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Biological Material at the Microscopic Level

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Biological Drawing �Rules

Labels:

Cell wall
Epidermal cells
Chloroplast
Guard cells
Thickened internal wall of guard cell
Stoma (singular) – open or closed
Cytoplasm
Nucleus (if you can see any)

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Leaf Tear – Rhubarb leaf

Lower Epidermal layer of a leaf – Identify and describe specialised Structures/Organelles
Guard Cells – how they control stomata
Epidermal Cells – how they protect the leaf

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Stomata and Guard Cells

- Stomata are small pores, underside of leaf. Open and closed by

a pair of bean shaped guard cells. WHY

- WHAT is the adaptive advantage of stomata and guard cells

- Stomata density depends on abiotic factors (temperature / humidity / light intensity)

as seen in an

epidermal leaf tear

Thorough explanation needed for merit WHY, WHY, WHY……

Eg: Stomata/Guard cells in epidermal tear

What are they / purpose (reduce desiccation - / enable effective gas exchange for processes such as respiration and photosynthesis – short definition of these processes)
Explain location /structure (stomata are pores that are mostly found on the lower surface of leaves, a pair of guard cells surround the stomata/shape and thickened inner walls of guard cells explained and related to function)
Explain mechanism/function (guard cells open and close stomata in response to environmental conditions and the needs of the plant / cells open and close using turgor pressure changes – explain what this means in terms of osmosis/the movement of water into and out of the cell (turgid/flaccid etc)

Leaf stomata are the principal means of gas exchange in vascular plants. Stomata are small pores, typically on the undersides of leaves, that are opened or closed under the control of a pair of banana-shaped cells called guard cells. When open, stomata allow CO2 to enter the leaf, and allow for water and oxygen to escape. In addition to opening and closing the stomata, plants may exert control over their gas exchange rates by varying stomata density in new leaves when they are produced (such as in the spring or summer). The more stomata per unit area is the stomata density.

Why might it be adaptive for a plant to control its rates of water loss and CO2 uptake? One answer can be found in the sun. Increases in heat could denature proteins of membranes of chloroplasts. When overheated, plants may open the stomata to evaporate water to lower the temperature. Based on this, you could hypothesize that leaves in the sun would have a higher stomata density than leaves in the shade.

On the other hand, if water is not available, such as under drought conditions, excessive evaporation might lead to desiccation (drying out.) Plants in hot areas may benefit from fewer stomata so that they can conserve water.

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Stomata and Guard Cells

Thorough explanation needed for merit WHY, WHY, WHY……

Eg: Stomata/Guard cells in epidermal tear

What are they / purpose (reduce desiccation - / enable effective gas exchange for processes such as respiration and photosynthesis – short definition of these processes)
Explain location /structure (stomata are pores that are mostly found on the lower surface of leaves, a pair of guard cells surround the stomata/shape and thickened inner walls of guard cells explained and related to function)
Explain mechanism/function (guard cells open and close stomata in response to environmental conditions and the needs of the plant / cells open and close using turgor pressure changes – explain what this means in terms of osmosis/the movement of water into and out of the cell (turgid/flaccid etc)

Leaf stomata are the principal means of gas exchange in vascular plants. Stomata are small pores, typically on the undersides of leaves, that are opened or closed under the control of a pair of banana-shaped cells called guard cells. When open, stomata allow CO2 to enter the leaf, and allow for water and oxygen to escape. In addition to opening and closing the stomata, plants may exert control over their gas exchange rates by varying stomata density in new leaves when they are produced (such as in the spring or summer). The more stomata per unit area is the stomata density.

Why might it be adaptive for a plant to control its rates of water loss and CO2 uptake? One answer can be found in the sun. Increases in heat could denature proteins of membranes of chloroplasts. When overheated, plants may open the stomata to evaporate water to lower the temperature. Based on this, you could hypothesize that leaves in the sun would have a higher stomata density than leaves in the shade.

On the other hand, if water is not available, such as under drought conditions, excessive evaporation might lead to desiccation (drying out.) Plants in hot areas may benefit from fewer stomata so that they can conserve water.

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Written Component– Specialised Structures

Write some reasons for how or why the stomata and guard cells enable the cells of the leaf to effectively carry out their specific functions

The detail in which you do this will determine your grade…..

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Written Component– Specialised Structures

E.g.: A good response for guard cells would include:

How guard cells function to enable effective gas exchange in the leaf for plant processes like respiration and photosynthesis.

- The bean shape, thin outer and

thickened inner walls of the guard cells (label)

How or why changes result from

changes in turgor pressure

- Open when turgid / closed when flaccid

- Balloon simulation / brainstorm

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Example of what you could write for Guard Cells

Cells found in the lower epidermis layer of Rhubarb leaves have specialised structures that assist with efficient gas exchange. Plants are autotrophs and need to synthesis their own glucose they do this via a process called photosynthesis. This glucose is then used in a process called respiration which converts the glucose into ATP energy for crucial cellular processes.

Stomata (plural) are microscopic pores (holes) mostly found on the lower epidermis layer of leaves. These pores are important for allowing the diffusion of gases such as carbon dioxide into the leaf and oxygen out of the leaf. These gases move down a concentration gradient from an area of high to low concentration. Water vapour can also be lost via the stomata through a process called transpiration. It is important the stomata can open and close to control the loss of water to prevent the leaves from desiccation (drying out).

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Example of what you could write for Guard Cells continued….

A pair of bean shaped guard cells surrounds each stoma, these cells open and close the stomata using turgor from the water in their vacuoles. When there is plenty of water in the leaf cells the vacuoles are full this causes the guard cells to bulge (turgid). When turgid the outer guard cell walls expand which causes the thickened inner cell walls to draw out away from the stoma, causing the stoma to open.

Plants only use a small amount of the water they gain via osmosis through the roots in photosynthesis, so loose water via transpiration through open stomata. If there is limited water then the vacuoles will loose water causing the guard cell to shrink and shrivel (flaccid) causing the outer wall to shrink inwards which causes the thickened inner cell wall of the guard cells to draw in towards the stoma which closes the stoma thus conserving water loss via transpiration.

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Example of what you could expand on for Epidermal Cells

Single layer of cells that cover the upper and lower surfaces of the leaf (similar to our skin)
Also find a layer of epidermal cells protecting the seeds, stem and roots of plants
Functions include secretion, selective absorption, and protection
Protect from environmental stressors (UV / water loss)
Protect from microbes and chemical compounds
Protects the other more specialised cells within the leaf
Close positioning of the cells is important for preventing water loss – looks like interlocking jigsaw pieces
Can contain chloroplasts
Contains guard cells – mainly in the lower epidermal layer
Often see small hair like structures (trichomes) projecting from epidermal cells