Al-Esraa University Biology Plant Course Lecture Notes PDF

Al-Esraa University College of science Biology Department plant course second stages Year : 2024 – 2025 Lecture presented by: Ass.Lec. Sara Mohammed  Lecture 1: Plant cell structures (living organelles) 1-1.The plant cell The plant cell...

Al-Esraa University College of science Biology Department plant course second stages Year : 2024 – 2025 Lecture presented by: Ass.Lec. Sara Mohammed  Lecture 1: Plant cell structures (living organelles) 1-1.The plant cell The plant cell is the basic structural and physiological unit of plants, in which most reactions characteristic of life occur. It is a membrane-bound unit containing hereditary and other components, including enzymes, by which it is able to metabolize substances to grow, and to reproduce. because they can manufacture their own food. Chlorophyll, which gives plants their green color, enables them to use sunlight to convert water and carbon dioxide into sugars and carbohydrates, chemicals the cell uses for fuel. 1-2. Cells structure There are two types of cells. 1- Prokaryotic Cell Prokaryotic cells are comparatively smaller and much simpler than eukaryotic cells. The other defining characteristic of prokaryotic cells is that it does not possess membrane-bound cell organelles such as a nucleus. Reproduction happens through the process of binary fission. found in bacteria and blue-green algae. 2- Eukaryotic cells A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments or sacs, called organelles, These units called organelles include the nucleus, mitochondria, plastids, microbodies, vacuoles, dictyosomes and endoplasmic reticulum. which have specialized functions. Plant cells are eukaryotic cells NOTE: Most organelles are common to both animal and plant cells. However , plant cells also have features that animal cells do not have: a cell wall, a large central vacuole, and plastids such as chloroplasts. Both animal and plant cells have mitochondria. Plants have very different lifestyles from animals, and these differences are apparent when you examine the structure of the plant cell. Plants make their own food in a process called photosynthesis. They take in carbon dioxide (CO2) and water ( H2O ) and convert them into sugars. The features unique to plant cells can be seen in Figure. 2- The protoplast The organelles of the plant cell are contained within a membrane-bounded protoplast, which in turn is encased within the cell wall. The major features of the protoplast are the outer membrane or plasma membrane, the cytoplasm, the nucleus, and the vacuole. a- cell membrane (plasma membrane): The cell membrane consists of a lipid bilayer that is semipermeable. he plasma membrane is a structure that forms a barrier between the cytoplasm inside the cell and the environment outside the cell. Without the plasma membrane, there would be no cell. The plasma membrane controls the passage of organic molecules, ions, water, and oxygen into and out of the cell. Wastes (such as carbon dioxide and ammonia) also leave the cell by passing through the plasma membrane. The membrane also protects and supports the cell and controls everything that enters and leaves it. It allows only certain substances to pass through while keeping others in or out. b- The cytoplasm is the semifluid substance of a cell that is external to the nuclear membrane and internal to the cellular membrane. Also within the cytoplasm is a very important network of membrane, the endoplasmic reticulum (ER). Proteins are synthesized on the surfaces of the ER through the cell, on small discrete structures called ribosomes. c- Plastids Plant plastids are a group of closely related membrane-bound organelles that carry out many functions, are located within the cytoplasm. They are responsible for photosynthesis, for storage of products such as starch, and for the synthesis of many types of molecules that are needed as cellular building blocks. Plastids have the ability to change their function between these and other forms and scientists think that plastids are descended from photosynthetic bacteria that allowed the first eukaryotes to make oxygen. The main types of plastids and their functions are:  Chloroplasts are the organelle of photosynthesis. They capture light energy from the sun and use it with water and carbon dioxide to make food (sugar)  for the plant. The arrangement of chloroplasts in a plant's cells can be seen in Figure.  Chromoplasts make and store pigments that give petals and fruit their orange and yellow colors.  