lesson 7- part 1: specialized and organized

Specialized and Organized (the Leaf)

• How does a plant, a multicellular organism, obtain food, water, and minerals?

• How does it respond to its environment?

• What structures allow the plant to perform these activities?

• How are these structures organized and how do they function?

Cell Specialization in Leaves:

• The Leaves of all plants perform a crucial function for the Plant: PHOTOSYNTHESIS

  ("Photo" Light, "Synthesis"= To Put Together)

  H2O+ CO2 + light energy -> C6H12O6 + O2

• Photosynthesis converts Light Energy into Chemical energy in the form of Glucose (A simple Carbohydrate)

• At the same time Carbon Dioxide and Water are used up while Oxygen is produced

• Photosynthesis occurs in the Chloroplasts of the Cells found in Leave's of plants

• In order for a leaf to function at its best it has different types of cells within it that perform specific tasks for the leaf and therefore the whole plant

Epidermal Tissue Cells:

• ("Epi" = Over/On, "Derma" - Skin) Top and Bottom layers of a leaf Flattened cells

• Create a one-cell-thick protective layer for the leaf Covered by a waxy cuticle (less water loss) Contain no Chloroplasts and are transparent to allow light to pass through

Palisade Tissue Cells:

• Found just beneath the Epidermal Cells Long and narrow cells (column-like)

• Tightly packed layer

• Main type of Photosynthetic cells in leaf exchange

• Packed with Chloroplasts

Spongy Tissue Cells:

• Layers of cells just beneath the Palisade Cells

• Round shape

• Very loosely packed with many air spaces between them

• Also contain Chloroplasts to carry out photosynthesis

• Structure allows gas and water exchange with the outside environment

Stomata and Guard Cells:

• Allow Carbon Dioxide to enter the underside of the leaf Allow Oxygen and Water Vapour to exit the underside of the leaf

• Surrounded by two guard cells that regulate how the Stomata open and close

Vascular Tissue Cells:

• Form a series of tubes that allow Water and Sugars to be

• transported into and out of the leaf Visible as Veins in a leaf

• Made up of Xylem and Phloem Tissues

• Xylem carries water and minerals from the roots to the leaves

• Phloem carries sugars from the leaves to the rest of the plant

Cell, Tissue, Organ, System, Organism:

• A multicellular organism has many advantages compared with single-celled organisms:

• A larger size

• A variety of specialized cells

• An ability to thrive in a broader range of environments

• However this means that a multicellular organism needs organization

-Atoms -Molecules -Organelles -Cells -Tissues -Organs -Organ Systems -Organisms

Lesson 7- part 2: Gas exchange in plants

Gas exchange in plants: something in the air

Air is made of a mixture of:

• Oxygen

• Carbon Dioxide

• Water Vapour

• Nitrogen

• Other Gases

• Photosynthesis requires Carbon Dioxide which is taken into a Leaf through the Stomata

• Photosynthesis produces Oxygen that is released out of the Leaf through the Stomata along with Water Vapour

Leaves and Lenticels

• Leaves are the main area for gas exchange in a plant

1. Carbon Dioxide diffuses into a leaf through Stomata

2. Carbon Dioxide circulates in the spaces between the Spongy and Palisade tissues cells

3. Carbon Dioxide diffuses into the Spongy and Palisade Tissue Cells down a concentration gradient

4. Chloroplasts in the Tissue Cells undergo Photosynthesis, converting the Carbon Dioxide into Glucose and Oxygen

5. The plant stores the Glucose for use later

6. The Oxygen and Water Vapour diffuse out of the Tissue cells, into the spaces between the Spongy and Palisade Tissue Cells and finally out of the leaf through the Stomata

   Leaves and Lenticels

• Some gas exchange can occur throughout the rest of the plant

• However, in woody plants (Ex. Trees) gas exchange is difficult

• Woody plants contain Lens-Shaped openings called Lenticels that allow for gas exchange in their stem/trunk

Gas Exchange is Tied to Water Loss

Transpiration:

• Spongy and Palisade Tissues are surrounded by a thin layer of water

• The water will evaporate out of the leaf through the stomata along with Oxygen and other gases

• This loss of water is called Transpiration

• Transpiration can account for the loss of 99% of the water absorbed by the roots of the plant.

Stomata/Guard Cells

• Stomata help the plant from drying out

• When the stomata are open they allow for lots of gas exchange and transpiration

• This gas exchange and transpiration allows for a high rate of Photosynthesis

• However, when closed, gas exchange, Transpiration and Photosynthesis decrease

• Most often Stomata are open during the day and closed at night

Turgor Pressure

• The opening and closing of Stomata is also linked to Turgor Pressure

• Turgor Pressure is caused by the movement of water into the Central Vacuole of a plant cell.

• The Vacuole swells and pushes against the Cell Wall causing the plant cell to become swollen and more rigid

• Water will move into the Guard Cells of the Stomata through Osmosis causing them to swell and gain Turgor Pressure

• As the Turgor Pressure increases the Guard cells swell and stomata.

• As the water transpires out of the Guard Cells they lose Turgor Pressure, deflate and then the Stomata Close

Plant Adaptations

• Desert plants will open their Stomata at night (not during the day) to conserve water. Carbon dioxide is taken in at night and stored as a different chemical until it is used for Photosynthesis later in the day.