Dicot and Monocot: roots and leaves

Roots

Absorb water and minerals from soil and move these to other parts of plant

Anchor plants in soil provide enough support to resist wind, gravity

Can also serve as area for storing excess energy such as starch

Includes: Epidermis, root hairs, cortex, endodermis and vascular cylinder

Root epidermis

Thin permeable to water. Cuticle and stomata absent

Young roots: immediately overview exodermis, no air spaces

Older roots: epidermal structures break down and exodermis assumes role of epidermis

Root hairs

Tubular outgrowths of epidermal cells. Found in zone of differentiation. Thin cell walls, large vacuole. Increase area for water and nutrient absorption.

Cells secrete acid which helps solubulize soil minerals into ionic forms making ions easier to absorb

Cortex

Large and loosely packed parenchyma cells. Functions:

1. Diffusion of water, mineral salts and oxygen from root hair inwards

2. Storage of food reserves especially starch

3. Endodermis and Caspariam strips-facilitatr movement of water to xylem

Endodermis

Barrel-shaped, side and end walls cemented together like bricks in a wall, radial and inner walls get thickened with suberin (suberized) =Casparian strips (force water to move through a layer of cells before it gets into xylem-exert some regulation on water passage into root) Non-suberized cells (passage cells) thin cell wall which allows flow of water.

Symplast pathway involving living contents of root cells membranes cytoplasm vacuoles water moves through plasmodesmata of adjacent cells

Apoplast pathway through cell walls and intercellular spaces

Vascular cylinder

1. Monocot: vascular bundles radial arranged in a ring. Phloem is between xylem more than 4 bundles of xylem and phloem, polyarch, xylem is exarch. Pith large and parenchymatous. Pericycle as per dicot.

2. Dicot: vascular bundles radial tetrarch. Pith absent. Pericycle- single layer of tightly packed parenchyma cells found inner to endodermis. Pericycle retaina ability to divide-gives rise to lateral roots

Leaves

1. Epidermis: Epidermal cells (Barrel shaped, compactly arranged, thick cuticle). Trichomes. Stomata

2. Ground tissue/mesophyll

3. Vascular tissue

   Dicot (reticulate [net] venation). Monocot (sheath which connects the blade to the stem parallel venation)

Stomata

Mostly on lower (abaxial/ventral) epidermis than upper (adaxial/dorsal), some lack stomata on upper epidermis.

Open aperture surrounded by 2 guard cells (responsible for opening and closing of stomata. Inner walls are thickened while other walls are thin. Kidney shaped in dicots, dumb bell shaped in monocots)

1. Photosynthesis CO2 let in and O2 let out

2. Respiration CO2 is sent out

3. Transpiration H2O vapor sent out

   Open when guard cells are turgid (due to water uptake in response to potassium influx)

   Close when guard cells are flaccid (due to water loss in response to potassium efflux)

Bulliform

Motor cells present on upper epidermis of monocots. During dry weather, help leaf roll over due to changes in turgity reduces transpiration

Ground tissue/mesophyll (Dicots)

1. Palisade: immediately below upper epidermis. 1-3 layers, compact tubular cells. Allow more cells, more chloroplast near surface. Contain 70-80% of chloroplast in leaves. Small intercellular air spaces for gaseous exchange.

2. Spongy: found above lower epidermis. Aerencyma cells, varied in shape and size. Fewer chloroplast, larger intercellular spaces. Store carbohydrates made by photosynthesis which diffuse into phloem- transported to rest of plant.

Vascular tissue

Vascular bundles closed.

Dicot: large middle vein (midvein) lateral veins emerge, both conduct water and food. Lateral veins branched into minor veins which help in releasing water from xylem

Monocot: leaves have parallel venation.

Phloem found towards lower epidermis, xylem towards upper epidermis, metaxylem facing phloem. Vascular bundle surrounded by bundle sheath (parenchyma)- provides support to conducting tissues. Fibers above and below bundle sheath-gives rigidity to leaf often referred to as bundle sheath extension

Petiole

Considered as transition between stem and blade. Mesophyll- less aerenchyma, more collenchyma (support). Vascular bundles from stem diverge towards petiole, most fuse and form midvein, others enter lamina as small lateral veins