Lab 2 Plant Tissues PDF

Angiosperm Tissues Practical 2  Plants have three general types of organs: Leaves Stems Roots Each organ is composed of tissues A tissue is a group of cells that has a common structure and function.  Epidermis Trichomes: “pubescence”...

Angiosperm Tissues Practical 2  Plants have three general types of organs: Leaves Stems Roots Each organ is composed of tissues A tissue is a group of cells that has a common structure and function.  Epidermis Trichomes: “pubescence” or hairs on epidermis Root Hairs: tubular extensions of epidermal cells Ground tissues Parenchyma: thin walled and alive at maturity Collenchyma: thick walled and alive at maturity. Sclerenchyma: thick walled and dead at maturity Vascular tissues Xylem Phloem Meristematic tissues Apical Lateral  Angiosperm Tissues Leaf epidermis Trichomes Root epidermis and root hairs Parenchyma cells Collenchyma cells Sclerenchyma cells Vascular root tissue Meristem Observe and make drawing of cells of each type (Page 14 to 17 Laboratory Manual) Leaf epidermis  Plant Tissues: 1. Dermal tissue Epidermis secretes a waxy cuticle to prevent water loss. Gases enter through pores (stomata) made up of guard cells. These close in dry conditions to prevent water loss. The mesophyll has 2 layers: a) Upper layer (facing the sun) is palisade mesophyll (parenchyma cells). These are closely packed together and carry out photosynthesis. b) Lower layer is spongy mesophyll (parenchyma cells). These are loosely packed (like a sponge) to allow air to circulate through the leaf. These cells are responsible for gas exchange: taking up CO2 during the day for photosynthesis and taking up O2 at night for respiration.  1. Leaf Epidermis Ficus Leaf Vein Apex Petiole Midvein or Midrib Net-veined leaves  1. Leaf Epidermis (cross-section of Ficus leaf) Ficus has two layers of epidermal Epidermal cells cells. Function of the epidermal cells: 1. Provide support to the leaf: Epidermal cells have thick walls to hold the large flat surface of the leaf in a horizontal position to collect UV light. 2. Secretes the cuticle: waxy layer that provides water-proof → important in arid regions. (two layers makes it difficult for animals to eat the leaves).  Tasks Observe and draw the leaf epidermis (Cross section of ficus) (Page 14 to page 17) Trichomes 2. Leaf and Stem Trichomes (hairs) Extension of epidermal cells to form long hairs. They have different functions and come in different types: Aerva Forsskaolea Poppy (Papaver) or Lewisia stems Stachys Teucrium  Poppy (Papaver) or Lewisia stems Dense layer of long stiff hairs to protect against insect herbivores (insects that eat plants). Insects are light weight and cannot push through the hairs to feed on the stem. Poppy stem X 20  Teucrium A high altitude plant e.g. in Jebel Shams. Exposed to high UV light, strong dehydrating winds and cold winter nights (below freezing). Stems and leaves are covered in a mass of white (UV reflecting) hairs to prevent wind, cold and UV from reaching the plant. Teucrium X 20 dissecting microscope  Aerva Lives in extreme arid conditions. Stems and leaves are covered in little umbrella-shaped trichomes to shade the plant from the sun. Aerva X 20 Stachys Examine the hairy leaves of Stachys (a native of Turkey). What do you think these hairs are an adaptation of ? To reduce water loss and trap surface humidity around the leaves when the climate is dry. Stachys X 20 Tasks Observe and draw the trichomes (Page 14 to page 17) Root Epidermis 3. Root Epidermis and Root Hairs on the bean (Vicia) Roots have a very thin cuticle to allow easy entrance of water. Most water is absorbed through the root hairs. Root hairs are tubular extensions of individual epidermal cells. Greatly increase the root’s surface area and efficiency of absorption. Root Epidermis and Root Hairs on the bean (Vicia) You draw this:  Tasks Observe and draw root epidermis and roots hairs(Page 14 to page 17) Ground tissues Ground Tissues Parenchyma-living cells with cell walls. Collenchyma-living cells with cell walls thickened at corners. Sclerenchyma-dead cells with thick cell walls. 27 Parenchyma cells in the stem Large rounded thin-walled cells with intercellular spaces between the cells. Store water and food. In leaves→ photosynthesis 4. Parenchyma cells in the stem Parenchyma cells  5. Collenchyma cells in the stem Found in growing plants of eudicots. Flexible tissue, provides mechanical strength. Consists of living cells. Cell walls are made up of irregular thickenings of cellulose and pectin (no lignin). 2 types; Annular and Angular 5. Collenchyma cells in the stem Angular Collenchyma cells Annular Collenchyma cells Parenchyma cells  5. Collenchyma Cells Some cells that students confuse: 1. Angular collenchyma 2. Annular collenchyma Cell walls not very thick, but thickened at corners ▪ Found below angular collenchyma (before reaching the vascular bundles). Layers of cells just underneath the ▪ Cells appear to be circular in shape. epidermis. ▪ Cell walls are separate from each other Cells appear to have an angle and because they are not lignified, can see polygonal shape. division between 1 cell and next. Cell walls are not very thick but ▪ Cell walls are uniformly thick and cell are thicker at the corners. contents are rounded. Which is angular collenchyma, and which is annular collenchyma? B  Helianthus Older stem Angular Collenchyma Annular Collenchyma (stained red)  Helianthus Older stem Angular Collenchyma  6. Sclerenchyma Cells Sclerenchyma is found in older stems as a permanent strengthening tissue. Sclerenchyma cells are dead and their walls are full of lignin. This means the cell walls are fused together, therefore no intercellular spaces. Note that unlike collenchyma, the inside of the cell is angular, so the cell wall has a more constant thickness. 6. Sclerenchyma cells in the stem Thick cell walls which are fused together (cannot separate cells). Cell walls have straight sides (so vacuole is angular) Sclerenchyma Parenchyma Lignin is impermeable to water and gases, so no gas exchange takes place. Sclerenchyma Sclerenchyma  Tasks Observe and draw collenchyma, parenchyma, and sclerenchyma cells (Page 14 to page 17) Vascular tissues  7. Dicot Root (Ranunculus) In the root, vascular tissue (xylem and phloem) is located at the center. Parenchyma Xylem vessels are large tubes arranged in a “X” shape in the center. They transport water. Phloem vessels are sieve Xylem tubes. They are small polygonal cells located Phloem between the arms of the X. They transport the product of photosynthesis (food substances such as sugar).  7. Dicot Root (Ranunculus) Xylem Parenchyma cells Phloem  7. Vascular tissue (Ranunculus root) Xylem Parenchyma Phloem Xylem Phloem Tasks Observe and draw vascular root tissues (Ranunculus) (Page 14 to page 17) Meristematic tissues 8. Meristem (Onion root tip) The root tip consists of regions: Root cap protects the apical meristem by secreting a polysaccharide slime as a lubricant (protect against damage as it pushes through the soil). Damaged cells are rapidly replaced. Apical meristem = cells having rapid mitotic divisions (so the cells are tiny). Elongation zone behind this = cells enlarge by 10x, so push the root down in to the soil. Maturation zone = the cells start to function. 8. Meristem (Onion root tip) Zone of cell division Root cap Root cap Root cap Zone of maturation Zone of cell division Zone of cell division Zone of Cell division Cells dividing  Zone of Cell Division in Onion root tip anaphase metaphase  Anaphase the stage of cell division in which separated chromatids (or homologous [like] chromosome pairs, as in the first meiotic division) move toward the opposite poles of the spindle apparatus. Tasks Observe and draw Onion root tip (Page 14 to page 17)