Biology: Chapter 7: Transport in plants: Parts of plants

Biology: Chapter 7: Transport in plants: Parts of plants

Flowering plants (Angiosperms)

• Cotyledon: First part of seedling to emerge from soil when it germinates.
• Monocotyledons (Monocot): Plants that have only one cotyledon. Usually have long narrow leaves and flower parts in multiples of 3 eg. grass.
• Dicotyledons (Dicot): Plants with 2 cotyledons. Usually have leaves with blades and stalks eg. sunflowers. All plants in this chapter are dicotyledons.

Parts of the plant

Cortex: 

• Outermost layer of root and stem tissue in plants. 
• Between Epidermis and Endodermis.
• Composed mostly of parenchyma and specialized cells.

Pith: Central region of stems.

Epidermis: 

• Outermost layer of whole plant structure.
• Covers the whole plant.
• One cell thick. Closely packed, without chloroplasts or space between cells.

Endodermis:

• Innermost layer of cortex.
• Surrounds vascular bundle.
• One cell thick.
• Controls entry of water and substances into vascular bundle by Casparian strip.

Mesophyll:

• Leaf cells
• Specialised parenchyma cells found between lower and upper epidermis of the leaf.
• Specialised for photosynthesis: contain chloroplasts. 
• Palisade mesophyll: Column shaped. Near the upper surface of leaf to recieve more sunlight. Contain more chloroplasts than spongy mesophyll.
• Spongy mesophyll: Irregular sponge shapes. Underneath palisade cells. Have many large air spaces between the cells to let gas from the stomata diffuse around cells.

Parenchyma:

• Thin walled cells.
• Living at maturity,
• Used as packing tissue.
• Metabolically active - many functions.
• Can specialize. 
• For example: Storage of starch. When turgid, help support plant and prevent wilting. Air spaces between these cells allow gas exchange. Water and mineral salts transported through walls and living contents of cell. 
• Contain chloroplasts in leaves - specializes to become palisade and spongy mesophyll tissue.
• Form cortex in roots and stems.
• Form pith in stems.

Collenchyma:

• Modified form of parenchyma with extra cellulose deposited at ends of cells, providing extra strength.
• Living at maturity.
• Midrib of leaves contains collenchyma.

Sclerenchyma:

• Thick secondary cell walls.
• Contain lignin for extra strength.
• Lignin: With cellulose, main component of wood. Water proof and strong.
• Dead at maturity.
• Cannot increase in length.
• Found anywhere in plant.
• Provide support in plants.

Pericycle:

• One to several cells thick.
• Between the endodermis and vascular bundle.
• In roots, is one cell thick, and new roots can grow from this layer by meristematic cells.
• Meristematic cells: Plant stem cells.
• In leaves, formed by sclerenchyma cells, which is dead and lignified for extra strength.

Stele: Contains vascular bundle in roots and stems.

Vascular tissue:

• Contain the types of xylem and phloem systems.
• Tubes for transportation of fluids.
• Xylem and phloem found in vascular bundles.
• Outsides made of sclerenchyma fibres which provide exta support.

Xylem:

• Long distance transport of water and mineral salts. 
• Xylem vessel elements: Tubes made of dead cells. Reinforced with lignin. 
• Dead at functional maturity.

Phloem:

• Long distance transport of organic compounds eg. Sucrose.
• Living cells.
• Have a companion cell alongside the tube.
• Contain tubes called sieve tubes 
• Sieve tube elements: Living cells that make up the sieve tubes.