Shoot, Architecture & Light Capture Flashcards
Describe the anatomy of typical dicot and monocot leaves
- In most vascular plants, leaves are the main photosynthetic organs
- The exchange of gases occurs through stomata in the upper and lower epidermis
- Epidermis is usually a single cell layer
- In between the upper and lower epidermis, there’s a ground tissue called the mesophyll
- This tissue consists of parenchyma cells specialized for photosynthesis
What are the main photosynthetic organs of most vascular plants?
Leaves
How does the gas exchange of typical monocot and dicot leaves occur?
Stomata in upper and lower epidermis
Where is the mesophyll located?
In-between the upper and lower epidermis
What’s the functions of the cells of the mesophyll?
This tissue consists of parenchyma cells specialized for photosynthesis
Describe dicot leaves
- In dicot leaves, stomata are mainly found in the lower epidermis
- The mesophyll consists of 2 distinct layers of cells called palisade and spongy
- Palisade mesophyll consists of elongated cells arranged in one or more layers. This can be found in the upper part of the leaf, just beneath the upper epidermis
- Spongy mesophyll can be found between the palisade layer and the lower epidermis
- They’re loosely arranged cells with many air spaces
- Spongy mesophyll cells have less chloroplasts than in palisade mesophyll cells
- The vascular tissue of the leaf is continuous with vascular tissue of the stem
- Veins in the leaf are highly branched (net like venation) in the mesophyll layer
- Each vein is protected by a bundle sheath layer
Where are stomata found in dicot leaves?
Mainly on the lower epidermis
Describe the cells present in dicot leaves
- The mesophyll consists of 2 distinct layers of cells called palisade and spongy
- Palisade mesophyll consists of elongated cells arranged in one or more layers. This can be found in the upper part of the leaf, just beneath the upper epidermis
- Spongy mesophyll can be found between the palisade layer and the lower epidermis
- They’re loosely arranged cells with many air spaces
- Spongy mesophyll cells have less chloroplasts than in palisade mesophyll cells
What are the 2 distinct cell layers of the mesophyll?
- Spongy mesophyll
- Palisade mesophyll
What’s the structure of palisade mesophyll?
- Palisade mesophyll consists of elongated cells arranged in one or more layers.
Where are palisade mesophylls found?
in the upper part of the leaf, just beneath the upper epidermis
Where are spongy mesophylls found?
Spongy mesophyll can be found between the palisade layer and the lower epidermis
What’s the structure of spongy mesophylls?
- They’re loosely arranged cells with many air spaces
What’s the vascular tissue of the leaf continuous with?
Vascular tissue of the stem
Describe the vein arrangement in the mesophyll layer of dicot leaves
Veins in the leaf are highly branched (net-like venation) in the mesophyll layer
Each vein is protected by a bundle sheath layer
What is each vein protected by?
A bundle sheath layer
Write the difference between palisade mesophylls and spongy mesophylls
Location: Palisade mesophylls are found in the upper part of the leaf, beneath the upper epidermis. Spongy mesophyll can be found between the palisade layer and the lower epidermis
Structure: Palisade mesophylls consist of elongated cells arranged in one or more layers. Spongy mesophylls are loosely arranged cells with many air spaces
Chloroplast Content: Spongy mesophylls cells have less chloroplasts than palisade mesophyll cells
Describe the structure of monocot leaf
- In monocot leaves, stomata are present in both the lower and upper epidermis
- Mesophyll are not differentiated into palisade and spongy layers
- Chloroplast are abundant in all mesophyll cells
- Vascular tissue of the leaf is continuous with vascular tissue of the stem
- Veins in the leaf are pararally arranged
- Each vein is protected by a bundle sheath layer
Write the functions of each part of the leaf
- Cuticle: Prevents water loss and for Protection
- Epidermis: Protection against pathogens and physical damage
- Stomata: Gaseous exchange and transpiration
- Palisade and Spongy mesophylls: Involving in efficient photosynthesis
- Spongy parenchyma/ air spaces: Photosynthesis and storage of gases
- Vein/ Vascular bundle/ xylem/ phloem: Involving in transport
- Sclerenchyma: Support
- Guard cells: Controlling gaseous exchange and transpiration
Write the differences between dicot and monocot leaf structures
Stomata: In dicot leaves, stomata are mainly found in lower epidermis. In monocot leaves, stomata are present in both the lower and upper epidermis
Mesophylls: In monocot leaves, mesophyll is not differentiated into palisade and spongy. In dicot leaves, there are 2 distinct cell layers called palisade and spongy
Vein arrangement: In dicot leaves, veins are highly branched, with a net like venation in the mesophyll layer. In monocot leaves, veins are parallelly arranged (pararall venation)
Define stomata
Pores surrounded by guard cells which can open and close, found in the epidermis of leaves and stems of plants
Define guard cells
Guard cells are modified epidermal cells which have a distinct shape, and are the only epidermal cells that contain chloroplasts
Describe guard cells
- Guard cells are modified epidermal cells which have a distinct shape, and are the only epidermal cells that contain chloroplasts
- Guard cells are typically bean shaped in angiosperms
- The cell walls of guard cells are unevenly thickened
- The inner cellulose wall is thicker and less elastic than the outer wall
- Some cellulose microfibrils are radially arranged to form inelastic hoops around guard cells
- Guard cells regulate the diameter of stomata by changing shape, widening or narrowing the gap between the pair of guard cells
In angiosperms, what is the shape of guard cells?
