G10 GEN BIO 2.1 – Plant Cells and Tissues Many different types of plant cell Each of these special types has a specific function Three essential plant cells Parenchyma Cells (Diagram labelling exercise) (Big table where they need to use word bank to connect structure and function) - Structure: Thin walls; flexible; spherical shape; cell walls flatten when packed tightly together Function: Storage; photosynthesis; gas exchange; protection Special functions: Undergo mitosis when mature; when a plant is damaged, parenchyma cells divide to repair it Split into two broad groups: with and without chloroplasts 1) With chloroplasts: Photosynthesis; found in leaves and green stems 2) Without chloroplasts: Roots and fruits location; large central vacuoles which store starch, water and oils Collenchyma - Found in Celery Structure: Elongated (long); occur in long strands or cylinders; unevenly thickened cell walls (not uniformly distributed) Function: Provide support for surrounding cells Growth abilities: As cell grows, thinner portions of the cell wall expand; allows collenchyma cells to be flexible and stretch; which enables plants to bend without breaking Cell division profile: can still undergo cell division when mature Sclerenchyma cells - No cytoplasm and lacks organelles; only has thick, rigid cell walls Function: Because of thickened cell walls Sclerenchyma cells are good at providing support for plants; also transport material within the plant Typically found in wood used for shelter, fuel and paper products Comes in two distinct flavors: 1) Sclereid: Aka stone cells; what makes the outer skin of a pear rough; short and irregularly shaped; makes the outer coat of seeds and nuts tough; contributes to transport 2) Fibers: Needle shaped with a thick cell wall and small interior space; stacking them end to end creates a tough elastic tissue Functions: to make ropes, linens, canvas, textiles G10 GEN BIO Plant Tissues [Diagram showing percentage composition of respective tissues and overall plant] What is a tissue? - A group of cells that work together to perform a specific function - Can involve many copies of the same type or different cells coming together to contribute towards a common goal Meristematic tissue - Equivalent of stem cell tissue - Meristematic tissue Meristems (regions of rapidly dividing cells) - Structure: Large nuclei; small/no vacuoles - Function: (plant) stem cells; can differentiate into any and all cells - Found in 3 distinct locations: 1) Apical meristems - Location: Tips of roots; stems of plants - Function: Cell division at these locations leads to increases in length (primary growth) 2) Intercalary meristems Location: Found along the stem of many monocots Function: Cell division at these locations leads to increase in stem or leaf length 3) - Lateral meristems Facilitate an increase in root and stem diameters (widths) This is secondary growth Unique to a few plant types: non-flowering seed plants, eudicots, monocots Two types: 1) Vascular cambium: Thin cylinder of meristematic tissue and can run whole length of roots and stems Function: produces new transport cells in some roots and stems 2) Cork cambium: Function: Produces cells that develop tough cell walls; forms a protective outside layer on stems and roots Location: Outer bark on a woody plant like an oak tree Dermal Tissue (Typically the surface of a leaf cell) - Dermal tissue represents the layer of cells which make up the outer covering of a plant - Jigsaw puzzle appearance; interlocking ridges and dips; - Function? Creates waxy substances which go on to form the cuticle (reduces water loss by slowing evaporation; also blocks entry of microbes) - Interesting takes on the epidermis: - 1) Stomata Typically found on the epidermis of a leaf (sometimes green stems) Structure: Small opening which has its size dictated by the opening and closing of guard cells (shape changes) G10 GEN BIO - Function: To allow carbon dioxide, water, oxygen and other gasses to pass - 2) Trichomes Hairlike projections; can leave a fuzzy appearance Function? Protects from insects and animal predators; can also release toxic substances when touched; also help to keep some plants cool by reflecting light - 3) Root hairs Fragile extensions of root epidermal cells Increase surface area and enable the root to take in a greater volume of materials versus without Vascular tissue - Global function: Transport water, food, dissolved substances across the plant XYLEM - What does it transport? Xylem carries water with dissolved minerals in it (vascular tissue) Where does the transported substance come from? From the soil via the roots Directionality? Away from the roots across the entire plant; one direction! Remember! The xylem is a TISSUE: has two cell types within it – Vessel element; tracheids At maturity these cell types only have a cell wall, allowing water to flow freely through them (no organelles) 1) - Vessel elements Tubular cells stacked end to end, forming vessels Open at each end with barlike strips at each end (end walls) In certain plants, these end walls (lids) are lost to allow the free movement of water and dissolved substances across vessel elements without pause 2) - Tracheids Long cylindrical cells with pitted ends (end walls) Cells are found end to end and form a tubelike strand Even mature tracheids have end walls (unlike vessel elements which can lose theirs) Less efficient PHLOEM - What does it transport? Food; dissolved sugars and other organic compounds Directionality? Up and down the plant: from leaf/stems to root and from root to leaf/stem Remember! The phloem is a TISSUE: has two cell types within it – sieve tube member; companion cells 1) - Sieve tube member Has cytoplasm but no nucleus or ribosomes when mature Has a sieve plate (end wall) with large pores to allow dissolved substances to flow You find sieve plates at the end of each sieve tube member G10 GEN BIO 2) Companion cells - Has a nucleus - Thought to support both cells Special plant structures: The Sinks - Excess glucose can be converted to carbohydrates for use by the plant and stored in regions called sinks Parenchyma cells in the root cortex behave as sinks; they are storage cells Transport of dissolved carbs from sources to sinks and other dissolved substances is called translocation Ground Tissue - Plant tissue which doesn’t belong to any of the three aforementioned categories Consists of: parenchyma cells; collenchyma; sclerenchyma Functions: Diverse – storage, support and photosynthesis Forms most of the plant Location specific roles Leaves and green stems - Ground tissue contains chloroplasts that produce glucose for the plant Stems, roots and seeds - Large vacuoles to store sugars, starch, oils and other substances
