue called the epidermal layer. Most stomata are on the lower epidermis of the leaves on plants (bottom of the

leaf). Unlike other plant epidermal cells, the guard cells contain chlorophyllto do

photosynthesis. This allows the cells to expand/ contract to open or close the stomata. Guard cells swell, through

the process ofosmosis, to allow opening of the stomata (for CO2 to enter and excess O2 and H2O to leave), and theyshrink in order to force the stomata shut (either partially or completely) to prevent dehydration. In order Plants

must also permit the movement of water from the roots to the leaves through the process of

evaporation/transpiration in order to make water available to the cells for photosynthesis. However, a constant

concern for terrestrial plants is controlling the rate of transpiration to prevent dehydration (desiccation).

To conserve water during dry times, the stomata remain closed to reduce the loss of water vapour. Due to the

requirement for carbon dioxide, it is possible for the lack of moisture that forces the stomata to stay closed to

prevent the process of photosynthesis from occurring. The number of stomata on the epidermal surface can tell you

a lot about a plant. Usually, a high concentration of stomata indicates fast growth and a wet climate. Lower

concentrations of stomata indicate lower rates of photosynthesis and growth or adaptations for dry weather.

Stomata are useful to drought-threatened plants because they can close to prevent dehydration.

When stomata close:1.Guard cells actively pump out K+ ions2. This raises the water potential inside the cells3. Water exits the guard cells by osmosis (moves into adjacent cells)4. Vacuoles shrink, guard cells become flaccid and stoma close

In general, having these openings located on the underside of leaves helps to prevent further loss of moisture.

However, this is not always an issue for plants growing in high moisture environments, and can result in some

unusual stomata configurations. For example, water lilies grow in ponds where their leaves generally float directly

on the surface of the water or slightly above it. To thrive in this environment, they have developed stomata on the

water lily's large leaf surface (rather than underside) making gas exchange more efficient. Another adaptation thathelps to keep lily leaves above the water where stomata can function, are the large number of spongy internal cells

that promote flotation.

Other adaptations plants use to reduce evaporation and infestation of insects is to use surface hairs. It is likely that

in many cases, hairs interfere with the feeding of at least some small herbivores and, depending upon stiffness and

irritability to the "palate", large herbivores as well. Hairs on plants growing in areas subject to frost keep the frostaway from the living surface cells. In windy locations, hairs break-up the flow of air across the plant surface,

reducing evaporation. Dense coatings of hairs reflect solar radiation, protecting the more delicate tissues

underneath in hot, dry, open habitats. And in locations where much of the available moisture comes from cloud

drip, hairs appear to enhance this process.

Introduction

a. Review how plants use solar energy, carbon dioxide and water to make their own food through

photosynthesis, releasing oxygen as a by product.

b. Identify the adaptation which allows plants to take in CO2 and expel excess O2 through the leaves (i.e.

stomata).

c. How do plants uptake of CO2 through leaf stomata?