Typically bean shaped
Describe the cell wall of guard cells
- The cell walls of guard cells are unevenly thickened
- The inner cellulose wall is thicker and less elastic than the outer wall
How are inelastic hoops formed in guard cells?
- Some cellulose microfibrils are radially arranged to form inelastic hoops around guard cells
What’s the function of guard cells?
- Guard cells regulate the diameter of stomata by changing shape, widening or narrowing the gap between the pair of guard cells
Describe the structure of stomata
- Stomata are pores surrounded by guard cells which can open and close, found in the epidermis of leaves and stems of plants
- Guard cells are modified epidermal cells which have a distinct shape, and are the only epidermal cells that contain chloroplasts
- Guard cells are typically bean shaped in angiosperms
- The cell walls of guard cells are unevenly thickened
- The inner cellulose wall is thicker and less elastic than the outer wall
- Some cellulose microfibrils are radially arranged to form inelastic hoops around guard cells
- Guard cells regulate the diameter of stomata by changing shape, widening or narrowing the gap between the pair of guard cells
Describe gaseous exchange
- Gaseous exchange is the exchange of gases between the cells of the organism and the environment
- In plants, gaseous exchange is possible via stomata and lenticels
- In addition to these, a small amount of gases can be exchanged via the cuticle
- There’s no special system within plants to transport O2 and CO2. These gases move entirely by diffusion
Define gaseous exchange
Gaseous exchange is the exchange of gases between the cells of the organism and the environment
What are the main modes of gaseous exchange in plants?
- In plants, gaseous exchange is possible via stomata and lenticels
- In addition to these, a small amount of gases can be exchanged via the cuticle
Explain the mechanism of opening and closing of stomata
- Stomatal opening and closing depends on changes in turgor of guard cells
- If water flows into the cells by osmosis, their turgor increases and they expand, but they do not expand uniformly in all directions
- The relatively inelastic inner walls make them bend and draw away from each other other
- The result is that the pore opens
- If the guard cells lose water, the reverse happens: their turgor decreases and their inner walls become straighter, thus closing the pore.
- The K+ influx explains the mechanism
Explain the K+ influx hypothesis
- During daytime, guard cells actively accumulate K+ from neighboring epidermal cells, thus lowering their water potential.
- That leads to the inflow of water by osmosis from the surrounding epidermal cells
- As a result, the turgor pressure in guard cells increase, opening stomata
- The accumulate of K+ in guard cells require energy which is provided by the transfer of electrons during photosynthesis of guard cells
- Stomatal closing occurs by losing K+ from guard cells to neighboring epidermal cells
- It leads to exosmosis of water from guard cells
- As a result, the turgor pressure of guard cells decrease, closing stomata.
- Abscisic Acid (ABA) plays a role in K+ influx mechanism as well
Explain stomatal opening in K+ influx mechanism
- During daytime, guard cells actively accumulate K+ from neighboring epidermal cells, thus lowering their water potential.
- That leads to the inflow of water by osmosis from the surrounding epidermal cells
- As a result, the turgor pressure in guard cells increase, opening stomata
- The accumulate of K+ in guard cells require energy which is provided by the transfer of electrons during photosynthesis of guard cells
Explain stomatal closure in K+ influx mechanism
- Stomatal closing occurs by losing K+ from guard cells to neighboring epidermal cells
- It leads to exosmosis of water from guard cells
- As a result, the turgor pressure of guard cells decrease, closing stomata.
What’s the role of ABA in K+ influx mechanism?
- ABA is produced in roots and leaves in response to water deficiency
- Production of ABA leads to closure of stomata in drought by the removal of K+ in guard cells
- This prevents wilting of the plant
Where is ABA produced?
In roots and leaves
What is ABA produced in response to?
Water deficiency
How does ABA prevent the wilting of the plant during a drought?
Production of ABA leads to closure of stomata in drought by the removal of K+ in guard cells. This prevents wilting of the plant
What are the factors affecting stomatal action?
- Light stimulates the accumulation of K+ in guard cells. Stomata open during the day and mostly close at night
- Decrease in CO2 concentration in substomatal cavity leads to opening of stomata
- Internal clock of guard cells controlling their daily rhythm of opening and closing stomata
- Environmental stresses such as drought, wind and high temperature can cause stomata to close during day time.
What are the environmental stresses that can cause stomata to close during day time?
Wind
Drought
High temperature
How does light affect stomatal action?
Light stimulates accumulation of K+ ions in guard cells.
So, stomata open during the day and close during the night
How does CO2 concentration affect stomatal action?
Decrease of CO2 concentration in substomatal cavity leads to opening of stomata
