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Transcript
Section 4 Section 4-4 Notes Plant Cells Plant cells have three additional kinds of structures than other eukaryotic cells; these are extremely important to plant function: cell walls, large central vacuoles, and plastids. Photosynthesis – plants take in carbon dioxide and water and convert it into sugar (glucose). Cell Wall Cell wall – a rigid layer that lies outside the cell’s plasma membrane. Cellulose – main component of cell walls. - carbohydrates that plant cell walls contain - embedded in a matrix of proteins and other carbohydrates that form a stiff box around each cell. Pores in the cell wall allow water, ions, and some molecules to enter and exit the cell. Primary and Secondary Cell Walls The cellulose is made directly on the surface of the plasma membranes by enzymes that travel along the membrane. The enzymes traveling along the membrane are guided by microtubules inside the plasma membrane. Growth of the primary cell wall occurs in one direction, based on the orientation of the microtubules. Other components of the cell wall are made in the ER; these materials move in vesicles to the Golgi and then to the cell surface. Some plants also produce a secondary cell wall. When the cell stops growing, it secretes the secondary cell wall between the plasma membrane and the primary cell wall. The secondary cell wall is very strong but can no longer expand. Central Vacuole Central Vacuole – a large, fluid-filled organelle that stores not only water but also enzymes, metabolic wastes, and other materials. - Forms as other small vacuoles fuse together. - Can make up 20% of the plant cell’s volume Other Vacuoles Some vacuoles store toxic materials Other vacuoles store plant pigments Plastids Plastids – organelles that are surrounded by a double membrane and contain their own DNA. Examples of plastids are chloroplasts, chromoplasts, and leucoplasts. Chloroplasts Chloroplasts – use light energy to make carbohydrates form carbon dioxide and water. Each chloroplasts contain thlaykoids. Thlaykoids - a system of flattened, membranous sacs Thlakoids contained chlorophyll Chlorophyll – the main main molecule that absorbs and captures light energy for the cell. it can be found in a wide variety of eukaryotic algae, such as seaweed. Chromoplasts Chromoplasts – plastids that contain colorful pigments and that may or may not take part in photosynthesis. Other Plastids Several other types of plastids share the general features of chloroplasts but differ in content. Ex:) amyloplasts store starch Proplastid – common precursor Comparing Cells Plant cells have features that animal cells do not. Prokaryotes versus Eukaryotes Prokaryotes differ from eukaryotes in that prokaryotes lack a nucleus and membrane-bound organelles, replacing with nucleoids. Prokaryotes also lack an internal membrane system Plant Cells versus Animal Cells 3 unique features distinguish plant cells from animal cells. - Cell wall - Large central vacuole - Contain a variety of plastids which are not found in animal cells. - These 3 things are important to plant functions.