Transcript Plant Cells
Plant Cells Cells All organisms are made up of cells Cells are the fundamental unit of life Small membrane-bound structures Can create copies of themselves by growing and dividing in two Viruses not classified as living as they require a host cell to replicate themselves Microscopes Developed in the 17th century Allowed us to re-evaluate our definition of life Several types of microscopes play critical roles in cell biology – even today Light microscope Transmission electron microscope Scanning electron microscope Microscope Cells 1665 - Robert Hooke created a set of lenses that were used to visualize the cell walls of cork 1838 – Matthias Schleiden 1839 – Theodor Schwann Both presented work that all living organisms are made of cells Mid 1800’s – Rudolf Virchow proposed that all cells arise from other cells Cell Theory Cell Theory (Schleiden, Schwann and Virchow) All organisms are composed of 1 or more cells Cells are the basic living unit of function and organization All cells come from other cells 1860’s – Louis Pasteur confirmed that cells come from existing cells Magnification Cells usually run 5 to 20 micrometers in diameter – 10 times smaller than what our eyes can resolve The light microscope can help us see things 1000 times smaller than normally seen by the human eye The electron microscope can help us see things 1000 times smaller than with the light microscope Light Microscopes Bright light source Set of lenses, arranged to focus the image Specimen must be thin enough for the light to pass through Cellular Detail In the light microscope you can visualize the outer boundary of the cell and the nucleus with little detail in the cytoplasm. Visualize Beyond Light At the light microscope level we are still unable to ‘see’ the small components of the cell Surface structures can be seen using a scanning electron microscope Internal structures can be seen using a transmission electron microscope Visualize structures in the nanometer range Not All Cells Are The Same The amount and type of organelles differs for various types of cells Based on their function Cells are defined by the presence or absence of a nucleus Prokaryotes have no nucleus, single celled Eukaryotes have a nucleus, may be single or multi-celled Nucleus Usually the most prominent organelle Contains the genetic material of the cell – DNA Chromatin is a complex of DNA and protein that is diffusely distributed in the nucleus DNA can be seen as chromosomes only during cell division Chromatin to Chromosome Nucleus Contains the nucleolus Nucleolar organizing area Contains the RNA molecules and proteins necessary for formation of ribosomes May be one or more depending on cell type Nuclear Membrane Nucleus is enclosed in a double layered membrane Also called the nuclear envelope Separates the nucleus from the rest of the cell Nuclear pores allow for communication between nucleoplasm and cytoplasm Small openings in the envelope Nucleus Nuclear envelope Nucleus Nucleolus Nuclear pore Cytoplasm Contents within the plasma membrane but outside the nucleus Organelles – the small membrane-bound components of the cell that allow it to function Cytosol – the aqueous part of the cytoplasm outside of the other membrane bound organelles Mitochondria and Chloroplasts Thought to originate from a symbiotic relationship between a bacterium and the cell Contain their own DNA Can replicate without cell replication Evolution Mitochondria Most conspicuous organelle Power-house of the cell - energy production Cells requiring large amounts of energy have numerous mitochondria Generates ATP from the oxidation of food molecules Requires oxygen and gives off carbon dioxide, called cellular respiration With oxygen – aerobic Without oxygen - anaerobic Mitochondria Outer membrane Intermembrane space Inner membrane Matrix Cristae Chloroplasts Found in plants, algae – contain chlorophyll More complex than mitochondria Function in photosynthesis Convert sun energy and carbon dioxide to sugars and oxygen Internal Membranes Cells contain other membrane-bound organelles Assist with movement of materials Usually single membrane Import and export Move molecules about within the cell The function of the cell determines the amount of these organelles per cell Endoplasmic Reticulum (ER) Irregular maze from a single membrane continuous with the nuclear membrane and surrounding a single lumen (opening) Involved in making some components for the cell as well as the materials for export Two types Rough ER (RER) – synthesize proteins Contain ribosomes on surface Smooth ER (SER) –synthesize and metabolize lipids No ribosomes Rough ER Ribosomes Ribosomes Non-membrane-bound organelle responsible for protein synthesis Complex of protein and RNA 2 subunits – 1 large and 1 small Complex allows for the formation of the peptide bond 2 types Attached to endoplasmic reticulum Exported proteins Free in the cytoplasm Internal proteins Ribosomes Golgi Apparatus Stack of flattened membrane-bound sacs resembling a stack of dinner plates Responsible for the modification of the proteins from the ER Directs proteins to the proper site Modification of proteins Adding sugars to the proteins glycoproteins Golgi Apparatus Vesicles Lysosomes Peroxisomes Digestive “organ” of the cell Digests food, recycles materials and eliminates wastes Generates and removes hydrogen peroxide from lipid metabolism Transport vesicles Moves materials around the cell between other organelles Plasma Membrane Material continually moves from outside the cell to inside and vise versa Import Capture things outside the cell Usually fuse with lysosome - digested Export Move things to outside the cell Cytosol Remove all the membrane-bound organelles from a cell and you are left with the cytosol Can be the largest component of the cell Site of many chemical reactions that keep the cell alive Cytoskeleton Elaborate network of filaments that function to give strength, shape and movement to cells 3 filament types Actin – thinnest fibers, generates contractile force (A) Intermediate – intermediate, strengthens (C) Microtubules – largest, hollow tubes, rearranges to help separate chromosomes during cell division (B) Microtubules X Visit www.worldofteaching.com For 100’s of free powerpoints Animal Cell Plant Cell Plant Cell Plant Cells have a few unique organelles: Vacuoles Plastids (e.g., chloroplasts) Cell wall Vacuoles Definition: membranous sacs filled with water that serve a variety of functions: Storage of “food”, water, oil, pigments, toxins, & waste. Helps to maintain turgor pressure. Young plant cells often contain many small vacuoles, but as the cells mature, these unite to form a large central vacuole. Vacuoles and vesicles are storage organelles in cells. Vacuoles are larger than vesicles. Either structure may store water, waste products, food, and other cellular materials. In plant cells, the vacuole may take up most of the cell's volume. The membrane surrounding the plant cell vacuole is called the tonoplast. Cell Sap The fluid contained in a vacuole is called the cell sap. Water soluble pigments called anthocyanins may be present. These pigments impart colors to flowers, fruit, seeds, leaves, stems, and roots. Calcium oxalate and other salts may be dissolved or present as precipitates. Crystals may serve to protect the plant from herbivores, storage of toxic substances, or act as a reservoir for calcium. About 75% of flowering plants produce calcium oxalate crystals in some or all of their organs. Anthocyanin and Pigmentation Plasmolysis Definition: the contraction of cells within plants due to the loss of water through osmosis. It is when the cell membrane “shrinks away” from the cell wall and the vacuole collapses. Occurs when water is drawn out of the cell (high water concentration low water concentration). Causes plants to wilt. Calcium Oxalate Crystals Druse type crystal Prismatics Plastids Definition: large organelles that are associated with pigments and other storage products (e.g., starch). A typical plant cell will usually have 20-40 plastids. Several Types: Chloroplasts Leucoplasts- Amyloplasts (starch)/Elaioplasts (oil) Chromoplasts Chloroplasts Definition: plastids that capture light energy from the sun to make “food”; contain chlorophyll (Elodea) Leucoplasts Definition: colorless plastids that store starch or oil Found in things like tubers (e.g., Irish potatoes), roots, leaves, grains, fruits, and seeds. Chromoplasts Definition: plastids that make & store carotenoid pigments Found in red & yellow peppers, tomatoes, flower petals … Carotenoid pigments are not water soluble, but it is fat soluble. β-carotene is broken down in the mucosa of the small intestine by beta-carotene dioxygenase to retinol, a form of vitamin A. Vitamin A, is a yellow fat-soluble, antioxidant vitamin important in vision, embryo development, and bone growth. Vitamin A is required in the production of rhodopsin, the visual pigment used in dim lights. VAD leads to night blindness, permanent blindness, and other medical problems. Cell Wall Definition: a flexible outer barrier made of cellulose fibrils that surrounds plant cells. Functions: Protection & Support Determines plant shape & size Maintains turgor pressure Regulates movement in and out Cell-cell communication Cellulose Cellulose is a polymer of β-D-Glucose, which in contrast to starch, is oriented with -CH2OH groups alternating above and below the plane of the cellulose molecule thus producing long, unbranched chains. Pectin Pectin is a polysaccharide that acts as a cementing material in the cell walls of all plant tissues. The white portion of the rind of lemons and oranges contains approximately 30% pectin. Pectin is an important ingredient of fruit preserves, jellies, and jams. Pectin is a complex polysaccharide consisting mainly of esterified Dgalacturonic acid resides in an α-(1-4) chain. Middle lamella The cell wall protects the cellular contents; gives rigidity to the plant structure; provides a porous medium for the circulation and distribution of water, minerals, and other small nutrient molecules; and contains specialized molecules that regulate growth and protect the plant from disease. A structure of great tensile strength, the cell wall is formed from fibrils of cellulose molecules, embedded in a water-saturated matrix of polysaccharides and structural glycoproteins. Plasmodesmata Definition: small tubes that connect plant cells to each other, establishing living bridges between cells. Allow certain molecules to pass directly from one cell to another. These channels, penetrate the cell wall and are lined with plasma membrane, uniting all connected cells with essentially one continuous cell membrane. Cell wall & Plasmodesmata- In addition to cell membranes, plants have cell walls. Cell walls provide protection and support for plants. Unlike cell membranes materials cannot get through cell walls. This would be a problem for plant cells if not for special openings called plasmodesmata. These openings are used to communicate and transport materials between plant cells because the cell membranes are able touch and therefore exchange needed materials. Cell Division The mechanism that allows the nuclei of cells to split and provide each daughter cell with a complete set of chromosomes during cellular division. Permits plants to grow & develop. Garlic Root Tip In plants cell division occurs in tissues called meristems, which are often found in root tips. Apical meristem Root cap Phases of Cell Division Interphase Mitosis: G1 phase S phase G2 phase Prophase Metaphase Anaphase Telophase Cytokinesis Interphase Cellular growth Preparation for mitosis Mitosis Prophase Appearance of stringlike chromosomes due to condensing of chromatin. Metaphase Chromosomes line up in the middle of the cell (equator) Anaphase Chromosomes separate and move to opposite ends of the cell (poles). Telophase & Cytokinesis Two new nuclei are formed and the cytoplasm is beginning to separate.