Leucoplasts do not contain pigments and are located in roots and non- photosynthetic tissues of plants. They may become specialized for bulk storage of starch, lipid, or protein. However, in many cells, leucoplasts do not have a major storage function. instead, they make molecules such as fatty acids and many amino acids. plant cell with visible chloroplasts Chloroplasts: capture light energy from the sun and use it with water and carbon dioxide to produce sugars for food. Chloroplasts look like flat discs and are usually 2 to 10 micrometers in diameter and I micrometer thick. A model of a chloroplast is shown in Figure. The chloroplast is enclosed by an inner and an outer phospholipid membrane. Between these two layers is the- intermembrane space. The fluid within the chloroplast is called the stroma, and it contains one or more molecules of small, circular DNA. The stroma also has ribosomes. Within the stroma are stacks of thylakoids, sub-organelles that are the site of photosynthesis. The thylakoids are arranged in stacks called grana (singular: granum). A thylakoid has a flattened disk shape. Inside it is an empty area called the thylakoid space or lumen. Photosynthesis takes place on the thylakoid membrane. Within the thylakoid membrane is the complex of proteins and light-absorbing pigments, such as chlorophyll and carotenoids. This complex allows capture of light energy from many wavelengths because chlorophyll and carotenoids both absorb different wavelengths of light. These will be further discussed in the "Photosynthesis" concept. d- Mitochondria are cytoplasmic bodies that are smaller than plastids. Like the chloroplasts, they surrounded by a double membrane, and contain a specialized inner membrane system. The mitochondria are sites of respiration and are also involved in protein synthesis. They produce energy- rich compounds such as adenosine triphosphate (ATP). Figure Figure: MITOCHONDRIA 3-Endoplasmic Reticulum (ER): The ER is a network of membranes involved in the synthesis, folding, and transport of proteins and lipids. There are two types: rough ER (with ribosomes on its surface) and smooth ER (lacking ribosomes). Figure  4-Ribosomes: are the cellular structures responsible for protein synthesis. They can be found attached to the rough ER or free in the cytoplasm. 5- Golgi Apparatus (Golgi Body) dictyosomes : The Golgi apparatus processes, packages, and distributes molecules, particularly proteins, that are synthesized in the cell. It consists of a series of flattened membranous sacs. In plant cells, the Golgi apparatus has the additional role of synthesizing polysaccharides, some of which are incorporated into the cell wall and some of which other cell parts use.Figure Golgi Apparatus 6- Nucleus : The nucleus is a prominent organelle within the cell. Enclosed by a double membrane and containing one or more bodies called nucleoli. Within the nucleus are the chromosomes, long lengths of deoxyribonucleic acid (DNA) and associated proteins that contain the genetic information coding for all cell functions, for differentiation of organism, and for reproduction. During cell division, the chromosomes replicate and set of chromosomes is passed on to each of the daughter cells, thus ensuring continuity of genetic information from old to new cell. During reproduction the new cell receives half of its chromosomes from the male parent and half from the female parent, resulting in genetic segregation. Genetic codes are transcribed from the DNA in the nucleus and translated into protein on the ribosomes. DNA is also found outside the nucleus in the mitochondria and in the chloroplast, thereby giving these bodies a role in heredity independent of the nucleus. Unlike nuclear DNA, mitochondrial DNA and chloroplast DNA are inherited only from female parent. These organelles work together to maintain the structure and function of plant cells, allowing them to carry out essential processes for growth, development, and survival. Figure Figure :Nucleus Structure Function Cytoplasm Where enzymes and other proteins are made. Location of reactions in anaerobic respiration. Nucleus Contains DNA which carries the genetic code for making enzymes and other proteins used in chemical reactions such as photosynthesis and respiration. Cell membrane Allows gases and water to diffuse freely into and out of the cell. Controls the transport of other molecules. Mitochondria Contains enzymes for the reactions in aerobic respiration (in animals, plants and yeast). Ribosome Where amino acids are joined together to make a protein. Chloroplast Contains the green pigment, chlorophyll, which absorbs light for photosynthesis, and the enzymes needed for photosynthesis. Cell wall Made from cellulose fibers. Strengthens the cell and supports the plant. Vacuole Filled with cell sap to help support the cell.